podolny and muller - construction and design of prestressed concrete segmental bridges

Construction and Designof Prestressed Concrete Segmental Bridges

Walter Podolny, Jr., Ph.D., P.E.Bridge Division

Office of EngineeringFederal Highway Administration

U.S. Department of Transportation

Jean M. MullerChairman of the Board

Figg and Muller Engineers, Inc.

1982

A Wiley-Interscience Publication

John Wiley &? SonsNew York Chichester Brisbane Toronto Singapore

Series PrefaceJ

The Wiley Series of Practical Construction Guidesprovides the Ivorking constructor \vith up-to-dateinformation that can help to increase the job profitmargin. These guidebooks, ivhich are scaledmainly for practice, but include the necessarytheory and design, should aid a construction con-tractor in approaching \+vork problems with moreknolvledgeable confidence. The guides should beuseful also to engineers, architects, planners,specification tvriters, project managers, superin-tendents. materials and equipment manufacturersand. the source of all these callings, instructors andtheir students.

Construction in the United States alone willreach $250 billion a year in the early 1980s. In allnations. the business of building will continue togrow at a phenomenal rate, because the populationproliferation demands new living, lvorking, andrecreational facilities. This construction will haveto be more substantial, thus demanding a more

professional performance from the contractor. Be-fore science and technology had seriously affectedthe ideas, job plans, financing, and erection ofstructures. most contractors developed theirknolv-holy by field trial-and-error. Wheels, smalland large. jvere constantly being reinvented in allsectors, because there was no interchange ofknolvledge. The current complexity of construc-tion, even in more rural areas, has revealed a clearneed for more proficient, professional methodsand tools in both practice and learning.

Because construction is highly competitive, somepractical technology is necessarily proprietary. Butmost practical day-to-day problems are common tothe Fvhole construction industry. These are thesubjectsGuides.

for the Wiley Practical Construction

M. D. MORRIS, P.E.

PrefaceJ

Prestressed concrete segmental bridge construc-tion has evolved, in the natural course of events,from the combining of the concepts of prestress-ing, box girder design, and the cantilever methodof bridge construction. It arose from a need toovercome construction difficulties in spanningdeep valleys and river crossings without the use ofconventional falsework, which in some instancesmay be impractical, economically prohibitive, ordetrimental to environment and ecology.

Contemporary prestressed, box girder, seg-mental bridges began in Western Europe in the1950s. Ulrich Finsterwalder in 1950, for a cross-ing of the Lahn River in Balduinstein, Germany,was the first to apply cast-in-place segmental con-struction to a bridge. In 1962 in France the firstapplication of precast, segmental, box girder con-struction was made by Jean Muller to the Choisy-Le-Roi Bridge crossing the Seine River. Since thenthe concept of segmental bridge construction hasbeen improved and refined and has spread fromEurope throughout most of the world.

The first application of segmental bridge con-struction in North America was a cast-in-placesegmental bridge on the Laurentian Autoroutenear Ste. Adele, Quebec, in 1964. This was fol-lowed in 1967 by a precast segmental bridge cross-ing the Lievre River near Notre Dame du Laus,Quebec. In 1973 the first U.S. precast segmentalbridge was opened to traffic in Corpus Christi,Texas, followed a year later by the cast-in-placesegmental Pine Valley Bridge near San Diego,California. As of this date (1981) in the UnitedStates more than eighty segmental bridges arecompleted, in construction, in design, or underconsideration.

Prestressed concrete segmental bridges may beidentified as precast or cast in place and cat-egorized by method of construction as balancedcantilever, span-by-span, progressive placement,or incremental launching. This type of bridge has

extended the practical and competitive economicspan range of concrete bridges. It is adaptable toalmost any conceivable site condition.

The objective of this book is to summarize in onevolume the current state of the art of design andconstruction methods for all types of segmentalbridges as a ready reference source for engineer-ing faculties, practicing engineers, contractors, andlocal, state, and federal bridge engineers.

Chapter 1 is a quick review of the historical evo-lution to the current state of the art. It offers thestudent an appreciation of the way in which seg-mental construction of bridges developed, thefactors that influenced its development, and thevarious techniques used in constructing segmentalbridges.

Chapters 2 and 3 present case studies of the pre-dominant methodology of constructing segmentalbridges by balanced cantilever in both cast-in-placeand precast concrete. Conception and design ofthe superstructure and piers, respectively, are dis-cussed in Chapters 4 and 5. The other three ba-sic methods of constructing segmental bridges-progressive placement, span-by-span, and incre-mental launching-are presented in Chapters 6and 7.

Chapters 2 through 7 deal essentially with girdertype bridges. However, segmental constructionmay also be applied to bridges of other types.Chapter 8 discusses application of the segmentalconcept to arch, rigid frame, and truss bridges.Chapter 9 deals with the cable-stayed type ofbridge and Chapter 10 with railroad bridges. Thepractical aspects of fabrication, handling, anderection of segments are discnssed in Chapter 11.

In selected a bridge type for a particular site, oneof the more important parameters is economics.Economics, competitive bidding, and contractualaspects of segmental construction are discussed inChapter 12.

Most of the material presented in this book is not

vii

Preface

original: Although acknowledgment of all the graphs, tables, and other data. Wherever possible,many.source$&. not possible, full credit is givenwherever the specific so;rce can be identified.

credit is given in the text.

Every effort has been. made to eliminate errors; WALTER PODOLNY, JK.the authors will appreciate notification from the JEAN M. MUILEKreader ‘of any that remain.

The authors are indebted to numerous publica- Burke, Virginia

tions, organizations, and individuals for their Par%, Francr

assistance and permission to reproduce photo- Jarmar? 1982

1 Prestressed Concrete Bridges andSegmental Construction

1 . 11 .2

1.3

1.4

1.5

1.61.71.8

1.9

1.10

1.11

Introduction, 1Development of CantileverConstruction, 2Evolution of PrestressedConcrete, 4Evolution of Prestressed ConcreteBridges, 5Long-Span Bridges withConventional PrecastGirders, 8Segmental Construction, 10Various Types of Structures, 12Cast-in-Place and PrecastSegmental Construction, 17Various Methods ofConstruction, 18Applications of SegmentalConstruction in the UnitedStates, 26Applicability and Advantages ofSegmental Construction, 28References, 30

Contents

2.81 2.9

2.102.112.12

2.13

2.14

2.152.16

2 Cast-In-Place Balanced Cantilever GirderBridges 3 1

2.12.22.32.4

2.5

2.6

2.7

Introduction, 3 1Bendorf Bridge, Germany, 35Saint Adele Bridge, Canada, 37Bouguen Bridge in Brest andLacroix Falgarde Bridge,France, 38Saint Jean Bridge over theGaronne River at Bordeaux,France, 4 1Siegtal and Kochertal Bridges,Germany, 43Pine Valley Creek Bridge,U.S.A., 46

Gennevilliers Bridge, France, 52Grand’Mere Bridge, Canada, 55Arnhem Bridge, Holland, 58Napa River Bridge, U.S.A., 59Koror-Babelthuap, U.S. PacificTrust Territory, 61Vejle Fjord Bridge,Denmark, 63Houston Ship Channel Bridge,U.S.A., 68Other Notable Structures, 71Conclusion, 8 1References, 8 1

3 Precast Balanced Cantilever GirderBridges 8 2

3.13.2

3.3

3.4

3.53.63.73.83.93.10

3.11

3.123.13

3.143.15

3.16

Introduction, 82Choisy Le Roi Bridge and OtherStructures in Greater Paris,France, 83Pierre Benite Bridges near Lyons,France, 89Other Precast Segmental Bridgesin Paris, 91Oleron Viaduct, France, 96Chillon Viaduct, Switzerland, 99Hartel Bridge, Holland, 103Rio-Niteroi Bridge, Brazil, 106Bear River Bridge, Canada, 108JFK Memorial Causeway,U.S.A., 109Saint Andre de Cubzac Bridges,France, 113Saint Cloud Bridge, France, 114Sallingsund Bridge,Denmark, 122B-3 South Viaducts, France, 124Alpine Motorway Structures,France, 129Bridge over the Eastern Scheldt,Holland, 134

i x

X

3.17 Captain Cook Bridge,Australia, 136

3.18 Other Notable Structures, 1 3 9References, 147

4 Design of Segmental Bridges 148

4.14.24.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

4.12

4.13

4.14

4.15

4.16

4.174.184.19

Introduction, 148Live Load Requirements, 149Span Arrangement and RelatedPrinciple of Construction, 149Deck Expansion, Hinges, andContinuity, 15 1Type, Shape and Dimensions ofthe Superstructure, 159Transverse Distribution of LoadsBetween Box Girders in MultiboxGirders, 164Effect of Temperature Gradientsin Bridge Superstructures, 170Design of Longitudinal Membersfor Flexure and TendonProfiles, 173Ultimate Bending Capacity ofLongitudinal Members, 190Shear and Design of CrossSection, 193Joints Between Match-CastSegments, 199Design of Superstructure CrossSection, 202Special Problems inSuperstructure Design, 203Deflections of Cantilever Bridgesand Camber Design, 205Fatigue in SegmentalBridges, 2 10Provisions for FuturePrestressing, 2 12Design Example, 2 12Quantities of Materials, 219Potential Problem Areas, 220References, 224

5 Foundations, Piers, and Abutments

5.1 Introduction, 2255.2 Loads Applied to the Piers, 2 3 05.3 Suggestions on Aesthetics of Piers

and Abutments, 2325.4 Moment-Resisting Piers and

Their Foundations, 234

225

5.5 Piers with Double ElastomericBearings, 24 1

5.6 Piers with Twin Flexible Legs, 2535.7 Flexible Piers and Their Stability

During Construction, 2635.8 Abutments, 27 15.9 Effect of Differential Settlements

on Continuous Decks, 276References, 280

6 Progressive and Span-by-SpanConstruction of Segmental Bridges 2,

6 .1 Introduction, 2816.2 Progressive Cast-in-Place

Bridges, 2836.3 Progressive Precast Bridges, 2896.4 Span-by-Span Cast-in-Place

Bridges, 2936.5 Span-by-Span Precast

Bridges, 3086.6 Design Aspects of Segmental

Progressive Construction, 3 14References, 3 19

7 Incrementally Launched Bridges 3 2

7.1 Introduction, 32 17.2 Rio Caroni, Venezuela, 3237.3 Val Restel Viaduct, Italy, 3277.4 Ravensbosch Valley Bridge,

Holland, 3297.5 Olifant’s River Bridge, South

Africa, 33 17.6 Various Bridges in France, 3337.7 Wabash River Bridge, U.S.A., 3357.8 Other Notable Bridges, 3387.9 Design of Incrementally

Launched Bridges, 3437.10 Demolition of a Structure by

Incremental Launching, 352References, 352

8 Concrete Segmental Arches, RigidFrames, and Truss Bridges 35

8.1 Introduction, 3548.2 Segmental Precast Bridges over

the Marne River, France, 3578.3 Caracas Viaducts, Venezuela, 3638.4 Gladesville Bridge, Australia, 37 18 .5 Arches Built in Cantilever, 3748.6 Rigid Frame Bridges, 382

Contents x i

8 . 7 Truss Bridges, 392 1 1 Technology and Construction ofReferences, 399 Segmental Bridges 465

9 Concrete Segmental Cable-Stayed Bridges 40011.111.2

11.3

1.1.4

Scope and Introduction, 465Concrete and Formwork forSegmental Construction, 466Post-tensioning Materials andOperations, 470Segment Fabrication forCast-In-Place CantileverConstruction, 475Characteristics of PrecastSegments and Match-CastEpoxy Joints, 485Manufacture of PrecastSegments, 493Handling and TemporaryAssembly of PrecastSegments, 507Placing Precast Segments, 509References, 5 17

9.19.2

9.39.4

9.59.69.7

9.89.9

9.10

Introduction, 400Lake Maracaibo Bridge,Venezuela, 405Wadi Kuf Bridge, Libya, 407Chaco/Corrientes Bridge,Argentina, 408Mainbrticke, Germany, 410Tie1 Bridge, Netherlands, 412Pasco-Kennewick Bridge,U.S.A., 418Brotonne Bridge, France, 419Danube Canal Bridge,Austria, 427Notable Examples ofConcepts, 430References, 439

10 Segmental Railway Bridges 4 4 1

10.1

10.2

10.3

10.4

10.5

10.6

10.7

10.8

10.9

10.10

10.11

Introduction to ParticularAspects of Railway Bridges andField of Application, 44 1La Voulte Bridge over theRhone River, France, 442Morand Bridge in Lyons,France, 442Cergy Pontoise Bridge nearParis, France, 444Marne La Vallee and TorcyBridges for the New ExpressLine near Paris, France, 444Clichy Bridge near Paris,France, 449Olifant’s Bridge, SouthAfrica, 452Incrementally LaunchedRailway Bridges for theHigh-Speed Line, Paris toLyons, France, 453Segmental Railway Bridges inJapan, 457Special Design Aspects ofSegmental Railway Bridges, 458Proposed Concepts for FutureSegmental Railway Bridges, 464

11.5

11.6

11.7

11.8

1 2 Economics and Contractual Aspects ofSegmental Construction 518

12.112.2

12.3

Bidding Procedures, 5 18Examples of Some InterestingBiddings and Costs, 523Increase in Efficiency inConcrete Bridges, 528References, 535

13 Future

13.113.213.3

13.4

13.5

13.6

Trends and Develofnnents 536

Introduction, 536Materials, 536Segmental Application toBridge Decks, 542Segmental Bridge Piers andSubstructures, 543Application to Existing or NewEridge Types, 544Summary, 548References, 549

Index of Bridges 5 5 1Index of Personal Names 5 5 5Index of Firms and Organizations 5 5 7Index of Subjects 5 5 9

Construction and Designof Prestressed Concrete

Segmental Bridges

1Prestressed Concrete Bridgesand Segmental Construction

1.1 INTRODUCI’ION1.2 DEVELOPMENT OF CANTILEVER CONSTRUCITON1.3 EVOLUTION OF PRESTRESSED CONCRETE1.4 EVOLUTION OF PRESTRESSED CONCRETE BRIDGES1.5 LONGSPAN BRIDGES WITH CONVENTIONAL PRE-

CAST GIRDERS1.6 SEGMENTAL CONSTRUCTION1.7 VARIOUS TYPES OF STRUCl-URFS

1.7.1 Girder Bridges1.7.2 Trusses1.7.3 Frames with Slant Legs1.7.4 Concrete Arch Bridges1.7.5 Concrete CabkStayed Bridges

1.8 CAST-IN-PLACE AND PRECAST SEGMENTAL CON-STRUCTION

1 . l Zntroduction,

The conception, development, and worldwide ac-ceptance of,segmental construction in the field ofprestressed concrete bridges represents one of themost interesting and important achievements incivil engineering during the past thirty years. Rec-ognized today in all countries and particularly inthe United States as a safe, practical, and economicconstruction method, the segmental concept prob-ably owes its rapid growth and acceptance to itsfounding, from the beginning, on sound construc-tion principles such as cantilever construction.

Using this method, a bridge structure is made upof concrete elements usually called segments(either precast or cast in place in their final positionin the structure) assembled by post-tensioning. Ifthe bridge is cast in place, Figure 1.1, travelers areused to allow the various segments to be con-structed in successive increments and progressively

1 .9

1.10

1.11

1 .8 .1 Characteristics of Cast-in-Place Segments1 .8 .2 Characteristics of Precast Segfnents1 .8 .3 Choice between Cast-in-Place and Precast

ConstructionVARIOUS METHODS OF CONSTRUCTION

1.9.1 Cast-in-Place Balanced Cantilever1.9.2 Precast Balanced Cantilever1.9.3 Span-by-Span Construction1.9.4 Progressive Placement Construction1.9 .5 Incremental Launching or Push-Out ConstructionAPPLICATIONS OF SEGMENTAL CONSTRUCTIONIN THE UNITED STATESAPPLICABILITY AND ADVANTAGES OF SEGMEN-TAL CONSTRUCI’IONREFERENCES

prestressed together. If the bridge is precast, seg-ments are manufactured in a special casting yardor factory, transported to their final position, andplaced in the structure by various types of launch-

FIGURE 1.1 Cast-in place form traveler.

1

Prestressed Concrete Stidges ad Segmental Constrt4ction

FIGURE 1.2. Oleron Viaduct, segmental construction in progress. One typicalprecast segment placed in the Oleron Viaduct.

ing equipment, Figure 1.2, while prestressingachieves the assembly and provides the structuralstrength.

Most early segmental bridges were built as can-tilevers, where construction proceeds in a symmet-rical fashion from the bridge piers in successive in-crements to complete each span and finally theentire superstructure, Figure 1.3. Later, other con-struction methods appeared in conjunction with

Llzcr---- --------------- ______--. ,%-77

/.#--------l-r

/------

---------------3-r

.-------

FIGURE 1.3. Cantilever construction applied to pre-stressed concrete bridges.

the segmental concept to further its field of appli-cation.

1.2 Development of Cantilever Construction

The idea of cantilever construction is ancient in theOrient. Shogun’s Bridge located in the city ofNikko, Japan, is the earliest recorded cantileverbridge and dates back to the fourth century. TheWandipore Bridge, Figure 1.4, was built in theseventeenth century in Bhutan, between India andTibet. It is constructed from great timbers thatare corbeled out toward each other from mas-sive abutments and the narrowed interval finallycapped with a light beam.’

FIGURE 1.4. Wandipore Bridge.

Develofwnent of Cantilever Construction 3

That half an arc should stand upon theground

Without support while building, or a rest;This caus’d the theorist’s rage and sceptic’s

jest.

Prefabrication techniques were successfullycombined with cantilever construction in manybridges near the end of the nineteenth century, asexemplified by such notable structures as the Firthof Forth Bridge, Figure 1.6, and later the QuebecBridge, Figure 1.7, over the Saint Lawrence River.These structures bear witness to the engineeringgenius of an earlier’ generation. Built more re-cently, the Greater New Orleans Bridge over theMississippi River, Figure 1.8, represents moderncontemporary long-span steel cantilever construc-tion.

Because the properties and behavior of pre-stressed concrete are related more closely to thoseof structural steel than those of conventional rein-forced concrete, the application of this material tocantilever construction was a logical step in thecontinuing development of bridge engineering.

FIGURE 1.7. Quebec Bridge.

FIGURE 1.8. Greater New Orleans Bridge.

4 Prestressed Concrete Bridges and Segmental Construction

This application has evolved over many years bythe successive development of many concepts andinnovations. In order to see how the present stateof the art has been reached, let us briefly trace thedevelopment of prestressed concrete and in par-ticular its application to bridge construction.

1.3 Evolution of Prestressed Concrete

The invention of reinforced concrete stirred theimagination of engineers in many countries. Theyenvisioned that a tremendous advantage could beachieved, if the steel could be tensioned to put thestructure in a permanent state of compressiongreater than any tensile stresses generated by theapplied loads. The present state of the art of pre-stressed concrete has evolved from the effort andexperience of many engineers and scientists overthe past ninety years. However, the concept of pre-stressing is centuries old. Swiss investigators haveshown that as early as 2700 B.C. the ancient Egyp-tians prestressed their seagoing vessels longitudi-nally. This has been determined from pictorialrepresentations found in Fifth Dynasty tombs.

The basic principle of prestressing was used inthe craft of cooperage when the cooper woundropes or metal bands around wooden staves toform barrels.3 When the bands were tightened,they were under tensile prestress, which createdcompression between the staves and enabled themto resist hoop tension produced by internal liquidpressure. In other words, the bands and staveswere both prestressed before they were subjectedto any service loads. The wooden cartwheel with itsshrunk-on iron rim is another example of pre-stressed construction.

The first attempt to introduce internal stresses inreinforced concrete members by tensioning thesteel reinforcement was made about 1886 whenP. H. Jackson, an engineer in San Francisco, obtaineda United States patent for tightening steel rods inconcrete members serving as floor slabs. In l&S,C. E. W. DGhring of Berlin secured a patent for themanufacture of slabs, battens, and small beams forstructural engineering purposes by embeddingtensioned wire in concrete in order to reducecracking. This was the first attempt to provide pre-cast concrete units with a tensioned reinforcement.

Several structures were constructed using theseconcepts; however, only mild steel reinforcementwas available at the time. These structures at firstbehaved according to predictions, but because solittle prestress force could be induced in the mild

steel, they lost their properties because of the creepand shrinkage of the concrete. In order to recoversome of the losses, the possibility of retighteningthe reinforcing rods after some shrinkage andcreep of the concrete had taken place wassuggested in 1908 by C. R. Steiner of the UnitedStates. Steiner proposed that the bond of em-bedded steel bars be destroyed by lightly tension-ing the bars while the concrete was still young andthen tensioning them to a higher stress when theconcrete had hardened. Steiner was also the first tosuggest the use of curved tendons.

In 1925, R. E. Dill of Nebraska took a furtherstep toward freeing concrete beams of any tensilestresses by tensioning high-tensile steel wires afterthe concrete had hardened. Bonding was to beprevented by suitably coating the wires. Heexplicitly mentioned the advantage of using steelwith a high elastic limit and high strength as com-pared to ordinary reinforcing bars.

In 1928, E. Freyssinet of France, who is creditedwith the modern development of prestressed con-crete, started using high-strength steel wires forprestressing. Although Freyssinet also tried themethod of pretensioning, where the steel wasbonded to the concrete without end anchorages,the first practical application of this method wasmade by E. Hoyer about 1938. Wide application ofthe prestressing technique was not possible untilreliable and economical methods of tensioning andend anchorage were devised. From approximately1939 on, E. Freyssinet, Magnel, and others de-veloped different methods and procedures. Pre-stress began to gain some importance about 1945,while alternative prestressing methods were beingdevised by engineers in various countries.

During the past thirty years, prestressed con-crete in the United States has grown from abrand-new idea into an accepted method of con-crete construction. This growth, a result of a newapplication of existing materials and theories, is initself phenomenal. In Europe the shortage of ma-terials and the enforced economies in constructiongave prestressed concrete a substantial start. De-velopment in the United States, however, wasslower to get underway. Designers and contractorshesitated mainly because of their lack of experi-ence and a reluctance to abandon more familiarmethods of construction. Contractors, therefore,bid the first prestressed concrete work conserva-tively. Moreover, the equipment available for pre-stressing and related techniques was essentiallynew and makeshift. However, experience wasgained rapidly, the quality of the work improved,

Evolution of Prestressed Concrete Bridges 5

FIGURE 1.9. Freyssinet’s Esblv Bridge on the MarneRiver.

and prestressed concrete became more and morecompetitive with other materials.

1.4 Evolution of Prestressed Concrete Bridges

Although France took the lead in the developmentof prestressed concrete, many European countriessuch as Belgium, England, Germany, Switzerland,and Holland quickly showed interest. As early as1948, Freyssinet used prestressed concrete for theconstruction of five bridges over the Marne Rivernear Paris, with 240 ft (74 m) spans of an excep-tionally light appearance, Figure 1.9. A surveymade in Germany showed that between 1949 and1953, out of 500 bridges built, 350 were pre-stressed.

FIGURE 1.10 Walnu t Lane Br idge , Phil,~dcll~hia(courtesy of the Portland Cement Association).

Prestressing in the United States followed a dif-ferent course. Instead of linear prestressing, cir-cular prestressing as applied to storage tanks tookthe lead. Linear prestressing as applied to beamsdid not start until 1949. The first structure of thistype was a bridge in Madison County, Tennessee,followed in 1950 by the well-known 160 ft (48.80m) span Walnut Lane Bridge in Philadelphia, Fig-ure 1.10. By the middle of 1951 it was estimatedthat 175 bridges and 50 buildings had been con-structed in Europe and no more than 10 structuresin the United States. In 1952 the Portland CementAssociation conducted a survey in this countryshowing 100 or more structures completed or

FIGURE 1.11. AASHTO-PC1 I-girder cross sections.


under construction. In 1953 it was estimated thatthere were 75 bridges in Pennsylvania alone.

After the Walnut Lane Bridge, which was cast inplace and post-tensioned, precast pretensionedbridge girders evolved, taking advantage of the in-herent economies and quality control achievablewith shop-fabricated members. With few excep-tions, during the 1950s and early 196Os, most mul-t ispan precast prestressed bridges bui l t in theUnited States were designed as a series of simplespans. T h e y w e r e d e s i g n e d w i t h s t a n d a r dAASHTO-PCI* girders of various cross sections,Figure 1.11, for spans of approximately 100 ft(30.5 m), but more commonly for spans of 40 to 80ft (12 to 24 m). The advantages of a continuouscast-in-place structure were abandoned in favor oft h e s i m p l e r c o n s t r u c t i o n o f f e r e d b y plant-produced standardized units.

At this time, precast pretensioned membersfound an outstanding application in the LakePontchartrain crossing north of New Orleans,Louisiana. The crossing consisted of more than2200 identical 56 ft (17 m) spans, Figures 1.12through 1.14. Each span was made of a single 200ton monolith with pretensioned longitudinal gird-

*American Associa t ion of Sta te Highway and Transpor ta t ionOfficials (previously known as AASHO, American Associationof State Highway Officials) and Prestressed Concrete Institute.

FIGURE 1.12. Lake Pontchartrain Bridge, U.S.A.

ers and a reinforced concrete deck cast integrally,rest ing in turn on a precast cap and two pre-stressed spun piles. The speed of erection was in-credible, often more than eight complete spansplaced in a single day.

In the middle 1960s a growing concern wasshown about the safety of highways. TheAASHTO Traffic Safety Committee called in a1967 report4 for the “ . . . adoption and use of two-span bridges for overpasses crossing divided high-ways . . . to eliminate the bridge piers normallyplaced adjacent to the shoulders,” Figure 1.15. In-terstate highways today require overpasses withtwo, three, and four spans of up to 180 ft (54.9 m)or longer. In the case of river or stream crossings,

FIGURE 1.13. Lake Pontchartrain Bridge, U.S.A.

33'4

18'4' I

I I

(b)

FIGURE 1.14. Lake Pontchartrain Bridge, U.S.A. (a) Longitudinal section. (b) Trans-verse section.

7

-

8 bestressed Concrete Bridges and Segmental Construction

STANMRD 4-SPAN INTERSTATE CROSSING

I

tg1 7 7 ’250’

FIGURE 1.15. Standard four-span interstate crossing(courtesv of the Portland Cement Association).

longer spans in the range of 300 ft (91.5 m) orlonger may be required, and there is a very distincttrend toward longer-span bridges. It soon becameapparent that the conventional precast preten-sioned AASHTO-PC1 girders were limited by theirtransportable length and weight. Transportationover the highways limits the precast girder to alength of 100 to 120 ft (30.5 to 36.6), dependingupon local regulations.

I .5 Long-Span Bridges with ConventionalPrecast Girders

As a result of longer span requirements a study wasconducted by the Prestressed Concrete Institute(PCI) in cooperation with the Portland Cement As-sociation (PCA).S This study proposed that simplespans up to 140 ft (42.7 m) and continuous spansup to 160 ft (48.8 m) be constructed of standardprecast girders up to 80 ft (24 m) in length joinedby splicing. To obtain longer spans the use of in-clined or haunched piers was proposed.

The following discussion and illustrations arebased on the grade-separation studies conductedby PC1 and PCA. Actual structures will be illus-

trated, where possible, to emphasize the particulardesign concepts.

The design study illustrated in Figure 1.16 usescast-in-place or precast end-span sections and atwo-span unit with AASHTO I girders.6 Narrowmedian piers are maintained in this design, but theabutments are extended into the spans by as muchas 40 ft (12 m) using a precast or cast-in-placeframe in lieu of a closed or gravity abutment.When site conditions warrant, an attractive type ofbridge can be built with extended abutments.

A similar span-reducing concept is developed inFigure 1.17, using either reinforced or prestressedconcrete for cantilever abutments. An aestheticabutment design in reinforced concrete was de-veloped for a grade-separation structure on theTrans-Canada Highway near Drummondville inthe Province of Quebec, Figure 1.18. This pro-vided a 324 ft (9.9 m) span reduction that led to theuse of type IV Standard AASHTO I girders tospan 974 ft (29.7 m) to a simple, narrow medianpier.

A cast-in-place reinforced concrete frame withoutward-sloping legs provides a stable, center sup-porting structure that reduces span length by 29 ft(8.8 m), Figure 1.19. This enables either standardbox sections or I sections 84 ft (25.6 m) long to beused in the two main spans. This layout was usedfor the Hobbema Bridge in Alberta, B.C., Canada,shown in Figure 1.20. This bridge was built withprecast channel girder sections, but could be builtwith AASHTO I girders or box sections. The me-dian frame with inclined legs was cast in place.

The schematic and photograph in Figures 1.21and 1.22 show the Ardrossan Overpass in Alberta.It is similar to the Hobbema Bridge except that thespans are longer and, with the exception of acast-in-place footing, the median frame is made upof precast units post-tensioned together, Figure1.21. The finished bridge, Figure 1.23, has a

Carl-in-place Froma

SECTION A-A

FIGURE 1.16. Extended abutments (courtesy of the Prestressed Concrete Institute,from ref. 6).

Long-Span Bridges with Conventional Precast Girders

APPROX. 36’ ELEVATION APPROX. *I’-

9

r;Its’-0” IS’ -0”

T Y P E lxT Y P E lxAASHO OIROERAASHO OlROtR

S E C T I O NS E C T I O N

FIGURE 1.1’7. Cantilevered abutments (courtesy of the Prestressed ConcreteInstitute, from ref. 6).

\,\_ \\\pleasing appearance. The standard units were

\ \\\\\ \ channel-shaped stringers 64 in. wide and 41 in.,, \\ \ \\

\\ \deep (1.6 m by 1.04 m). The use of precast unitsallowed erection of the entire superstructure, in-\ \\ eluding the median frame, in only three weeks.The bridge was opened to traffic just eleven weeksafter construction began in the early summer of1966.

By use of temporary bents, Figure 1.24,standard units 60 ft (18.3 m) long can be placedover the median pier and connected to main spanunits with cast-in-place reinforced concrete splices

FIGURE 1.18. Drummondville Bridge (courtesy of located near the point of dead-load contraflexure.the Portland Cement Association).

ELEVATION

SECTIONS A -A

FIGURE 1.19. Median frame cast in place (courtesy of the PrestressedConcrete Institute, from ref. 6).

1 0 Prestressed Concrete Bridges and Segmental Construction

FIGURE 1.20. Hobbema Bridge, completed structure(courtesy of the Portland Cement Association).

This design is slightly more expensive than previ-ous ones but it provides the most open type two-span structure.

The structural arrangement of the SebastianInlet Bridge in Florida consists of a three-span unitover the main channel, Figure 1.25. The end spanof this three-span unit is 100 ft (30.5 m) long andcantilevers 30 ft (9 m) beyond the piers to supporta 120 ft (36.6 m) precast prestressed drop-in span,Figure 1.26. The end-span section was built in twosegments with a cast-in-place splice with the help ofa falsework bent. The Napa River Bridge at Val-lejo, California (not to be confused with the NapaRiver Bridge described in Section 2.1 l), used aprecast concrete cantilever-suspended span con-cept similar to the Sebastian Inlet Bridge, at aboutthe same time. The only difference was that thecantilever girder was a single girder extending

from the side pier over the main pier to the hinge-support for the suspended span.

The type of const ruct ion that uses long,standard, precast, prestressed units never quiteachieved the recognition it deserved. As spans in-creased, designers turned toward post-tensionedcast-in-place box girder construction. The Califor-nia Division of Highways, for example, has beenquite successful with cast-in-place, multicell, post-tensioned box girder construction for multispanstructures with spans of 300 ft (91.5 m) and evenlonger. However, this type of construction has itsown limitations. The extensive formwork usedduring casting often has undesirable effects on theenvironment or the ecology.

1.6 Segmental Construction

Segmental construction has been defined’ as amethod of construction in which primary load-supporting members are composed of individualmembers called segments post-tensioned together.The concepts developed in the PCI-PCA studiesand described in the preceding section come underthis definition, and we might call them “longitudi-nal” segmental construction because the individualelements are long with respect to their width.

In Europe, meanwhile, segmental constructionproceeded in a slightly different manner in con-junction with box girder design. Segments werecast in place in relatively short lengths but in full-rpadway width and depth. Today segmental con-struction is usually understood to be the type de-veloped in Europe. However, as will be shownlater, the segments need not be of full-roadway

E L E V A T I O N

81p-40AASHO-PCIBOX SECTION 3’-6” 6’-6* b’-6”

&X-IONS A - A

FIGURE 1.21. Median frame precast (courtesy of the Prestressed CotInstitute, from ref. 6).

xrete

Segmental Construction

FIGURE 1.22. Ardrossan Overpass precast medianframe (courtesy of the Portland Cement Association).

width and can become rather long in the lon-gitudinal direction of the bridge, depending on theconstruction system utilized.

Eugene Freyssinet, in 1945 to 1948, was the firstto use precast segmental construction for pre-stressed concrete bridges. A bridge at Luzancyover the Marne River about 30 miles east of Paris,Figure 1.27, was followed by a group of five precastbridges over that river. Shortly thereafter, UlrichFinsterwalder applied cast-in-place segmental pre-stressed construction in a balanced cantileverfashion to a bridge crossing the Lahn River at Bal-duinstein, Germany. This system of cantileversegmental construction rapidly gained wide ac-ceptance in Germany, after construction of abridge crossing the Rhine at Worms in 1952, asshown in Figure 1.28,s with three spans of 330,371, and 340 ft (100, 113, and 104 m). More than300 such structures, with spans in excess of 250 ft(76 m), were constructed between 1950 and 1965

FIGURE 1.23. Completed Ardrossan o\crpass(courtesy of the Portland Cement Association).

in Europe.s Since then the concept has spreadthroughout the world.’

Precast segmental construction also was evolvingduring this period. In 1952 a single-span countybridge near Sheldon, New York, was designed bythe Freyssinet Company. Although this bridge wasconstructed of longitudinal rather than the Euro-pean transverse segments, it represents the firstpractical application of match casting. The bridgegirders were divided into three longitudinal seg-ments that were cast end-to-end. The center seg-ment was cast first and then the end segments werecast directly against it. Keys were cast at the jointsso that the three precast elements could be joinedat the site in the same position they hid in the pre-casting yard. Upon shipment to the job site thethree elements of a girder were post-tensioned to-gether with cold joints. l”,ll

The first major application of match-cast, pre-cast segmental construction was not consummated

SECflON A-A

FIGURE 1.24. Field spike for continuity (courtesy of the Prestressed Con-crete Institute, from ref. 6).


FIGURE 1.25. Sebastian Inlet Bridge (courtesy of thePortland Cement Association).

until 1962. This structure, designed by Jean Mullerand built by Entreprises Campenon Bernard, wasthe Choisy-le-Roi Bridge over the Seine Riversouth of Paris, Figure 1.29. This concept has beenrefined and has spread from France to all parts ofthe world.

The technology of cast-in-place or precast seg-mental bridges has advanced rapidly in the last

decade. During its initial phase the balancedcantilever method of construction was used. Cur-rently, other techniques such as span-by-span, in-cremental launching, or progressive placementalso are available. Any of these constructionmethods may call on either cast-in-place or precastsegments or a combination of both. Consequently,a variety of design concepts and constructionmethods are now available to economically pro-duce segmental bridges for almost any site condi-tion.

Segmental bridges may be classified broadly byfour criteria:

1. The ultimate use of the bridge-that is, high-way or railway structure or combinationthereof. Although many problems are com-mon to these two categories, the considerableincrease of live loading in a railway bridgeposes special problems that call for specific so-lutions.

2. The type of structure in terms of staticalscheme and shape of the main bending mem-bers. Many segmental bridges are box girderbridges, but other types such as arches orcable-stayed bridges show a wide variety inshape of the supporting members.

3. The use of cast-in-place or precast segments ora combination thereof.

4. The method of construction.

The sections that follow will deal briefly with thelast three classifications.

1.7 Various Types of Structures

From the point of view of their statical scheme,there are essentially five categories of structures:(1) girders, (2) trusses, (3) rigid frames, (4) archframes, and (5) cable-stayed bridges.

1.7.1 GIRDER BRIDGES

Box girders in the majority of cases are the mostefficient and economical design for a bridge. Whenconstructed in balanced cantilever, box girderdecks were initially made integral with the pierswhile a special expansion joint was provided at thecenter of each span (or every other span) to allow

\

Conventional

Section A-A

FIGURE 1.26. Sebastian Inlet Bridge (courtesy of the Prestressed Concrete In-stitute, from ref. 6).

Various Types of Structures 13

FIGURE 1.27. I,uzanc~ Bridge over the Marne River.

FIGURE 1.28. b’ornx Bridge (courtesy of Dyckerhoff& LVidmann).

CF E N D PIEIf -

MAIN PIER

6lb’ 176’-0’ 1 I _ 176’-0“ I

FIGURE 1.29. Choisy-le-Roi Bridge.

for volume changes and to control differentialdeflections between individual cantilever arms. It isnow recognized that continuity of the deck is desir-able, and most structures are now continuous overseveral spans, bearings being provided betweendeck and piers for expansion.

Today, the longest box girder bridge structurethat has been built in place in cantilever is theKoror Babelthuap crossing in the Pacific Trust ter-ritories with a center span of 790 ft (241 m), Figure1.30.r2 A box girder bridge has been proposed for

L

\ 12% ._

/J I

12/-O”

FIGURE 1.30. Koror-Babelthuap Bridge, elevation and cross section (ref. 12).


Longitudmal section

r 1G-r-r

Typical sections at span centerand over main piers

IF-4FIGURE 1.31. The Great Belt Project.

the Great Belt Project in Denmark with a 1070 ft(326 m) clear main span, Figure 1.31. The boxgirder design has been applied with equal suc-cess to the construction of difficult and spectacularstructures such as the Saint Cloud Bridge overthe Seine River near Paris, Figure 1.32, or to theconstruction of elevated structures in very con-gested urban areas such as the B-3 Viaducts nearParis, Figure 1.33.

1.7.2 TRUSSES

When span length increases, the typical box girderbecomes heavy and difficult to build. For the pur-pose of reducing dead weight while simplifyingcasting of very deep web sections, a truss with openwebs is a very satisfactory type that can be conve-niently built in cantilever, Figure 1.34. The tech-nological limitations lie in the complication of con-nections between prestressed diagonals andchords. An outstanding example is the Rip Bridgein Brisbane, Australia, Figure 1.35.

FIGURE 1.33. R-3 Viaciuc t\. FI ‘111~ e.

The cantilever method has potential applicationsbetween the optimum span lengths of typical boxgirders for the low ranges and of stayed bridges forthe high ranges.

1.7.3 FRAMES WITH SLANT LEGS

When the configuration of the site allows, the useof inclined legs reduces the effective span length.

FIGURE 1.34. Long-span concrete trusses.

FIGURE 1.32. Saint Cloud Bridge, France. FIGURE 1.35. Rip Bridge, BI ishne, Xu\tl nli,l

Various Types of Structures 1 5

FIGURE 1.36. Long-span frame.

Provisional back stays or a temporary pier areneeded to permit construction in cantilever, Figure1.36. This requirement may sometimes presentdifficulty. An interesting example of such a schemeis the Bonhomme Bridge over the Blavet River inFrance, Figure 1.37.

The scheme is a transition between the boxgirder with vertical piers and the true arch, wherethe load is carried by the arch ribs along the pres-sure line with minimum bending while the deck issupported by spandrel columns.

FIGURE 1.37. Bonhomme Bridge.

1.7.4 CONCRETE ARCH BRIDGES

Concrete arches are an economical way to transferloads to the ground where foundation conditionsare adequate to resist horizontal loads. EugeneFreyssinet prepared a design for a 1000 meter(3280 ft) clear span 40 years ago. Because of con-struction difficulties, however, the maximum spanbuilt to date (1979) has been no more than 1000 ft(300 m). Construction on falsework is madedifficult and risky by the effect of strong windsduring construction.

The first outstanding concrete arch was built atPlougastel by Freyssinet in 1928 with three 600 ft(183 m) spans, Figure 1.38. Real progress wasachieved only when free cantilever and provisionalstay methods were applied to arch construction,Figure 1.39. The world record is presently the KirkBridge in Yugoslavia, built in cantilever and com-

FIGURE 1.38. Plougastel Bridge, France.


FIGURE 1.39. Concrete arches.

,,,) . . . \ ,. . . , , ~ \ ,_

i

FIGURE 1.40. Kirk Bridges, Yugoslavia.

pleted in 1979 with a clear span of 1280 ft (390 m),Figure 1.40.

1.7.5 CONCRETE CABLE-STAYED BRIDGES’”

When a span is beyond the reach of a conventionalgirder bridge, a logical step is to suspend the deckby a system of pylons and stays. Applied to steelstructures for the last twenty years, this approachgained immediate acceptance in the field of con-crete bridges when construction became possible

FIGURE 1.41. Long-span concrete cable-stayed bridges.

I a nmdrthm1.a l

Cast-in-Place and Precast Segmental Construction 1 7

the structure’s deformability, particularly duringconstruction. Deflections of a typical cast-in-placecantilever are often two or three times those of thesame cantilever made of precast segments.

The local effects of concentrated forces behindthe anchors of prestress tendons in a young con-crete (two or four days old) are always a potentialsource of concern and difficulties.

FIGURE 1.42. Krotonne Bridge, France.

and economical in balanced cantilever with a largenumber of stays uniformly distributed along thedeck, Figure 1.41, The longest span of this type isthe Brotonne Bridge in France with a 1050 ft (320m) clear main span over the Seine River, Figure1.42. Single pylons and one line of stays are locatedalong the centerline of the bridge.

1.8 Cast-in-Place and Precast SegmentalConstruction

1.8.1 CHARACTERISTICS OF CAST-IN-PLACESEGMENTS

In cast-in-place construction, segments are cast oneafter another in their final location in the structure.Special equipment is used for this purpose, such astravelers (for cantilever construction) or formworkunits moved along a supporting gantry (for span-by-span construction). Each segment is reinforcedwith conventional untensioned steel and some-times by transverse or vertical prestressing or both,while the assembly of segments is achieved by lon-gitudinal post-tensioning.

Because the segments are cast end-to-end, it isnot difficult to place longitudinal reinforcing steelacross the joints between segments if the designcalls for continuous reinforcement. Joints may betreated as required for safe transfer of all bendingand shear stresses and for water tightness in ag-gressive climates. Connection between individuallengths of longitudinal post-tensioning ducts maybe made easily at each joint and for each tendon.

The method’s essential limitation is that thestrength of the concrete is always on the criticalpath of construction and it also influences greatly

I.82 CHARACTERISTICS OF PRECAST SEGMENTS

In precast segmental construction, segments aremanufactured in a plant or near the job site, thentransported to their final position for assembly.Initially, joints between segments were of conven-tional type: either concrete poured wet joints ordry mortar packed joints. Modern segmental con-struction calls for the match-casting technique, asused for the Choisy-le-Roi Bridge and further de-veloped and refined, whereby the segments areprecast against each other, preferably in the samerelative order they will have in the final structure.No adjustment is therefore necessary betweensegments before assembly. The joints are eitherleft dry (in areas where climate permits) or made ofa very thin film of epoxy resin or mineral complex,which does not alter the match-casting properties.There is no need for any waiting period for jointcure, and final assembly of segments by prestres-sing may proceed as fast as practicable.

Because the joints are of negligible thickness,there is usually no mechanical connection betweenthe individual lengths of tendon ducts at the joint.

Usually no attempt is made to obtain continuityof the longitudinal conventional steel through thejoints, although several methods are available andhave been applied successfully (as in the PascoKennewick cable-stayed bridge, for example).Segments may be precast long enough in advanceof their assembly in the structure to reachsufficient strength and maturity and to minimizeboth the deflections during construction and theeffects of concrete shrinkage and creep in the finalstructure.

If erection of precast segments is to proceedsmoothly, a high degree of geometry control is re-quired during match casting to ensure accuracy.

1.8.3 CHOICE BETWEEN CAST-IN-PLACE ANDPRECAST CONSTRUCTION

Both cast-in-place methods and precast methodshave been successfully used and produce substan-


tially the same final structure. The choice dependson local conditions, including size of the project,time allowed for construction, restrictions on ac-cess and environment, and the equipment availableto the successful contractor. Some items of interestare listed below:

1. Speed of Construction Basically, cast-in-placecantilever construction proceeds at the rate of onepair of segments 10 to 20 ft (3 to 6 m) long ever)four to seven days. On the average, one pair oftravelers permits the completion of 150 ft (46 m) ofbridge deck per month, excluding the transferfrom pier to pier and fabrication of the pier table.On the other hand, precast segmental constructionallows a considerably faster erection schedule.a . For the Oleron Viaduct, the average speed ofcompletion of the deck was 750 ft (228 m) per monthfor more than a year.b. For both the B-3 Viaducts in Paris and theLong Key Bridge in Florida, a typical 100 to 150 ft(30 to 45 m) span was erected in two working days,representing a construction of 1300 ft (400 m) of-finished bridge per month,c. Saint Cloud Bridge near Paris, despite the ex-ceptional difficulty of its geometry and designscheme, was constructed in exactly one year, itstotal area amounting to 250,000 sq ft (23,600 sqm).

It is evident, then, that cast-in-place cantilever con-struction is basically a slow process, while precastsegmental with matching joints is among the fas-test.

2. Investment in Special Equipment Here thesituation is usually reversed. Cast-in-place requiresusually a lower investment, which makes it com-petitive on short structures with long spans [forexample, a typical three-span structure with acenter span in excess of approximately 350 ft (100Ml.

In long, repetitive structures precast segmentalmay be more economical than cast-in-place. Forthe Chillon Viaducts with twin structures 7000 ft(2 134 m) long in a difficult environment, a detailedcomparative estimate showed the cast-in-placemethod to be 10% more expensive than the pre-cast.

3. Size and Weight of Segments Precast seg-mental is limited by the capacity of transportationand placing equipment. Segments exceeding 250tons are seldom economical. Cast-in-place con-struction does not have the same limitation, al-

though the weight and cost of the travelers are di-rectly proportional to the weight of the heaviestsegment.

4. Environment Restrictions Both precast andcast-in-place segmental permit all work to be per-formed from the top. Precast, however, adjustsmore easily to restrictions such as allowing work toproceed over traffic or allowing access of workmenand materials to the various piers.

1.9 Various Methods of Construction

Probably the most significant classification of seg-mental bridges is by method of construction .41-though construction methods may be as varied asthe ingenuity of the designers and contractors,they fall into four basic categories: (1) balancedcantilever, (2) span-by-span construction, (3) pro-gressive placement construction, and (4) incre-mental launching or push-out construction.

1.9.1 CAST-I.\‘-PL4CE BAL,-I,VCED C.4.iTILEC’ER

The balanced or free cantilever construction con-cept was originally developed to eliminatefalsework. Temporary shoring not only is expen-sive but can be a hazard in the case of suddenfloods, as confirmed by many failures. Over naviga-ble waterways or traveled highways or railways,falsework is either not allowed or severely re-stricted.’ Cantilever construction, whether cast inplace or precast, eliminates such difficulties: con-struction may proceed from the permanent piers,and the structure is self-supporting at all stages.The basic principle of the method was outlined inSection 1.1 (Figure 1.3).

In cast-in-place construction the formwork issupported from a movable form carrier, Figure1.1. Details of the form travelers are shown in Fig-ure 1.43. The form traveler moves forward on railsattached to the deck of the completed structureand is anchored to the deck at the rear. With theform traveler in place, a new segment is formed,cast, and stressed to the previously constructedsegment. In some instances a covering may be pro-vided on the form carrier so that work may pro-ceed during inclement weather, Figure 1.44.

The operation sequence in cast-in-place bal-anced cantilever construction is as follows:

1 . Setting up and adjusting carrier.

2. Setting up and aligning forms.

Various Methods of Construction

CENTERJACK

i-J?FORM TRAVELLER

8, i,!-Lu,. ! I

ADDITIONAL i-HUN I ALWORKING PLATFORM

REAR GANG-BOARD \BOTTOM ~ONTAL LOWERFRAME WORK WORKING PLATFORM

FIGURE 1.43. Form traveler (courtesy of Dyckerhoff & Widmann).

3. Placing reinforcement and tendon ducts.4. Concreting.5. Inserting prestress tendons in the segment and

stressing.6. Removing the formwork.7. Moving the form carrier to the next position

and starting a new cycle.

Initially, the normal construction time for asegment was one week per formwork unit. Ad-vances in precast segmental construction have beenapplied recently to the cast-in-place method inorder to reduce the cycle of operations and in-crease the efficiency of the travelers. With today’stechnology it does not seem possible to reduce the

FIGURE 1.44. Bendorf Bridge form traveler (cour-tesy of Dyckerhoff & Widmann).

construction time for a full cycle below two work-ing days, and this only for a very simple structurewith constant cross section and a moderate amountof reinforcing and prestress. For a structure withvariable depth and longer spans, say above 250 ft(75 m), the typical cycle is more realistically three tofour working days.

Where a long viaduct type structure is to be con-structed of cast-in-place segments, an auxiliarysteel girder may be used to support the formwork,Figure 1.45, as on the Siegtal Bridge. This equip-

FIGURE 1.45. Siegtal Bridge, use of an auxiliary trussin cast-in-place construction.


ment may also be used to stabilize the free-standingpier by the anchoring of the auxiliary steel girderto the completed portion of the structure. Nor-mally, in construction using the form traveler pre-viously described, a portion of the end spans (nearthe abutments) must be cast on falsework. If theauxiliary steel girder is used, this operation may beeliminated. As soon as a double typical cantilever iscompleted, the auxiliary steel girder is advanced tothe next pier. Obviously, the economic justificationfor use of an auxiliary steel girder is a function ofthe number of spans and the span length.

I-9.2. PRECAST BALANCED CANTILEVER

For the first precast segmental bridges in Paris(Choisy-le-Roi, Courbevoie, and so on, 1961 to1965) a floating crane was used to transfer the pre-cast segments from the casting yard to the bargesthat transported them to the project site and wasused again to place the segments in the structure.The concept of self-operating launching gantrieswas developed shortly thereafter for the construc-tion of the Oleron Viaduct (1964 to 1966). Furtherrefined and extended in its potential, this concepthas been used in many large structures.

The erection options available can be adapted toalmost all construction sites.

1. Crane Placing Truck or crawler cranes areused on land where feasible; floating cranes maybe used for a bridge over navigable water, Figure1.46. Where site conditions allow, a portal cranemay be used on the full length of the deck, prefer-ably with a casting yard aligned with the deck near

FIGURE 1.46. Segment erection by barge-mountedcrane, Capt. Cook Bridge, Australia (courtesy of G. Be-loff, Main Roads Department, Brisbane, Australia).

one abutment to minimize the number of handlingoperations, Figure 1.47.

2. Beam and Winch Method If access by land orwater is available under the bridge deck, or at leastaround all permanent piers, segments may belifted into place by hoists secured atop the previ-ously placed segments, Figure 1.48. At first thismethod did not permit the installation of precastpier segments upon the bridge piers, but it hasbeen improved to solve this problem, as will be ex-plained later.

3. Launching Gantries There are essentiallytwo families of launching gantries, the details ofwhich will be discussed in a later chapter. Here webriefly outline their use.

In the first family developed for the Oleron Via-duct, Figures 1.49 and 1.50, the launching gantryis slightly more than the typical span length, andthe gantry’s rear support reaction is applied nearthe far end of the last completed cantilever. Allsegments are brought onto the finished deck andplaced by the launching gantry in balanced can-tilever; after completion of a cantilever, afterplacing the precast segment over the new pier, thelaunching gantry launches itself to the next span tostart a new cycle of operations.

In the second family, developed for the De-venter Bridge in Holland and for the Rio NiteroiBridge in Brazil, the launching gantry has a lengthapproximately twice the typical span, and the reac-tion of the legs is always applied above the perma-nent concrete piers, Figures 1.51 and 1.52.

Placing segments with a launching gantry is nowin most cases the most elegant and efficientmethod, allowing the least disturbance to the envi-ronment.

1.9.3 SPAN-BY-SPAN CONSTRUCTION

The balanced cantilever construction method wasdeveloped primarily for long spans, so that con-struction activity for the superstructure could beaccomplished at deck level without the use of ex-tensive falsework. A similar need in the case oflong viaduct structures with relatively shorterspans has been filled by the development of aspan-by-span methodology using a form traveler.The following discussion explains this methodol-%Y* 13.14.15.16

In long viaduct structures a segmental span-by-span construction may be particularly advanta-geous. The superstructure is executed in one direc-

Various Methods of Construction 21

COUPE TRANSVERSALE

FIGURE 1.47. Mirabeau Bridge at Tours, France.

tion, span by span, by means of a form traveler, the field. The form traveler may be supported onFigure 1.53, with construction joints or hinges lo- the piers, or from the edge of the previously com-cated at the point of contraflexure. The form car- pleted construction, at the joint location, and at therier in effect provides a type of factory operation forward pier. In some instances, as in the ap-transplanted to the job site. It has many of the ad- proaches of Rheinbrticke, Dusseldorf-Flehe, the

: . . movable formwork may be supported from theground, Figure 1.54. The form traveler consists ofa steel superstructure, which is moved from thecompleted portion of the structure to the next spanto be cast. For an above-deck carrier, largeformwork elements are suspended from steel rodsduring concreting. After concreting and post-ten-sioning, the forms are released and rolled forwardby means of the structural steel outriggers on bothsides of the form traveler’s superstructure. For abelow-deck carrier, a similar procedure is followed.

Many long bridges of this type have been built inGermany, France, and other countries. Typicalconstruction time for a 100 ft (30 m) spansuperstructure is five to eight working days, de-pending upon the complexity of the structure.Deck configuration for this type of construction isusually a monolithic slab and girder (T beam ordouble T), box girder, or a mushroom cross sec-


J-I5 2 . 0 0 m 170ft 54.OOm _ 180 ft

1 0 6 . 0 0 Ill 3 5 0 ff

(6)

J 1 0 6 . 0 0 Ill 3 5 0 ft I

Cc)

FIGURE 1.49. First family of launching gantries (Ole-ron Viaduct).

tion. This method has been used recently in theUnited States on the Denny Creek project in thestate of Washington.

In its initial form, as described above, the span-by-span method is a cast-in-place technique. Thesame principle has been applied in conjunctionwith precast segmental construction for two verylarge structures in the Florida Keys: Long KeyBridge and Seven Mile Bridge, with spans of 118 ft(36 m) and 135 ft (40 m), respectively. Segmentsare assembled on a steel truss to make a complete

4 80.00 m 2 6 0 f t c

FIGURE 1.51. Second family of launching gantries,Rio Niteroi Bridge.

span. Prestressing tendons then assure the assem-bly of the various segments in one span whileachieving full continuity with the preceding span,Figures 1.55 and 1.56. The floating crane used toplace the segments over the truss also moves thetruss from span to span. The contractor for theSeven Mile Bridge modified the erection schemefrom that used for Long Key Bridge by suspendinga span of segments from an overhead falseworktruss. This is the first application of a method thatseems to have a great potential for trestle struc-tures in terms of speed of construction and econ-omy.

1.9.4 PROGRESSIVE PLACEMENT CONSTRUCTION

Progressive placement is similar to the span-by-span method in that construction starts at one endof the structure and proceeds continuously to the

FIGURE 1.50. Placing precast segments on the Ole-ron Viaduct.

FIGURE 1.52. Rio Niteroi launching girder.

i of Construction 2 3

FIGURE 1.56. Placing segments on assembly t russ forLong Key Bridge.

other end. It derives its origin, however, from thecantilever concept. In progressive placementthe precast segments are placed from one end ofthe structure to the other in successive cantileverson the same side of the various piers rather thanby balanced cantilevers on each side of a pier. Atpresent, this method appears practicable andeconomical in spans ranging from 100 to 300 ft(30 to 90 m).

Because of the length of cantilever (one span) inrelation to construction depth, a movable tempo-rary stay arrangement must be used to limit thecantilever stresses during construction to a reason-able level. The erection procedure is illustrated inFigure 1.57. Segments are transported over thecompleted portion of the deck to the tip of thecantilever span under construction, where they arepositioned by a swivel crane that proceeds fromone segment to the next. Approximately one-thirdof the span from the pier may be erected by thefree cantilever method, the segments being held inposition by exterior temporary ties and final pre-stressing tendons. For the remaining two-thirds ofthe span, each segment is held in position by tem-porary external ties and by two stays passingthrough a tower located over the preceding piers.All stays are continuous through the tower and an-chored in the previously completed deck structure.The stays are anchored to the top flange of the boxgirder segments so that the tension in the stays canbe adjusted by light jacks.

Used for the first time in France on severalstructures, Figure 1.58, progressive placement isbeing applied in the United States for the con-struction of the Linn Cove Viaduct in NorthCarolina. In this bridge the precast pier construc-

FIGURE 1.55. Span-by-span assembly of precast seg- tion proceeds also from the deck to solve a difhcultm e n t s . problem of environmental restrictions.


FIGURE 1.57. Progressive placement erection procedure.

The progressive placement method may also be Segments of the bridge superstructure are castapplied to cast-in-place construction. in place in lengths of 30 to 100 ft ( 10 to 30 m) in

stationary forms located behind the abutment(s),1.9.5. INCREMENTAL LAUNCHING OR PUSH-OUT Figure 1.59. Each unit is cast directly against the

C O N S T R U C T I O N previous unit. After sufficient concrete strength isreached, the new unit is post-tensioned to the pre-

This concept was first implemented on the Rio Ca- vious one. The assembly of units is pushed forwardroni Bridge in Venezuela, built in 1962 and 1963 in a stepwise manner to permit casting of the suc-by its originators, Willi Baur and Dr. Fritz ceeding segments, Figure 1.60. Normally a workLeonhardt of the consulting firm of Leonhardt cycle of one week is required to cast and launch aand Andra (Stuttgart, Germany).” segment, regardless of its length. Operations are

Various Methods of Construction 25

FIGURE 1.60. Incremental launching sequence(courtesy of Prof. Fritz Leonhardt).

superstructure under its own weight at all stages oflaunching and in all sections. Four methods for thispurpose are used in conjunction with one another.

1. A first-stage prestress is applied concentricallyto the entire cross section and in successive in-crements over the entire length of thesuperstructure.

2. To reduce the large negative bending mo-ments in the front (particularly just before thesuperstructure reaches a new pier) a fabricatedstructural steel launching nose is attached tothe lead segment, Figure 1.62.

3. Long spans may be subdivided by means oftemporary piers to keep bending moments to areasonable magnitude. This constructiontechnique has been applied to spans up to 200ft (60 m) without the use of temporaryfalsework bents. Spans up to 330 ft (100 m)have been built using temporary supportingbents. The girders must have a constant depth,which is usually one-twelfth to one-sixteenth ofthe longest span.

4. Another method has been used successfully inFrance to control bending moments in the


FIGURE 1.61. Incremental launching o n J GUI ve(courtesy of Prof. Fritz Leonhardt).

deck in the forward part of the superstructure.A system using a tower and provisional stays isattached to the front part of the superstruc-ture. The tension of the stays and the corre-sponding reaction of the tower on the deck areautomatically and continuously controlledduring all launching operations to optimize thestress distribution in the deck, Figure 1.63.

After launching is complete, and the oppositeabutment has been reached, additional prestress-ing is added to accommodate moments in the finalstructure, while the original uniform prestressmust resist the varying moments that occur as thesuperstructure is pushed over the piers to its finalposition.

Today, the longest incrementally launched clearspan is over the River Danube near Worth, Ger-many, with a maximum span length of 550 ft (168m). Two temporary piers were used in the river forlaunching. The longest bridge of this type is theOlifant’s River railway viaduct in South Africa with23 spans of 147 ft (45 m) and a total length of 3400

‘FIGURE 1.62. Steel launching nose (courtesy of Prof.Fritz Leonhardt).

ft (1035 m). The incremental launching techniquewas used successfully for the first t ime in theUnited States for the construction of the WabashRiver Bridge at Covington, Indiana.

1 .I 0 Applications of Segmental Constructionin the United States

The state of the art of designing and constructingprestressed concrete segmental bridges has ad-vanced greatly in recent years. A wide variety ofstructural concepts and prestressing methods areused, and at least a thousand segmental bridgeshave been built throughout the world. We mayconclude that segmental prestressed concrete con-struction is a viable method for building highwaybridges. There are currently no known majorproblems that should inhibit utilization of seg-mental prestressed concrete bridges in the UnitedStates. They have been successfully consummatedin other countries and are increasingly being em-ployed in the United States.

Applications of Segmental Construction in the United States 2 7

fbJ

Cd)

FIGURE 1.63. Incremental launching with provi-sional tower and stays.

One of the earliest projects for which segmentalconstruction was considered was the proposed In-terstate I-266 Potomac River Crossing in Wash-ington, D.C., Figure 1.64, otherwise known as theThree Sisters Bridge. This structure contemplateda 750 ft (229 m) center span with side spans of 440ft (134 m) on reverse five-degree curves, built withcast-in-place segmental construction. Because ofenvironmental objections, this project never

FIGURE 1.64. ‘Three Sisters Bridge.

FIGURE 1.65. JFK hlcnwr ial Causewav. CorpusChristi, Texas.reached fruition.

The JFK Memorial Causeway (IntracoastalWaterway), Corpus Christi, Texas, Figure 1.65,represents the first precast, prestressed, segmental,balanced cantilever construction completed in theUnited States. It was opened to traffic in 1973. De-signed by the Bridge Division of the Texas High-way Department, it has a center span of 200 ft (61m) with end spans of 100 ft (30.5 m).

The first cast-in-place, segmental, balanced can-tilever, prestressed concrete bridge constructed inthe United States is the Pine Valley Bridge inCalifornia, on Interstate I-8 about 40 miles (64 km)east of San Diego. Designed by the California De-partment of Transportation, .the dual structure, FIGURE 1.66. Pine Valley Bridge (courtesy of

Figure 1.66, has a total length of 1716 ft (53.6 m) CALTRANS).

Pt-estressed Concrete Bridges and Segmental Construction

FIGURE 1.67. Rendering of Houston Ship Channel Bridge.

with spans of 270, 340, 450, 380, and 276 ft (82.3, 1 .I 1 Applicability and Advantages of Segmental103.6, 137.2, 115.8, and 84.1 m). Construction

As indicated previously, numerous segmentalbridge projects have been constructed or are con-templated in the United States. Many of them willbe discussed in detail in the following chapters.Among the most significant are the Houston ShipChannel Bridge with a clear span of 750 ft (228 m),which will be the longest concrete span in theAmericas, Figure 1.67, and the Seven Mile Bridge,which will be the longest segmental bridge inNorth America, Figure 1.68.

Segmental construction has extended the practicalrange of span lengths for concrete bridges. Practi-cal considerations of handling and shipping limitthe prestressed I-girder type of bridge construc-tion to spans of about 120 to 150 ft (37 to 46 m).Beyond this range, post-tensioned cast-in-placebox girders on falsework are the only viable con-crete alternative. At many sites, however, falseworkis not practical or even feasible, as when crossingdeep ravines or large navigable waterways.Falsework construction also has a serious impactupon environment and ecology.

FIGURE 1.68. Rendering of’ Seven Mile Bridge.

Prestressed concrete segmental construction hasbeen developed to solve these problems while ex-tending the practical span of concrete bridges toabout 800 ft (250 m) or even 1000 ft (300 m). Withcable-stayed structures the span range can be ex-tended to 1300 ft (400 m) and perhaps longer withthe materials available today.13 Table 1.1 sum-marizes the range of application of various formsof construction by span lengths.

Although the design and construction of very-long-span concrete segmental structures pose animportant challenge, segmental techniques may

S p a n

o- 150 ftloo- 300 ftloo- 300 ft250- 600 ft200- 1000 ft800-1500 ft

Applicability and Advantages of Segmental Construction 29

TABLE 1.1 Range of Application of Bridge Type by Span Lengthsa

Bridge Types

I-type pretensioned girderCast-in-place post-tensioned box girderPrecast balanced cantilever segmental, constant depthPrecast balanced cantilever segmental, variable depthCast-in-place cantilever segmentalCable-stay with balanced cantilever segmental

“1 fi = 0.3048 tn.

find even more important applications in moderatespan lengths and less spectacular structures. Espe-cially in difficult urban areas or ecology-sensitivesites, segmental structures have proven to be a val-uable asset.

Today most sites for new bridges can be adaptedfor segmental concrete construction. The principaladvantages of segmental construction may besummarized as follows:

1. Segmental construction is an efficient andeconomical method for a large range of spanlengths and types of structure. Structures withsharp curves and variable superelevation may beeasily accommodated.

2. Concrete segmental construction often pro-vides for the lowest investment cost. Savings of 10to 20% over conventional methods have beenrealized by competitive bidding on alternate de-signs or by realistic cost comparisons.

3. Segmental construction permits a reductionof construction time. This is particularly true forprecast methods, where segments may be man-ufactured while substructure work proceeds andbe assembled rapidly thereafter. Further cost sav-ings ensue from the lessening of the influence ofinflation on total construction costs.

4. Segmental construction protects the envi-ronment. Segmental viaduct-type bridges canminimize the impact of highway constructionthrough environmentally sensitive areas. Whereasconventional cut-and-fill type highway construc-tion can scar the environment and impede wildlifemigration, an elevated viaduct-type structure re-quires only a relatively narrow path along thealignment to provide access for pier construction.Once the piers have been constructed, all con-struction activity proceeds from above. Thus, theimpact on the environment is minimized.

5. Interference with existing traffic duringconstruction is significantly reduced, and expen-sive detours can be eliminated. Figure 1.69 indi-

cates how precast segments may be handled whiletraffic is maintained with a minimum disturbance.

6. Segmental construction contributes towardaesthetically pleasing structures in many differentsites. A long approach viaduct (Brotonne, Figure1.70), a curved bridge over a river (Saint Cloud,Figure 1.7 l), or an impressive viaduct over a deepvalley (Pine Valley, Figure 1.66) are some exampleswhere nature accepts human endeavor in spite ofits imperfections.

7. Materials and labor are usually available lo-cally for segmental construction. The overall laborrequirement is less than for conventional con-struction methods. For the precast option a majorpart of the work force on site is replaced by plantlabor.

8. As a consequence, quality control is easier toperform and high-quality work may be expected.

9. Segmental bridges when properly designedand when constructed by competent contractorsunder proper supervision will prove to be practi-cally free of maintenance for many years. Onlybearings and expansion joints (usually very few forcontinuous decks) need to be controlled at regularintervals.

FIGURE 1.69. Saint Cloud Bridge, segments placedover traffic.


FIGURE 1.70. Brotonne Bridge approach.

10. During construction, the technique showsan exceptionally high record of safety.

Precast segmental construction today is compet-itive in a wide range of applications with othermaterials and construction methods, while it adds afurther refinement to the recognized advantagesof prestressed concrete.

FIGURE 1.71. Saint Cloud Bridge, France, curvedbridge over a river.

References

1 . H. G. Tyrrell, History of Bridge Engineeting, Henry G.Tyrrell, Chicago, 1911.

2. Elizabeth B. Mock, The Architecture of Bridges, TheMuseum of Modern Art, New York, 1949.

3. T. Y. Lin, Design of Prestressed Concrete Structures,John Wiley & Sons, Inc., New York, 1958.

4. Anon., “Highway Design and Operational PracticesRelated to Highway Safety,” Report of the SpecialAASHO Traffic Safety Committee, February 1967.

5 . Anon., Prestressed Concrete for Long Span Bridges, Pre-stressed Concrete Institute, Chicago, 1968.

6. Anon., “Long Spans with Standard Bridge Girders,”PC1 Bridge Bulletin, March-April 1967, PrestressedConcrete Institute, Chicago.

7. “Recommended Practice for Segmental Construc-tion in Prestressed Concrete,” Report by PC1 Com-mittee on Segmental Construction, Journal of thePrestressed Concrete Instztute, Vol. 20, No. 2, March-April 1975.

8. Ulrich Finsterwalder, “Prestressed Concrete BridgeConstruction,” Journal oj the Amerzcan Concrete Instz-tute, Vol. 62, No. 9, September 1965.

9. F. Leonhardt, “Long Span Prestressed ConcreteBridges in Europe,” Journal of the Pre.,tressed ConcreteInstitute, Vol. 10, No. 1, February 1965.

10. Jean Muller, “Long-Span Precast Prestressed Con-crete Bridges Built in Cantilever,” Fzrst InternationalSymposium, Concrete Bridge Design, AC1 P u b l i c a t i o nSP-23, Paper 23-40, American Concrete Institute,Detroit, 1969.

11. Jean Muller, “Ten Years of Experience in PrecastSegmental Construction,” Journal of the PrestressedConcrete Instatute, Vol. 20, No. 1, January-February1975.

12. Man-Chung Tang, “Koror-Babelthuap Bridge-AWorld Record Span,” Preprint Paper 3441, ASCEConvention, Chicago, October 16-20, 1978.

13. C. A. Ballinger, W. Podolny, Jr., and M. J. Ab-rahams, “A Report on the Design and Constructionof Segmental Prestressed Concrete Bridges in West-ern Europe- 1977,” International Road Federa-tion, Washington, D.C., June 1978. (Also availablefrom Federal Highway Administration, Offices ofResearch and Development, Washington, D.C., Re-port No. FHWA-RD-78-44.)

14. Ulrich Finsterwalder, “New Developments in Pre-stressing Methods and Concrete Bridge Construc-tion,” Dywzdag-Berzchte, 4-1967, September 1967,Dyckerhoff & Widmann KG, Munich, Germany.

15. Ulrich Finsterwalder, “Free-Cantilever Constructionof Prestressed Concrete Bridges and Mushroom-Shaped Bridges,” First International Symposaum, Con-crete Bridge Deszgn, AC1 Publication SP-23, Paper SP23-26, American Concrete Institute, Detroit, 1969.

16. C. A. Ballinger and W. Podolny, Jr., “SegmentalConstruction in Western Europe-Impressions ofan IRF Study Team,” Proceedings, Conference con-ducted by Transportation Research Board, NationalAcademy of Sciences, Washington, D.C., TRR 665,Vol. 2, September 1978.

17. Willi Baur, “Bridge Erection by Launching is Fast,Safe, and Efficient,” Czvzl Engineerzng-AXE, Vol.47, No. 3, March 1977.

18. Walter Podolny, Jr., and J. B. Scalzi, “Constructionand Design of Cable-Stayed Bridges,” John Wiley &Sons, Inc., New York, 1976.

INTRODUCTION

2.5

2.62.72.82.92.102 .112.12

BENDORF BRIDGE, GERMANYSAINT ADELE BRIDGE, CANADABOUGUEN BRIDGE IN BREST AND LACROIK FAL-GARDE BRIDGE, FRANCESAINT JEAN BRIDGE OVER THE GARONNE RIVERAT BORDEAUX, FRANCESIEGTAL AND KOCHERTAL BRIDGES, GERMANYPINE VALLEY CREEK BRIDGE, U.S.A.GENNEVILLIERS BRIDGE, FRANCEGRAND’MFRE BRIDGE, CANADAARNHEM BRIDGE, HOLLANDNAPA RIVER BRIDGE, U.S.A.KOROR-BABELTHUAP, U.S. PACIFIC TRUSTTERRITORY

2.18 VEJLE FJORD BRIDGE, DENMARK

2Cast-in-Place Balanced Cantilever Girder Bridges

2.1 Introduction

Developed initially for steel structures, cantileverconstruction was used for reinforced concretebridges as early as fifty years ago. In 1928, Freys-sinet used the cantilever concept to construct thespringings of the arch rib in the Plougastel Bridge,Figure 2.1. The reactions and overturning mo-ments applied by the falsework to the lower part ofthe arch ribs were balanced by steel ties connectingthe two short cantilevers. A provisional prestresswas thus applied by the ties to the arch ribs with theaid of jacks and deviation saddles.

The first application of balanced cantilever con-struction in a form closely resembling its presentone is due to a Brazilian engineer, E. Baumgart,who designed and built the Herval Bridge over theRio Peixe in Brazil in 1930. The 220 ft (68 m)center span was constructed by the cantilevermethod in reinforced concrete with steel rods ex-tended at the various stages of construction bythreaded couplers. Several other structures fol-

2.14 HOUSTON SHIP CHANNEL BRIDGE, U.S.A.2.15 OTHER NOTABLE STRUCXURFS

2.15.1 Medway Bridge, U.K.2.15.2 Rio Tocantins Bridge, Brazil

‘2.153 Pueute Del Azufre, Spain2.15.4 Schubeuamdie Bridge, Canada2.15.5 Inci- Bridge, Guatemala2.15.6 !3etubal Bridge, Argentina2.15.7 Kipapa Stream Bridge, U.S.A.2.15.8 Parrots Ferry Bridge, U.S.A.2.15.9 Magnan Via’duct, France2.15.10 Puteaux Bridge, Frame2.15.11 Tricastiu Bridge, France2.15.12 Eschachtal Bridge, Germauy

2.16 CONCLUSIONR E F E R E N C E S

lowed in various countries, particularly in France.Albert Caquot, a leading engineer of his time, builtseveral reinforced concrete bridges in cantilever.Shown in Figures 2.2 through 2.4 is BezonsBridge over the River Seine near Paris, with a clearcenter span of 310 ft (95 m), being constructedin successive cantilever segments with auxiliarytrusses. This bridge design was prepared in 1942.The method was not widely used at that time,because the excessive amount of reinforcing steel

J a c k , / Ties

fOver turn ingmoment dueto centering

FIGURE 2.1. Cantilever construction of arch spring-ings for Plougastel Bridge, France.

31

FIGURE 2.2. Bezons Bridge over the Seine River, France, typical longitudinal andtransverse sec t ions .

Introduction 3 3

h’,w--. ---.-._ -_-..--._ - _._.._- _______ _ ..*gr- _ _ ._- -.__. --I .- ._-__ ____L_I z ::

: : :--/

I- .! .I

il

FIGURE 2.3. Bezons Bridge, construction procedure.

required to balance the cantilever moments pro- Used successfully in 1950 and 195 1 by Finsterwal-duced the tendency toward cracking inherent in der with the German firm of Dyckerhoff & Wid-an overreinforced slab subject to permanent ten- mann for the construction of the two bridges ofsile stresses. Balduinstein and Neckarrews, balanced cantilever

The introduction of prestressing in concrete construction of prestressed concrete bridges ex-structures dramatically changed the situation. perienced a continuous popularity in Germany

FIGURE 2.4. Bezons Bridges under construction.

34 Cast-in-Place Balanced Cantilever Girder Bridges

FIGURE 2.5. La Voulte Bridge, France.

and surrounding countries. Nicolas Esquillan de-signed and built a large bridge by the cantilevermethod over the Rhine River in France, La VoulteBridge (J952), where an overhead truss was usedduring construction, Figure 2.5.

Between 1950 and 1965 more than 300 suchbridges were constructed in Europe alone. Initially

various spans. Later other prestressing methodswith parallel wire or strand tendons were also used.More important, a significant improvement instructural behavior and long-term performancewas made possible by the achievement of deckcontinuity between the various cantilever arms.The first cantilever bridges with continuous deckswere designed and built in France in 1962: theLacroix Falgarde Bridge and Bouguen Bridge,Figures 2.6 and 2.22. Subsequently, the advantagesof continuity were recognized and accepted inmany countries.

From 1968 to 1970 cantilever construction wasconsidered for the Three Sisters Bridge in Wash-ington, D.C., Figure 1.64. This project neverreached the construction stage. The first cast-in-place balanced cantilever segmental bridge built inthe United States is the Pine Valley Creek Bridgein California (1972 to 1974), Figure 2.7. To date,all segmental bridges constructed in the UnitedStates have been either precast or cast-in-placecantilever construction, with the following excep-tions:

Wabash River Bridge, incrementally launched(Chapter 7)

all &uctures were prestressed by high-strength Denny Creek and Florida Keys Bridges, span-by-bars, and hinges were provided at the center of the span construction (Chapter 6)

FIGURE 2.6. Bouguen Bridge in Brest, France. First continuous rigid-frame structurebuilt in balanced cantilever.

Bendorf Bridge, Germany 35

FIGURE 2.7. Pine Valley Creek Bridge.

Linn Cove Viaduct, progressive placement con-struction (Chapter 6)

The balanced cantilever method of constructionhas already been briefly described. In this chapterwe shall see how this method has been im-plemented on various structures before we go onto consider specific design and technological as-pects.

2.2 Bendorf Bridge, Germany

An early and outstanding example of the cast-in-place balanced cantilever bridge is the Bendorfautobahn bridge over the Rhine River about 5miles (8 km) north of Koblenz, West Germany.Built in 1964, this structure, Figure 2.8, has a totallength of 3378 ft (1029.7 mj with a navigation spanof 682 ft (208 mj. The design competition allowedthe competing firms to choose the material,configuration, and design of the structure. Navi-gation requirements on the Rhine River dictated a328 ft (100 m) wide channel during constructionand a final channel width of 672 ft (205 mj. Thewinning design was a dual structure of cast-in-place concrete segmental box girder construction,consummated in two distinct portions. In part one

FIGURE 2.8. Bendorf Bridge (courtesy of Dvckerhoff& Widmann).

(west) are the river spans consisting of a symmetri-cal seven-span continuous girder with an overalllength of 1721 ft (524.7 mj. In part two (east) arethe nine-span continuous approach girders withthe spans ranging from 134.5 ft (41 m) to 308 ft (94mj and having an overall length of 1657 ft (505 mj,Figures 2.9 and 2.10.

The continuous, seven-span, main river struc-ture consists of twin, independent, single-cell boxgirders. Total width of the bridge cross section is101 ft (30.86 mj. Each single-cell box has a topflange width of 43.3 ft (13.2 mj, a bottom flangewidth of 23.6 ft (7.2 mj, and webs with a constantthickness of 1.2 ft (0.37 m). Girder depth is 34.28 ft(10.45 m) at the pier and 14.44 ft (4.4 mj atmidspan representing, with respect to the mainspan, a depth-to-span ratio of l/20 and l/47, re-spectively. Girder depth of the end of this seven-span unit reduced to 10.8 ft (3.3 mj. The mainnavigation span has a hinge at midspan that is de-

Hinge

Longitudinal sect ion

Cross sectton at Cross sectionr iver p ier at pier G

FIGURE: 2.9. Bendorf Bridge, Part one (West), lon-gitudinal section, plan, and cross secnons at the riverpier and pier G, from ref. 1 (courtesy of Beton- undStahlbetonbauj.


-~~ ss,o -L- SP.0 --L-- so0 -$A----5O$Om- - - ~


Plan

FIGURE 2.10. Bendorf Bridge, Part Two (East), longitudinal section and plan, fromref. 1 (courtesy of Beton- und Stahlbetonbau).

signed to transmit shear and torsion forces only,thus allowing the superstructure to be castmonolithically with the main piers.1,2 After con-struction of the piers, the superstructure over thenavigable portion of the Rhine was completedwithin one year. The repetition of the procedure in240 segments executed one after the other offerednumerous occasions to mechanize and improve theerection method.3,4

The deck slab has a longitudinally varying thick-ness from 11 in. (279.4 mm) at midspan to 16.5 in.(419 mm) at the piers. The bottom flange varies inthickness from 6 in. (152 mm) at midspan to 7.87 ft(2.4 m) at the piers. To reduce dead-weightbending-moment stresses in the bottom flangeconcrete, compression reinforcement was usedextensively in regions away from the piers.Thicknesses of the various elements of the crosssection are controlled partly by stress requirementsand partly by clearance requirements of the ten-dons and anchorages.

The structure is three-dimensionally pre-stressed: longitudinal prestressing uniformly dis-tributed across the cross section; transverseprestressing in the top flange; and inclined pre-stressing in the webs. A total of 560 Dywidag barsla-in. (32 mm) in diameter resists the negative bend-ing moment produced by a half-span, Figure 2.11.

FIGURE 2.11. Bendorf Bridge, cross section showingtendons in the deck, ref. 2, (courtesy of the AmericanConcrete Institute).

The maximum concrete compressive stress in thebottom flange at the pier is 1800 psi (12.4 MPa). Asa result of the three-dimensional prestress the ten-sile stresses in the concrete were negligible. Thelongitudinal prestressing is incrementally de-creased from the pier to the hinge at midspan andto the adjacent piers; thus, shear stresses in thewebs on both sides of the main piers are almostconstant. Therefore, the web thickness remainsconstant and the diagonal prestressing remainsvery nearly constant.

Construction began on March 1, 1962. Aftercompletion of the foundations and piers, balancedcantilever operations began from the west riverpier in July 1963 and were completed at the end ofthat year. Segments were 12 ft (3.65 m) in length inthe river span and 11.4 ft (3.48 m) in the remainingspans. Segments were cast on a weekly cycle. As thesegments became shallower, the construction cvclewas advanced to two segments per week. Duringwinter months, to protect operations from inclem-ent weather, the form traveler was provided withan enclosure, Figure 2.12.

FIGURE 2.12. Bendorf‘ Bridge, protective coveringfor form traveler (courtesy of Ulrich Finsterwalder).

Saint Adele Bridge, Canada

FIGURE 2.13. Ste. Adele Bridge, elevation, from ref. 5 (courtesy of Eng$mritzg ~V~7o.~-R~cord).

In the construction of the approach spans, thefive spans from the east abutment were built in aroutine manner with the assistance of falseworkbents. The four spans over water were constructedby a progressive placement cantilever method (seeChapter 6), which employed a temporary cable-stay arrangement to reduce the cantilever stresses.

2.3 Saint Adele Bridge, Canada

This structure, built in 1964 (the same year as theBendorf Bridge), represents the first segmentalbridge, in the contemporary sense, constructed inNorth America. It crosses the River of the Mulesnear Ste. Adele, Quebec, and is part of theLaurentian Autoroute. It is a single-cell box girdercontinuous three-span dual structure with a centerspan of 265 ft (80.8 m) and end spans of 132 ft 6 in.(40.4 m), Figure 2.13. At one end is a prestressedconcrete 55 f-t (16.8 m) simple span. The bridge hasa 100 ft (30.5 m) vertical clearance over the river inthe canyon below.

The variable-depth girder is 16 ft 3 4 in. (4.96 m)deep at the piers and 6 ft (1.83 m) deep at midspanand its extremities, Figure 2.14. Each dual struc-ture consists of a single-cell rectangular box 23 ft (7m) wide with the top flange cantilevering on eachside 9 ft (2.75 m) for a total width of 41 ft (12.5 m),Figure 2.15, providing three traffic lanes in eachdirection. Thickness of bottom flange, webs, andtop flange are respectively 1 ft l# in. (0.35 m), 1 ft 6in. (0.46 m), and 1 ft (0.3 m).5

A total of 70 prestressing tendons were requiredin each girder. Each tendon of the SEEE systemconsists of seven strands of seven 0.142 in. (3.6mm) wires. The seven strands are splayed outthrough a steel ring in the anchorage and held in acircular pattern by steel wedges between each ofthe strands. The number of tendons anchored offat each segment end varies with the distance fromthe pier, increasing from an initial six tendons toeight tendons a t the e ighth segment , then de-creasing to two tendons at the eleventh segment atmidspan. There are an additional 44 positive-moment tendons in the center span located in thebottom flange.5

FIGURE 2.14. Stc. Adele HI idge, view 01 variable- FIGURE 2.15. Ste. Adele Bridge, view of end of boxdepth box girder (courtesy of the Portland Cement AS- girder segment (courtesy of the Portland Cement As-sociation). sociation) .

3 8 Cast-in-Place Balanced Cantilever Girder Bridges

FIGURE 2.16. Ste. Adele Bridge, dual structureunder construction by the balanced cantilever method,from ref. 5 (courtesy of Engineering News-Record).

Forty-seven segments are required for eachstructure, eleven cantilevered each side of eachpier, a closure segment at midspan of the centerspan, and a segment cast in place on each abut-ment. Segments cast by the form traveler were 10ft 78 in. (3.24 m) in length.5 Four traveling formswere used on the project: one pair on each side ofthe pier for each of the dual structures, Figures2.16 and 2.17.

The forms were supported by a pair of 42 ft(12.8 m) long, 36 in. (914.4 mm) deep structuralsteel beams spaced 15 ft (5.57 m) on centers, thatcantilevered beyond the completed portion of thestructure. Initially the cantilevered beams were

FIGURE 2.17. Ste. Adele Bridge, view of form travel-ers cantilevering from completed portion of the struc-ture, from ref. 5 (courtesy of Engineering News-Record).

counterweighted with 70 tons (63.5 mt) of concreteblock, which was gradually diminished as con-struction proceeded and the depth of the segmentsdecreased. The first pair of segments (at the pier),each with a length of 21 ft 23 in. (6.47 m), were caston a temporary scaffolding braced to the pier,Figure 2.18, which remained fixed in positionthroughout the erection process.5

Construction of four segments per week, one ateach end of a cantilever from two adjacent piers,was attained by the following five-day constructioncycles:

First day: Traveling forms moved, bottom flangeformed, reinforced, and cast. In the parallel spanthere was a one-day lag such that crews could shiftback and forth between adjacent structures.

Second day: Reinforcement placed for webs andtop flange.

Third day: Concrete placed for webs and topflange, cure begun.

Fourth day: Tendons placed and pres t ress ingjacks positioned while concrete was curing.

Fifth day: Prestressing accomplished. Formsstripped; preparations made to repeat cycle.

The cycle began on Monday. Since there was alag of one day on the parallel structure, a six-daywork week was required. Upon completion of theeleventh segment in each cantilever the contractorinstalled temporary falsework to support theabutment end and then cast the closure segment atmidspan. Counterweights were installed at theabutment end to balance the weight of the closureforms and segment weight. After installation andstressing of the continuity tendons, abutment seg-ments were cast and expansion joints installed.5

2.4 Bouguen Bridge in Brest and Lacroix FalgardeBridge, France

The Bouguen Bridge in Brittany, West Province inFrance, is the first rigid-frame continuous struc-ture built in balanced cantilever (1962 to 1963).The finished bridge is shown in Figure 2.6, whiledimensions are given in Figure 2.19. It carries athree-lane highway over a valley 145 ft (44 m)deep-Le Vallon du Moulin H Poudre-and pro-vides a link between the heart of Brest city and LeBouguen, a new urban development.

The total length of bridge is 684 ft (208 m). Themain structure is a three-span rigid frame with

Bouguen Bridge in Brest and Lacroix Falgarde Bridge, France 3 9

FIGURE 2.18. Ste. Adele Bridge, schematic of construction sequence, fromref. 5 (courtesy of Engineering News-Record).

piers elastically built-in on rock foundations withspan lengths of 147,268, and 147 ft (45,82, and 45m). At one end the deck rests on an existingmasonry wall properly strengthened; at the otherend a shorter rigid frame with a clear deck span of87 ft (26.5 m) provides the approach to the mainbridge.

The deck consists of two box girders with verticalwebs of variable height, varying from 15 ft 1 in.(4.6 m) at the support to 6.5 ft (2 m) at midspanand the far ends of the side spans. Width of each

box girder is 10 ft (3 m); web thickness also is con-stant throughout the deck and is equal to 9$ in.(0.24 m).

Piers consist of two square box columns 10 ft by10 ft (3 x 3 m) with wall thickness of 9$ in. (0.24 m)located under each deck girder. Two walls 84 in.(0:22 m) thick with a slight recess used for ar-chitectural purposes connect the two columns.Both piers are of conventional reinforced concreteconstruction, slip-formed at a speed reaching 14 ft(4.25 m) per day in one continuous operation.

Midspan section Pier section Plan section at pier

(b)

FIGURE 2.19. Bouguen Bridge, France, general dimensions. (a) Longitudinal section.(6) Cross sections.


FIGURE 2.20. Bouguen Bridge, construction of eastcantilever.

The superstructure box girders are connected tothe pier shaft by transverse diaphragms made in-tegral with both elements to insure a rigid connec-tion between deck and main piers. Construction ofthe deck proceeded in balanced cantilever with 10ft (3 m) long segments cast in place in form travel-ers with a one-week cycle, Figures 2.20 and 2.21.High-early-strength concrete was used and nosteam curing was required. Concrete was allowedto harden for 60 hours before application of pre-stress. The following cube strengths were obtainedthroughout the project:

60 hours (time of pre- 3700 psi (25.5 MPa)stress)7 days 5500 psi (37.9.MPa)

28 days 7000 psi (48.3 MPa)90 days 8200 psi (56.5 MPa)

Only one pair of form travelers was used for theentire project, but each traveler could accommo-date the construction of both girders at the sametime.

.\’

FIGURE 2.21. Bouguen Bridge, view of’ the traveler.

During construction of the deck, much attentionwas given to the control of vertical deflections.Adequate camber was given to the travelers to fullycompensate for short- and long-term concretedeflections. The cumulative deflection at midspanof the first cantilever arm was 14 in. (40 mm) attime of completion. Concrete creep caused thisdeflection to reach 3 in. (75 mm) at the time thesecond cantilever arm reached the midspan sec-tion. Proper adjustment of the travelers allowedboth cantilever arms to meet within t in. (3 mm) atthe time continuity was achieved. Flat jacks wereprovided over the outer supports to allow for anyfurther desired adjustment.

The structure is prestressed longitudinallv bytendons of eight 12 mm strands:

76 tendons over the top of the pier segment,

32 tendons at the bottom of the crown section,

20 tendons in the side spans,

and transversely by tendons of seven 12 mmstrands.

The Lacroix Falgarde Bridge over AriegeRiver in France, built in 1961 and 1962, is similarto the Bouguen Bridge and represents the firstcontinuous deck built in balanced cantilever (seethe photograph of the finished bridge, Figure2.22). It consists of three continuous spans 100,200, and 100 ft (30.5, 61, and 30.5 m). The singlebox girder has a depth varying between 4 ft 5 in.and 10 ft 6 in. (1.35 to 3.2 m). Dimensions aregiven in Figure 2.23. The superstructure rests onboth piers and abutments through laminatedbearing pads.

The deck was cantilevered and the constructionstarted simultaneously from the two piers withfour travelers working symmetrically. During con-

FIGURE 2.22. Lacroix-Falgardc Bridge, view of’ thestructure during construction.

Saint Jean Bridge Over the Gardonne River at Bordeaux, France

FIGURE 2.23. Lacroix-Falgarde Bridge, elevation and cross section.

struction, the deck was temporarily fixed to thepiers by vertical prestress. The structure is pre-stressed longitudinally by tendons of twelve 8 mmstrands and transversely by tendons of twelve 7mm strands.

2.5 Saint Jean Bridge over the Garonne River atBordeaux, France

Completed in April 1965, the Saint Jean Bridge inBordeaux is a remarkable application of the newconcepts developed at that time in cast-in-placecantilever construction. The main structure has anoverall length of 1560 ft (475 m) and is continuouswith expansion joints only over the abutments. Thedeck is f’ree to expand on neoprene bearings lo-cated on all river piers, Figure 2.24. A veryefficient method of pier and foundation construc-tion was also developed, which will be described inmore detail in Chapter 5.

The bridge was built in the heart of the city ofBordeaux over the Garonne River between a 175-year-old multiple-arch stone structure and a 120-year-old railway bridge designed by Eiffel, the en-gineer who designed the Eiffel Tower.

The main structure includes six continuousspans. The central spans are 253 ft (77 m) long andallow a navigation clearance of 38 ft (11.60 m)above the lowest water level, while the end spansare only 222 ft (67.80 m) long. Short spans at bothends, 50 ft (15.40 m) long, provide end restraint ofthe side spans over the abutments. The overallwidth of the bridge is 88 ft (26.80 m), consisting ofsix traffic lanes, two walkways, and two cycle lanes.Superstructure dimensions are shown in Figure2.25.

41

The deck consists of three box girders. The con-stant depth of 10.8 ft (3.30 m) has been increasedto 13 ft (3.90 m) over a length of 50 ft (15 m) oneach side of the piers to improve the bendingcapacity of the pier section and reduce the amountof cantilever prestress. No diaphragms were usedexcept over the supports. The results of a detailedanalysis performed to determine the transversebehavior of the deck confirmed this choice (seedetailed description in Chapter 4).

Longitudinal prestressing consists of tendonswith twelve 8 mm and twelve t in. strands. Trans-verse prestressing consists of tendons with twelve 8mm strands at 2.5 ft (0.75 m) intervals. Verticalprestressing is also provided in the webs near thesupports.

As indicated in Figure 2.26, three separate piercolumns support the three deck girders. They arecapped with large prestressed transverse dia-phragms. The piers are founded in a gravel bed lo-cated at a depth of 45 ft (14 m) below the river levelby means of a reinforced concrete circular caisson

FIGURE 2.24. Saint Jean at Bordeaux, view of thecompleted structure.

COUPE LONGITUDINALE

CULEE R D CVLEE NE

- _5

FIGURE 2.25. Saint Jean ar Bordeaux. (a) Longitudinal and (6) cross sections.

FIGURE 2.26. Saint Jean Bridge at Bordeaux, typical section at river piers.

42

Siegtal and Kochertal Bridges, Germany 4 3

FIGURE 2.27. Saint Jean Bridge at Bordeaux, workprogress on piers and deck.

18.5 ft (5.60 m) in diameter and 10 ft (3 m) high,floated and sunk to the river bed and then open-dredged to the gravel bed. Precast circular match-cast segments prestressed vertically make up thepermanent walls of caissons, while additional seg-ments are used temporarily as cofferdams andsupport for the deck during cantilever construc-tion. A lower tremie seal allows dewatering andplacing of plain concrete fill inside the caisson. Thereinforced concrete footing and pier shaft arefinally cast in one day.

The superstructure box girders were cast inplace in 10 ft (3.05 m) long segments using twelveform travelers, allowing simultaneous work on thethree parallel cantilevers at two different piers.The 20 ft (6.1 m) long pier segment was cast on thetemporary supports provided by the pier caissons,allowing the form travelers to be installed and can-tilever construction to proceed. Six working dayswere necessary for a complete cycle of operationson each traveler. Work progress is shown in Fig-ures 2.27 and 2.28. Total construction time for theentire 130,000 sq ft (12,000 m*) was approximately

FIGURE 2.28. Saint Jean Bridge at Bordeaux, can-tilever construction on typical pier.

one year, as shown on the actual program of worksummarized in graphic form in Figure 2.29. Tomeet the very strict construction deadline of thecontract, it was necessary to bring to the project siteanother set of three travelers to cast the last can-tilever on the left bank and achieve continuity withthe southern river pier cantilever. Altogether,meeting the two-year construction schedule wasrecognized as an engineering achievement.

Exactly one hundred years earlier, Gustave Eif-fel had built the neighboring railway bridge inexactly two years-food for thought and a some-what humbling reflection for the present genera-tion.

2.6 Siegtal and Kochertal Bridges, Germany

The Siegtal Bridge near the town of Sieger, northof Frankfort, Germany, represents the first indus-trial application of cast-in-place cantilever con-struction with an auxiliary overhead truss. Thismethod was initially developed by Hans Wittfohtand the firm of Polensky-und-Zollner and sub-sequently used for several large structures in Ger-many and other countries. One of the most recentand remarkable examples of this technique is theKochertal Bridge between Ntiremberg and Heil-bron, Germany. Both structures will be briefly de-scribed in this section, while a similar application inDenmark is covered in another section of thischapter.

Siegtal Bridge is a twelve-span structure 3450 ft(1050 m) long resting on piers up to 330 ft (100 m)high, with maximum span lengths of 344 ft (105m), Figure 2.30. Two separate box girders carrythe three traffic lanes in each direction for a totalwidth of 100 ft (30.5 m), Figure 2.31. Structuralheight of the constant-depth box girder is 19 ft (5.8m), corresponding to a span-to-depth ratio of 18.The deck is continuous throughout its entirelength, with fixed bearings provided at the threehighest center piers and roller bearings of high-grade steel for all other piers and end abutments.Piers have slip-formed reinforced concrete hollowbox shafts with a constant transverse width of 68ft (20.7 m) and a variable width in elevation witha slope of 40 to 1 on both faces.

The superstructure was cast in place in balancedcantilever from all piers in 33 ft (10 m) long seg-ments with an auxiliary overhead truss supportingthe two symmetrical travelers, and a cycle of oneweek was obtained without difficulty for the con-struction of two symmetrical 33 ft (10 m) long seg-

PONT USCttAMPS

I ’ em6 I 7x00 I 7200 :_ n,oo ’ 77.w ,r

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- I

DEC

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UPPHASEJANV

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M A R S / EWEIJVES 2 AWL 1965

FIGURE 2.29. Saint Jean Bridge at Bordeaux, actual program of work.

Elevation t

Cross section 1

‘Cross sect ion 2

Horizontal section

FIGURE 2.30. Siegtal Bridge, general dimensions.

Siegtal and Kochertal Bridges, Germany 4 5

Jo.MII 59 _ 2.m . u.97 L_ t.7~ 1125 .n -.fl 0 57 ni

I3s _ ‘.IS L9.m 5m T.W 3.75 3.?5

i 1so I <rn L

FIGURE 2.31. Siegtal Bridge, typical cross section.

merits. The auxiliary truss was also first used to castthe pier segment above each pier, Figure 2.32, be-fore cantilever construction could proceed, Figure2.33. Because the pier shafts are flexible and havelimited bending capacity, it was inadvisable to sub-ject them to unsymmetrical loading conditionsduring deck construction. Thus, the overheadtruss also served the purpose of stabilizing the can-tilever arms before continuity was achieved withthe previous cantilever.

The auxiliary steel truss is made of high-strengthsteel (50 ksi yield strength). Prestressing is appliedto the upper chord, which is subjected to high ten-sile stresses in order to reduce the weight of theequipment. The overall length of the truss is 440 ft(135 m) long to accommodate the maximum spanlength of 344 ft (105 m). The total weight of thetruss and of the two suspended travelers, allowingcasting of two 33 ft (10 m) long segments, was 660 t(600 mt). Deck concrete was pumped to the varioussegments through pipes carried from the finisheddeck bv the auxiliary truss, Figures 2.34 and 2.35.

Work commenced on the superstructure inMarch 1966. The first box girder was completed in

April 1968. The truss and travelers were im-mediately transferred to the second box girder,which was completed in September 1969. Thus,the average rate of casting was as follows:

Fir s t b r idge : 3450 ft (1050 m) in 25 months, or 140ft (42 m) per monthSecohd br idge: 3450 ft (1050 m) in 17 months, or200 ft (62 m) per monthBoth br idges : 6900 ft (2100 m) in 42 months, or160 ft (50 m) per month

An outstanding contemporary example of thesame technique is the Kochertal Bridge in Ger-many, shown in final progress in Figure 2.36. Gen-eral dimensions of the project are given in Figure2.37. Total length is 3700 ft (1128 m) with typicalspans of 453 ft (138 m) supported on piers up to600 ft (183 m) in height. The single box girdersuperstructure with precast outriggers carries sixtraffic lanes for a total width of 101 ft (30.76 m).Box piers were cast in climbing forms with 14.2 ft(4.33 m) high lifts. The top section is constant forall piers with outside dimensions of 16.4 by 28.2 ft

FIGURE 2.32. Sicgtal Bridge, pier segment ca5ting. FIGURE 2.33. Siegtal Bridge, canClever construction.

II


105m 105m

FIGURE 2.34. Siegtal Bridge, elevation of overhead truss and travelers.

(5 by 8.6 m). The four faces are sloped to increasethe dimensions at foundation level to a maximumof 31.2 by 49.2 ft (9.5 by 15 m) for the highestpiers. Wall thickness varies progressively from topto bottom, to follow the load stresses, from 20 in.(0.5 m) to 36 in. (0.9 m).

The constant-depth superstructure is cast in twostages, Figure 2.38: (1) the single center box with awidth of 43 ft (13.1 m) and a depth of 23 ft (7 m),and (2) the two outside cantilevers resting on a se-ries of precast struts. To meet the very tight con-struction schedule of 22 months it was necessary touse two sets of casting equipment, working simul-taneously from both abutments toward the center.Each apparatus was made of an overhead truss

FIGURE 2.35. Siegtal Bridge, typical section of trussand travelers.

:4

equipped with a launching nose to move from pierto pier and two suspended travelers working inbalanced cantilevers, casting segments on a one-week cycle, Figure 2.39.

2.7 Pine Valley Creek Bridge, U.S.A.

The first prestressed concrete cast-in-place seg-mental bridge built in the United States was thePine Valley Creek Bridge on Interstate I-8 betweenSan Diego and El Centro, California, Figures 1.66and 2.7, opened to traffic late in 1974. This struc-ture is located approximately 40 miles (64 km) eastof San Diego and 3 miles (4.8 km) west of the

F I G U R E 2 . 3 6 . Kochertal Bridgr, gt~nenl vim o fproject.

FIGURE 2.37. Kochertal Bridge, elevation, plan andcross section.

community of Pine Valley and within the Cleve-land National Forest. Interstate I-8 crosses over asemiarid region that is highly erodible when theground cover is disturbed; consequently stringentcontrols were imposed on access roads andground-cover disturbances. Structure type wasinfluenced by the following factors: site restric-tions, economics, ecological considerations, andForest Service limitations. After comparing variouspossible schemes such as steel arch, deck truss, orsteel box girder, the California Department ofTransportation selected a concrete box girderbridge medicated on the use of cantilever seg-

(b)FIGURE 2.38. Kochertal Bridge, typical cross sec-tions. (a) First stage casting. (6) Final stage.


FIGURE 2.39. Kochertal Bridge, cantilever construc-tion.

mental construction, particularly well suited to thesite because the depth and steep slopes of the valleymade the use of falsework impractical. Also, the

cantilever method minimized scarring of thenatural environment, which was a major consider-ation for a project located in a National Forest.

The bridge has an average length of 17 16 ft (523m) and consists of twin two-lane single-cell,trapezoidal box girders each 42 ft (12.8 m) out-to-out. The deck is 450 ft (137 m) above the creekbed. The superstructure consists of five spans ofprestressed box girders 19 ft (5.8 m) deep. Thecenter span is 450 ft (137 m) in length, flanked byside spans of 340 ft (103.6 m) and 380 ft (115.8 m),with end spans averaging 270 ft (82.3 m) and 276 ft(84.1 m). The bridge was constructed with fourcantilevers. Pier 2 has cantilevers 115 ft (35.1 m) inlength, piers 3 and 4 have 225 ft (69.6 m) cantile-vers, and pier 5 has 155 ft (47.2 m) cantile-vers,6*7*8 Figure 2.40. Provisions were made in thedesign to permit the portions of spans 1 and 5 ad-jacent to the abutments to be constructed segmen-tally or on falsework at the contractors’ option. Thelater option was exercised by the contractor.g*10

DATUM LLLV. woo;

ELEVATION

FIGURE 2.40. Pine Valley Creek Bridge, elevation and typical section, from ref. 8.

Pine Valley Creek Bridge, USA. 49

Hinges were provided in spans 2 and 4 at theend of the main cantilevers. In the preliminary de-sign, consideration was given to the concept of acontinuous structure for abutment to abutmentwithout any intermediate joints. Continuity hasmanv advantages insofar as this particular struc-ture’is concerned. However, it has the significantdisadvantage of large displacements under seismicloading conditions. Because of the extreme dif-ference in height and stiffness between piers, it wasdetermined that all the horizontal load was beingtransmitted to the shorter piers, which were notcapable of accepting it.s

The pier foundations posed some interestingconstruction problems. The top 20 ft (6 m) of therock material at the structure site was badlyfissured, with some fissuring as deep as 40 ft (12m). Narrow footings only 1 ft (0.3 m) wider thanthe pier shafts, tied down with rock anchors, werepreferred to the conventional spread footings tominimize the amount of excavation.

Although the piers are spectacular because oftheir size, they are not unique in concept. The twomain piers, 3 and 4, are approximately 370 ft (113m) in height and are made up of two vertical cellu-lar sections interconnected with horizontal ties. Ina transverse direction the piers have a constant.width to facilitate slip-form construction, while inthe longitudinal direction the section variesparabolically, with a minimum width of 16 ft (4.9m) approximately one-third down from the top. Atthis point they flare out to 23 ft by 24 ft (7 by 7.3 m)at the soffit. The pier wall thickness is a constant 2ft (0.6 rn).‘jps

Earthquake considerations produce the criticaldesign load for the piers. The 1940 El Centro earth-quake was used as the forcing function in the de-sign analysis. Design criteria required that thec,ompleted structural frame withstand this forcelevel without exceeding stress levels of 75% ofyield. The pier struts are an important element inthe seismic design of the piers. They provide duc-tility to the piers by providing energy-absorbingjoints and an increased stability against bucklingfor the principal shaft elements. Because of the sizeof the struts in relation to the pier legs, the major-ity of the rotation in the strut-leg joint occurs in thestrut. Thus, a very high percentage of transverseconfining reinforcement was required in the strutto insure the ductility at this location.“j9

Although preliminary design anticipated theslip-forming technique for construction of thepiers, the contractor finally elected to use a self-climbing form system. Steel forms permitted 22 ft

(6.7 m) high lifts, and they were given a tefloncoating to facilitate stripping while producing ahigh-quality finished concrete surface.

Construction of the pier caps was especiallychallenging. The pier caps, Figure 2.41, consist oftwo arms 60 ft (18.3 m) in height, which projectoutward at an approximate angle of 60” from eachstem of the pier shafts. These arms are constructedin four lifts in such a manner that the forms foreach lift are tied into the previous lift. Upon com-pletion of the pier cap arms they are tied togetherand the top strut is formed, reinforcement placed,and cast. The pier cap is prestressed transversely inorder to overcome side thrust from-the super-structure.

The superstructure consists of two paralleltrapezoidal box girders 42 ft ( 12.8 m) wide and 19 ft(5.8 m) deep with a 38 ft (11.6 m) space betweenthe boxes, such that an additional box girder maybe constructed for future widening, Figures 2.40and 2.42. The boxes, in addition to being post-tensioned longitudinally, have transverse prestress-ing in the deck slab, together with sufficient mildsteel reinforcement to resist nominal constructionloads, allowing the transverse prestressing opera-tions to be removed from the critical path. The

ELEVATKIN OF PER SIOE MW cf PIER

E PIER 1

x - xSECTIPlERSHlFTl

-I

I9 t-

SC?

-

110’zeo’zw6d

iFFooTING

w

i

FIGURE 2.41. Pine Valley Creek Bridge, elevation,side view, and cross section of pier, from ref. 7 (courtesyof the Portland Cement Association).


FIGURE 2.42. Pine Valley Creek Bridge, typical boxgirder cross section, from ref. 7 (courtesy of the PortlandCement Association).

sloping webs and large deck overhangs were usedto minimize the slab spans and the number ofgirder webs and to accentuate a longitudinal shad-ow line, thus reducing the apparent depth. The webthickness of 16 in. (406 mm) was selected to permitside-by-side placement of the largest tendon thenbeing used in bridge construction and to keep theshear reinforcement to a reasonable size andspacing, Figure 2.42. The bottom slab at midspanis 10 in. (254 mm) thick and flares out to 6.5 ft (1.98m) at the pier. 6*7,g Construction of the superstruc-ture proceeded in a balanced cantilever fashion,Figures 2.7 and 2.43.

As shown in Figure 2.44, the erection schemeproposed by the contractor allowed all super-structure work to be performed in a continuoussequence, essentially from the top. Four formtravelers were used for the cantilever constructionof this project, one at each end of each cantileverarm. Basically, one traveler consisted of an over-head steel truss used to support the formwork forthe typical 16.5 ft (5 m) long segments. The truss isanchored, at the rear, to the previously cast seg-ment, while the front end is equipped with hy-draulic jacks used for grade adjustment. High-density plywood was used for all formed surfaces.A total of 172 cast-in-place segments were requiredfor the entire structure. Falsework was requiredclose to abutments 1 and 6 to complete the sidespans beyond the balanced cantilever arms.Formwork used in that portion of the structurecould be reused above each intermediate pier capto construct the 35 ft (10.7 m) long pier segmentbefore the actual cantilever construction pro-ceeded.

The cross section of the superstructure allowed

PIE

FIGURE 2.43. Pine Valley Creek Bridge, auxiliarybridge, from ref. 7 (courtesy of the Portland Cement As-sociation).

an auxiliary truss to be located between the twoconcrete box girders, Figure 2.43. This auxiliarybridge consisted of a structural steel truss 10 ft(3.05 m) square in cross section and 320 ft (97.5 m)in length. In a stationary position it was supportedat the leading end on the pier cap strut and at therear end of a steel saddle between the two concreteboxes. It was designed such that the front endcould be cantilevered out 225 ft (68.6 m), which isone-half the main span. Electric winches allowedlongitudinal launching between the concrete boxgirders. When pier 5 was completed, the auxiliarybridge was erected in span 5-6, utilizing tempo-rary support towers near abutment 6. Subsequent30 ft (9.1 m) lengths of auxiliary truss were attachedat the abutment and incrementally launched to-ward pier 5, until its front end was supported on thepier cap. The pier table was then constructed andcantilever construction commenced until thestructural hinge in span 4-5 was reached. Uponcompletion of the closure joint in span 5-6 the aux-iliary truss was launched forward until the frontend reached pier 4. The form travelers were dis-mantled from the tip of the cantilever andreerected on the pier table at pier 4, and cantilever

FIGURE 2.44. (Opposite) Pine Valley Creek Bridge,erection scheme proposed by the contractor, from ref.1 0 .

Stage 1Canti lever

0\__ construction on

($l

+L

conventionalConstructionf r o m p i e r 5

s t a g e 2f r o m p i e r 4

Stage 3from pier 3

\

\

S t a g e 5cOmpletion


construction was started again. This cycle was re-peated until closure was achieved in span l-2.

The use of the auxiliary truss had the followingadvantageslO:

2.8 Genneuilliers Bridge, France

The Gennevilliers Bridge, Figures 2.45 and 2.46, isa five-span structure with a total length of 2090 ft(636 m). At its southern end it is supported on acommon pier with the approach viaduct from theport of Gennevilliers. It crosses successively an en-trance channel to the port, a peninsula situatedbetween the channel, and the Seine River itself,Figure 2.47. It is part of the Al5 Motorway, whichtraverses from the Paris Beltway through Gen-nevilliers, Argenteuil, the valley d’Oise, and on tothe city of Cergy-Pontoise. The present structureprovides a four-lane divided highway with provi-sion for a future twin structure.

1. Men and materials for the superstructurecould reach the location of construction fromabutment 6 over the auxiliary bridge and thealready completed portion of the superstruc-ture without interfering with the valley below.

2. The construction equipment (tower cranes andhoists) at the piers was required only for theactual construction of the piers and could berelocated from pier to pier without waiting forcompletion of the superstructure.

3. Except for construction of abutment 1 andpier 2, site installation for the entire projectwas located at one location, near abutment 6.

Concrete was supplied from a batching plant lo-cated approximately 2 miles (3.2 km) from the site.Ready-mix trucks delivered the concrete at abut-ment 6. The concrete was then pumped through 6in. (152 mm) pipes down the slope to the foot ofpiers 5 and 4. The concrete for the superstructurewas pumped through a pipeline installed in theauxiliary truss right into the forms. A secondpump with a similar installation was located atabutment 1 to supply concrete for abutment 1 andpier 2.1°

A 5000 psi (35 MPa) concrete was specified forthe superstructure, presenting no unusual prob-lems. However, to maintain a short cycle for theconstruction of the individual segments it was nec-essary to have sufficient strength for prestressing30 hours after concrete placement. This wasdifficult to achieve, since the specifications did notallow type III cement and certain additives. A so-lution Gas to prestress the individual tendons nec-essary to support the following segment to 50 per-cent of their final force. The form carrier couldthen be advanced and the remainder of the pre-stressing force applied after the concrete reachedsufficient strength and before casting the nextsegment.r”

Prestressing was achieved using lf in. (32 mm)diameter Dywidag bars. Longitudinal tendonswere provided in 33 ft (10 m) lengths and coupledas the work progressed. Temporary corrosionprotection of the bars was obtained by blowing“VPI” powder into the ducts and coating each barwith vinyl wash or “Rust-Van 310.“*

The superstructure is a variable-depth two-cellbox girder with spans of 345, 564, 243, 564 and371 ft (105, 172, 74, 172 and 113 m). Depth variesfrom 29.5 ft (9 m) at intermediate piers to 11.5 ft(3.5 m) at midspan of the 564 ft (172 m) spans andits extremities, with a depth of 23 ft (7 m) atmidspan of the short center span, Figure 2.46.Depth-to-span ratios of the 564 ft (172 m) spans atmidspan and at the piers are respectively l/49 andl/19. The curved portion of the structure has aradius, in plan, of 2130 ft (650 m). The longitudi-nal grade is a constant 1.5 percent within the zoneof curvature. Because the short center span is sub-jected to negative bending moment over its entirelength, the structure behaves much as a continuousthree-span beam.

In cross section, Figure 2.48, the two-cell boxgirder has a bottom flange varying in width from42.2 ft (12.86 m) at midspan to 30.5 ft (9.3 m) atthe pier, for the 564 ft (172 m) span. Thickness ofthe bottom flange varies from 47 in. (1.2 m) at thepier to 8 in. (20 cm) at midspan. The top flange has

FIGURE 2.45. Gennevilliers Bridge, view of curvedfive-span structure.

Gennevilliers Bridge, France

FIGURE 2.46. Gennevilliers Bridge, plan and elevation, from ref. 11.

an overall width of 60.6 ft (18.48 m) with a 6 ft from 16 in. (400 mm) at the pier to 12 in. (300 mm)(1.83 m) overhang on one side and 6.2 ft (1.88 m) at midspan. Diaphragms, Figure 2.49, are locatedon the other. Thickness of the top flange is a con- at the supports. The superstructure is prestressedstant 8 in. (20 cm). The center web has a constant in three directions, with strand tendons beingthickness of 16 in. (400 mm). Exterior webs, which utilized longitudinally and transversely and barare inclined 18” to the vertical, vary in thickness tendons utilized for the webs. Interior anchorage

FIGURE 2.47. Gennevilliers Bridge, aerial view of the completed bridge.


At Support At Mid Span

la55

1I1 3 6 6 3 5 6 , 364 ,m@ 3 6 6 , 3 6 6 ‘ m

611 6Za3 1 6Zls

I aTI5 I 677’

FIGURE 2.48. Gennevilliers Bridge, cross section, from ref. 11.

blocks for the longitudinal prestressing are locatedat top slab level.

The superstructure is fully continuous over itstotal length of 2090 ft (636 m) between the north-ern abutment and the southern transition pier withthe approach viaduct. The deck rests upon thefour main piers supported by large elastomericpads. The superstructure was cast in place usingthe balanced cantilever method according to thestep-by-step scheme shown in Figure 2.50. Seg-ments over the piers (pier segments) were con-structed first on formwork, in a traditional man-ner, except for their unusual length [26 ft (7.9m)Iand weight [850 t (770 mt)].

Four travelers were used for casting the typical11 ft (3.35 m) long segments varying in weightfrom 242 t (220 mt) near the piers to 110 t (100 mt)at midspan. l1 The travelers were specially designedto achieve maximum rigidity and prevent the usualtendency to crack a newly cast segment under thedeflections of the supporting trusses of conven-tional travelers. The framework used for this pur-pose was made of self-supporting forming panelsassembled into a monolith weighing 120 t (110 mt)and prestressed to the preceding part of thesuperstructure to make the unit substantiallydeflection free, Figure 2.5 1. Stability, especiallyunder wind loads or in the event of an accidental

FIGURE 2.49. Gennevilliers Bridge, interior view failure of the travelers during the construction pe-showing diaphragm. riod, was maintained by a pair of cables on each

FIGURE 2.50. Gennevilliers Bridge, erection sequence, from ref. 11.

side of the pier connecting the superstructure topier base.

2.9 Grand’Mere Bridge, Canada

This three-lane cast-in-place segmental bridge islocated on Quebec Autoroute 55 and crosses theSt. Maurice River approximately 3 miles (4.8 km)north of Grand’Mere, Quebec, Figure 2.52. Waterdepth at the bridge site is over 110 ft (35.5 m), withan additional 150 ft (45.75 m) depth of sand, silt,

FIGURE 2.51. Gennevilliers Bridge, superstructureunder construction.

and debris above bedrock. The river flow at thebridge site is 3.6 ft/sec (1.1 m/set).

During the preliminary design stage in 1973 and1974, several structural solutions were considered.The use of short spans of precast concreteAASHTO sections or structural steel girders re-quiring a number of piers was immediately aban-doned because of river depth and current velocityat the site. Site conditions required the develop-ment of an economical long clear span with as fewpiers as possible in the river. Options available

FIGURE 2.52. GrandMere Bridge, general viewshowing parabolic soffit of center span, (courtesy of thePortland Cement Association).


were structural steel, post-tensioned precast seg-mental, and several options of cast-in-place pre-stressed concrete, varying in span, cross section,and pier requirements. The design finally selectedfor preparing the bid documents was a concretecantilever single-cell box with a center span of 540ft (165 m), a 245 ft (75 m) western land span, and a150 ft (46 m) eastern land span for a total length of935 ft (285 m). The design actually used for con-struction, Figure 2.53, for the same total length,has a main span increased to 59.5 ft (181 m) andtwo equal 170 ft (52 m) long side spans. The corre-sponding slight increase in cost of the superstruc-ture was far more than offset by eliminating theneed to build a caisson in 48 ft (15 m) of water 98 ft(30 m) above bedrock for the west pier. This rede-sign, developed in cooperation with the contractor,allowed an overall saving of approximately 20% ofthe project cost.

The two identical 170 ft (5 1.9 m) long land spanscantilever from the main piers and act as counter-weights for the main span. From a depth of 32 ft(9.8 m) at the main piers they taper to a depth of 28ft (8.5 m) at a point 130 ft (39.6 m) from the main

\t

\\

F I G U R E 2 . 5 3 . Granti’Mcrc Bx-icige. ccntt’~~ $p;tnparabolic arch soffit (courtesy of’ the Portland CementAssociation).

piers, where they are supported by a secondarypair of 4 ft by 4 ft (1.2 by 1.2 m) bearing cappedpiers. The 40 ft (12.2 m) wedge-shaped shore endsof the land spans taper from the secondary piers tograde at the top of the abutment. The abutments,which are just 16 in. (406 mm) thick, are designedto support the approach slab only, Figure 2.54.

1*170’ i 595’ 170’

E L E V A T I O N

T Y P I C A L SECTION

D E T A I L O F A B U T M E N T

FIGURE 2.54. Grand’Mere Bridge, general arrangement. (a) Elevation.(6) Typical section. (c) Detail of abutment.

Grand’mere Bridge, Canada 57

Modular, confined rubber expansion joints are m) outboard of the secondary piers to form aprovided in the roadway above the abutments. The chamber between the solid wedge end and thewedge portions of the land spans are solid con- diaphragms. This chamber was incrementally filledCrete, helping counterbalance the weight of the with gravel in three stages to counterbalance themain span under service conditions as well as dur- main span as it was progressively constructed. Theing the construction stage. The land spans have a bottom soffit of the west land span was supportedweb thickness of 2 ft (0.6 m), a 3 ft (0.9 m) thick on temporary steel scaffolding. However, becausebottom slab, and a 15 in. (38 1 mm) thick top flange. of the terrain slope, the east land-span bottomA 2 ft (0.6 m) thick diaphragm is located 78 ft (23.8 soffit was plywood-formed on a bed of sand spread

Elevation

fb)

FIGURE 2.55. Arnhem Bridge. (a) Plan. (b) Elevation.


over the rock. Upon completion of concreting andcuring, the sand was hosed out from under theformwork, allowing it to be stripped.‘”

double-cell box girders that vary in depth from 6.5ft (2.0 m) at midspan to 17 ft (5.3 m) at the piers.The western rectangular box girder has a width of49 ft (14.8 m) with 10 ft (3 m) top flange cantileversfor an overall width of 68.4 ft (20.84 m). The east-ern rectangular box girder has a width of 35.4 ft(10.8 m) with top flange cantilevers of 8.6 ft (2.62m) for a total width of 52.6 ft (16.04 m), Figure2.56a.

2.10 Arnhem Bridge, Holland

The Arnhem Bridge, Figure 2.55, is a cast-in-place, lightweight concrete, segmental bridge cross-ing the Rhine River with a center span of 448 ft(136 m), a south end span of 234 ft (71 m), and anorth end span of 238 ft (72 m) connecting to ap-proach ramps. It is a dual structure composed oftwo-cell box girders, Figure 2.56a. The westernstructure has two 30 ft (9.1 m) roadways for au-tomobile traffic. The eastern structure has a 23 ft(7 m) roadway reserved for bus traffic, a 17 ft (5.3m) roadway for bicycles and motorcycles, and a 7 ft(2.1 m) pedestrian walkway. Ramp structures areof prestressed flat slab construction, Figure 2.566.

The main three-span river crossing with anoverall width of 122.7 ft (37.4 m) consists of two

Construction of the main spans is by the conven-tional cast-in-place segmental balanced cantilevermethod with form travelers. The form travelersare owned by the Dutch Government and leased tothe contractors. Strand tendons were used forpost-tensioning, and the lightweight concrete had aweight of about 110 lb/ft3 (1780 kg/m3), Figure2.57.

Temporary supports at the pier were used forunbalanced loading during construction, Figure2.58. Precast exposed aggregate facia units wereused for the entire length of the structure and itsapproaches, Figures 2.59 and 2.60.

0.13 j 2.62 1

E,

VAR

fb)FIGURE 2.56. Arnhem Bridge, typical cross sections of main bridge and flat-slabramp. (a) Main structure. (6) Prestressed flat-slab ramp.

Napa River Bridge, U.S.A. 59

FIGURE 2.57. Arnhem Bridge, center-span cantilev-ers.

FIGURE 2.58. Arnhem Bridge, temporary pier sup-ports for unbalanced moments.

2.11 Napa River Bridge, U.S.A.

The Napa River Bridge, Figure 2.61, is located onHighway 29 just south of the city of Napa, Califor-nia, and provides a four-lane, 66 ft (20 m) wideroadway over the Napa River to bypass an existingtwo-lane lift span and several miles of city streets.The 68 ft (20.7 m) wide, 2230 ft (679.7 m) longbridge consists of 13 spans varying in length from120 to 250 ft (36.58 to 76.2 m) and a two-celltrapezoidal box girder varying from 7 ft 9 in. (2.36m) to 12 ft (3.66 m) in depth, Figure 2.62. Threehinged joints were provided at midspan in spans 2,6, and 10. These joints involved elaborate connec-tions incorporating elastomeric bearing pads andhard-rubber bumper pads to withstand severemovement and shock during an earthquake, Fig-ure 2.63. All other joints between the cantileverswere normal cast-in-place closure joints.13 Thesuperstructure is fixed to the piers, primarily forseismic resistance.

The Structures Division of the California De-partment of Transportation (CALTRANS) de-veloped plans and specifications for three alterna-

FIGURE 2.59. Arnhem HI-idgc, Ge\\- of‘ prwtwssedflat-slab ramp structure.

FIGURE 2.60. Arnhem Bridge, precast exposedaggregate facia units.

FIGURE 2.61. Napa River Bridge, aerial view.

tive types of construction, Figure 2.62, as follows:

A. A conventional continuous cast-in-place pre-stressed box girder bridge of lightweight con-crete.

B. A continuous structural-steel trapezoidal boxgirder composite with a lightweight concretedeck.

C. A cantilever prestressed segmental concretebox girder bridge allowing either cast-in-place


2820’ vck/C q -0 24863 % Sto

108 +20 PRVCElev 63 18

‘SO&

PROFILE GRADE

P i e r 2 3 4 5 6 7 i 9 IO I I I2 13

ELEVATION

Contllever Segmental P / SCmveAmol tip P/S Lightweight Cone B o x Gtrder

Llghtwelght Cone B o x Girder Welded Steel Box Girder

ALTERNATIVE A ALTERNATIVE B ALTERNATIVE C

FIGURE 2.62. Napa River Bridge, profile grade, elevation, and alternate sections.

AnchorB o l t

L Elas tomer i c Pad

FIGURE 2.63. Napa River Bridge, mid-span hingejoint with seismic bumbers.

or precast segments. Erection was allowed onfalsework or by the free cantilever method.

Because of poor foundations and a readily avail-able aggregate supply, all alternatives utilizedlightweight concrete in the superstructure. Alter-native C utilized transverse prestressing in the deckto reduce the number of webs to three, as com-pared to seven webs required in alternative A. Ofseven bids received and opened on November 6,1974, six were for alternative C and the seventhand highest was for alternative B. No bids weresubmitted for alternative A.

Design of the superstructure required l ight-weight concrete with a compressive strength of4500 psi (3 16 kg/cm2) at 28 days and 3500 psi (246kg/cm2) prior to prestressing. The three-web win-ning alternative required a minimum of formedsurfaces and forced the majority of longitudinalprestressing into the flanges, result ing inmaximum prestress eccentricity, and therefore aneconomical solution.

Contract plans showed the minimum prestressforce required at each section and permitted theuse of either 270 ksi (1862 MPa) strand or 150 ksi(1034 MPa) bar tendons. Prestressing force dia-grams were provided for both materials. The con-tractor had the option of balancing segment lengthagainst prestress force to achieve the most eco-nomical structure. In addition, the plans providedthe contractor with the option of a combination ofdiagonal prestressing and conventional reinforce-

Koror-Babelthuap, U.S. Pacajic Trust Territory 61

ment in the webs for shear reinforcement or theutilization of conventional stirrup reinforcementonly. The design was based upon a 40,000 psi (276MPa) prestress loss for the 270 ksi (1862 MPa)strand and 28,000 psi (193 MPa) loss for the 150ksi (1034 MPa) bars. Because the loss of prestress isa function of the type of lightweight aggregateused, the contractor was required to submit testvalues for approval concerning the materials to beused and relevant calculations.t4

The contractor elected to use the canti levercast-in-place alternative supported on falseworkuntil each segment was stressed, Figure 2.64.Falsework bents with ten 70 ft (21.3 m) long, 36 in.(914 mm) deep, wide-flange girders support eachbalanced cantilever. The falsework was thenmoved to the next pier, leaving the cantileverfree-standing, Figure 2.65. The entire formwork,steel girders, and timber forms were lowered bywinches from the cantilever girder after all nega-tive post-tensioning was completed. Positive post-tensioning followed midspan closure pours.13

FIGURE 2.64. Napa Kiver Bridge, free-standing can-tilever and supporting bents for falsework

The 250 ft (76.2 m) long navigation span wasconstructed with a complicated segment sequencebecause of a U.S. Coast Guard requirement that a70 ft (21.3 m) wide by 70 ft (2 1.3 m) high naviga-tion channel be maintained. Approximately 60 ft(18.3 m) of span 4, over the navigable channel, wasconstructed in three segments on suspendedfalsework by the conventional cast-in-place seg-mental method.13

All transverse and longitudinal post-tension-ing tendons consist of t in. (12.7 mm) diameterstrands. Longitudinal tendons are twelve t in. (12.7mm) diameter strand, with anchorages located inthe top and bottom flanges such that all stressingwas done from inside the box girder. Loops areused for economy and efficiency, as shown in Fig-ure 2.66. The longest span over the navigationchannel is prestressed by 50 (twelve 4 in. strand)tendons. Transverse prestress in the top flange al-lowed a 10 ft (3 m) cantilever on each side of thetwo-cell box girder. Transverse tendons consist offour -f in. diameter strands encased in flat ducts2.25 by 0.75 in. (57 by 19 mm) with proper splay atboth ends to accommodate a flat bearing at theedge of the deck slab.

2 .12 Koror-Babelthuap, U.S. PacijkTrust Territory

This structure currently represents (1979) thelongest concrete cantilever girder span in theworld. It connects the islands of Koror and Babel-thuap, which are part of the Palau Island chain ofthe Caroline Islands located in the United StatesTrust Territory some 1500 miles (2414 km) east ofthe Philippines, Figure 2.67.

FIGURE 2.65. Napa River Bridge, falsework bents(courtesy of Phil Hale, CALTRANS).

FIGURE 2.66. Napa River Bridge, longitudinal looptendons.


FIGURE 2.67. Koror-Babelthuap Bridge, locationmap, from ref. 15.

In elevation this structure has a center span of790 ft (241 m) with side spans of 176 ft (53.6 m)that cantilever another 61 ft (18.6 m) to the abut-ments, Figure 1.30. Depth of this single-cell boxgirder superstructure varies parabolically from 46ft (14 m) at the pier to 12 ft (3.66 m) at midspan ofthe main span, Figure 2.68. The side span de-creases linearly from the main pier to 33 ft 8 in.(10.26 m) at the end piers and then to 9 ft (2.74 m)at the abutments. The structure has a symmetricalvertical curve of 800 ft (243.8 m) radius fromabutment to abutment with the approach roadwaysat a 6% grade.15

Superstructure cross section, Figure 1.30, is asingle-cell box 24 ft (7.3 m) in width with the topflange cantilevering 3 ft 9$ in. (1.16 m) for a totaltop flange width of 31 ft 7 in. (9.63 m), providingtwo traffic lanes and a pedestrian path. The webshave a constant thickness of 14 in. (0.36 m). Bot-tom flange thickness varies from 7 in. (0.18 m) atmidspan of the center span to 46 in. (1.17 m) at the

FIGURE 2.68. Koror-Babelthuap Bridge, parabolicsoffit of main span (courtesy of Dr. Man-Chung Tang,DRC Consultants, Inc.).

main pier and then to 21 in. (0.53 m) at an inter-mediate diaphragm located in the end span. Thisdiaphragm and the one at the end pier form a bal-last compartment. Another ballast compartment islocated between the end-pier diaphragm and theabutment. The bottom flange under the ballastcompartments is 3 ft (0.9 m) thick in order to sup-port the additional load of ballast material. Topflange thickness varies from 11 in. (0.28 m) atmidspan of the main span to 17 in. (0.43 m) at themain pier and has a constant thickness of 17 in.(0.43 m) in the end spans.15

The superstructure is monolithic with the mainpiers, with a permanent hinge at midspan to ac-commodate concrete shrinkage, creep, and ther-mal movements. The hinge can only transfer verti-cal and lateral shear forces between the twocantilevers and has no moment-transfer capacity.15The superstructure was constructed in segmentswith the end spans on falsework and the main spanin the conventional segmental cantilever manner,using form travelers. After f-oundations were com-pleted, a 46 ft (14 m) deep by 37 ft (11.3 m) piersegment was constructed, Figure 2.69, in three op-erations: first the bottom flange, then the webs anddiaphragm, and finally the top flange. Upon com-pletion of the pier segment, form travelers wereinstalled and segmental construction begun. Twoform travelers were used to simultaneously ad-

FIGURE 2.69. E;oror-Baheltlluap Bridge, pier seg-ment (courtesy of Dyckerhoff & Widmann).

Vejle Fjord Bridge, Denmark

FIGURE 2.70. ~oror-K;tt,clthrl;lp Bridge. main-spancantilevers advancing (courtesy of Dyckerhoff PC Wid-mann).

Vance the main-span cantilevers, Figure 2.70. Seg-ments for this project were 15 ft (4.57 m) inlength. l5

On this project, each segment took slightly morethan one week to construct. A typical cycle was asfollows : I5

1.

2.

3.

4.

5.

6.7.

When the concrete strength in the last segmentcast reached 2500 psi (17.2 MPa), a specifiednumber of tendons, ranging from six to 12,were stressed to 50 percent of their final force,thus enabling the form traveler to advance inpreparation for the following segment.Advancing the form traveler also brought for-ward the outside forms of the box. The formswere cleaned while rough adjustments of ele-vation were made.

Reinforcement and prestressing tendons wereplaced in the bottom flange and webs. The in-side forms were advanced and top flange rein-forcement and tendons placed.

After the previous segment concrete hadreached a strength of 3500 psi (24.1 MPa), theremaining tendons were stressed. The previ-ous segment had to be fully prestressed beforeconcrete for the subsequent segment could beplaced.Fine adjustment of the forms for camber andany required correction was made.

New segment concrete was placed and cured.

When the new segment reached a concretestrength of 2500 psi (17.2 MPa), the cycle wasrepeated.

The structure was prestressed longitudinally,transversely, and vertically. Three hundred and

two longitudinal tendons were required at the piersegment. As the cantilever progressed, 12 to 16tendons were anchored off at each segment, witheight longitudinal tendons remaining for the lastsegment in a cantilever at midspan. As the struc-ture has a hinge at midspan, there were no con-tinuity tendons in the bottom flange. Transversetendons in the top flange were spaced at 22 in.(0.56 m) centers. Vertical tendons were used in thewebs to accommodate shear. Spacing for the verti-cal web tendons was 30 in. (0.76 m) in the centerspan and 15 in. (0.38 m) in the end spans. All ten-dons were la in. (32 mm) diameter barsI

Side spans were constructed on falsework restingon compacted fill. The sequence of segmental con-struction in the side spans was coordinated withthat in the main span, so that the unbalanced mo-ment at the main pier was maintained within pre-scribed limits.

2.13 Vejle Fjord Bridge, Denmark

This structure crosses the Vejle Fjord about 0.6mile (1 km) east of the Vejle Harbor. It is part ofthe East Jutland Motorway, which will provide abypass around the city of Vejle, Denmark. A totallength of 5611 ft (17 10 m) makes it the secondlongest bridge in Denmark.

Bid documents indicated two alternative designs,one in steel and one in concrete. The steel alterna-tive called for a superstructure composed of acentral box girder with cantilevered outriggerssupporting an orthotropic deck and fjord spans of413 ft (126 m). The second alternative required aprestressed concrete superstructure with a centralbox girder to be constructed by the balanced can-tilever method utilizing either precast or cast-in-place segments, with fjord spans of 361 ft (110 m).The successful alternative was the cast-in-placesegmental prestressed concrete box girder.

The bridge, in plan, is straight without any hori-zontal curvature. It does have a constant grade of0.5% falling toward the north. Navigation re-quirements were a minimum 131 ft (40 m) verticaland 246 ft (75 m) horizontal clearance. Waterdepth in the fjord is generally 8 to 11.5 ft (2.5 to3.5 m) except at the navigation channel, where thedepth increases to 23 ft (7 m). Under the fjord bedare layers of very soft foundation materials, vary-ing in depth from 26 to 39 ft (8 to 12 m). There-fore, the piers in the fjord are founded on 8 in. (0.2m) square driven reinforced concrete piles varyingin length from 100 to 130 ft (30 to 40 m), Figure2.71. Piers on the south bank are founded on


mCAST I FlXCD rcmuwan

USTw4nEw.Y

_----_-------_..,---

as1

,‘,“‘,‘.‘,‘,‘,‘,

FIGURE 2.71. Vejle Fjord Bridge, fjord piersfounded on driven reinforced concrete piles.

bored reinforced concrete piles, 59 in. (1500 mm)in diameter, Figure 2.72. On the north bank onepier is founded on driven reinforced concrete pilesand one is supported directly on a spread footing.

The cross section of the bridge, Figure 2.73,which carries four traffic lanes with a median bar-rier, is a variable-depth single box with a verticalweb and prestressed transverse ribs. Total widthbetween edge guard rails is 87 ft (26.6 m). Boxgirder width is 39.4 ft (12 m), with a depth vary-ing from 19.7 ft (6 m) at the pier to 9.8 ft (3 m)at midspan. Each segment is cast with a length of11.3 ft (3.44 m). Transverse top flange ribs arespaced at 22.6 ft (6.88 m) centers-that is, everyother segment joint.

The total bridge length is divided into four sepa-rate sections by three expansion joints located atthe center of spans 4-5, 8-9, and 12-13. Lon-gitudinal prestress is achieved by Dywidag (twelve

MICACEOUS

R E D P I L E SDII rs

0 1 5 0 C M

.I _on bored piles.FIGURE 2.72. Vejle Fjord Bridge, land piers foundedon bored piles.

0.6 in. diameter strand) tendons, as are the trans-verse prestress in the top slab and the continuityprestress in the bottom slab.

A 492 ft (150 m) long steel launching girder andtwo special form travelers were used for casting inplace the full width of the 11.3 ft (3.4 m) long seg-ments in balanced cantilever. Insulating formsfollowed the form travelers in order to prevent theformation of fissures due to adverse temperaturegradients. In addition, the steel girder stabilizedthe concrete structure during construction and wasused for the transportation of materials, equip-ment, and working crew. The total weight of thegirder including the two travelers was approxi-mately 660 t (600 mt). A typical longitudinal sec-tion of a cantilever is shown in Figure 2.74, alongwith the structure erection procedure.

Work on the bridge started in the summer of1975 and was scheduled for completion in 1980.

C R O S S S E C T I O N 1:200

2660l

50 300 50 750 5010030

AT MID SPAN - - I - - OVER PIER

FIGURE 2.73. Vejle Fjord Bridge, elevation, plan, and cross section.

BOX-TYPE GIRDER

zLONGITUDINAL SECTION POSITION OF PRESTRESSING TENDONS

II

SUPERSTRUCTURE, PRINCIPLE OF EXECUTION AUXILIARY EQUIPMENT ETC. CONSTRUCTION PRINCIPLES

FIGURE 2.74. Vejle Fjord Bridge, longitudinal section and erection sequence.

Vejle Fjord Bridge, Denmark 67

FIGURE 2.75. Vejle Fjord Bridge, launching girder.

\ ;->, :\ I_\\ 1

FIGURE 2.76. Vejle Fjord Bridge, transverse ribs.

Construction progress in the spring of 1978 is il-lustrated in Figures 2.75 through 2.78. Figure 2.79is an aerial view showing the structure nearingcompletion. To keep within the constructionschedule, it was finally necessary to use two com-plete sets of launching girders and twin travelersworking simultaneously from both ends of thebridge.

\\\:: ,:< >~‘\\ \ \

\ \\\\ \\

\\ .:,

FIGURE 2.77. Vejle Fjord Bridge, pier segment withdiaphragm.

FIGURE 2.78. Vejle Fjord Bridge, construction \iew,spring 1978 (courtesy of H. A. Lindberg).

FIGURE 2.79. Vqjle Fjord Bridge. aerial view fromthe northwest.


2.14 Houston Ship Channel Bridge, U.S.A. shrinkage, superimposed dead loads, and liveloads). They are, therefore, heavilv reinforced;their dimensions are:This bridge, a rendering of which is shown in Fig-

ure 1.67, includes a main structure over the ShipChannel in Houston, Texas, and two approachviaducts. The main structure is a three-span con-tinuous box girder, cast in place in balanced can-tilever. Span lengths are 375, 750, and 375 ft (114,229, and 114 m). The navigation channel is 700 ft(213 m) wide at elevation 95 ft (29 m) and 500 f-t(752 m) wide at elevation 175 ft (53.4 m), Figure2.80.

The three-web box girder carries four trafficlanes separated by a 2 ft 3 in. (0.7 m) central bar-rier and has two 3 ft 9 in. (1.14 m) parapets. Thebox girder is fixed to the top of the main piers tomake the structure a three-span rigid frame. Sup-port for the box girder is provided by elastomericbearings on top of the transition piers, where it isseparated from the approach viaducts by expan-sion joints.

Foundations The two center piers and two tran-sition piers rest on 24 in. (610 mm) diameterdriven steel pipe piles. The center piers each restupon 255 piles with a unit pile capacity of 140 t(127 mt). Footings are 81 ft (24.7 m) wide, 85 ft (26m) long, and 15 ft (4.6 m) deep. These footings aresurrounded by a sheet pile cofferdam and arepoured on a 4 ft (1.2 m) thick subfooting seal con-crete. The transition pier footings are 50 ft (15.2m) wide, 35 ft (10.7 m) long, and 5.5 ft (1.7 m)thick and rest on 70 piles each of 100 t (90 mt)bearing capacity.

Piers The main piers provide for the stability ofthe cantilevers during construction (unbalancedconstruction loads and wind loads) and participatein the capacity and behavior of the structure underservice loads (long-term loads due to creep and

Total height (from top of footing to bottom of piersegments): 160 ft 10 in. (49 m)Length (parallel to centerline of highway): 20 ftconstant (6.1 m)Width: variable from 38 ft at the bottom to 27 ft 7in. at the top (11.6 to 8.4 m)

Pier cross section: rectangular box, with 2 ft (0.6 m)constant wall thickness

The transition piers support the last segment ofthe main structure side span and the last span ofthe approaches. The pier shaft is a rectangular boxwith 1 ft 4 in. (0.4 m) thick walls. Their heights are152 ft (46 m) at one end and 164 ft (50 m) at theother end of- the bridge. The length, parallel to thecenterline of the highway, varies from 18 to 8 ft(5.5 to 2.4 m); the width is 38 ft (11.6 m) constant.Atop the pier, a 6 ft 8 in. (2 m) cap carries the per-manent elastomeric bearings and all the temporaryjacks and concrete blocks that will be used at thetime of the side-span closure pour. All four piers

are slip-formed.Box Gzrder Superstructure Dimensions of the

variable-depth box girder were dictated by vervstringent geometry requirements. Vertical align-ment of the roadway was determined by themaximum allowable grade of the approach via-ducts and the connection thereof with the roadwaysystem on both banks. The clearance required fatthe ship channel left, therefore, only a structuraldepth of 2 1.8 ft (6.6 m) at the two points located250 ft (76 m) on either side of the midspan section.The soffit is given a third-degree parabolic shapeto increase the structural depth near the piers inorder to compensate for the very lirnited height of

FIGURE 2.80. Houston Ship Channel Bridge, longitudinal section.

Houston Ship Channel Bridge, USA 69

the center portion of the main span. Maximum Longitudinal prestress is provided by straight-depth at the pier is 47.8 ft (14.6 m), with a span- strand tendons (twelve 0.6 in. diameter or nineteento-depth ratio of 15.3. Minimum depth at midspan 0.6 in. diameter strands), as shown schematically inis 15 ft (4.6 m), with a span-to-depth ratio of 49. Figure 2.82.

-Over the 500 ft (152 m) center portion of the mainspan the span-to-depth ratio is 23, compared to a

Transversely, the top slab is post-tensioned by ten-

usual value between 17 and 20. Typical dimensionsdons (four 0.6 in. diameter strands) in flat ducts

of the box section are shown in Figure 2.8 1. Post-placed at 2 ft (0.6 m) centers.

tensioning is applied to the box section in three Vertically, the three webs are also post-tensioned asdimensions: prescribed in the specifications to a minimum

t

k B r i d g e

FIGURE 2.81. Houston Ship Channel Bridge, box section.

T r a n s v e r s e t e n d o n s 4xO.G;

/

C a n t i l e v e r p r e s t r e s s o v e r m a i n p i e r s

/

Tendons ( 1 2 x 06%a..ond (19xO.6’dia. I C o n t i n u i t y p r e s t r e s s a t m i d - s p a n

FIGURE 2.82. Houston Ship Channel Bridge, longitudinal prestress.


FIGURE 2.83. Houston Ship Channel Bridge, details of travelers

compressive stress equal to 3Ji; that is, 230 psi (1.6MPa) for a concrete strength J‘i = 6000 psi (41.4MPa).

Details of the form traveler are shown in Figure2.83.

Pier segments over the main piers are of unusualsize and posed a very interesting design problem,arising from the transfer of the superstructure un-

balanced moments into the pier shafts. Additionalvertical post-tensioning tendons are provided inthe two 2 ft (0.6 m) thick pier diaphragms for thispurpose. End segments over the transition pierswere designed to allow either the approaches orthe main structure to be completed first, as theseare two separate contracts.

It is possible to make an adjustment at the endpiers to compensate either for differential settle-

Other Notable Structures 71

(a)

FIGURE 2.84. Xlrti~av Bridge, U.K. ((I) I‘)pical COII-struction sequence. (h) View of’ finished bridge.

ments or for any deviation of the deflections fromthe assumed camber diagram used for construc-tion.

Provisions have been made for unexpected ad-ditional concrete shrinkage and creep problems;empty ducts have been placed in the pier segmentdiaphragms and at midspan to allow for futurepossible installation of additional tendons locatedinside the box girder but outside the concrete sec-tion, should the need for such tendons arise.

2.15 Other Notable Structures

There are so many outstanding and interestingcast-in-place cantilever bridges in the world todaythat it is impossible to discuss the subject ade-quately in the space available here. Mention shouldbe made, however, of several notable structuresnot yet covered by a detailed description.

2.15.1 MEDWAY BRIDGE, U.K.

One of the first very long-span cantilever bridgeswas the Medway Bridge. This structure used a se-ries of temporary falsework bents to provide sta-bility during construction, Figure 2.84.

2.15.2 RIO TOCANTINS BRIDGE, BRAZIL

This structure has a center span of 460 ft (140 m)and two side spans of only 174 ft (53 m), Figures2.85 and 2.86.

2.15.3 PUENTE DEL AZUFRE, SPAIN

This bridge is located very high over a deep canyonof the Rio Sil. Cantilever cast-in-place was the idealanswer to allow construction with a minimal con-tact with the environment, Figures 2.87 and 2.88.

2.15.4 SCHUBENACrlDIE BRIDGE, CANADA

This three-span bridge with a center span of 700 ft(213 m) crosses the Schubenacadie River, nearTruro, Nova Scotia. High tidal range, swift cur-rents, ice, and adverse climatic conditions madethe construction of this structure very challenging,Figures 2.89 and 2.90.

2.15.5 INCIENSO BRIDGE, GUATEMALA

The main three-span rigid frame structure with acenter span of 400 ft (122 m) is of cast-in-place bal-anced cantilever construction, and the approachspans are of precast girders, Figures 2.91 and 2.92.The very severe 1977 earthquake left the centerstructure completely undamaged, while the usualdamage took place in the approach spans.


FIGURE 2.85.

1 1.72S j6.551 1.725 1

Rio Tocantins Bridge, Brazil, typical elevation and cross section.

2.15.6 SETUBAL BRIDGE, ARGENTINA

This three-span structure with a main span of460ft (140 m) rests on two main river piers with twinvertical walls and piles, with a transition footing atwater elevation, Figures 2.93 and 2.94.

2.15.7 KIPAPA STREAM BRIDGE, U.S.A.

This bridge is located in the Island of Oahu in theState of Hawaii. The dual structure has an overall

FIGURE 2.86. Rio Tocantins Bridge, Brazil, view ofthe finished bridge.

width of 118 ft (36 m) to accommodate six trafficlanes, three in each direction, and consists of twodouble-cell box girders of constant depth withinterior spans of 2.50 ft (76.2 m), Figures 2.95 and2.96. Construction was by cast-in-place cantileverwith segments 15 ft 3 in. (4.65 m) long. The bridgehas pleasant lines, which blend aestheticallv withthe rugged deep-valley site.

2.15.8 PARROTS FERRY BRIDGE, U.S.A.

This structure, built in California for the Corps ofEngineers, represents a major application of light-weight concrete for cast-in-place cantilever con-struction, Figure 2.97.

2.15.9 MAGNAN VIADUCT, FRANCE

Located just off the French Riviera in SouthernFrance, this four-span continuous structure restson 300 ft (92 m) high twin piers of an I-shapedsection. Superstructure was cast in place in twostages (first the bottom slab and webs and then thetop slab) to reduce the weight and cost of travelers.Figures 2.98 and 2.99 show the principal dimen-sions and views of one cantilever and the finishedstructure, Figure 2.100.

Other Notable Structures 7 3

6S.00 130 00 I cm I*+t I

I

Ad

*I d

FIGURE 2.87. Puente de1 Azufre, Spain, typical elevation and sections.

2.15.10 PUTE4UX BRIDGE, FRANCE

These are twin bridges crossing the Seine Rivernear Paris. Because of very stringent clearance andgeometry requirements, the available structuraldepth was only 5.9 ft (1.8 m) for the clear 275 ft(83.8 m) span and 4.8 ft (1.47 m) for the clear 214

FIGURE 2.88. Puente &%I Azuir e, Spun.

ft (65.3 m) span, making both structures very slen-der, Figures 2.101 and 2.102. Stiff “V” piers inboth structures help reduce the flexibility of thedeck.

2.15.11 TRICASTIN BRIDGE, FRANCE

This structure spans the Rhone River with no piersin the river, which necessitates a long center spanand two very short side spans anchored at bothends against uplift. The center portion of the mainspan is of lightweight concrete, while the two zonesover the piers where stresses are high are of con-ventional concrete, Figures 2.103 and 2.104.

2.15.12 ESCHACHTAL BRIDGE, GERMANY

This bridge is located near Stuttgart, Germany.The superstructure consists of a large single-cellbox girder with large top flange cantilevers sup-ported by precast struts. Because of the weight in-volved, the central box was cast in one operation;struts were installed and flanges cast subsequently,Figures 2.105 and 2.106.

Elevat ion

16'~0" 1 16’4”

Q

I

,6,-o” i 16’4”

Section at Midspan

II 20’~0” 4

Section pver Piers

FIGURE 2.89. Shubenacadie Bridge, elevation and sections, from ref. 16.

FIGURE 2.90. Shubenacadie Bridge, supper t avstemfor unbalanced cantilever moment at pier (courtesy ofthe Portland Cement Association).

74

FIGURE 2.91. Incknso Bridge, Guatemala, view ofthe structure.

E L E V A T I O N

@@Gp7 50

M A I N B R I D G E‘/2 S E C T I O N ‘/2 S E C T I O N

O N S U P P O R T O N S P A N

FIGURE 2.92. Incienso Bridge, Guatemala, dimensions.

FIGURE 2.93. Setubal Bridge, Argentina, dimensions.

75

FIGURE 2.94.bridge.

Setubal Bridge, Argentina, view of the

A b u t 2

1 2 3 4 5 6 7Elevation

c 29’&” -...v.&-.-.-__. 29’4” ._~ ..__. i)

~~,2,,-- - -FIGURE 2.95. Kipapa Stream Bridge, elevation and cross section.

FIGURE 2.96. Kipapa Stream Bridge, constructionview (courtesy of Dyckerhoff & Widmann).

FIGURE 2.97. ParrotsFerry Bridge, dimensions,ref. 17.

COUPE LONGITUDINALE=2? 0 T ?? 99 00 @ UC

FIGURE 2.98. MagnanViaduct, longitudinal section.

FIGURE 2.99. Ilagnan Viaduct, view of a cantilever. FIGURE 2.100. Magnan Viaduct, aerial view of thecompleted bridge.

FIGURE 2.101. Puteaux Bridge, aerial view of the completed bridge.

Ill1 rlnrn - Ml

h“t// \10.00

5 00 5.00

1 2 . 4 0 ++-j 2 . 4 0

FIGURE 2.103. Tricastin Bridge, dimensions.

c

79

FIGURE 2.104. Tricastin Bridge, view of finished bridge.

FIGURE 2.105. Eschachtal Bridge, casting flangecant i l evers .

FIGURE 2.106. Eschachtal Bridge, view of outriggers t r u t s .

8 0

References 81

2.16 Conclusion

‘I‘he I~;III\~ structures described above show theversatilitv of’ cast-in-place balanced cantilever con-struction, particularl\~ in the field of vet-v-long-spanbridges with tew repetitive spans. The design as-pect 01‘ these structures will be discussed in Chap-ter 4 attd construction problems in Chapter 11.

References

1. H. I‘llUl, “RlYlcLentMll,” Bdot/- uuct S~nhlh/e~r//~crtc, 6 1JAIJI-g;~t~g. Hct t 5 . \I;ti 1966.

2 . L‘lt-ich Fitistrrwaldet-. “Prestressed Concrete BI-idge<:onst~~tction.” Jounrcll of tha .4ttrwicntr COPIUP~P It~cti-tlrtr. Vol. 62. So. 9, Seprember 1965.

3 . L’lricti Finster\val(ler. “Sew Developments in Pre-streshing .\Iethotls and Concrete Bridge Construc-rioti.” I)~711/,/1~-Br,-rchlr, 4-1967, S e p t e m b e r 1 9 6 7 ,I)\ckerhof’t K- Widmann Kc;, hlunich, Germanv.

4 . L‘lt-ic-h Fiiister~valder, “Fi-ee Cantilever Construction01 Prestressed CoIlcrete Bridges and Mushroon-Shaped Bridges,” I;/,.\[ I~tprrccct~or~rtl Svmpo.tiu~, Cowor/r Hr/f/gfj Dr.\rgt/, r\Cl Publication- SP-23, PapetSP23-26. American Concrete Institute. Detroit ,1969.

.5. “Bridge Built :Itop the Scenery With CantileveredI‘m\ elcrc,” Etrgitrwrttcg .\‘Pu~.\-RPCO~, June 18, 1964.

6. Dale F. I)o\vning, “Cantilever Segmental PrestressedCast-in-Place Construction of’ the Pine Valley CreekBridge.” presented to the X.-\SHO Annual &leering,I.0 .-\ngeles. Caliti~rnia. So\,ember 1 I- 15, 19i3.

, “Pine \‘alle\ Creek Bridge, Calit’ornia,” Bridge Re-port SK 16 1 .O 1 E. Portland Cement Association,Skokie. 111.. 19i4.

8 . R ichard A. Dokken, “CAL.I‘RANS Experience inSegmental Bridge Design.” Bririp Sotu, Division of

Structures, Departmenr ot .[‘I-ansportation, State ofCalifornia, Vol. XVII, No. 1, March 1975.

9 . A . P . Berzone, “Pine Val ley Creek Bridge-Designing for Segmental Construction,” \leetingPrepr-int 1 9 4 4 , AXE N a t i o n a l S t r u c t u r a l E n -gineering hleeting, April 9-13, 1973, San Francisco.

10. Richard Heinen, “Pine Valley Creek Bridge: Use otCantilever Construction,” Meeting Preprint 198 I,ASCE Sational Strucrural Engineer ing Meet ing ,.-\pt-il 9 -13, 1973, Sail Francisco.

1 1. “A. 15 et A.86 raccordement autoroutiel- dans lenerd du departement ties hauls-de-seine,” Ministered e L’Equipemenr D i r e c t i o n Departemental d eL’Equipement des Hauts-de-Seine, Paris, September1976.

12. “Bridge Has 595 ft Post-tensioned Span,” Hmy~CoKam-tio~l ‘VfWS, August 2, 1976.

IS. “Napa River Br idge , Sapa, Calif~~rnia,” PortlandCement Association, Bridge Report , SR 194.01 E,1977.

14. “Alternate Bidding for California’s Napa RivetBridge Won by Cast-in-Place Prestressed ConcreteSegmental Construction,” Prestressed Concrete In-stitute, Post-‘I‘ensioning Division, Special BridgeReport.

1 5 . hian-Chung ‘Tang, “Koror-Babelthuap B r i d g e - AWorld Record Span,” Preprint Paper 3441, ASCEConvention, Chicago, October 16-20, 1978.

1 6 . D . W . Macintosh a n d R . A . W h i t m a n , “ T h eShubenacadie Bridge, .Maitland, Nova Scotia,” An-nual Conference Preprints, Roads and ‘I‘ransporta-tion Xssociation of Canada, Ottawa, 1978.

15. “Concrete Alternate Wins Competit ive BiddingContest f’or Long Span California Bridge,” BridgeReport, PostGensioning Institute, April 1977.

3Precast Balanced Cantilever Girder Bridges

3 . 1 INTRODUCITON3 . 2 CHOISY-LE-ROI BRIDGE AND OTHER STRUC-

TURES IN GREATER PARIS, FRANCE3.3 PIERRE BENITE BRIDGES NEAR LYON, FRANCE3.4 OTHER PRECAST SEGMENTAL BRIDGES IN PARIS

3.4.1 Paris Belt (Downstream)3.4.2 Paris Belt (Upstream)3.4.3 Juvisy Bridge3.4.4 Twin Bridges at GmfIans

3.5 OLERON VIADUCT, FRANCE3.6 CHILLON VIADUCT, SWITZERLAND3.7 HARTEL BRIDGE, HOLLAND3.8 RIQNITEROI BRIDGE, BRAZIL3.9 BEAR RIVER BRIDGE, CANADA3.10 JFK MEMORIAL CAUSEWAY, U.S.A.3.11 SAINT ANDRk DE CUBZAC BRIDGES, FRANCE3.12 SAINT CLOUD BRIDGE, FRANCE3.13 SALLINGSUND BRIDGE, DENMARK

3.1 Zntroduction

As indicated in Chapter 1, precast segmental con-struction had its origins (in the contemporarksense) in France in 1962 as a logical alternative tothe cast-in-place’ method of construction. To theadvantage of segmental cantilever construction,primarily the elimination of conventional false-work, the technique adds the refinements im-plicit in the use of precasting.

The characteristics of precast segmental con-struction are:

1. Fabrication of the segments can be accom-plished while the substructure is under con-struction, thus enhancing erection speed of thesuperstructure.

2. BY virtue of precasting and therefore maturity.of the concrete at the time of erection, the timerequired for strength gain of the concrete isremoved from the construction critical path.

82

3.14 B-3 SOUTH VIADUCTS, FRANCE3.15 ALPINE MOTORWAY STRUCTURES, FRANCE3.16 BRIDGE OVER THE EASTERN SCHELDT, HOLLAND3.17 CAPTAIN COOK BRIDGE, AUSTRALIA3.18 OTHER NOTABLE STRUCTURES

3.18.1 Calix Bridge, France3.18.2 Vail Pass Bridges, U.S.A.3.18.3 Tent Viaduct, U.K.3.18.4 L32 Tauernautobahn Bridge, Austria3.18.5 Kishwaukee River Bridge, U.S.A.3.18.6 Kentucky River Bridge, U.S.A.3.18.7 I-205 Columbia River Bridge, U.S.A.3.18.8 Zilwaukee Bridge, U.S.A.3.18.9 Ottmarsheim Bridge, France3.18.10 Overstreet Bridge, Florida, U.S.A.3.18.11 F-9 Freeway, Melbourne, Australia

REFERENCES

3. As a result of the maturity of the concrete atthe time of erection, the effects of concreteshrinkage and creep are minimized.

4. Superior quality control can be achieved forfactory-produced precast concrete.

However, geometric control during fabrication ofsegments is essential, and corrections during erec-tion are more difficult than for cast-in-place seg-mental construction. In addition, the connectionof longitudinal ducts for post-tensioning tendonsand the continuity of reinforcing steel, if they arerequired in the design, are less easily achieved inprecast than in cast-in-place methods.

Although precast segmental had been used asearly as 1944 for the Luzancy Bridge over theXlarne River, Figure 1.27, wide acceptance beganlvhen match-casting techniques were developed.Basically, the principle of fabrication of precastsegments is to cast them in a series one against theother in the order in which they are to be assem-

Choisy-le-Roi Bridge and Other Structures in Greater Paris, France 8 3

bled in the structure. The front face of a segment,thus, serves as a bulkhead for casting the rear faceof the subsequent segment. Methods of fabricationof precast segments will be discussed in Chapter11.

Segments are erected in balanced cantileverstarting from a segment over the pier, which is thefirst to be placed. Modifications to the initial prin-ciple hau e further inc-rea>& the %,ex;lbcl(clty of eye<-tion procedures. Two major modifications are (1)temporary prestress ties to secure two or more suc-cessive segments and thus free the erection equip-ment, and (2) cantilever prestressing tendons an-chored inside the box sections instead of at thesegment face as on early structures. These refine-ments mean that the placing of segments and thethreading and stressing of tendons become inde-pendent operations.

Efficient application of this method has resultedin the use of cantilever construction in moderate-to small-span structures where it had previouslybeen considered uneconomical. Examples are theB-3 South Viaduct (Section 3.14) composed ofspans ranging from 98 ft (30 m) to 164 ft (50 m)and the Alpine Motorway Bridges (Section 3.15)where the spans range between 60 ft (18 m) to 100ft (30 m).

It is interesting to note a constant evolution to-ward increased transverse dimensions and weightof precast segments. Problems in precasting,transporting, and placing segments that are con-stantly becoming heavier and wider are beingprogressively resolved. Chapter 4 will deal with thisprogressive evolution as applied to some Frenchprecast segmental bridges and will discuss typicalcross sections of some precast segmental bridgesconstructed or in the design stage in the UnitedStates.‘.*

In continuous structures expansion joints maybe spaced very far apart. Continuous bridges up to3300 ft (1000 m) in length have been constructedwithout intermediate joints; however, this may notbe an upper limit, provided that the design ofbearings and piers is correctly integrated into thetotal design of the structure. Free longitudinalmovement of the bridge due to creep and temper-ature change is allowed for by placing the structureon elastomeric or sliding (teflon) bearings. We canalso use pier flexibility to accommodate thesemovements by fixing the superstructure to thepiers. In this case, flexibility can be obtained eitherby pier height or by the use of single or doublethin-slab walls, thus reducing the piers flexural re-sistance.

The first precast segmental bridge to be built onthe North American Continent was the LievreRiver Bridge on Highway 35,s miles (13 km) northof Notre Dame du Laus, Quebec, with a centerspan of 260 ft (79 m) and end spans of 130 ft (40m), built in 1967. It was followed in 1972 by theBear River Bridge, Digby, Nova Scotia (Section3.9), with six interior spans of 265 ft (81 m) andend spa-m of ‘Lo4 ft (65i -i-ix\. The 3FU KcnQxia(Causeway, Corpus Christi, Texas (Section 3.10),opened to traffic in 1973, was the first precast seg-mental bridge to be constructed in the UnitedStates. In the United States, as of this writing, theauthors are aware of more than 30 precast seg-mental bridge projects that are either completed,under construction, or in the design stage. Someare listed in Table 3.1 .3

3.2 Choisy-le-Roi Bridge and Other Structures inGreater Paris, France

The first bridge to use the precast segmental can-tilever technique with epoxied match-cast jointswas built at Choisy-le-Roi near Paris between 1962and 1964. It carries National Highway 186, a partof the Paris Great Belt system, over the Seine Riverjust east of Orly Airport, Figure 3.1. This structureis a three-span continuous bridge of constantdepth with end spans of 123 ft (37.5 m) and acenter span of 180 ft (55 m), Figures 3.2 and 3.3.

This bridge replaced one constructed in 1870,which had a superstructure of six steel girders withfive spans of approximately 75 ft (23 m). Thisstructure, determined to be no longer adequate asearly as 1939, was severely damaged during WorldWar II. It in turn had replaced an ancient bridgeof five 66 ft (20 m) oak arch spans designed bythe famous mathematician Claude-Louis-MarieNavier.4

In 1961, a study by the Administration ofBridges and Roads allowed two options, one inprestressed concrete and the other in steel, eachhaving three continuous spans of 123 ft (37.5 m),180.4 ft (55 m), and 123 ft (37.5 m). Four pre-stressed concrete solutions were considered. Thesuccessful solution is illustrated in Figure 3.2.

The overall width of the superstructure for thisdual bridge is 93.2 ft (28.4 m), Figure 3.3. Eachbridge consists of two single-cell rectangular boxgirders. The superstructure accommodates dualtwo-lane roadways of 23 ft (7 m), two 13 ft (4 m)sidewalks, and a 10 ft (3 m) median.4*5 Individualbox girders have a constant depth of 8.2 ft (2.5 m),

84 Precast Balanced Cantilever Girder Bridges

TABLE 3.1. Precast Segmental Concrete Bridges in North America

Date of Method of Span Lengths,Name and Location Construction Cons t ruc t ion” tt (m)

Lievre River, Notre Damedu Laus, Quebec

Bear River, Digby,Nova Scotia

JFK Memorial Causeway,Corpus Christi, Texas

Muscatuck River, U.S. 50,North Vernon, Indiana

Sugar Creek, State Route 1620,Parke County, Indiana

Vail Pass, I-70 West of Denver,Colorado (4 bridges)

Penn DOT Test Track Bridge,Penn Sate University,State College, Pa.

Turkey Run State ParkParke County, Indiana

Pasco-Kennewick, ColumbiaRiver between Pascoand Kennewick, Washington(cable-s tay spans)

Wabash River, U.S. 136,Covington, Ind.

Kishwaukee River, Winnebago CO.near Rockford, Ill.(dual structure)

Islington Ave. Ext., Toronto,Ontario

Kentucky River, Frankfort, Ky.(dual structure)

Long Key, Florida (contract letlate 1978)

Linn Cove, Blue RidgeParkway, N.C.(contract let late 1978)

Zilwaukee, Michigan(dual structure)(bids opened late 1978)

1967 B.C. 130-260- 130(39.6 - 79.2- 39.6)

1972 B.C. 203.75 - 6 (12 265 - 203.75(62.1 - 6 ((I 80.77 - 62.1)

1973 B.C. loo-200- 100(30.5 - 6 t - 30.5)

1975 B.C. 95 190-95(29 - 58 - 29)

1976 B.C. 90.5 - 180.5 - 90.5(27.6 - 53 - 27.6)

1977 B.C. 134 - 200 - 200 - 134(40.8 - 61 - 61 - 40.8)134-200-200- 145(40.X-61 -61 -44)151-155-210-210-154( 4 6 - 4 7 . 2 - 6 4 - 6 4 - 4 7 )153-210-210- 154(46.6 - 64 - 64 - 47)

1977 O.F. 124(37.8)

1977 B.C. 180 - 1x0(54.9 - 54.9)

1978 B.C. 406.5 - 98 1 - 406.5(124 - 299 - 124)

1978 1.L. 93.3 - 4 (a 187 - 93.5(28.5 - 3 (@ .57 - 28.5)

1979 B.C. 170-3 @I 250- 170(51.8 - 3 G 76.2 - 51.8)

B.C.

B.C.

S.S.

P . P .

1979

1979

2 @ 161 -200-5 @ 272(2 @ 49 - 61 - 5 (if X3)228.5 - 320 - 228.5(69.6 - 97.5 - 69.6)II3 - 101 fin 118 - 113(34.4 - 101 @i 36 - 34.4)9X.5- 163-4@ 1X0- 163-98.5(30 - 49.7 - 4 Q 54.9 - 49.7 - 30)

B.C. 26 N.B. spans total length8.087.5 (2,465)

25 S.B. spans total length8.0575 (2,456)maximum span 392 (119.5)

“Method-of-cons t ruc t ion nota t ion: B.C.-ba lanced cant i lever , l.L.-incremental launching , O.F.-on talsework. P.P.-Progressiveplacement, S.S.-span-by-span.

top flange width of 21.65 ft (6.6 m), and a bottom crown, Figure 3.3. The bottom flange thickness isflange width of 12 ft (3.66 m). Webs have a con- 6 in. (0.15 m), except near the river piers wherestant thickness of la in. (0.26 m), and the top the thickness increases to 15.75 in. (0.4 m) to ac-flange is of constant section throughout its length commodate cantilever bending s t resses . Thewith a minimum thickness of 7 in. (0.18 m) at its downstream half of the bridge (consisting of two

Choisy-le-Roi Bridge and Other Structures in Greater Paris, France 85

Precast Segmental Bridges

Choisy-le-Roi 1962-64Courbevoie 65-66Ring .Motorlva\ 66-68Ring .Motor\vav 6i-68St Cloud 72-74Juvis) 66-68Conflans 50-72St Maurice Interchange 78B-3 South L’iaduct 71-72Marne la Vallee 7.s77Torcv RR 78Clichv RR 78

Cast-in-Place Segmental Bt-idges

13 Gennevilliers 1974-7614 North \Vest A-86 Intel-change 7815 Clichy High\va\ i3-i<i

16 Puteaus Bridges 7.3-77

17 Issv lea Moulineaus il-5418 CravelIe 74-7.5

19 .Joinville 74-7620 Neuillv sul- Marnc 6 6 - 6 8

FIGURE 3.1. Location map of’ segmental bridges in greater Paris, France.

box girders) ~\‘as constructed first, alongside theesisting bridge. After removal of the existingbridge. the second or upstream half was con-structed. Each dual structure was constructed b\the balanced cantilever method utilizing Frevssinettendons f’or the longitudinal prestressing. Boxgirder segments \vere 8.2 ft (2.5 m) in length andlveighed 22 tons (20 nit), except the pier segments

FIGURE 3.2. Choisv-lc-Roi Bridge.

which were 16.4 ft (5 m) in length and weighed60.6 tons (55 mt). The pier segments also con-tained two diaphragms which provided continuitvwith the inclined wall piers, Figure 3.3.

The segments were fabricated in a precastingvard on the left bank of the Seine approximately amile (1.6 km) upstream of the project site, Figure3.4. Although this bridge might be considered ofmoderate importance with respect to span lengths,its importance lies in the method of fabrication. Itwas the first to use segments precast by the match-casting technique. Segments were cast in the pre-casting yard as a series of 8.2 ft (2.5 m) long units,one against the other, on a continuous soffit formwhich had been carefully adjusted to the intradosprofile of the bridge with allowance for camber.This came to be known as the “long-line” method(see Chapter 11). Two sets of steel forms riding thesoffit form and overnight steam curing allowed theproduction of two segments per working day. Toprevent bonding of the segments to each other inthe casting form, a special peel-off bond breakerwas sprayed over the end of the segment beforethe adjacent segment was cast. The segments were


Elevation

Elevation and cross section of river piers

subsequently stripped from the soffit form at theirmatch-castjoints and reassembled at the bridge sitein balanced cantilever on each side of the riverDiers.4

A floating crane handled the segments at the, casting yard. After the units were loaded on barges

and transported to the project site, the same craneplaced the segments over a retractable jig rolling

-..I mr-&aL&. ,66 3M I--1-e-. ,x130 inside the box girder in the completed portion ofthe bridge and was thus freed for another segment

20‘ohp--- A placing operation. A platform mounted on jacksCross section of superstructure on the jig, Figure 3.5, allowed for adjustment of

FIGURE 3.3. Choisy-le-Roi Bridge, dimensions: ele- the segment at the desired position.4 A 1 ft (0.3 m)vation, elevation and cross section of River piers, cross wide gap was temporarily maintained between thesection of superstructure. faces of the segments to allow workmen to apply

Choisy-le-Roi Bridge and Other Structures in Greater Paris, France a 7

FIGURE 3.4. Choisy-Iv-Koi Kritlge. view of’ the precasting yard.

P------ -JFIGURE 3.5. Choisy-le-Roi Bridge, retractable erection jig.

the epoxy joint material. The jig was then retractedand prestressing tendons were placed and stressedto connect the two symmetrical segments on eachside of the previously completed portion of thecantilevers on either side of the pier.5

Placing of the precast segments in a cantileverfashion on each side of the pier progressed step bystep, as indicated in Figure 3.6. Tendon layout isillustrated in Figure 3.7. Upon completion of thetwo twin cantilevers from the river piers, a cast-in-place closure pour was consummated at midspanand a second series of prestressing tendons wereplaced in the bottom flange to achieve continuitybetween the two center-span cantilevers. Thesetendons were given a draped profile to allow thelocation of tendon anchorages in the top flange ofthe box girder. Both series of tendons, cantileverand continuity, overlap each other and contribute

FIGURE 3.6. Choisy-le-Rot Bridge, segment placingwith floating crane.

Precast Balanced Cantiher Girder Bridges

l3cdes1208) / 8cablesl2# 7

FIGURE 3.7. Choisv-le-Roi Bridge, tendon lavout

to a substantial reduction in the shear forces in thewebs as a result of the vertical component of theprestress. The side spans were constructed in asimilar manner. The three precast segments adja-cent to the abutments were assembled onfalsework. After a closure pour between thesesegments and the cantilever from the river pier,positive-moment tendons were placed and stressedin the end span to achieve continuity. Because themidspan area of the center span had little capacityto withstand moment reversal under ultimate load,

additional short tendons were located in the topflange to achieve full reinforcement continuitywith the longest cantilever tend0ns.j

The same construction technique used for theChoisy-le-Roi Bridge was used for the CourbevoieBridge, built between 1965 and 1967, which alsocrosses the Seine in the northwest suburb of Paris,Figure 3.1. The bridge has three symmetricalspans of 130,200, and 130 ft (40,60, and 40 m) fora total length of 460 ft (140 m), Figure 3.8. Fourbox girders of constant depth carry the 115 ft (35

FIGURE 3.8. Courbevoie Bridge, elevation.

Pierre Benite Bridges near Lyon, France 89

m) wide deck, Figure 3.9. The available depth ofonly 7.5 ft (2.28 m) made necessary a very slenderstructure; depth-to-span ratio for the main span is1 /26.5,6

Each river pier is an assembly of two half-piers,Figures 3.9 and 3.10, which are fixed at the level ofthe foundation. Each half-pier consists of a rectan-gular shaft 9 by 26 ft (2.8 by 8 m), which supportstwo pairs of prestressed concrete walls, above thenormal water level, in the form of a parallelogramof 18 in. (0.45 m) thickness and 10.5 ft (3.2 m)width. The walls are arranged in a “V” in thetransverse direction of the bridge and have a di-mension of 6.7 ft (2.05 m) out-to-out of walls in thelongitudinal direction.6 The girders are fixed at thepiers and supported on elastomeric bearings at theabutments. A total of 148 precast segments of 12.5ft (3.8 m) length were required for the super-structure. They were fabricated in four months atthe rate of two segments per day, in two sets ofsteel forms, electrically heated and insulated withpolyurethane 1ining.j

Erection at the site was accomplished by a float-ing crane. After careful adjustment of the piersegments, they were erected at the rate of four perday. The temporary jig used at Choisy-le-Roi foradjustment of the segments was replaced in thisproject by two temporary steel beams bolted to thetop of each segment and connected to the com-pleted section of the cantilever by prestressingbars.j

The girder was prestressed longitudinally andtransversely, through three longitudinal cast-in-place strips between the top flange cantilevers ofthe box girders. The completed structure is shownin Figure 3.10.

3.3 Piewe Benite Bridges Near Lyon, France

These two large bridges carry the motorway fromParis to the Riviera south of Lyon near the PierreBenite hydroelectric plant, Figure 3.11. There aretwo separate bridges, one over the draft channel ofthe power plant and the other over the RhoneRiver. Both structures are twin bridges, eachbridge consisting of two single-cell box girders.Typical dimensions in longitudinal and cross sec-tions are shown in Figures 3.12 and 3.13. The sameconstant depth of 11.8 ft (3.6 m) is used for allspans of the two bridges. However, a haunchunder the intrados of the box girders increases the

FIGURE 3.9. Courbevoie Bridge, cross section at rive1pier and abutment.

FIGURE 3.10. Courbevoie Bridge, view of completedbridge.

FIGURE 3.11. Pierre Benite Bridge, view of thefinished bridge.

1 I I 9 4 0 0 I * 7wotslr Ibxo5600 I 84@J ! 56m -4

I Im0 0

ISJOO4


Bridge over draft channel

(a)259,OO/ 7500

FIGURE 3.12. Pierre Benite Bridge, longitudinal sections. (a) Bridge over draft chan-nel. (b) Bridge over Rhone River.

i

16.92 ..?.O

- ..3.26-- (t

13.00 166

16 30

FIGURE 3.13. Pierre Benite Bridge, typical cross section.

structural depth over the piers to a maximum of 14ft (4.28 m) for the 276 ft (84 m) span. All piers reston compressed-air caissons and are made of solidcylindrical columns 6.5 ft (2 m) in diameter whichsupport the cast-in-place pier segment, includingskew diaphragms between the two individual boxgirders of each bridge. This pier segment served asthe starting base for precast segment placing inbalanced cantilever for the superstructure.

The 528 segments were precast near the southernbank of the draft channel. This application of pre-cast segmental construction was the occasion toconceive and develop for the first time the short-

line precasting method, whereby the segments arecast in a formwork located in a stationary position.Each segment is cast between a fixed bulkhead andthe preceding segment, in order to obtain a perfectmatch. After a learning curve of a few weeks, eachof the two short-line-method casting machines wasused to cast one segment every day. Details andspecific problems of the short-line method will bedescribed in Chapter 11. Figure 3.14 shows theprecast segments as they were fabricated, tem-porarily stored, loaded on barges by a very simpleportal structure equipped with winches, and finallytransported to the construction site.

Other Precast Segmental Bridges in Paris 91

FIGURE 3.14. Pierre Henitc Bridge, precasting yardand loading portal. (a) Precasting yard. (6) Loading portal.

Placing of all segments in the two twin structureswas achieved in balanced cantilever, using thecast-in-place pier segments as a starting base. Thisproject used the newly developed “beam-and-winch” erection system, illustrated in Figure 3.15together with a close-up view of a typical seg-ment-placing operation. Electric winches are sup-ported in a cantilever position from the com-pleted part of the deck to allow each segment to belifted off the barge and placed in its final position.

Because of high-velocity river currents on onestructure, it was considered advisable to transferthe segments from the barge to the winch systemclose to the piers to allow temporary anchorage ofthe barge. Therefore, segments had to be movedlongitudinally from the barge position to thtir finallocation. A special trolley carried the winches andthe suspended segment while riding along railsfixed to the finished deck. A general view of the

construction site with segment placing in progressis shown in Figure 3.16.

Both precasting and placing operations werecarried out successfully. All the segments wereplaced in the structures in 13 months. The only re-gret was that this erection system did not providefor precast pier segments. The geometry of thecast-in-place pier segments was further compli-cated by the skew of the bridges, such that thecontractor expended as much labor on this aspectof construction as in precasting and positioning allthe precast segments..

3.4 Other Precast Segmental Bridges in Paris

The first two match-cast bridges, Choisy-le-Roi andCourbevoie, were followed by a series of othercrossings over the Seine River. All contracts for de-sign and construction were obtained on a competi-tive basis with other types of materials or construc-tion methods:

The next two structures were for the construc-tion of the Paris Belt Motorway which crosses theSeine at two locations, one downstream of the cityand one upstream; see the location map, Figure3.1. They were followed by several others, whichare briefly described in this section.

3.4.1 PARIS BELT (DOWNSTREAM)

These twin bridges, Figure 3.17, carry four trafficlanes. Dimensions are shown in Figures 3.18 and3.19. Maximum span length is 302 ft (92 m) andthe structural depth of the four box girders is 11 ft(3.4 m), increased toward the piers to a maximumof 21.3 ft (5.5 m) by straight haunches. Because ofthe skew between the axis of the bridge and theflow of the Seine, the pier shafts were given a spe-cial lozenge shape, which proved very efficient forthe hydraulic flow and is of pleasant appearance.The limited bending capacity of the shafts calledfor temporary supports during cantilever con-struction operations.

Precast segments were manufactured on thebank of the Seine with two casting machines(short-line method). For the part of the bridgesuperstructure located over the river, segmentswere placed with a floating crane, Figure 3.20. Infact, almost half the bridge length was placed overland out of reach of the floating crane. The beam-and-winch equipment used at Pierre Benite Bridgewas substituted for the crane to place these seg-ments. There was also need of additional falseworkon one bank to compensate for the unusually long

FIGURE 3.15. Pierre Benite Bridge, segment placingscheme (left and top right).

92

FIGURE 3.16. Pierre Benite Bridge, underconstruction.

FIGURE 3.17. Paris Belt (Downatrearn), \ itw offinished bridge.

9950-------r-

._._ ~i6_~-~~j~~--rlps--~:

ng.3 ___--.- i-

FIGURE 3.18. Paris Belt (Downstream), typical longitudinal section.

FIGURE 3.19. Paris Belt (Downstream), typical cross section.


FIGURE 3.20. Paris Belt (Downstream), segmentplacing.

end span, which could not be changed because ofstringent pier location requirements.

3.4.2 PARIS BELT (UPSTREAM)

On the other sihe of Paris another segmentalstructure, also carrying the Belt Motorway over theSeine, was designed for five traffic lanes in either

56,62 asa

FIGURE 3.21. Pal i\ Belt (C‘pstlum), \iew of thefinished bridge.

direction, Figure 3.21. The twin bridges have di-mensions similar to those of the downstreambridge, and each structure has two parallel boxgirders connected by transverse prestress. Dimen-sions are shown in Figures 3.22 and 3.23. A circu-lar intrados profile was used in lieu of the straighthaunches. All segments were precast on the riverbank in the immediate vicinity of the bridge, using

Id GAUCHE I

FIGURE 3.22. Paris Belt (Upstream), longitudinal section.-.w4.504. 0

E

II 18g3.50 m 3.50 n-l 3.50 m 3.50 m 3.50

m

Ill I 3.50 mi 3.50 m 3.50 m

13.50 m

1 1 II 71 I -

3.50 m

IlII A /\

FIGURE 3.23. Paris Belt (Upstream), typical cross section.

Other Precast Segmental Bridges in Paris

RUSES D’EMCUTIDN D” T- S?QUl?4CCS~~ISCKceMRucnar

FIGURE 3.24. Paris Belt (Upstream), typical segment placing scheme.

the same two casting machines used previously forthe downstream bridge.

Placing segments in the structure posed someinteresting problems, as shown in the sequencediagrams of Figure 3.24. Pier segments were tooheavy to be handled as one unit and were sub-divided into two segments, assembled upon thepier shaft before cantilever placing could start. A

FIGURE 3.25. JUVISV Bridge, completed stl ucture.

crane, either on crawlers or on a barge, togetherwith the beam-and-winch equipment handled allsegment placing.

3.4.3 JUVISU BRIDGE

This bridge, Figure 3.25, is also on the Seine justsouth of Choisy-le-Roi; see the location map, Fig-ure 3.1. Dimensions are shown in Figure 3.26.Segments were cast by the short-line method nearthe site and placed with a floating crane. An aux-iliary falsework on both banks allowed segmentplacing and assembly beyond the reach of thefloating crane.

3 .4 .4 TWIN BRIDGES AT CONFLANS

These twin bridges, Figure 3.27, placed about 320ft (100 m) apart to allow for interchange ramps onboth banks, are upstream of Paris where the Seineand Marne Rivers merge; see the location map,Figure 3.1. Dimensions and construction methodswere similar to those of the Courbevoie Bridge al-ready described.

9 6 Precast Balanced Cantilever Girder Bridges

I 24:3@ 1 2413’ IO’ 1

ClEd I33.-

FIGURE 3.26. Juvisy Bridge, cross section.

Balanced cantilever construction was accom-plished utilizing a launching gantry for erection.

In the approach spans the superstructure has aconstant depth of 8.2 ft (2.5 m). Depth of thecenter spans varies from 14.9 ft (4.5 m) at the piersto 8.2 ft (2.5 m) at midspan, Figure 3.29. The rec-tangular box segment has a bottom flange widthof 18 ft (5.5 m) and a top flange width of 34.8 ft(10.6 m). Webs have a constant thickness of 12 in.(0.3 m), while the top and bottom flanges are 8 in.(0.2 m) and 7 in. (0.18 m) thick, respectively, Fig-ure 3.30. Typical segment length is 10.8 ft (3.3 m).

Expansion of the deck is provided in everyfourth span by a special stepped (ship-lap) jointwith horizontal elastomeric bearing pads, Figure

FIGURE 3.27. Twin Bridges at Conflans, finishedbridge.

3.5 Oleron Viaduct, France

The Oleron Viaduct provides a link between themainland of France and the resort island of Oleronoff the Atlantic West Coast 80 miles (128 km) northof Bordeaux. This structure has a total length be-tween abutments of 9390 ft (2862 m). In the navi-gable central part of the structure are 26 spans of260 ft (79 m), Figure 3.28. Approach spans consistof two at 194 ft (59 m), sixteen at 130 ft (39.5 m),and two at 94 ft (29 m). The superstructure is sup-ported by 45 piers and was assembled by pre-stressing match-cast segments, using epoxy joints. FIGURE 3.28. Olevon Viaduct, complcred strllcrllre.

Oh-on Viaduct, France 97

3sllo’

3!2’ j 2916’ , 3!2’I I I I

i/

1 8 ' c I34!9” I\t

FIGURE 3.29. Oleron Viaduct, typical cross section, from ref. 5 (courtesy ofthe American C:oncrete Institute).

3.30. Throughout the total length of structurethere are ten expansion joints: one at each abut-ment and eight intermediate ones. The latter arelocated at points of contraflexure in a typicalinterior span subjected to a continuous uniformload.” The segments with the expansion joint havethe same length as typical segments and are in facttwo half-segments that are temporarily preassem-bled with bolts, with a special layout of temporaryand permanent prestressing tendons. It is thenpossible to maintain the balanced cantilever erec-tion procedure beyond the expansion joint tomidspan. Later on, when continuity has beenachieved in the adjacent spans, the expansion-.joint segment is ‘!unlocked” to perform in the in-tended manner.

The precasting plant was located in the vicinityof the mainland abutment. Production in this plantwas scheduled so that the 24 segments required fora typical 260 ft (79 m) central span could be fabri-cated in nine working days. Segments were pro-duced by the long-line method, described inChapter 11. Four sets of steel forms rode a benchthat was carefully aligned to the longitudinalprofile of the roadway and the variable-depth soffitwith due provision for camber. Segments werematch-cast in the same relative order in which theywere subsequently assembled at the site.5 An aerialview of the casting yard is shown in Figure 3.31.

Handling of segments in the casting and storageyard was accomplished by a special railway-mounted gantry capable of handling loads varying

FIGURE 3.30. Oleron Viaduct, typical center span elevation, from ref. 5 (cour-tesy of the American Concrete Institute).

Precast Balanced Cantilever Girder Bridges

FIGURE 3.31. Oleron Viaduct, aerial view of castingyard.

from 45 tons (42 mt) for the center-span segmentto 80 tons (73 mt) for the pier segment. A lowboydolly riding on rails of the finished bridge andpushed by a farm tractor transported the segmentsfrom storage to their location for assembly.

Cantilever erection at the site was accomplishedby a launching gantry, Figure 3.32. This gantrywas the key to the successful operation of this proj-ect. Although the structure is erected over water,the use of floating equipment would have beendifficult, expensive, and subject to uncertainty be-cause of the great tidal range and the shallownessof water in most of the area traversed by thestructure. Floating equipment would have beenable to reach the approach piers only at high tide.During low tide the marsh area, which is the loca-tion of France’s famed Marennes oyster beds,could not accept any tire-mounted or crawler-mounted equipment. Consequently, it was decidedto work entirely from above with a launchinggantry. This new technique was developed for thefirst time for this structure and was later refinedfor other structures. For the typical central spansthe erection cycle required between eight and tenworking days.5

Construction began in May 1964, three monthsafter design work had started. The first segmentwas cast in July and placed in August 1964. Sidespans laid on a curve were completed in Decemberand the launching gantry was then modified forconstruction of the center spans. The last of the870 precast segments was in place in March 1966,and the bridge opened to traffic in May, after anoverall construction time of two years5; see thesummary of the work program in Figure 3.33. A

FIGURE 3.32. Oleron Viaduct, construction viewshowing cantilever span, from ref. 5 (courtesy of theAmerican Concrete Institute).

view of the final structure is shown in Figures 3.28and 3.34.

The Oleron Viaduct was the first application ofthe launching-gantry concept for placing segmentsin cantilever. Several structures were later de-s igned and bu i l t w i th t he s ame cons t ruc t ionmethod. Mention should be made here of threespecial bridges:

1. Blois Bridge over the Loire River The princi-pal dimensions are given in Figure 3.35. Thesuperstructure box girders rest on the pier shaftsthrough twin elastomeric bearings, which allowthermal expansion while providing partial re-straint for bending-moment transfer between deckand piers. Consequently, savings are obtained bothin the deck and in the foundations. All segmentswere placed in the bridge with an improved ver-sion of the launching gantry first designed for theOleron Viaduct. High-strength steel and stayswere used to provide minimum weight with a sat-i s f ac to ry s t i f fne s s du r ing ope ra t i ons , F igu re3.36. High-strength bolt connections were usedthroughout to make the gantry completely capableof dismantling and easily transportable to otherconstruction sites.

2. Aramon Bridge over the Rhone River This wasthe next structure where the same gantry could beused, Figure 3.37.

3. Seudre Viaduct Located just a few milessouth of Oleron over the Seudre River, this 3300 ft(1000 m) long viaduct was also of precast segmen-tal construction and used the same launching gan-

Chillon Viaduct, Switxerland 9 9

CONTINENT OLERON

i PIERS ON FOOTINGS 1 1 PIERS ON PILES1 1

-------$ )- PIERS ON FOOTINGSi

FIGURE 3.33. Oleron Viaduct, program of work.

try. The finished structure is shown in Figure 3.38.Foundations for the center spans were built insidesheet pile cofferdams in spite of very swift tidalcurrents.

3.6 Chillon Viaduct, Switzerland

The 7251 ft (2210 m) long dual structures of theChillon Viaduct are part of European Highway E-2and are located at the eastern end of Lake Genevapassing through an environmentally sensitive areaand very close to the famed Castle of Chillon, Fig-ure 3.39. In addition, the structures have verydifficult geometrical constraints consisting of 3%grades, 6% superelevation, and tight-radius curvesas low as 2500 ft (760 m). Each structure has 23spans of 302 ft (92 m), 322 ft (98 m), or 341 ft (104m). The variable spans allowed the viaduct to befitted to the geology and topography, providingminimum impact on the scenic forest. The viaductsare divided by expansion joints into five sections ofan approximate length of 1500 ft (457 m).

Twin rectangular slip-formed shafts were usedfor the piers, varying in height from 10 to 150 ft (3to 45 m). Stability during construction was excel-lent and required little temporary bracing exceptbetween the slender walls to prevent elastic insta-bility.’ With the exception of three piers in each

FIGURE 3.34. Oleron Viaduct, aerial view of’ finishedbridge.


@ MVATlOli -ELEVATIONEch l/ZCd

t

6 1 . 5 0 I 9.1 m P\OO I 9l.00 L 61,SO

1 1 1 t

Culie R.G Pl P2 P3 PL Cult* R D

0 COUPE TRAtlSVfRSALrErh : IIlOO=

CROSS SECTION

,lzqoo

I I

too L 7,oo I zoo $00D",

to 4.79 m at midspan I

FIGURE 3.35. Blois Bridge, elevation and typical cross section.

viaduct, all piers are hinged at the top. The piersthat are less than 72 ft (22 m) high are hinged atthe base; taller piers are fixed at their base, beingsufficiently flexible to absorb longitudinal move-

ment of the superstructure.The superstructure consists of a single-cell rec-

tangular box with a cellular cantilever top flange,Figure 3.40, and with a depth varying from 18.5 ft

FIGURE 3.36. Blois Bridge, launching gantry

operating on the superstructure. FIGURE 3.37. Aramon Bridge, launching gantry.

Chillon Viaduct, Switzerland 101

FIGURE 3.38. Seudre Bridge, fItli\hcd \I I IIC 1111 e.

(5.64 m) at the longer-span piers to 7.2 ft (2.2 m) atmidspan. Widths of top and bottom flange are re-spectively 42.7 ft (13 m) and 16.4 ft (5 m). Dimen-sions of the tw& typical cantilevers are noted inFigure 3.4 1. Maximum segment weight was 88 tons(80 nit). A cellular cantilever top flange was usedbecause the overall width of the top flange ex-

FIGURE 3.39. Chlllon Viaducl. aerial LICI\.

ceeded 40 ft (approx. 12 m) and the cantileverlength was 13.15 ft (4 m). An alternative wouldhave been to provide stiffening ribs as used in theSaint Andre de Cubzac Viaducts (Section 3.11) andthe Sallingsund Bridge (Section 3.13).

Segments were precast in a yard at one end ofthe structure with five casting machines, allowing i

Over supports

(4

b4 500

At mid-span

(b)

FIGURE 3.40. Chillon Viaduct, cross sections. (a) Over supports. (b) At midspan.

PORTIQUE - TYPE 48.OOm

PORTIOUE-TYPE 4 2 OOm

.,a0 I

73x320

i

**lo 1 O,Q20

EOXSOIE 42 00 boo L---CDNSOlC 42 00

82 DO

FIGURE 3.41. Chillon Viaduct, longitudinal sections of typical cantilevers.

Hartel Bridge, Holland 1 0 3

Sections I, II, and V, conventional cast-in-placeprestressed concrete box girdersSections III and IV, precast prestressed concretesegmental box girdersTwo steel bascule bridges.

FIGURE 3.42. Ch~llon \.~ndu~t, precasting yard.

an average production of 22 to 24 segments perweek (see aerial view, Figure 3.42).

Erection was by the conventional balanced can-tilever method with a launching gantry designed toaccommodate the bridge-deck geometry in termsof curve and variable superelevation. The overalllength of the gantry was 400 ft (122 m) and thetotal weight 250 tons (230 mt). Special features ofthis gantry will be discussed in Chapter Il. Can-tilever placing of precast segments is shown in Fig-ure 3.43.

This structure is truly an achievement of mod-ern technology with emphasis upon the aestheticand ecological aspects of design.

3.7 Hartel Bridge, Holland

The 1917 ft (584.5 m) long Hartel Bridge crosses acanal in Rotterdam, Figure 3.44, and consists ofthe following elements:

FIGURE 3.43. Chillon Viatiuct, cant i lever constrUC-tion with launching gantry.

The original design contemplated that the totalstructure would be constructed as conventionalcast-in-place box girders on falsework. Substitutionat the contractor’s request of cast-in-place seg-mental construction by precast skgmental con-struction for sections III and IV saved the exten-sive temporary pile foundation system necessary toavoid uneven settlement of falsework because ofinitial soil conditions. The redesign proposed twosingle-cell rectangular box girders as opposed toone three-cell box girder, Figure 3.44, omitting thecenter portion of the bottom flange and providingthinner webs and a thicker bottom flange.

In the segmental box girder design the dimen-sions of the deck slab are constant over the entirelength, girder depth varies from 4.92 ft (1.5 m) to17 ft (5.18 m), the webs have a constant thicknessof 13.8 in. (0.35 m), and the bottom flange thicknessvaries from 10 in. (0.26 m) to 33 in. (0.85 m). Up toa depth of 9.35 ft (2.85 m) the segments have alength of 15.8 ft (4.8 m); over 9.3 ft (2.85 m) thelength decreases to 12.3 ft (3.75 m).

The vertical curvature of the bridge was madeconstant for the full length of sections III and IVby increasing the radius from 9842.5 ft (3000 m) to19,029 ft (5800 m), which resulted in a repetitionof eight times half the center span. This repetitionjustified precast segments.

A long-line casting bed (see Chapter 11) was con-structed on the centerline of the bridge box girdersat ground level, Figure 3.45. Thus, a portal cranewas able to transport the cast segments to the stor-age area and also erect them in the superstructure,Figure 3.46. The end spans have three more seg-ments than half the center span; these were sup-ported on temporary falsework until all the pre-stressing tendons were placed and stressed, Figure3.46.

The first segment cast was the pier segment;each of the remaining segments was then match-cast against the preceding segment. The pier seg-ment was positioned on bearings on top of the pier,Figure 3.47, and the two adjoining segments werepositioned (one after the other) and the jointsglued with epoxy resin. Temporary high-tensilebars located on the top of the deck slab and in thebottom flange were stressed to prestress the three


I I I IV

Flevation

Cross sections of the redesign

Cross section of theor iginal design

FIGURE 3.44. Hartel Bridge, typical dimensions: elevation, cross sections of the origi-nal design, cross sections of the redesign (courtesy of Brice Bender, BVNLSTS).

segments together. After the epoxy had hardened, of the outside struts of a steel scaffolding bearing onthe permanent tendons were placed and stressed. the pier foundation. Thus, the flat jacks were used

The two segments adjoining the pier segment were for adjustment of the segments to achieve proper

supported during erection on flat jacks on the top geometry control. The remaining segments were

FIGU?E 3.43. Hare1 BridgG nxrbod of castjng segments /courtesy of BrjceBender, BVNISTS.

Hartel Bridge, Holland 105

FIGURE 3.46. H,~~tcl H~~tigc, p t,tl (I<II~C for h‘in-dling segments.

erected in the conventional balanced cantilevermethod. The completed structure is shown in Fig-ure 3.48.

Other structures using precast segmental con-struction were subsequently designed and built inthe Netherlands. Shown in Figure 3.49 is thebridge over the I.jssel at Deventer, where segmentsin the 247 f’t (74 m) spans were placed with alaunching gantry. The overall length of’ the gantrywas 520 f‘t (156 m), allowing the legs to bear on thepermanent concrete piers and impose no loadingon the deck during construction, Figure 3.50.

FIGURE 3.48. H,II tel RI idgc. complctcd \tl II< ture.

FIGURE 3.49. Ikventex Bridge, placing segmentswith the launching gantry.

FIGURE 3.47. Hartel Bridge, erection sequence and detail of tempo-rary pier bracing (courtesy of Brice Bender, BVN/STS).

106

Real


I - 156 m (520 ft) rl74 m (247 ft) 7 8 m (260 ft)

Max bridge span 74 m (247 ft)

FIGURE 3.50. Deventer Bridge, elevation of gantry.

Front

3.8 Rio-Niteroi Bridge, Brazil

The Rio-Niteroi Bridge crosses the Guanabara Bayconnecting the cities of Rio de Janeiro and Niteroi,thereby avoiding a detour of 37 miles (60 km). Thisstructure also closes the gap in the new 2485 mile(4000 km) highway that interconnects north andsouth Brazil and links the towns and cities on theeastern seaboard, Figure 3.51. Although the routetaken by the bridge across the Bay seems somewhatindirect, it was selected because it avoids very deepwater and is clear of the flight path from SantosDumont Airport.

Total project length is approximately 10.5 miles(17 km), of which about 5.65 miles (9.1 km) is overwater. The alignment begins at the Rio side with a3940 ft (1200 m) radius curve, then a straight sec-tion, within which are located steel box girdernavigation spans totaling 2872 ft (848 m) in length.This is followed by an island, where the viaduct isinterrupted by a road section of 604 ft (184 m), andfinally another 3940 ft (1200 m) radius curve ar-riving at Niteroi.

The precast segmental concrete viaduct sectionshave a total length of 27,034 ft (8240 m) repre-senting a total deck area of 2,260,OOO sq ft (210,000

The _.- Rio-Niteroi RmdeJaneir

/n Brii

FIGURE 3.51. Rio Niteroi Bridge, site location map

Rio-Niteroi Bridge, Brazil

m*), making this bridge the largest structure of itstype. An aerial view of the crossing under traffic isshown in Figure 3.52. The superstructure has 262ft (80 m) continuous spans with an expansion jointat every sixth span, Figure 3.53. It consists of tworectangular box girders for a total width of 86.6 ft(26.4 m) and a constant depth of 15.4 ft (4.7 m). A2 ft (0.6 m) cast-in-place longitudinal closure joint

107

between the top flange cantilevers provides con-tinuity between the two box girder segments. Typi-cal segments have a length of 15.75 ft (4.8 m) andweigh up to 120 tons (110 mt). The pier segmentsare 9.2 ft (2.8 m) in length. Special segments areused for expansion joints.

Longitudinal prestressing tendons consist oftwelve f in. (13 mm) diameter strands in the topand bottom flanges with a straight profile, whilethe resistance to shear stresses is obtained by verti-cal web prestress, Figure 3.54.

FIGURE 3.52. Rio-Sire] oi 131 dge, view of the com-pleted structure.

All segments were manufactured in a large pre-casting yard on a nearby island. Ten castingmachines (eight for the typical segments and twofor the pier and hinge segments) were laid in twoindependent parallel lines, each equipped with aportal crane for carrying the segments to the stor-age area and the loading dock. More than 3000segments were subsequently barged to their loca-tion in the structure and erected by four launchinggantries working simultaneously on each of the twoparallel box girders and on either side of the bay,Figures 3.55 and 3.56. The rate of segment placingwas remarkable. A typical span was assembled andcompleted in five working days. Between themonths of February and July 1973, an average of

Cross section

Elevation

fb)

FIGURE 3.53. Rio-Niteroi Bridge, cross section and elevation. (a) Cross section. (b)Elevation.


E L E V A T I O N

PLAN CABLAGE SUPERIEUR

*

P L A N C A B L A G E INFERIEUR

FIGURE 3.54. Rio-Niteroi Bridge, typical span dimensions and tendon layout.

278 precast segments per month were installed inthe structure by the four launching gantries, rep-resenting an area of 180,000 sq ft (17,000 m’) offinished bridge per month. At the same speed,Oleron Viaduct could have been built in twomonths. Such is the measure of the determinationand enthusiasm of engineers and constructors ofthe New World.

3.9 Bear River Bridge, CanadaThe Bear River Bridge is about 6 miles (9.7 km)east of Digby, Nova Scotia, on trunk route 101between Halifax and Yarmouth, near the An-napolis Basin; it replaces an 85-year-old structure.Preliminary studies showed, and construction bidprices verified, that precast segmental was moreeconomical than steel construction by nearly 7%.7*8

JFK Memorial Causeway, U.S.A. 109

tive-moment tendons were inclined in the weband anchored at the face of the segments. Anchor-age of six tendons at the face of the first segmentadjacent to the pier segment (three in each web)produced a large upward shear force at the face ofthe pier segment, which was not overcome untilthe erection of several additional segments. Themidspan positive-moment tendons are continuousthrough the cast-in-place closure joint at midspan.These tendons, indicated by capital letters in Fig-ure 3.59, were placed in preformed ducts uponcompletion of erection of the segments in a spanand the closure pour consummated. All positive-moment tendons were anchored in the top flange.The precast segments are typically 14 ft 2 in. (4.3m) in length and the closure pour at midspan is 4ft 4 in. (1.3 m) long.7,R

F I G U R E 3 . 5 5 . RIO-NIICI oi 131 dgc, wnrile\el COII-

strut tion.

Total structure length is 1998 ft (609 m) with sixinterior spans of 265 ft (SO.8 m) and end spans of204 ft (62.1 m), Figure 3.57. The layout has verysevere geometry constraints. In plan, the east endof the bridge has two sharp horizontal curves con-nected to each other and to the west end tangent bytwo spiral curves; minimum radius is 1150 ft (350m). In elevation, the bridge has a 2044 ft (623 m)vertical curve with tangents of 5.5 and 6.0 percent.Two sets of short-line forms employed by the con-tractor to cast the segments met the variablegeometry requirements admirably. The accuracyof casting was such that only nominal elevationadjustments were required at the abutments andthe center-span closure pours.s

The precast segments are reinforced with pre-fabricated mild steel reinforcement cages, in addi-tion to the primary longitudinal prestressing ten-dons, Figure 3.60, and transverse prestressing inthe top flange. Web shear reinforcement variesdepending on the location of the segment. The 145precast segments were cast in a plant located nearthe bridge. This plant was equipped with two cast-ing molds, each producing one segment per day. A12-hour steam curing period was used and a con-crete strength at 28 days of 5000 psi (34.5 MPa)was achieved.’

The single-cell box girder superstructure is con-tinuous for the total length of the bridge. Typicalcross-section dimensions are indicated in Figure3.58. Prestressing tendon layout is illustrated inFigure 3.59 for a typical interior span. Fifty-fivetendons were required for negative moments and22 for positive-moments. The majority of nega-

Because of the curved layout of the bridge andits relative shortness, the use of a launching gantrywould have been uneconomical. Segments wereplaced by a 200 ton (180 mt) mobile crane on land,or on a barge over water, Figure 3.61. Construc-tion of this bridge started in May of 1971, and itwas opened to traffic on December 18, 1972.

3.10 JFK Memorial Causeway, U.S.A.

FIGURE 3.56. Rio-Niteroi RI dgr. launching gan-tries.

A portion of the JFK Memorial Causeway repre-sents the first precast, prestressed, segmental boxgirder completed in the United States. Opened totraffic in 1973, this 3280 ft (1000 m) long structurespans the Gulf Intercoastal Waterway in Texas toconnect Corpus Christi and Padre Island. It wasdesigned by the Bridge Division of the TexasHighway Department under the supervision ofWayne Henneberger. The Center for HighwayResearch, University of Texas at Austin, under thesupervision of Prof. John E. Breen, assisted in thedesign and also built and tested a one-sixth scalemodel of the bridge to check design requirementsand construction techniques.g

E LIRGS. E PIER I E P IER 2 E PIER 3 E PIER 4

203’.9” 2 6 5 .- 0 ‘, 265’.0 ” 265*-O”I I

E PIER 4 E PIER 5 t P I E R 6 E PIER 7265’-0” 265,-O” 203’.9”

ELEVATION

U N I T S N O . 7. 2 7 . 4 7 . 6 7 . 67,107. 1 2 7 AND 147A R E C A S T IN P L A C E (DECK CLOSlNG U N I T S )

FIGURE 3.57. Bear River Bridge, elevation, f’ron~ ref. 8 (courtesy of the PrestressedConcrctc Institute).

I--- % R O A D W A Y

39’-6”2-6’! I5’-0’ 6’4

I’-()”

Ia’-0” yI_ 4”I - I

FIGURE 3.58. Bear River Bridge, typical cross section, from ref. 8 (Courtesyof the Prestressed Concrete Institute).

HALF INTERIOR SPAN TENDON ELEVATION

HALF SECTION AT MIDSPAN HALF SECTtON AT PIER

TENDON DISTRIBUTION

FIGURE 3.59. Bear River Bridge, typical center-span tendon elevation anddistribution, from ref. 8 (courtesy of the Prestressed Concrete Institute).

111

1 1 2 Precast Balanced Cantilever Girder Bridges

FIGURE 3.60. Bear Kiver Bridge, longitudinal pre-stress ducts in forms (courtesy of the Prestressed Con-crete Institute).

FIGURE 3.61. Be,u Ki\ cl Bi idge, crcc tion b vbarge-mounted crane (courtesy of the Prestressed Con-crete Institute).

The structure consists of thirty-six 80 ft (24.4 m)long approach spans of precast, prestressed bridgebeams and the 400 ft (122 m) total length segmen-tal bridge spanning the Intercoastal Waterway.The segmental portion of this structure has acenter span of 200 ft (61 m) with end spans of 100ft (30.5 m). The segments were precast, trans-ported to the site, and erected by the balancedcantilever method of construction using epoxyjoints, Figure 3.62. The precast, segmental super-structure consists of constant-depth twin boxgirders with a 2 ft (0.61 m) cast-in-place longitu-

’ P

FIGURE 3.62. JFK Memorial Causeway, balancedcantilever construction (courtesy of J. E. Breen).

dinal closure strip, Figure 3.63. Segments are10 ft (3.05 m) in length and in cross section, are 8 ft(2.44 m) in depth, and have a nominal top flangewidth of 28 ft (8.53 m). The top flange or deck is ofconstant dimension longitudinally but of variablethickness in a transverse direction. The bottomflange is of constant dimension transversely butvaries longitudinally from 10 in. (254 mm) at thepier to 6 in. (152 mm) at 25 ft (7.62 m) from thepier center.

Segments were cast with male and f-emale align-ment keys in both the top and bottom flanges aswell as large shear keys in the webs, Figure 3.64.Integral diaphragms were cast with the pier seg-ments, Figure 3.65. Both matching faces of thesegments were coated with epoxy, and temporaryerection stressing at both top and bottom of thesegments precompressed the joint before installa-tion of the permanent post-tensioning tendons.The segments were erected by a barge-mountedcrane. As each segment was erected, it was tilted 21degrees from the in-place segment, so that a pair ofhooks in the top of the segment being erected en-gaged pins in the segment previously erected. Thenew segment was then pivoted down by the slinguntil its shear key slipped into the mating shear keyof the previously erected segment.g Figure 3.66shows a permanent tendon being tensioned andthe temporary working platform.

The design concept on this project utilized pre-stressing tendons in the top flange for dead-loadcantilever stresses; after closure at midspan, con-tinuity tendons were installed for the positive mo-ment, Figure 3.67. Research on the model testingof the bridge is documented in references 10through 15 with particular emphasis in reference14 on lessons learned during construction thatmight facilitate or improve similar projects.

Saint And& de Cubzac Bridges, France 113

28 f t . (8 .53 m)Sym. B Q

L -m

6 ft. (1.83 ml

l---l6’-8” (2.03 m)

2z 8 al

h .? :- s

7 ft. (2.13 m) 13 ft. (3.96 m) T-10” (2.39 m)/- I -

FIGURE 3.63. JFK Memorial Causeway, typical cross section. Bottom slabthickness varies from 10 in. (254 mm) at pier to 6 in. (152 mm) at 25 ft (7.62m) from pier center.

FIGURE 3.64. JFK Memorial Causeway, precast seg-ment in casting yard (courtesy of J. E. Breen).

FIGURE 3.65. J FK Xlemorial Causeway, constructionview showing pier segments with diaphragms (courtesyof J. E. Breen).

FIGURE 3.66. JFK Memorial C;IUSC\V;I~, prestressingpermanent tendon (courtesy of J. E. Breen).

3.11 Saint And& de Cubzac Bridges, FranceOpened to traffic in December 1974 after a con-struction period of 29 months, this importantstructure crosses the Dordogne River north ofBordeaux on the South Atlantic Coast. A view ofthe finished bridge is shown in Figure 3.68. Themain river crossing has a total length of 3800 ft(1162 m) with approach land spans of 190 ft (59 m)and main river spans of 312 ft (95.3 m), Figure 3.69.Two intermediate expansion joints located at thepoint of contraflexure in the transition spans sepa-rate the deck into three sections for concrete vol-ume changes. The center section has a length of1920 ft (585 m). The main piers have rectangularhollow box shafts supported by circular open-dredged caissons 30 ft (9 m) in diameter. Ap-proach piers have an I section.

Another structure, constructid under the samecontract, consisted of twin bridges 1000 ft (307 m)in length with typical 162 ft (49.5 m) spans in an


Canti lever (negative moment) tendons

8 Main pier

100 ft (30.5 mJ

C$ Central span

-I

FIGURE 3.67. JFK Memorial Causeway, system of prestressing tendons.

FIGURE 3.68. Saint Andre de Cubzac Bridge, view ofthe finished bridge over the Dordogne River.

area north of the main crossing where poor soilconditions did not permit stability of an embank-ment. Altogether the deck area is 97,000 sq ft(29,500 m2), entirely of precast segmental con-struction. The typical cross section is a single box54.4 ft (16.6 m) wide with transverse ribs both inthe side cantilevers and between webs, Figure 3.69,to provide structural capacity to the deck slabunder traffic loads. A casting yard located alongthe bank of the Dordogne River produced the 456segments for both bridges (main crossing andnorth viaducts) in three casting machines (two forthe typical segments and one for the special seg-ments such as pier, hinge, or end segments). Mod-erate steam curing at 86°F (30°C) for 12 hours in amovable kiln enclosing the newly cast segment andits match-cast counterpart allowed a one-day cycleand proved very efficient in avoiding any geomet-ric corrections.

Segments were placed in the structure by thebeam-and-winch method either on land (for thenorthern viaducts or the approach spans of themain river crossing) as shown in Figure 3.70 orover water for the main spans as shown in Figure3.71. This project was the occasion for a furtherimprovement in the placing scheme by beam andwinch, whereby the pier segments could be precastand placed with the same type of equipment asshown in principle in Figure 3.72. A provisonaltower prestressed against the pier side face allowedthe pier segment to be installed upon the pier cap,with the beam and winch later used for cantileverp lac ing . To keep the segment we igh t to amaximum of 110 t (100 mt) the pier segment, rep-resenting the starting base of each cantilever, hadbeen divided into two halves placed successively,Figure 3.73. Figure 3.74 shows the lifting of thelast closure segment.

3.12 Saint Cloud Bridge, France

A connection between the peripheral Paris RingRoad and the Western Motorway (A- 13) requiredthe construction of a bridge over the Seine ex-tended by a viaduct along the left bank leading tothe Saint Cloud Tunnel, Figures 3.75 and 3.76.This structure has two traffic lanes in each direc-tion. It will be duplicated later by a similar adjoin-ing structure when the congested Saint CloudTunnel is duplicated. Or ig ina l des ign of th isbridge contemplated a steel structure. However, analternative design utilizing precast segments and

+ BORDEAUX 8' Al’iDRE DE CUBZAC I)

I II I

0,”

/

I

6,001 ,

(0aN

---H8m

FIGURE 3.69. Saint Andrk de Cubzac Bridge, elevation and cross section.

FIGURE 3.71. Saint Andrk de Cubzac Bridge, beam-and-winch segment placing over water.

FIGURE 3.70. Saint And& de Cubzac Bridge, beam-and-winch segment placing over land.

115

WlNCt

B E A M

0 1 0 2 0 3FIGURE 3.72. Saint Andrk de Cubzac Bridge, placing precast pier segments.

FIGURE 3.73. Saint Andre Cubzac Bridge, liftingsecond half pier segment.

116.

117Saint Cloud Bridge, France

the balanced cantilever method of construction,submitted by the contractor, permitted substantialsavings and was accepted by the authorities.

The bridge has a total length of 3618 ft (1103 m)with a constant-depth superstructure. It includestwo sections: the bridge over the Seine, which is a1736 ft (529 m) long curved structure; and a 1883ft (574 m) long viaduct, which follows a straightlayout along the bank of the Seine and then crossesthe Place Clemenceau, on a 2260 ft (690 m) radiuscurve, by an access ramp to the Saint Cloud Tun-nel. It includes 16 spans divided as follows (refer toFigure 3.76):

Seine Bridge: 160.8,288.7,333.8,296.0,150.9,andtwo 219.5 ft spans (49, 88, 101.75, 90.25, 46, andtwo 66.9m)

Common area: 66.4 ft (20.24 m) up to the expansionjoint, and then 153.1 ft (44.66 m), total 219.5 ft(66.9 m)

Viaduct: five219.5; 285.4,210.0,and 137.8ftspans(five 66.9; 87, 64, and 42 m)

Architectural considerations led to the choice ofa 11.8 ft (3.6 m) constant-depth three-cell boxgirder with slopingexternalwebs with nooverhangs,Figure 3.77. Segments are 7.4 ft (2.25 m) in lengthwith a record width of 67 ft (20.4 m), their averageweight varying from 84 to 143 tons (76 to 130 mt).Since the superstructure has a constant depth, thebending capacity is adjusted to the moment dis-

tribution by varying the bottom flange thickness,which decreases from 3 1.5 in. (800 mm) at the riverpiers to 7 in. (180 mm) at midspan. To accommo-date the curvature of the bridge the segments inthis area are cast, in plan, in a trapezoidal shape. A4.5% superelevation is obtained by placing theunits over the piers in an inclined position.

Three-dimensional prestressing was used in thesuperstructure: the main longitudinal prestress,transverse prestress in the deck, and a vertical pre-stress in the webs to accommodate shear. After theclosure joint at midspan was cast, additional lon-gitudinal prestress tendons were installed to pro-vide continuity.

Superstructure segments were precast in a planton the right bank of the Seine. Two casting moldswere used for fabrication of the segments. Eachmold had an external formwork and an internalretractable formwork. The adjacent, previously castsegment was used as a bulkhead to achieve amatch-cast joint.

For erection, segments were transported on atrolley to a cable-stayed launching gantry of un-usual size and capacity. It was of high-yield steelconstruction, 402 ft (122.5 m) in length andweighing 250 tons (235 mt), with a maximum loadcapacity of 143 tons (130 mt). The constant-depthgantry truss was supported on central and rearlegs, which were tunnel shaped to allow passage ofthe precast segments endwise. At the central sup-port, a 52.5 ft (16 m) high tubular tower topped

,.,. 59_ls .,’

- --

FIGURE 3.76. Saint Cloud Bridge, plan view.

COUPE TRANSVERSALED’UNVOUSSOIR TYPE

FIGURE 3.77. Saint Cloud Bridge, longitudinal and typical cross section.


with a saddle provided a large eccentricity to sliding on pads placed at the central and rear legs.the three pairs of cable stays, which improved the The launching girder, in cross section, was trian-negative-moment capacity at this support location. gular in shape. The base of this triangle includedAt the forward end of the gantry an additional leg two structural steel I sections, which served aswas used as a third support point during launching tracks for the segment transportation trolley. Theand p ie r segment p lac ing , F igure 3 .78 . The diagonal bracing of the launching girder consistedlaunching g i rder was moved forward on ra i l s of tubular steel members. The girder was fabri-mounted on the completed superstructure, by cated in ten sections, approximately 39 ft (12 m)

FIGURE 3.78. Saint Cloud Bridge, segment placing.

PLACING OF PILE UNITS

AVANCEMENT DU

+ORTlQUE D ELANCEMENT.MOVING THE TRUSS

MISE E N PLACE

DES

PLACING THE UNITS IN CANTELIVER

FIGURE 3.79. Saint Cloud Bridge, sequence of operations in moving launching girder.

Saint Cloud Bridge, France 121

in length, so as to be transportable over the high- temporary front leg supported just in front of theways. These units were assembled at the job site by pier.prestressing bars. Launching of the gantry: The gantry slid on rails at

The sequence of operations in moving thelaunching girder forward is illustrated in Figure

the rear leg and rolled over an auxiliary support

3.79 and included the following operations:placed atop the pier segment. The central leg,during this travel, crossed the gap between thecantilever end and the pier unit.

Placing pier se<gment: The gantry was supported on Placing typical segments in cantilever: In this phasethree points: the rear leg, the central leg placed the gantry was supported at two points: the centralnear the end of the completed cantilever, and the leg placed over the pier and the rear leg anchored

“2

3F6

FIGURE 3.80. Saint Cloud Bridge, sequence of operations of launching gantry overthe river.


FIGURE 3.81. Angers Bridge, longitudinal section.

at the end of the last completed cantilever. Thesegments were lifted by the trolley at the rear endof the girder, moved forward, after a rotation of aquarter turn, and then placed alternatively at eachend of the cantilevers under construction.

As a result of the horizontal curvature of thestructure, the transverse positioning of a segmentwas accomplished both by moving the segmenttransportation trolley sideways relative to thegirder [possible side travel of 3 ft (0.9 m) on ei-ther side] and by moving the launching gantry it-self sideways relative to its bearing support on thebridge. Thus, the construction of a cantilever re-quired one, two, or three different positions of thegantry, according to the curvature radius andlength of span, as shown in Figure 3.80. Workstarted in October 1971 and was completed in Dk-cember 1973. Placing the 527 precast segments inthe 3600 ft (1097 m) long superstructure tookexactly one year.

In terms of erection speed, a more interestingproject was successfully carried out on a precastsegmental bridge awarded,to Campenon Bernard.A unique set of circumstances arose where a bridgeover the Loire River at Angers could be fitted touse simultaneously the dimensions and castingmachines of Saint Andre de Cubzac Bridge, whichhad recently been completed, and the gantry ofSaint Cloud Bridge.

The 2577 ft (786 m) long structure rests on 10piers and has 280 ft (85.1 m) typical spans, Figures3.81 and 3.82, using a single box girder with ribbed

FIGURE 3.82. Angers Bridge, view of the completedstructure.

deck slab units identical to the sections used atSaint Andre de Cubzac. The construction contractwas signed in August 1974 and the superstructurewas completed in May 1975. All segments wereplaced between January and May 1975, in a littleless than five months, corresponding to an aver-age erection speed of 26 ft (8 m) per day of fin-ished deck.

3.13 Sallingsund Bridge, Denmark

Sallingsund in Northern Jutland between Arrhusand Thisted is a site of great natural beauty. Con-struction of a bridge in such an environment wasthe object of careful study, which concluded, afteran international competition, in the selection of aprecast segmental structure, Figure 3.83, restingon piers of a unique design.

This structure has two end spans of 167 ft (5 1 m)and 17 interior spans of 305 ft (93 m). There are18 piers between the two abutments. The level ofthe roadway reaches 100 ft (30.5 m) above thewater at the center span and 82 ft (25 m) at theabutments. The two center spans are navigationspans requiring 85 ft (26 m) vertical clearance overa width of 197 ft (60 m). The bridge deck accom-modates two traffic lanes, approximately 13 ft (4m) each, two cycle paths, and two sidewalks for atotal width of 52.5 ft (16 m), Figure 3.84. The

FIGURE 3.83. Sallingsund Bridge, view of the com-pleted structure.

fFIGURE 3.84. Sallingsund Bridge, typical dimensions.

t

L


superstructure consists of precast concrete boxgirder segments 11.7 ft (3.57 m) in length, withepoxy match-cast joints, which are prestressed to-gether. Segment depth varies from 8.2 ft (2.5 m) atmidspan to 18 ft (5.5 m) at the pier.

The precast superstructure segments werematch-cast by the short-line method (see Chapter11). There are altogether 453 segments varying inweight from 86 t (78 mt) to 118 t (107 mt). Thetypical segment shown in Figure 3.85 has web cor-rugated shear keys together with top and bottomflange keys. Hinge segments equipped with aroadway expansion joint for thermal movement ofthe superstructure are placed every other spannear the point of contraflexure. A hinge segmentwith its diaphragm is shown in Figure 3.86. Seg-ments are placed in the structure in cantilever witha cable-stayed launching gantry. Transfer from thecasting area and the storage yard to the construc-tion site and the launching gantry is achieved by alow-bed dolly pushed by a tractor, Figure 3.87.The gantry shown in Figure 3.88 should look

FIGURE 3.85. Sallingsund Bridge, view of a typical FIGURE 3.87. Sallingsund Bridge, segment rrans-segment. port.

FIGURE 3.86. Sallingsund Bridge, hinge segmentwith diaphragm. FIGURE 3.88. Sallingsund BI idge, I,~un&ing g,~ntry.

B-3 South Viaducts, France 125

FIGURE 3.89. Sallingsund Bridge, elevation of mainpiers in water.

and have 860,000 sq ft (80,000 m”) of bridge deck.The project is in a congested area that required thecrossing of railway tracks, canals, and more than 20roads; its diverse structural geometry containscurves, superelevation ranging from 2.5 to 6% andgrades up to 5%.

.

FIGURE 3.90. B-:l South Viaduct, overall view.

Figure 3.91 presents a plan of this project andshows a subdivision in accordance with the type ofcross sections used. It includes the following mainsubdivisions:

1 . The main viaduct VP 1-A through VP 1-J.2. The main viaduct VP 2-A and VP 2-B.3. The viaducts Vl and V2, which are access

ramps to the main viaduct VP 2.4. The viaducts V3 and V4, which are access

ramps to the National Road RN3.

The original design for this project, prepared bythe French authorities, was based on conventionalcast-in-place construction of the superstructure incomplete spans using movable formwork. Thecontractor proposed a more economical designbased on the use of precast segments. The alterna-tive design had advantages in erection, whereinparts were erected by a launching truss and partsby a mobile crane in conjunction with an auxiliarytruss and winch. The use of precast units allowed adeeper and thus a more economical superstruc-ture, because the space required for formwork didnot have to be deducted in the clearance require-ments over existing roads and other facilities.

The superstructure has a constant depth of 6.5 ft(2 m), consisting of three different cross sections,Figure 3.91. Different width and transitions wereaccommodated by varying the width of the cast-in-place median slab connecting the top flanges ofthe precast segments. Only the V3 and V4 accessramps were of conventional cast-in-place construc-tion.

The webs of the precast segments have a con-stant thickness of 12 in. (310 mm), increased insome cases to 20 in. (500 mm) near a pier. Webs arestiffened by an interior rib, which also serves to an-chor the longitudinal prestressing inside the boxrather than in the web at the end of a segment.Where the webs are not thickened near a support,they are prestressed vertically by bars to accommo-date shear forces. The top flanges of the segmentsare cantilevered 10 ft (3 m). In the case of segmenttypes 2 and 3, Figure 3.9 1, the top flange cantileverbetween box sections is 9 ft (2.75 m). The topflange follows the superelevation of the roadway.The thickness of the cast-in-place longitudinal slabbetween box girders varies from 7.9 to 13.8 in. (200to 350 mm), depending upon its width.

The total superstructure is supported on neo-prene or sliding bearings. Expansion joints arespaced at distances up to 1970 ft (600 m) and are


1 5 . 2 5 in

T- - - - - - - 1 T Y P E 1 795VOUSSOlR5.L.1,50ou2,5Om

T Y P E 2 1014 VCUSSOIRS. L= 2,SO w 3,401-n

TYPE 3 392 VCkl5501RS.L~ 2,SOw 3,40m

S U DS O U T H

R N 3+

FIGURE 3.91. B-3 South Viaduct, plan showing segment type location.

located in special hinge joints near a pier.Superstructure spans vary from 89.6 to 174 ft (27to 53 m), with 90% of them being in the range of111 to 125 ft (34 to 38 m).

This project required 2225 precast segments, allmanufactured by the short-line method (seeChapter 1 l), which involved the following opera-tions:

1 .

2.3.

4.5.6.

7.

Subassembly of mild steel reinforcing on atemplate.Storage of subassembly units.Assembly of complete reinforcement cages in-cluding tendon ducts.Placing of the cages in the forms.Concreting and curing of the segments.After concreting and curing, transportation ofthe segment by a dolly to a position where oneend would act as a bulkhead for the casting ofthe next segment. At the same time its positionwas adjusted to conform to the propergeometric configuration of the superstructure.Transfer of the segment that had previouslyacted as the bulkhead to temporary storage forfurther curing.

8. Transfer of the segment, eight hours aftercuring, to a more permanent storage until re-quired for erection.

9. Return of the mold bottom, after temporarystorage, to the casting area for reuse.

Curing of the segments was accomplished withlow-pressure steam in the following 4&-hour cycle:

1 . An initial l&hour curing period at 35°C.2. A two-hour temperature rise reaching 65°C.3. A one-hour curing period at a level of 65°C.

The short curing cycle can be accomplished if thefollowing conditions are satisfied: use of a propercement, preheating of the materials to 35”C, rigidforms, and proper supervision. Casting of a seg-ment required nine hours, allowing two segmentsper day per form; the four forms used produced atotal of eight segments per day.

Erection of precast segments by the launchinggantry shown in Figure 3.92 is schematically illus-trated in Figure 3.93. After being rotated 90”,segments V2 and V’2 were placed at the same timeby means of two trolleys suspended from the bot-tom chord of the launching girder, Figure 3.94.

B-3 South Viaducts, France 127

V2 and V’2 were then attached to the previouslyerected segments by temporary prestressing.During the erection operation of V2 and V’2 atransport dolly delivered segment V’3, then V3,and so on. In this manner the erection of segmentscould be carried out without being delayed bytransportation of the segments from the storagearea. In addition, the threading and stressing ofthe permanent prestressing tendons were inde-pendent of the erection cycle, since the tendonswere anchored in the internal ribs and could beprestressed inside the box girder.

FIGURE 3.92. H-:5 South Viaduct, launching gantryin operation.

The matching faces of the segments being erectedand the previously erected segments, V 1 and V’l,were coated with epoxy joint material. Segments

Where the span length was less than 125 ft (38m), the pier segments were placed by the gantry inits normal working position. The pier segment po-sition was adjusted from a platform fixed to the topof the pier to avoid delaying the placement of can-tilever segments at the preceding pier. For the few

(b)

FIGURE 3.93. B-3 South Viaduct, erection sequence. (a) Placing the units: The twotrolleys bring the units V2 and V’2 which will be placed, after rotation at 90”, againstthe units VI and V’l. During this time, the lorry carries the units V’3, then V3, and so on.(b) Launching the truss: The rear and the central legs are lifted above the piers PO and Pl.‘The truss is supported by trestles and trolleys in Pl and P2 and moves forward by theaction of the trolley motors until the legs reach Pl and P2. Thus the truss has advancedalong one span length and can place the pile-unit in P3 and the cantilevers from P2.


-- t.*FIGURE 3.94. B-3 South Viaduct, placing two seg-ments in balanced cantilever.

larger spans, the pier segment was placed after clo-sure of the preceding completed spans and ad-vancement of the launching gantry. The center legwas advanced out onto the last completed half-span cantilever, but it remained in the proximity ofthe pier. Launching of the gantry to the next spanwas achieved by using the two segment transporta-tion dollies temporarily fixed on the completedsuperstructure by two auxiliary steel trusses. Thehigh degree of mechanization of the gantry to-gether with the repetitive nature of the project al-lowed speedy erection. A typical 130 ft (39 m) spanwas erected and completed in two working days.

To maintain the construction schedule 2ndminimize required erection equipment, the super-

structure segments were placed simultaneouslyby two different methods. The launching gantrypreviously described placed 57% of the seg-ments and a mobile crane in conjunction with amovable winch frame erected the remaining ones.The latter method was used where access wasavailable for a truck-mounted crane and the seg-ment transportation dolly. The truck-mountedcrane could easily be used along the centerline ofthe structure to place segments at outboard can-tilever ends. However, its use became complicatedin the midspan area, particularly when it was usedto place the closure segments. To solve this prob-lem, an auxiliary truss equipped with a winch wasused in conjunction with the mobile crane. Thistruss was supported at one end over the pier wherecantilever construction proceeded and at the otherend over the last completed cantilever arm, whichmight or might not require a temporary supportpier, Figure 3.95. The segments were lifted by atrolley-mounted winch traveling along the truss.This truss was also used to stabilize the cantileversduring erection, since it was fixed to the pier andthe completed portion of the superstructure. Afterthe pier segment was positioned by the mobilecrane, the frame was launched with the trolley in acounterweight position at the rear of the frame.When the span exceeded 65 ft (20 m), the front ofthe frame was held by the crane,

This structure exemplifies an innovative appli-cation of precast balanced cantilever segmentalconstruction to a difficult urban site and shows itsadaptability to almost any site conditions.

FIGURE 3.95. B-3 South Viaduct, auxiliary truss for segment assembly (crane placing).(1) Auxiliary truss, (2) winch for segment lifting, (3) precast segment, (4) possible tempn-rary support (as required), and (5) concrete cantilever stability device.

Alpine Motorway Structures, France 129

3.15 Alpine Motorway Structures, France

The new Rhone-Alps Motorway system in SouthEast France includes 220 miles (350 km) of toll-ways, of which 60 miles (100 km) are an optionalsection, between the cities of Lyons, Grenoble,Geneva, and Valence in order to improve com-munications between Germany and Switzerland onone hand and South France and Spain on theother. The motorway is situated among the beauti-ful western slopes of the Alpine mountain range(see the location map, Figure 3.96). The first 160miles (250 km) include the following structures:

Ten viaducts varying in length between 500 and1300 ft (150 to 400 m)

Two hundred overpass bridges

Fifty underpasses

Such a project afforded an exceptional occasion to

optimize the structures in terms of initial invest-ment and low maintenance costs.

The underpasses had to accommodate a variableand often considerable depth of fill to reduce theconstraints of the longitudinal profile in thismountainous region. The ideal answer was foundin the use of reinforced concrete arch structures,which proved extremely well adapted and had acost approximately half that of conventional girderbridges.

Apart from the first section of the motorway(East of Lyons), which had to be built immediatelyand therefore called for conventional solutions(cast-in-place prestressed concrete slab), and ex-cept for certain special situations (excessive skew,railroad crossing, and so on), a careful studyshowed that the remaining 150 overpass bridgesshould be of precast concrete segmental construc-tion, which were 20% more economical than othermethods and practically maintenance free. Thestudy further showed that segmental construction

FIGURE 3.96. Alpine Motorway, location map.


should be extended to viaduct structures and thatall segments for both overpasses and viaductscould be economically built in a single factory lo-cated near the center of gravity of the motorwaynetwork. The maximum carrying distance was nomore than 75 miles (120 km) and the average was40 miles (60 km). Figures 3.97 and 3.98 are viewsof a typical viaduct and a typical overpass in themotorway network.

The two-span and three-span overpass bridgeshave spans ranging from 59 to 98 ft (18 to 30 m). Avariety of standardized precast cross sections weredeveloped for this project, depending upon spanand width requirements. The first structures usedsingle and double-cell trapezoidal box sections, al-though later on voided slab sections were pre-ferred, as illustrated in Figure 3.99a. This solutionproved aesthetically pleasing and very simple tomanufacture and assemble. The viaducts had tosatisfy a wide range of environmental require-ments. It was found that span lengths could belimited at all sites to a maximum of 200 ft (60 m),

FIGURE 3 . 9 ’ 7 . Alpine Motorway, view of a viaduct

FIGURE 3.98. Alpine Motorway, view of an overpass.

4 2.60 c

\ I -4+.. ---. 4.m -. (.

FIGURE 3.99. Alpine Motorway, typical sections ofoverpass and viaducts. (a) Overpass segments. (b) Via-duct segments.

which allowed a constant-depth superstructurewith precast segments, Figure 3.996.

Segment manufacture was carried out in a fac-tory close to the new motorway with easy access tothe existing highway system, which was used tohaul all segments to their respective sites. The fac-tory had two parallel bays, Figures 3.100 and3.10 1, one for the overpass segments and one forthe viaduct segments. Segments for the overpasses,Figure 3.100, were match-cast by the short-linemethod with their longitudinal axis in a verticalposition. The bottom segment was a previously castunit. The segment at the top was then match-castagainst the segment on the bottom. After the unitbeing cast had reached the required strength, thebottom unit was removed for storage, and the en-

-

40' PORTAL (RAIit

fb)

FIGURE 3.100. Alpine Motorway, precasting factory.


FIGURE 3.101. Alpine Motorway, general view ofprecast factory and segment storage.

tire process repeated. Figure 3.102 is a view of asegment in a vertical match-casting position.

Erection procedure for a typical three-spanoverpass structure was as follows:

1 . After the foundations and pier columns hadbeen constructed, precast concrete slabs wereplaced on sand beds adjacent to the piers to formfoundations for the steel falsework towers. Theprecast slabs and towers were reusable for sub-sequent bridges. The erection commenced withplacement of the first segment on top of four par-tially extended 25-ton jacks, Figure 3.103~.

2. The second and third segments were placedand prestressed to the first segment, Figure3.103b. The joints between the segments wereepoxy coated as the segments were erected. Theprestressing of the second and third segments tothe first segment consisted of temporary barsabove the top surface of the segments, and othertemporary tendons within the segments near thebottom of the segments. The four 25-ton hydraulicjacks under the first segment were then replacedby four partially extended loo-ton hydraulic jackspositioned under segments two and three. Thejacks were supported on teflon sliding bearings.

3. The remaining segments were then erected,forming cantilevers on each side of the falseworktowers, Figure 3.103~. The prestressing of thesegments consisted of temporary tendons posi-tioned above the segments, as indicated in Figure3.103.

4. The erection of the segments could takeplace simultaneously at both piers, or one couldprecede the other, Figure 3.103d. Observe that atthis stage of erection each assembly of segmentswas independently supported on four large hy-draulic jacks and hence could be raised, lowered,

FIGURE 3.102. Alpine hlororway, vertical matchcasting of segments.

or rotated if required to adjust its position with re-spect to its pier or to its counterpart at the oppositepier. This method eliminated the need for a cast-in-place closure joint at midspan of the centralspan. Through the adjustment of the hydraulicjacks, perfect mating of the two centermostmatch-cast segments could be achieved when theassemblies of segments were slid together as indi-cated. The time required to erect the superstruc-ture was significantly reduced by avoiding the useof a cast-in-place closure joint.

5. At this point in the erection, the first groupof permanent prestressing tendons were insertedin preformed holes through the segments, afterwhich they were stressed and grouted, Figure3.103e.

6. The process proceeded with the erectiomofthe remaining segments, Figure 3.103f

7. After installation of precast match-castabutments, a second group of permanent tendonswas installed, and finally the temporary falseworkand temporary prestressing was removed, Figure3.103g.

Alpine Motorway Structures, France 133

SECMENlS 18 b 2ST

SPAN I8 te 30 m J

lb)

TEMPORARY TIE URS

FIGURE 3.103. Alpine Motorway Bridges, erectionscheme for typical three-span overpasses. (a) Placing thefirst and second segments. (b) Transfer to loo-ton jacks.(c) First half completed. (d) Joining precast assemblies bysliding. (e) Threading and stressing cables. v) Placingthe end segments. (g) Threading and stressing last ca-bles.

Overpass structures of two spans could beerected using the technique illustrated above forthree-span structures, Figure 3.104. As would beexpected, the longer spans required the use of ad-ditional falsework towers. An overpass bridge,foundations plus piers and superstructure, couldbe constructed in less than two weeks. Figure 3.105shows a typical segment being placed in the over-

pass bridge with a mobile crane. Temporary pre-stress over the deck slab is shown in Figure 3.106.

The viaducts required the manufacture of largersegments in the same precasting factory used forthe overpass segments, but with casting proceedingin the usual short-line horizontal fashion. Threecasting machines were used simultaneously to pro-duce all viaduct segments.


HYORAULIC JAcu5 EMFORARY PRE5TR6’59

SLIDE _ 5ilDE

FIGURE 3.104. Alpine Motorway Bridges, erection scheme for two-span overpassbridges.

Erecting segments in the various structures re-quired the use of a launching gantry of an excep-tionally light and elaborate design, allowing easytransportation and erection from site to site, Figure3.107. A typical 200 ft (60 m) long cantilever in-

FIGURE 3.105. Alpine Motorway, segment placing inoverpass with crane.

eluding 25 segments, one pier segment weighing48 t (44 mt), and 24 typical segments weighing 36 t(33 mt) could be accomplished in six to eightworking days, including launching the gantry tothe following pier and achieving continuity withthe preceding cantilever. The maximum rate ofsegment placing was 12 units in a single day.

This project is another interesting application ofmass-production techniques and the standardiza-tion of segmental construction.

3.16 Bridge over the Eastern Scheldt, Holland

The bridge over the Eastern Scheldt, otherwiseknown as the Oosterschelde Bridge, Figure 3.108,

FIGURE 3.106. Alpine Motorway, provisional pre-stress over deck slab.

Br-idge Over the Eastern Scheldt, Holland 135

time restraints for construction, and scarcity oflabor, prefabrication was required to a very highdegree. Since the precast pile elements would belarge and heavy, it was decided that the pier andsuperstructure segments should be equally largeand heavy, in the range of 400 to 600 tons.i6

A casting yard, Figure 3.110, capable of pro-ducing all the various precast elements for thestructure was constructed near one end of thebridge. This facility provided all the advantages ofyard production techniques and the potential forhigh quality control.

FIGURE 3.107. ,\lpine >lotol wn, segment placing inviaducts with launching gantry.

The 14 ft (4.27 m) diameter cylinder piles have14 in. (0.35 m) thick walls and were cast vertically in20 ft (6 m) lengths. They were then rotated into ahorizontal position where they were aligned,jointsconcreted, and the pile post-tensioned. In thismanner piles were produced in required lengthsup to 165 ft (50 m). The assembled pile was thentransported by barge to the site, where a derrickpicked it up at one end and rotated it into its verti-

FIGURE 3.108. Bridge over the Eastern Scheldt,overall view of the structure.

is part of a project known as the Delta Works,which c losed the mouths o f many r ive r s andstreams southwest of Rotterdam to protect thecoastline from flooding. The bridge consists offifty-five 300 ft (9 1.4 m) spans, a roadway width of35 ft (10.7 m), and a vertical navigation clearanceof 50 ft (15.2 m). Parameters considered in thechoice of structural type and span were economics,foundation restraints, and ice loads.

Substructure consists of three cylinder piles witha caisson cap and an inverted V pier, Figure 3.109.The superstructure was assembled from sevenprecast elements, one pier segment, and two eachof three progressively smaller segments to produceone double cantilever span of 300 ft (91.4 m). Thebridge design, therefore, consists of very large pre-stressed cylinder piles, precast pier elements post-tensioned together, and precast superstructureelements erected and post-tensioned together toform a double cantilever system with a joint at eachmidspan location. Because of open-sea conditions,

600 tons

Cytindrml hollow

FIGURE 3.109. Bridge over the Eastern Scheldt,schematic of precast elements in the structure (courtesyof the Portland Cement Association).

FIGURE 3.110. Bridge over the Eastern Scheldt, viewof precasting plant (courtesy of the Portland Cement As-sociation).


cal position. Cylinder piles weighted from 300 to550 tons (270 to 500 mt). The pier cap was alsoprecast at the same yard, where it was post-ten-sioned circumferentially and vertically. The in-verted V portion of the pier was also precast withprovision for on-site post-tensioning to achieve finalassembly.16

Figure 3.111 shows the bridge under construc-tion. The temporary enclosures between each sec-tion are to protect the cast-in-place joint concreteagainst cold weather. Cast-in-place joints 16 in. (0.4m) wide were used, with faces of the precast ele-ments serrated to act as shear keys.

The superstructure segments were all set from atraveling steel gantry, Figure 3.111, that extendedover two and one-half spans at a time. Segmentswere barged to their final location, then hoisted insymmetrical order about each pier. The joints wereconcreted and the primary stressing completed be-

FIGURE 3.111. Bridge over the Eastern Scheldt, viewof launching truss and enclosure for cast-in-place joints(courtesy of the Portland Cement Association).

FIGURE 3.112. Bridge over the Eastern Scheldt,schematic of erection sequence (courtesy of the PortlandCement Association).

fore the next series of segments were hoisted intoposition. Erection sequence is depicted in Figure3.112. An aerial view of various stages of construc-tion is shown in Figure 3.113. A typical cycle fortwo spans of superstructure, not including the piersegment, involving the raising, concreting, andstressing of 12 segments, was three weeks.

3.17 Captain Cook Bridge, Australia

This structure carries a six-lane highway over theBrisbane River in Brisbane, Australia, as part ofthe Riverside Expressway and South-West Freewaydesigned to relieve the city’s overloaded trafficsystem.

The navigation requirements were for a 300 ft(91.4 m) wide horizontal clearance with a verticalclearance of 45 ft (13.7 m) across 200 ft (61 m) and40 ft (12 m) at either extremity. However, a 600 ft(183 m) span became necessary because of theskew crossing. Adequate bearing rock, at a reason-able depth, was found at the south bank such thatthe pier could be founded on a spread footing. Atthe north end, because of the steeply rising bank,the anchor span was limited to a span of 140 ft(42.7 m) and the abutment was designed as acounterweight connected to the superstructure bya prestressed tie-down wall, Figure 3.1 14.17

Once the navigation span requirements hadbeen met, the remaining span lengths were se-lected to meet design requirements, while thesuperstructure depth boundaries had to fall withina maximum allowable grade requirement of 3%and the flood level. The superstructure is a dual

FIGURE 3.113. Bridge over the Eastern Scheldt, ae-rial view of construction showing various phases (cour-tesy of the Portland Cement Association).

E L E V A T I O N

FIGURE 3.114. Capt. Cook Bridge, plan and elevation, f‘rom ref.. 17.


structure of prestressed concrete segmental two-cell boxes, Figures 3.115 and 3.1 16.17

Steel rocker bearings were used to support thesuperstructure at piers 1, 3, and 4, and large-diameter single steel roller bearings were used atpier 2. Lubricated bronze bearings sliding onstainless steel were used at the north abutment andfor the movable bearings at the suspended spans.Steel finger joints, allowing a 10 in. (250 mm)maximum movement, were provided at each slid-

II H-=---

FIGURE 3.115. Capt. Cook Bridge, cross section atpier 3, from ref. 17.

FIGURE 3.116. Crpt. Cook Bridge, two-cell box gir-der segment being erected (courtesy of G. Beloff, MainRoads Department).

ing bearing location and rubber and steel fingerjoints at the remaining locations.”

The box gi rder segments have a maximumdepth of 32 ft (9.75 m) and a minimum depth of 6ft (1.83 m). Segment length is 8 ft 8 in. (2.64 m). A16 in. (0.4 m) cast-in-place, fully reinforced jointwas used between segments. Maximum segmentweight is 126 tons (114 mt). A total of 364 precastsegments were required in the superstructure withthe two segments over the tie-wall in the southabutment being cast in place.”

The ContracEor chose to locate the precastingoperation on the river bank near the south abut-ment. This casting yard consisted of a concretemixing plant, steam-curing plant, three adjustablesteel forms, segment tilting frame, and a gantrycrane to transport the segments to a storage areaalong the river bank. Segments were designed sothat the top flange and upper portion of the webshad a constant thickness. The depth and lowerportion accommodated all variations, allowing thecontractor to cast in two sets of adjustable forms.Segments were cast with their longitudinal axis in avertical position for ease of concrete placementaround the prestressing ducts. Separate interiorforms were constructed for each box to permitvariations in the bottom flange and web thicknessand size of fillets. Aft.er casting and curing, seg-ments were lifted into a tilting frame to realign thesegment into its normal position ready for han-dling and storage.i7

A floating crane, designed and built by the con-tractor, was used for erection of the segments. It wasessentially a rectangular pontoon with mountedA-frame lifting legs rising to 120 ft (36.6 m) withadequate clearance to service the finished decklevel, while the stability was sufficient to transportthe segments to the erection position, Figure 3.117.An extended reach was required to position seg-ments on the first two spans in the shallow waternear the bank.17

Segments on each side of the pier were sup-ported on falsework anchored to the pier shafts,Figure 3.118. From this point additional segments,as they were erected, were supported on a can-tilever falsework from the completed portion ofthe structure. This falsework was fixed under thecompleted girder and supported from deck level,Figure 3.119. When the capacity of the pier tocarry the segment unbalanced load was reached, atemporary prop support on driven piles was con-structed before cantilever erection could continue..Segment erection then proceeded on each sideuntil either the joint position of the suspended


FIGURE 3.117. Cap. Cook Bridge, segment beingtransported by barge derrick to final position (courtesyof G. Beloff, Main Roads Department).

span was attained or the closure gap in span 3 wasreached. The completed structure was opened totraffic in 1971, Figure 3.120.


In Sections 3.2 through 3.15 the historical de-velopment of precast segmental bridges withmatch-cast joints has been illustrated by examples,

FIGURE 3.118. Capt. Cook Bridge, support for seg-ments on each side of pier (courtesy of G. Beloff, MainRoads Department).

FIGURE 3.119. Capt. Cook Bridge, cradle supporttrusses and temporary support tower (courtesy of G.Beloff, Main Roads Department).

ranging from the first structure at Choisy-le-Roi tothe largest applications such as the Rio Niteroi andSaint Cloud bridges. Emphasis has been placedon North American experience as well as on theadvantages of precast segmental construction forurban structures (B-3 Viaducts) or repetitive ap-plications (Alpine Motorways). Two particularlyoutstanding structures, deserving special mentionbecause of their size and characteristics where pre-cast segmental was used with conventional joints(not match-cast) were the Oosterschelde and Cap-tain Cook Bridges (Sections 3.16 and 3.17). Beforeclosing this important chapter, let us briefly givedue credit to several other contemporary match-cast segmental bridges.

3.18.1 CALIX BRIDGE, FRANCE

This 14-span superstructure has a maximum spanlength of 512 ft (156 m) over the maritime

FIGURE 3.120. Capt. Cook Bridge, completedstructure (courtesy of G. Beloff, Main Roads Depart-ment).


3.h2 1 . 3 9

1 3 . 4 2e L

FIGURE 3.121. Calix Viaduct, near Caen, France general dimensions.

FIGURE 3.122. Calix Viaduct, placing precast seg-ments in superstructure.

Section near midspan

FIGURE 3.123. Vail Pass Bridge, cross-section gen-eral dimensions.

waterway and typical 230 ft (70 m) spans in the ap-proaches on both banks. Dimensions are shown inFigure 3.12 1. The deck consists of two parallel boxgirders connected by a precast prestressed slabstrip. All segments, with a maximum weight of 49 t(43 mt), were cast in a long bench and placed with atower crane traveling between the box girders inthe approaches. Segments were barged in for themain span, and a beam and winch system was usedfor hoisting them into place, Figure 3.122.

3.18.2 VAIL PASS BRIDGES, U.S.A.

These bridges are located on Interstate I-70 overVail Pass near Vail, Colorado, in a beautiful set-ting at an altitude between 9000 and 10,000 ft(2700 and 3000 m) above sea level where winterconditions are critical and the construction periodis very short. Dimensions are shown in Figure3.123, and a view of one finished bridge appears inFigure 3.124.

3.18.3 TRENT VIADUCT, U.K.

This structure carries the M-180 South Humber-side motorway over the River Trent and consists ofdual roadways of three lanes each, with a centralmedian. Precast segmental construction was se-lected against a steel plate girder design with areinforced concrete deck slab. The bridge is sym-


FIGURE 3.124. \‘A Pass bridge, a completed precastsegmental structure (courtesy of International En-gineering Company, Inc.).

metrical with four spans of 159, 279, 279, and 159ft (48.5, 85, 85, and 48.5 m).

Each roadway is supported by an independentsuperstructure of twin concrete box girders vary-ing in depth from 16 ft (4.9 m) at the piers to 7 .ft(2.1 m) at midspan of the center spans. Principaldimensions are shown in Figure 3.125. Each boxgirder is made up of 91 precast segments 10 ft (3m) long, varying in weight between 38 t (35 mt) to82 t (75 mt). All segments were placed in balancedcantilever with a launching gantry shown in opera-tion in Figure 3.126, with precast units being deliv-ered on the finished deck.

3.18.4 L-32 TAUER,~AUTOBAHN BRIDGE, AUSTRIA

This structure is located between Salzburg andVillach, Austria, as part of a new motorway con-necting Germany and Yugoslavia. The 22-spantwin bridge has a total length of 3820 ft (1167 m)distributed as follows: 110, twenty at 180, and 110

F I G U R E 3 . 1 2 6 . I‘rellt Bridge, l a u n c h i n g ganrryfinishing the deck.

ft (33.5, twenty at 55, and 33.5 m). Box piers have amaximum height of 330 ft (100 m). The constant-depth superstructure of 12.5 ft (3.8 m) is made upof 722 segments match-cast in a job-site factoryequ ipped wi th four cas t ing mach ines , F igure3.127. A launching gantry was used to place allsegments in the two bridges in balanced cantilever,Figure 3.128.

3.18.5 KISHWAUKEE RIVER BRIDGE, U.S.A.

This dual structure carries U.S. Route 51 over theKishwaukee River near the city of Rockford, Il-linois. Dimensions are shown in Figure 3.129. Pre-stressing is achieved in the transverse and lon-gitudinal directions by bar tendons. All segmentswere placed in the structure by a launching gantry,shown in Figure 3.130, which represents the firstapplication of this method in the United States.

17.400M O T O R W A Y

CENTRALL RESERVE 4-

INSITU JOINT\

t

WEST I - I - EAST

NAVIGATION CNANNEL

Elevation

FIGURE 3.125. Trent Bridge, typical dimensions.

FIGURE 3.127. L-32 Tauernautobahn Bridge, cast-ing machine.

3.18.6 KENTUCKY RIVER BRIDGE, U.S.A.

This structure crossing the Kentucky River is lo-cated in Franklin County just south of Frankfort,Kentucky. It is a three-span structure with a 323 ft(98.5 m) center span and 228.5 ft (70 m) side spans.In cross section the superstructure consists of tworectangular boxes. It is,the first precast segmentalbridge to be constructed in the United States usingthe long-bed casting method, Figure 3.131. A viewduring construction is shown in Figure 3.132.

FIGURE 3.128. L-32 Tauernautobahn Bridge,launching gantry.

3.18.7 I-205 COLUMBIA RIVER BRIDGE, U.S.A.

This large project represents one of the major ap-plications of precast segmental construction in theUnited States. The 5770 ft (1759 m) long structurecarries Interstate I-205 from Vancouver, Wash-ington, across the North Channel of the ColumbiaRiver to Government Island near Portland, Ore-gon. Twin structures carry two 68 ft (20.7 m) wideroadways with span lengths varying between 600 ft(183 m) and 242 ft (74 m). Typical dimensions of

170’-0’

I_--

E L E V 6 9 4 . 0

- T R A N S V E R S EPOST-TENSIONIN

-!k-Ao.‘-L+- ._21 0

fb) fcJ

FIGURE 3.129. Kishwaukee River Bridge, superstructure elevation and cross sections.(a) Elevation. (b) Section at midspan. (c) Section at pier. (From ref. 18.)


FIGURE 3.130. Klrhwaukte River Bridge, v~elv dur-ing construction showmg launching truss.

the main spans over the river are shown in Figure3.133. Dimensions of the cross section, as designed,are shown in Figure 3.134. However, the contrac-tor, under a value engineering option in the con-tract documents (see Chapter 12), elected to re-design the cross section to a two-cell box section,Figure 3.135. The contractor exercised the op-

FIGURE 3.131. Kentucky River Bridge, long-linecasting bed.

FIGURE 3.132. kcntut k\ Rncxt 131 idgc. (In1 111% con-struction.

tion allowed in the bidding documents to selecthis own construction method and proceeded withcasting in place in conventional travelers the twocantilevers adjacent to the main navigation chan-nel (piers 12 and 13), while all other spans areof precast segmental construction. Figure 3.136shows a rendering of the structure.

FIGURE 3.133. I-205 Columbia River Bridge, elevation and plan.

1 4 4 Precast Balanced Cantilever Girder Bridges .

ll'-10"

I 67'-10" 1I

I 67'-11" II

FIGURE 3.134. I-205 Columbia River Bridge, cross sections.

FIGURE 3.135. I-205 Columbia River Bridge, revisedcross section.

3.18.8 ZILWAUKEE BRIDGE, U.S.A.

This bridge is another important example of pre-cast segmental construction in the United States.Located in central Michigan, this 8080 ft (2463 m)long structure carries dual four-lane roadwaysover the Saginaw River near Zilwaukee, Michigan.Principal dimensions are shown in Figure 3.137.

FIGURE 3.136. I-205 Columbia Rner Bridge, ren-dering of the structure.

CROSS SECTION OF PRECAST SEGMENTS

366’i 389’ 377’ ! 392’ ! 368’ j 372’ , 372’ 1351’

FIGURE 3.137. Zilwaukee Bridge, typical dimensions.

The 5 1 spans vary m length from 155 ft to 392 ft(47 to 119 m). An additional three-span ramp car-ries some traffic onto the southbound high-levelbridge. Navigation clearance is 125 ft (38 m) abovethe Saginaw River.

For a total deck area of 1,180,OOO sq ft (110,000


1 1 . 7 0 IFIGURE 3.138. Ottmarsheim Bridge, general dimensions.

m*) there a re 1590 la rge segments vary ing inlength from 8 to 12 ft (2.4 to 3.65 m) with amaximum weight of 160 t (144 mt). Segments wereproduced in a production-line operation withshort-line casting and placed in the structure inbalanced cantilever with a large launching gantryaccommodating two successive spans.

3.18.9 OTTMARSHEIM BRIDGE, FRANCE

This bridge in East France close to Germany andthe Rhine River at the Ottmarsheim hydroelectricplant is today the longest clear span of precastsegmental construction and the first major appli-cation of lightweight concrete to this type ofstructure. Principal dimensions are shown in Fig-ure 3.138. As shown in the longitudinal section,lightweight concrete was used only in the centerportion of the two main spans over the navigablewaterway and over the outlet channel of the powerplant. Figure 3.139 is a view of the completedstructure.

3.18.10 OVERSTREET BRIDGE, FLORIDA, U.S.4.

This structure crosses the lntracoastal Waterwaynear Panama City in Western Florida. Dimensionsare shown in Figures 3.140 and 3.141. The mainnavigation span is 290 ft (88 mm) long betweenpiers to avoid any construction in the water fendersystem during operation. Approach spans are 125ft (38 m) long and rest on I-shiped piers bearingon precast piles. The main piers consist of twin Ipiers of the same design. The total length ofstructure is 2650 ft (808 m) divided as follows: 95,seven at 125, 207.5, 290, 207.5, seven at 125, and95 ft (29, seven at 38, 63, 88, 63, seven at 38, and29 m). Precast segments 10 ft (3 m) long and

weighing a maximum of 50 t (45 mt) are designedto be placed in balanced cantilever with an aux-iliary overhead truss (and winch system) in theapproach spans to stabilize the deck over the flexi-ble piers during construction.

3.18.11 F-9 FREEWAY, MELBOURNE, AUSTRALIA

This very important project is a recent applicationof precast segmental construction to urban ele-vated structures. The constraints relating to loca-tion of piers and construction over highway andrailway traffic are comparable to the conditions en-countered at the B-3 South Viaducts in Paris,France.

The principal project dimensions are shown inFigure 3.142. All segments will be placed in thetwin bridge using two launching gantries, whichincorporate the latest technological developmentsin safety and efficiency.

FIGURE 3.139. Ottmarsheim Bl-idge, vic\v of’ thecompleted structure.

2650’-0” Overall Length of Bridge

21t 207’b!i” ;125,-O&l 25’-0225’.0’2 25’-0’~25’-0~125-0’~125-0’~i’-0r;l 2’-6”

1-4-

Sand Cement 3 :

FIGURE 3.140. Overstreet Bridge, blot-da, elevation

t,

L2ig”

LOLO” I

Riprap. (Typ.1

al

FIGURE 3.141. Overstreet Bridge, Florida, cross sections.

References 1 4 7

References

1. Jean Muller, “Ten Years of Experience in PrecastSegmental Construction,” Journal of the Prestressed

Concrete Institute, Vol. 20, No. 1, January-February1975.

2. C. A. Ballinger, W. Podolny, Jr., and M. J. Ab-rahams, “A Report on the Design and Constructionof Segmental Prestressed Concrete Bridges in West-ern Europe- 1977,” International Road Federa-tion, Washington, D.C., June 1978. (Also availablefrom Federal Highway Administration, Office ofResearch and Development, Washington, D.C., Re-port No. FHWA-RD-78-44.)

3. Walter Podolny, Jr., “An Overview of Precast Pre-stressed Segmental Bridges,” Journal of the Prestressed

Concrete Institue, Vol. 24, No. 1, January-February1 9 7 9 .

4. J. Mathivat, “Reconstruction du Pont de Choisy-le-Roi,” Travaux, Janvier 1966, No. 372.

5. Jean Muller, “Long-Span Precast Prestressed Con-crete Bridges Built in Cantilever,” First International

Symposium, Concrete Bridge Design, Paper SP 23-40,AC1 Publication SP-23, American Concrete Insti-tute, Detroit, 1969.

6. Andre Bouchet, “Les Ponts en Beton Precontraintde Courbevoie et de la Grande-Jatte (Hauts-de-Seine),” La Technique des Travaw, Juillet-Aout1 9 6 8 .

7. “Bear River Bridge,” STUP Bulletin of Information,November-December 1972.

8. “Nova Scotia’s Bear River Bridge-Precast Seg-mental Construction Costs Less and the MoneyStays at Home,” Bridge Bulletin, Third Quarter 1972,Prestressed Concrete Institute, Chicago.

9. “John F. Kennedy Memorial Causeway, CorpusChristi, Texas,” Bridge Report SR 162.01 E, Port-land Cement Association, Skokie, Ill., 1974.

10. G. C. Lacey, and J. E. Breen, “Long Span Pre-

stressed Concrete Bridges of Segmental Construc-tion State of the Art,” Research Report 12 l-l,Center for Highway Research, The University ofTexas at Austin, May 1969.

1. S. Kashima and J. E. Breen, “Epoxy Resins forJointing Segmentally Constructed Prestressed Con-crete Bridges,” Research Report 121-2, Center forHighway Research, The University of Texas at Aus-tin, August 1974.

2. G. C. Lacey and J. E. Breen, “The Design and Op-timization of Segmentally Precast Prestressed BoxGirder Bridges,” Research Report 121-3, Center forHighway Research, The University of Texas at Aus-tin, August 1975.

13. R. C. Brown, Jr., N. H. Burns, and J. E. Breen,“Computer Analysis of Segmentally Erected PrecastPrestressed Box Girder Bridges,” Research Report121-4, Center for Highway Research, The Univer-sity of Texas at Austin, November 1974.

14. S. Kashima and J. E. Breen, “Construction and LoadTests of a Segmental Precast Box Girder BridgeModel,” Research Report 121-5, Center for High-way Research, The University of Texas at Austin,February 1975.

15. J. E. Breen, R. L. Cooper, and T. M. Gallaway,“Minimizing Construction Problems in SegmentallyPrecast Box Girder Bridges,” Research Report121-6F, Center for Highway Research, The Univer-sity of Texas at Austin, August 1975.

16. Ben C. Gerwick, Jr., “Bridge over the EasternScheldt,” Journal of the Prestressed Concrete Institute,

Vol. 11, No. 1, February 1966.17. “A Proud Achievement-The Captain Cook

Bridge,” Issued by the Commissioner of MainRoads-1972, Main Roads Department, Brisbane,Queensland, Australia.

18. “Prestressed Concrete Segmental Bridges on FA 412over the Kishwaukee River,” Bridge Bulktin, No. 1,1976, Prestressed Concrete Institute, Chicago.

4Design of Segmental Bridges

4.14.24.3

4.4

4.5

4.6

4.7

4.8

INTRODUCTIONLIVE LOAD REQUIREMENT?3SPAN ARRANGEMENT AND RELATED PRINCIPLESOF CONSTRUCTIONDECK EXPANSION, HINGES AND CO-

4.4.1 Hinges at Midspan4.4.2 Continuous Su~tructures4.4.3 Expansion of Long BridgeTYPF, SHAPE AND DIMENSIONS OF THE SUPER-sTRu-

4.5.1 Box Sections4.5.2 Sbape of Superst~cture in Elevation4.5.3 Choice of Typical Cross Section4.5.4 Dimensions of the Typical Cuss SectionTRANSVERSE DISI’RIBUI’ION OF LQADS BETWEENBOX GIRDERS IN MULTIBOX GIRDERSEFFECT OF TEMPFXATI-JRF, GRADIENTS IN BRIDGEsuPFRsl-RucrUREsDESIGN OF LONGITUDINAL MEMBERS FOR FLE-XURE AND TENDON PROFILES

4.8.1 Principle of Pre&ess Iayout4.8.2 Draped Tendons4.8.3 Shaight Tendons4.8.4 Summary of Tendon Profiles and Anchor Locations4.8.5 Special Problems of Continuity PresWss and An-

cbonge Thereof4.8.6 Iayout of Pmskess in Strucaups with Hinges and

Expansion Joints4.8.7 Redistribution of Moments and Stresses Through

concrete creep

4.1 Introduction

Design of concrete highway bridges in the UnitedStates conforms to the provisions of The AmericanAssociation for State Highway and TransportationOfficials (AASHTO) “Standard Specificationsfor Highway Bridges.” For railway structures,specifications of the American Railway EngineersAssociation (AREA) should be consulted. For the

148

4.8.8 Prediction of Preskess Losses4.9 ULTIMATE BENDING CAPACITY OF LONGITUDI-

NAL MEMBERS4.10 SHEAR AND DESIGN OF GROSS SECITON

4.10.1 Introduction4.10.2 Shear Tests of Reinforced Concx~te Beams4.103 DifIiculties in Actual Structmw4.10.4 Design of h@dinal Members for Shear

4.11 JOINTS BETWFEN MATCH-CAST SEGMENTS4.12 DESIGN OF SUPERSTRUCl-URE CROSS SECl’ION4.13 SPECIAL PROBLEMS IN SUPmUCIWRE DESIGN

4.13.1 Diapluagms4.13.2 Superstructure over Piers4.13.3 End Abutments4.13.4 Expansion Joint and Hinge Segment

4.14 DEFLECITONS OF CANTILEVER BRIDGES ANDCAMBER DESIGN

4.15 FATIGUE IN SEGMENTAL BRIDGES4.16 PROVISIONS FOR FUTURE PmING4.17 DEhGN FXAMPLE

4.17.1 Longitudinal Beding4.17.2 Redktribution of Moments4.17.3 Stresses at Midspan4.17.4 shear4.17.5 Design of the Cross-Section Frame

4.18 QUANTITIES OF MATERIALS4.19 POTENTL4L PROBLEM ARF.AS

REFERENCES

most part, the provisions in these specificationswere written before segmental construction wasconsidered feasible or practical in the UnitedStates.

Before discussing design considerations, theauthors wish to emphasize that no preference foreither cast-in-place or precast methods of con-struction is implied here. The intent is simply topresent conditions that the designer should be

Span Arrangement and Related Principles of Construction 149

aware of to produce a satisfactory design. Bothconcepts are viable ones, and both have been usedto produce successful structures.

In general, the segmental technique is closelyrelated to the method of construction and thestructural system employed. This is why segmentalconstruction, either cast in place or precast, hasbeen often identified with the cantilever construc-tion used in so many applications. It is logical totake bridge structures built in cantilever as a basisfor the design considerations developed in thischapter. Where other methods, such as incremen-tal launching or progressive placement, requirespecial design considerations, such problems arediscussed in the appropriate chapters.

The depth-to-span and width-to-depth ratios forsegmental construction presently advocated in theUnited States have been adopted from Europeanpractice. The lighter live loads used in the UnitedStates should permit further refinements in ourdesign approach.

4.2 Live-Load Requirements

In comparing practices in other countries to thosein the United States, an important parameter tokeep in mind is that of live-load requirements. Fig-ure 4.1 illustrates the considerable differencesamong code requirements in various countries.’For a simple span of 164 ft (50 m) and width of24.6 ft (7.5 m), the German specification requires alive-load design moment 186% greater and theFrench requires one 290% greater than that ofAASHTO. Some Canadian provinces use theAASHTO specifications but arbitrarily increase thelive load by 25%.

4.3 Span Arrangement and Related Principlesof Construction

In the balanced cantilever type of construction,segments are placed in a symmetrical fashion abouta pier. The designer must always remember thatconstruction proceeds with symmetrical cantileverdeck sections centered about the piers and not withcompleted spans between successive piers.2

For a typical three-span structure, the side spansshould preferably be 65 percent of the main centerspan instead of 80 percent in conventional cast-in-place structures. This is done to reduce to aminimum the length of the deck portion next tothe abutment, which cannot be conveniently builtin balanced cantilever, Figure 4.2~.

Where span lengths must vary, as between amain span and an approach span, it is best to intro-duce an intermediate span whose length will aver-age the two flanking spans, Figure 4.26. In thismanner the cantilever concept is optimized.

Individual cantilever sections are generally madecontinuous by insertion of positive-moment ten-

M km)f

AASHTO 100%

P(m) A A S H T O IRC DIN 1072 CPC50 1 0 0 1 3 8 1 8 6 290

1 0 0 l o o 1 3 8 1 7 3 1 7 7

5000

tP

A

4000 l-//

q M a x . M France - / / /

8 I DIN l07i /

0 1 0 2 0 30 4 0 50 6 0 70 8 0 9 0 l o o ah)

Span

FIGURE 4.1. Maximum live-load moment (simple span)(F. Leonhardt, New Practice in Concrete Structures, IABSE, NewYork, 1968).

Design of Segmental Bridges

0.65-07OL 065-O 70L

(a)

ILI ‘ 2 (LITL2) L2

, ..I

(b)

fc)

FIGURE 4.2. Cantilever construction showing choiceof span lengths and location of expansion joints.

dons upon closure. It is preferred not to have anypermanent hinges at midspan. Continuous deckswithout joints have been repeatedly constructed tolengths in excess of 2000 ft (600 m) and haveproved satisfactory from the standpoint of mainte-nance and riding quality.

For very long viaduct-type structures, inter-mediate expansion joints are inevitable to accom-modate volume changes. These joints should be lo-cated near points of contraflexure, Figure 4.2c, toavoid objectionable slope changes that occur if thejoint is located at midspan. This consideration willbe discussed in more detail in Section 4.4.

In many cases it may not be possible to providethe desirable optimum span arrangement. Thus,the end span may be greater or less than the op-timum span length desired.2 In the case of a longend span, the superstructure might be extendedover the abutment wall to provide a short addi-tional span. As shown in Figure 4.3, a conventional

Section A-A

FIGURE 4.4. End restraint at abutment.

bearing (1) is provided over the front abutmentwall. A rear prestressed tie (2) opposes uplift andpermits cantilever construction to proceed out-ward from the abutment to the joint t’Jl), where aconnection can be effected with the cantilever fromthe first intermediate pier. Figure 4.4 shows an al-ternative scheme with a constant-depth section, asopposed to a haunched section, where the deck hasbeen encased within the abutment wing walls forarchitectural purposes. For the normal end span, aspecial segment is temporarily cantilevered out soas to reach the first balanced cantilever constructedfrom the next pier, Figure 4.5. Alternatively thisportion could be cast in place on falsework, if siteconditions permit.

In a short-end-span situation, cantilever con-struction starts from the first pier and reaches theabutment on one side well before the midspan sec-tion of the adjacent span, Figure 4.6. An upliftreaction must be transferred to the abutmentduring construction and in the completed struc-ture. Consequently, the webs of the main boxgirder deck are cantilevered over the expansion

FIGURE 4.3. End restraint in abutment.

Deck Expansion, Hinges and Continuity 151

FIGURE 4.5. Conventional bearing on abutment.

FIGURE 4.6. Anchorage for uplift in abutment.

joint into slots provided in the main abutmentwall, Figure 4.7. The neoprene bearings areplaced above the web cantilever rather than belowto transfer the uplift force while allowing the deckto expand f-reely.

Interesting examples of such concepts are givenin the three following bridges:

Givors Bridge over the Rhone River, France,shown in Figure 4.8. The main dimensions aregiven with the typical construction stages of thesuperstructure.

Tricastin Bridge over the Rhone River, France(Section 2.15.11). No river piers were desired forthe structure, which dictated a main span of 467 ft(142.50 m), and there was no room on the banks toincrease the side spans so as to avoid the end uplift.Two very short side spans of only 83 ft (25.20 m)provide the end restraint of the river span. Theuplift is transferred to the abutments, which areearth tilled to provide a counterweight, Figure 4.9.The magnitude of the uplift force has been re-

Prestressing units

FIGURE 4.7. Longitudinal section.

duced by the use of lightweight concrete in thecenter of the main span.

Puteaux Bridges over the Seine River, near Paris(Section 2.15.10).

A few bridges have even been built in cantileverentirely from the abutments. The Reallon Bridgein Frarice is one such structure, Figure 4.10, wherevery special site conditions with regard to bridgeprofile and shape of the valley were best met withthis concept.

Another set of circumstances may be encoun-tered when it is not possible to select the desiredspan lengths to optimize the use of cantilever con-struction. Such was the situation of the bridge overthe Seine River for the Paris Ring Road, where aside span on the left bank could not be less than 88percent of the main river span over the river, whilevery stringent traffic requirements governed theplacement pattern of precast segments on the rightbank, Figure 4.11.

4.4 Deck Expansion, Hinges and Continuity

4.4.1 HINGES AT MIDSPAN

Historically, the first prestressed concrete bridgesbuilt in cantilever were provided with a hinge atthe center of the various spans. Such hinges weredesigned to transfer vertical shear between the tipsof two adjacent cantilever arms (which could de-velop under the live loading applied over one armonly in half the span length) while enduring a freeexpansion of the concrete deck under volumechanges (concrete creep and seasonal variations oftemperature). Continuity of the deflection curve

RIM CiMCHE 6 s 3 2 1 RP.‘E CRXTE

152

FIGURE 4.8. Givors Bridge over the Rhone River, France, span dimensions and typicalconstruction stages. (1) Construction of left bank river pier segment. The eight segmentseither side of the pier are erected, and pier stability is assured by temporary props. (2)The connection between deck and abutments is made. Temporary props are removedand the seven remaining segments are placed in cantilever. (3) The above operation isrepeated on the right bank. The central pier segments are poured. Two segments areerected on either side of each pier, supported by scaffolding. (4) The last segment isplaced in the central span, continuity is achieved between the two cantilevers, and thescaffolding is removed. (5) The remaining 16 segments on either side of the central piersare placed. (6) The 110 m spans are completed by pouring the closure segments andtensioning the continuity prestress. The superstructure is now complete.

Elevation

Section A-A ’ ’

I I

Plan

FIGURE 4.9. Tricastin Bridge over the Rhone River, France.

FIGURE 4.10. Reallon Bridge, France.

154

PHASE 1

PHASE 2

PHASE 3

PHASE 4

PHASE 5

PHASE 6

PHASE 7

construction of central cantilever

1 2

n &z---4

construction of right bank cantilever

1 2 33 * \ 1 1 1j - c

e &

closure of central and right bank cantilever

1 2 3

\ ! il n 5d f ”

joining of right bank cantilever with abutment

construction of left bank cantilever

closure of left bank and central cantilever

joining of left bank cantilever with abutment

Deck Expansion, Hinges and Continuity 155

Cc) I

FIGURE 4.11. Paris Belt (Downstream). (0) Typicalconstruction stages. (b) Segment assembly-right bank.(c) Segment assembly-left bank.

was thus obtained in terms of vertical displacementbut not insofar as rotation at the hinge point wasconcerned.

Remember that in this type of structure the deckis necessarily fixed at the various piers, which mustbe designed to carry the unbalanced moments dueto unsymmetrical live-load patterns over the deck.On the other hand, these structures are simple todesign because they are statically determinate forall dead loads and prestressing, and the effect oflive load is simple to compute. Because there areno moment reversals in the deck, the prestressingtendon layout is simple.

Some disadvantages were accepted as the priceof simplicity of design:

The deck has a lower ultimate capacity as com-pared with a continuous structure, because there isno possible redistribution of moments.

Hinges are difficult to design, install, and operatesatisfactorily.

There are many expansion joints, and regardlessof precautions taken in design, construction, andoperation they are always a source of difficulty andhigh maintenance cost.

The major disadvantage, revealed only by experi-ence, related to the exceeding sensitivity of suchstructures to steel relaxation and concrete creep.

Because of the various hinges at midpoints of thespans, there is no restraint to the vertical and an-gular displacements of the cantilever due to the ef-fect of creep. Steel relaxation and the corre-sponding prestress losses tend to make mattersworse, while concrete creep is responsible for aprogressive lowering of the center of each span.With time, there is an increasing angle break in thedeck profile at the hinge. The magnitude of thedeflection has been reported to be in excess of onefoot (0.03 m).

The difficulties experienced with this type ofconstruction are such that most government offi-cials in Western Europe will no longer permit itsuse.3

4.4.2 CONTINUOUS SUPERSTRUCTURES

Further research concerning the exact propertiesand behavior of materials for such structures hav-ing a midspan hinge would enable more accurateprediction of the expected deflection and thusbetter control. A far more positive approach is toeliminate the fundamental cause of the phenome-non by avoiding all permanent hinges and achiev-ing full continuity whenever possible.

To show the relative behavior of a continuousstructure and one with hinges at midspan, a nu-merical application was made for the center spanof the Choisy-le-Roi Bridge in two extreme cases:

156 Design of Segmental Bridges

TABLE 4.1. Comparison of Crown Deflections (Hinged versus Continuous Structure)

No. Load Stage

1 Girder weight2 Initial prestress3 Cumulative4 5% Deviation of prestress5 Continuity prestress6 Superimposed load7 Finished structure (initial)8 Concrete and lossescreep9 Finished structure (final)10 Live loads

Cast-in-Place PrecastHinged Structure Continuous Structure

E ? 0 E ? 6J

( lo6 psi) (in.) (in. X 103/in.) ( lo6 psi) (in.) (in. X 103/in.)

4.3 1.80 2.4 5.1 1 .50 2.04.3 - 1.50 -2.0 5.1 -0.90 - 1.24.3 0.30 0.4 5.1 0.60 0.8- 23% - 7%- - - 6.4 -0.30 06.4 0.30 0.4 6.4 0.10 0- 0.60 0.8 0.40 0.82.1 1 .10 1.4 2.1 -0.10 0- 1.70 2.2 0.30 0.86.4 0.90 1.1 6.4 0.30 0

Explication of symbols:E = modulus of elasticity for each particular loading stagey = vertical deflection at crowno = total angular break at crown (expressed in thousandths of inch per inch)Derivation of results:(3) = (1) + (2) girder weight and initial prestress(7) = (3) + (5) + (6) finished structure (initial stage)(9) = (7) + (8) finished su-ucture (final stage)

Cast-in-place cantilever with a hinge at midspan,and

Precast segmental continuous construction.

Results comparing the two structures are shown inTable 4.1 and in Figures 4.12 through 4.14.

The study shows no significant difference be-tween the two types of structures with respect tothe theoretical behavior of the cantilever methodunder combined dead load and initial prestress,Figure 4.12. In fact, the angle change at midspan iseven slightly less for the hinged structure, because

the prestress offsets a greater percentage ofdead-load moments, 83 percent instead of 58 per-cent.

fCIilCREl;t ClEEP

;11.5 I

Ed

CISI II race ClnIInw

nim swuciure rrecw Slrrcw

FIGURE 4.13. Comparison of deflection caused bycreep (hinged versus continuous structure).

2’ -== CISI II me

,= nln181 struclnrc IcloIIoIIII

rrecna Wrrlrre

FIGURE 4.12. Comparison of deflection under deadload and prestressing (hinged versus continuous struc-ture).

LIYE’ LILI3 I.0

E= m 11 rince I Clntlnrl~:

llnltd Strwri rrecul ltrrclrre

FIGURE 4.14. Comparison of deflections caused bylive load (hinged versus continuous structure).

Deck Expansion, Hinges and Continuity 1 5 7

When the effect of concrete creep is considered,however, there is a significant difference betweenthe two types of structures, Figure 4.13. Thehinged structure has a vertical deflection of 1.1 in.(28 mm) and a corresponding total angle break of0.0028 in./inch. This value is twice that shown inTable 4.1 and Figure 4.13 for the angle change ofone cantilever, the value of 2.8 being the total anglebreak of the two abutting cantilevers. The continu-ous structure indicates a camber of 0.1 in. (3 mm),and no angle break will ever appear because of fullcontinuity.

Further, the effect of deviation of actual pre-stress load from the design prestress load pointsout an important difference in the sensitivity of thetwo systems. Assuming the actual prestress in thestructure to differ from the design assumption by5%, the corresponding maximum deflection is in-creased by 23% in the hinged structure but only

7% in the continuous structure. Therefore, thecontinuous structure is three times less sensitive topossible deviations from the assumed materialproperties.

Live-load deflections of the continuous structureare three times more rigid than the hinged struc-ture, Figure 4.14. The deflection of a typical spanof the Oleron Viaduct in France is compared with acontinuous span and with a crown hinged span inFigure 4.15.

From these data it is obvious that the fullest useof continuity and the elimination of hinges atmidspan whenever possible is beneficial to thestructural behavior of the bridge, to safety andcomfort of traffic, and to the structure’s aestheticappearance.

In practice, the continuity of the individual can-tilever arms at midspan is obtained by another setof prestressing tendons, usually called continuity

\ /’ I ’

\(0 , 6 I. %

Y I

260 I-L

FIGURE 4.15. Comparisons between live-load deflections for continuous orhinged structures.

1 5 8 Design of Segmental Bridges

prestressing, which is installed along the span in acontinuous structure. Details of the design aspectsof this prestress will be discussed in Section 4.8.

4.4.3 EXPAMSIO,V OF LOAVG BRIDGES

When the continuity of the superstructure is se-lected as optimum for the behavior of the struc-ture, one must keep in mind that proper measuresshould be concurrently taken to allow for expan-sion due either to short-term and cyclic volumechanges or to long-term concrete creep.

The piers may be made flexible enough to allowfor such expansion or may be provided with elas-tomeric bearings to reduce the magnitude of hori-zontal loads to acceptable levels when applied tothe substructure. This important aspect of theoverall bridge design concept is considered inChapter 5.

Several structures are currently made continu-ous in lengths of 1000 to 2000 ft (300 to 600 m)and in exceptional cases even 3000 ft (900 m). Forlonger structures, full continuity between endabutments is not possible because of the excessivemagnitude of the horizontal movements betweensuperstructure and piers and related problems.Therefore, intermediate expansion joints must beprovided. For long spans they should not be placedat the center of the span, as in the early cantileverbridges, but closer to the contraflexure point tominimize the effect of a long-term deflection. Sucha concept was developed initially for the OleronViaduct and is currently used on large structuressuch as the Saint Cloud Bridge in Paris, Sal-lingsund Bridge in Denmark, and the ColumbiaRiver and Zilwaukee Bridges in the United States.

Detailed computations were made in the case ofthe Oleron Viaduct to optimize the location of theexpansion joint in a typical 260 ft (80 m) span, Fig-ure 4.15 shows the shape of the deflection curvefor a uniform live loading with the three followingassumptions:

Fully continuous span

Span with a center hinge

Span with an intermediate hinge located at 29 per-cent of the span length from the adjacent pier (ac-tual case)

The advantages of having moved the hinge awayfrom the center toward the quarter-span point areobvious:

Maximum deflection under live load is reduced inthe ratio of 2.2 to 1.

Maximum angle break under live load is reducedin the ratio of 3.0 to 1.

For dead-load deflections the difference is evenmore significant, such that there is no substantialdifference between the actual structure and a fullycontinuous one.

The variation of the angle break at the hingepoint versus the hinge location along the spanlength is shown in Figure 4.16. There seems to belittle doubt that the structure is improved by selec-tion of a proper location for the hinge and the ex-pansion joint.

Theoretically, the ideal hinge position is betweenpoints ,4 and B, which are the contraflexure pointsfor dead and live loads. From a constructionstandpoint, such a location f-or the hinge compli-cates the erection process, for the hinge must betemporarilv blocked and subsequentlv releasedwhen the span is complete and continuitv isachieved. We will consider this subject in detailafter examining the layout of longitudinal pre-stress in cantilever bridges (Section 4.8.6).

It was recently discovered, in the designing ofthe Sallingsund Bridge, that the optimum location

L O C A T I O N O F H I N G E B E T W E E N

M I D - S P A N A N D PIER

FIGURE 4.16. Variation of angle break at the hingewith hinge location along the span.

Type, Shape, and Dimensions of the Superstructure 159

of the hinge to control the deflect ions underservice-load conditions does not simultaneouslypermit achievement of the overall maximumcapacity under ultimate conditions. This questionwill be discussed later in this chapter.

The preceding discussion of hinge locationapplies particularly for very long spans or for slen-der structures. For moderate spans with sufficientgirder depth it has been found that careful detail-ing of the prestress in the hinged span can allowthe hinge to be maintained at the centerpoint forsimplicity (spans less than 200 ft with a depth tospan ratio of approximately 20). Such was the casefor the cantilever alternatives of the Long Key andSeven Mile Bridges in Florida.

4.5 Type, Shape, and Dimensions ofthe Superstructure

4.5.1 BOX SECTIONS

The typical section best suited for cantilever con-struction is the box section, for the following rea-sons:

1. Because of the construction method, dead-load moments produce compression stresses at thebottom fiber along the entire span length, andmaximum moments occur near the piers. Thetypical section therefore must be provided with alarge bottom flange, particularly near the piers,and this is achieved best with a box section.

The efficiency of the box section is very good,and for a given amount of concrete provides the

least amount of prestressing steel. The efficiency ofa section is usually measured by the following di-mensionless coefficient:

r2p=-

C&2

with the notations as given in Figures 4.17 and4.18, where some basic formulas are presented.

The efficiency would be p = 1 if the concretewere concentrated in thin flanges with webs ofnegligible thickness. On the other hand, a rectan-gular section has an efficiency of only l/3. Theusual box section efficiency is p = 0.60, which issignificantly better than that of an I girder.

2. Another advantage of the large bot tomflange is that the concrete area is sufficiently largeat ultimate load to balance the full capacity of theprestressing tendons without loss in the magnitudeof the lever arm. ’

3. The elastic stability of the structure is excel-lent both during construction and under serviceconditions, because the closed box section has alarge torsional rigidity.

4. In wide bridge decks where several girdersmust be used side by side, the large torsional stiff-ness of the individual box girders allows a verysatisfactory transverse distribution of live loadswithout intermediate diaphragms between piers.

5. Because of their torsional rigidity, boxgirders lend themselves to the construct ion ofcurved bridge superstructures and providemaximum flexibility for complicated tendon trajec-tories.

(0) 6)Longitudinal sect ion Typical tramverSe section

FIGURE 4.17. Typical characteristics of a box section: Total section height: h; cross-section area: A; moment of inertia: I; position of centroid; c,, c2; radius of gyration: rgiven by rp = Z/A; efficiency ratio: p = r%,c,; limits of central core: r*/c, = PC,; r%, = pc2;for the usual box girder: p = 0.60.


dlh -F

Cl

Ypc2/ I,x(a)

(b)

The optimum selection of the proportions of thebox section is generally a matter of experience. Acareful review of existing bridges provides an ex-cellent basis for preliminary design. The variousparameters that should be considered at the startof a design are:

Constant versus variable depth

Span-to-depth ratio

Number of parallel box girders

Shape and dimensions of each box girder, includ-ing number of webs, vertical or inclined webs,thickness of webs, top and bottom flanges

Ph

-

h

ICc)

FIGURE 4.18. ‘rypical prestress requirements of abox girder. (u) For maximum negative moment over thepier (LX + LL): total moment = M; required prestress =F = M/z with z = c, - cf, + cp; usually over the piel- z =0.75 12. (b) For maximum positive moment at midspan(LX + IL): total moment = ‘M; required prestress = F =M/i with z = cp - cf2 + c ,; usually at midspan z = 0.70h. (c)For variable moments (LL): total moment variation =AM (sum of positive and negative L.C. moments); re-quired prestress = F = hM/ph (p = 0.60).

All these factors are closely related to each other,and they also depend largely upon the construc-tion requirements-for example, the size of theproject that will require a large investment insophisticated casting equipment.

4.5.2 SHAPE OF SUPERSTRUCTURE IiYELEVz4TlOh’

Constant depth is the easiest choice and affords thebest solution for short and moderate spans, up to200 ft (60 m). However, constant depths have beenused for aesthetic reasons for spans to 450 ft (140m), such as the Saint Cloud Bridge in Paris and the

Type, Shape, and Dimensions of the Superstructure 161

Pine Valley and Columbia River Bridges in theUnited States, Figure 4.19~.

When the span increases, the magnitude ofdead-load moments near the piers normally re-quires a variation of structural height and a curvedintrados. When clearance requirements allow, acircular intrados is the easier and more aestheti-cally pleasing choice, although in some cases (suchas the Houston Ship Channel Bridge) a more com-plex profile must adjust to the critical corners ofthe clearance diagram. Between the constant-depth and the curved-intrados solutions, Figure4.19, intermediate options may be used, such as:

The semiconstant depth, where the concrete re-quired in the bottom flange near the piers is placedoutside the typical section rather than inside thebox (constant dimension for the interior cell). Thissolution has been used on two bridges in Franceand is aesthetically satisfactory, Figure 4.196.

Straight haunches (bridge for the Ring Road inParis). In this case caution must be exercised to in-sure compatibility of the local stresses induced bythe abrupt angle change of the bottom soffit at thestart of the haunch, where a full diaphragm is usu-ally needed inside the box, Figure 4.19~.

Increase thicknessat pier ,

Ii?!’

l/15< h<1/30

A ,_ ,,,.,, _.optimum l/18 to l/20

, ,-Yw“’ .““. ” -

_.,

1116 <h,lL < l/20optimum 1118

II22 <hr,lL < l/28

1/16<h,lL<1/20o p t i m u m l/l8

1/30<holL < l/50I

Circular intrados orthird-degree parabola

Cd)

FIGURE 4.19 Longitudinal profile for segmental bridges. (k) Constant depth.(b) Semiconstant depth. (c) Straight haunches. (d) Variable depth.


4.53 CHOICE OF TYPICAL CROSS SECTION

Web spacing is usually selected between 15 and 25ft (4.5 and 7.5 m) to reduce the number of webs toa minimum, simplifying construction problemswhile keeping transverse bending moment in thetop and bottom flanges within reasonable limits.

A superstructure up to 40 ft (12 m) in width isthus normally made up of a single cell box girderwith two lateral cantilevers, the span of which isslightly less than one-fourth the total width (7 to 8ft for a 40 ft width).

For wide bridges, multicell box girders may beused:

Three webs, two cells: as in the B-3 South Viaductand the Deventer BridgeFour webs, three cells: as in the Saint Cloud Bridgeand the Columbia River Bridge

Alternatively, large lateral cantilevers and a largespan length between webs are accepted with specialprovisions to carry the deck live loads transversely:

Transverse flange stiffeners as in the Saint Andrede Cubzac, Vejle Fjord, and Zilwaukee BridgesSide boxes as in the Chillon Viaduct

Alternatively several boxes may be used side byside to make up the superstructure. Figures 4.20through 4.24 give the dimensions of a few struc-tures selected at random from various countriesthroughout the world.

4.5.4 DIMENSIONS OF THE TYPICALC R O S S S E C T I O N

Three conditions must be considered in deter-mining the web thickness:

Shear stresses due to shear load and torsional mo-ments must be kept within allowable limitsConcrete must be properly placed, particularlywhere draped tendons occur in the webTendon anchors, when located in the web, mustdistribute properly the high prestress load con-centrated at the anchorages

Following are some guidelines for minimum webthicknesses:

8 in. (200 mm) when no prestress ducts are locatedin the web

10 in. (250 mm) when small ducts for either verti-cal or longitudinal post-tensioning tendons occurin the web12 in. (300 mm) when ducts for tendons (twelve 3in. diameter strands) occur in the web14 in. (350 mm) when an anchor for a tendon(twelve 4 in. diameter strands) is anchored in theweb proper

Most codes underestimate the capacity of two-way slabs, such as the roadway slab or top flange ofa box girder bridge, whether prestressed trans-versely or mild-steel reinforced. There is a greatreserve of strength due to the frame action be-tween slabs and webs in the transverse direction.

The minimum slab thickness to prevent punch-ing shear under a concentrated wheel load is ap-proximately 6 in. (150 mm). However, it is recom-mended that a slab thickness of not less than 7 in.(175 mm) be used to allow enough flexibility in thelayout of the reinforcing steel and prestressingducts and obtain an adequate concrete cover overthe steel and ducts.

Recommended minimum top flange thicknessversus the actual span length between webs shouldbe:

Span less than 10 ft (3 m)Span between 10 and 15 ft(3 to 4.5 m)Span between 15 and 25 ft(4.5 to 7.5 m)

7 in. (175 mm)8 in. (200 mm)

10 in. (250 mm)

Over 25 ft (7.5 m), it is usually more economical tosubstitute a system of ribs or a voided slab for asolid slab.

Early bridges used very thin bottom flanges inorder to reduce critical weight and dead-load mo-ments. A 5 in. (125 mm) thickness was used inbridges, such as the Koblenz Bridge in Germany. Itis very difficult to prevent cracking of such thinslabs due to the combined effect of dead load car-ried between webs and longitudinal shear betweenweb and bottom flange. For this reason, it is nowrecommended that a minimum thickness of 7 in.

FIGURE 4.20. Typical dimensions of some cast-in-place segmental cantilever bridges in France. Year ofconstruction and maximum span length (ft): (a) Moulina Poudre (1963), 269. (6) Morlaix (1973), 269. (c) Bor-deaux St. Jean (1965), 253. (d) Givors (1967), 360. (e)Oissel (1970), 328

-I--=-+

(fl)

(b)

t

s,

(4

(e)

163


FIGURE 4.20 (Continzx~) (f) Viosne (1972), 197. (g) Jo i n v i l l e (twin deck) (1976), 354. (h)Gennevilliers (1976), 564.

(175 mm) be used, regardless of the stress re-quirements. Where longitudinal ducts for prestressare distributed in the bottom flange, a minimumthickness of 8 to 10 in. (200 to 250 mm) is usuallynecessary, depending on the duct size.

Near the piers, the bottom slab thickness is pro-gressively increased to resist the compressivestresses due to longitudinal bending. In the Ben-dorf Bridge, 680 ft (207 m) span, the bottomflange thickness is 8 ft (2.4 m) at the main piersand is heavily reinforced to keep the compressivestresses within allowable limits.

After this brief review of the various conceptualchoices for dimensioning the deck members, con-

sideration should be given to the design of suchmembers with particular emphasis on the follow-ing points:

Distribution of load between box girders in mul-tibox girder bridgesEffect of temperature gradients in the structure

4.6 Transverse Distribution of Loads Between BoxGirders in Multibox Girders

We noted earlier that wide decks can convenientlyconsist of two or even three separate boxes trans-

3 4.600(1))

10.92 I

! 10.60 1-t 7I 1 5.50 g I

1 ’ 10.60 ’ ,

FIGURE 4.21. Typical dimensions of some precast segmental cantilever bridges inFrance. Year of construction and maximum span length (ft): (a) Choisy-le-Roi (1965),180; (b) Courbevoie (1967), 197; (c) Oleron Viaduct (1966), 260; (d) Seudre (1971), 260;(e) B-3 South Viaduct (1973), 157; cf) St. Andre de Cubzac (1974), 312; (g) St. Cloud(1974), 334; (h) Ottmarsheim (1976), 564.

165

(4

(e)

(h)

166

%I 900 ,96, %1 9cKl 1961 1

9 50c_-t

cI

.-

-

Cc)

(4

(ft): (a) Koblenz, Germany (1954), cast in place,374; (b) Bendorf, Germany (1964), cast inplace, 682; (c) Chillon, Switzerland (1970), pre-cast, 341; (d) Sallingsund, Denmark (1978),.precast, 305; (e) Vejle Fjord, Denmark (1979),cast in place, 361.

167

(b)

(c)

1 6 8

FIGURE 4.23. Typical dimensions of some segmental cantilever bridges in Europe.Year of construction and maximum span length (ft): (a) Felsenau, Switzerland (1978),cast in place, 512; (6) Tarento, Italy (1977), cast in place, 500; (c) Kochertal, Germany(1979), cast in place, 453.

Transverse Distribution of Loads Between Box Girders in Multibox Girders 169

Typical Cross Section

!22'-6"!

t

!22'-;q6,

4

, 20'4 1r r

t3a'-6"

4

, 17'-5" ,

t' 38'-6" T

4

, 36' 1

4 T 59'-3" r

mI 381 11 T

FIGURE 4.24. Typical dimensions of some segmentalcantilever bridges in the Americas. Year of constructionand maximum span length (ft): (n) Rio Niteroi, Brazil(1971), precast, 262: (h) Pine Valley, U.S.A. (1974), castin place, 450; (c) Kipapa, U.S.A. (1977). cast in place,250; (n) Kishwaukee, U.S.A., precast, 250; (e) Long Key,U.S.A., precast, 118;(r) Seven Mile, U.S.A., precast, 135;(y) Columbia River, U.S.A., cast in place and precast,600: (h) Zilwaukee, U.S.A., precast, 375; (i) HoustonShip Channel, U.S.A., cast in place, 750.

versely connected by the top flange. A detailedanalysis was made of such decks with regard to thedistribution of live load between the various boxes.It was found that in normal structures of this type,the combined effect of the flexural rigidity of theroadway slab acting transversely as a rigid framewith the webs and bottom slab of the various box

girders, on one hand, and the torsional rigidity ofsuch box girders on the other hand, would result ina very satisfactory transverse distribution of liveloads between box girders. There is no need fordiaphragms between girders as normally providedfor I-girder bridgers.

Comprehensive programs of load testing of sev-eral bridges, including accurate measurements ofdeflections for eccentric loading, fully confirmedthe results of theoretical analysis. This analysis hasbeen reported in various technical documents, andonly selected results will be presented in this sec-tion.

The first bridge analyzed in this respect was theChoisy-le-Roi Bridge. A knife-edge load P is con-sidered with a uniform longitudinal distributionalong the span, Figure 4.25. When this load travelscrosswise from curb to curb, each position may beanalyzed with respect to the proportion of verticalload carried by each box girder, together with thecorresponding torsional moment and transversemoment in the deck slab. These analyses havemade it possible to draw transverse influence linesfor each effect considered, such as longitudinalbending m o m e n t s ( o v e r t h e s u p p o r t o r a tmidspan), torsional moments, or transverse mo-ments.

For longitudinal moments it is convenient to usea dimensionless coefficient, Figure 4.25c, whichrepresents the increase or decrease of the load car-ried by one box girder in comparison with theaverage load, assuming an even distribution be-tween both girders. Numerical results show thatthe transverse distribution of a knife-edge loadplaced on one side (next to the curb) of a twin boxgirder produces bending moments in each box thatare 1.4 and 0.6 times the average bending moment.For the same configuration, a typical deck with Igirders would have an eccentricity coefficient ofapproximately 4 compared with 1.4 for the boxgirders. There are, however, two side effects tosuch an encouraging behavior, which relate to tor-sion stresses and transverse bending of the deck

slab.

Torsional Moments in the Box Girder An unsym-metrical distribution of live loads in the transversedirection tends to warp the box girders and causeshear stresses. It is their high torsional rigiditywhich produces a favorable distribution of loadsbetween girders. However, the maximum torsionalmoments usually occur when only one-half thestructure (in cross section) is loaded, and the re-sulting stresses do not cumulate with the shearstresses produced by the full live-load shear force.

170 Design of Segmental Briees

Span length,L P

(A)I

4 41(z

I 4

I +

ho (at midspan) 2 d(

c---hCenter of span

h, (over support ) 2d’* 4

67)

FIGURE 4.25. Principle of transverse distribution of loads between boxgirders. (a) Dimensions. (b) Influence line of the shear in the connecting slab.(c) Transverse influence line of longitudinal moment. (d) Transverse bend-ing influence line at section A.

Transuer Moments in the Deck Slab The deck slabcannot be considered as a continuous beam onfixed supports because of the relative displace-ments on the two boxes due to unsymmetricalloading. Figure 4.25d shows the consequence. Ifthe slab were resting on fixed supports, theinfluence line for the moment in a section such as(A) would be the typical line (1). Because the boxgirders undergo certain deflections and rotations,the effect is to superimpose the ordinates of an-other line such as (2).

Numerically, the difference is not as great asmay be expected at first sight, because line (1) per-tains to the effect of local concentrated truck loadswhile line (2), being the result of differentialmovements between box girders, pertains to theeffect of uniformly distributed loads. In summary,deck moments are increased by only 20 to 30%over their normal values if flexibility of the box

girders is ignored. As a matter of practical interest,actual numerical values for several bridges inFrance with either two or three box girders thathave all shown excellent performance for morethan 10 years are presented in Figures 4.26 and4.27.

4.7 Effect of Temperature Gradients inBridge Superstructures

Experience has shown the sensitivity of long-spancantilever bridges to concrete creep. This resultedin the preference for continuous rather thanhinged cantilevers. However, two more problemsarose from this significant change in design ap-proach, both being the immediate result of con-tinuity. These problems are (1) effect of tempera-ture gradient in bridge decks and (2) redistribution

Effect of Temperature Gradients in Bridge Superstructures

2d

Bridge Spans (ft)

0 Givors 7360' 1 - (1lOiy 15.',

0 D/S Paris -300' b y 13.1Ring Park-way

0U/S Paris ' I 15.4Ring Park- (90m) 7 295' r

way

co Corde l(79m)T 260' T14.1

50 ,Juvisy yp220' 14.6

__- -.-

@ Choisy-le- \ 1Roi y 180' 7 (55m) 11.1

2d' ho/h1

(ft)

29.5 6.6/18.0

26.2 11.1/18.0

33.9 9.2115.7

23.3 5.9114.'

24.9 5.2/10.7

t

Eccen.Coeff.

1.23

22.3 1 co;;fant 1 1.28

i

t?d' I

t2d

: I 1

FIGURE 4.26. Transverse distribution of loads between box girders, numerical valuesfor several two-box girders.

of internal stresses due to long-term effects (steelrelaxation and concrete creep). The importance ofthese two new problems was discovered experi-mentally. All structures are designed, according tothe provisions of the various codes, for changes oftemperature that are assumed to apply to the en-tire section. Significant bending moments in thesuperstructure occur only as a result of the frameaction with the piers where a rigid connection isachieved between sub- and superstructure. Actual

measurements on existing structures confirm thisassumption. The average concrete section under-goes a progressive shortening due to shrinkageand concrete creep superimposed naturally withthe usual seasonal temperature variations, Figure4.286. The total concrete strain of 120 X 10m6in./in. was very moderate for a period of fouryears.

Daily readings, on the same bridge, of strainsand magnitude of reactions over the abutment


1 I Calculated deflection2 I (E = 6.4 X lo6 psi)

Measured deflection

Measured deflection

Calculated deflection(E = 6.9 X lo6 psi)

0 I ..~1 deflection, I I 1 I I , Measurec

/II

--- --

I-

Calculated deflection(E = 7.4 X lo6 psi)

FIGURE 4.27. Transverse distribution of loads between box girders.

brought to light a factor that had previously been flange concentrates the sun’s radiation. Within aignored. This was the differential exposure of the 24-hour period the reaction over the abutmentbridge deck to the sun on warm summer days. This could vary as much as 26%, Figure 4.28~. Thesituation is aggravated for bridges crossing a river, equivalent temperature difference between topwhere the bottom flange is kept cool by the water and bottom flanges reached 18°F (10°C). Theand the usual black pavement placed over the top maximum stress at the bottom flange level, due

Design of Longitudinal Members for Flexure and Tendon Profile 173

Cc)

FIGURE 4.28. Champigny Bridge, observed values ofconcrete strains and deck reactions. (a) Typical dimen-sions. (b) Long-term shortening of bridge deck due toconcrete creep superimposed with temperature varia-tions. (c) Daily temperature variations as exemplified bychange in reactions over abutments.

only to this temperature gradient, reached 560 psi(3.9 MPa), a value completely ignored in the designassumptions.

Various countries of Western Europe have nowincorporated special provisions on temperaturegradients as a result of this knowledge. In France,the following assumptions are required:

1. Add the effect of a 18°F (10°C) temperaturegradient to the effect of dead loads and normalvolume changes (such as shrinkage, creep, andmaximal temperature differences). The effectof gradient is computed with an instantaneousmodulus of elasticity (usually 5 million psi).

2. Add the effect of a 9°F (5°C) temperature gra-dient to the combined effect of all loads (in-cluding live load and impact) and volumechanges, again using an instantaneous mod-ulus of elasticity.

The effect is usually computed by assuming thegradient to be constant throughout the bridgesuperstructure length, which is not necessarily thecase.

Figure 4.29 shows the result for the case of atypical span built-in at both ends (this is the case ofa long structure with many identical spans). Thestress at the bottom fiber depends only upon thefollowing two factors:

Variation of height between span center and sup-port (ratio hi/h,)

Position of the center of gravity within the section(ratio c,lh,)

The lowest stress is obtained for a symmetrical sec-tion and a constant-depth girder.

The stress increases rapidly when the variationin depth is more pronounced. For normal propor-tions the effect of gradient is increased by 50% invariable-depth girders compared to constant-depth girders (240 psi versus 160 psi for a 9°F gra-dient and a modulus of 5 x lo6 psi).

4.8 Design of Longitudinal Members for Flexureand Tendon Pro$le

4.8.1 PRINCIPLE OF PRESTRESS LAYOUT

The longitudinal prestress of a cantilever bridge,whether cast in place or precast, consists of twofamilies of tendons:

1 . As construction in cantilever proceeds, the in-creasing dead-load moments are resisted ateach step of construction by tendons located inthe top flange of the girder and symmetricallyplaced on either side of the pier, Figures 4.30and 4.31~. These are known as cantilever ten-dons.

2. Upon completion of individual cantilevers,continuity is achieved by a second family oftendons essentially placed at the center of thevarious spans, Figure 4.316. Because girderload moments are small, except throughlong-term redistribution, because of the con-struction procedure, the continuity prestress isdesigned to resist essentially the effect of:a. Superimposed loads (pavement, curbs,

and the like).

b. Live loads.

C . Temperature gradient.


II 1.5 2 .0 2 .5 3.0 ho

-L

ELEVATION OF SPAN SECTION AT CENTER

FIGURE 4.29. Effect of thermal gradient on box girder decks.

d. Subsequent redistribution of girder loadand cantilever prestress.

Tensile stresses are large at the bottom flangelevel, but seldom will continuity prestress gain thefull advantage of the available eccentricity becauseof the stress conditions at the top flange level. Usu-ally this prestress is divided into tendons, B 1 or B2,located in the bottom flange, and a few tendonssuch as B3 which overlap the longer cantilevertendons, Figure 4.3 lb.

For the best selection of prestressing methods, itis essential to use prestressing units of a capacitylarge enough to reduce the number of tendons inthe concrete section, particularly in very longspans. On the other hand, there must be asufficient number of tendons to match with thenumber of segments in the cantilever arms. Also,units with an excessive unit capacity will pose seri-ous problems for the transfer of concentrated highloads, particularly for cast-in-place structures,where concrete strength at the time of prestress isalways a critical factor within the constructioncycle.

In practical terms, prestress bars are as welladapted to short and medium spans as strand ten-

dons (such as twelve 3 in. diameter strands). Forvery long spans (above 500 ft) large-capacity ten-dons (such as nineteen 0.6 in. diameter strands)with a final prestress force of about 700 kips afforda very practical solution for cantilever prestress.For continuity prestress the size of tendons is gov-erned by the possibility of locating the tendon an-chors in such areas and with such provisions as toallow a proper distribution of the concentratedload to the surrounding concrete section. Unitssuch as twelve 3 in. diameter or twelve 0.6 in.diameter are usually well adapted with careful de-tailing for this purpose.

4.8.2 DRAPED TENDONS

In early applications, both families of prestresswere given a draped profile in the web of the boxsection to take advantage of the vertical componentof prestress to reduce the shear stresses. In such aconfiguration there is a considerable overlappingof tendons in the web, because the cantilever pre-stress is anchored in the lower part of the web andthe continuity prestress is anchored at the topflange level; see the layout in Figure 4.31~. For aconstant-depth section and for segments of equal

Diagrams of moments in a cantilever

FIGURE 4.30. Typical cantilever moments and prestress. When placingunit 8, the increase of bending moment is represented by the hatched areaand the resultant curve is transferred from position 7 to position 8. Addi-tional sets of cantilever prestressing tendons are placed each time a pair ofsegments is erected. This procedure allows the magnitude of prestress tofollow very closely the various steps of construction.

length, it is easy to completely standardize the lay-out of prestress in various segments.

Mechanization of the casting operations is a verydesirable feature, all prefabricated reinforcingcages being identical, with ducts always at the samelocations. A substantial amount of repetition maystill be obtained in variable-depth members as seenin Figure 4.32, which represents a typical span ofthe Oleron Viaduct. The two disadvantages of sucha prestress layout are:

Cantilever tendon anchors are located in the weband it is difficult to prevent web cracking, particu-larly in cast-in-place structures, except through theuse of thicker webs and smaller tendons.Continuity tendons extend above deck level at bothends. The installation of the anchor with theblock-out for stressing is difficult in the casting

form, and good protection against water seepageto the tendons in the finished structure is a criticalfactor.

4.83 STRAIGHT TENDONS

Tendons are in this configuration located in theupper and lower flange of the box girder and an-chored near the web in their respective flanges.There is no draped profile for the tendons withinthe web and consequently no reduction of shearstresses due to a vertical component of prestress.This is a disadvantage of this scheme, which mayoften require vertical prestress to maintain shearstresses within allowable limits. On the other hand,the two advantages are:

Simplicity in both design and construction


(AI )

span L

Average length of cantilever tendons 0.52 LI

fd

Average length of contlnuit? tendons : 0 35 - 0.50 L

(b)

.4 : cantilever tendonsB : continuity tendons 0A AQ

FIGURE 4.3 1. Typical layout of longitudinal prestress. (a) Cantilever tendons. (b)Continuity tendons. (c) Standardized layout of tendons for constant-depth segments.

Significant reduction in friction losses of the pre- Span length 262 ftstress tendons for both curvature and wobble ef- Width of a box 42 ftfects, and consequent savings on the weight andcost of the longitudinal prestress of at least lo%, all

Two webs at 14.2 in. each

else being equalLongitudinal cantilever 42 (12 4 in. diam.prestress strands)

The Rio Niteroi Bridge (described in Section Longitudinal continuity 14 (12 f in. diam.

3.8) used straight tendons, Figure 4.33. Typical prestress strands)

characteristics of the deck are as follows: Vertical prestress 1 in. diameter bars

Cantilever prastress30412 x 1.2” 6)

+8-(12x .315”9)

15 I< 13 I? 1�1 ,o

Continuity prestress---

14-(12x l/2” @I+ 4(12 x .315” $1

Detail B

Detail A

Transverse prestress

r

Longitudinal prestress

FIGURE 4.32. Oleron Viaduct, longitudinal prestress.

dist r ibut ion


Vertical bars 25 mm 9 (typ. )

TOP PRESTRESS

12 strand 12.7 mm # cablas

FIGURE 4.33. Rio-Niteroi Bridge, typical prestress layout.

Critical stresses near the pier are:

Longitudinal compressionVertical compressionMaximum shear stressDiagonal stresses

850 psi400 psi580 psi

- 110 psi (tensile),a n d1360 psi(compressive)

Typical details of tendon profiles and anchor-ages are portrayed for Linn Cove Viaduct in NorthCarolina, U.S.A., in Figures 4.34, 4.35, and 4.36.

4.8.4 SUMMARY OF TENDON PROFILES ANDA N C H O R L O C A T I O N S

In the two preceding configurations, tendons wereanchored in the following manner:

1. For cantilever prestress:a. On the face of the segment in the fillet

between top flange and web.b. On the face of the segment along the web.c. In a block-out near the fillet between top

flange and web, but inside the box.2. For the continuity prestress:

a . At the top flange level.b. In a block-out near the fillet between web

and bottom flange.

c. In a block-out in the bottom flange properaway from the webs.

Configurations lc, 2b, and 2c all permit pre-stressing operations to be performed safely andefficiently inside the box, Figure 4.37, permittingsuch operations to be removed from the criticalpath of actual placement or construction of thesegments. Only those tendons required forbalancing the self-weight of the segments need tobe installed at each step of construction. The bal-ance of the required prestressing may thus be in-stalled later, even after continuity is achieved be-tween several cantilever arms. Tendons for theadditional prestress may then be given a profilecomparable to that used in cast-in-place bridgeswith a length extending over several spans. Thepractical limit to this procedure is excessive so-phistication and related high friction losses in thetendons.

4.8.5 SPECIAL PROBLEMS OF CONTINUITYPRESTRESS AND ANCHORAGE THEREOF

Tendons for continuity prestress may not, or evenshould not, always be located in the fillet betweenweb and bottom flange. They may be located in thebottom flange proper. When a variable-depthmember is used, the bottom flange has a curvaturein the vertical plane, which must be followed by theprestress tendons. Unless careful consideration is

Design of Longitudinal Members for Flexure and Tendon Profile

5 s&u e 7 “: Z-‘/1 .’

c .I.\

8’ e ; ” 3 SW 0 7”,1!4’

FIGURE 4.34. Linn Cove Viaduct, typical cross section showing prestress ducts.

given to that fact at the concept and detailed designstages, difficulties are likely to develop; we may seethis by looking at Figures 4.38 and 4.39, whichshow the free-body diagrams of stresses in thebottom flange due to the curvature, together with anumerical example. Curvature of a tendon inducesa downward radial load, which must be resisted bytransverse bending of the bottom flange betweenthe webs.

Longitudinal compressive stresses in the bottomflange similarly induce an upward radial reactionin the flange, counteracting at least in part the ef-fect of the tendons. Unfortunately, when the fulllive load and variable effects, such as thermal gra-dients, are applied to the superstructure, the lon-

gitudinal stresses vanish and consequently the par-tial negation of the effect of tendon curvature islost. Therefore, the effect of tendon curvatureadds fully to the dead-load stresses of the concreteflange. The corresponding flexural stresses arefour to five times greater than the effect due todead load only, and if sufficient reinforcement isnot provided for this effect, heavy cracking is to beexpected and possibly failure. Practically, the situ-ation may be aggravated by deviations in the loca-tion of the tendon ducts in the segments comparedto the theoretical profile indicated on the drawings.At the point between segments, ducts are usuallyplaced at their proper position; but if flexible tub-ing is used with an insufficient number of sup-

F

ANCHORAGE A /I

.?:o* Ii

__------------

t

FIGURE 4.35. Linn Cove Viaduct, top flange prestress details.

180

:‘s HOLES FOR TEMPORARY PRESTRESSING 1’1)‘8 BARS~-~--~

D U C T 3 ‘/I$’ 0

I.--__~__---.-.--p.p.FIGURE 4.36. Linn Cove Viaduct, bottom flange prestress details.

181


FIGURE 4.37. B-3 South Viaduct, prestressing oper-ations in box girder.

porting chairs or ties, the duct profile will have anangle break at each joint. In addition to the in-creased friction losses, there is a potential dangerof local spalling and bursting of the intrados of thebottom flange, Figure 4.40. Rigid ducts properlysecured to the reinforcement cage and placed atthe proper level over the soffi t of the castingmachine or traveler will avoid this danger.

Another item concerning potential difficulties incontinuity prestress relate to the projection of theanchor block-out in the bottom flange and whereanchor blocks are not close to the fillet betweenweb and bottom flange. When this method is usedin conjunction with a very thin bottom flange (a

PARTIAL CROSS-SECTION

COMPRESSIVESTRESSES

FREE BOOY DIAGRAM

FIGURE 4.38. Secondary stresses due to curved ten-dons in the bottom flange.

flange as thin as 5 or 6 in. has been used in earlybridges), it is almost impossible to distribute theconcentrated load of the anchor block in the slabwithout subsequent cracking. For a 7 or 8 in. flangeit is recommended that no more than two anchor

Assumed Longitudinal Radius 1,000'

(12 x l/2"+ tendons) Typ.

a. = 15.67'

lo'-0"4

I_ lo'-0"

FIGURE 4.39. Secondary stresses due to curved prestressing tendons, nu-merical example. Assumed longitudinal radius = 1000 ft. Weight of bottom slab= 100 psf. Effect of compressive stresses: unloaded bridge,f, = 2000 psi, com-pressive radial load: f,tlR = (2000 x 8 x 12)/1000 = 200psf; loaded bridge, 0psi. Effect of prestressing tendons: stranded tendons (twelve f in. dia strands) at10 in. interval with a 280 kip capacity, corresponding radial load: F/R =280,000/[( 10/12)1000] = 336, say 340 psf. Total loads on bottom slab: (1) duringconstruction, load = 100 psf; (2) unloaded bridge, load = 100 - 200 + 340 =240 psf; (3) loaded bridge, load = 100 + 340 = 440 psf, moment = we2112 = 9kips ft/ft, stress in bottom slab: f = M/S = (9000 x 12)/[( 12 x 64)/6] = 840 psi.

Design of Longitudinal Members for Flexure and Tendon Profile

Pamal elevation

FIGURE 4.40. Ef‘fect of’ misalignment of’ continuityprestress.

blocks for (I2 f in. diameter strands) tendons beplaced in the same transverse section in conjunc-tion with additional reinforcing to resist burstingstresses. Wherever possible, the anchor blocks forcontinuity tendons should be placed in the filletbetween the web and flange where the transversesection has the largest rigidity.

4.8.6 L,-iYOI’T OF PRESTRESS I.Y STRUCTURESIZ’ITH HI.Z’GES ,4SD EXP,4.\‘SION JOINTS

Section 4.4.3 explained how the expansion joints inthe superstructure should be located preferablynear the contraflexure point of a span rather thanat midspan as in previous structures. However,there is a resultant complication in the constructionprocess, because cantilever erection must proceedthrough the special hinge segment. A typical con-struction procedure and the related prestress lay-out are presented in Figure 4.4 1. For the geometryof the structure in this figure, the constructionproceeds as follows:

a. Place the first five segments in balanced can-tilever and install cantilever prestress for re-sistance against dead load.

b. Place the lower half of the special segment andthe corresponding tendons.

C . Install the upper half of the special hinge seg-ment with permanent, or provisional bearings,and provisional blocking to permit transfer oflongitudinal compressive stresses. Cantilever

tendons may be made continuous through theexpansion joint or equipped with couplers.

d. Resume normal cantilever segment placingand prestressing to the center of the span, withtendons crossing the joint.

e. Achieve continuity with previous cantilever bypouring closure joint and stressing continuitytendons. Layout of these tendons includes an-chors in the special hinge segment to transferthe shear forces in the completed structure.

f. Remove temporary blocking at hinge. Releasetension in cantilever tendons holding segments7, 8, and 9 or cut tendons across the hingeafter grouting.

4.8.7 REDISTRIBUTION OF MOME,VTS ANDSTRESSES THROUGH CONCRETE CREEP

In a statically indeterminate structure the internalstresses induced by, the external loads dependupon the deformation of the structure. In pre-stressed concrete structures such deformationsmust include not only short-term but also long-term deformation due to relaxation of prestressingsteel and concrete creep. In conventional struc-tures such as cast-in-place continuous superstruc-tures, the effect is not significant if all loads andprestress forces are applied to the statical design ofthe completed structure, which is the common caseof construction on scaffolding. The behavior ofcantilever bridges, particularly cast-in-place struc-tures, is quite different, because the major part ofthe load (the girder load often represents 80% ofthe total load in long spans) is applied to a staticalconcept that is different from the completed de-sign. As soon as continuity is achieved, the struc-ture tends to resist the new situation in which it hasbeen placed; this is one aspect of a very general lawin mechanics whereby consequences always opposetheir cause.

A very simple example is presented in Figure4.42, which will provide the basis for a better ap-preciation of the problem. Assume two identicaladjacent cantilever arms built-in at both ends andfree to deflect at the center. The self-weight pro-duces a moment:

at both ends with a corresponding deflection androtation at the center of y and o.


I

Canti levertendons

&$qqq 11115 4 3 2

67)

Tendon

Cant i lever tendonsfor construction

FIGURE 4.41. Construction procedure and prestress in a span with anexpansion joint.

If the load is applied for a short time, the valueof E to take into account is Ei (instantaneous mod-ulus). Assuming that continuity is achieved be-tween the cantilevers as shown in Figure 4.42c,there cannot be an angle break at the center, butonly a progressive deformation of the completedspan. After a long time the concrete modulus haschanged from its initial value Ei to a final value E,,which may be approximately 2.5 times less than Ei .

Because the external loads are unchanged andthe structure is symmetrical, the only change in (hestate of the structure is an additional constant mo-ment M, developing along the entire span and in-creasing progressively with time until the concretecreep has stabilized. At all times the magnitude ofthis moment adjusts in the structure to maintainthe assumed continuity at the center.

The additional deflection at midspan, y2, takesplace in a beam with fixed ends under the effect ofits own weight and only because of the progressivechange of the concrete modulus from the value Eito the value E,.

Considering the concrete strain at any point ofthe structure, the total strain q is the sum of twoterms:

Ef = E, + Ep

where cr = strain before continuity is achieved,E2 = strain after continuity is achieved.

Hooke’s law relating stress and strain at a particu-lar point in time states:

E, =g1

Design of Longitudinal Members for Flexure and Tendon Profile 185

MO-MI

cMl Cd)

FIGURE 4.42. Redistribution of stresses through con-crete creep.

Similarly there is a relationship between the addi-tional strain e2 and the corresponding stressfi pro-duced at the same location by the same loadsapplied in the continuous structure. One maywrite:

f2E$ = -EC

where E,, the creep modulus, is given by:

1 1 1-= - - -E, Ef Ei

or

l 2=f2 i1--+Ef 1 1

Thus:

The corresponding total stress in the structure thenbecomes:

In other words, the effect of concrete creep is toplace the final stresses in the structure in an inter-nal state (either of moments, shear forces, deflec-tions, or stresses) intermediate between:

The initial statical design with free cantilevers, andThe completed design with continuity.

Assume, for example, EfIEi = 0.40. Thus:

f= 0.4Of, + O.SOf,

The relationship is equally true for moments,shear forces, or deflections.

Moments over the support are:

In the free cantilevers, M = M,In the continuous structure, M = 3M,

The final moment is therefore:

M, - M, = 0.40M, + 0.6O(fA4,) = 0.80M,

a n d

M, = 0.20 M,.

At midspan, moments are:

In the free cantilevers, M = 0In the continuous structure, M = MO/3

and the actual final moment:

M, = 0.60 +- = 0.20M,

The above derivation applies not only to exter-nal loads but also to the effect of prestressing.Continuity prestress applied to a continuousstructure gives little internal redistribution of mo-ments except in multispan structures, where thespans react with one another according to the ac-tual construction procedure. Cantilever prestress,which acts to offset an appreciable part of thedead-load moments, tends to reduce the distribu-tion of moments due to external loads, Figure 4.43.

Up to now the concrete modulus has been as-sumed to take only the two values Ei and E,(short-term and long-term values). In fact, becauseconstruction of a cantilever takes several weeks (oreven several months in the case of cast-in-placestructures), account must be taken of the concretestrains versus the age and the duration of loading.


a = L/2I

MGL = Girder Load Cantilever Moment

Pe

ia 1 dx

= Cantilever Prestress Moment

MO= n M= MGL - Pe Moment Inducing Redistribution

a dx{ T MO = Moment at 6 under M in continuous beam

I = Moment of Inertia (variable)

FIGURE 4.43. Computation of moment redistribution due to dead load andcantilever prestress.

Such relat ionships are presented for normal-weight prestressed concrete and average climate inFigure 4.44.

Concrete strains are presented for convenienceas a dimensionless ratio between the actual strainand the reference strain of a 28-day-old concretesubjected to a short-term load.

We see that short-term strains vary little with theage of the concrete at the time of loading except ata very early age. However, long-term strains aresignificantly affected by the age of the concrete.For example, a three-day-old concrete will show afinal strain 2.5 times greater than a three-month-old concrete. This is particularly important forcast-in-place structures with short cycles of con-struction (two pairs of segments cast and pre-stressed every week, which has now become com-mon practice).

Two other factors play an important role in theredistribution of stresses in continuous cantileverbridges:

1. Relaxation of prestressing steel and prestresslosses. Because the stress in the prestressingsteel varies with time (a part of that variationbeing due precisely to the concrete creep), theinternal moments that produce the deforma-tion of the structure and therefore originatethe redistribution of stresses varv continuallv.This factor is important because’the resultantmoments in the cantilever arms (dead load andprestress) are given bv the difference of twolarge numbers, and a variation on one usual+has an important effect upon the result, Figure4.43.

2. Change of the mechanical properties of theconcrete section. For the sake of simplicity thegross concrete section is usually adopted forcomputation of bending stresses. In fact, thesection to be used should be:

a. The net sect ion (ducts for longitudinalprestress deducted from the concrete sec-

Design of Longitudinal Members for Fkxure and Tendon Profile 1 8 7

L -mp”p--v

DAYS MONT,,-3 Y E A R S

FIGURE 4.44. Concrete strains versus age and dura-tion ot loading. Note that strain is given as a dimension-less ratio beuqeen the actual strain and the referencestr-ain of a 2%dav-old concrete subjected to shot-t-termhid.

b.

tion) for effect of girder load and prestressup to the time of tendon grouting.

The transformed section (with incorpora-tion of the prestress steel area with a suit-able coefficient of transformation) aftergrouting, where the coefficient of equiva-lence n = E,JE,, ratio of the modulus ofsteel and concrete, should be taken as avariable with time, from 5 to 12 or even 15.

The above discussion indicates the complexity ofthe problem with respect to the material propertiesand indicates the unreliable results of the early de-signs.

The only acceptable solution is the global ap-proach, whereby a comprehensive electronic com-puter program analyzes step by step the state ofstresses in the structure at different time intervalsand whenever any significant change occurs, thusfollowing the complete history of construction.

Such programs are now available and haveproven invaluable in helping us understandthe behavior of segmental bridges. They provideefficient tools for the final design of the structure.

Because it is difficult for some engineers to de-pend fully upon computer solutions in approach-ing a design problem, it is desirable to have ordersof magnitude of the moment redistribution forpreliminary proportioning and dimensioning ofthe structure. The following guidelines are basedon experience and judgment.

1. Consider the case of a symmetrical spanmade up of two equal cantilevers fixed at the endsand built symmetrically. Compute girder loadmoments of the typical cantilever and prestressmoments using the final prestress forces and thetransformed concrete sections with n = 10 (average).

2. Compute the moment at midspan due to thedifference of the above two loading cases (Figure4.43). More generally, compute in the final struc-ture the moments in the various spans due to thedifference between cantilever girder load andmoments and final prestress moments, includingthe restraint due to piers if applicable.

3. Reference is made now to the formula givenpreviously and repeated here for convenience:

w h e r e f = final stress (or moment or shear loadin the structure at any point),

,ft = stress at the same point obtained byadding all partial stresses for eachconstruction step using the corre-sponding stat ical scheme of thestructure,

f2 = stress at the same point assuming allloads and pres t ress forces to beapplied on the final structure withthe final statical scheme,

Ei = initial or intermediate modulus ofelasticity (short-term or for the dura-tion of loading before continuity),

E, = final modulus (long-term).

Using different assumptions on the constructionsequence of bridge decks and the correspondingstrains as given by Figure 4.44, we find that theaverage value of EfIEi would vary from 0.50 to0.67. It is recommended that the conservativevalue of 0.67 be used in this approximate method.Thus the actual moment due to redistr ibutionshould be 0.67, the value computed under para-graph 2. This moment must be added to the effectof live load and thermal gradient at midspan.


MOMENTSDUE 10

REDISTRIBUTION

ft-kips

+1260

a BOTH CANTILEVER5 OF SAME AGE (BUILT IN 100 DAYS)

@ CANT(l) BUILT O-100 DAYSCANT(2) BUILT 100-200 DAYS

@ CANT(2) ONE YEAR OLDER THAN CANT(I)

FIGURE 4.45. Variation of redistribution moment incantilever construction with the construction procedure.

4. Correspondingly, the support moment (overthe piers) is decreased by the same amount. In fact,the construction of cantilevers in successive stagesis such that continuity is achieved in each span be-

-Ir2/c2

1 I r2/c1

i

tween cantilevers of different ages, and the redis-tribution of support moment may thus vary in wideproportions, Figure 4.45. To keep on the safe side,it is not recommended that the reduction in sup-port moment be taken into account in designingthe prestress forces.

It is interesting at this stage to give some ordersof magnitude of moment redistribution by consid-ering some fundamental formulas given as refer-ence in Figure 4.46.

It has been assumed:

That the secondary moment due to the stressing ofcontinuity tendons is 6% of the total moment overthe support,

That the distance, n, between the center of gravityof the cantilever tendons and the top slab is equalto 0.05h.

That the center of gravity, depending upon thesection dimensions, may vary between (c,lh = 0.4and c,lh = 0.6) and (c,lh = 0.6 and c,lh = 0.4).

That the efficiency factor is p = 0.60.

From the data indicated above and in Figure4.46, the percentage of prestressing steel,p, may bedetermined as follows:

assuming a final stress in the tendons of 160 ksi

assuming a maximum compressive stress in thebottom flange of 2000 psi:

P = AJ&, = 2 0 0 0 +

T r\” limit of the central core

Cl r2 r2

s;

.fi

= PC2 -= PC1CZ

p = efficiency factor

c2 average stress = 2000 g

\ ~200~ psi

FIGURE 4.46. Approximate moment redistribution (moments over support). Totalmoment: MT = MGL + MSL + ML,,where MGL = girder load moment, MSL = superim-posed load moment, ML, = live-load moment (including impact). Assumed secondarymoment due to continuity prestress: 0.06 M,. Final prestress force: P = 0.94M,l[r +(r*/c,)] = 0.94MJ(e + pc2). Prestress moment (1): Pe = 0.94M,l[l + (pcJ~)]. Moment-inducing redistribution: MGL - Pe, given by (2): (MGL - Pe)IM, = M,,lM, - 0.94/[1 +

hJe)l.

Design of Longitudinal Members for Flexure and Tendon Pro@ 189

AS --P = A,- 8;))

For a symmetrical section, cr = 0.5h, andp would,thus, be equal to 0.63%, a reasonable and commonvalue. The transformed percentage area of thesteel with n = 10 is equal to:

np = 0.125 +

All mechanical properties of the section changeto make the denominator of equation (2) in Figure4.46 increase and, consequently, the moment-inducing redistribution increase also. This fact,which was completely overlooked for many years,is clearly seen in Figure 4.47, where the percentageof moment-inducing redistribution in the various

sections is plotted versus the position of the cen-troid with or without transformed area.

It is interesting to study the effect of an acci-dental variation in the prestress load due to exces-sive friction in the ducts. Assume, for example, areduction of 5% in the prestress load for the casec,lh = 0.5 (symmetrical section over the support)and M,,lM, = 0.80.

The intial values of (M,, - Pe)IM, are changedas follows:

Gross areaTransformedarea

100% 9 5 %Prestress Prestress

0.236 0.2640.265 0.292

PercentVariation

1.121.10

The combined effect of tendon grouting and ofadded friction losses increases the redistribution ofmoments by 25%.

0.600 - I I I I I

-.--- GrossArea

0.500 - Transformed Area

I I I I ICl lh 0.35 0 .40 0 .45 0 .50 0 .55 0 .60 0 .65

czlh 0 .65 0 .60 0 .55 0 .50 0 .45 0 .40 0 .35

Figure 4.47. Moment redistribution, numerical values over support.


4.8.8 PREDICTION OF PRESTRESS LOSSES

The prediction of losses in prestressed concretehas always been subject to uncertainty. This is dueto the high stress levels used for the prestressingsteel, the variable nature of concrete, and its pro-pensity to creep and shrink. As recently as 1975,AASHTO made a major revision to its code to pro-vide improved methods for predicting prestresslosses. The Structural Engineers Association ofCalifornia has an excellent report on creep andshrinkage control for concrete in general. The re-port concludes that special attention should begiven to material selection and proportioning. Forcreep and shrinkage calculations many Europeanengineers recommend the guidelines of the Feder-ation Internationale de la Precontrainte, ComitiEuropeen du B&on (FIP-CEB).

In simply supported structures, the ultimatecapacity is very simply analyzed by comparing inthe section of maximum moment:

The total design load moment including girderload and superimposed load (DL) and live load(LL )The ultimate bending moment of the prestressedsection M,

Depending on the governing codes and the usualpractice in various countries, this comparison maybe done in various ways:

Apply a load factor on DL and LL and a reductionfactor for materials on M,

The design computations for segmental pre-stressed concrete bridges are very involved for theconstruction phase. Every time a segment is addedor a tendon is tensioned, the structure changes,and it must be reanalyzed. As the segment ages, theconcrete and prestressing steel creep, shrink, andrelax. Thus, each segment has its own life historyand an elastic modulus that depends upon the ageand composition. To accurately compute all ofthese effects by hand, throughout the life of thestructure, would be very difficult, particularlyduring the construction phase. Comprehensivecomputer programs such as “BC” (Bridge Con-struction) and others have been recently developedand are now available to aid the design engineer.

Apply a single factor K on (DL + LL) and comparewith M,Apply a single factor K on LL only and compare DL+ KLL with M,

In all cases, the designer must first compute theultimate capacity of the section considering theconcrete dimensions and characteristics of pre-stressing tendons (and possible conventional rein-forcement). From previous studies it may be shownthat the ultimate moment of a prestressed section iscomputed very simply by considering a dimen-sionless factor called the weight percentage of pre-stressing steel, q (see Figure 4.48).

In addition to construction analysis, these pro-grams will check the completed bridge in accor-dance with AASHTO specifications. It is possibleto revise them to satisfy other codes or loadings,such as AREA.

To account for the fact that the concrete char-acteristics are less reliable than those of the pre-stressing steel, which are well known and very con-stant, fs is usually taken equal to the guaranteedminimum tensile strength, whereas,fi is assumed tobe only 80% of the 28-day cylinder strength.

Not only are all prestress losses properly evalu-ated and taken into account, but redistributions ofmoments due to concrete creep and steel relaxa-tion are automatically incorporated in the designanalysis.

4.9 Ultimate Bending Capacity ofLongitudinal Members

Considering now the case ofsegmental super-structures, which are most generally continuousstructures, one may take the conventional ap-proach of considering the various sections of themember (for example, support section andmidspan sections in the various spans) as inde-pendent from one another in much the same wayas for simple members. Such simplification over-looks the capacity of the redundant structure toredistribute, internally, the applied loads, whichseems to be a conservative assumption.

Basically, the design approach of segmental In fact, it is not always as conservative and safe asbridges is one of service load. It is important, how- it looks, as will be shown by an example computedever, not to lose sight of the ultimate behavior of numerically for a typical span of the Rio Niteroithe structure to ensure that safety is obtained Bridge. For such a span the design moments are asthroughout. follows (in foot-kips x 1000):

Ultimate Bending Capacity of Longitudinal Members 191

As prestressingsteel

FIGURE 4.48. Ultimate moment of a prestressed section. (1) Dimensionless coefficient,q’ = (A,lbd) f&/f:), whereA, = area of prestressing steel, 6 = width of section,d = effectivedepth of section (distance between centroid of prestress and extreme compression fiber),f,i = ultimate tensile strength of prestressing steel,fi = ultimate compressive strength ofconcrete. (2) Value of ultimate moment: for q’ < 0.07, M, = 0.96A&d; for 0.07 < q’ <0.50, M, = (1 - O.Gq’)A,J-?‘d.

Support Midspan

Girder load 116Superimposed load 10

Total dead load (DL) 126Total live load (LL) 29

Total (DL + l.L) 155Live-load moment in simple span: 37

05-5

22-27

The ultimate moments have been computed for allsections for both positive and negative bending.The envelopes of ultimate moments are shown inFigure 4.49.

Neglecting any moment redistribution, the situ-ation would be the following over the support andat midspan:

Section

M o m e n t Support Midspan

IV”D LL LM, =

or .M, =

256 79126 529 22

1.65(DL + LL) 2.93(DL + LL)DL + 4.5 LL DL + 3.4LL

The picture is substantially different when lookingat redistribution due to plastic hinges. Assumingan overall increase of both dead and live loadsimultaneously (loading arrangement A), we ob-

tain the overall safety factor by comparing the sumof ult imate moments over the support and atmidspan:

256 + 79 = 335

and the sum of simple span moment due to DL andLL:

DL: 126 + 5 = 131LL 37

Total iii

The overall safety factor is thus:

K = $ = 2.0-

approximately 20% higher than for the supportsection considered alone. In fact, it is more impor-tant and more realistic to consider only an increaseof the live load, which is the only variable factor inthe structure. Proceeding as before, the safetyfactor on LL only would be:

K = 335 - 13’ = j j

37 .

However, this is not the actual safety factor of thestructure, because there exists a more aggressiveloading arrangement than that where all spans arelive loaded. In the case where the live load isapplied to only every second span [arrangement

r


2 6 0 2 6 0 2 6 0 I I -*!-

I IElevation

I I

I I Live-load arrangement (A)!

I Support ! , support I I

I II I 1 i i-----f

FIGURE 4.49. Ultimate bending capacity of’ a continuous deck.

(b) in Figure 4.491, the first plastic hinge will ap-pear at the center of the unloaded spans with anegative moment (tension at the top fiber) and thesupport moment reaches the following limitingvalue:

Ultimate negative moment at midspan: 3 8

Actual dead-load moment in simple span:126 + 5 = 131

1 6 9

This value of 169 is substantially lower than the ul-timate moment at that support section consideredby itself (M, = 256).

The failure appears when the second plastichinge appears at the center of the loaded spanunder positive moment (tension at the bottomfiber). The limiting value of the safety factor K issuch that:

169 + 79 = 131 + K . 37 and K = 3.2

In such structures a very important characteristicmust be emphasized. At the time of ultimate loadfailure, due either to negative moment in the un-loaded spans or positive moments in the loadedspans, the maximum moment over the support hasonly slightly increased above the value at designload ( 169 against 155) and is far below the ultimatemoment of the section (256). Three interestingconsequences may be derived from this fact:

1. Because the overall safety of the structure isnot dependent upon the ultimate momentnear the supports, it is not necessary to dimen-sion the bottom flange of the concrete sectionin this area to balance the ultimate capacity ofthe prestressing tendons.

2. The global safety factor of the structure de-pends directly on the capacity of the sectionsnear midspan for both positive and negativemoments. The capacity for positive moments isgiven by the continuity tendons placed in the

Shear and Design of Cross Section 193

bottom flange for service-load conditions. Thecapacity for negative moments depends uponthe tendons placed at the top flange level tooverlap the cantilever tendons of the two indi-iidual cantilever arms. The magnitude of thisoverlap prestress does not appear as a criticalfactor when designing the structure for serviceloads, yet it plays an important role in the ulti-mate behavior of the structure.

3. At ultimate load, it was shown that the areas ofthe members close to the supports are sub-jected to moments only slightly in excess of de-sign load moments and in most cases belowcracking moments. No early failure due tocombined shear and bending is anticipated.

In long structures where hinges and expansionjoints are provided in certain spans, the same de-sign principles may be applied to analyze the ulti-mate capacity. Hinges represent singular pointsthrough which the moment diagrams must go re-gardless of the loading arrangement under consid-eration. It was found that the optimum location ofthe hinge with regard to ultimate safety is some-what different from the location allowing the bestcontrol of long-term deflections. It may be ofinterest therefore to move the hinge slightly to-ward the center of the span, which has a furtheradvantage of simplifying construction.

4.10 Shear and Design of Cross Section

4.10.1 I,\‘TRODUCTIO,V

Designing prestressed concrete members for shearrepresents a challenging task for the engineer, be-cause there are many differences of opinion andlarge variations in the requirements of the variouscodes. In particular t h e AC1 c o d e a n d t h eAASHTO specifications differ in several waysfrom the FIP-CEB and other European codes.

It is common practice in many countries to de-sign reinforced concrete and prestressed concretemembers for shear by allowing the concrete tocarry a proportion of the shear loads while stirrups(formerly in conjunction with inclined bars) carrythe rest. A complete agreement has not yet beenreached on this aspect of design for shear:

The French codes (CCBA, for example) allownothing to be taken by the concrete and the totalshear to be carried by the transverse steel, which iscertainly an overconservative approach. Obviously,

the beneficial effect of longitudinal compression(either in columns subject to axial load or in pre-stressed members) is taken into account.The recent FIP-CEB code allows some proportionof the shear to be carried by the concrete.AC1 code allows a larger proportion of shear tobe carried by the concrete with a consequent sav-ings in stirrup requirements.

4.102 SHEAR TESTS OF REINFORCEDCONCRETE BEAMS

Tests were recently carried out in France in orderto increase the knowledge of this phenomenon,both on simply reinforced concrete and on pre-stressed members.4 Static tests on reinforced con-crete I beams showed that the steel stress in stir-rups increases linearly with the load and is threetimes smaller than it would be if the concrete car-ried no shear, Figure 4.50. In this respect, all codesare fully justified in taking the concrete into ac-count as a shear-carrying component.

However, dynamic testing on the same beamsshowed a very different behavior. A cyclic load wasapplied between one-third and two-thirds of theultimate static load for one million cycles, where-upon the beam was statically tested to failure, Fig-ure 4.51. Before cracking, the elastic behavior ofthe homogeneous member kept the steel stress inthe stirrups very low. However, before 10,000 cy-cles, a crack pattern had appeared that remainedto the end of the test and became more and morepronounced with a continuous increase of the in-clined crack width. Crack opening reached &r in.(1.5 mm) at the end of the dynamic test. Mostprobably stirrup rupture took place about 600,000cycles, although the ultimate static capacity of the

FIGURE 4.50. Static test of reinforced concrete I-beam steel stress in stirrups.


lbre de cycles~ (log N) ,

1, +aa 106

FIGURE 4.51. Dynamic test of reinforced concreteI-beam web cracking and variation of steel stress in stir-rups.

beam after dynamic testing was substantially thesame as for the other beams, which were testedonly under static loads. Such tests show that theconventional approach of designing web rein-forcement for static loading with a large part of theshear carried by the concrete may not provide ade-quate safety in the actual structures as soon as webcracking is allowed to develop.

4.103 DIFFICULTIES IN ACTUAL STRUCTURES

Another source of information is afforded by thebehavior of existing structures. Fortunately,examples of difficulties imputable to shear in can-tilever box girder bridges are scarce. The authorsare aware of only two such contemporary exam-ples, which are summarized here for the benefit ofthe design engineer.

The first example relates to a box girder bridgedeck constructed by incremental launching and

shown in Figure 4.52. Permanent prestress wasachieved by straight tendons placed in the top andbottom flanges, as required by the distribution ofmoments. During launching an additional uniformprestress was applied to the constant-depth singlebox section, which produced an average compres-sive stress of 520 psi (3.60 MPa). Near each pierthere was a vertical prestress designed to reduceweb diagonal stresses to allowable values.

During launching a diagonal crack appearedthrough both webs between the blisters provided inthe box for anchorage of top and bottom prestress.The corresponding shear stress was 380 psi (2.67MPa), and there was no vertical prestress in thatzone. The principal tensile stress at the centroid ofthe section was 200 psi (1.40 MPa), which is farbelow the cracking strength of plain concrete. Infact, the webs of the box section were subjected toadditional tensile stresses due to the distribution ofthe large concentrated forces of the top and bot-tom prestress. The truss analogy shown in Figure4.52 indicates clearly that such tensile stresses aresuperimposed on the normal shear and diagonalstresses due to the applied dead load and maytherefore produce cracking. This could have beenprevented by extending the vertical prestress in thewebs further out toward midspan.

The second example concerns a cast-in-placevariable-depth double box girder bridge withmaximum span lengths of 400 ft. Because thebridge was subsequently intended to carrymonorail pylons, two intermediate diaphragmswere provided at the one-third and two-thirdspoints of each span, as shown in Figure 4.53. Pre-stress was applied by straight tendons in the topand bottom flanges and vertical prestress in thewebs to control shear stresses. Diagonal crackingwas observed in the center web only near the in-termediate diaphragms with a maximum crackopening of 0.02 in. (0.6 mm). Repair was easily ac-complished by adding vertical prestress aftergrouting the cracks.

A complete investigation of the problems en-countered revealed that cracking was the result ofthe superposition of several adverse effects, anyone of which was almost harmless if consideredseparately: (1) The computation of shear stressesfailed to take into account the adverse effect (usu-ally neglected) of the vertical component of con-tinuity prestress in the bottom flange of a girderwith variable height. (2) The distribution of shearstresses between the center and side webs wasmade under the assumption that shear stresseswere equal in all three webs. In fact the center web


,,i:‘,: t:“:“, \ , AI’ NO VERTICAL PRESTRESS IN THAT ZONETOP PRESTRESS

/

TYPICAL tIAlF (ROSS SKTlOIi A- AFIGURE 4.52. Example of web cracking under application of’ high prestress forces.

f

FIGURE 4.53. Example of web cracking in a 400 ft span. (a) Typical crosssection. (6) Partial longitudinal section.

carries a larger proportion of’ the load, and shear Present design codes do not provide a consistentstresses were underestimated for this web. (3) The margin of safety against web cracking when verti-vertical web prestress was partially lost into the in- cal prestress is used. This margin decreasestermediate diaphragms, and the actual vertical significantly when the amount of vertical prestresscompressive stress was lower than assumed. (4) increases. In the present French code, the safety


factor against web cracking is 2 when no verticalprestress is used and only 1.3 for a vertical pre-stress of400 psi. (5) At present, vertical prestress isusually applied with short threaded bars, and evenwhen equipped with a fine thread they are notcompletely reliable unless special precautions aretaken under close supervision. Even a small anchorset significantly reduces the prestress load, and it isnot unlikely that the actual prestress load is onlkthree-fourths or even two-thirds of the theoreticalprestress.

It should, however, be emphasized that thedifficulties mentioned above have led to progressin this field, and the increase in knowledge has en-sured that these examples remain rare exceptions.Practically all existing box girder bridges have per-formed exceptionally well under the effects ofshear loads and torsional moments.

The essential aspects of this important problemare:

Dimensioning of the concrete section particularlyin terms of web thickness

Design of transverse and/or vertical prestress andof conventional reinforcement

The twvo major considerations are:

At the design stage (or, in modern code language,serviceability limit state) prevent or control crack-ing so as to avoid corrosion and fatigue of rein-forcement.

c\t the ultimate stage (or load factor design conceptstate or ultimate limit state) provide adequatesafetv.

For the box sections used in cantilever bridges thebehavior under shear must be investigated:

In the webs.

At the connections between web and top flange (in-cluding the outside cantilevers) and web and bot-tom flange. Figures 4.54 and 4.55 show a suggestedmethod to compute shear loads and shear stresses.

Modern computer programs analyze the boxgirder cross sections perpendicular to the neutralaxis and take into account all loads projected onthe neutral axis and the section. Equivalent results

FIGURE 4.54. Computation of net applied ~IGII-load. (0) \Terrical comporicrit of’ pr-esrr.css. (h) k:f fvc t 01inclined bottom flange (Resal effec-t). (0 Net \hr;rt- ~OI-cc.Shear f’orce due to applied loada = I.: dcdrrct \cr-tic alcomponent of‘dr-aped tendons = - 1 P 5irr a,; aclcl \-erti-cdl component of continuitv tendons = * 2 t’ 4irr a?: tic-duct Red effect = - f,v.tlB tan p: total ih ner appliedshear t’k~ = I’,,.

are obtained bv considering stresses on sectionsperpendicular to the top flange (\vhich is usuallythe orientation of joints betlveen segmenta) andprojecting the loads on the section for determiningshear stresses. The total net shear force is the sum.of the following terms:

Shear force due to applied loads.

Reduction due to vertical component of drapedtendons where used.

Increase due to inclination ofcontinuitv tendons inthe bottom flange for variable-depth girders.

Reduction due to the inclined principal compres-sive stresses in the bottom flange (usuallv called theResal effect after the engineer who fi;st studiedmembers of variable depth). Because the directionof the principal stresses in the web is not fullv de-termined, it is usual to neglect the added reductionof shear force derived from web stresses.

Shear stresses may further be computed fromshear force and torsion r;loment using the conven-tional elastic methoils.

Tests have shown that the presence of drapedtendon ducts in the webs, even if grouted after ten-sioning, changes the distribution of’ shear stresses.To take this effect into account, it is suggested tocompute all shear stresses using a net web thicknessthat is the actual thickness minus one-half the duct


t

b

b’ Gross web thickness

d diameter of duct

(a)

FIGURE 4.55. Computation of shear stress. Typical box section:net web thickness = h = b’ - Id; shear stress due to shear force V, netapplied shear load = v = V,;Q/[(Xb).I], where Q = statical moment atcentroid, b = net web thickness, I = gross moment of inertia, V,, = netapplied shear load; shear stress due to the torsion moment = v =CI(P.b.3, where C = torsion moment, b = net web thickness, S = areaof the middle closed box. Note: check the shear stress at centroid level.

diameter. Ducts for vertical prestress need not betaken into account because they are smaller andparallel to the vertical stirrups, which compensatesfor the possible small effect of the prestress ducts.

Web-thickness dimensioning depends upon themagnitude of shear stress in relation to the state ofcompressive stress. In the case of monoaxial com-pression (only longitudinal prestress and no verti-cal prestress) the diagonal principal tensile stressmust be below a certain limit to insure a properand homogeneous margin of safety against webcracking with its resulting long-term damaging ef-fects. Figure 4.56 suggests numerical values basedon the latest state of the art that are believed to berealistic and safe. Numerical values for.allowableshear stresses under design loads are given in Fig-ures 4.5’7 and 4.58 for 5000 and 6000 psi concrete.

Web thickness must therefore be selected in thevarious sections along the span to keep shearstresses within such allowable values. It may bethat construction requirements or other factorsmake it desirable to accept higher shear stresses.It is necessary in this case to use vertical prestressto create a state of biaxial compression. Figure4.566 indicates the corresponding procedure.The vertical compressive stress must be at least 2.5times the excess of shear stress above the valuefor monoaxial compression.

When vertical prestress is used, the beneficial ef-fect of increasing the length of the horizontal com-ponent of the potential crack in the web created by

the horizontal compression due to prestress is par-tially lost. In fact, if both horizontal and verticalcompressive stresses are equal,f, = fU, the direc-tion of the principal stress is given by /3 = 45” as in

Y

fx v ,‘p fx-'\u-I t-

7

(a)

q1;�1 -&l�u(b)

FIGURE 4.56. Allowable shear stress for mono- andbiaxial compression in box girders. (a) Monoaxial com-pression: allowable shear stress = v = 0.05f:. + 0.2Of,;corresponding diagonal tension = fP given by v2 = fPcfs +f,). (6) Biaxial compression: allowable shear stress = zl =0.05f:. + 0.2Of, + 0.4Of,; corresponding diagonal ten-sion = fp given by v’ = cfs +f,) (fU +fP).


FIGURE 4.57. r\llo\<able shear stresses forf:. = 5000psi.

FIGURE 4.58. Allowable shear stresses forf:. = 6000psi.

ordinary reinforced concrete. If a higher verticalstress is used, a crack with p > 45” could develop,with a *consequent reduction of the horizontallength over which concrete and reinforcementmust carry the total shear. To prevent such a situa-tion, it is deemed preferable to use a vertical com-pressive stress not greater than the longitudinalcompressive stress, fu < fz.

Finally, considering present knowledge on thebehavior of prestressed concrete beams under highshear stresses, it is not recommended that shear

stresses higher than a limiting value of lo* beaccepted prior to careful investigation based onspecific experimental research.

In this respect, a very interesting case arose forthe cons t ruc t ion o f t he Bro tonne Viaduc t i nFrance (described in Chapter 9), where an excep-tionally long span called for minimum weight andconsequently high concrete stresses. The mostcritical condition for shear stresses developed inthe 8 in. (0.20 m) webs near the piers of the ap-proach spans, where a maximum shear stress of640 psi (4.5 MPa) was accepted together with anunusually low longitudinal compression stress of500 psi (3.45 MPa). Vertical prestress was used inthis case. The chart for a 6000 psi concrete, Figure4.58, would give:

In monoaxial state withf, = 500 psi, V = 400 psi.

In biaxial state withf, = 550 psi, V = 620 psi, whichis substantially equal to the actual shear stress of640 psi.

A test was conducted to study the behavior of theprecast prestressed web panels in the normal de-sign load stage and up to failure, Figure 4.59. Re-sults are shown in Figure 4.60. The ultimatecapacity of the web was very large and probably farin excess of the needs. It is believed that web

PLAN V IEW

TRANSVERSE SECTION

FIGURE 4.59. Brotonne Viaduct, test set-up for pre-cast web panels.

Strrssrs at &sign stug~ (approach viaduct):

Horizontal compressive stressVertical compressive stressShear stress

Joints Between Match-Cast Segments 199

same allowable values as set forth previously forthe webs and that a proper amount of reinforcingsteel crosses each section.500 psi

550 psi640 psi

Rrsulb of test at rufduw:840x 1.3

Normal L o a d 630 t 630Ultimate shear 84o’tHorizontal compressive stressVertical compressive stressShear stress (elastic theory)

uniform

1650 psi580 psi

3300 psi2200 psi

This leads to the design of transverse reinforce-ment in the cross section to resist shear stresses.According to the provisions of the AC1 Code andthe AASHTO specifications, the web shear steelrequirements are controlled by the ultimate stage.The net ultimate shear force is given by the fol-lowing formula, based on the current partial loadfactors:

.JoinI destroyed and multiple keys shearedoff. Panels intact.

FIGURE 4.60. Brotonne Viaduct, results of precast\\,eb panel tests.

cracking control can be obtained only by properstress limits at the design load level.

When designing longitudinal bridge membersfor shear, another important factor remains to beconsidered, which has sometimes been overlookedt& inexperienced designers. It concerns longitudi-nal shear stresses developing between the webs andthe top and bottom flanges as shown in Figure4.6 1. When web stresses have been verified at thelevel of the centroid, it is not necessary to make adetailed study at other points of the web [such aslevels (d) and (e)], although the principal tensilestress near the pier may be slightly higher at point(d) than at the center of gravity. On the otherhand, to keep the integrity of the box girder, it isverv important to verify that shear and diagonalstresses in sections (a), (b), and (c) are within the

/ ///

FIGURE 4.61. Longitudinal shear between web andflanges.

V, = 1.3OV,,, + 2.17V,, + V,

w h e r e V, =VDL =

VLL =

VP =

net shear force at ultimate stage,actual shear force due to the effectof all dead loads, including the re-duction due to variable depth whereapplicable,shear force due to live loads in-cluding impact,unfactored vertical component ofprestress where applicable.

Effects of temperature gradients and volumechanges are usually small in terms of shear loadand may be neglected except in rigid frames. Onthe contrary, shear due to moment redistributionand secondary effects of continuity prestress mustbe included. A partial safety factor on materialproperties is applied to the ultimate load state.

4.11 Joints Between Match-Cast Segments

Joints between match-cast segments are usuallyfilled with a thin layer of epoxy to carry normaland shear stresses across the joint. In the earlystructures, a single key was provided in each web ofthe box girder to obtain the same relative positionbetween segments in the casting yard and in thestructure after transportation and placing. Thiskey was also used to transfer the shear stressesacross the joint before polymerization of theepoxy, which has substantially no shear strengthbefore hardening. Figure 4.62 summarizes theforce system in relation to a typical segment bothduring erection and in the completed structure.

Provisional assembly of a new segment to thepreviously completed part of the structure is usu-ally achieved by stressing top (and sometimes bot-tom) longitudinal tendons, which induce forces F,(and F2). The resultant F of F, + F2 resolves withthe segment weight W into a resultant R. The verti-cal component of R can be balanced only by a reac-


FIGURE 4.62. Typical segment in relation to the force system. (0) Provisional assemblyof segment(s). (b) Segment(s) in the finished structure.

tion such as R, given by the inclined face of the key,while the balance of the normal force is R, whichproduces a distribution of longitudinal compres-sive stresses. In the finished structure, all normaland shear stresses are naturally carried throughthe joints by the epoxy material, which has com-pressive and shear strengths in excess of the seg-ment concrete.

A series of interesting tests were performed forthe construction of the Rio-Niteroi Bridge in Brazilto verify the structural behavior of epoxy jointsbetween match-cast segments. A l-to-6 scale modelwas built and tested to represent a typical deckspan near the support and the correspondingseven segments as shown in Figure 4.63.

ELEVATION

A crack pattern developed in the web when thetest load was increased above design load, as shownin Figure 4.64. The epoxy joints had no influenceon the continuity of the web cracks, and the be-havior of the segmental structure up to ultimatewas exactly the same as that of a monolithic struc-ture. Failure occurred for concrete web crushingwhen the steel stress in the stirrups reached theyield point. The corresponding shear stress was970 psi (6.8 MPa) for a mean concrete cylinderstrength of 4200 psi (29.5 MPa).

The first bending crack had previously occurredfor a load equal to 93 percent of the computedcracking load, assuming a tensile bending strengthof 550 psi (3.9 MPa). Other tests were performed

DETAIL OF JOINT

FIGURE 4.63. Rio-Niteroi Bridge, partial elevation and joint detail.

Joints Between Match-Cast Segments 201

FIGURE 4.64. Rio-h’itcroi Bridge. ~vel) crack pattern at ultimate in model test.

in order to study the transfer of diagonal principalcompressive stresses across the segment joints asshown in Figure 4.65. Prismatic test specimens

I

fdPRlSMATlC PRISMATIC

WITH KEYS

PI I

P

Pt 1

P

(b)FIGURE 4.65. Rio-Niteroi Bridge, test specimens forweb. (a) Crack pattern in web and related test specimen.(b) Actual test specimens.

were prepared, some with and some without shearkeys across the joint, and tested for various valuesof p, the angle between the principal stress and theneutral axis of the girder. In the case of the RioNiteroi Bridge the value of /3 is between 30 and35”. For a reinforced concrete structure p = 45”.

A preliminary test showed that the epoxy jointhad an e f f i c i ency o f 0 .92 a s compared t o amonolithic specimen with no joint (ratio betweenthe ultimate load P on the prismatic specimen withan epoxy joint and with a monolith specimen). Forvarious directions of the joint the results are asfollows:

P 0” 15” 30” 45” 60”Efficiency 0.94 0.92 0.98 0.95 0.70

It can be seen that for values of p smaller than 45”(which covers the entire field of prestressed con-crete members) the compressive strength is hardlyaffected by the presence of the inclined joint. Allthese tests confirmed earlier experimental studiesto show that epoxy joints are safe provided thatproper material quality together with proper mix-ing and application procedures are constantly ob-tained.

Several early incidents in France, and some morerecently in the United States, have shown thatthese conditions are not always achieired. The logi-cal step in the development and improvement ofepoxy joints was therefore to relieve the epoxy of

202 Design of Segmental Bri&es

any structural function. The multiple-key (orcastellated-joint) design embodies this concept andprovides for simplicity, safety, and cost savings.Webs and flanges of the box section are providedwith a large number of small interlocking keys de-signed to carry all stresses across the joint with nostructural assistance from the resin. Figure 4.66shows the comparison between the structural be-havior of an early joint with a single web key and ajoint with multiple keys, assuming that the epoxyresin has improperly set and hardened. It is nowrecommended that multiple keys be used in all pre-cast segmental projects, as shown in Figure 4.67.With the current dimensions used for depth andheight of multiple keys, the overall capacity of thejoint is far in excess of the required minimum totransfer diagonal stresses safely up to the ultimateload state.

Continuous transferof shear stresses

(It) Cb)

FIGURE 4.66. Joint between match-cast segments,comparison between single- and multiple-key concepts.

FIGURE 4.67. Precast segment with multiple keys.

4.12 Design of Superstructure Cross Section

The typical cross section of a box girder deck is aclosed frame subjected to the following loads, Fig-ure 4.68:

Girder weight of the various components (top andbottom flanges, webs)

Superimposed loads essentially applied to the topflange (barrier, curbs and pavement) and some-times to the bottom flange, as when utilities are in-stalled in the box girder

Live loads applied on the deck slab

A typical box girder element limited by two parallelcross sections, Figure 4.686, is in equilibrium be-cause the applied loads are balanced by the dif-ference between shear stresses at the two limitingsections. To design the typical cross section the as-sumption is usually made that the shape of the sec-tion remains unchanged and that the closed framemay be designed as resting on immovable supportssuch as A and B. Bending moments are created inthe various sections of the frame due to the appliedloads. Maximum moments occur in the deck slabdue to live loads in sections such as (a), (b), and (f).

Cd)FIGURE 4.68. Design of deck cross section. (a) Typi-cal loading on cross section. (b) Free-body diagram.

Special Problems in Superstructure Design 203

Because the webs are usually much stiffer than theflanges and the side-deck slab cantilevers and thecenter-deck slab between webs are built into thewebs, most of the deck-slab moments are trans-ferred to the web, with a maximum value in section(d) at the connection between web and top flange.In bridges where transverse or vertical prestress orboth are used, the design of the deck cross sectionis not greatlv affected by the fact that moments andnormal forces computed in the frame superimposetheir effects on the shear stresses due to longitudi-nal bending mentioned in Section 4.10.

The case is more critical when only conventionaltransverse reinforcing steel is used in both flangesand webs. A common method, based on experi-ence, is to compute the steel area required oneither face at critical sections such as (a) through(e), shown in Figure 4.68, for the following:

1. Shear stresses in the longitudinal members.2 . Transverse bending of the frame.

The minimum amount of steel should not be lessthan the larger of the following:

item 1 plus one-half of item 2,item 2 plus one-half- of item 1, or0.7 times the sum of item 1 and item 2.

4.13 Special Problems in Superstructure Design

All design aspects covered in the preceding sec-, tions pertain to the design of deck members for

bending and shear regardless of the local problemsencountered over the piers or abutments and atintermediate expansion joints when required. Thissection will now deal with such local problems,which are of great practical importance.

4.13.1 DIAPHRAGMS

It was mentioned in Section 4.6 that the combinedcapacities of the deck slab in bending and the boxgirder in torsion allow a very satisfactory trans-verse distribution of live loads between girders inthe case of multiple box girder decks. It has there-fore been common practice to eliminate all trans-verse diaphragms between box girders except overthe abutments. Diaphragms inside the box sectionare still required over the intermediate piers inmost projects.

4.13.2 SUPERSTRUCTURE OVER PIERS

The simplest case is exemplified in Figure 4.69,where a deck of constant depth rests upon the piercap with bearings located under the web of the boxgirder. The reaction is transferred directly fromthe web to the bearings, and there is need only fora simple inside diaphragm designed to transfer theshear stresses, due to possible torsion moments, tothe substructure. A more complicated situationarises when the bearings are offset with regard tothe webs, Figure 4.70. Reinforcing and possiblyprestressing must be provided in the cross sectionimmediately above the pier to fullfill the followingfunctions:

Suspend all shear stresses carried by the web underpoint A, where a 45” line starting at the bearingedge intersects the web centerline (hatched area inthe shear diagram).Balance the moment (R * d) induced by the bear-ing offset.

Looking at other schemes, we find that decks ofvariable depth pose several challenging problems.Figure 4.71 shows an elevation of a box girderresting on twin bearings designed to improve therigidity of the pier-to-deck connection and con-sequently reduce the bending moments in thedeck, which will be described in greater detail inChapter 5.

When the loading arrangement is symmetrical inthe two adjacent spans, the transfer of the deckreaction into the piers through the four bearings isjust as simple as for the case shown in Figure 4.69.Matters look very difficult for an unsymmetricalloading condition either in the completed struc-ture, Figure 4.71, or during construction, Figure4.72. Let us assume that the total deck reaction istransferred to the pier through one line of bearingsonly (for example, R, in Figure 4.71, for an excessof load in the left span). The compression C, car-ried by the bottom flange at the right is no longerbalanced by the corresponding reaction R,, and anabrupt change in the system of internal forces re-sults in a large vertical tensile force T,, which has tobe suspended on the total width of the box sectionby special reinforcement or prestress. In long-spanstructures, these local effects are of no small mag-nitude. Taking the example of a 40 ft (12 m) widebox with a 20 ft (6 m) wide bottom flange and aspan of 300 ft (90 m), the load carried by the bot-tom flange will probably be around 3000 t (2720mt) and the angle change above the right bearing


t

~~~~ t-

bear ings

SECTION A-A SECTION c-c

FIGURE 4.69. Pier segment for deck of constant depth and simple support.

FIGURE 4.70. Deck over piers with offset bearings.

about 10 percent. The corresponding unbalancedload is therefore 300 t (272 mt), and this is morethan enough to split the pier segment along thesection between the web and the bottom flange ifproper consideration has not been given to theproblem with respect to design and detailing.

The situation may be even more critical duringconstruction, Figure 4.72, if the unbalanced mo-

ment induces uplift in one of the two bearings. Theload of the anchor rods (2) has to be added to theunbalanced load resulting from the angle changeof the bottom flange.

The diaphragm systems shown in Figures 4.71and 4.72 are of the A type where both inclineddiaphragm walls intersect at the top flange level.Any unsymmetrical moment that produces a ten-sion force in the top flange T and a compressionforce in the bottom flange may thus be balanced bynormal loads such as F, and C,, Figure 4.7 1, withno secondary bending. In this respect, then, it is asatisfactory scheme. Detailing may, however, bedifficult because of the concentration of rein-forcement or prestress tendon anchors in the topflange area, which usually is already overcrowdedwith longitudinal tendon ducts. A simple and morepractical design, although less satisfactory from atheoretical point of view, is to provide verticaldiaphragms above the bearings. This is the logicalchoice when the deck is rigidly connected with a

Dejections of Cantilever Bridges and Camber Design 205

4.13.4 EXPANSION JOINT AND HINGE SEGMENT

Neoprene bearings -

I?

FIGURE 4.71. Deck of variable depth, permanentdeck-to-pie]- bearing arrangement.

box pier and where the pier walls are continued inthe deck, as shown in Figure 4.73. Here again the

. transfer of all symmetrical loads between deck andpier is simple, and design difficulties arise for un-symmetrical loading. .4t the connecting points Aand R, Figure 4.73, between the top flange and thevertical diaphragms, the part of the top flange ten-sion load T such as T, induces into the diaphragmanother tension load T,, and both loads result in anunbalanced diagonal component T,, which must beresisted both by the webs and bv special provisionssuch as stiffening beams.

4.13.3 E.VD ABUTME,VTS

A special segment will be provided at both ends ofthe bridge deck with a solid diaphragm to transfertorsional stresses to the bearings, as shown in Fig-ure 4.74. The expansion .joint is, therefore, ade-quately supported by the end diaphragm on oneside and the abutment wall on the other side.

The expansion joints required at intermediatepoints in very long structures need a special seg-ment to transfer the reaction between the two sidesof the deck. When the expansion joint is locatedclose to the point of contraflexure there is no pro-vision for any uplift force, even with a load factoron the live loading.

The hinge segment is therefore made up of twohalf-segments, as shown in Figure 4.75:

The bearing half (reference A), which is connectedby prestress to the shorter part of the spanThe carried half (reference B), connected by pre-stress to the longer part of the span

Measures are taken to continue cantilever con-struction through the hinge segment until closureis achieved at midspan; see Section 4.8.6.

Inclined diaphragms provide an efficient way tosuspend or transfer the reaction through thebearings into the flanges and webs on both sides ofthe box section, Figure 4.75.One of the largest structures incorporating a hingesegment of this type is the Saint Cloud Bridge, de-scribed in Section 3.12. A typical detail of this seg-ment is shown in Figure 4.76.

4.14 Dejections of Cantilever Bridges andCamber Design

Each cantilever arm consists of several segments,fabricated, installed, and loaded at different pointsin time. It is important therefore to predict accu-rately the deflection curves of the various cantile-vers so as to provide adequate camber either in thefabrication plant for precast segmental construc-tion or for adequate adjustment of the form travel-ers for cast-in-place construction.

When the structure is statically determinate, thecantilever arm deflections are due to:

The concrete girder weightThe weight of the travelers or the segment placingequipmentThe cantilever prestress

After continuity between individual cantilevers isachieved, the structure becomes statically indeter-minate and continues to undergo additionaldeflections for the following reasons:


e

FIGURE 4.72. Temporarv pier and deck connection.

Continuity prestressRemoval of travelers or segment placing equip-mentRemoval of provisional supports and release ofdeck to pier connectionsPlacing of superimposed loads

Subsequent long-term deflections due to con-crete creep and prestress losses will also take place.Compensation for the following three types ofdeflections must be provided for by adequatecamber or adjustment:

1. Cantilever arms.2. Short-term continuous deck3. Long-term continuous deck.

It has already been mentioned that the concretemodulus of elasticity varies both with the age at thetime of first loading and with the duration of theload (see Section 4.8.7). Deflections of types 2 and3 above are easily accommodated by changing thetheoretical longitudinal profile by the corre-sponding amount in each section to offset exactlyall future deflections. A more delicate problem is to

Dejections of Cantilever Bridges and Camber Design 207

FIGURE 4.73. Pier segment with vertical diaphragms.

accurately predict and adequately follow thedeflections of the individual cantilever arms duringconstruction. It is necessary to analyze each con-struction stage and to determine the deflectioncurve of the successive cantilever arms as construc-tion proceeds, step by step. A simple case with afive-segment cantilever is shown in Figure 4.77.The broken line represents the envelope of thevarious deflection curves or the space trajectoryfollowed by the cantilever tip at each constructionstage.

By changing the relative angular positions of thevarious segments by small angles, such as -LY,,-(Y*, and so on, the cantilever should be assembledto its final length with a satisfactory longitudinalprofile as shown in Figure 4.78, for the simple caseconsidered. The practicalities of this importantproblem are covered in Sections 11.4 and 11.6.

It

50 2.2 5 bSECTION AmA S E C T I O N c-c

I

, 2.25 I-? +

SECTION B-BFIGURE 4.74. Outline of end segment over abut-m e n t .


3.43

SECTIOS A-A SECTION C-C

6 30

bl.CTIOS B-B

FIGURE 4.75. Hinge segment \vith espmsion joint.

C O U P E A . A

PB

20.40

C O U P E B . B & ELEVATION

A1 4.00r J 4.00

FIGURE 4.76. Saint CIOL~CI Br-idge, hinge segment \cith expansion joint

It is interesting to compare the relative impor- culational assumptions given in Figure 4.79 indi-tance of deflections and camber for cast-in-place cate that in most cases the difference would beand precast construction. Figure 4.79 shows values even more significant if a cast-in-place cvcle of lessfor an actual structure, where computations have than one week were emploved and if precast seg-been made for the two different methods. The cal- ments were stored for more than two weeks. Hove-

.

ENVELOPE OFDE’YECTION CURVES

Segments N’

FIGURE 4.78. Choice and control of camber.

FIGURE 4.77. Deflections of a typical cantilever.

tCl SUPPORT 45.00 CROWN_z c

I /ASSUMPTIONS :

Id+5 d+b de7 i d*8 ~ d+9 d+lO d+ll dtl2

db24 d+24 d+25 dt25 ~ de26 d+26 d+27 ‘dc27/ I

I

II

1 I I

PRECAST : Casting : one segment per day_ _ _ _ _ _ _ _ _Placing : two segments par daySegments at least 2 weeks old for placmg

CAST-IN-PLACE :, -----_---_______Casting : one segment per weekP r e s t r e s s i n g : 30 days after casting

1

E

2 L-.-

in

g

E3 Y- LL

x

4- -

-L-

FIGURE 4.79. Comparison of deflections between precast and cast in place structures.

209


ever, one would normally expect a cast-in-placecantilever arm to resist deflections two or threetimes greater than the precast equivalent.

4.15 Fatigue in Segmental Bridges

Basically, prestressed concrete resists dynamic andcyclic loadings very well. Eugene Freyssinet dem-onstrated this fact fifty years ago. He tested twoidentical telegraph poles under dynamic loading.One was of reinforced concrete and the other ofprestressed concrete; both were designed for thesame loading conditions. The reinforced concretemember failed after a few thousand cycles, whilethe prestressed concrete member sustained thedynamic load indefinitely (several million cycles).

Fatigue in concrete itself has never been a prob-lem in any known structure, because a variation ofcompressive stress in concrete may be supportedindefinitely. When reference is made to fatigue inprestressed concrete, it is always inferred thatfatigue problems arise in the prestressing steel orconventional reinforcing steel as a result of crack-ing due either to bending or to shear. If crackingcould be avoided in prestressed concrete struc-tures, the fatigue problem would be completelyeliminated.

.6 -

4 -

2 -

Figure 4.80 shows the resistance to fatigue ofprestressing strands currently used in prestressedconcrete structures. The diagram shows the limitof stress variation causing fatigue failure versus themean stress in the prestressing steel. For conve-nience, both values are expressed as a ratio withrespect to the ultimate tensile strength. For a steelstress of 60% of the ultimate the acceptable rangeof variation is 28% of the ultimate for a number ofcycles between lo6 and 10’. Using, for example,270 ksi quality strand, this variation is therefore222,000 psi or a total range of 44,000 psi.

Because dynamic loading on a bridge is of ashort-term nature, the concrete modulus is highand the ratio between steel and concrete moduli isof the order of 5. Consequently, the maximumconcrete stress in an untracked section that wouldcause a fatigue failure would be 44,000/5 = 8800psi, a value which is probably ten times the stressvariation under design live loads in highway boxgirder bridges. An untracked prestressed concretestructure is therefore completely safe with respectto fatigue, regardless of the magnitude of liveloads. A limited amount of cracking, although con-sidered unadvisable f-rom a corrosion point ofview, is not critical if kept under control.

Tests and experience show that a grouted pre-stressing tendon can transfer bond stresses up to

Stress variationcausing fai lure

fs ? Afs

FIGURE 4.80. Resistance to fatigue of prestressing strands.

Fatigue in Segmental Bridges 211

500 psi to the surrounding concrete. Taking theexample of a typical (twelve 3 in. diameter strand)tendon with an outside diameter of 2.5 in. (64mm), a stress variation of 40,000 psi in the steelproduces a tendon force variation of 73,000 lb (33mt), and the bond development length across acrack is then 73,000/(500 x 2.5 x 7r) = 18 in. (0.46m), see Figure 4.81. The ,corresponding crackwidth l is equal to the elongation of the pre-stressing steel between points A and B with thetriangular stress diagram-that is, 40 ksi over anaverage length of 18 in., or

4 0' = EL = 26,000 x 18 = 0.028 in. (0.7 mm)

A safe crack width limit of 0.015 in. (0.4 mm) canbe accepted to eliminate the danger of fatigue inthe prestressing steel. In fact, instances of fatiguein segmental structures are extremely few and farbetween.

An isolated case has been reported of a bridge inDusseldorf, Germany, where failure occurred as aresult of fatigue of prestressing bars. The cast-in-place structure was prestressed with high-strengthbars coupled at every construction joint. After tenyears of service, a joint opened up to # in. (10 mm)and caused bar failures at the couplers. An investi-gation revealed that a bearing had frozen and pre-vented the structure from following the longitudi-nal movements due to thermal variations. Thisaccidental restraint induced high tensile stresses inthe concrete and caused cracking, which first ap-peared in the construction joints precisely wherebar couplers were located. The live-load stress levelin the prestressing steel increased from 850 psi (6

I 07./d’nw,” Jf

FIGURE 4.81. Fatigue in prestressing steel across acracked section.

MPa) for the previously untracked section to14,000 psi (96 MPa) for the cracked section andinduced failure in the bars. A recommendation wasmade as a result of this fatigue problem that coup-lers should be moved at least 16 in. (0.40 m) awayfrom the construction joints and that reinforcingsteel should be provided through the joints ifpractical. Another sensitive factor relating tofatigue in web reinforcing steel was mentioned inSection 4.10.2 for reinforced concrete test beams.No such danger would exist in prestressed con-crete if shear and diagonal stresses were keptwithin the limits that control web cracking.

In conclusion, fatigue in prestressed concrete isnot a potential danger if design and practical con-struction take into account a few simple rules:

1 . Avoid bending cracks in girders by allowing notension or only a limited amount at either topor bottom fibers for normal maximum loads,such as the combination of dead loads, pre-stressing, and design live loads including mo-ment redistribution and half the temperaturegradient.

2. Avoid web cracking by keeping diagonal ten-sile stresses within allowable limits by properweb thickness and possibly vertical prestress.

3. Design and maintain bearings and expansionjoints that allow free volume changes in decks.Temperature stresses that cannot be con-trolled can give rise to enormous forces thatmay either tear the deck apart or destroy thepiers and abutments. In this respect, elas-tomeric bearings, which work by distortion andcannot freeze, are safer than friction bearings,which are more easily affected by dust andweathering of the contact surfaces.

Insofar as crack control in segmental structuresis concerned, it is usually felt in Europe that exces-sive concrete cover over the reinforcing steel andprestress tendons does not prevent corrosion butmerely increases the crack width.3 For example,the typical 2 in. (50 mm) cover commonly used inbridge decks in the United States is considered ex-treme in Europe. The 4 in. (100 mm) cover forconcrete exposed to sea water would be a completesurprise to European engineers.

Several examples of common practice in seg-mental bridges are given as a simple comparativereference in Table 4.2.


TABLE 4.2. Concrete Cover to Reinforcing Steeland Prestress Tendons in Europe

Concrete cover(in.)

Germany1) to 21tlfFrance

11t

Description

Reinforcing steelOutside exposure, tendonsInside exposure, tendons

Transverse reinforcing steelLongitudinal reinforcingsteel or tendons(normal atmosphere)

2 Corrosive atmosphere(salt water)

Netherlandslb Reinforcing steel and tendons

(normal exposure)1;A2 to 2;R

Lightweight concreteSalt water exposure

4.16 Provisions for Future Prestressing

For larger segmental bridges, it may be necessaryto modify the prestress forces after construction.An example would be a bridge built using can-tilever construction where positive-moment (con-tinuity) tendons are added after erection. Or, asdiscussed in Section 4.8.6, some tendons may bereleased to articulate a joint. In addition to theseadjustments immediately after construction, addi-.tional prestressing may be required at a later dateto correct for unanticipated creep deflection or foradditional loads such as for a new wearing surface.In Europe on some bridges spare tendon ducts areprovided for this reason. A reasonable assumptionwould be to provide for 5 to 10% of the total pre-stress force for possible future addition.

Since the tendon anchorages for the spare ductsare inside the box girder and generally located atthe web-flange fillet, they are readily accessible. Iffuture prestressing is needed, it is only necessary toinsert the required tendon in the duct, jack it to itsdesigned load, anchor and grout it. Since all thiswork can be done inside a box girder, it is not nec-essary to interrupt traffic, and the workmen arefully protected.3

4.17 Design Example

The Houston Ship Channel Bridge now underconstruction in Texas, U.S.A., is an outstandingexample of segmental construction and represents

the longest box girder bridge in the Americas as ofthis writing. Typical dimensions were given in Sec-tion 2.14. This section will deal with some designaspects of this prestressed concrete segmentalbridge.

4.17.1 LONGITUDINAL BENDING

Each of the four identical cantilever arms is madeup of:

Ten segments 8 ft long (maximum weight 4 15kips)

Six segments 12 ft long (maximum weight 464kips)

Thirteen segments 15 ft long (maximum weight457 kips)

Longitudinal tendons are as follows:

Cantileuer t e n d o n s : 4 2 ( n i n e t e e n 0 . 6 i n . d i astrands) + 50 (twelve 0.6 in. dia). Twelve addi-tional bars used during construction are incorpo-rated in the permanent prestress system.

Continuity tendons in side spans: 20 (twelve 0.6 in.dia).

Continuity tendons in center span: 40 (twelve 0.6 in.dia).

A typical layout of the cross section was given inFigure 2.82.

The main loading combinations considered inthe design are summarized in Table 4.3. The lon-

TABLE 4.3. Houston Ship Channel Bridge, MainDesign Load Combinations

Load-ing Case Description

AllowableTension on

ExtremeFiber, Topor Bottom

(ksf)

(1) (G) + (P) + (E) 0(2) CD) + (P) + CL + 1)(3) (D) + (P) + (L + I) + l(AT) + (T) 2:(4) (D) + (I’) + t(L + I) + (AT) + (T) 25(5) CD) + (f’) + (W 25

Notations: (C) girder load, (D) total dead load includingsuperimposed dead load, (L + I) live load plus impact, (P) pre-stress, (E) construction equipment, (AT) temperature gradientof 18°F between top and bottom fiber, (T) temperature and vol-ume changes, (W) wind load on structure.Concrete strength and stresses:rC = 6000 psi = 864 ksf (42.1MPa).Basic allowable compressive stress: 0.4fi = 346 ksf (16.8MPa).

Design Example 213

gitudinal bending of the box girder has beenanalvzed using the BC program, which considersthe effects of the creep, shrinkage, and relaxationat each construction phase. Figure 4.82 shows thediagram of prestress forces due to cantilever andcontinuitv tendons at two different dates:

After completion of the structure and opening totraffic (780 days after start’of deck casting)After relaxation and creep have taken place (4000davs)

Significant values of the prestress forces are givenin ‘Table 4.4. The variation of stresses in the centerand side spans is shown in the following diagramsfor the corresponding loading cases:

Figures 4.83 and 4.84, all dead loads and prestressat top and bottom fibers

Figures 4.85 and 4.86, live load and temperaturegradient at top and bottom fibers

It is easily shown from these diagrams that allstresses in the various sections are kept withinthe allowable values mentioned in Table 4.3. The

WEISYT O F O N E TRLwLm : 130 I(. (mmt)

FIGURE 4.82. Houston Ship Channel Bridge, typicalsegment layout and longitudinal prestress.

TABLE 4.4. Houston Ship Channel Bridge,Significant Values of Prestress Forces

Prestress Force (kips)

Maximum cantileverprestress in sidespan

Maximum cantileverprestress in centerspan

Maximum continuityprestress in sidespan

Maximum continuityprestress in centerspan

Day Day Percent780 4000 L o s s

54,710 51,310 6.2

54,390 49,280 9.4

9,540 8,760 8.2

18,130 16,780 7.5

maximum compressive stress at the bottom fiberlevel appears in the section located 124 ft from thepier and is equal to 335 ksf under the combinedeffect of all dead and live loads and prestress.

4.17.2 REDISTRIBUTION OF MOMENTS

The exceptional size of the structure gives rise to amoment redistribution of particular importance.The BC program allows a complete analysis of thebehavior of the structure under the separate andcombined effects of loads and prestress; also theeffect of concrete creep and steel relaxation can beconsidered separately.

Figure 4.87 shows the variation of stresses at topand bottom fibers along the center span betweendays 780 and 4000, which correspond to bridgeopening date and the time when materials will havestabilized (concrete creep and shrinkage havingtaken place and prestress having reached its finalvalue). The magnitude of the variation is remark-able, particularly at bottom flange level where itexceeds IO0 ksf (700 psi or 4.90 MPa).

To isolate the effect of concrete creep on mo-ment and stress redistribution, a section nearmidspan may be analyzed where cantilever pre-stress is neglibile. Results for the section located ata distance of 352 ft from the pier are summarizedin Figure 4.88. The redistribution moment is equalto 52,000 ft-kips.

It is interesting to compare this result, obtainedthrough the elaborate analysis of the BC program,with the result of the approximate method out-lined in Section 4.8.7. Figure 4.89 shows the mo-ments in a typical cantilever under girder load andfinal prestress. The prestress moment has beencomputed using a reduced eccentricity obtained by


! f TOPc o(-)

T O P F I B E R

HIDSPANHIDSPAN

FIGURE 4.83.FIGURE 4.83. Houston Ship Channel Bridge, top fiber prestress for (LX.) t (P) at timeHouston Ship Channel Bridge, top fiber prestress for (LX.) t (P) at time780 days and 4000 days. Stresses at top fiber of the deck. Dead load at time 780 days \vhen780 days and 4000 days. Stresses at top fiber of the deck. Dead load at time 780 days \vhenthe bridge is just opened to traffic and at time 4000 days.the bridge is just opened to traffic and at time 4000 days.

transforming the steel area in the concrete section.Therefore, the prestress moment is equal to:

Pe( 1 - 7zP)

where e = geometric eccentricity,n = 10, transformed coefficient,p = percentage of prestress steel in the sec-

tion (varying between 0.5 and 0.7%).

The total midspan moment produced in the con-tinuous span with fixed ends under the combinedeffect of girder load and final prestress is equal to84,000 ft-kips. Therefore, the actual redistributionmoment obtained by the BC program is equal to:

52 000) = 62% of the total moment8 4 , 0 0 0 -

The recommendation given in Section 4.8.7 to takea ratio of 2/3 gives a satisfactory approximation.

4.173 STRESSES AT MlDSPAlV

Because of the moment redistribution the bottomfiber near midspan is subjected to increasing ten-sile stresses while the top fiber is always undercompression. It is therefore sufficient to considerthe state of stresses at the bottom fiber after creepand relaxation.

The results are shown in Table 4.5. It is instruc-tive to compare the relative magnitude of the vari-ous factors influencing the stresses at midspan(stresses in ksf at bottom fiber):

1. Live load 4 42. Moment redistribution 91

(difference between 250 forCL and 159 for prestress)

3. Temperature gradient 484. Temperature fall 1 8

Design Example 215

TABLE 4.5. Houston Ship Channel Bridge, Stressesat Midspan

Bot tom Fiber

Stresses (ksf) Partial Cumulat ive

.Moment redis tr ibut ion due +250

to GLSlomenr r e d i s t r i b u t i o n d u e - 1 5 9

10 presr ress

Uoment redistr ibut ion due + 9 1

to (GL) + (P)All dead loads and all final

prestress (from BC pro-

gram including moment

redis tr ibut ion)

Live load + impact 4 4

~Teniperarure gradient , 48AT = 18°F

Temperature tal l , 18

T = -40°FLoading combinat ion (‘L),”

(D) + (P) + (L + 1)Loading combinat ion (4),’

(D) + (P) + $(L + I) + AT + T

- 6 6-

- 2 2 M a x-

+22 ( 2 5 )

“See loading combinations in Figure 4.85.

Tombination of Maximum AT + T (maximum temperaturedifferential is improbable in winter).

The influence of the temperature fall (effect 4) isimputable to the frame action between deck andpiers and would not appear in a conventional deckresting on its piers with flexible bearings. Consid-ering only the other three factors combined, as inload ing combina t ion (4 ) o f Tab le 4 .3 , t hemaximum tensile stress at the bottom fiber of themidspan section is:

91 +44+48= 159ks f2-

The live-load stress is only 44 ksf or 44/l 59 = 28percent of the total.

In all good faith, a design engineer would havecompletely overlooked effects 2 and 3 only a fewyears ago and consequently underdesigned con-siderably the continuity prestress. The situationhas now completely changed, and the knowledgeof materials together with the powerful tool of thecomputer allows segmental structures to be de-signed safely and realistically.

It is as well to remember that the Houston ShipChannel Bridge is of exceptional size (which tendsto increase the importance of dead load and mo-ment redistribution) and that American live loads

are light in comparison with those used in othercountries, particularly in France and Great Britain.These two factors tend to increase the importanceof moment redistribution in relation to the effectof loads computed in the conventional manner.

4.17.4 S H E A R

The variation of shear stresses along the centerspan under design loads is given in Figure 4.90 to-gether with the corresponding longitudinal com-pressive stress at the centroid.

The most critical section is located 187 ft fromthe pier centerline. The numerical values in thissection are as follows:

1 .

2.

3.

4.

5.

6.

Vertical dead-load shear force: 4350 kips.Resal effect: the compressive stress at the cen-terline of the bottom slab is 192 ksf and theangle with the horizontal is 0.055 radians.Bottom slab area: 53.5 sq ft.Resal effect: 192 x 53.5 x 0.055 = 570 kips.Net dead-load shear: 3780 kips.

Live-load shear force: 430 kips.Corresponding shear stresses in this section:

I/Q = 14 ft web thickness

b=4ft

Total shear stress under design load (no loadfactor) :

V = 3780 + 430 = 4210 kips

Shear stress:

4210v = ~ = 75.2 ksf14 x 4

Longitudinal compressive stress:f; = 160 ksf

Vertical prestress. The contract specificationscalled for a vertical prestress for the entiredeck giving a minimum compressive stress of:

3q = 232 psi = 33.5 ksfVerification of allowable shear stress.Using the formula proposed in Section 4.10.4:

u = 0.05fi + 0.2Of* + 0.40fy

the allowable shear stress is:

Vlll,, = 0.05 x 864 + 0.20 x160 + 0.40 x 33.5 = 88.6 ksf

while the actual shear stress is only 75.2 ksf


f BOTTOM B O T T O M Fl0ER

c w

FIGURE 4.84. Houston Ship Channel Bridge, bottom fiber stresses for (DL) + (P) attime 780 days and 4000 days. Stresses at bottom fiber of the deck. Dead load at time 780days when the bridge is opened to traffic and at time 4000 days.

7 . Principal stresses at design loads for the stateof stress:

u = 75.2, fJp = 160, and fu = 33.5 ksf

The two principal stresses are 3 (tension) and195 (compression).The angle of the principal stress with the hori-zontal is given by:

tan p = 0.466

If vertical prestresses were not used, the prin-cipal stresses would become:

-30 (tension) and 190 (compression)

8. Principal stresses at ultimate stage.For the load factors 1.30 + 2.17L, includingthe effect of prestress, the ultimate shear forceis:

V, = 5710 kips

Corresponding shear stress:

VU = 102 ksf

Principal stress: - 23 (tension) and 217 (com-pression).

Direction of the principal stress given by:

tan p = 0.56

Web shear cracking at this level of stress wouldbe unlikely. Assuming that the concrete carriednone of the ultimate shear across the potentialcrack shown in Figure 4.91, the total shear loadshould be resisted by the vertical tendons and theconventional stirrups acting on a length equal to:

‘x 1Q

-=&=25fttan/3 .

The unit force per foot of girder is therefore:

Design ExampleDesign Example 2

TEMPERATURE GRADIENT/

/ \L I V E L O A D MAXI

MINI //

TEMPERATURE GRADIENT/ \ T O P F I B E R

t 18-F \

/ \\

\ LIVE LOAD MAxILIVE LOAD MAxI

375 FT 3 7 5 F T 4

FIGURE 4.85. Houston Ship Channel Bridge, top fiber stresses for (L + I) and (AT =18°F).

5710- = 228 kips/lineal ft25

The ultimate capacity of tendons and stirrups is:

Tendons in three webs 220 kips/lineal ftStirrups-O.88 in.Vineal ft 158 kips/lineal ft

per web at 60 ksi278 kips/lineal ft

The condition V,/C#I < V, becomes:

228- = 268 < 378 kips/lineal ft0.85

and is easily met.If no vertical prestress had been used, the slope

of the shear crack would be:

tan /3 = 0.487

Using the limiting value tan /3 = 0.5 instead of theactual value (as explained in Section 4.10.4), the

1 7

shear force per unit length of girder to be carriedacross the crack is:

1 5710- x - x 0.5 = 240 kips/lineal ft0 . 8 5 0 . 1 4

The corresponding amount of steel (grade 60)would be for each web:

L,2!&3

1.33 in.*/lineal ft

This amount of steel would still be reasonable(0.7%).

4.17.5 DESIG,V OF THE CROSS-SECTION FRAME

Owing to the magnitude of the project, particularattention was given to this problem. Five finiteelement analyses were performed to analyze:

The local effects in the transverse frame,


$BOTTOM L I V E L O A D [::,:

40 KSF

1 LIVE LOAD “Axi 1

L I V E L O A D MAxiI

H I DSPAN

,/’ \ TEMPERA&7E G R A D I E N T (+18-F) ,-jI \

\\ /I\ ‘.375 FT 375 F T

- A - - - -

FIGURE 4.86. Houston Ship Channel Bridge, bottom fiber stresses for (L + I) and (AT= 18°F).

The possible differential deflections between thethree webs of the box section,

The relative behavior of sections close to the piersor at midspan,

The effect of diaphragm restraint near the pier.

The dimensions of the cross section at midspan aregiven in Figure 4.92 with the nine critical sectionswhere moments and axial loads were computed foras many as fourteen loading combinations.

A typical set of results is shown in Figure 4.93 forthe midspan section. For the section located 187 ftfrom the pier centerline (already considered formaximum shear stresses), the moments and axialloads are substantially the same as for the midspansection. Excluding the vertical prestress, the mostcritical loading arrangement gives the following

values at the upper section of the outside web (sec-tion e of Figure 4.92).

Moment 1 I .9 kip-ft/ft

Axial load 5.4 kip/ft

The steel section required at design stage for grade60 steel stirrups is 0.34 in.2/lineal ft. Applying therecommendations of Section 4.10.4 for the simplecase of a section without web prestress, the re-quirements for steel on both faces of the webwould be:

For shear of the longitudinal member:

3 x 1.33 = 0.67 in.2/lineal ft

For bending of the transverse member:

0.34 in.2/lineal ft

Quantities of Materials 2 1 9

A f TOP GIRDER LOAD

S T R E S S V A R I A T I O NA T T O P F I B E R

Af B O T TOM PRESTRESSDz

S T R E S S V A R I A T I O N 8A T BOTTOM F I B E R

c_-----v_

A f BOTTOtl G I R D E R L O A D

FIGURE 4.87. Houston Ship Channel Bridge, variation of stresses due to creep andrelaxation.

.The minimum area should thus be the higher ofthe f’ollowing values:

0.67 + 1 x 0.34 = 0.84 in.*/lineal ft

1 x 0.67 + 0.34

0.i(0.67 + 0.34)

= 0.67 in.*/lineal ft

= 0.71 in.2/lineal ft

In the actual structure, the stirrups in this sectionare #6 bars at 12 in. centers, giving on each face asteel area of 0.44 in.* together with the minimumvertical prestress of 44.2 kips/lineal ft (averagecompressive stress of 230 psi).

‘I‘he ultimate capacity of the section reinforce-ment is theref-ore:

With vertical prestress: 378/3 = 126 kips/lineal ft

Without vertical prestress: 2 x 0.84 x 60 = 101kips/lineal ft

4.18 Quantities of Materials

Before closing this chapter, it is interesting to givesome statistical results concerning the quantities ofmaterials required in segmental box girderbridges. Unit quantities have been computed bydividing the’ total quantities for the bridgesuperstructure by the deck area, using the totalwidth of the prestressed concrete structure. The


Loading Case

Cantilever PrestressGirder + superimposed

dead load

TotalVariation from

780 davs to 4000 davs

Stresses, ‘Top Fiber (ksf)

780 Days 4000 Dqt

- 6.36 130.32- 56.93 -266.50

-63.29 - 136.18

-72.89

Srresses, Bottom Fiber- (list)

780 Dny.\ 4000 lkJ\

-20.20 - 161.0861.89 293.50

4 1.69 132.42

+9o.i3

No& I: .I‘ensile stresses are positive.

Note 2: This moment is the difference between girder load, 142,000 tt-kips, and cantilever prestress, 90.000 t’t-kips.

f, = - 72.89f, = - 72.89

(I = 4774 FZ4)(I = 4774 FZ4)

-in

I+?

2II

cd4

IIc?

Afz= + 90.73fz= + 90.73

FIGURE 4.88. Houston Ship Channel Bridge, analy-FIGURE 4.88. Houston Ship Channel Bridge, analy-sis of section at 352 ft from pier.sis of section at 352 ft from pier.

Corresponding moment variation:

AM = (f, ffd +

= (72.89 + 90.73) F

AM = 52,000 ft-kips

average concrete quantity per span foot varies withthe span length. For each structure considered, thespan length used is the average span of the varioustwo-arm cantilevers. The longitudinal prestressingsteel is given in pounds per cubic yard of deck con-crete versus the same span length. It is assumedthat prestressing tendons are made up of strandswith 270 ksi guaranteed ultimate strength. Fromthe charts given in Figures 4.94 and 4.95, it may beseen that the average quantities of materials ma)be represented by the following approximate for-mulae:

Concrete (ft3/ft2) = 1.0 + (L/250)

Longitudinal prestress (lb/ft”) 2- 1.0 + (L/60) (forspans up to 750 ft)

4.19 Potential Problem Areas

As with any type of construction with any material,problems arise that require the attention of notonly the designers, but contractors and subcon-tractors as well. No matter how good the design, if

FIGURE 4.89. Houston Ship Channel Br-idge, rapidcomputation of moment redistribution.

Potential Problem Areas 221

60

40

i.20

I60

.----

140

120

IO0

80

60

40

20

20

Ifx(I

- . .\\ ‘3

/EFPG

I 2 4

FIGURE 4.90. Houston Ship Channel Bridge, variation of web shear stress and aver-age compressive stress in center span under design load.

FIGURE 4.91. Houston Ship Channel Bridge, shearand principal web stresses in section 187 ft from Pier(under design loads).

the structure is not properly constructed, there willbe problems. Conversely, no matter how diligentthe contractor, if the design details are poor,problems will result. Obviously, if the design andthe construction are poor, problems are com-pounded.

8d 1

110" I’ 13s’ 7 i

I

diFIGURE 4.92. Houston Ship Channel Bridge, designof transverse frame at midspan.


Section-5?67

b d f h iM, dead load - 6 . 2 9 2c37 - 6 . 0 5 1e22 - 3 . 1 5 -:96 2.14 - 5 . 2 9M, PrestressingM, DL + PITM, live loadwith 1 M 1 maxiM, DL + PIT + LL

+IN, dead loadN, transverseprestressingN, DL + PITN, live loadN,DL +PIT+LL

+I

16.59 13.22 -0.92 8.01 3 .01 0 .22 0.08 0 0.0610.92 6 .93 1.45 1.96 4 .23 - 2 . 9 3 - 2 . 8 8 2 .14 - 5.23

- 5 . 2 4 - 6 . 6 8 5 .03 - 8 . 8 2 5 .88 - 1.25 ~ 1.25 0 .35 -0.78

4.11 - 1.75 7.98 - 9 . 5 1 11.87 - 4 . 5 5 - 4 . 5 0 2.59 - 6 . 2 5

0 .06 - 0 . 5 3 - 0 . 6 5 -0.59 4.24 6 .08 0.5550.75 51.06 51.26 51.35 - 0 . 3 1 - 0 . 3 1 -0.29

50.8 1

50.8 1

50 .53

50.53

50.61 50.76

50.61 50.76

3.931.105 .36

5 .77

5 .77

0 .26 0.37- -0.26 0 .37

0.24

0.24

,Vote: Web vertical prestress is not included.

a bI I i

4:

F4 -=- - -------.\\

c

I Compressive axial forces are\

f -\ -

positive. Positive bending mo-ments cause tension at the

B---------

1 1 Ibroken line face.

9

SIGN CONVENTION

FIGURE 4.93. Houston Ship Channel Bridge, mo-ments and axial forces in transverse frame at midspan.

Problems are generally associated with qualitycontrol, poor design details, or a lack of under-standing as to how the structure will behave, eitherthrough ignorance or because a particular phe-nomenon is unknown to the current state of theart, or a combination of all these factors. The fol-lowing list of problem areas, as they are known tothe authors, is presented so that those involved indesigning and building segmental bridges maytake adequate measures and precautions to avoidthese problems.

1 . Improper performance of epoxy due to mis-handling of mixing and application procedure,particularly in rain and cold weather. The con-sequences are largely reduced by the use ofadequate shear keys in webs and in both topand bottom flanges of the box section.

2. Grout leakage between adjoining ducts atjoints between segments, particularly in pre-cast segmental construction. Conformity of theducts at the joints is a desirable feature if prac-tical. The use of tendons outside the concreteeliminates this problem.

3 .

4.

5.

6.

7.

8.

II‘ensile cracks behind tendon anchorages,particularly for high-capacity continuity ten-dons in the bottom flange of box sections.

Transverse cracking or opening of Joints, oradjacent thereto, due to the combination ofseveral factors such as:

a. Underestimation of moment redistributiondue to concrete creep.

b. Thermal gradients in the box section.

c. Warping of segments due to impropercuring procedures.

Several such points have been already a d -dressed in this chapter; others are discussed inChapter 11. Should the recommendationsgiven be followed both in design and construc-tion methods and in supervision, no moredifficulties of this nature are to be expected.Laminar cracking in deck slab or in bottomflange due to wobble and improper alignmentof ducts at the joints between ad-jacent seg-ments. Such incidents have been experiencedmore often in cast-in-place construction thanin precast construction. However, care shouldalways be taken insofar as deck alignment isconcerned in all segmental projects.Freezing of water in ducts during construction,especially those anchored in the deck slab(vertical prestressing tendons or draped con-tinuity tendons).

Excessive friction in ducts due to wobble.Proper alignment will reduce friction factors insegmental construction to those currently ob-served in conventional cast-in-place post-tensioned construction.

Improper survey control in segment man-ufacture for precast segments as well as in thefield for cast-in-place segments.

500 600 700 600AVERAGZ SPAN L ( f t )

FIGURE 4.94. Average quantities of deck concrete.

15 T /

I AVERAGE SPAN L(ft)FIGURE 4.95. Average quantities of longitudinal prestressing steel.

223

i

I100 200 300 400

224 , Design of Segmental Bridges

References

1. F. Leonhardt, “New Trends in Design and Construc- 3. C. A. Ballinger, W. Podolny, Jr., and M. J. Abrahams,tion of Long Span Bridges and Viaducts (Skew, “A Report on the Design and Construction of Seg-Flat Slabs, Torsion Box),” International Asso- mental Prestressed Concrete Bridges in Westernciation for Bridge and Structural Engineering, Europe- 1977,” International Road Federation,Eighth Congress, New York, September 9-14, Washington, D.C., June 1978. (Also available from1968. Federal Highway Administration, Offices of Re-

2. Jean Muller, “Ten Years of Experience in Precast search and Development, Washington, D.C., Report

Segmental Construction,” Journul of the Prestressed No. FHWA-RD-78-44.)

Concrete Institute, Vol. 20, No. 1, January-February 4. “Effets de I’effort tranchant.” Federation Inter-1 9 7 5 . nationale de la Precontrainte, London, 1978.

Foundations, Piers, and Abutments

5.15.2

INTRODUCTION 5.6.2LOADS APPLIED TO THE PIERS

5.3

5.2.1 Loads Applied to the Finished Structure5.2.2 Loads Applied During ConstructionSUGGESTIONS ON AESTHETICS OF PIERS ANDABUTMENTS

5.4

5.3.1 structure Layout5.3.2 Aesthetics of Piers5.3.3 Aesthetics of AbutmentsMOMENT RESISTING PIERS AND THEIR FOUNDA-TIONS

5.4.1 Main Piers for the Brotonne Viaduct, France5.4.2 Piers and Foundations for the Sallingsund Bridge,

Denmark5.4.3 Concept of Precast Bell Pier Foundation for the

I-205 Columbia River Bridge, U.S.A.5.4.4 Main Piers for the Houston Ship Channel Bridge,

U.S.A.5.5 PIERS WITH DOUBLE ELASTOMERIC BEARINGS

5.5.1 Scope and General Considerations5.5.2 Description of Structures

Oberon Viaduct, FranceBlois Bridge, FranceUpstream Paris Belt Bridge, France

5.5.3 Properties of Neoprene BearingsNotations

5.6

Deformations of Neoprene Bearings5.5.4 Deformation of Piers with a Double Row of Neop

rene Bearings5.5.5 Properties of Piers with a Double Row of Neoprene

Bearings5.5.6 Influence of Thickness and Arrangement of Neo-

prene Bearings on the Variation of Force in aThree-Span Structure

PIERS WITH TWlN FLEXIBLE LEGS

5.6.1 Inttoduction

5.1 Introduction

Probably the area most challenging to the civil en-gineer is that of foundation design and construc-tion, presenting the largest potential dangers but

5.6.3

5.6.4

5.6.5

5.6.6

River Piers and Foundations for Choisy-le-Roi,Courbevoie, and Juvisy Bridges, FrancePiers and Foundations of Chillon Viaducts, Switrer-landMain Piers and Foundations of the Magnan Viaduct,FranceMain Piers and Foundations for the Dauphin IslandBridge, U.S.A.Deformation and Properties of Piers with Flexible

Legs5.6.7 Elastic Stability of Piers with Flexible Legs

5.7 FLEXIBLE PIERS AND THEIR STABILITY DURINGCONSTRUCTION

5.7.1 Scope5.7.2 Description of Representative Structures with Tem-

po’;uy SupportsDownstream Paris Belt Bridge, FranceSaint Jean Bridge In Bordeaux, France

5.7.3 Review of the Various Methods of Providing Stabil-ity During Cantilever Construction

5.8 ABUTMENTS

5.8.1 Scope5.8.2 Combined Abutment/Retaining Wall5.8.3 Separate End Support and Retaining Wall5.8.4 Through Fill Abutment5.8.5 Hollow Box Abutment5.8.6 Abutments Designed for Uplift5.8.7 Mini-Abutment

5.9 EFFECT OF DIFFERENTIAL SETTLEMENTS ON CON-TINUOUS DECKS

5.9.1 Effect of an Assumed Pier Settlement on theStresses in the Superstructure

5.9.2 Practical Measures for Counteracting DifferentialSettlements

REFERENCES

also yielding the most significant savings to properdesign concepts or refined construction methods.The first industrial application of prestressed con-crete was related to solving an insurmountableproblem of foundation underpinning.

225


The transatlantic terminal built in Le HavreHarbor in France on the English Channel wasopened for operation in 1934 to receive the newgeneration of fast passenger ships between Europeand America. Improper foundation of the rearbays of the new building caused immediate con-stant settlements at the rate of 1 in. (12.7 mm) permonth with no foreseeable limit, except the totalruin of the facility, Figure 5.1. Eugene Freyssinetproposed a unique system of underpinning, whichwas immedia te ly accep ted and implemented ,whereby prestressed concrete piles were man-ufactured in the basement of the existing buildingin successive increments and progressively drivenby hydraulic jacks to reach the stable lower soilstrata, found at a depth of more than 100 ft (30.5m), Figure 5.2. This example should certainlymake one cautious against excessive optimism infoundation design; at the same time it exemplifiesthe remarkable potential of prestressed concrete insolving unusual problems.

In concrete bridges, often greater savings maybe expected from optimization of foundation andpier design than from the superstructure itself.This chapter will deal with certain specific aspectsof piers, abutments, and foundations for bridgesbuilt in balanced cantilever. Similar concepts maybe extended to cover other construction methods(span-by-span, incremental launching, and so on).

Piers with many different shapes have been usedin conjunction with cantilever construction. Forexample, single piers, double piers, and moment-resistant piers have all been used. The cantileversegmental construction method has an importantinfluence and bearing on the design concept of thestructure. Resistance and elastic stability of piersduring construction require careful investigation.Temporary piers or temporary strengthening ofpermanent piers or a combination of both havebeen used. However, the choice of piers that haveadequate stability without temporary aids is highlydesirable. Piers of a box section, or twin flexiblelegs, either vertical or inclined, are equally satis-factory.

The use of full continuity in the superstructureimplies that proper steps have been taken to allowfor volume changes (shrinkage, creep and thermalexpansion) at the supports. Bridges such as theChoisy-le-Roi (Section 3.2), Courbevoie (Section3.2), and the Chillon Viaduct (Section 3.6) showhow the use of piers with flexible legs makes it pos-sible to achieve full deck continuity and to buildframe action between deck and piers without im-pairing the free expansion of the structure. Theconverging pier legs used at Choisy-le-Roi reduceand even cancel the amount of bending trans-ferred to the pier foundations. Vertical parallellegs such as those in the Courbevoie and Chillon

-__iI

FIGURE 5.1. Le Havre transatlantic terminal, typical section.

Introduction 227

Jaws Ior str.efchmngEStee l Rods .

Shee t I r onInternal Uould.

mjE n d P l a t e of Mould

b insu/at/nq fnveiope,

Horizontal Section

internal Moo/U

FIGURE 5.2. Le Havre transatlantic terminal. (a) Vertical section and plan ofcomposite foundation girder. (6) Details of pile mold.

structures may be used on multispan structures be- If in the finished structure single slender pierscause their additional flexibility accommodates are designed solely to transfer the deck loads to thelarger horizontal displacements. For longer struc- foundations (including horizontal loads), the pierstures, bearings with a variable number of lami- may be unable to resist the unsymmetrical mo-nated elastomeric pads may be used to provide the ments due to the cantilever construction (i.e., withdesired horizontal flexibility. an unbalance of one segment and the equipment


load). Thus, temporary shoring is required, oftenat considerable cost. In some cases, the stability ofthe cantilever under construction has been pro-vided by the launching gantry used for placing thesegments.

With double piers, two flexible legs (either in-clined or vertical) make up the pier structure,which usually is supported on a single foundation.Stability during construction is excellent and re-quires little temporary equipment, except for somebracing between the slender walls to prevent elasticinstability.

Moment-resistant piers are designed to with-stand the unbalanced moments during construc-tion by providing a temporary vertical prestressbetween the deck and the pier cap, thus producinga rigid connection. Flat jacks are usually placedbetween the pier top and the pier segment soffit topermit the substitution of temporary bearings forthe permanent neoprene pads. When the ratiobetween span lengths and pier height allows it, therigid connection and corresponding frame actionmay be maintained permanently between thesuperstructure and piers.

Piers do not necessarily have to be a massive solidcross section; a box section, Figure 5.3, mav bemore effective and more economical. In theUnited States it was generally felt that a solid pierwas more economical. However, for tall piers theeconomics of pier casting should be evaluatedagainst the cost of the additional dead load sup-ported by the pier shaft and transferred to thefoundations. It may be desirable to precast the pieras tubular segments that are prestressed verticallyto each other as well as to the foundation; this con-cept was used for the Linn Cove Viaduct in NorthCarolina and the Vail Pass structures in Colorado.

In certain cases the tubular section may be re-placed by an I section, Figure 5.4. However, the lowresistance to torsion of this section imposes certainprecautions to limit the deformation of the can-tilevering superstructure during construction, inparticular with respect to the effect of wind forces.

For the case of a continuous structure on shortstiff piers, the volumetric changes of the concrete(shrinkage, creep, and thermal expansion) com-pound the redundant effect of longitudinal pre-stressing to produce, by virtue of the rigidity of the

+ I 42’ Il

I_-

f/q pIO’ 13’ IO’

FIGURE 5.3. Code Bridge, box pier.

Introduction 229

+ 29’ +

u-

FIGURE 5.4. Pyle Bridge, I-section pier.

piers, bending forces that must be transmitted tothe foundations, thus condemning the use of arigid connection between the superstructure andits support. This disadvantage then requires theintroduction of a continuous superstructure rest-ing on a number of supports that permit thelongitudinal movement of the superstructure (neo-prene pads, teflon, and the like). However, it is nec-essary to insure the stability of the superstructureduring cantilever construction. This may be ac-complished as stated earlier by the use of tempo-rary shoring in the proximity of the pier or by pro-viding a temporary fixity at the pier.

Another solution is the use of piers with twinslender flexible legs. The transmission of horizon-tal loads in the direction of the longitudinal axis ofthe bridge is accommodated by the legs’ flexibility.This type of pier offers three advantages:

1. Efficient fixity of the superstructure to thepiers with regard to the vertical loads by theaction of the separate supports,

2. Large flexibility in the horizontal plane (rela-tive to the displacements parallel to the lon-gitudinal axis of the superstructure), per-mitting the resolution of the problem ofexpansion posed by the continuous structure,

3. Stability of the superstructure during con-struction by a simple temporary bracing.

In the final structure, the leg flexibility is sufficientto accommodate the longitudinal braking forces.

When the geometry of the structure permits, it ismore economical to incline the walls in order to re-duce the bending moment transmitted to thefoundation. If the legs are hinged at the super-structure and if the axes of the two legs convergenear the level of the foundation, the bendingmoment is either canceled or minimized and thedistribution into the supporting soil is essentiallyuniform, as for a vertical reaction, Figure 5.5. Thistype of structure is similar to a frame or an arch.The thrust produced by the effect of a horizontalload parallel to the longitudinal axis of the bridgeis translated into a tension force on one leg, whichthen acts as a tie beam, and a compressive force inthe other leg, which then acts as a strut. For thisreason it is often necessary to prestress the legs toaccommodate the tension force.

When the legs are vertical, they do not profit ap-preciably from the frame or arch action, and thestability is essentially contained in their bending re-sistance. For the case where the legs are hinged atboth ends, no resistance is offered and it is neces-

FIGURE 5.5. Piers with flexible walls.


sary to stiffen a pier to provide a fixed point in thestructure.

Because of pier flexibility a careful analysis is re-quired to assure the elastic stability of the struc-ture. The legs supporting the superstructure are ineffect very slender, and their resistance to bucklingmust be carefully examined. This type of pierstructure will be examined in greater detail in thesections that follow.

Another family of piers that lends itself to can-tilever construction is that of moment-resistingpiers with a double row of neoprene bearings be-tween the pier top and the superstructure, such asto benefit from pier rigidity during construction orin the finished structure while allowing free expan-sion of the continuous deck, Figure 5.6. Theproper choice of dimensions for the neoprenebearings will allow control of the amount of bend-ing transferred to the foundation; in fact, rigidpiers with double neoprene bearings behave inmuch the same way as piers with twin flexible legs.

We see, then, that piers and foundations forcantilever concrete bridges will fall into one of thefour following categories:

1. Moment-resisting piers either fixed or hingedto the superstructure.

2 . Moment-resisting piers with double neoprenebearings.

3. Piers with twin flexible legs.4. Conventional flexible piers properly

strengthened during construction to resist un-balanced loading conditions.

FIGURE 5.6. Piers with twin neoprene bearings.

After reviewing the loads applied to the piersand considering some suggestions pertaining tothe aesthetics of piers and abutments for concretesegmental bridges, we shall deal separately witheach of the four pier types. The chapter will con-clude with a review of several types of abutmentsand the effect of unequal pier settlements on thestress in the superstructure.

5.2 Loads Applied to the Piers

All loads must be carefully considered in the de-sign of the piers and their foundations, both in thefinished structure and during its construction.

5.2.1 LOADS APPLIED TO THE FIAVISHEDSTRUCTURE

In addition to the various loading arrangementstaken into account for conventional structures andused in combination as set forth in the AASHTOspecifications, for example, it is necessary to in-clude some design aspects particular to segmentalcantilever construction as follows:

1. When a frame action is realized betweensuperstructure and piers, proper transfer of mo-ments to piers must be considered, particularlyunder unsymmetrical live loading. The piers arethus an integral part of the structural system andtheir flexibility must be first evaluated and then in-corporated in the overall structural system. Figure5.7 shows the usual parameters used to define theflexibility of a pier as the relationship between theapplied loads (M, Q, and N) and the correspondingcomponents of the deformation at the same point(0, u, and v). The four flexibility coefficients A, B,C, and K must include all components of the pierand its foundation: soil, piles (if used), footing, piershaft (or walls), neoprene bearings (if used). Loadsand deformations are taken at the level of the deckgirder neutral axis.

The deck construction scheme usually imposesspecial loads to the substructure. Piers adjacent toan expansion joint located at the point of con-traflexure (see discussion of this aspect in Chapter4) are subjected to appreciable bending momentsdue both to the relaxation of the hinge after can-tilever construction and to live loading placed oneither side of the hinge. Loads applied to thestructure by the construction equipment result alsoin moment transfer in piers connected to thesuperstructure. Two typical cases often encoun-tered are:

Loads Applied to the Piers 231

i

_ APPLIEO LOADS

M,Q,N,

cOIRESPOH313G OEFOeUATioN

-0 ,Mu,W,

0= AM + BQ

AA r BM+CO

IJ = KN

FIGURE 5.7. Basic components of pier flexibility.

a. In precast segmental construction with seg-ments placed with a launching gantry, the gantryleg reactions are applied to a temporary staticscheme and released in another static scheme(after continuity between two adjacent cantileverarms is realized).

b. In case-in-place cantilever construction, theweight of travelers is applied to the free cantileverarms during construction but it is removed fromthe structure after continuity is achieved. On longspans the effect on the deck is usually beneficial,but important moments may simultaneously be in-duced.

2. Volume changes (shrinkage and thermalvariations) and long-term shortening of materials(concrete creep and steel relaxation) both inducemoments and horizontal loads in the piers, whichmust be included in the design.

5.2.2 LOADS APPLIED DURING CONSTRUCTION

Balanced cantilever construction imposes on thepiers a loading configuration that is globally sym-metrical. Unbalanced conditions appear, however,as a result of intermediate construction stages(normal loads due to a traveler or a segment out of

balance), the application of random loads (dif-ference between actual and computed dead loadsor wind gusts), or accidental conditions (such as thefall of a traveler).

Normal Loua The most critical condition ap-pears for one segment out of balance at the out-board end of the cantilever arm. Even in the caseof cast-in-place construction with symmetricaltravelers allowing simultaneous casting of bothcorresponding segments, the assumption of thetotal segment weight out of balance is a safe one,because no total guarantee can be given that con-crete pouring will proceed simultaneously at eitherend of the cantilever. If construction equipment isdesigned to be installed on the deck, Figure 5.8, it

FIGURE 5.8. Loading conditions duringtion.

construc-

.


must be accounted for in the design of the pier.For example, a tower crane is often used on oneside of a cantilever.

Random Loads Random loads essentially aresuch a s t o p roduce systematic geometric dif-ference, although within acceptable tolerances.With proper workmanship and supervision, it isreasonable to assume such difference in weight at22%. It corresponds to a variation of top slabthickness of 2 in. (9.5 mm) for a 40 ft (12 m) widebox with a cross-sectional area of 60 ft2 (5.6 m’).However, it is very unlikely that the maximumweight decrease in one cantilever arm would ap-pear simultaneously with the maximum weight in-crease in the other. It is therefore reasonable tolimit the moment transferred to the pier to 2% ofthe maximum deck cantilever moment due to thegirder weight. Other random loads related to theconstruction are produced by the small equipment,trucks, storage on the deck of materials such aspost-tensioning tendons, and so on. An equivalentuniform load of 5 psf (24.4 kg/m*), together with amoving concentrated load of 20 k (9 mt), should bea safe allowance to cover these random loads.

Taking as an example the Houston Ship Chan-nel Bridge, which was considered in Section 4.17,the effect of these three random loads would be:

difference in dead weight,1,600,OOO ft-kips x 2%

random uniform load,( 5 x 60)/1000 x 365*/2

random concentrated load,20 kips x 365 ft

32,000 ft-kips

20,000 ft-kips

7,000 ft-kips

59,000 ft-kips

This moment should be compared to the effect ofone segment out of balance at the far end of a can-tilever:

300 kips X 367 ft = 110,000 ft-kips

One last source of random loading is providedby gusts of wind that apply an uplift pressure orsuction to the box girder intrados during con-struction. For long spans and construction sites ex-posed to hurricanes, it is desirable to make specialaerodynamic tests. For an incident angle of 10”above the horizon, the upward pressure would be 5psf (0.2394 MPa) during construction. This valuemay be substantially increased in exposed sites. Forcons t ruc t ion o f the Gennev i l l i e r s Bridge, a

maximum pressure of 9 psf (0.4309 MPa) was re-corded in the wind-tunnel tests.

Accidental Loads These are the result of a con-struction incident or of human failure, causingeither the fall of a traveler in cast-in-place con-struction or of the lifting equipment in the case ofprecast construction. Such loads should be multi-plied by a factor of 2, representing the impactcoefficient for the case of immediate loading. It isnever envisaged to consider the fall of a cast-in-place segment and traveler after casting, nor thefall of a precast segment immediately after itsplacement in the structure. A very long record ofsafety in such construction methods justifies thatapproach. However, in the case where the conse-quences of such major accident would be excep-tionally disastrous (where, for example, the worktakes place over a highway or a railway under op-eration), special provisions should be incorporatedin the design and in construction procedures todouble all safety features at each step of erection.

5.3 Suggestions on Aesthetics of Piers andAbutments

The problem of aesthetics is subjective and con-troversial. There is, however, a consensus amongengineers, owners, and users that certain bridgestructures are more pleasing than others. At a timewhen so much emphasis is being placed on protec-tion of our environment and of nature from ag-gressive man-made structures, it may be helpful toreview some ground rules based on experiencethat contribute to aesthetics of concrete bridgeswith very little added cost.

53.1 STRUCTURE LAYOUT

Generally speaking, an attempt should be made tomatch the structure to the environment and to pre-serve the existing landscape. Avoid long, high em-bankments at the ends of the bridge as well as long,high retaining walls that accentuate the intrusionof the new structure. Allow the number and shapeof the piers to maintain a maximum of transpar-ence. Cost optimization of superstructure spanlengths will normally help to avoid serious aestheti-cal mistakes. It is equally disgraceful to see a heavy,long-span superstructure rampant over theground as a multitude of closely spaced, high pierssupporting a slender deck floating up in the air.The true appearance of a structure is usually not

Suggestions on Aesthetics of Piers and Abutments

conveyed by the drawings, where often a distortedscale is used for convenience.

233

Finally, it is very important to keep the unity ofappearance of a structure crossing different obsta-cles, in spite of the practical difficulties that may beentailed when project coordination involves differ-ent owners or agencies. When an overpass crosses,for example, a freeway and a parallel railroadtrack, nothing may be worse than to build twoseparate structures (probably of different height)connected by a short embankment contained at‘both ends by wing walls of variable height, Figure5.9. FIGURE 5.10. Piers for the Broronne ,~pp~o;~ch via-

duct.5.3.2 AESTHETICS OF PIERS

A significant advantage of segmental constructionis to allow deck continuity, rather than simply sup-ported structures. There is no longer a need forheavy bents protruding underneath the super-structure soffit. Piers can have simple gracefullines and be designed to receive directly the boxgirders of the superstructure.

Box piers of prismatic section but with cur-vilinear shapes improve the appearance over theconventional rectangular section. The approachp ie r s o f the Bro tonne Viaduc t , F igure 5 .10 ,utilized that concept and also the piers for the LinnCove Viaduct in North Carolina. More refinedshapes may be used, such as for the river piers ofthe Blois Bridge, Figure 5.11, where the sculptureof the faces was designed to recall the appearanceof a pier with twin inclined walls similar to that ofthe Juvisy Bridge, Figure 3.25. Architecturalstudies may be pursued further and reach beyondthe immediate structural needs of the designer. Aninteresting example is afforded by the river piers

FIGURE 5.9. An unacceptable example of’ an over-pass built as two separate structures.

of the railroad bridge at Clichy near Paris, Figure5.12.

A difficulty arises often for skewed bridges whenbents include multiple pier shafts. A satisfactorysolution was developed for the Paris DownstreamBelt Bridge, Figure 5.13. The four columns of ariver pier are given the shape of a lozenge, withone axis of symmetry matching the alignment ofthe superstructure while two of the four facesexactly align the four columns in the direction ofthe river flow.

FIGURE 5.11. Piers with architectural shapes forBlois Bridge.

2 3 4 Foundations, Piers, and Abutments

FIGURE 5.12. Piers for Clicln Railroad Bridge.

FIGURE 5.13. Piers for a skew bridge (Paris RingRoad).

When the piers will be seen only from a greatdistance, it is usually not worthwhile to call for aspecial treatment of the concrete faces. The eyewill judge only the general shape of the structureand its overall proportions. For urban bridgesthe situation is very different and often justifiessome architectural treatment of the piers. The riverpiers of the Saint Cloud Bridge were cast with asystem of closely spaced vertical grooves, whichgreatly enhance their appearance at very littleadded cost, Figure 5.14.

5.3.3 AESTHETICS OF ABUTMENTS

At both ends, the structure has to blend with theexisting landscape with a minimum of disturbance.Between the two systems of wing walls shown inFigure 5.15, the preference should strongly bewith type (a), which allows a much more gradualtransition between the lines of the superstructureand those of the approach embankment.

When tapered webs are used in the superstruc-ture box girders, it has been found that the lateralwing walls in the abutments can be given the same

FIGURE 5.14. Saint Cloud Bridge. (CL) River piers.(b) General view.

inclination to improve the transition between deckand abutments, Figure 5.16.

5.4 Moment-Resisting Piers and TheirFoundations

We shall cover this topic by describing salient fea-tures of several characteristic structures.

5.4.1 MAIN PIERS FOR THE BROTONNEVIADUCT, FRANCE

The two main pylon piers for the Brotonne Via-duct rest on 41 ft (12.46 m) diameter cylindrical

Moment-Resisting Piers and Their Foundations 235

Wing walls parallel to bridge Q

-.__.-. -.---.-.-.-.-- - - _-.-.- -!I

__.-.__ -.-.-.-.-Wing walls perpendicular to bridge F.

(b)

FIGURE 5.15. Wing walls and abutments.

columns with a maximum wall thickness of 9.3 ft(2.83 m) and are 115 ft (35 m) below ground levelin a limestone stratum overlain by alluvium, silt,and gravel beds. The maximum reaction at footinglevel is 19,000 tons. Typical dimensions of a mainfoundation syst.em are shown in Figure 5.17.

It was decided to select the theoretical founda-tion level at 115 ft (35 m) below the originalground level, where the limestone bed had thefollowing minimum characteristics determinedfrom laboratory soil tests and in situ tests: angle ofinternal friction 20”, cohesion 5 tons/ft2, and apressure limit (on triaxial tests) of 45 tons/ft2. Thefoundation system had to resist very large loads(both vertical and horizontal) together with im-portant overturning moments.

The main foundation column embedded in thesoil and resting on the lower limestone stratum wasanalyzed as a rigid body subjected to the appliedloads (M, V, and H) shown in Figure 5.18 and re-ceiving from the soil lateral reactions along theshaft and vertical reactions under the base. Valuesof lateral and vertical reactions were ascertainedfor the various soil strata and the equilibrium wasdetermined by considering the total body to besubjected to an angle of rotation cy around the in-

i: ”::.*i .: .*\q*> \‘;:i c :&\ . >.~ ..: ,.j \ ;\;A. \-. .,I .., .:- .\ ‘,;,., . .>;.yFIGURE 5.16. Inclined wing walls in end abutment(Bordeaux St. Jean Bridge).

stantaneous center of rotation C. The coordinatesof point C are the following:

Vertically, it represents the level where lateralreactions from the soil change sign (change fromdirect passive pressure on the front face to coun-terreaction at the back face).Horizontally, it is the position of the neutral axisfor the stress under the base.

The maximum loading configuration is repre-sented numerically in Figure 5.18 along with thediagrams for:

Lateral reactions on the columnBending moments along the columnBearing stress under the base

If there were no lateral support, the bending mo-ment at the base would have been 370,000 ft-kips.In fact, the actual moment is only 130,000 ft-kips,


FIGURE 5.17. Brotonne Viaduct, pylon foundations.

which explains why the extreme fiber stress is nomore than 24 tonsIft while the average bearingpressure is 14.25 tons/ft2.

The actual safety factor for the foundationagainst soil failure is between 3 and 4, dependingon the assumptions of soil characteristics.

Insofar as the construction method is concerned,each main foundation column was built in the dryinside a cofferdam made up of a continuous slurrytrenched concrete wall excavated down to thelimestone stratum, Figure 5.19. Grouting of thebase allowed dewatering of the site after excavationto inspect the foundation material and confirma-tion of the actual soil characteristics by in situ soiltests. Following this inspection, the cofferdam wasflooded and a tremie seal was placed at the base toprevent any risk of washing out of the footing con-crete due to water seepage; the water head wasabove 100 ft (30 m). The reinforced concretefooting was cast in the dry above the seal and thefoundation shaft was then slip-formed inside thecofferdam. The pier shaft was given the shape ofan octagon with curvilinear sides for aesthetic rea-sons. The general dimensions of the foundationshaft and of the pier shaft allowed a very natural

and direct transfer of loads at ground level with noneed for a heavily reinforced footing. The con-struction of both foundations went very satisfac-torily. The only incident was created by the factthat one panel of the cofferdam in the south pierwas excavated out of plumb at its lower end. Con-sequently, the continuity of the horizontal ring toresist the hydrostatic pressure was not realized atthe lower part of the cofferdam. Grouting of thesurrounding soil was achieved in this area and anadditional reinforced concrete ring was cast insidebefore the completion of excavation and final de-watering.

Regular survey measurements at the site haveshown that settlements of both pier foundationshave been very minimal and are now stabilized.

5.4.2 PIERS AND FOUNDATIONS FOR THESALLINGSUND BRIDGE, DENMARK

The substructure and piers of this structure pre-sent an interesting construction methodology anduse of materials, Figures 3.89 and 5.20. The pilesare steel tubes, which are concreted after driving.Their length is about 98 ft (30 m), the diameter is

Moment-Resisting Piers and Their Foundations

n. 230.050 FT. k.v, 19.000 t

TSF

“““‘J1 ,.--Jre

FIGURE 5.18. Brotonne Viaduct, loads and soil reactions on columnof main foundations.

274 in. (700 mm) and the wall thickness is about 0.4in. (10 mm). Each pier has 24 piles. The first pilesdriven are tested in compression and tension be-

FIGURE 5.19. Brotonne Viaduct, view of pier exca-vation.

237

fore the remaining piles are driven. When thedriving is accomplished, the template trough isfilled with tremie concrete around the pile tops upto the upper edge of the template.

The template is precast at a plant located in theharbor. It is shaped like a circular slab surroundedby an annular trough, in which there are holes forthe piles. The template is transported to the pierlocations by the floating crane and lowered downto rest on three temporary vertical piles. The bot-tom is about 52.5 ft (16 m) below the water level.For an exact positioning in its submerged position,it is provided with an alignment tower, the top ofwhich is always above water, Figure 5.21.

The pier box, shaped like a truncated cone ap-proximately 39.3 ft (12 m) high, is precast in threelifts at the precasting plant in the harbor. First itslower part is cast on staging above water. Duringthe following lifts it is progressively sunk. Sinceafter the third stage it is too heavy to be lifted by thefloating crane, it is provided with a lid, and com-


Assembled pier

/-y-7 Gmcmting

r Template

Il.3

Concreting of piles

concrete plug

FIGURE 5.20. Sallingsund Bridge. schematic of sub-StrllCtlll-e.

pressed air is pumped into the cavity. The floatingcrane then transports the pier box to the pier loca-tion and lowers it down to rest on the template. Areinforced concrete ring structure is made by con-necting the pile tops to the pier box by reinforcingand concreting the space between them, Figure5.21.

The icebreaker’s shell is a reinforced concretebox, precast at the harbor site, Figure 5.22, trans-ported to the pier location by means of the floatingcrane and placed on top of the pier box. Its top isthen 8.2 ft (2.5 m) above and its bottom 8.2 ft (2.5m) below the water level. When the box is in place,the water in the cavity of the pier box and the ice-breaker box is pumped out. Next, the piles are filledwith concrete and the pile tops and the lower partof the pier box are cast together. Finally the cavity ofthe icebreaker is filled with concrete. A schematicsequence of operations in constructing the sub-structure is shown in Figure 5.21.

Piers are cast in place in lifts 10 ft (3 m) high bymeans of climbing forms and are hexagonal, Fig-

ure 5.23. The finished bridge is shown in Figure5.24.

5.4.3 CO,VCEPT OF PRECAST BELL PIERFOC,VDATION FOR THE I-205 COLL’,WBI,4 RIVER

BRIDGE, C’.S.A.

A somewhat comparable system to that used forthe Sallingsund Bridge was contemplated for ap-proach spans 15 through 26 of the I-205 ColumbiaRiver Bridge in the State of Oregon, as shownschematically in Figures 5.25 and 5.26. Steel Hpiles of 200 ton capacity were to be driven througha template box, allowing tremie concrete to beplaced inside the trough. The precast segmentswere designed to be stacked upon one anotherabove the template to make up the pier shaft andtransfer the superstructure load to the piles.

This scheme was not actually used, as the con-tractor decided on a more conventional method ofconstruction. However, the scheme of precast bellpier foundations was used on the Richmond-SanRafae l Br idge and the San Mateo-HaywardBridge, both in San Francisco Bay, and the Colum-bia River Br idge a t As tor ia , Oregon. A com-prehensive discussion of these structures is pre-sented by Gerwick in reference 3.

5.4.4 MAI,: PIERS FOR THE HOUSTOS SHIPCHA,V,VEL BRIDGE, U.S.A.

Each main channel pier, Figure 5.27, is made upof the following:

A rectangular shaft 161 ft (49 m) high with a crosssection varying in dimensions from 20 X 38 ft (6.10x 11.60 m) at the base to 20 x 28 ft (6.10 X 8.50 m)at the top. The section is a single-cell box with wallthicknesses of 2 ft (0.61 m).

A reinforced concrete footing 75 X 81 X 15 ft(22.90 x 24.70 x 4.60 m).

A group of two hundred and twenty-five 24 in.(0.61 m) diameter steel pipe piles having a wallthickness of 4 in. (12.7 mm).

The superstructure is completely integral with thetwo main channel piers to form a rigid frame, bothduring construction and in the finished structure,Figures 1.67 and 2.80.

Stresses in the concrete and reinforcing steelwere analyzed in both stages with the service-loaddesign approach, and u l t ima te s t r eng th wasverified by the load-factor method. The analysis is

Moment-Resisting Piers and Their Foundations 239

TEST LOADING

PLACING OF PIER BOX

PLACING OF TEMPLATE

dteel pik

PILE DRIVING

PLACING OF ICE BREAKER BOX

CONCRETING OF STEELPILES AND FOUNDATION

FIGURE 5.21. Sallingsund Bridge, schematic of substructure opera-tions.

rather strenuous, because in the completed struc-ture only there were 19 unit loads combined into37 load combinations for service-load design andinto 42 loading combinations for load-factor de-sign.

The concrete cross-sectionalthe corresponding reinforcinglows:

top: A, = 176 ft2,

area together withsteel area is as fol-

A, = 200 no. 11 bars = 297 in.*,p = 1.17%

bottom: A, = 216 ft2,A, = 264 no. 11 bars = 392 in.*,fi = 1.26%

Under service load the average concrete stress ofthe cross section is as follows:

top: 3 1,700 kips + 176 ft* = 180 kips/ft*bottom: 36,600 kips + 2 16 ft2 = 170 kips/ft*

In large structures, such as the Houston ShipChannel Bridge, the average concrete stress in thepier shafts usually varies between 160 and 200kips/ft*. The use of a varying-width pier in thetransverse direction allows the maximum stressand the required amount of reinforcing steel to in-crease at a slow rate with the pier height, while aprismatic pier shaft will be subjected to a very criti-cal stress at the base.

Ice-breaker-

:’ . Pierbox

CROSS SECTION

04Om0

FIGURE 5.22. Sallingsund Bridge, aerial view of pre-cast yard and harbor for substructure construction.

CLIMBING FORM

Tower crane

3 50m

55Om

FIGURE 5.23. Sallingsund Bridge, schematic of pier construc-tion

FIGURE 5.24. Sallingsund Bridge, view of finishedbridge.

Piers with Double Elastomeric Bearings

TYPICAL PIER

241

5810’ ,TYPICAL

I_ S E G M E N T 5 _I I I

DESIGN HIGH WATERELEV. 28.0’ -

116’-2”CAST-IN-PLACE

CONCRETE

SEGMENT 4

SEGMENT 3 // \\ I

SEGMSEGM

FIGURE 5.25. I-205 Columbia River Bridge, mainpiers and foundations.

PRECAST BELL PIERS

SEGMENT 4

SEGMENT

SEGMENT

SEGMENT

FIGURE 5.26. I-205 Columbia River Bridge, sche-matic of construction of precast bell piers.

P I E R ELEUTION MER PROFILE

r

PLA.h S E C T I O N B.B

PLAN SECTION 4.A

FIGURE 5.27. Houston Ship Channel Bridge, mainriver piers.

5.5 Piers with Double Elastomeric Bearings

5.5.1 SCOPE AND GEAVERAL CONSIDERATIO,VS

Recognizing the inherent advantages of a rigidconnection between piers and superstructure (sta-bility during construction and increased super-structure stiffness reducing the effect of live load),the designer is rapidly limited in its use in longbridges because of unacceptable effects of vol-ume changes. This situation allowed the birth ofa new type of structure developed to maintain thetwo desirable features that were previously con-tradictory: flexural rigidity on one hand and hori-zontal flexibility on the other. The concept of thedouble row of elastomeric bearings was first de-veloped for the Oleron Viaduct and used thereaf-ter on a great many bridges.


With piers of this type, two observations are re-quired concerning the transfer of forces betweenthe superstructure and pier. The first observationconcerns the transfer of service loads, Figure5.28~. Under the effect of unsymmetrical loads,the upper and lower flanges of the superstructureare respectively subjected to unequal tension forcesTL and T, and compressive forces CL and CR. If avertical diaphragm is positioned over each of thetwo rows of bearings, the center portion of the topflange of the pier segment, to be in equilibrium,must accept the tension force TL - TR. This is not asatisfactory disposition, as the thickness of theflange and amount of reinforcing have to be in-creased between the two rows of bearings, andthere is the risk of cracking.

However, if the two diaphragm: are inclined andconverge at the level of the top flange, the differ-ential in tension, T, - T,, is divided into two com-ponents of force, C (compression) and T (tension),directed into the plane of the diaphragm, while thetension force may be accommodated by prestress-ing the diagonal bracings.

Another important aspect of the pier segmentdesign relates to the imbalanced loading conditionresulting at the bottom flange from the unequalreactions R1 and R, of the bearings, which calls forcareful analysis of the stress developing in thediagonal bracings in all loading stages of thestructure.

The second observation concerns the super-structure-pier connection during the temporaryphase of constructing the superstructure in can-tilever, Figure 5.286. To accommodate a mo-ment unbalance resulting from the constructionprocedure, the pier segment is supported on fourtemporary bearings of steel or concrete, 0, andtemporarily fixed by prestressing to the top of thepier, 0. After closure at midspan occurs, producinga continuous span, the joint is “unlocked” by re-leasing the prestressing. Flat jacks, 0, are then acti-vated so as to substitute permanent bearings forthe temporary bearings.

5.5.2 DESCRIPTION OF STRUCTURES

Many structures have been designed and builtutilizing the system of piers incorporating a doublerow of neoprene bearings. This section will de-scribe the salient features of three particularbridges as exemplifying the advantages of this sys-tem as used in connection with a variety of foun-dation schemes.

TL-

Neoprenebearings

CO++ i‘3 Flatjacks

Steel bandedconcrete block

fb)FIGURE 5.28. Connection of superstructure andpier. (a) In service. (6) In temporary construction phase.

Piers with Double Elastomeric Bearings

Oleron Viaduct, France tice by a factor of 1.33. The comparable designload would then be 250 t (230 mt) for a pipe pile 20in. (500 mm) in diameter with a thickness of 3 in.(12.7 mm) driven to refusal in the rock and filledwith concrete after driving. The correspondingsteel stress of the pipe alone would be 16 ksi (110MPa), a somewhat higher value than normally usedin similar circumstances. When considering theglobal section of concrete and steel, the stress in theconcrete is only 800 psi (5.5 MPa)-a very reason-able value, confirmed by the fact that none of the15 piers showed any sign of settlement duringthe fifteen years of operation of this viaduct. Thepipe piles were driven open-ended and excavatedinside by a homemade airlift system conceivedby the driving subcontractor. It took only a fewminutes to perform this operation on each pile.

Of the 45 piers, only the 27 piers supporting thecenter portion of the viaduct with span lengths of260 ft (79 m) are designed with a double row ofbearings. In this portion of the viaduct there is anexpansion joint every fourth span, and the elas-tomeric bearings had to accommodate the volumechanges of the deck in a maximum distance ofthree spans (i.e., 780 ft or 237 m). Out of these 27piers equipped with a double row of bearings, 12are founded on spread footings constructed di-rectly on limestone rock inside a temporary sheetpile cofferdam, Figure 5.29. The other 15 piers aresupported by a system of pipe piles driven to thelimestone, which in this area is at a depth of 75 ft(23 m) below mean water level, Figure 5.30.

The 12 piles in each pier consist of four verticalpiles, one at each corner, and eight battered piles,so inclined as to resist the horizontal loads (lon-gitudinal and transverse) applied to the structure.For the most critical loading combination (compa-rable to the AASHTO requirements) the max-imum load in a pile is 330 t (300 mt), whichshould be reduced to compare to American prac-

For the piers on piles, a tremie seal was used in-side the cofferdam to allow dewatering and con-s t ruc t ion o f t he r e in fo rced conc re t e foo t ingpoured in the dry.

A l l b o x p i e r s h a f t s w e r e s l i p - f o r m e d t o amaximum height of 82 ft (25 m) at the rate of 15 to20 ft (4.5 to 6 m) a day, and the construction of ashaft took approximately one week, Figure 5.31.

243

FIGURE 5.29. Oleron Viaduct, piers on spread footings.

0.30

Treme conc re te

+

I-,‘..I,-*.I’ :9’

r

1.30

p-i-

.-. . . ..’ .,

Vertical prestresslng

. 5 . 6 0 -

c 7.30l

FIGURE 5.30. Oleron Viaduct, pier-s on piles.

244

FIGURE 5.31. Oleron Viaduct, aerial view of founda-tions.

Blois Bridge, France

The Blois Bridge crossing the Loire River is a five-span, prestressed, precast concrete segmentalsuperstructure consisting of twin box girders withthe following span dimensions: 202, three at 300,202 ft (61, three at 91, 61 m). It is supported byfou r r i ve r p i e r s elastically restrained at thesuperstructure with a double row of bearings. Di-mensions of a typical pier are given in Figure 5.32and a view of a finished pier in Figure 5.11.

t65'

I I t I

FIGURE 5.32. Blois Bridge, dimensions of river piers.

The special feature of this project is that a verycomprehensive optimization study of the sub-structure system with a double row of bearings al-lowed the use of only half as many piles as the basicscheme with single bearings, without increasing theunit bearing capacity of the piles.

Upstream Paris Belt Bridge, France

This important bridge was built over the SeineRiver to carry Europe’s most heavily traveledurban freeway, the Paris Beltway. As shown in alongitudinal section, Figure 3.22, it has two majorriver piers resting on a unique foundation system,while land piers and abutments are conventionallyfounded on piles.

A typical transverse section of the bridge showsthe orientation of the piers, Figure 5.33, and vari-ous cross sections through the piers is shown inFigure 5.34. Each of the twin bridges carries fourlanes of traffic on two box girders, which are sup-ported on two separate pier shafts connected belowwater by a single footing. Two lower foundationshafts extend under this footing to a maximumdepth of 70 ft (21 m) to carry the bridge loads tothe supporting soil strata through a series ofheterogeneous seams of silt, fine sand, and clay.

Each of these lower shafts (there are eight suchshafts for the two river piers) w; s built inside a rec-tangular steel sheet pile cofferdam, driven as lowas possible before excavation. The shafts were ex-tended below the tip of the sheet piles to reach theload-bearing soil by incremental stages of excava-tion and continuous concrete lining, Figure 5.35.Cement grouting and temporary lowering of theaquifer by pumping allowed this work to be per-formed in the dry. Except for the minor blowout inone of the eight shafts, which called for specialgrouting work, the foundation project was per-formed safely and successfully. Figure 5.36 showsone of the river piers completed and receiving theprecast pier segment of the superstructure.

5.5.3 PROPERTIES OF NEOPRENE BEARINGS

Notation

A neoprene bearing may be designated by the fol-lowing physical parameters, Figure 5.37a:

a and b = plan dimensions of bearing (a < 6)12 = number of elastomer sheetst = thickness of one elastomer sheet

2e = thickness of the internal steel sheet(twice the external sheet)

Ab = a * b = area of bearing


Cc-

Dt-

EL 124

1 34’ 1 ? 4 ’ 1 3 4’ 1T

FIGURE 5.33. Upstream Paris Belt Bridge, typical elevation of river piers.

An example, with dimensions in millimeters, is asfollows:

a x 6 x n(t + 2e)300 x 400 x 2(10 + 2)

Where differing thickness of steel plates are used,the successive thicknesses of steel and elastomerare given:

aXbXn( )300 x 400 x 2(5 + 8 + 2 + 8 + 1)

Deformation of Neoprene Bearings

The relationship between Young’s modulus (E)and the shear modulus (G) is presented in Table5.1. The shear modulus, G, of neoprene varies not

TABLE 5.1. Elastic Constants

Hardness(IRHD ?4)

Young’s ShearModulus E Modulus G

(N/mm*) (N/mm*)

only with the material hardness, as indicated inTable 5.1, but also with the rate of loading. Tabu-lated values are for the case of slow loading; for aninstantaneous loading the value of G is doubled.

Vertical Deformation (Compression) Under a nor-mal force V every lamination is subjected to a verti-cal shortening, v, Figure 5.376, such that:

v=C t3z&-z V

C is a coefficient that depends on the plan dimen-sions of the bearing and that expresses the re-straint effect on the lamination by the steel plate;refer to Table 5.2.

For a bearing consisting of n stacks or lamina-tions, the value of the shortening is equal to:

(5 - l )

45 1.80 0.5450 2.20 0.6455 3.25 0.8160 4.45 1.0665 5.85 1.37

Rotational Deformation Under a bending mo-ment M the upper face of each lamination under-goes a rotation 8 relative to the lower face:

tI=C’&Mb

Piers with Double Elastomeric Bearings 247

5ECllDN : D.-D

II

FIGURE 5.34. Upstream Paris Belt Bridge, typical horizontal sections of river piers.

C’ is a coefficient that depends on the plan dimen- refer to Table 5.3. The value a is the dimension insions of the bearing and that expresses the re- plan of the bearing measured perpendicular to thestraint effect on the laminations by the steel plate; axis of rotation, Figure 5.376.

TABLE 5.2. Values of the Coefficient C

bla 0.5 0.6 0.7 0.75 0.8 0.9 1 . 0 1 . 2 1 . 4 1 . 5 2 3 4 5 1 0 30C 5.83 4.44 3.59 3.28 3.03 2.65 2.37 2.01 1 . 7 8 1 . 7 0 1 . 4 6 1 . 2 7 1 . 1 8 1 . 1 5 1 . 0 7 1

TABLE 5.3. Values of the Coefficient C’

bla 0.5 0.6 0.7 0.75 0.8 0.9 1.0 1.2 1.4 1.5 2 3 4 5 10 30

C’ 136.7 116.7 104.4 100.0 96.2 90.4 86.2 80.4 76.7 75.3 70.8 66.8 64.9 63.9 61.9 60

Foundations, Piers, and Abutments

FIGURE 5.35. Upstream Paris Belt Bridge, detail of concrete lining of lower shafts.

For a bearing consisting of n stacks or lamina-tions, the value of the rotation is equal to:

FIGURE 5.36. Upstream Paris Belt Bridge, view of afinished pier.

Horizontal Deformation (Distortion) Under a hori-zontal force, Q, the upper face of each lamination,relative to the lower face, undergoes a horizontaldisplacement u :

with a corresponding distortion u/t.For a bearing consisting of n stacks or lamina-

tions, the value of the horizontal displacement isequal to:

5.5.4 DEFORMATION OF PIERS WITH A DOUBLEROW OF NEOPRENE BEARINGS

In structures where deck and piers are rigidlyfixed, it is necessary to analyze accurately the de-formation of ihe various piers to incorporate theirproper stiffness into the model of the total struc-ture. This is particularly important for unsymniet-rical live loading applied to one pier and for theeffect of volume changes. There is a relationshipbetween the loads applied at the top of one pier(usually at the level of the neutral axis of the deckover the pier) and the corresponding displace-ments at the same point that depends solely uponthe mechanical properties of the pier and its foun-


s ~(arbj

(a)

(b)

(4 Cc)

C” * hBp-‘p rdhep-cp ‘n: -

cf)

FIGURE 5.37. Piers with double row neoprene bearings (Oleron Viaduct). The mostlcidely used polychloroprene is Neoprene (trademark of Du Pont de Nemours).

dation, Figure 5.7. The elasticity coefficients A, B,C, and K may be computed from the materialproperties and dimensions of the pier.

For example, a pier with constant section and thefollowing properties:

Height h, area of cross section A,

Moment of inertia IModulus of elasticity E

assumed to be fixed at the base onto a totally rigidfoundation, has the following elasticity coefficients:

h*A=&, -B = 2EI’

h3C=m,

B* hK=A-C=4EI

In structures where neoprene bearings areplaced between piers and deck, the correspondingchange in elasticity of the system must be takeninto account. In fact, the presence of two rows ofneoprene bearings, spaced at a distance d, pro-

duces a partial fixity of the superstructure on thepiers. The neoprene bearings intervene in the de-formation of the pier by their normal force( 2 M lpd) produced by the moment M, Figure5.37~. The rotational stiffness of the neoprenebearings may be neglected.

The moment M applied at the top of the piermay be divided into componentsf and m in thebearings, Figure 5.37d, such that:

M =fd + 2m, e = 2vld

with:

from which:

In the majority of cases the quantity 2a*/C’ is smallrelative to d */2C.


Example

Dimensions of the neoprene bearing: 600 X 600mm. Spacing between the axes of the neoprenebearings: d = 2.4 m.

b 1-=a ’

C = 2.37, C’ = 86.2

= +$ (1.215 + O.OOS)e

In neglecting the second term in the parenthesis,in other words the rotational stiffness of the neo-prene, it can be seen that the error is slight, of theorder of 1%. Therefore:

2nCt3’ = pGAgzd2 M

Accordingly, the flexibility coefficients of theneoprene bearings may be written as:

A,=(+? t3pd2 m

B, = 0 (5-4)

Cn=2LL2P GAb

wherep represents the number of neoprene bear-ings per row. Therefore, if the flexibilitycoefficients of the pier shaft are denoted by A,, B,,C,, and K,, the total flexibility coefficient may bedefined as:

A =Ap+A,

B =B,

c = c, + c,

K = K, + K,

5.5.5 PROPERTIES OF PIERS WITH A DOUBLE ROWOF NEOPRENE BEARINGS

Piers with a double row of neoprene bearings haveproperties similar to those of piers with flexiblelegs, by insuring an effective fixity for loads whileallowing the free expansion of the superstructure.

This fixity presents the advantage of reducingthe bending moments in the spans without much

increase of the moment in the bearings, Figure5.37e.

During construction of the superstructure bycantilevering, stability in the temporary construc-tion phase may be provided by the substitution ofconcrete pads for the neoprene bearings and theuse of a temporary vertical prestressing.

By a judicious choice of neoprene thickness, it ispossible to reduce the bending moments applied tothe foundation. Consider a pier with a double rowof neoprene bearings supporting a continuoussuperstructure. For a bending moment M at thetop of the pier, under the effect of a loading in thesuperstructure with no horizontal displacement,the bending moment transmitted to the base of thepier is (Figure 5.37f):

M’=M +Qh

where h represents the height of the pier. Becauseu = 0, one may write:

BM+CQ=O

from which:

a n d

M’ = (1 - +)M = (1 - c,B$cn)M = 4M

The value of the coefficient 4 varies with thethickness of neoprene pads. If it is desired to trans-fer no moment to the foundation at the level of thepier base, M’ = 0, the transfer coefficient 4 mustbe equal to 0, from which:

C, = hB, - C, (5-5)

On the other hand if the neoprene thicknessbecomes very large, the value of 4 tends to thelimiting value of 1 and the bending moment re-mains constant in the pier; that is, M’ = M, Figure5.37f.

As an example, consider a pier with a constantmoment of inertia, fixed at its base, with a doublerow of neoprene bearings and supporting amaximum reaction of 1000 tons.

Pier characteristics: Assume a box section with ex-ternal dimensions of 5.0 x 3.0 m and a wall thick-ness of 0.30 m, h = 33 m, I = 7 m4:

E/&,=+= 4.71


EB, = & = 77.7

EC, = & = 1715

Four neoprene bearings are arranged in two rowsat a spacing of 2.4 m in the longitudinal directionof the bridge. Dimensions of each bearing are 600X 400 X 3(12 + 2) (see Section 5.5.3).

Flexibility of the neoprene bearing: a = 0.40 m, bla =1.5, C = 1.7, Ah = 0.24 m*, n = 3,p = 2, t = 1.2 X10m2 m, G = 160 t/m’, E, = 3.9 X lo6 t/m’:

EB, = 0

ntEC,=E-2PGA h

= 915

Totaljlexibilit? qf the pier:

EA = 4.71 + 0.97 = 5.68

EB = 77.7

EC = 1717 + 915 = 2630

Elasticit? of the pier in the structure:

EK = E (.4 - g) = 5 . 6 8 - ‘:;;;’ = 3 . 3 8

Elasticity qf’ the pier zuithout neoprene:

Ek’ = E [;4 - $1 = 0.25+ = 1.18

Coe@cieut of momerlt transmission in the pier:

4 = 1 - B; - 1 - 77;76;033 = +0.03

The bending moment M’ transmitted to the baseof the pier is very small (3% ofM). For the momentM’ to be theoretically equal to zero:

EC,, = 9 = 860

and the corresponding thickness of neoprene isthen:

EC,=n t E2p G A ,

or

nt = ‘L(EC.)PGA,E

2 x 860 x 2 x 160 x 0.24= =3.9

o 034 mx 106

nt = 34 mm

A comparison of the constants A, B, C, and K withthe number of neoprene laminations (for thisexample) is presented in Table 5.4. If the height ofpier Were changed from 33 m to 20 m, the totalneoprene thickness would correspondingly changefrom 34 mm to 8 mm.

5.5.6 INFLUE,VCE OF THICKNESS AAiDARRA,VGEME,vT OF ,YEOPRE,\‘E BEARI,XIGS ON THE

VARIATIOX OF FORCE IS A THREE-SPANSTRUCTURE

In order to better understand the influence of thethickness of neoprene pads, studies have beenconducted to determine the variation of the bend-ing moment in a three-span continuous structurewhen only the number ofneoprene laminations atthe top of the intermediate piers is modified.

The structure considered is a symmetricsuperstructure of three continuous spans sup-ported on two identical piers; it consists of a boxgirder with a variable moment of inertia, whosespans are 44 m, 70 m, and 44 m.

Bending moments in the superstructure andpiers are calculated under the following assump-tions:

Superstructure fixed at the pier

Superstructure partially fixed elastically at thepiers with neoprene bearings with the varyinglamina of 1, 2, 3, 6, or 9 (thickness 12 mm)

Superstructure supported on the piers by simplesupports

Assumptions used in the conduct of the study are:

Superimposed dead load represented by a uniformload, q = 1.9 t/m

Expansion of the deck at a rate of 2 X 10e4, corre-sponding to an increase in temperature of 20°C.

Shrinkage of the deck at a rate of 4 x 10P4, corre-sponding to a decrease of temperature of 20°Ccombined with the effect of shortening and time-dependent deformations (creep) resulting fromprestressing (2 X 10m4).


TABLE 5.4.

Number of Neoprene Lamina

Coefficient

EAEBEC

Diagram ofbending momentin the pier(h = 33 m)

Diagram ofbending momentin the pier(h = 20 m)

1.18

5.0377.7

2020

2.03

-0.27

5.3677.7

2325

2.76

5.6877.7

2630

3.38

6.0077.7

2935

3.93

+ 0.64

6.3377.7

3240

4.46

Applied load Sz = 4.5 t/m in the center span

Applied load S, = 6.8 t/m in the end spansBraking force F = 15 t on the superstructure, cor-responding to approximately one-twentieth of thestructure dead load

The bending moments in the superstructure as aresult of the above loads are tabulated in Tables5.5a through 5.5~:

Table 5.5a: bending moment at the top of the pierTable 5.56: bending moment at the base of the pierTable 5.5~: maximum bending moments in thesuperstructure

This study leads us to the following observations:

1. Regarding the superstructure, the maximummoments vary little with the number of neo-

prene laminations. When the number of lami-nations increases from one to six, themaximum bending moment at the support de-creases by 4% and the maximum positive mo-ment in the center span increases by 10%. Theextreme case of nine lamina is to be avoidedbecause of risk of instability presented by thetall stack of neoprene (alnt < 5). Comparedwith a simple bearing support, the double rowof bearings provides an important decrease inmoment in the spans for a relatively smaller in-crease of moment at the pier support.

2. Regarding the pier, there exists an optimumthickness of neoprene allowing a minimaltransfer of moment to the level of the founda-tions. In the example considered this thicknessis equal to three lamina of 12 mm, which corre-sponds closely to the value determined in Sec-tion 5.5.4 for the case of a structure restrainedhorizontally.

Piers with Twin Flexible Legs 253

TABLE 5.5~. Bending Moment at the Top of the Pier as Function of the Bearing Thickness0

Number of’ Neoprene Lamina

0(Fixed

Loading Pier) 1 2 3 6 9

Superstructure D.L., + 1 2 4 + 106 + 93 + 84 + 68 + 58q = 1.9 t/111

Deck expansion, + 92 + 68 + 53 + 43 + 27 + 19+ 2 x 10-4

Deck shrinkage, - 1 8 4 - 36 - 106 - 86 - 54 - 38- 4 x 10-4

I: moments I + ,\I + 2 1 6 + 174 + 146 + 1 2 7 + 95 + 77(no L.L. ) -‘VI - 60 - 3 0 - 13 - 2 + 6 + 20

L.L in center span,si = 4.5 t/m + 1700 + 1440 + 1270 + 1150 + 930 + 790

L.L. in end spans, - 1420 - 1240 - 1120 - 1030 - 850 - 740S, = 6.8 t/m

Braking force, F = 15 t ? 1 0 1 + 97 2 93 k 90 2 80 k 74Maxi 1llu111

I

+‘M +2017 +1711 + 1059 + 1367 + 1105 +941m o m e n t s - ‘\/I - 1 5 8 1 - 1367 - 1226 - 1 1 2 2 - 924 - 795

“Values have heen calculated at the intersection of the axis of the pier with the center of gravitv of. the super-structure.

TABLE 5.5b. Bending Moment at the Base of the Pier as Function of the Bearing Thickness


Loading

0

(FixedPier) 1 2 3 6 9

Simple

Support,t = 24 mm

Superstructure D.L.,q = 1.9 t/m

Deck expansion+2 x 1o-4

Deck shrinkage- 4 x 10-4

C moments

I

+M( 1 1 0 L . L . ) -M

L.L. in center span,S, = 4.5 t/m

L.L. in end spansS, = 6.8 t/m

Braking force, F = 15 tM a x i m u m + M

Im o m e n t s - M

- 62 - 3 1 - 15 - 4 + 13 + 2 0 0

- 2 0 2 - 1 5 7 - 1 2 9 - 1 1 1 - 7 7 - 6 0 - 1 3 0

+ 4 0 4 +314 +258 +222 +154 +120 +260

+ 3 4 2 4283 +243 +218 +167 + 140 +260- 2 6 4 - 1 8 8 - 1 4 4 - 1 1 5 - 6 4 - 4 0 - 1 3 0- 8 2 0 - 4 3 5 -198 - 4 7 +176 + 265 0

+ 1 9 7 - 7 4 - 2 0 7 - 2 6 5 - 3 8 0 - 4 0 0 0

+ 1 5 9 2163 *167 -e170 +180 ?I86 (+520)+ 6 9 8 +609 +577 +558 +527 +591 +780- 1243 - 7 8 6 - 5 1 8 - 5 5 0 - 6 2 4 - 6 2 6 - 6 5 0

5.4 Piers with Twin Flexible Legs precast segmental bridges either in France or

5.6.1 INTRODUCTION Europe and more recently in the United States.Several examples of such structures will be de-

The concept of piers with twin flexible legs was first scribed below with particular emphasis on the de-used with the first match-cast segmental bridge of sign and construction methods of the foundationChoisy-le-Roi. It was further used on several other system.


TABLE 5.5~. Maximum Bending Moments in the Superstructure as Function of the Bearing Thickness


0(Fixed Simple

Loading Pier) 1 2 3 6 9 Supporl

Moments 1 Center span -3125 -3060 -3020 -2985 -2925 -2895 -2660atsupport Side span -3105 -2960 -2845 -2770 -2635 -2545 -2055

Center span,Moments (0.5 &) + 910 + 960 + 990 +1015 + 1060 + 1090 +1270in Side span,span (0.4 11) + 890 + 935 + 965 + 980 + 1020 + 1040 + 1200

5.6.2 RIVER PIERS AND FOUNDATIONS FORCHOISY-LE-ROI, COURBEVOIE, AND JUVISY

BRIDGES, FRANCE

These structures were described in Chapter 3.

Choisy-le-Roi Bridge over the Seine

This structure is composed of two parallel twinbridges, Figure 3.3 and 5.38. Each structure has acontinuous three-span superstructure in pre-stressed concrete with spans of 123 ft (37.50 m),180.4 (55 m), and 123 ft (37.50 m), fixed at thecenter piers and forming a symmetric frame.

Piers are supported on a system of steel pipepiles driven to refusal in rock. The superstructureis supported on two slender inclined legs having athickness of 16 in. (0.40 m) and inclined to the ver-tical axis at 0.065. Dimensions of the substructureare shown in Figure 3.3. The precast legs with anapproximate weight of 27.5 ft (25 mt) have theircenterlines converging to a point approximately atthe level of the foundations so as to reduce thebending moments to .the foundation. The legs arejoined to the body of the pier at one end and to thesuperstructure at the other end by prestressingtendons. Before construction of the superstruc-ture by the balanced cantilever .method, the legsare temporarily stiffened by a triangular steelframework in the space between them. The con-struction stages are described graphically in Figure5.38.

Courbevoie and Juvisy Bridges over the Seine

The Courbevoie Bridge is very similar in conceptto the Choisy-le-Roi Bridge. It consists of a con-tinuous three-span superstructure with symmetri-

cal spans of 131 ft (40 m), 197 ft (60 m), and 131 ft(40 m).

Each river pier consists of two half-structureswhose foundations are fixed in dense rock, Figure3.9. The top portion of each half-pier consists oftwo vertical slender legs, oriented, in plan, per-pendicular to the longitudinal axis of the bridge,and in a transverse section of the bridge, disposedin the shape of a V. These legs, which have aparallelogram form, are spaced in a longitudinaldirection at 6 ft 9 in. (2.05 m) on center with a con-stant wall thickness of 18 in. (0.45 m). The legswere precast and joined to the superstructure andthe lower portion of the pier by prestressing ten-dons.

The Juvisy Bridge consists of six prestressedconcrete continuous spans with a total length of700 ft (213.5 m). Spans are successively from theleft bank 62 ft (18.8 m), 62 ft (18.8 m), 137 ft (41.8m), 218 ft (66.6 m), 137 ft (41.8 m), and 84 ft (25.7ml.

The two piers located in the Seine are split piersresting on a common foundation, Figure 3.26. Thefoundations were constructed inside a sheet pilecofferdam, which permitted the flexible legs tobe fixed at the bottom and hinged at the top. Thethickness of the legs varied from 24 in. (0.60 m) attheir base to 16 in. (0.40 m) at the top. They weresymmetrically inclined at 0.0805 to the vertical andwere cast in place and prestressed.

5.6.3 PIERS AND FOUNDATIONS OF CHILLONVIADUCTS, SWITZERLAND

This structure, 1.24 miles (2 km) in length, is a twinparallel viaduct overlooking Lake Leman and fol-lowing a sinuous route corresponding to the contourof the hillside on which it is located, Figure 5.39. It

5

FIGURE 5.38. Choisy-le-Roi Bridge, construction stages of foundations and piers.


FIGURE 5.39. Chillon Viaduct, general view.

consists of 23 continuous spans of prestressed con-crete, span lengths being 301.8 (92 m), 321.5 (98m), or 341.2 ft (104 m). Four expansion joints di-vide each viaduct into sections with a maximumlength of 1890 ft (576 m). The longitudinal stabil-ity of each section is provided either through afixed bearing over the end abutment or by specialfixed piers designed to withstand the horizontalreactions of the superstructure.

The piers, Figure 5.40, consist of two slendervertical legs with a constant thickness of 2 ft 8 in.(0.80 m). Height of pier varies in increments of 26ft (8 m) with a maximum height of 118 ft (36 m).Legs less than 72 ft (22 m) in height are hinged atthe top and bottom. Legs over 72 ft (22 m) inheight are fixed at the base and hinged to thesuperstructure.

Because of the leg spacing there is no tensiongenerated in the legs, so no vertical prestressing isrequired. During construction of the superstruc-ture the stability of the pier is increased by tempo-rary steel bracing anchored into the legs.

5.6.4 MAIN PIERS AND FOUNDATIONS OF THEMAGNAN VIADUCT. FRANCE

The Magnan Viaduct consists of four continuousspans; span lengths are 413 ft (126 m), two at 433 ft(132 m), and 249 ft (76 m), Figure 2.98. The piersare constructed of twin H-shaped shafts 40 ft (12m) on center and with a maximum height of 3 18 ft(95 m) above the valley floor, Figures 5.41~ and5.41b. These piers are similar to slender verticallegs of variable cross section fixed at the base. Be-cause this structure is located in an area of seismicactivity, the superstructure is fixed at the westabutment and restrained transversly at the piersand the other abutment.

116-6 (y

l-

Ia56-1-

t

FIGURE 5.40. Chillon Viaduct, pier section.

5.6.5 MAIN PIERS AND FOUNDATIONS FOR THEDAUPHIN ISLAND BRIDGE. U.S.A.

The Dauphin Island Bridge is an 18,000 ft (5.5km) long structure over Mobile Bay connectingDauphin Island to the mainland of Alabama. Inorder to permit ship traffic, the central portion ofthe structure was designed with a three-span con-tinuous unit of 2 11, 400, and 211 ft (64, 122, and64 m). This provided a clear shipping channel of350 ft (107 m) horizontally and 85 ft (26 m) verti-cally. This project is currently (1980) under con-struction and is anticipated to be completed by late1981.

Each main pier of this three-span structure con-sists of twin, I-shaped walls spaced longitudinally at21.5 ft (6.6 m) on center, Figure 5.42. An indi-vidual wall is 24 ft 7 in. (7.5 m) wide and ismoment-connected to the single cell box girdersuperstructure as well as to the footing.

Piers with Twin Flexible Legs 257

2f.4"i

E L . 3 1 5v

, -*

EL630

21:4*

EL.266f

* ‘5’ * *. 65.60' )

i.1 J

FIGURE 5.41. Magnan Viaduct. (n) Pier section. (h)Completed pier.

The foundation is to be made with circular,standard sheet pile construction. Alternate pilingswere detailed on the plans to be either 30 in. (0.76m) squa re p r eca s t , p r e t ens ioned conc re t e o r54 in. (1.37 m) hollow, cylindrical, precast, post-tensioned concrete. Piling will be driven to acapacity of 450 kips (204 mt) for the 30 in. (0.76 m)square pile or 550 kips (249 mt) for the 54 in. (1.37m) cylindrical pile. A dewatering seal will bepoured under water after the piles have been driv-en. This seal will be located 25 ft (7.6 m) below thewater surface and have a thickness of 5 ft (1.5 m).After dewatering, a circular footing with a diame-ter of 44 ft (13.4 m) and a thickness of 10 ft (3.05m) will be poured. The twin wall piers will be con-structed from a point 10 ft (3.05 m) below thewater level and reach a total height of approxi-mately 93 ft (28 m).

The des ign inc luded checking of AASHTOloads and combinations, including a stream flow of3.5 fps (1 mps). Additionally, the structure waschecked at an ultimate condition for a storm windof 200 mph (322 km/h). The load factor for thiscondition was taken as 1.0.

5.66 D E F O R M A T I O N A N D P R O P E R T I E S O F P I E R SWITH FLEXIBLE LEGS

The following notation is used (Figure 5.43):

M, Q, W components of external load acting atpoint 0,

m, t, n = components of load acting at the top ofthe leg of the pier, oriented to the axis ofthe leg,

8, U, z, = displacements corresponding to M, Q, Nat point 0,

W, (Y, /3 = displacements corresponding to m, t, n atthe top of the leg,

E = modulus of elasticity of the concrete leg,1= length of the leg between points A and B,

2d = spacing of the legs at the top betweenpoints A and A’,

a = cross sectional area of leg,i = moment of inertia of a leg,

p0 = ad V2i dimensionless coefficient,4 = angle of inclination of the legs with the

vertical.

Identical and symmetrical legs, of length 1, areinclined to the vertical by the angle 4. The cross-sectional area and moment of inertia of each leg ata distance x from the top, A or A ‘, are respectivelya(x) and i(x).


6 BRIDGE

r-h-

HER SEGMENT

STEEL SHEET PILING

EL 0 0 0

L SEAL CONCRETE

SECTION

24’. 7 ”

I

I-- E BRfDGt-

f PIER

PLAN VIEW

FIGURE 5.42. Dauphin Island Bridge, dimensions ofmain piers and foundations.

t f BRIDGE

2 4 ’ 7 ’

SECTION

The symbol u is designated as an equivalent areaof the leg such that:

1 l’u!x-=-u 1 s0 a(x)

and U, V, and W the characteristic integrals as:

UT -s

’ dx0 i(x)’

v= -s

‘xdx0 i(x) ’

w =s

‘x2d.xO;(x)’

At the level of’the superstructure, AA ‘, the com-bined area and moment of inertia of the two legs,designated by A and I respectively, is representedbv:

A = 2a and I = 2i + 2ad2

with 2d being the distance between the two legs atthe top.

Setting p. = ad2/2i, the combined moment of in-ertia of the two legs becomes I = 2i( 1 + 2p,).

Piers with Twin Flexible Legs

*-A---+ mA*

FIGURE 5.43. Piers with flexible legs, notations.

The positive directions of forces and displace-ments are indicated by the arrows in Figure 5.43.

The deformations of the pier are given by linearequations that relate the displacements of the topof the pier (0, U, v) to the applied forces (M, Q, N).Legs AB and A ‘B ’ are assumed to be connected attheir ends by two rigid and indeformable sectionsAA’ and BB ‘. Section BB’ is assumed fixed (notranslation), and the deformation equations aregiven by:

8=AM+BQ

u=BM+CQ

v=KN

where A, B, C, and K represent deformationcoefficients of the legs.

Force components M, Q, N acting at point 0(center of AA’) are the resultant of the externalforces applied to the pier, and 8, U, u are the corre-sponding components of displacement of the sec-tion AA’ at point 0 (Figure 5.436). To determinethe forces m, t, n and m’, t’, n’ in the legs atA and A’requires the formulation of the equations ofequilibrium, deformation, and compatibility.

1. Equilibrium equutions: The equilibrium of thesystem about point 0 is given by

2.

M = m + m’ + d sin 4(t + t’)- d cos +(n - n’)

(5-6)Q = (t + t’) cos 4 + (n + n’) sin 4N = - (t - t’) sin 4 + (n + n’) cos 4

Deformation equations: Displacement o, (Y, Pand w’, cr’, p’ at pointsA and A’ (with respect tothe axis of the legs) are given by:

w=w,+ s‘m + t x mU +tvoTdx=o,+E E

a=o,,l+s

‘m + t x mV tw-xdx=cq,l+- -

o Ei E + E

p=pY=lr0 a EU (5-7)

where w. is the rotation of the leg AB at B, andE is the modulus of elasticity of the concrete.Corresponding equations give the displace-ments o’, (Y’, /3’ at point A’.

Displacements of points A and A’ with respectto the axis of the pier, 8, A, p and 0’, A’, p’ aredetermined as

8=6J

A = a cos 4 + p sin 4

p = Q sin 4 + p cos 4


Legs hinged at both ends

A’ = CY’ cos 4 - p’ sin 4

p’ = CY’ sin 4 + j3’ cos 4

3. Compatibility equations: The conditions ofcompatibility between the displacements ofpoint A, A ‘, and 0 require that

exoEw’ (if there are no hingesatA andA’)

(5-9)

p) = 7l + de‘The foregoing equations are sufficient to cal-culate 8, U, and 11 as fSunctions of the appliedloads represented by ,M, Q, and ,V.

Four practical cases need to be considered:

Legs fixed at both ends

Legs fixed at the superstructure and hinged at thebase

Legs hinged at the superstructure and fixed at thebase

For any of these four cases the legs may be of con-stant or variable cross section, either inclined orvertical. A comprehensive study was made of thisproblem by J. Mathivat and reported in references1 and 2, with several complete derivations of for-mulas applying to each particular case.

An important practical application is that of twinvertical walls with constant cross section, for whichequations become very simple. Table 5.6 sum-marizes the value of the global equivalentcoefficients of elasticity of the pier. In this case p,, =nd2/2i, which becomes p0 = 6(dlh)2 with 2d the dis-tance on centers of both legs and h the wall thick-ness. Usually p0 varies between 30 and 80.

It is evident, in fact, that a pier made up of twinlegs behaves much in the same way as a conven-tional pier with a cross-sectional area A and a mo-ment of inertia I insofar as the effect of verticalloads and moments on vertical displacements androtation is concerned.

The behavior is completely different when con-sidering the horizontal displacement due to theapplication of a horizontal load (braking force orthermal expansion). The conventional value of the

TABLE 5.6 Flexibility Coefficients of a Pier with Twin Vertical Walls of Constant Cross Section”

End Conditions for Legs

Flexibilit\Coefficient

E.wct Fonttui~i,s.4

5lultiplierCoefficient

1E l

Fixed stopand Botrom

1

Fixed .I‘opHinged Bottom

I+12P,t

Hinged .I‘op Hinged ‘I‘opFixed Bottom rind Bottom

1+1 1+12P” 2 PO

B

C

1 0

133EI

(1 + $)(3 + 2/J,,)1 + 2Po

1+-p

.4pproxitttntr Forttt~clnsh‘4 I

E l

0

x

“Notation: I = 2i(l + 2p,), equivalent global inertia of twin walls. p,, = nci2/2i = C(~/IZ)~, with 2~f distance between walls, h wallthickness.*When l/p, is negligible with regard to 1.

Piers with Twin Flexible Legs 2 6 11:’elasticity coefficient C = -

3EI IS multiplied by the

dimensionless factor 1 + po/2 in the case of verti-cal walls fixed top and bottom or by (1 + 2 pO) forwalls hinged at one end.

The elasticity coefficient becomes infinitely largefor double-hinged vertical walls, which proves sim-ply that stability toward horizontal loads must beobtained through some other restraint in thestructure such as fixed connections or elastomericbearings over the abutments.

A detailed study of several typical cases was con-ducted for the Choisy-le-Roi Bridge, consideringin particular:

Legs fixed at both ends

Legs hinged at both ends

Legs fixed on top and hinged at the base

Table 5.7 presents the essential results of thisstudv, which also includes consideration of theflexibility of the body of the pier to the base of thefoundation, where:

MO = bending moment in the superstructureat the pier section (side of the centerspan),

M, = bending moment in pier (top section),Q = horizontal reaction in the pier.

The following conclusions may be drawn fromthe study:

The superstructure is very efficiently fixed overthe river piers by the twin inclined wall system. Theend moment for the center span totally fixed atboth ends would be 255. The actual end momentvaries between 230 and 232 (i.e., 90% of the fixedend moment).

The elasticity of the pier depends very little uponthe conditions of fixity of the walls at the top andbottom (0.92 to 1.03).

The position of the point of contraflexure in thepier varies very little when the pier is subjected to amoment only; it is considerably more sensitive tothe effect of a horizontal load.

The horizontal rigidity of the pier varies appreci-ably with ttie degree of fixity of the legs.

5.6.7 ELASTIC STABILITY OF PIERS WITHFLEXIBLE LEGS

It has been shown that the use of twin Hexible legs(whether vertical or inclined) provides an eco-nomic solution to the dilemma between rigidity forbending versus rotation and flexibility for hori-zontal load versus displacement. In this respect theelastic stability of the system is the limiting factor,because there must always be an ample marginagainst buckling.

Assume the bridge superstructure to be dis-placed horizontally by 11 under a random horizon-tal load. The resistance against such displacementis offered by the pier rigidity, including the bend-ing resistance of the legs if they are at least partiallyfixed at the top or bottom and possibly includingthe horizontal rigiditv of the bearings over theabutments.

The minimum value of the vertical reaction inthe pier (or the normal force in the legs), for whichthe imposed displacement does not have a ten-dency to spontaneously diminish until the causeprovoking the displacement vanishes, representsthe critical buckling load of the pier. This criticalload is generally smaller than that where the legsare considered Isolated and subjected to the sameload conditions.

TABLE 5.7. Choisy-le-Roi Bridge: behavior of River Piers under Horizontal and Vertical Load@

Unit Vertical Unit Horizontal UnitFlexibilit) Load in Load Applied Volume

Coefficients Center Span to Deck ChangeType of ElasticityLegs A B c El, M,, iv, Mll iM1 iv,, iv, Q

Fixed 4.06 54.6 973 0.92 -232 -157 +3.4 +5.7 +7.4 +24.7 2.4Fixed/hinged 12.7 234 4670 0.98 -231 -154 +5.1 +a.7 +6.4 +21.5 1.3Hinged - - 1.03 -230 -150 +6.3 + 10.7 +5.9 + 19.7 0.9

“Notation: A, B, C = flexibility coefficients of pier. E L = global elasticity of pier. M, = end moment of center span (in tm). ,M, =bending moment at pier top (m tm). Q = horizontal reaction in pier.*Units: All coefficients in metric system. A uniform vertical load of 1 t/m is applied over the center span. A unit horizontal load of I tis applied at deck level. A unit shortening of the deck is applied such that EA = lo?


The deformations (8, U) produce internal forces of the three equations is nil, which allows us to ob-(m, t, n and m’, t’, n’) in the top of the legs, which tain the value of critical load nIc.require the following conditions: The critical buckling force of one pier leg may be

m , = mi, t, = t;, 72, = -n; expressed as:

If R. represents the rigidity of the superstruc- Eincr = r2-

ture against rotation and R, toward longitudinal l2

displacements, and if M and Q represent the mo-ment and horizontal force that the superstructure

where r is a dimensionless coefficient which may be

transmits to the pier, we have:related to the usual Euler formula for buckling:

M = - RoO f h, b, n,) (5-10) ncr = T2Ei

x2Q = - R,u gh nd

with h equal to the effective buckling length. ThusThese equations may be transformed to substi- the equivalent buckling length of one leg as part of

tute the deformations of the superstructure (0, U) the total pier system will be:for those of the legs:

Ref(m,, t,, n,) (5-l 1)*A&

r

R,(a cos 4 - P sin 4) g’(n,, tJwith aw = (Y sin 4 + /3 cos 4 and /3 = (IIEc)n,.

The condition of initial load of the leg (ex-pressed by no) is modified from the case of the dis-placement imposed to the structure and becomes:

Normal force: no + nlB e n d i n g m o m e n t : m,Transverse force: t ,

The additional forces m, and t, may be expressedas a function of the displacement of the legs (w, (Y)and of the initial force rzo. By substituting theseforces, as functions of (Y and o, into equations 5- 11,we obtain a system of linear equations in three un-knowns, n, a, w.

When we assume that the displacements (a, w)are different from zero when the cause inducingthe displacement vanishes, the determinate form

The example of the Choisy-le-Roi Bridge willagain be considered. Seven typical cases were in-vestigated with either vertical or inclined legs anddifferent leg end restraints. Also the horizontal re-straint of the bridge over the abutment was varied.Table 5.8 summarizes the results for the followingnumerical values:

Wall length 1 = 8.50 m, on center spacing 2 d =2.00 m

Area a = 6.40 m2, moment of inertia i = 0.085 m4

Neoprene pads over the abutments: area A b = 1.28m2, E/G = 20,000

The first six cases are hypothetical assumptionsused for comparison. Case 7 is the actual case ofthe Choisy-le-Roi Bridge with the legs hinged atthe base and fixed to the superstructure.

TABLE 5.8. Choisy-le-Roi Bridge: Elastic Stability of Twin-Flexible-Legged Pier forVarious Support Conditions

Case Conditions of LegsN u m b e r at River Piers

1 Hinged vertical legs2s I Vertical legs hinged at the base and fixed at the

4 top

5 Vertical legs fixed top and bottom6 Legs inclined 6.5%, hinged at base, fixed at top7 Legs inclined 6.5%, hinged at base, fixed at top

(actual case of Choisy-le-Roi)

Support Conditionat Abutments

Rigidity neglectedRigidity neglectedFive neoprene padsThree neoprene padsRigidity neglectedRigidity neglectedThree neoprene pads

Ac

Factor ofSafety

2.G1.201.001.000.880.97

01.12.84.04.05.24.8

Flexible Piers and Their Stability During Construction 263

The designer should be aware that the followingthree factors play an essential role in the elastic sta-bility of the structure:

Inclination of the legs to the verticalHorizontal rigidity of the neoprene bearings at theabutmentsFixity conditions of the ends of the legs in the piers

The fundamental difference between cases 2 and 6(Table 5.8) indicated by the considerable increasein the factor of safety (1.1 to 5.2) is due to the in-troduction in case 6 of the arch effect of the in-clined legs. Horizontal displacements of thesuperstructure cannot occur without mobilizingthe bending stiffness of the pier assembly. For case2 the elastic stability relies solely on the bendingstiffness of the legs, and the critical buckling forceis the same as for a beam fixed at one end and freeat the other.

5.7 Flexible Piers and Their StabilityDuring Construction

5.7.1 SCOPE

In the preceding paragraphs we considered piershaving a bending capacity allowing the deck can-tilever construction to proceed with no furtherstrengthening. Such moment-resisting piers areusually joined to the superstructure to benefit fromthe frame action, both to reduce the cost of foun-dations and minimize the effect of live loading in thesuperstructure.

Another type of substructure remains to be con-sidered here, one more conventional in design andwhere the piers receive the vertical reaction of thesuperstructure through a single row of bearings.Such piers are usually flexible, and the stabilityduring cantilever construction requires that tem-porary supports be added to the self-bendingstrength of the pier shaft.

5.7.2 DESCRIPTION OF REPRESENTATIVESTRUCTURES WITH TEMPORARY SUPPORTS

Downstream Paris Belt Bridge, France

The four river pier shafts previously described andillustrated in Section 5.3.2 rest on a reinforcedconcrete substructure built inside a cofferdamsealed with tremie concrete. Dimensions are shownin Figure 5.44.

Because of the limited dimensions of the piershafts and their consequent marginal bendingcapacity, a temporary support was used duringconstruction for stability of the superstructure be-fore deck continuity was achieved. Only one sup-port was used for each pier, Figure 5.45, on oneside of the concrete shaft within the space availableinside the temporary cofferdam. Consequently thelever arm between the pier and support centerlineswas only 8.5 ft (2.40 m), so that a heavy reactionwas imposed on the temporary support.

The maximum reaction computed for the caseof one precast segment out of balance, includingthe lifting equipment, was 1170 tons (1060 mt). In-cluding provisions for random loads and theadded reaction of the temporary prestressing ten-dons, the maximum design reaction in the supportwas 2030 tons (1840 mt). Each temporary supportconsisted of:

A 40 in. (1 m) steel pipe filled with concrete, Figure5.46, resting on the spread footing of the ‘perma-nent pierA V-shaped concrete frame placed upon the pipeand allowing the deck reaction to be transferreddirectly from the box section webs to the pipe

Vertical prestressing tendons were also an-chored in the pier footing and stressed from decklevel to prevent accidental overturning of the can-tilever, although limitations were imposed duringconstruction to always start segment placement onthe side of the temporary support.

Temporary connection between the pier seg-ment and the concrete pier shaft included onelooped tendon and four high-strength bars. Animmediate consequence of the high vertical reac-tion imposed upon the deck by the temporary sup-port in case of unbalanced loading was a reversal ofshear stresses between the temporary and thepermanent supports. This situation was even morecritical because of the permanent draped tendons,shown in the detail of Figure 5.47, located in thatzone together with the Resal effect produced bythe inclined bottom flange. The correspondingshear stress in the webs reached a maximum of 680psi. Two special tendons (twelve 3 in. diameterstrands) were placed on either side of each web ofthe box girder to reduce the shear stresses to al-lowable values. In fact, these four tendons workedas a tension tie between the top and bottom flangesof the box girder across the distance between thepermanent and temporary support.

T R A N S V E R S A L SECTION

llllln KOLW- ------PLE UP

cl+44

/'f Ed-P-Y -Tiffi

PLAN VIEW HOFUONTAL SECTION

FIGURE 5.44. Downstream Paris Belt Bridge, dimensions of river piers.

-SEGMENT W E I G H T S : 6 0 t o 40 t

-MAX. STATICAL REACTION IN SUPPORT :

42.40 In.- -.-____cU360 t

VERTICAL PRESTRESSING.-

PROVISIONAL SUPPORT__~ -.~

\PRESTREZfSING R O D S

FIGURE 5.45. Downstream Paris Belt Bridge, schematic of temporary support andstability of river pier during construction.

264

Flexible Piers and Their Stability During Construction 265

STEEL CAP

NM FLANG

P/T ANCHORS

FIGURE 5.46. Downstl c;m Paris Belt Bridge, detailsof temporary support. (a) Dimensions of support. (b)View of support.

This problem has been described at some lengthto show that a single temporary support subjectedto high loads may call for a rather complex ar-rangement to satisfy all requirements of stabilityand resistance of all parts of the structure at eachconstruction stage.

JOINT

Saint Jean Bridge In Bordeaux, France

For aesthetic reasons the river piers were designedas rather slender shafts, which had to accommo-date an important variation of the waterline due totidal effects in the mouth of the Garonne River.The bridge was relatively low above the water,particularly at high tide.

Each p ie r sha f t was founded on an open-dredged concrete caisson anchored in a bed ofsand and gravel of good quality, overlying a deepformation of marl and clay.

Dimensions of the piers and foundations areshown in Figure 5.48. The caisson had a cutting-edge diameter of 18 ft 4 in. (5.60 m) and themaximum average bearing pressure on the sandand gravel bed was 8.1 t/ft2 at the time of firstloading; the foundation settlement was a maxi-mum of 1.1 in. (28 mm) and the long-term addi-tional settlement was negligible, 0.16 in. (4 mm).

Construction of the piers called for the use of anauxiliary floating platform that could be raised oneight temporary pipe piles, comparable in princi-p le to the l egged jack ing p la t fo rms used onoffshore work, Figures 5.49 and 5.50. The rein-forced concrete caisson was floated into place, sus-pended from the platform resting on its legs, andincorporated into the permanent structure. As ex-cavation proceeded inside the caisson to lower it toits final elevation, precast segments were added toincrease the height of the caisson wall as required.

SHEAR AT SECTION OFTEMPORARY SUPPORT

v, 1ooot

t / TEMPORARY BEARING PADS

TRANSFORMED CONCRET R A N S F O R M E D S E C T I O N : L%m

RAIN CONCR~

TREMIE C O N C R E T E,

FIGURE 5.47. Down-stream Paris Belt Bridge,detail of loads on canti-lever and temporarysupport.

FIGURE 5.49. cop-posite). St. Jean Bridgein Bordeaux, schematicof construction of riverpiers.

FIGURE 5.48. St.Jean Bridge, in Bor-deaux, dimensions ofriver piers.

266

TING C L A M- - -

FLEXI F L O A T 5

R / C CAl%ONc -

BORDEAUX - PLACING RIVER CAlSON _ ELEVATIONlow- 72.

FLOATING CLAM

5HELL C R A N E

V_ERTICAL F’PE PIL

267


P

FIGURE 5.50. St. Jean Bridge at Bordeaux, platformon legs used for river pier caissons. (a) Platform in float-ing stage. (6) Platform on legs and caisson during exca-vation.

Match casting was used for making the varioussegments, and it proved very efficient and verysimple.

The cofferdam required to build the pier shaftin the dry was made up of temporary additionalcaisson ring segments stacked upon the permanentcaisson and bolted together. This cofferdam wasused during construction of the deck to make amoment-resisting pier shaft as a substitute to theflexible permanent pier. The deck was thereforeresting only upon the cofferdam and the lowercaisson through two temporary caps, offering astable base for unbalanced loading, Figure 5.51~.

After cantilever construction was finished andcontinuity achieved in the deck, flat jacks wereused to transfer the total reaction of the box girderfrom the temporary caps and cofferdam onto thepermanent concrete piers. All the temporary ringsegments above low water were further removed.This example shows how the foundations and evenpart of the substructure can be used to minimizethe cost of temporary supports required for can-tilever construction.

5.7.3 REVIEW OF THE VARIOUS METHODS OFPROVIDING STABILITY DURING CANTILEVER

CONSTRUCTION

A situation is considered here where the perma-nent pier cannot provide adequate stability duringcantilever construction. Several methods may beused, either separately or in combination, to pro-vide the required stability under the loading com-binations briefly reviewed in Section 5.2.

Temporary Eccentric Prestress In the general casewhere the construction procedure allows the un-balanced segment in a typical cantilever to beplaced always on the same side of the pier, the un-balanced moment varies between 0 and Wd (seg-ment weight W at a distance d from the pier cen-terline as shown in Figure 5.52).

Assume a temporary vertical tendon, anchoredin the pier foundation or in a separate dead-man,to be stressed for this unbalanced loading configu-ration to a load P such that

and the unbalanced moment in the pier now be-comes

+wd- 2

and the actual bending capacity of the pier istheoretically doubled. The true gain is somewhatlower, because it is not practical to change the ten-don load at each stage of segment placing. Aproper temporary connection with high-strengthrods between pier and deck must always be pro-vided.

Unsymmetrical Distribution of Segments with Regardto the Pier If the pier segment is eccentricallyplaced with regard to the pier shaft centerline,Figure 5.53, a permanent moment is applied to thepier when an even number of segments is incorpo-rated in the deck. Dimensions may be such that themaximum unbalanced moment due to one seg-ment’s being placed on the proper side of the pierwill result in applying only half to the pier. Thisapproach results in significant complications in thelayout of the prestress tendons in the deck. Bothmethods described thus far have one disadvantage,in that the deck cantilever is never in balance overthe pier and so it is more complicated to followingup the geometry of the deck during construction.

FIGURE 5.51. St. Jean Bridge at Bordeaux, tempo-rary arrangement of piers for deck cantilever construc-tion. (a) Schematic of temporary cofferdam and decksupport. (b) View of the pier segment and travelers.

2 6 9


///I/Py”Hf d

FIGURE 5.52. Temporary stability of deck and pier during con-struction by prestressing tendon.

FIGURE 5.53. Unsymmetrical pier segment.

Stability of the Concrete Cantilever Provided by theDeck Construction Equipment Figure 5.54 outlines afew typical schemes developed for either cast-in-place or precast construction where the stabilityduring cantilever placing is achieved by the con-struction equipment itself, such as an overheadtruss or launching gantry. Several such exampleswere previously described in Chapters 2 and 3:

Overhead truss Ties for stability

WinchOverhead beam

FIGURE 5.54. Cantilever stability by deck construc-tion equipment.

Overhead truss in cast-in-place construction, Sieg-tal Bridge or Pine Valley Creek BridgeLaunching gantry in precast construction, RioNiteroi Bridge and the B-3 South ViaductsOverhead beam in precast construction, B-3 SouthViaducts; a similar scheme is being contemplatedfor several contemporary projects in the UnitedStates.

Temporary Su@orts (Figure 5.55) If a singletemporary support is used on one side of the pierat a distance a, the reactions are as follows:

pMa

temporary support: +Ma

c M=W.dIV

Q---_ -- -__-- - -

M = W dQV

FIGURE 5.55. Cantilever stability by temporary sup-port(s).

Abutments

If two symmetrical temporary supports are used,the system is statically indeterminate and the actualdistribution of reactions depends upon the respec-tive flexibilities of the pier and of the supports.The load distribution is as follows:

271

TemporarySupport, T, Pier, P

TemporarySupport, T,

Effect of vertical load Y

Effect of moment M

PV

M2 a

(1 - 2P)V PV

M0 +2a

Total Pv-g (1 - 2P)V PV +$

If it is desired that the temporary supports neverbe subject to an uplift force, to resist which re-quires anchors and adequate foundations, thestiffness of the support must be such that asufficient proportion of the vertical load compen-sates the effect of the moment. The minimumvalue of p must be such that:

M MpV--20 o r p2---2a 2a

Consequently the maximum reaction at support T2becomes at least equal to M/a, which is preciselythe value of the reaction for a single support with

FIGURE 5.56. Cantilever stability by temporary stays.

the same loading configuration. The double sup-port system is therefore exactly twice as expensiveas the single support system. The only advantage isto allow the construction of the deck to proceedindifferently from either side of the pier or tomaintain an equal safety of the system should amistake be made in the required sequence of oper-ations for the case of a single support.

Temporary Stays In a limited number of struc-tures, stability during construction was provided bytemporary vertical or inclined stays anchored inspecial foundation blocks or in the permanentfooting of the pier, Figure 5.56.

When feasible, this last system is particularlysimple, because the temporary stays are usuallymade of simple prestressing tendons and are farless expensive than rigid temporary supports. Sucha system must be used in conjunction with a strongtemporary connection between pier and deck toreach an adequate level of safety.

5.8 Abutments

5.8.1 SCOPE

Although the abutments provided at both ends ofthe bridge are not necessarily of special designwhen associated with cantilever and segmentalconstruction, it may be of interest to review brieflyseveral types of structures actually used in com-pleted projects.

The abutments serve a twofold purpose:

They provide the first and last support to thebridge superstructure, allowing a smooth transi-tion of the roadway surface from the deck to the


approaches while allowing free expansion with anadequate roadway and sidewalk joint,

They make the retaining wall contain the fill of theapproach embankment where geometric condi-tions require it. Design and construction methodsof the abutments depend greatly upon the soilconditions and the level of the water table whenpresent.

Basically, the two functions outlined above ma!either be integrated into a single structure or filledby two separate structures. On the other hand, thefunction of a retaining wall may be greatly mini-mized by allowing the approach fill to take a slopeof repose under the structure.

By variously combining these characteristics,twelve different sketches were prepared in Figures5.57 through 5.68 as an outline of typical struc-tures encountered in practice. For convenience,these designs have been grouped into six differentcategories as described in the following para-graphs.

5.8.2 COMBINED ABUTlMESTIRETAI.VI.1’G WALL

Type IA (Figure 5.57) A simple retaining wallperpendicular to the bridge centerline and an-chored to a conventional spread footing both con-tains the approach fill and provides the deck endbearing. The back wall receives a transition slab toavoid the roadway profile discontinuity so frequentin earlier bridges between the rigid deck and theflexible pavement over the approach embankment.Two side walls of triangular shape contain the fillinside the abutment.

Type ZB (Figure 5.58) The retaining wall ismade of a vertical wall and a lower slab properlystrengthened by longitudinal buttresses. The en-tire system is founded on piles.

Type IC (Figure 5.59) Where the poor quality ofthe soil makes it difficult to resist the horizontalloads due to earth pressure combined with brakingand thermal reactions, the previous system may befounded on a system of vertical piles, while the

FIGURE 5.57. Abutment type IA.

1 If/ 1

FIGURE 5.58. Abutment rype IB.

t-‘--tFIGURE 5.59. Abutment type IC.

273


horizontal loads are resisted by embedded pre-stressed concrete ties anchored in the back into acontinuous dead-man.

5.83 SEPARATE END SUPPORT ANDRETAINI,VG WALL

Type ZZ (Figure 5.60) The two functions of decksupport and retaining wall are entrusted to twoseparate structures. Shown in this figure is a frontvertical column, resting on spread footings or piles,which provides the deck end bearing. Behind thiscolumn and separate thereto, a reinforced earthretaining wall contains the approach fill.

5.8.4 THROUGH FILL ABUTMENT

The fill extends under the bridge deck with a stableslope (3 : 2 to 2 : 1) to reduce as much as possible theamount of earth pressure applied to the abutment.

Type ZZZA (Figure 5.61) Vertical longitudinalwalls connect the lower spread footing to theabutment superstructure. It is important to avoidhorizontal cross bracings at intermediate levelsembedded in the fill, because settlements maycause significant overloads in such members suchas to cause failure.

t-4.G- - -

& ~~~-FOUR-4’@m PILES-_ _

(b)

FIGURE 5.60. Abutment type II with reinforced earth. (a) Cross section. (b) Elevationand longitudinal section.

Abutments 275

FIGURE 5.61. Abutment type IIIA.

Type ZZZB (Figure 5.62) The same system maybe adapted to the case where a high water table andpoor soil conditions call for pile foundation built ina cofferdam.

5.8.5 HOLLOW BOX ABUTMENT

Trpe WA (Figure 5.63) Another way to avoidhigh earth-pressure loads on the abutment, whereit is not possible or desired to extend the approachfill under the deck, is to build the abutment as abox with a front wall providing the deck end sup-port and the cover slab carrying the roadway be-tween the bridge deck and the approach fill. Such astructure may be founded on spread footing or onpiles (as shown in the sketch).

Type ZVB (Figure 5.64) The same structure mayrest both at the front and at the rear on open-dredged caissons excavated under water to theload-bearing soil.

5.8.6 ABUTMENTS DESIGNED FOR UPLIFT

The principle has been described previously inChapter 4 (design) and for actual structures inChapters 2 and 3 (cast-in-place or precast can-tilever bridges).

Type VA (Figure 5.65) A large caisson is open-dredged and filled after completion of the excava-tion to the required foundation level with tremieconcrete so as to obtain a sufficient weight to resistthe uplift reaction from the deck.

Type VB (Figure 5.66) Another variation of thesame concept was developed for the Saint JeanBridge at Bordeaux to combine into a single abut-ment a front downward bearing and a rear upliftingbearing to fix the last span of the bridge while re-taining its free expansion.


FIGURE 5.62. Abutment type IIIB.

5.8.7 MINI-ABUTMENT 5.9 Effects of Differential Settlements onContinuous Decks

For decks of small height, when prevailing condi-tions allow the fill to be placed around the deck, the The question has often been raised as to the ade-abutment reduces to a very simple inexpensive quacy of allowing continuous decks to rest on piersstructure shown as types VIA and VIB in Figures subjected to possible differential settlements. The5.67 and 5.68. authors are aware of a few cases where differential

Effects of Differential Settlements on Continuous Decks 277

6 ”d-t

Ii'

/

FIGURE 5.63. Abutment type IVA.

settlements were responsible for problems per-taining to the integrity of the superstructure (suchas opening of joints between successive segments).Differential settlements, however, are very seldomcritical in most soil conditions. In the isolated caseswhere they may be critical, precautions can betaken to counteract their eventual effects upon thestructure.

5.9.1 EFFECTS OF AN ASSUMED PIERSETTLEMENT ON THE STRESSES IN THE

SUPERSTRUCTURE

Starting with the simple case shown in Figure 5.69,where a continuous beam of constant depth with alarge number of identical spans is subjected to the

settlement of one pier by a given amount, one mayeasily derive the effect in terms of moments andstresses in the superstructure. Taking the fixedend moment p = 6 EZu/12, the moments over thepiers and at midspan are:

Over the pier subjectedto settlement

Over the adjacent piersMidspan momentQuarter-span moment

+0.732p

-0.464~+0.134/L+0.433p

The stress produced in the superstructure is f =MC/I, where c is the distance between the centroid


FIGURE 5.64. Abutment type IVB.

FIGURE 5.65. Abutment type VA.

and upper or lower flange. If the moment is ex-pressed as A4 = Ap, the stress becomes:

6Ecuf=+r

which can be rewritten as follows:

The value of clh varies between 0.4 and 0.6 andthat of hll between & aud &.

Considering the quarter-span .point close to thepier where settlement occurred, the stress in thesuperstructure will be, with k = 0.433 and E =300,000 kips/fP (for long-term loading):

f = 23,400;

For a settlement u = r$6a the stress is equal to 23kips/ft2 at the bottom fiber, a very nominal value.For a 100 ft span, the corresponding settlement isu = 0.1 ft = 1.2 inches.

The amount of settlement to be considered isonly that part taking place after continuity isachieved in the deck and so after most of the loadhas been applied to the structure.

Effects of Differential Settlements on Continuous Decks 279

awble 1

FIGURE 5.66. Abutment type VB.

5.9.2 PRACTICAL MEASURES FOR For some structures the situation may call forCOUNTERACTING DIFFERENTIAL SETTLEMENTS special consideration. Such was the case, for exam-

ple, with the Houston Ship Channel Bridge, whereIn most cases, the foreseeable differential settle- large long-term settlements could be anticipated atments may be absorbed by the structure without the time of design. In such instances, provisions forany corrective measures and no special provisions eventual realignment of the deck profile must beneed be taken in that respect. incorporated into the design.


FIGURE 5.67. Abutment type VIA. FIGURE 5.68. Abutment tvpe VIB

Inertia : I

Modulus : z

FIGURE 5.69. Effect of differential settlement on a continuous beam with equal spansand constant depth.

References

1. J. Mathivat, “Reconstruction du pont de Choisy-le- 3. Gerwick, Ben C. Jr., “Bell-Pier Construction, RecentRoi,” Trauaux, Janvier 1966, No. 372. Developments and Trends,” Journal of the American

2. J. Mathivat, “Structures de piles adaptees a la con- Concrete Institute, Proc. V. 62, No. 10, October 1965.

struction par encorbellement,” Problems speciauxd’etude et d’execution des overages, JourneesA.F.P.C., Avril 22-23, 1974.

6Progressive and Span-by-Span

Construction of Segmental BridgesJ

6.1 INTRODUCTION

6.1.1 Progressive Placement Method6.1.2 Span-by-Span Method

6.2 PROGRESSIVE CAST-IN-PLACE BRIDGES

6.2.1 Approach Spans to the Bendorf Bridge, Germany6.2.2 Ounasjoki Bridge, Finland6.2.3 Vail Pass Bridges, U.S.A.

6.3 PROGRESSIVE PRECAST BRIDGES

6.3.1 Rombas Viaduct, France6.3.2 Linn Cove Viaduct, U.S.A.

6.4 SPAN-BY-SPAN CAST-IN-PLACE BRIDGES

6.4.1 Kettiger Hang, Germany6.4.2 Krahnenberg Bridge, Germany6.4.3 Pleichach Viaduct, Germany6.4.4 Elztalbticke, Germany

6.1 Introduction

The concepts of the progressive placement andspan-bv-span methods of segmental constructionwere introduced in Sections 1.9.4 and 1.9.3, re-spectivelv. .fhis chapter will explore these conceptsin greater detail. These two methods have notmade the conventional cast-in-place on falseworkmethod obsolete; the conventional method is stillapplicable and economical where site, environ-mental, ecological, and economic considerationspermit. What these two methods do is to open up aheld where prestressed concrete structures werehitherto not practical and where they now can eco-nomically compete with structural steel.

.The progressive placement and span-by-spanmethods are similar in that construction of thesuperstructure starts at one end and proceeds con-tinuously to the other, as opposed to the balancedcantilever method where superstructure is con-structed as counterbalancing half-span cantilevers

6.4.5 Guadiana Viaduct, Portugal6.4.6 Loisach Bridge, Germany6.4.7 Rheinbriicke Dusseldorf-Flehe, Germany6.4.8 Denny Creek Bridge, U.S.A.

6.5 SPAN-BY-SPAN PRECAST BRIDGES

6.5.1 Long Key Bridge, U.S.A.6.5.2 Seven Mile Bridge, U.S.A.

6.6 DESIGN ASPECTS OF SEGMENTAL PROGRESSIVECONSTRUCTION

6.6.1 General6.6.2 Reactions on Piers During Construction6.6.3 Tensions in Stays and Deflection Control During

Construction6.6.4 Iayout of Tendons for Progressive ConstructionREFERENCES

on each side of the various piers. Also, bothmethods are adaptable to either cast-in-place orprecast construction.

6.1.1 PROGRESSIVE PLACEMENT METHOD

This method was developed to obviate the con-struction interruption manifested in the balancedcantilever method, where construction must pro-ceed symmetrically on each side of the variouspiers. In progressive placement, the constructionproceeds from one end of the project in continu-ous increments to the other end; segments areplaced in successive cantilevers from the same sideof the various piers. When the superstructurereaches a pier, permanent bearings are placed andthe superstructure is continued in the direction ofconstruction.

The first implementation of this method, whichused cast-in-place segments, was on the OunasjokiBridge near the Arctic Circle in Finland. It was

281

282 Progressive and Span-by-Span Construction of Segmental Bridges

later extended to the first use of precast segmentsin the Rombas Viaduct in eastern France.

The essential advantages of this method are asfollows:

1. The operations are continuous and are carriedout from that part of the structure alread,constructed. Access for personnel and mate-rials is conveniently accomplished over the sur-face of the structure already completed (freeof the existing terrain). This may be of impor-tance with regard to urban viaducts cantile-vering over numerous obstacles.

2 . Reactions to the piers are vertical and not sub-ject to any unsymmetrical bending moments,thus avoiding the need for temporary bracingduring construction.

3. The method is adaptable to curved structuregeometry.

The following are the disadvantages:

1 . It is difficult, if not impossible, to utilize thismethod in the construction of the first span.Usually the first span must be erected onfalsework. In some rare instances it may bepossible to cantilever the first span from theabutment.

2. Forces imposed upon the superstructure, de-pending on the method of construction, arecompletely different (in sign and order ofmagnitude) from those present in the struc-ture under service load. Consequently, a tem-porary external support system is requiredduring construction in order to maintain thestresses within reasonable limits and minimizethe cost of unproductive temporary pre-stressing. Falsework bents may be used (as inthe Linn Cove Viaduct), but the more usualsolution is that of a mobile temporary mastand cable-stay system (Figure 1.57). For theprogressive placement method the mast andcable-stay system is relocated progressivelyover the piers as construction advances.

3. In this system the piers are subjected to a reac-tion from the self-weight of the superstructureapproximately twice that in the final static ar-rangement of the structure. However, this isgenerally not critical to the design of the piersand foundations, as the effect of the dead loadis rarely larger than half the total load includ-ing horizontal forces.

When cast-in-place segments are used in con-junction with the progressive placement method,the rate of construction is less than that t’or the bal-anced cantilever method, in that there is onlv onelocation of construction activitv. That is, onlv onesegment can be cast (at the end of the completedportion of the structure) rather than two (one ateach end of the balanced cantilevers). ~fhis slow-ness may be minimized by the use of longer seg-ments, but this solution is limited bv the low resis-tance of the young concrete. On the other hand,the use of epoxy-joined precast segments ma!permit an average rapidity of construction compa-rable to that of balanced cantilever with a launch-ing girder.

As indicated in Chapter 1, the span-by-spanmethod was developed to meet the need for con-structing long viaducts with relatively short spans

such as to incorporate the advantages of balancedcantilever construction.

From a competitive point of view, the capital in-vestment in the equipment for this type of con-

struction is considerable. It has been suggested’that one-third of the cost of the equipment be de-preciated for a given site and that at least four useswould be required to achieve full depreciation, in-cluding interest on the capital investment. How-ever, costly modifications that may be requiredbecause of changes in bridge widths or span limi-tations are not considered in the above write-offpolicy. It would, therefore, be advisable for a con-tractor investing in this tvpe of equipment to con-

sider some type of modular planning so thatmodification for future projects might be kept to aminimum. It might be possible to have a basic pieceof equipment with interchangeable elements.There is, of course, the potential of leasing thisequipment to others as a means of retiring thecapital investment.

Wittfoht1s2 has categorized stepping segmentalconstruction intb four subgroups:

1. With-on-the ground nontraveling formwork.2. With traveling formwork or on-the-ground

stepping formwork.

3. With off-the-ground stepping formwork.4. In opposite directions starting from a pier.

The first category is generally used where thereare a large number of approximately equal spans

Progressive Cast-in-Place Bridges 283

of a low height above existing terrain. It is gener-ally limited to structure lengths of approximately1000 ft (300 m) and to nonuniform span lengthsthat prohibit a forming system of uniform size.

Normally in span-by-span construction thesuperstructure is of constant cross section (at leastinsofar as external dimensions are concerned), andthe work proceeds from one abutment to theother. If a large center span exists, it will be formedfirst, possibly to an inflection point in the adjacentspans. The formwork is allocated such that it isused to cast the spans in the approaches proceed-ing from the center, in both directions, toward theabutments. Forms and scaffolding are disassem-bled and reerected in an alternating sequence andin elements that can be conveniently handled by acrane.

In the second category of span-by-span con-struction, for economical justification of equip-ment, the total length of structure must be at least1000 ft (300 m), the overall cross section constant,the structure of low height, and the terrainalong the longitudinal axis approximately level.Maximum span for this category is approximately165 ft (50 m), and a large number of equal spansare required to achieve repetitiveness and thuseconon1v.3

The falsework and forms are generally a spanlength (either the dimension from pier to pier orfrom inflection point to inflection point), Figure6.1 .3 The formwork is fixed to the scaffolding andtravels with it. The bottom of- the formwork is de-signed with a hinge or continuous trap-door devicesuch that the scaffolding and forms can travel pastand clear the piers. The scaffolding is moved for-ward on rails. If a foundation for the scaffolding,forms, and weight of superstructure is found to betoo costlv or unsafe, a scheme may be used wherethe rails ‘carry only the load of the scaffolding andformwork. Once in position, the scaffolding issupported at the piers, or at the forward pier, andthe completed structure at the rear by auxiliarybrackets; thus construction loads are transmitted tothe pier foundations.

Where conditions exist as in the previous cate-gory, but the structure is high with reference to theterrain or crosses over difficult terrain or water,the third category may be used, whereby duringthe stepping and casting operations the equipmentis supported by the piers or by a pier and the pre-viously completed portion of the structure.

Where consecutive spans in the range of 160 to500 ft (50 to 150 m) are contemplated and the fac-tors mentioned above prevail, the type of con-

i-2 rf

Scaffolding at concret ing posit ion

Construction direction

‘Under-carriageAdvancement of Scaffolding

ffoldm

r e

_.,.._

Hinged bottom plate

Section l-l Section 2-2

FIGURE 6.1. Schematic of procedure for movablescaffolding, from reference 3 (courtesy of Zement undBeton).

struction indicated by the fourth category may beconsidered. This system uses a gantry rig that has alength one and one-half times that of the span. Inthis method segments are cast in each directionfrom a pier, as in the balanced cantilever method,except that the form traveler and segment beingcast are supported by the gantry. This method isactually a balanced cantilever method and not aspan-by-span method of construction as definedhere.

The advantages of the span-by-span method ofconstruction, besides those associated with seg-mental construction in general, pertain to the pre-stressing steel requirements. Since the segmentsare supported by the form travelers, there are nocantilever stresses during construction, and pre-stress requirements are akin to those of conven-tional construction on falsework or those for thefinal condition of the structure.

6.2 Progressive Cast-in-Place Bridges

6.2.X APPROACH SPANS TO THE BENDORFBRIDGE, GERMANY

As discussed in Section 2.2, the Bendorf Bridgewas constructed in two parts. The western portion


Main r iver F lood

Construction infree canti lever 216.50 m Construction on falsework 288.50 mI-.___--.-__i

‘Phase 5 by progressive placing, segment length 4.00 m.

FIGURE 6.2. Bendorf Bridge, Part Two (East), construction procedure, from refer-ence 1 (courtesy of Beton- and Stahlbetonbau). Phase 5 by progressive placing, segmentlength 4.00 m.

manner on falsework inside a temporary wind-shielded protective cover, Figure 6.3. Outsidetemperature during this operation ranged from

(part one), Figure 2.9, consists of a symmetricalseven-span continuous girder constructed by thecast-in-place balanced cantilever method. Theeastern portion (part two), Figure 2.10, consists ofa nine-span continuous approach structure havingan overall length of 1657 ft (505 m) with spansranging from 134.5 ft (41 m) to 308 ft (94 m).

In the construction of the approach spans, Fig-ure 6.2, the five spans from the east abutment werebuilt in a routine manner with the assistance offalsework bents. The four spans over water wereconstructed by the progressive placement method,using cast-in-place segments and a temporarycable-stay arrangement to reduce the cantileverstresses. The temporary stay system consisted of astructural steel pylon approximately 65 ft (20 m)high and stays composed of Dywidag bars.

6.2.2 OUNASJOKI BRIDGE, FINLAND

This structure is near the city of Rovaniemi, Fin-land, and crosses the Ounas River just above itsjunction with the River Kemi near the Arctic Cir-cle. The structural arrangement consists of two 230ft (70 m) interior spans and end spans of 164 ft (50m), prestressed longitudinally and transversely.

The first end span and 75 ft (22.75 m) of thesecond span were cast-in-place in a conventional

- 2 0 t o -30°C. Subsequent progressive cantileverconstruction was performed-with the aid of a tem-porary pylon and stays, Figure 6.4. The samestages were repeated in the remaining spans. Thesuperstructure was cast-in-place with the assis-tance of one form traveler, Figure 6.5. Duringthese stages of construction, for protection againstlow temperatures, form traveler and form werefully enclosed, Figure 6.5. This enclosure was insu-lated with 4 in. (100 mm) of fiberglass.

Hardening of the concrete took an average of 76hours. Temperature of the concrete was main-tained between 35 and 45°C at mixing and between20 and 25°C during casting. Curing inside theform traveler enclosure was assisted by warm-airblowers. Concrete strength was 5000 psi (34.5MPa). Segment length was 11.5 ft (3.5 m), and itwas possible to reach a casting rate of two segmentsa week.

Construction started in 1966 and was completedin 1967. Table 6.1 lists the temperatures recordedduring seven months of the construction period.The progressive placement method proved effec-tive and work progressed throughout the yeareven during arctic conditions.

FIGURE 6.3. Ounasjoki Bridge, temporary protectivestructure (courtesy of Dyckerhoff & Widmann).

Progressive Cast-in-Place Bridges

TABLE 6.1. Ounasjoki Bridge, Temperature Variations

Month

285

Temperature March

Average “C -2.5Maximum “ C +5.8Minimum “C: -26.4

April

-0.4+9.9

- 16.8

May

+5.6+24.6- 12.2

June

+11.7+24.9+0.1

July

+ 14.3+25.7

+3.0

August

+ 14.8+28.5

+5.8

September

+8.7+ 19.3

-4.7

FIGURE 6.4. Oulla+ki Bridge, winterproof travel-ing form (courtesy of Dyckerhof’f & Widmann).

62.3 VAIL PASS BRIDGES, U.S.A.

The Vail Pass structures are part of Interstate I-70near Vail, Colorado, in an environmentally sensi-tive area. Of the 21 bridge structures in this proj-ect, seventeen were designed and bid on the basisof alternate designs (Chapter 12). In the segmentalalternative the contractor was allowed the optionto construct as cast-in-place segmental. A group offour bridges approximately 7 miles (11.3 km)southeast of Vail were successfully bid as cast-in-place segmental and used the concept of progres-sive placement.

Two of these structures are contained in a four-span dual structure over Black Gore Creek, Figure6.6. The other two structures are a three-span

FIGURE 6.5. Ounasjoki Bridge, progressive placing scheme.


Existing grcamdlim

TYPICAL ELEVATION

MID-SPAN NEAR Q PIER

TYPICAL SECTION

FIGURE 6.6. Vail Pass B -‘clI I ges, Black Gore Creek Bridge, typical elevation and section

eastbound bridge and a four-span westboundbridge, both crossing Miller Creek, Figure 6.7.

Because the structures are relatively short andthe spans small, they were constructed by theprogressive placement method with temporaryfalsework bents. ‘The work and time required totransport and reassemble the form travelers (as inthe balanced cantilever method) was therebvminimized. Construction started from both abu;-ments and proceeded progressively toward thecenter of each bridge.”

For each of the two structures in the MillerCreek Bridge, form travelers were assembled atop30 ft (9.1 m) long segments at the abutments. Assegment casting began, the side spans were sup-ported at every second segment by a temporarybent. After reaching the first pier, segment con-

struction proceeded in normal fashion to midspanof the eastbound structure. In the westboundstructure, when midspan of both interior spans wasreached, temporarv bents were again used to conl-

plete the remaining half-spans to the center pier.After reaching the center of the bridge, one formtraveler of each bridge was dismantled, and theremaining form traveler was used to cast the clo-sure pour. In this manner the form travelers foreach bridge were assembled and dismantled only

once, as opposed to the method of assembling t\voforms at each pier and dismantling upon comple-tion of two half-span cantilevers about each pier.

For the Black Gore creek structures, to save criti-cal construction time, both end spans of onestructure and one end span of the other structurewere built on falsework, while the form travelers

Progressive Cast-in-Place Bridges

455’- 3 ”

E. 8 ELEVATION

518’-3”

B r i d g e a b u t . 2

E Dridge abut 1

W. 8. ELEVATION

42'-0"e Elriige 1

,_ : r2" Asphalt

lo’-o- 9’- 33-e.

I'-8f'

TYPICAL SECTION

FIGURE 6.7. Vail Pass Bridges, Miller Creek Bridge, typical elevation and section.

were occupied at the Miller Creek Bridges. Uponcompletion of their work at Miller Creek, the form

struction continued in the progressive placement

travelers were transported over the completed endmanner, Figure 6.8.

Because of the limited construction time aspans of the Black Gore Creek Bridges and con- three-day cycle was required for segment casting.


FIGURE 6.8. Vail Pass Bridges, Black Gore CreekBridge, under construction (courtesy of Dr. Man-ChungTang, DRC Consultants, Inc.).

Construction specifications required a concretestrength of 3500 psi (24 MPa) at the time of post-tensioning and 5500 psi (38 MPa) at 28 days. Sincethe time required for f-orming and placing of rebarand tendons is somewhat fixed, the only operationthat could be adjusted was the concrete curingtime. This was accomplished by using a specialwater-reducing agent that allowed the develop-ment of 3500 psi (24 MPa) concrete in 18 hours.Because of lack of experience with the specificwater reducer, honeycombing was experienced inthe early stages of construction. Eventually a 24 da)cvcle was achieved.

ROM BAS

- P L A N VlEL/-

(a)

FIGURE 6.9. Rombas Viaduct, plan and sections. (a) Plan. (6) Typical bridge sections.(c) Typical segment section.

C o u p e A

Progressive Precast Bridges 289

coupe c

Coupe El C o u p e D

/ VariableI

Var 680 760

I - - l

F i g u r e 6 . 9 . (C,‘o~rtitr~rd)

6.3 Progressive Precast Bridges

The Rombas Viaduct is a constant-depth super-structure, supported on neoprene bearings, withnine continuous spans ranging from 75 ft (23m) to 14X ft (45 m). This structure is curved in planwith a minimum radius of 900 ft (275 m) and of avariable width, owing to the presence of an exitramp, Figure 6.9. Total length is 1073 ft (327 m),

and the viaduct has two parallel single-cell boxes.In cross section each single-cell box is 8.2 ft (2.5 m)deep and has a width of 36 ft (11 .O m). A construc-tion view of the end of a segment is presented inFigure 6.10.

Construction of this structure employed theprogressive placing of the precast segments. Tem-porary stability was provided by a cable-stay sys-tem, Figures 1.57 and 6.11, which advanced frompier to pier as the construction progressed. Seg-ments were progressively placed, starting from one


FIGURE 6.10. Rombas Viaduct, end view of segment.

FIGURE 6.11. Rombas Viaduct, view of cable staysand mast.

abutment, by means of a swiveling hoist, Figure6.12, advancing along the deck.

6.32 LJNN COVE VIADUCT, U.S.A.

A progressive placement scheme is being used forthe Linn Cove Viaduct on the Blue Ridge Parkwayin North Carolina, Figures 6.13 and 6.14. It is a

FIGURE 6.12. Rombas Viaduct, view ot swivel crane.

FIGURE 6.13. Linn Cove Viaduct, photomontage.

FIGURE 6.14. Linn Cove l’iaduct, artist’s rendering.

Progressive Precast Bridges 291

1243 ft (378.84 m) eight-span continuous structurewith spans of 98.5, 163, 4 at 180, 163, and 98.5 ft(30.02, 49.68, four at 54.86, 49.68, and 30.02 m)and sharp-radius curves, Figure 6.15. In cross sec-tion it is a single-cell box girder with the dimen-sions indicated in Figure 6.16.

Because of the environmental sensitivity of thearea, access to some of the piers is not available.Therefore, the piers will be constructed from thetip of a cantilever span, with men and equipment

being lowered down to construct the foundationand piers. The piers are precast segments stackedvertically and post-tensioned to the foundation,Figure 6.17.

The extreme curvature of the alignment makesthe use of temporary cable stays impractical. Tem-porary bents at midspan will be used to reducecantilever and torsional stresses during construc-tion to acceptable levels. The temporary bents areerected in the same manner as the permanent

ii

+ Pier 3

$ Pier 4

FIGURE 6.15. Linn Cove Viaduct, plan.

HALF SECTION AT POST- TENSIONING BLOCK T Y P I C A L H A L F S E C T I O N THRU SEGMENT_--- ~~~~

FIGURE 6.16. I,inn Cove Viaduct, typical segment cross section.

Span-by-Span Cast-in-Place Bridges 293

Constructionbar tendonst h r o u g hs e g m e n t snot shown

FIGURE 6.17. Lint1 Cole Viatiuct, segtnental pier.

piers, using a stiff-leg derrick at the end of’ thecompleted cantilevered portions of’ the structure,Figure 6.18. When the temporary bents are nolonger required, they are dismantled and removedbv equipment located on the completed portion ofthe bridge deck.

4.4 Span-by-Span Cast-in-Place Bridges

6.4.1 KETTIGER H,4,VG, GER.LC4.Yk

The first application of’ the ot‘t-ground tnethodol-ogy (category 3), Section 6.1.2. was in 1955 on theKettiger Hang structure neat- Andernach (FederalHighway 9), Figure 6.19.3 This system consists off’our scaffblding trusses of’ slightly more than aspan length and two cantilever girders of’ about atwo-span length. The scat‘folding trusses supportthe entire concrete weight during casting. Thecantilever girders serve to transfer or advance thescaf’folding trusses to the next span to be cast. Theconcrete fortn or mold rides with the scat‘foldingtrusses and is thus repeatedly reused.

h.-l.2 KRz4H.\‘E.\‘BERG BRIDGE, GERA11.4.Y).

A variation of the of‘f-the-ground system was usedon the Krahnenbergbrticke near Andernach con-structed from 1961 to 1964, Figure 6.20.‘*3 Thisstructure has a length of’ 3609 f’t (1100 m), a con-stant depth of 6.56 fi (2.0 m), a width of’ 60.i f’t(18.5), and spans of’ 105 f’t (32 m). The site is on aslide-susceptible hillside, requiring difficult foun-dations, and its curved alignment follo\vs the to-pography, all of which economically favored thespan-by-span technique.

STIFF LEG DERRICKLACING PRECAST SEGMENTS

FIGURE 6.18. Linn Cove Viaduct, erection scheme for progressive placement.

39,26-39, M

Scaffolding truss at concreting posit ion Section l-l

Canti lever

39,20-t----3Q,M-39,20~39,20~3920~3Q,20

Advancement of the Scaffolding truss including forms3% slope Forward R e a r

0n;

I

39,20--c-------39>20 39.20-39.20 39.20 , 39.20

Advancement of the canti lever beams

FIGURE 6.19. Kettiger Hang, schematic of’ the construction procedure, from reter-ence 3 (courtesy of’ Zement und Beton).

Exteriorscaffoldgirder

I’I ‘\Interiorscaffoldgirder

(b)

%i%fSection 2-2

m t

t

294


In this project four fbrmwork supporting gird-ers were used. Two interior girders were rigidlyconnected together by transverse horizontal brac-ing. The formwork was arranged so that the formshinged at the bottom and folded down to allowpassage, during advancement, past the piers, Fig-ure 6.200. ‘The four girders were supported on thehexagonal piers by transverse support beams at-tached to the pier. In this manner the four lon-gitudinal formwork support girders were sup-ported on two piers, while an additional set oftransverse support beams were attached to theforward pier. Figure 6.206.

Latticework cantilever extensions at both ends ofthe longitudinal formwork support girders ex-tended their length to twice the span length, so thata stable support was provided by the transversesupport girders during advancement. The outsidegirders had joints or links at the connection withthe cantilever latticework so that the curvature ofthe structure could be accommodated during theiradvancement. The elevation of the outside girderswas adjusted by hydraulic jacks to accommodatesuperelevation. During the advancement opera-tion the outside girders were advanced first andthen the center two girders, Figure 6.20~. Whenthe forward end of the interior girders reached thetransverse supporting beams, the rear transversebeams of the previously cast span were no longerrequired. They were dismantled from the pier.These transverse beams were erected on the nextforward pier by a crane, Figure 6.20b.

The exterior formwork of’ the two-cell box gird-er was attached to the longitudinal support gird-ers and only required adjustment for curvature.The interior forms of- the cells were dismantledand reassembled on the next span after reinforce-ment was placed in the bottom flange and webs.

FIGURE 6.20. (Opposite). Krahnenberg Bridge, sche-matic of construction, from reference 1 (courtesy of theAmerican Concrete Institute). (a) Cross section. (6)Formwork equipment in working position. (c) I: Work-ing position: reinforcing, and concreting on formworkequipment; installing the supporting construction on thenext following pier by means of derrick and straight-linetrolley. II: After concreting and prestressing: loweringof equipment; opening of formwork flaps; shifting for-ward of outer girders; dismantling of the first rear sup-porting girder by straight-line trolley; intermediate stor-age at center pier. III: Partial pony-roughing of centergirder; dismantling and placing in intermediate for stor-age of second rear girder. IV: Final shifting forward ofcenter girders; jacking up of equipment; closing offormwork flaps; new working position.

Average casting rate was 706 ft3 per hr (20 m3).Fourteen days was required for construction of aspan.

6.43 PLEICHACH VMDUCT, GERMANY

In 1963 construction started on the 1148 ft (350 m)long Pleichach Viaduct1a3 carrying a federal high-way between Wurzburg and Fulda; it was the firstuse of the span-by-span technique for a dualstructure, Figure 6.21. Span length is 119 ft (36.25

Rear crane truck

//Forward crane truck

rk /

1’;

! ‘“__ -.-_-----~~-c-~~--~- __---

” ,I ,A +;R Fiv I

I IScaffolding girder at concreting position

36.25+-x,25- --i -36.25

Advancement of the scaffolding girder including forms

Construction joint

Advancement of the scaffolding and cantilever girders

R-Scaffoldinggirder and formsW-Scaffoldingandcantilever girder

I, i I I I ! i

Cross section

FIGURE 6.21. Pleichach Viaduct, schematic of theconstruction procedure, from reference 3 (courtesy ofZement und Beton).


m), with each two-cell box girder having a width of47.2 ft (14.4 m) and a depth of 7.2 ft (2.2 m). Thesuperstructure construction equipment w a serected behind an abutment in a position to con-struct one superstructure. Upon reaching the op-posite abutment, the equipment was shifted later-ally for the return trip to construct the othersuperstructure. Because of the narrowness, onlyone longitudinal support girder was required, asopposed to the two girders required for theKrahnenberg Bridge. This girder is slightly longerthan twice the span length. The two outside girdersare approximately one span length.

The outside girders were advanced simultane-ously by a carrier traveling at the front of the cen-tral girder and at the rear by carriers running onthe deck of the previously completed section.During concreting, the two outside girders aresupported on brackets at the forward pier and sus-pended from the completed portion of thesuperstructure. The center girder, relieved of theload of the two outside girders, is then advancedone span and again connected to the outside gird-ers by the hinged bottom formwork, thus func-tioning as an auxiliary support girder. This se-quence of operations is commonly referred to asthe “slide-rule principle.”

The piers have a width of 16.4 ft (5 m) and havean opening at the top to allow passage of the cen-tral support girder, Figure 6.21. The width of thepier is determined by the need for sufficient bear-ing area for the bearings and clearance for thecentral support girder. Whether the central open-ing at the top of the pier should be concreted in isone of aesthetics.

64.4 ELZTALBRUCKE,GER~~A~

The Elztalbrticke,5,6 Figure 6.22, was constructedin 1965 at Eifel, West Germany, approximately18.6 miles (30 km) west of Koblenz. It crosses thedeep valley of the Elz River with a total structurelength of 1244 ft (379.3 m), Figure 6.23. Thesuperstructure has a width of 98.4 ft (30 m) and issupported on a single row of octagonal piers up to328 ft (100 m) in height, Figure 6.24. Owing to theheight of the valley, conventional construction onfalsework would have been economically prohibi-tive. Therefore, a span-by-span system of self-supporting traveling scaffolding was used, Figure1.53.

The Autobahn between Montabauer and Trier,which had been in planning before World War II,

FIGURE 6.22. El,t,dtmde, \ ie\\ of c0111plrtetistructure (courtesy of Dipl. Ing. Manfred Bockel).

had to cross two large natural obstacles, the RhineRiver north of Koblenz (see the Bendorf Bridge,Section 2.2) and the Elz Valley. In 1962 tenderswere called for on the Elz Valley structure. Bidderswere provided with the grade requirements, di-mensions for a single or a dual structure, the loca-tion of the abutments, and the foundation condi-tions.

A consortium of Dyckerhoff SC Widmann AG,W a y s s SC Freytag K G , and Siemens-BauunionGmbH investigated four possible prestressed con-crete construction possibilities?

1. A three-span variable depth structure similarto the Bendorf Bridge

2. A six-span constant-depth structure3. A frame bridge4. A nine-span “mushroom” construction with a

center row of piers

These four schemes were proposed, as were a largenumber of different ones in both steel and con-crete by other firms. The successful low bid was forscheme 4 above. The nine-span “mushroom” con-struction was approximately 4% less costly than anorthotropic-deck, three-span continuous steelgirder and 7% less costly than a prestressed con-crete girder bridge of six spans.6

The Elztalbrticke, extending the methodologyused earlier for primarily low-level urban viaducts,was the first application of the “mushroom” crosssection for a high-level structure crossing a deepvalley. Previously, this type of construction, be-cause of its short, stiff piers, required a number ofexpansion joints in the deck to accommodatethermal forces, elastic shortening, creep, andshrinkage. In this structure, owing to the flexibilityof the tall piers, only one expansion joint was used,

Koblenzeast abutment

3m5-4 A 31aYlo

Trier

c D E F 6 H I west abutment

319 ,941 xu,514 321 ,128 321 ,779 322 4m

D&W rock anchors ;; z

Longitudinal cross section

(a)

Total length = 379.30 m ~~~ ~

Plan

(b)

FIGURE 6.23. Elztalbticke, longitudinal cross section and plan, from reference 5(courtesy of Der Bauingenieur). (a) Longitudinal cross section. (h) Plan.


28 .

435

in the center span. This joint is located 38 ft (11.6m) from pier E. The superstructure is monolithi-cally connected at all piers and the abutments.

At the center of each span is a 43 ft (13.1 m)long, massive flat plate, which in cross section has athickness varying from the centerline (crown otroadway) of 2% in. (650 mm) to 17% in. (450 mm) atthe outside edges. The “mushroom” portion ot thespan varies in thickness, transversely and lon-gitudinally, to 8 ft (2.45 m) at the pier. Thesuperstructure is prestressed longitudinally andtransversely.

The octagonal piers have, in cross section, exter-nal dimensions 01 15.75 by 19 ft (4.8 by 5.8 m) witha wall thickness of 11% to 1% in. (300 to 350 mm).Any given pier has a constant cross section for itsentire height. The percentage of vertical rein-forcement, with a concrete cover on the outer andinterior faces of 1.5 in. (40 mm), varies from 0.8 to1.2% of the gross concrete area. Piers were con-structed by slip-forming. The eight pier shaftswere constructed in seven months. The tallest pier,3 11.6 ft (95 m) in height, was slip-formed and castat a rate of about 26 ft (8 m) per day and thus re-quired 12 days to construct. The top 4 ft (1.2 m)portion of the pier was cast with the superstructureby the traveling scaffolding. On the top of the slip-formed pier four 7.2 ft (2.2 m) high pedestals werecast to provide the support for the cantilever gir-der from the traveling scaffolding, Figure 6.25.’

The traveling scaffolding was assembled atabutment A after completion of the abutment andthe half-mushroom projecting therefrom. Thisform traveler, Figure 6.26, accommodates a full-width span-length segment of 123 ft (37.5 m).After the first span, two weeks were required tocomplete a superstructure span. The first opera-

FIGURE 6.24. Elztalbticke, cross section at pier E,from reference 5 (courtesy of Der Bauingenieur).

FIGURE 6.25. Elztalbticke, construction view (cour-tesy of Dipl. Ing. Manfred Bockel).

Side longi tudinal g i rder

i-9000--+- &Q*Llo L+P-.-- dp

I / Center support bearing i C a t w a l k

Center longitudinalgirder

Upper catwalk

Travel direction -3 7 5 0 0

Longitudinal cross section

Concreting sequence

II) III)

concreting posi t ion t rave l ing pos i t ion

Center longitudinalgirder

Side longi tudinalgirder

, + Hydraulic jack

a Formwork at Forms in stripped

concret ing posit ion Ipos i t ion

Scaffolding afteradvancement

Section CD

Section A-B

Cc)

Cd)

FIGURE 6.26. Elztalbticke, form traveler, from reference 5 (courtesy of DerBauingenieur). (a) Longitudinal cross section. (b) Plan. (c) Section A-B. (d) Section C-D.

299


tion was to cast a 42.65 ft (13 m) wide center por-tion of the bridge. After hardening and initialstressing, the two outside edges, each 27 ft (8.25 m)wide, were cast. Subsequently the form travelerwas advanced to cast the next span.5

As mentioned previously, an expansion joint islocated in the center span. During construction thisjoint was “locked” until construction reached pierG; then the joint was released.5

During concreting the forms are suspended bysteel bars, and during advancement the forms arecarried by the bottom arm of the transverse can-tilevered steel members. The form traveler, Figure6.26, essentially consists of two approximately 141ft (43 m) long longitudinal girders and eight trans-verse frames in a “C” configuration which sur-rounds the deck construction. The transverseframes may be provided with a covering to protectthe workmen and the construction from theweather. At the forward end an approximately 72ft (22 m) long cantilever beam, located on the cen-terline, is projected to the next pier for support.

This structure is located on national route 260crossing the Guadiana River between Beja and

Serpa, Portugal. The viaduct has a total length of’11 15 ft (340 m) and consists of 197 ft (60 m) spansexcept for the river spans, which are 164 ft (50 nl).

Transversely, the superstructure is 53.8 ft (16.4 m)in width composed of two single-cell box girders.Each box girder is 19.35 ft (5.9 111) wide, with thedepth varying from 6.5 ft (2.0 nl) at midspan to 9.8ft (3.0 m) at the piers. After construction of the boxgirders, a longitudinal centerline closure is pouredand cantilevered sidewalks are constructed.

The superstructure is constructed by the span-by-span method, from inflection point to inflectionpoint, by an overhead self-launching f’orm carrier,Figure 6.27. The form carrier consists of 279 ft (X5m) long trusses of a depth varying f‘ronl 9.8 ft (3.0m) lo 16.4 ft (5.0 m). Forms fol- concreting thesuperstructure are supported bv two series of sus-penders. One set pierces the concrete flanges and

Forward support , IEnd traveler support

Elevation

(a)

Typical cross section

Section at forward support-forms open

(b)

FIGURE 6.27. Guadiana Viaduct, elevation and sections of form carrier. (a) Elevation.(b) Section at forward support-forms open. (c) Typical cross section.


is located inside the box cell. The other set is ar-ranged outside the box and supports the formswhen stripped and traveling past the piers in anopen position, Figure 6.27.

During concreting of the superstructure thef’orm carrier is supported on the forward pier b\an arrangement of a telescoping tubular crossframe, at the rear: it is supported on thesuperstructure at a location 26 ft (8.0 m) forwardof’ the rear pier. When the form carrier is beinglaunched forward, it moves over a support at thetip of rhe completed superstructure cantilever(near the inflection point), and its rear supportrides on the surface of the completed superstruc-ture. ‘The form carrier (including all equipment)weighs 209 tons (190 mt).

6.4.6 LOISACH BRIDGE, C;ER,\lA,\‘k

‘l-he federal autobahn between Munich and Lin-dau has an alignment that transverses the Mur-nauer swamp area near Ohlstadt and thus crossesthe Loisach River and the old federal highway B-2(Olympiastrasse), Figure 6.28. Because of floodingand poor soil conditions an embankment was notpossible, and a decision was made requiring a dualviaduct bridge structure with a total length of 43 14f’t (1315 Ill).’

.I‘he 232.8 ft (70.96 m) main span crossing theLoisach River is a variable-depth single-cell boxgirder constructed by the free cantilever method.Depth of’the box girder varies from 9.84 ft (3.0 m)to 5.58 ft (1.7 m), Figure 6.29. The approach spansare of a T-beam cross section, Figure 6.29, con-structed by the span-by-span method with the formcarriers running below the superstructure. Figure6.30 is a longitudinal section of the bridge withinthe area of the approach spans, showing the formcarrier running below the level of the top slab. Fig-ure 6.31 shows the form traveler in action.

Box girder T-beam

FIGURE 6.29. Loisachbriicke, cross sections, fromreference 8 (courtesy of Dyckerhoff & Widmann).

The dual structure has a total width of 100 ft(30.5 m), Figure 6.29, and each half is supportedon two circular piers, excepting the Loisach spanwhich is supported on wall piers. In the totallength, the dual structures are subdivided intothree sections by two transverse joints, Figure 6.28.In plan the structure has a radius of 4265 ft (1300m) at the Munich end, and the curvature reversesat the Loisach with a radius of 6562 ft (2000 m).”The completed structure is shown in Figure 6.32.

The circular piers are 4 ft (1.2 m) in diameterand are supported on 20 in. (500 mm) driven pileswith an allowable load capacity of 176 tons (160mt). Pile depths vary from 42 to 72 ft (13 to 22 m).A total of 1182 piles were driven for a total lengthof piling of 63,650 ft (19,400 m), with an averagelength of pile of 53.8 ft (16.4 m). Load capacity ofthe piles was determined from eleven load teststaken to 265 tons (240 mt).

Because of the poor soil conditions andground-water pressure, the substructure was con-

FIGURE 6.28. Loisachbriicke, layout and underside view of bridge, from reference 8(courtesy of Dyckerhoff & Widmann).


FIGURE 6.30. Loisachbriicke, longitudinal and cross section showing form traveler(courtesy of Dipl. Ing. Manfred Bockel).

FIGURE 6.31. Loisachbriicke, view of form travelerin action (courtesy of Dipl. Ing. Manfred Bockel).

FIGURE 6.32. Loisachbticke, view of’ completedstructure (courtesy of Dipl. Ing. Manfred Bockel).

strutted in pits enclosed by sheet piling. The roundpiers vary in height from 9.8 to 23 ft (3 to 7 m).Because of the delay in pile driving, resulting fromthe soil conditions, the foundation completion wasdelayed from October 1970 to April 1971.

The 73 T-beam spans were constructed with twospan-by-span form travelers whose operationswere synchronized. On the Munich side of theLoisach four 223 ft (68 m) long and 4.26 ft (1.30 m)high principal form support girders are supportedin the 100 ft (3 1 m) spans on cross beams at eachpier, which in turn are supported off the pile caps.For the longer spans an auxiliary support was re-

quired at midspan. The radius and superelevationin a support length were held constant. Superele-vation varies from +5.5 to -4%. For a normal span8830 ft3 (250 m3) of concrete were placed in ninehours.s

Because of the tight time schedule, work wascontinued through the winter months in defianceof the extreme harsh weather conditions in theLoisach Valley. A weather enclosure was mountedon the form traveler and heated by warm-air blow-ers. In this enclosure the reinforcement and pre-heated concrete was placed. In addition, the freshconcrete was protected by heat mats. In this man-ner the work could proceed up to an outside tem-perature of 5°F (- 15°C). Construction cycle perspan was gradually reduced, after familiarization,from an original 14 days to seven days. Followingcompletion of the western roadway up to theLoisach the form traveler was transferred to theeastern roadway for the return trip to the Munichabutment. All 38 spans on the Munich side werecompleted by the end of February 1972, savingnine weeks in the construction schedule.

On the Garmisch side of the Loisach the movablescaffold system consisted of four principal girders292 ft (89 m) in length and 9.8 ft (3.0 m) deep,Figure 6.33. Superelevation varies from +4 to-5.5%.

Because of the delay in the pile driving, the firstspan was started in December 1970 with a 12-weekdelay. The last approach span on the left of theGarmisch side was completed in August of 1971.The traveler was then transferred to the otherroadway for the return trip and all 35 bridge spanswere completed by March 1972. By a gradual re-duction of thk work cycle from 14 days to sevendays, nine weeks were saved in the constructionschedule. Not only was the loss of time resultingfrom the foundation work made up, but a time ad-vantage was attained.

The four box girder spans (two in each dualstructure) on either side of the principal span overthe Loisach were cast on stationary falsework. Aux-iliary cross beams to support the falsework girderwere supported on driven piles. The two main


FIGURE 6.33. Loisachbrucke, cross section of mov-able scaffold system, from reference 8 (courtesy ofDyckerhoff & Widmann).

spans of 232.8 ft (70.96 m) were constructed by thefree cantilever method. Thirteen segments of 16.4ft (5 m) were required; six segments were castfrom one pier and then the cantilever form travel-

ers were transferred to the opposite pier for theremaining seven segments.”

After a construction time of approximately 30months the bridge was completed in 1972, shortlybefore beginning of the Olympic Games.

6.4.7 RHEINBRikKE DUSSELDORF-FLEHE,G E R M A N Y

This is an asymmetric cable-stayed bridge with aninverted concrete Y-pylon, Figures 6.34 through6.37. The overall length from abutment to abut-ment is 3764 ft (1147.25 m). The Rhine River spanis 1205 ft (367.25 m) long and is a rectangularthree-cell steel box girder with outriggers to sup-port a 135 ft (41 m) wide orthotropic deck, Figures6.36 and 6.37. At the pylon there is a transitionfrom the steel box girder to prestressed concretebox girders, which are used for the thirteen 197 ft(60 m) spans in the approach viaduct. The struc-ture is continuous throughout its entire length,having expansion joints only at the abutments.

The approach viaduct has from pier 9 up to pier13, Figure 6.37, a five-cell box girder cross sectionwith a width of 96.8 ft (29.5 m) and a depth of 12.5ft (3.8 m). This heavy cross section, Figure 6.36,resists the anchorage forces from the cable stays.For the balance of the viaduct length from abut-ment to pier 9 the cross section consists of twosingle-cell boxes, a continuation of the exteriorcells of the five-cell box girder cross section. How-ever, the interior webs of each box are of less

FIGURE 6.34. Rheinbticke Dusseldorf-Flehe, artist’s rendering (courtesy of Dyck-erhoff & Widmann).


:

FIGURE 6.35. Rheinbticke Dusseldorf-Flehe, viewfrom construction end of approach viaduct looking to-ward the pylon under construction.

thickness than that of the five-cell cross section.The width of each box then becomes a constant 23ft (7.0 m) outside-to-outside of webs. A diaphragmoccurs at each pier.

The approach spans were constructed segmen-tally by the span-by-span method with constructionjoints at approximately the one-fifth point of thespan. As described in Section 6.1.2, the methodused here employed movable falsework, Figures1.54 and 6.38, supported from the ground. The197 ft (60 m) spans were poured in place in oneunit from construction joint to construction joint.This required continuous placement of as much as3200 cubic yards (2500 m3) of concrete. After eachsection was cast in place and reached sufficientstrength, the prestress tendons were stressed andthe falsework was moved forward to repeat thecycle.

6.4.8 DENNY CREEK BRIDGE, U.S.A.

The Denny Creek Bridge is the first implementa-tion of the span-by-span method of construction in

the United States. It is located a few miles west ofSnoqualmie Pass in the state of Washington andwill carry the I-90 westbound traffic down off thepass. It is a three-lane, 20-span, prestressed con-crete box girder design with a total length of 3620ft (1103 m) on a 6% grade, Figure 6.39. The con-tractor, Hensel Phelps Construction Company,elected a construction method similar to those usedin many German and Swiss designs where the areais environmentally sensitive.

Because of the ecological and environmentalsensitivity of the project site, construction of thepiers was carried out under extreme space restric-tions. The contractor was allowed a narrow accessroad for the full length of the project and addi-tional work and storage area at each pier.”

The 19 pier shafts have a hollow rectangularcross section with exterior dimensions of 16 by 10ft (4.88 by 3.05 m), a wall thickness of 2 ft (0.61 m),and heights ranging from 35 to 160 ft (10.7 to 48.8m), Figure 6.40. Twelve piers are supported on rec-tangular footings. The other seven piers are sup-ported on pier shafts sunk through talus and tilland keyed into solid bed rock, Figure 6.41. Pier-shaft diameter is 12 ft (3.66 m) with a maximumdepth of shaft below the terrain of 80 ft (24.38 m).

The superstructure was constructed in threestages, Figure 6.42. In the first stage, bottom flangeand webs were constructed from a 330 ft (100 m)long movable launching truss, Figure 6.43. Thetwo trusses used for constructing the “U” portionof the box section rested on landing wings at thepiers, Figures 6.44 and 6.45, as the launching trussmoved up the valley, sliding from pier top to piertop. The construction schedule called for one spanevery two weeks. The entire scaffold system wassupported on six jacks to adjust for proper align-ment, two jacks at the rear of the span or initialpier and four jacks at the advance section or nextpier.

The launching truss was designed to support theoutside steel forms of the box section, Figure 6.46,and to facilitate removal of the inside forms,9 Fig-ure 6.42. Track-mounted cranes installed at thetop of the truss frame lifted and moved the insideforms from the web, hanging them on the truss sothat they were moved forward with the advance-ment of the launching truss. Figure 6.47 is aninterior view of the working area between trusses.Visible are the overhead track for the 15 ton ( 13.6mt) cranes located near each web. Also visible arethe cable hangars from the roof frame for thebottom slab support during casting.

The steel trapezoidal box form used for con-

Stee l Supers t ruc ture

Reinforced Concrete Supers t ructureHeavy Sect ion

.*It.*LL-

Rein forced Concrete Supers t ructureNormal Sec t ion

FIGURE 6.36. Rheinbticke Dusseldorf-Flehe, elevation of pylon and cross sections.

13. 60.0 * 760.0 367.25 SD

11‘7.26

Bearingcordnion6

ffl- -+ + + + + + + + + + + + +

G4FIGURE 6.37. Rheinbticke Dusseldorf-Flehe, plan and elevation.

+ unreai3aimd=windbeE&lg+ u-nad


FIGURE 6.38. Rheinbticke Dusseldorf-Flehe, endview of girder.

struction was insulated with Styrofoam, Figure6.48, and had heat cables installed (actuated ifneed be) to help maintain the temperature andrate of cure. Also, heat blankets were available togo over the section to reduce heat loss and main-tain a constant temperature in cold weather.

Concrete was batched from a plant erected nealthe west abutment using the highway right-of-way.‘[‘he contractor used three 8 cu vd (6.1 m3) ready-

mix trucks for mixing the concrete, which was thenpumped to the proper location. Superstructurepours were about 300 cu yd (229.4 m3) and tookabout nine hours, using two concrete pumps andthe track-mounted cranes installed in the trussframe. Concrete strength required was 5000 psi(34.47 MPa). The contractor obtained 3500 psi(24.13 MPa) in three days using $ in. (19 mm)aggregate. The 28-day strength ranged fi-om 6100to 6600 psi (42.06 to 45.51 MPa).

In stage two the top flange between the webs wasplaced. Metal f’orms, Figure 6.49, were supportedfrom the bottom flange and webs, Figure 6.42.’

In stage three the two top flange cantilevers wereplaced, Figure 6.42, by a movable carriage thatrode on top of’ the box cast in stage two, Figure6.42. Upon completion of’ stage three, the trans-verse prestressing of’ the top flange was accom-plished. The completed section is 52 f’t (15.08 m)wide, providing three traflic lanes.

The Washington DOT sponsored the design.Three alternatives were prepared f’or biddingpurposes. One was an in-house state design; theother two were prepared by outside consultants.‘l‘he Dyckerhof‘t‘ & Widmann design proved to be

FIGURE 6.39. Denny Creek Bridge, perspective sketch.

Progressive and Span-by-Span Construction of Segmental Bridges

FIGURE 6.40. Denny Creek Bridge, view of piersunder construction (courtesy of J. L. Vatshell, Wash-ington DOT).

FIGURE 6.4types.

. Denny Creek Bridge, substructure

the most economical. VSL Corporation was the an artist’s rendering showing the precast V-pierssubcontractor providing the prestressing expertise. with the 7 ft (2m) deep box girder segments.

6.5 Span-by-Span Precast Bridges

6.5.1 LONG KEY BRIDGE, U.S.A.

Long Key Bridge in the Florida Keys carries U.S.Highway 1 across Long Key south to Conch Key.The existing bridge consists of 2 15 reinforced con-crete arch spans, ranging in length from 43 to 59 ft(13.1 to 18 m) for a total bridge length of 11,960 ft(3645 m).

The new bridge, presently under construction, is50 ft (15.2 m) between centerlines and just northand parallel to the existing structure. It is a precastsegmental box girder constructed by the span-by-span method and consisting of 101 spans of 118 ft(36 m) and end spans of 113 ft (34.4 m) for a totallength of 12,144 ft (3701 m). The roadway widthbetween barrier curbs is 36 ft (11 m), Figure 6.50,to accommodate a 12 ft (3.66 m) roadway and a 6 ft(1.83 m) shoulder in each direction. Figure 6.51 is

In the preliminary design stage three methods ofsegmental construction were considered: balancedcantilever, span-by-span, and progressive place-ment. The progressive placement method was dis-carded because it was felt (at the time) to be toonew for acceptance in U.S. practice. It was laterintroduced on the Linn Cove Viaduct in NorthCarolina (see Section 6.3.2).

This is the first use of a precast span-by-spanmethod in the United States. The segments aretransported from the casting yard to their locationin the structure by barge. The segments are thenplaced with a barge crane on an erection truss,which is supported by a steel grillage at the V-piers.Each span has a 6 in. closure pour after all thesegments have been placed on the erection trussand properly aligned. The essential operations areindicated in Figure 6.52.

Segment weight is approximately 65 tons (59mt). Each segment is placed on the erection trusson a three-point support and brought into its finalposition. It takes approximately four to six hours

Schematic of movable scaffolding

I 5 0

Overheaddollies

Jacks for grade,superelevation and camber

Stripped position

7 Staga 2 7

T

Stage one

S t a g e two

Rollers and jacks -- LJacks

Stage three

FIGURE 6.42. Denny Creek Bridge, schematic of construction stages, from reference 9(courtesy of the Portland Cement Association).

FIGURE 6.43. Denny Creek Bridge, view of launch-ing truss.

FIGURE 6.44. Denny Creek Bridge, view of landingwings at piers (courtesy of J. L. Vatshell, WashingtonDO-I-).

309

FIGURE 6.45. Denny Creek Bridge, close-up view oflanding wing (courtesy of J. L. Vatshell, WashingtonD O T ) .

to place the segments required for one span. Thecontractor has placed as many as three spans perweek for a total of 354 ft (108 m) of completedsuperstructure per week and has averaged 2.25spans per week.

Another major deviation from United Statespractice in this project was the use of external pre-stressing tendons (located inside the box girdercell). This requires that the tendons be consideredas unbonded for ultimate-strength analysis. Plac-ing the tendons inside the box girder void allowsthe web thickness to be minimized. Tendongeometry is controlled by deviation blocks castmonolithically with the segments at the proper lo-cation in the span, Figure 6.53. These blocks per-form the same function as hold-down devices in apretensioning bed. The tendon ducts between de-viation blocks or anchorage locations or both arecomposed of polyethylene pipe, which is thengrout-injected upon completion of stressingoperations- a corrosion protection system similarto that used for the cable stays on some cable-staybridges. l”,ll

FIGURE 6.46. Denny Creek Bridge, view of outsidesteel forms (courtesy of J. L. Vatshell, WashingtonDOT).

FIGURE 6.47. Denny Creek Bridge, view of interiorworking area between trusses (courtesy of Herb &hell,FHWA Region 10).

FIGURE 6.48. Denny Creek Bridge, insulation onexterior steel forms with installed heat cables (courtesyof Herb Schell, FHWA Region 10).

Span-by-Span Precast Bridges 311

FIGURE 6.49. l)c~lny Creek Bridge, vie\v 01‘ tnc.talform used for stage-two construction (courtesy of J. L.Vatshell, Washington DOT).

The external tendons overlap at the pier seg-ment to develop continuity. The bridge is continu-ous between expansion joints for eight spans, 944ft (288 m). After the closure pour reaches the re-quired strength, the post-tensioning is accom-plished and the span is complete. A 30 in. (‘760mm) diameter waterline is installed inside the voidof the box girder. The erection truss is then low-ered and moved away from the completed span.The erection truss is handled at a one-pointpick-up location by a C-shaped lifting hook, Figure6.52. The truss is supported against the bargecrane and moved parallel to the new bridge until it

Section at pier Section at midspan

FIGURE 6.50. Long Key Bridge, typical cross section of superstructure.


The span by span erection concept utilizes a temporary steel assembly trussIn conjunction with a barge mounted crane as shown. The steel truss

3 between the piers is equipped with post-tensiontng tendons along)m chord to facilitate ad jus tments fo r de f lec t ions and kwenng the

LIUw ,,on comple t ion o f the span .

PREVIOUSLY A55EMBLfP 5PAN 3

\,

i1 # .

A55E’40~Y TRUSS

FIGURE 6.52. Long Key Bridge, span-by-span erection scheme.

reaches the position for a new span, and the cycle is The existing structure consists of 209 masonryrepeated. arch spans, 300 spans of steel girders resting on

_ _masonry piers, and a swing span ove r Mose r

6.5.2 SEVEN MILE BRIDGE, U.S.A. Channel. The spans range in length from 42 ft 7tin. (13 m) to 47 ft 4$ in. (14.4 m) for the masonry

The Seven Mile Bridge, Figure 6.54, in the Florida arches and from 59 ft 9 in. (18.2 m) to 80 ft (24.4Keys carries U.S. Highway 1 across Seven Mile m) for the steel girders resting on masonry piers,Channel and Moser Channel from Knights Key which along with the 256 ft 10 in. (78.3 m) swingwest and southwest across Pigeon Key to Little span, produce a total bridge length of 35,716 ft 3Duck Key. in. (10,SSS m).

Span-by-Span Precast Bridges 313

PERSPECTIVE VIEW

DETAIL 2

ELEVATION

FIGURE 6.53. Long Key Bridge, typical tendon lay-

FIGURE 6.54. Seven Mile Bridge, artist’s rendering.

The new bridge, presently under construction, islocated to the south of the existing bridge. It is aprecast segmental box girder constructed by thespan-by-span method with 264 spans at 135 ft(41.15 m), a west-end span of 81 ft 7$ in. (24.88 m),and an east-end span of 141 ft 9 in. (43.2 m) for atotal length of 35,863 ft 44 in. (10,931 m). Theroadway requirements are the same as for theLong Key Bridge and the cross section is almostidentical, Figure 6.50. Seven Mile Bridge crossesthe Intracoastal Waterway with 65 ft (19.8 m) verti-cal clearance, and its alignment has both verticaland horizontal curvature.

The consultants, Figg and Muller Engineers,Inc., used the same concepts as had been used forthe Long Key Bridge, except they omitted theV-pier alternative in favor of a rectangular hollowbox-pier scheme that is precast in segments andpost-tensioned vertically to the foundation system.

As mentioned in Section 1.9.3, the contractorelected to alter the construction scheme in thisbridge from that of the Long Key Bridge by sus-pending the segments from an overhead trussrather than placing them on an underslung truss.The essential operations for construction of a typi-cal span are as follows:

1 . Transportation of all segments by barge to theerection site.

2. Assembly of all segments in a span (with theexception of the pier segment) on a structuralsteel frame supported by a barge.

3. Placing the pier segment on the pier adjacentto the previously completed portion of thedeck with the overhead truss working in can-tilever.

4. Launching the overhead truss onto this newlyplaced pier segment.


5. Lifting in place the entire assembly of typicalsegments with four winches supported by thetruss.

6. Post-tensioning the entire span after the clo-su re j o in t has been poured be tween thefinished span and the new span.

7. Launching the overhead truss to repeat a newcycle of operations.

After a period of adjustment, the method hasallowed a speed of construction equal to that forthe assembly truss scheme used for the Long KeyBridge. One complete span may be constructed inone day, and as many as six 135 ft spans have beenplaced in a single week. Figure 6.55 shows the as-sembly of segments being erected in a typical span.

6.6 Design Aspects of Segmental ProgressiveConstruction

6.6.1 GENERAL

. ,

The use of temporary stays to carry the weight ofsegments during construction induces only a nor-mal compression load in the deck and a very lim-ited amount of bending. Consequently, the staticscheme of the structure during construction is veryclose to that of the finished structure. This is asignificant advantage over the conventional can-tilever construction scheme, where continuity ofthe successive cantilever arms results in two staticschemes significantly different between construc-tion and service.

Because of this similarity of static schemethroughout erection and service, it is expected thatthe layout of prestress tendons found in cast-in-place structures or in span-by-span construction

FIGURE 6.55. Seven Mile Bridge, erection of a typicalspan.

should be applicable to progressive construction,with the added advantage that the tendons can beregularly stressed and anchored at the successivejoints between segments in a simple manner.

On the other hand, progressive construction dif-fers in several aspects such as pier design anddeflection control during construction, calling for amore detailed examination.

6.62 REACTIONS ON PIERS DURINGCONSTRUCTION

Construction of a typical span proceeds in twostages, as shown in Figure 6.56: (1) pure cantilevererection, of a length a from the pier, and (2) con-struction with temporary stays on the remaininglength (L - a). Length a should be selected (withinthe nearest number of segments being placed) suchas to keep the girder load moments over the pierwithin allowable limits.

Assuming that this moment is of exactly thesame magnitude as the fixed end moment of atypical span under the same unit load W, one maywrite:

Wa2 WL’-=-2 1 2

FIGURE 6.56. Progressive construction, deck reac-tions on piers.

Design Aspects of Segmental Progressive Construction 315

for a constant-depth girder, which is the generalcase for- progressive construction. Thus:

0 = 0.408L = 0.4OL

For (1 = 0.4OL the moment over the pier is equal to,M = 0.08WL’. l‘he moment over the precedingpier, for a structure with a large number of’ identi-cal spans, is equal to 0.26&\1. Therefbre. the reac-tion over the pier at the end of’ this first stage ofconstruction can be easilv computed as:

R = 0.4OWL + 1.268 x 0.08WL = O..5OW’L

During the second construction stage the lveightof the remaining part of’ the span is supported b:,t h e temporarv stays, which are anchored in therear span as close as possible to the previous pier soas not to induce undesirable variations of. momentsin t he last c o m p l e t e d s p a n . ConsequentI!,, t h elveight of’t hat part of’t he span induces in the pier areact ion equal to:

1 .io0.6W’L + - = 1.02WL

1 . o o ___

The total reaction during construction applied tothe pier is t bus:

R = 0.5OWL + 1.02WL = 1.62WL

as opposed t o R = N’L for cast-in-place or span-h\--span construction. ‘l‘his temporary increase of’girder load reaction of’ 62% \vill eventuall!- \,anishIvhen construction proceeds. It is important to\.erifv how critical this pier temporary overloadma! be f’or the design of’ the substructure. Takingthe example of’ a 150 to 200 f’t span, the averageloads are as follows fi)r a 40 f’t wide bridge de-signed f’or three lanes of’ traf’fic:

Girder load 8.0 ksf

Superimposed load 1.5 ksfEquivalent live load including impact 2.6 ksf

The maximum reaction during construction com-pares jvit h that after completion as follows (valuesgiven are the ratio between reaction and spanlength):

1. During construction, 1.62 X 8.0 = 13 ksf2. Completed structure:

a . Girder load 8.0b. Superimposed load 1.5

C. Live load, includingprovision tot- continuity

over the support

(15%), 2.6 x 1.15 = 3.0

12.5 ksf‘

-I‘he dif‘ference i s smal l and usuallv more thanoffset hy the fact that horizontal loads during con-struction are smaller than during service.

As shown previously, progressive construction of’ atypical span entails two successive stages:

Cantilever construction on a length (I

~l‘emporary suspension by stays on the remainingpart of’ the span (L - n)

.I‘his second stage induces small deflections androtation, provided that the vertical component of’the sta!- loads balances the total deck weight. Onthe other hand, the first-stage construction notonly creates substantial deflections but also changesthe geometric position of’the entire span, as mav beseen in Figure 6.5f.

The xveight (Wa) of’ the deck section produces:

A rotation of’ the previous span, w,, which willproject at the f’ollowing pier and create a verticaldeflection, J,

a deflection of’ the cantilever proper, yr

a rotation at the end of the cantilever, wL, whichLvill p ro jec t aga in a t t h e f’ollowing p i e r i n t o adeflection mt (L - n)

Altogether the total deflection is:

Wa’ (2Ll v5 + 4nL - n’)I’= 2 4 E I

If’we let 14 = N/L, the deflection can then be writtenas:

WL1)‘= 2 4 E I

u’(2 fi + 4U - u’)

With u = 0.4 as assumed betore, the total deflec-tion is:

WL4y = 0.0327 EI

where W = unit deck load,L = span length,


IZ’ = concrete modulus,I = section inertia.

A simple parametric analysis will reveal the im-portance of this problem. If W is the specific gravityof concrete and A the cross-sectional area, then W= GA. It was shown in Chapter 4 that the efficiencyfactor of a box section is:

I- = 0.60 to 0.63= Ac,c,

If the section is symmetrical, c, = cz = 0.5 h (h =section depth), and I = 0.157 Ah” max. If c, =0.33 h and cg = 0.67h, which is the practical dis-symmetry of a box section, I = 0.133Ah2 min. Forall practical purposes, assume I = O.l4Ah*. The de-flection then becomes:

Ey = 0.23ZL2 + *t 1

Because the construction proceeds rapidly, Eshould be taken for short-duration loading; that is,E = 800,000 ksf; the specific gravity of concrete is W= 0.15 kcf. The slenderness ratio L/h varies be-tween 18 and 22. Results are shown in Figure 6.58.

Construction of a 200 ft span, for example, witha slenderness ratio of 20 will be accompanied by adeflection under girder load (without prestress) atthe next pier of 8.3 inches. The constructionmethod is therefore very sensitive to concretedeflections, which are magnified by the great leverarm of the first-stage construction of the spanprojecting its intrinsic deformation to the follow-ing pier.

Fortunately, prestress will give a helping handand contribute to substantially decreasing thegirder load deflection. The minimum prestress re-quired at this stage is to balance the tensile stressesinduced by the girder load moments. With thesame notations as above, one may compute theprestress force and the corresponding moment forthree positions of the neutral axis:

c,lh = 0.5c,lh = 0.5

L-o 1

FIGURE 6.57. Progressive construction. def’ot-ma-tions.

For an efficiency factor p = 0.65 the correspondingvalues would be:

0.58 0.47 0.39

The prestress will therefore reduce the deflectionsby the same amount-that is, approximately halfthe total girder load deflections. The resultantdeflection (girder load + prestress) still remainsvery significant as soon as the span length is above150 ft. These deflections must be taken into fullaccount to compute the camber diagram (for seg-ment precasting).

The next important point to consider here is thesecond-stage construction of a typical span whenthe remaining part of the girder is suspended fromthe temporary stays. The concrete girder and thegroup of stays form an elastic system that supportsthe applied loads: girder load for the segments al-ready in place, swivel crane and new segment

c,lh = 0.4 c,lh = 0.33c,lh = 0.6 c,lh = 0.67

Efficiency factorDistance fi-om

centroid of‘ prestress to top fiberEccentricity of’ prestressLower central core

Lever arm of prestress

p = 0.60 p = 0.60 p = 0.60d = 0.05h d = 0.05h d = 0.05h

e = 0.45h c = 0.35h c = 0.28h72/c, = 0.30h flc, = 0.36h r21c, = 0.40h

0.75h 0.71h 0.68hPrestress moment 0.45

(ratio of’ girder load moment)- = 0.600.75 E

Design Aspects of Segmental Progressive Construction 3 1 7

ICI I

FIGURE 6.58. Progressive construction, deflections.

traveling over the bridge with the trailer and trac-tor. -Two examples have been considered to showthe relative response of the various components ofthis elastic svstem toward the application of a load.

1. 108) (JJm) s p a n This was one typical spanof’ the Rombas Viaduct. The span has been as-sumed to be completed except for the pier segmentover the next pier. For this construction stage, theswivel crane and the new segment apply to thestaved cantilever a load of 88 tons (80 mt). In viewof the great stiffness of the concrete girder com-pared to the group of stays, the total moment in-duced bv the load remains ahnost entirely in theconcrete girder and there is only a small spontane-ous increase of the stay loads, as shown in Figure6.59. The magnitude of temporary prestress in thedeck must be designed accordingly to keep alljoints under compression for all intermediateloading cases.

2. 260 ft (80 m) span This example is takenfrom a recent design for a large project in Europe

where progressive construction was contemplatedfor a viaduct with a large number of identical 260ft (80 m) spans all made up of 26 segments 10 ft (3m) long. Figures 6.60 and 6.61 show the distribu-tion of moments between concrete girder andtemporary stays at three successive stages of seg-ment placing: segments 15, 20, and 25, respec-tively. The first nine segments are placed in can-tilever; the following 15 segments are suspendedfrom tern porary stays, while the last typical seg-ment and the adjacent pier segment are placedwithout stays.

The proportion of the load (and correspondingmoment) taken by the stays increases as the can-tilever length increases and, when the last segmentis placed, more than half the load is supported bythe stays. For verv-long-span stayed bridges, thisdistribution of load between stays and concretegirder reaches the situation where the load is al-most entirelv supported by the stays and the con-crete girder’is subjected only to an axial force, ex-cept in the area of the longest stays.

The consideration of distribution of loads andmoments between stays and concrete girder has animportant aspect during construction-that is, theaccuracy of the tension in the stays and conse-quences of an accidental deviation between com-puted values of stressing loads in the stays andtheir actual values in the field. For example, take

the simple case of a span L with 40% built in purecantilever and the remaining 60% suspended bystays (see Figure 6.56). The moment over the pierdue to the second-stage construction load is M =0.42WL’. Assume that an accidental deviation took

place of 5% between the design loads for the staysand the actual values obtained in the field (owing tofriction in the jacks, inaccuracy in the pressuregauges, and so on). As a result, an additional mo-ment will appear over the pier of AM = & 0.42 WL’= 0.021 WL’. The corresponding tensile stress atthe top fiber (assuming the error in stay loads wasto reduce the theoretical values by 5%) can be eas-ily computed by:

Af=AM’-c- 0.02 IZAL2c,I APC,C,

= 0.0217X~PC2

With W = 0.15 kcf, p = 0.60, and cp = 0.60/z:

Af= 0.0088:


FIGURE 6.59. Pt-ogwssi\t’ co11structiotl. incwase of’ hta\ Ioatlittg

‘l‘hc stress in kst’ t’or L//r = 20 (slcndert~ess ratio) i3the l’ollo~vit~g 1’01. sewx~l spmi l eng ths :

L (11) 100 130 “ 0 0 250

.I/ = O.li.il. (tdl) 1 X “6 3 .i -l-l

I‘his stress is not critkil 1’01. short spans but I~;IIhecome sigtiificatIt t’or lotig ones. .I‘he simple der-vation given above sho~3 that control of the stab-tetisiottitig operations at the site shoitld albx~~s beott the salt side Ivith due allo\vatice fol. iti;icciIr;ic~~.

.-I dcviatioti in the tension of‘ the stavs bill aisoal‘f’ect the deflections during constructio;l. Withoutthe presence of the stavs the total deflection overthe next pier due to the load 011 the length (L - n)w o u l d be:

which gives t’or u = 0.4 as befixe:

A-\ssutiie that the itiaccutx~~ of the sta\ lo;itts lea\,esitI the concrete girder 5% of its O\VII lveigtit to becarried lx bending: the resulting deflection m.etthe pier ~vould be:

.I‘his value should be compared to ttte ef‘tect of‘ thefirst-stage cotistructiotl, lvhich bxs pre\iortsl\ gilen:1s:

Ill sLltllm;II‘~ ( il 5% de\iatioti of the st;t\. tctisiotlloads will increase the cantilever defectiotl due togirder load by 36%. Considering the twneficial et-feet of prestressitlg fi)r the latter, \ve see that ap-proximately 7% deviation ot’the sta!. l0;1d producesthe same defection 2s the first-stage cotistructiot~loads including prestressing. .I‘tiis 41~0~3 that thedef lec t ions a re itnportant, particulart\ fi)r lotlgspa~is built in progressive construction, hut thatproper deflection control is an excellent tool to

References 319

F I G U R E 6 . 6 0 . I’rogrc\si\c ~ott~tt~tt~~tiott. clistt-ibrttiotto f lttolttclt1 tx~t\\wll sl;l\s ;Illcl gitxlcT.

Let-it\ t ttal st xwcs in t tie c-ottc‘rele girder ,tt-e ;11\\-;t\ 5Lcpl \vittiitt alfo\v;lt)fe littiila.

Because the silatic wttente at the cticl of’ cacti con-slrttctiott 5tep ia idctttical to that of‘ ;I ca\t-itt-placeslntct tire, (tie pet~tttatietit tendotis can Ix ittstalletli i i t t t r sttxtctttw itiitiiediatel~, vAthut the tratisi-t i o t i s i t u a t i o n s I-eqttil-ed t,y o t h e r cotistrttctiotittt~tlioclologies such 2s itict-emetital lautictiitig.

~1 t\ pical pi-esttws la\ out for progressive COII-struction b,iff thus include:

.-I f i t - t f;ttttil\ of. tettclotts located in the top flangeo\‘et‘ 1 tie \~t~ious piers, h,itti atictiol-s s~tiitiietl-icall~~loc;tlecl in hfistet-s, the purpose of Ivtiicli is to resistticgtti\ c tttotttetits 01 er t tic suppot-ts.

.A wcottcl f’atttil\ of‘ tendons located aloti~ the spatiiii the tmtlom flatige and Am ;itictiored in blistersinside the tms section. L’suall\. the top atid bottomhlisterh ~tre,joitieci to ;t \veb rib, allowing tetiipotxt-1pi-estt-css hi-s t o Ix atictiored during s e g m e n tplacittg.

BY CONCRETL OIMDCR

3 S.GML”T,*~~~~~~ I5 ?2WR”DEDI” CANmEYER ----i w’ 9*hSCfMLNTS

FIGURE 6.61. (I’ro~t~c’~~i\ c consli~uc lion. (li\tt~itttttiotto f IlIoItlcI1t twt\\cul \t,t\s ‘Incl ~itxlcl

Possit)l\. ;I third fatnil\ 01’ tendotta mtde of intet~tt;ilst;i\ s b,‘itli ;I dl-aped profile and attchot-ed over thepiet-s iii t tie di~tptirqp~. the put.posc of’ lvttictt is tosttpplettietit both ottiet- f;itiiilies Ichile t~ecittcittg thettet stie;tt- sttwses in the \vet)s txcattse of’ the \,ctTi-Cd

1

”

3

-I

cotiipotietit o f prestt‘ess.

References

H . \Vitttoht. "l'lY?sllw\ed ~:oIIcl~cIc Rlxlge c:or1-

sti-tictiott bitti Steppittg Form\\-0t.L E:qttipilit’itt.”F i rs t Iittet-~tatiortal S\ tttlx~sit~itt (Zorict-ctc 13ritlgc lbsign, t’;~pcr SP 2%2X. .-\C:l l’t~t~lic~ttiott SI’-23..\tttt~Cc;ttt C:ottct-ete Itlstitute. lkti-oil. lWi9.

H . \Vitttottt. “Die \‘ei-~eiidrtttg VOII \~ol-scttt)l-its-

tuiigeil bictn Bt~iickeithu” ( I‘ttc L‘w of I‘i-:t\eliitgFoi~rn~~o~L iii Bridge Constrttctioii), Itttc’i~n;ttiott;tI.Association B r i d g e a~td Sttxctui-al kkgittceriitg,Siitttt Congress. ;\tttatet-da~tl, .\l;r\ H- 13, lYi2.H . I‘hul. “Spatttttxton im BriicLelltxttt.” Zawrtl rrtcdHem. H e f t 4”. Ik/ctttt,el~ 196X.M;rl~-<:tlullg I‘mg, “Recent lkvelol~itiertt of Con-structiott ~I‘cchniclties in (Ionct-etc Br idges.” I’rans-pot-tatioit Keswrch Kewi-tl 66.5. Kridgr Ettgtneel--ing. \‘ot. 2. Procwd~nq~ of the 7‘,n,~.rportcctrorl RPWIW/I

Rof~rd Co,,Jrrf~rrcf~, September 2.5’Li 19i8. S t . Imttis;,..\fo., Satioital Ac;tdeiii\~ ot Sc iences . ~l’astiittgtott.D.C.


5 . U. Finsterwalder and H. Schambeck, “Die Elztal-briicke,” Der Buuzngenieur, Hefi 6 , June 1966, andHeti 1, January 1967.

6 . H . .I‘hul, “Bt-iickenbau,” Beton- und Stnhlhetorrbnu,Heft 5, May 1966.

7 . A n o n . , “Bau del- Loisachbriicke bei O h l s t a d t , ”Dyu&g-Berichte 19713, D y c k e r h o f t 8s N’idmann,AC, Munich.

8. .Anon., “Bauausf‘iihrLlng d e r XutobahnbrLicke ilbeldie Loisach bei Ohlstadt,” Dydq-Betichte 1972-5,Dvckerhoff & Widmann, AG. 1lunich.

9 . AIlon., “ D e n n y Creek-FrallkliII E‘,~lls \‘i;ttluct.Washington,” Bt-idge Report SK 202.01 E, l’ortl;t11(1Cement Association, Skokie, 111.. 1978.

10. Anon., “Florida’s Long E(e) Bridge to Ltilile l’rcca\tSegmental Box Girder Span-b\-Spa11 <:onstI.uctiot~,”Bridge Report, Post ‘I‘ensioning IIIstitute. l’hoellix.Arizona, January 1979.

11. Walter Podolny, J r . , “;\n O\ et-k iew of t’reca\t Prc-stressed Seynental Bridges.“Jo~c,-,/NI of /AC, ~w\l,r\wtlConcrete Ztt,ditute. 1.01. 24, So. 1, jaI~II;in -Fe111 udn

1979.

7Incrementallv Launched Bridges

J

7.1 INTRODUCTION7.2 RIO CARONI, VENEZUELA7.3 VAL RESTEL VIADUCl-, ITALY

7.4 RAVENSBOSCH VALLEY BRIDGE, HOLLAND7.5 OLIFANT’S RIVER BRIDGE, SOUTH AFRICA7.6 VARIOUS BRIDGES IN FRANCE

7.6.1 Luc Viaduct7.6.2 Creil Viaduct7.6.3 Oli Viaduct

7.7 WABASH RIVER BRIDGE, U.S.A.

7.8 OTHER NOTABLE STRUCTURES

7.8.1 Mtihlbachtalbriicke, Germany7.8.2 Shepherds House Bridge, England

7.1 Introduction

-The concept of’ incrementally launched segmentalpres’ressed concrete bridges was described in Sec-tion 1.9.5. .Fhis chapter will describe the im-plementation of this innovative concept in severalrepresentative projects.

Since the in~plementation of the incrementallaunching technique on the Rio Caroni Bridge,some eight\ bridge superstructures have been con-

srructed 1;~ t h i s m e t h o d t h r o u g h 1 9 7 6 , w i t hgradual refinements and improvements in themethod.’ Bv concentrating the casting of segmentsbehind an ;Ibutment with a temporary shelter, ifrequired, this method can provide the same qualitycontrol procedures and quality of concrete that canbe achieved in a concrete ‘precasting plant. Itminimizes temporarv falsework, extensive form-ing, and other teniporary expedients requiredduring construction bv the conventional cast-in-place on falsework meihod. Basically the methodentails incremental fabrication of the superstruc-ture at a stationarv location, longitudinal move-ment of the fabridated segment an incremental

7.9 DESIGN OF INCREMENTALLY LAUNCHED BRIDGES

7.9.1 Bridge Alignment Requirements

7.9.2 Type, Shape, and Dimensions of Superstructure7.9.3 Span Arrangement and Related Principle of Con-

struction7.9.4 Design of Longitudinal Members for Flexure and

Tendon Profile7.9.5 Casting Area and Launching Methods

7.9.6 Launching Nose and Temporary Stays7.9.7 Piers and Foundations

7.10 DEMOLITION OF A STRUCTURE BY INCREMEN-TAL LAUNCHINGREFERENCES

length, and casting of a new segment onto the onepreviously cast. In other words, the procedure canbe considered as a horizontal slip-form technique,except that the fabrication and casting occur at astationary location. Stringent dimensional control,however, is an absolute necessity at the stationarycasting site, since errors are very difficult to correctand result in additional costs in launching.’

Straight superstructures are the easiest to ac-commodate; however, curvature (either vertical orhorizontal) can be accomplished if a constant rateof curvature is maintained. If the grade of thestructure is on an incline, it is preferred to launchthe structure, wherever possible, downward.Where the fall is 2’$%, the superstructure has to bepushed or held back, depending upon thecoefficient of friction. Where the fall is in excess of4%, special provisions are required to prevent a“runawav” superstructure during launching.’ Tothe authors’ knowledge, this situation has never oc-curred. Piers, either temporary or permanent,should be designed to resist the lateral force pro-duced by the launching operation. A friction forcevarying from 4 to 7% has been considered for de-

321

322 Incrementally Launched Bridges

sign purposes, although values of’ only 2 to 34%have been observed in the field.

At present, it is felt that this system cm be used

for superstructures up to 2000 t‘t (610 m) in length;fbr longer structures incremental launching is ac-complished f’rom both abutments toward thecenter of’ the structure. .l‘he technique has beenapplied f’or s p a n s up to 200 f’t (60 m) lvithout theuse of’ temporal-v supporting bents and for spans

u p t o 3 3 0 ft ( 1 0 0 m with such bents. Girders IISU-)ally have a depth-to-span ratio ranging f‘romone-tbvelfth to one-sixteenth of’ the longest spanand are of’ a constant depth. ‘l-he launching nosehas a length of’ approximately 60% of’ the longestspa11.

.I‘he principal advantages of the incrementallaunching method are the following’:

1 .

2.

3 .

4.

5.

6.

No f’alseworh is required f’or the constructionof’ the superstructure o t h e r t h a n possibl!f’alsework bents to reduce span length duringconstruction. In this manner cantilever stressesduring launching can be maintained lvithinallo~vable limits. If‘ fhlsework bents shouldprove to be impractical, then a system of‘tempo-rare stays can be used as indicated in FigureI .63. Obviously, depending on site conditions,;Inv or all combinations of’ temporary bents,launching nose, and temporar!. stays may beused, the point being that conventional use of’f’alsework is qreatlv minimized. -l-his is par-ctitularly interesting f’or projects in urban areasor spanning over water, highways, or railroads.

Depending on the size of’the prqject there canbe a substantial reduction in form investment.Because casting of’ the segments is centralizedat a location behind the abutment, the eco-nomic advantages of mass production and aprecasting plant operation can be duplicated.‘l-he method eliminates transportation costs ofsegments cast at a fixed plant and transportedto the site.It eliminates heavy cranes or launching trussesand associated erection costs.

It eliminates epoxy joints. Since epoxy is notinvolved, construction can continue at lowertemperatures.

Camber control and other geometry controlsare easily obtained.

Disadvantages are as follows:

1. As mentioned in Section 1.9.5, bridge align-ment fbr this type of’ construction must be

2 .

3.

4.

either straight or curved: holvever, cur\‘ature,either vertical or horizontal, must be of’ a COWstant radius.

As mentioned above, strict dimensional controlduring casting is required. .4n\ mistakes incasting are difficult and expensive to correct,especially if the\. are not discovered until af.tersome length of’ bridge has been launched.

l‘he superstructure must be of’ a constant sec-tion and depth. .l‘his is a disad\.antage in longs p a n s , lvhere a variable-depth section \vouldprovide a better econom\ of’ materials.

Considerable area is required behind theabutment(s) for casting the segments. In someproject sites this may not he feasible.

In the present state 01’ the art of i~icrementall\launched bridges there appear to be basicall\ tlvomethods of’ construction, \\,tiicli we shall call co?/-tirluou.c ctstrng and trnluncd cas t i ng . .l‘hey are dif-f‘erent in mode of’ execution and in their areasof‘ utilization. The continuous casting method issome\\.hat analogous to the span-by-span method.and halanced casting is similar to the cantilevermethod.

.l‘lie continuous casting method is generall! usedfor long viaduct-type structures with numerousequal (or nearI>, equal) spans. Its principal charac-teristics are the f,llo\ving:

1 .

2 .

3.

4.

5.

Entire spans, or portions of’ spans, are con-creted in fixed forHIS. The f’orms are reused, asin the span-bv-span method, except that theforma are fised instead of mobile and aremoved from s p a n to s p a n . Subsequent spans(or portions of a span) are cast and joined tothe one previously cast, and the superstructureis progressively launched.

Usually the casting area behind the abutmeIltis long enough to accommodate either a spanlength plus launching-nose length or somemultiple of span segment length plus launch-ing-nose length.Operations involve successive concreting andlaunching. The principal phases aI-e: forming;placing of’reinf’orcing and tendons; concretingand curing; tensioning and launching.

The two types of’ superstructure cross sectionused ha1.e been box girder and double I‘.Longitudinal prestressing consists of’ twofhmilies of tendons: tendons concentricall\placed and tensioned before launching, andtendons placed and tensioned af’ter launch-

Rio Caroni, Venezuela 323

ing-that is, negative-moment tendons overthe supports and positive-moment tendonsin the bottom of the section in the central por-tion of the span.

The balanced casting method is used for smallerprojects up to a total length of 650 ft (200 m). It isused for symmetric three-span structures wherethe central span is twice the end span. Its principalcharacteristics are:

1 . Concreting of segments is accomplished sym-metrically with respect to a temporary supportlocated in the embankment behind the abut-ments. This method is similar to the balancedcantilever except that the forms are supportedon the embankment fill.

2. Two areas of casting are required, one behindeach abutment. The half-superstructures areconstructed at opposite ends of the project.The distance between the abutment and theaxis of the temporary massive support is gen-erally slightly less than one-fourth the lengthof the project.

3. After the two half-superstructures have beenconcreted on the access fill, the two halves arelaunched over the piers and joined at midspanof the central span by a closure pour, whichusually has a length of 3 ft (1 m).

4. Longitudinal prestressing consists of threefamilies: cantilever tendons for each segment,located in the upper portion of the cross sec-tion and stressed before launching; continuitytendons, tensioned after closure and situatedin the lower flange; and provisional tendons,located in the lower flange, tensioned beforelaunching, and opposing the cantilever ten-dons.

There are two methods of launching. Themethod used on the Rio Caroni Bridge, Figure1.67, has the jacks bearing on an abutment faceand pulling on a steel rod, which is attached bylaunching shoes to the last segment cast. The sec-ond, and more current, method is essentially alift-and-push operation using a combination ofhorizontal and vertical jacks, Figure 7.1. The verti-cal jacks slide on teflon and stainless steel plates.Friction elements at the top of the jacks engagethe superstructure. The vertical jacks lift thesuperstructure approximately & in. (5 mm) forlaunching. The horizontal jacks then move thesuperstructure longitudinally. After the super-structure has been pushed the length of the hor-

FIGURE 7.1. Incremental launching-jacking mech-anism (courtesy of Prof. Fritz Leonhardt).

izontal jack stroke, the vertical jacks are low-ered and the horizontal jacks retracted to restartthe cycle.’ Figure 7.2 is a schematic depiction ofthis cycle.

To allow the superstructure to move forward,special temporary sliding bearings of reinforcedrubber pads coated with teflon, which slide onchrome-nickel steel plates, are provided at thepermanent piers and temporary bents, Figures 7.3and 7.4. A sequence of operations showing thebearing-pad movement on the temporary bearingis depicted in Figure 7.5. A temporary bearing witha lateral guide bearing is shown in Figure 7.6.

7.2 Rio Caroni, Venezuela

The design for this structure was proposed by con-sulting engineers Dr. Fritz Leonhardt and WilliBaur of the firm Leonhardt and Andra, Stuttgart,West Germany, in an international competition.Design and planning occurred in 1961 and con-struction in 1962 and 1963. This structure, Figure7.7, consists of a two-lane bridge with end spans of157.5 ft (48 m) and four interior spans of 3 15 ft (96m), for a total length of 1575 ft (480 m).’ The siteprovided some formidable construction problems.The Rio Caroni River during flood stage reaches adepth of 40 ft (12 m) with velocities of 13 to 16ft/sec (4 to 5 m/set), thus eliminating the consider-ation of a cast-in-place concrete superstructure onfalsework. Balanced cantilever segmental con-struction was considered; however, the interrup-tions during high-water periods would require anextensive construction period with attendant highcosts.3

The proposed method consisted of assemblingand prestressing the entire length of bridge on

(a)

fb)


Cd)

FIGURE 7.2. Schematic of’ launching jack operation.(cr)‘Lit‘t. (h) Push. (c) Lower. (cl) Retract.

land adjacent to the bridge site, using precast seg-ments, and launching in a longitudinal direction,over the piers, into final position. Temporary pierswere used at midspan of’ each interior span to pro-duce ten equal spans of 157.5 ft (48 m) during thelaunching of the superstructure. Accommodationof’ on-site assembly of’ the total superstructure re-quired a 1600 f’t (500 m) long f’abrication bed to therear of one abutment, which was partly excavatedin rock and had to be backfilled and compactedupon completion of’the project. At the f’ar end of

FIGURE 7.3, Incremental launching-longituclinalsection of launching bearing, from reference 3 (courtes,of the American Concrete Institute).

FIGURE 7.4. Launching bearing, I+‘abash RiverBI idge, Indiana.

this fabrication bed stationary steel forms were in-stalled to cast the precast box segments, which were18 ft 4 in. (5.6 m) high and cast in 30 ft (9.2 m)lengths.

After the precast segments attained sufhcientstrength thev were stripped from the f’orm and po-sitioned in the fabrication bed to correspond withtheir location in the final structure. The segmentswere moved f’rom the form on wooden rails accu-rately positioned in the assembly bed, employingformica sheets and a petroleutn-base lubricantbetween the bottom of the segment and the top ofthe wood rails, Figure 7.8. A space of 1 ft 4 in. (40cm) wx lefi between the precast segments f’or an insitu joint. Accurate positioning of’ the segments inthe assembly bed was required before casting ofthe joints. To avoid shrinkage damage, the jointswere cast during the second half’ of’ the night sothat the temperature expansion of the precastsegments during the heat of the day wc~ulcl com-pensate for the shrinkage in the cast-in-place joint.”

After the joints were cast, concentric prestress-ing located inside the box and passing throughopenings in the web stif’f’ening ribs, Figure 7.9, wasprestressed with a force of’ 5000 tons in one opera-

Rio Caroni, Venezuela

iIv--5’ +

325

FIGURE 7.7. Completed Rio Caroni Bridge, fromreference 3 (courtesy of the American Concrete Insti-tute).

FIGURE 7.5. l‘emporarv sliding bearing, sequence ofoperations.

FIGURE 7.6. I~~c~xmrc~r~al I;tut~chitlg-tetll~)ot~~l~~bearing and lateral guide bearing (courtesy of Prof. FritzLeonhardt).

FIGURE 7.8. Precast segments in assembly I)ed(courtesy of Arvicl Grant).

tion. The prestress tendons were continuousaround a large half-round concrete block at oneend of the structure, Figure 7.10. This blockreacted against a number ofjacks and a 10 ft (3 m)thick concrete bulkhead wall. Bv activating thejacks between the block and the bulkhead andcausing a movement of 9 ft (2.X m) in the stressblock, the initial prestress force was induced intothe tendons. The prestressing tendons were notattached to the webs. To reduce the hazard of an\accidental elastic instability condition, temporarvsteel bracing frames were installed at 60 ft (20 m)intervals.” The 33 ft 10 in. (10.3 m) top flange ofthe box girder section was transversely prestressed,Figure 7.9.

Upon completion of the prestressing operationsthe superstructure was ready for launching overthe temporary and permanent piers to its final PO-sition. To maintain acceptable levels of concretestresses, as the girder was launched over the 157.5ft (48 m) spans, a 56 ft (17 m) tapered structuralsteel launching nose was attached to the leading


- ’ /r9’-l0’16’-51-y.---uI-9~-10’~

FIGURE 7.9. Rio Caroni, girder cross section, fl-om reference 3 (courtesyof the American Concrete Institute).

FIGURE 7.10. Kio Ckror~i, patressing Mock (wur-tesy of Awiti Grant).

FIGURE 7.11. Rio Carom. Ltu1~111ng nose, 11 OIII ref-e~ence 3 ((ourtesy of the American Concrete Institute).

end of the superstructure, Figure 7.11. Two dou-ble jacks with a total capacity of 600 tons, mountedagainst the bridge abutment and pulling on steelrods fastened to the girder, provided the horizon-tal force required for the longitudinal launchingmovement. To accommodate movement over thepiers, two sliding bearings were provided at eachtemporary and permanent pier top. These bear-ings conststed of chrome, polished steel plateswhich supported teflon covered bridge bearingswhich were placed in an inverted position such thatthey bore against the underside of the girder andslid on the steel plates. After a launching move-ment of 3 ft (96 cm) in the longitudinal direction

the operation was halted to allow the entiresuperstructure to be jacked vertically, simultane-ously at all piers. The teflon plates were thenmoved back to their original position (the one theyoccupied when the launching operation started)and rotated 180 degrees, with respect to a verticalaxis, to compensate for any one-directional move-ment of the teflon coating. Longitudinal launchingmovement occurred at a rate of 24 in./min (6 cm/min); thus, one 3 ft (6 cm) increment of movementtook 16 minutes. A total cycle of operation, aftersubsequent synchronization, which included thesimultaneous jacking at 22 locations and reposi-tioning of 22 teflon bearings, required 30 minutes

Val Restel Viaduct, Ztaly 3 2 7

for each 3 ft (96 cm) of movement. In this manner,a daily movement of 63 ft (19.2 m) could be ac-compiished. The required initial jacking force forlaunching was 220 tons; this gradually increased to400 tons f’or the total girder weight of 10,000 tons,which indicates a friction of 2 to 47c.3

After the launching operation was completed,the initial concentric prestressing tendon profilewas changed to accommodate the loading condi-tion in the superstructure after temporary pierswere removed. To accomplish the change in ten-don profile, special L-shaped rods were installedso that the! projected upward through the topflange or downward through the bottom flange,the tendons being cradled in the U rods. The rodsivere then jacked simultaneously at 24 points up-~\a~-ct or downward, depending on their location.During this operation the half-round stress block,Figure i. 10, ~vas gradually released such that uponfinal positioning of the tendons it had retracted 8 ft6 in. (2.6 III). After the tendons had been relocated,they lvere attached to the \veb and concreted forcorrosion protection.”

The procedure used for the construction of theRio Caroni Bridge, although technically adequate,is prohibitively expensive. The methodology hassince been refined such that segments are cast di-rectly behind the abutment in lengths of 33 to 100ft (10 to 30 m) and incrementally launched aftercuring of the last segment cast.’

7 . 3 Val Rested Viaduct, Italy

Because of rugged mountain terrain the alignmentof’ a 1050 ft (320 III) portion of this viaduct re-

quired a sharp horizontal curvature of 492 ft (150m) radius, and a vertical curvature of approxi-mately 8860 ft (2700 m) radius, Figure 7.12.Maximum pier height is 212 ft (64.61 m). Site con-ditions and alignment precluded construction bythe balanced cantilever method or conventionalcast-in-place on falsework, leading to the decisionto construct by the incremental launching method.

The curved 1050 ft (320 m) length of this via-duct consists of 52.5 ft (16 m) long segments, whichwere fabricated in an enclosed shed behind anabutment. The bottom flange and bottom stubs ofthe webs of the first segments were cast first, Figure7.13~1, 6, in a 52.5 ft (16 m) length, and approxi-mately 118 ft (36 m) behind the first abutment.After curing and stressing of the partial segment itwas jacked forward an increment of 52.5 ft (16 m)toward the abutment, where the balance of thesection was cast, Figure 7.13~2, c. At the same timethe formwork vacated by the first-segment bottomflange was reused for the casting of the bottomflange of the second segment, monolithically withthe previous segment. After launching another52.5 ft (16 m) increment the cycle was repeateduntil the superstructure was completed.4

Placement of the bottom flange mild steel rein-forcement is shown in Figure 7.14, with the webforms in the background. The side forms for thewebs and underside of the top flange cantilever,and the hydraulic jacking arrangement for strip-ping, are illustrated in Figure 7.15. Reinforcementin the top flange is shown in Figure 7.16 and thecompleted top flange with the following segment inthe background in Figure 7.17. The completedsegment with rails in place as it emerges from thecasting shed is shown in Figure 1.6 1.

e=t t 320.00mt

Elevation

FIGURE 7.12. Plan (n) and longitudinal profile (6) of the Val Restel Viaduct, showing:.-\, shed for the construction of the deck segments; B, hydraulic equipment used forIannching. From reference 4.

(b)Cc) Cd)

FIGURE 7.13. Construe tion stages Val Rested \&duct, from 1 eference 4.

FIGURE 7.14. Val Restel, placement of bottom flangereinforcement, from reference 4.

FIGURE 7.15. Val Restel, side form stripping mecha-nism, from reference 4.

328

FIGURE 7.16. Val Restel, top flange reinforcement.from reference 4.

FIGURE 7.17. Val Restel, completed top flange. withreinforcement for next segment in background, fromreference 4.

Ravensbosch Valley Bridge, Holland 329

The superstructure cross section is shown inFigure 7.18~. Width of the segment is 29.5 ft (9.0m). Total depth ofsegment is 8.13 ft (2.48 m), for adepth-to-span ratio of l/13. The top flange has athickness of 9.8 in. (250 mm) and the bottomflange a thickness of 5.9 in. (150 mm). Figure 7.186is a longitudinal section of the superstructureshowing a layout of the second-stage prestressingtendons required after launching to accommodateloads on the final structure. Figures 7.19 and 7.20s h o w t h e i n t e r i o r a n c h o r a g e b l o c k s f o r t h esecond-stage prestressing before and after con-creting, respectively.

A complete cycle of fabricating and launching a52.5 ft (16 m) segment was accomplished in fournine-hour working days. Actual launching time forone segment was 60 to 65 minutes.4 Figures 7.21and 7.22 show the launching nose approachingand landing on a pier. Views of the completedstructure are shown in Figures 7.23 and T.24. Con-struction of this bridge was accomplished in tenmonths, from Januarv 1972 through October1972.

7.4 Ravensbosch Valley Bridge, Holland

The 1378 ft (420 m) long Ravensbosch ValleyBridge near Valkenburg represents the first bridgein Holland built by the incremental launchingmethod of’ segmental construction, Figure 7.25.‘This dual structure has end spans of 137.8 ft (42m) and six interior spans of 183.73 ft (56 m). Hol-low rectangular piers vary in height from 21 ft (6.5m) to 77 ft (23.5 m) and have exterior dimensions

:I tt40 32.00111

of 6 ft (1.8 m) by 19 ft (5.8 m) with wall thickness of1.3 ft (0.4 m), Figure 7.26.

The superstructure consists of two siigle-celltrapezoidal box girders connected at the interiorupper flange tips by a 8.3 ft (2.5 m) slab and pre-stressed transversely, Figures 7.26 and 7.27. Eachbox has a width of 56.8 ft (17.32 m) and a constantdepth of 10.8 ft (3.3 m) for a depth-to-span ratio ofl/17. The top flange has a thickness of 9.8 in. (250mm) and the bottom flange a thickness of 7.9 in.(200 mm). Top flange cantilever is 13 ft (4.01 m).

Each dual structure consists of 22 segments ap-proximately 62 ft 4 in. (19 m) in length. The con-

FIGURE 7.19. Val Restel, second-stage prestressinganchorage block before concreting, from reference 4.

FIGURE 7.20. Val Restel, second-stage prestressinganchorage block after concreting, from reference 4.

t32.00m

t

ICavi 4207mm-Cab/es 4207mm Ccrvo 16 17mm - Cob/e /617mm

(b)

FIGURE 7.18. Val Restel. (a) Cross section of deck. (b) Longitudinal section of deck.From reference 4.

Incrementally Launched Bridges

FIGURE 7.21. VA Kc\td, launching IIOW C~l~l~~ o,~h-ing pier, from reference 4.

FIGURE 7.24. Val Kesrel, ~on~plctctl \‘iaclur.c, 1 ’ 1 ornreference 4.

FIGURE 7.22. VA Kestel, launching nose landing onpier, from reference 4.

F I G U R E 7 . 2 3 . Vitl Kestcl, \,ic\c o f incrcnlcntallylaunched curved viaduct after launching, from refer-ence 4.

FIGURE 7.25. Ka\;ensbosch Valley IS1itlge, generalview (courtesy of Brice Bender, BVNiS’TS).

struction of’ the superstructure was based upon acycle of one segment per week.

To accommodate bending moments duringlaunching operations a 52.5 fi (16 m) long launch-ing nose was used, Figure 7.28, in conjunction witha concentric first-stage prestressing consisting of’2612 in. (32 mm) diameter Dywidag bars per boxgirder. In addition, temporary piers were used atmidspan, Figure 7.28. During launching, frictionamounted to 2 to 4%, equivalent to a maximumpushing force of 430 tons for a completed boxgirder.

Olifant’s River Bridge, South Africa 331

FIGURE 7.26. Ravensbosch Valley Bridge, dual structure cross section (courtesy ofBrice Bender, BVNISTS).

FIGURE 7.27. Ravensbosch Valley Bridge, girdercross section (courtesy of Brice Bender, BVNISTS).

FIGURE 7.28. Ravensbosch Valley Bridge, view oflaunching nose (courtesy of Brice Bender, BVNLSTS).

After completion of the launching, second-stageprestressing following a parabolic profile and con-sisting of 12-0.62 in. (16 mm) diameter strands wasinstalled and stressed. This structure was com-pleted in 1975.

7.5 Olifant’s River Bridge, South Africa

This railroad structure, upon completion, held theworld’s record for the longest bridge accomplishedby incremental launching. It has a total length of3395 ft (1035 m), consisting of 23 equal spans of147.6 ft (45 m). The final structural arrangementconsists of 11 continuous spans on each side fixedat the abutment and one simply supported centerspan-that is, an expansion joint on either side ofthe center span. With this structural arrangementthe braking force of the trains (transporting ironore) is transmitted to the abutments (10% of liveload). In this manner the flexible piers can be used,resulting in an economy in the foundations bycomparison with the classical solution, where thelongitudinal force is transmitted through the piersto the foundations.

All 23 spans were incrementally launched as 23continuous spans from one abutment, Figure 7.29.During launching the two expansion joints weremade temporarily continuous by temporary pre-stressing. The joints were released after the struc-ture was in place and before it was rested on itspermanent bearings. A launching nose, 59 ft (18m) long, was prestressed to the first segment tomaintain the cantilever stresses, during launching,in the concrete within allowable limits. The tip of


E N D B E N T PO Pl/

4

FIGURE 7.29. OMant’s Rive]- Bridge. incrementallaunching awangenwnt.

the launching nose had a -jacking arrangement toaccbmmodate deflection of’ the nose as it ap-proached the pier.

In cross section, Figure 7.30, the superstructureis a constant-depth rectangular single-cell boxgirder. Depth is 12.5 f‘t (3.80 tn); the top flangeis 18 f‘t (5.50 m) wide and the bottom flange 10 f’t(3.10 m) wide. The webs and flanges are of a con-stant thickness throughout the structure. Webthickness is 13.75 in. (0.35 m) and contains verti-cal bar prestressing tendons to carry shear. Longi-tudinal prestressing is straight and contained inthe flanges. Anchorage blocks for the longitudinaltendons at-e continuous across the width of bothflanges (interior buttresses) to assure a more favor-able distribution throughout the section. Thereare no diaphragms at the piers; the interior cor-ner fillets are such as to permit the ef’f’ect of’ tor-sion to be accommodated by a transverse boxframe.

r 5.50

-I

/ . . . . . . . ‘:. “., -JL. .

Lm

$____41Safe ty

s .:l-4

I”” I

p l a t f o r m

L 3.10 4

FIGURE 7.30. Olifant’s River Bridge, cross section

Construction of the superstructure \vas accom-plished in nine months. Segments lvere span

length, with the theoretical cycle per span of tenhours attained in the tenth operation and grx!u-

ally reduced to seven hours at the conclusion of’casting operations. Reinforcing cages Ivet-e pref’Ah-

ricated in templates at the side of. the tornis. Aqcle of operations consisted of the follo~ving:

Clealling and adjustment of forms

Placement of reinforcing a n d t e n d o n s for t h eloiver flange and \+.ebs

Concreting of this first phase

Placement of‘ reinforcing a n d t e n d o n s t’or t h eupper flange

Concreting of’ this phase

Tensioning of’tendons in second phase of’ pre\ iouss p a n c a s t

-1‘ensioning of’ tendons in first phase of span informs

Stripping of forttis

Launching

Af‘ter launching, and before placing the structureon its final bearings, it \vas necessary to adjust thejoints lvithin 2 itt. (10 mm). l‘he principal &f.ticu-ties in accomplishing this operation lvere:

‘l‘emperature differential between night and da!.,

which produced a \ariation in length of’ thesuperstructure of 9.X in. (250 mm)

Age of‘ concrete at time of‘ adjustment, lvhich V;II‘-

ied t‘rom nine months to ten hours

J a c k i n g p ‘; t ’o e1 1 IOIIS, which could not retract thestructure in case of an error in pushing forward

.I‘he solution of the temperature problem ~~1s toquickly accomplish the adjustment early in themorning. Because of’ the constant temperatureduring the night the temperature of the super-structure was known, and its length was deter-minable inspite of the thermal inertia of theconcrete.

The superstructure w a s then j a c k e d into itstheoretical position on the abutment and firnil\,maintained by a system of blockage. The temporarytendons that had fixed the first joint were releasedand jacks were placed into the joint to push theremaining 12 spans and place the central simplespan in its exact position. The second joint wasthen opened, and jacks at the other abutment po-

Various Bridges in France 333

sitioned the last 1 l-span portion of the super-structure.

M’hcn rhc superstructure had thus been placedin position, it was -jacked up off the piers, and thetemporar\ sliding bearings were replaced bv rhepetmatiet~l bearings.

7.6 Various Bridges in France

7.6.1 I.1.C I~I.-lDl’C7

‘I‘his is a dual structure 912 f’t (278 in) long on acurve of a 3280 ft (1000 m) radius. The super-structure \vas constructed by incretnental launch-ing of’ complete spans on sliding bearings. Resis-tance of rite structure to its dead load duringlaunching \vas ~iccotntiiod~tretl b!- a temporal-!cable-stay s! h,tetn in which the tension \vas adjusteda s c.otistt~uctioti proceeded, Figure 7.3 1. Nosupplementary prestressing \vas provided duringthe taunching phases. A 26 ft (8 m) launching noseleas pro\Gied at the leading end in order to reducethe Jveight of’ the cantilevered structure.

It is a continuous structure supported on neo-prene bearings and has a double-T cross section,as indicated in Figure 7.32. Roadway width is 46 ft(14.0 m), and depth of superstructure is a constant10.3 f’t (3.15 in). Spans at-e 133.5 ft (40.i in).

‘l‘his structure consists of eight continuous spans

having a total length of 1102 ft (336 m), crossing arailroad and the Oise Ri\-er. The project is of inter-est in that it \vas launched from both abuttnents\vit bout the use of a launching nose or a tetnporarkcable-sta\- svstem. However, tetnporarv bents wereused to control the cantilever stresses. In cross sec-tion the superstructure is a single-cell bos, Figure7 .3 3

S e g m e n t s f’or e a c h o f t h e t w o h a l f - s u p e rstructures were from 65.6 to 98.4 ft (20 to 30 m)in length. .A launching \vas effected upon com-pletion of’ each segment. After the two half-superstructures had been launched to their finalposition, a closure pour of 3.3 ft (1 m) in length wasc.onsutiitiiated to provide continuit\..

Longitudinal prestress consists of six sets:

Cantilever tendons, tensioned bef-ore launching,located in the top flange and anchored in fillets atthe intersection with the web

Concentric tendons frotn one end to the other ofeach half-superstructure, coupled together at eachphase of concreting of segments

Straight, short tendons in the top flange over thepiers and in the bottom flange, centered in thespan and tensioned after launching

Continuity tendons, tensioned af’ter launching,situated in webs and anchoring at the upper flange

Short parabolic tendons, located in the webs anda n c h o r i n g i n t h e t o p flange, t e n s i o n e d a f t e rlaunching

‘retnporary tendons in the upper flange, havingthe satne effect as the cantilever rendons

i.h.3 0I.I L’I‘-tDI’CT

I‘his viaduct spans the valley of Oli in 15 spans of134.5 ft (41 m) for a rotal length of 2017 ft (615 m)at a height of 197 ft (60 tn). The structure hasa grade of 5.355% and a horizontal curve lvith aradius of 6700 ft (2046 tn). Total weight of thesuperstructure is 16,500 tons (15,000 mt).

Incremental launching in this structure, ratherthan pushing the superstructure out over the piers,was accomplished bv a restrained lowering downthe grade. The fo;-ce required in braking thestructure was approximately 660 tons (600 tnt) ascompared to the estimated force of 1540 tons(1400 tnt) to push the structure uphill.

In its final configuration, because it was difficultto accommodate horizontal forces due to brakingand seismic effects in the tall flexible piers, thesuperstructure is anchored in the terrain in thearea of the abuttnents by a tie of a large stiffness.All of this longitudinal global force is accomtno-dared in the large stiff tie, the abutments, and therelativelv short stiff piers in each bank. A centraljoint diiides the structure into two independentsrructures.

Upon cotnpletion of launching and before plac-ing the superstructure on its pertnanent bearings,it was necessary to “unlock” the joint that held thetwo half-superstructures together during con-struction and to adjust its position within approxi-matelv i in. (10 mm). This operation was con-ducted as follows:

The superstructure was restrained at the upperabuttnent until the distance between its theoreticalposition and the end of the lower abutment wasapproximately 8 in. (200 mm).


6 F+ 1 c;:--..,,. n. . r.placing of the launching noseconcreting and prestressing of the first spanlaunching of the first span

concreting and prestressing of the second s?anerecting the cable-stay systemlaunching of the first two spans

concreting and prestressing of the third spanlaunching of the first three spans

concreting and prestressing of the fourth spanlaunching of the first four spans

thing operationsdisassembling of the launching nose andcab1 e-s Lay systmplacing on permenant bearingsplacing and tensioning of phase 2 prestressing

FIGURE 7.31. Luc \‘iaduct. incremental launching phases. ((I) Placing of the launchingIIOSC. concreting atd prestressing of the fit-st span. launching of the first span. (b) (:OII-

creting and prestressing of the second span. erecting of the cable-sta! s\ stem, launchingof the first t\vo spans. (c) Concreting and PI estressing of the third span. launching of‘ thefirst three spans. (rl) (:oncreting and Prestressing of the fourth span, launching of‘thc firatfour spans. (P) Completion of launching operations. disassembling of’ the launching 11osc

and cable-stay system, placing on permanent bearings, placing md tensioning of’phase-two prestressing.

.The temporary tendons connect ing the two hal f - sys t em o f ‘ p res t r e s s b a r s a n d c.otn~,lementar\supers t ruc tures were successivelv d e t e n s i o n e d .However, two temporary tendons’ restrained the

re inforcement ins ta l led in the upper abutment .

lower hal f -supers t ructure . The upper half-super-.l‘he t w o temporat-!- tendons res t ra ining the lowethalf-superstt-uctttre lvere d e t e n s i o n e d i n incre-

s t ruc tu re was f ixed to the upper abu tment by a ments, al lowing the lolver half-super-strttcrure t o

Wabash River Bridge, U.S.A. 335

t-14.65

I 1

FIGURE 7.32. Luc Viaduct, cross section.

FIGURE 7.33. Creil \‘iaduct. cross section.

descend to a blocking system in the lower abutment.Fixing of the lower half-superstructure to thelower abutment was then accomplished.

The superstructure was positioned on its finalbearings.

7.7 Wabash River Bridge, U.S.A.

‘I-his structure, the first incrementally launchedsegmental bridge constructed in the United States,carries two lanes of U.S. 136 over the WabashRiver near Covington, Indiana. It is a six-spanstructure with end spans of 93 ft 6 in. (28.5 m) andfour interior spans of 18i ft (57 m), Figure 7.34.

Roadway width is 44 ft (13.4 m). Pier heights areapproximately 40 ft (12 m); average river depth is11 ft (3.35 m) with low water at 8 ft (2.4 m) andhigh water at 24 ft (7.3 m). The superstructure is at\\‘o-cell box girder with a constant depth of 8 ft(2.4 m). .I‘he prqject was awarded in September of1976 lvith a completion date of October 1978. Theentire superstructure was completed in Novemberof 1977.

Original design plans prepared by AmericanConsulting Engineers, Inc., of Indianapolis for theState Highway Commission called for a precastsegmental balanced cantilever design; however,the bid documents permitted alternative methodsof constructing the superstructure. The successfulcontractor, a .joint venture of Weddle Bros. Con-

struction Co., Inc., and the Ralph Rodgers Con-struction Co., both of Bloomington, Indiana, in-vestigated three alternatives for the superstructureconstruction. These alternates included cast-in-place segments supported on falsework, incre-mental launching, and the cast-in-place segmentalbalanced cantilever method. Incremental launch-ing was the successful method and reportedl)saved $100,000 over the other precast segmentalmethod:j The V.S.L. Corporation of Las Gatos,California, was the subcontractor for prestressingand launching.

A 140 ft (42.7 m) casting bed was located behindthe west abutment of the bridge and could accon-modate three 46 ft 9 in. (14.25 m) segments. .I‘heforms for casting were supported on I beams,which were supported on steel piling to provide asolid foundation and prevent any settlement of thecasting bed, Figure 7.35. The bottom third ot. thetwo-cell box superstructure was cast at the mostwesterly end of the casting bed, Figure 7.35. It wasthen advanced 46 ft 9 in. (14.25 In), where formsfor the balance of the section were positioned, mildsteel reinforcement and prestressing tendonsplaced, and the balance of the segment cast, Figure7.36. After the segment had been poured andcured, the 20-ton jacks that held the forms in posi-tion, Figure 7.37, were released to break the bondand remove the forms. ‘I-he large metal formsstayed in place and were simplv swung in and outas needed. The segment was then advanced to theforward third of the casting bed for surfacefinishing by a conventional Bidwell screed, Figure7.38, before launching over the abutment. In thism a n n e r a production-line methodolog! W;lS

maintained. Three segments were always in vari-ous stages of fabrication, with reinforc&,lent andprestressing tendons continuous between seg-ments.

The first-stage pour required approsimately 53vd3 (40.5 m”) and the second pour required fromiO1 to 130 yd3 (77.2 to 99.4 111”). It took approxi-mately four hours for each pour. ‘I‘jventy-eight-da)design strength \\‘as 4800 psi (3.37 kg/mm”), and6000 to 7000 psi concrete strengths were actualI>attained (4.2 to 4.9 kg/mm’). A 3500 psi (2.46 kg/mm2) strength was required before stressing, andthis was normally achieved in 24 to 30 hours. Assegments were completed, each was stressed to itspredecessor by first-stage prestressing consisting ofeight tendons of twelve f in. (12.7 mm) diameter 27ksi (190 kg/mm2) strands, Figure 7.39. Initially thecontractor was able to complete one cycle of seg-ment fabrication and launching in two weeks:

A T MIDSPAN AT PIERS

PLAN

DIRECT ION OF MOVEMW wFabrication area

CON>mJON ELEVA.-.

FIGURE 7.34. Wabash River Bridge: cross section of girder, from reference 6; con-struction details, from reference 2.

however, as experience was gained, two cycles per equal spans of 93 ft 6 in. (28.5 m) during theweek were attained. launching procedure.

To accommodate the launching stresses a 56 ft(17 m) launching nose was attached to the leadsegment, Figures 7.34 and 7.40. In addition, thefour interior spans had temporary steel bents atmidspan, Figures 7.34 and 7.41. In this mannerthe total structure length was divided into ten

Because of the longitudinal force on the piersduring launching, the permanent piers were tiedback to the abutment with four prestressingstrands each. These strands were stressed to 96kips (43,545 kg) before launching commenced.Each temporary pier was tied back to the preced-

FIGURE 7.35. Wabash River Bridge, casting-bedsupport.

FIGURE 7.39. Wabash River Bridge, first-stage pre-stressing.

FIGURE 7.37. Wabash River Bridge, side form jacks.

FIGURE 7.38. Wabash River Bridge, surface finishingtop flange.

incrementally Launched Bridges

FIGURE 7.40. Wabash River Bridge, launching nose.

FIGURE 7.41. W,lb,1sh Rile1 BI Age, temporary steelbent.

ing permanent pier by two stays of 10 in. by 10 in.(254 mm by 254 mm) structural steel tubing, Fig-ures 7.34 and 7.42.

The jacking procedure during launching usedthe two-jack system (one vertical and one horizon-tal) and teflon pads, as described in Figure 7.2. Thevertical jacks had a 2 in. (50 mm) stroke and the

FIGURE 7.42. Wabash River Bridge, structural steeltubing tie.

horizontal jacks an 18 in. (457 mm) stroke. Thevertical jacks lifted the superstructure about 4 in.(13 mm) and the horizontal jack pushed it forward17 in. (432 mm). Each jacking cycle required aboutfive minutes, and the entire launching of a 46 ft 9in. (14.25 m) segment required about three hours.

Temporary bearings, Figure 7.4, were located ateach temporary bent and permanent pier. Duringthe launching operation workmen were stationedat each bearing location to insert the teflon pads asthe superstructure slid over the bearings. Tomaintain lateral alignment of the superstr&ture,lateral guide bearings, Figure 7.43, were also lo-cated at each temporary bearing and also usedteflon pads. Workmen would tighten bolts on oneside of the superstructure and loosen them on theopposite side to push the superstructure laterally.Final positioning of the superstructure on the eastabutment was within & in. (0.8 mm) of its pre-scribed location.


7.8.1 MiiHLBACHTALBRiiCKE, GERMANY

Another example of this type of construction is theMiihlbachtalbriicke about 30 miles (50 km) south-west of Stuttgart, West Germany, Figure 7.44. Thisstructure has an overall length of 1903 ft (580 m)with 141 ft (43 m) spans. The far-side trapezoidalbox girder is shown in Figure 7.44 completed fromabutment to abutment; the near-side trapezoidalbox girder has been launched from the left abut-ment and the launching nose has reached the firstpier. A general view of the structure is presented inFigure 7.45.

F I G U R E 7 . 4 3 . Walmsh Ki\;er Br-idge, lareral g u i d ebearing.

FIGURE 7.44. Miihlbachtalbrticke. aerial view

FIGURE 7.45. Miihlbachtalbriicke, general view.

Some idea of the size of the box girder may beobtained from Figure 7.46, showing the interior ofthe formwork at the rear of the abutment. First-stage prestressing tendon anchorage at the top ofthe web may be seen in Figure 7.47. The anchor-age block for the second-stage prestressing is lo-cated inside the completed box, Figure 7.48.

FIGURE 7.46. Miihlbachtalbriicke, segment in sta-tionary forms.

FIGURE 7.47. Miihlbachtalbriicke, first-stage pre-stressing tendon anchorage.

FIGURE 7.48. Miihlbachtalbriicke, second-stage pre-stressing anchorage block.

7.8.2 SHEPHERDS HOUSE BRIDGE. ENGLAND

The Shepherds House Bridge is the first incre-mentally launched bridge constructed in England.This highway structure crosses four railroad tracksat Sonning Cutting, near Reading, about 30 miles(48 km) west of London. The new structure con-trasts sharply with an existing brick arch structurebuilt in 1838 by Brunel, a famous English en-gineer. The existing structure consists of three cir-cular brick arches supported on tall brick pierswith the abutments founded in the sides of thecutting.’ A general plan showing the existingbridge, railroad tracks, and alignment of the newstructure is presented in Figure 7.49.s


FIGURE 7.49. Shepherds House Bridge, general plan, from reference 8 (courtesy ofInstitution of Civil Engineers).

In 1971 the north abutment settled and theexisting bridge was temporarily closed for repairs.In March of 1972, because the life expectancy ofthe existing structure was in question and becauseit did not comply with current highway standards,the Ministry of Transport instructed consultingengineers, Bullen and Partners, to prepare a studyto determine the type and method of constructionfor a new structure. The new bridge provides adualing of the existing road, and in the future theexisting bridge will be replaced by a parallel struc-ture.

Because British Rail was engaged in extensivemaintenance and upgrading of the tracks prior tointroduction of high-speed trains, there would besevere limitations on track possession. Further, itwas dictated that piers between tracks were to beavoided and that f-oundations on the north slope ofthe cutting were not to disturb the foundations ofthe existing bridge abutment. Construction work-ing area was restricted because traffic was to bemaintained on a residential street at one end and atrunk road at the other end. Soil conditions re-quired that any temporary conditions that wouldload or disturb the slopes was to be avoided, thusrequiring pile foundations with the pile caps at thesurface to avoid extensive excavation in the slopes.s

The consultants initially studied five possibleschemes for construction of a bridge. Schemesusing cast-in-place construction on falsework hadearlier been rejected.

An incremental launching scheme was recom-mended, even though there were no accurate cost

data for construction in the U.K. The consultantsconcluded that this scheme, although of shorterlength than customary for this type of construc-tion, would solve the problems of restricted work-ing space and interference with residential streetsand would require the least track downtime.

The west elevation of the bridge is shown in Fig-ure 7.50. Span lengths, determined by track loca-tion, are 75.5 ft (23 In), 121.4 ft (37 m), and X2 ft(25 III). The bridge is fixed at the south abutmentwith an expansion joint at the north abutment. ‘Thecasting bed for the production of 31.5 ft (9.6 rn)

segments was located to the rear of the southabutment. The south abutment was located to pro-vide maximum work space for the casting bed andto clear a large number of Post Office communica-tion cables. Interior piers b and c were designed towithstand the friction forces exerted duringlaunching operations. In addition, pier c, locatedclose to the railroad tracks, was subject to damageor complete demolishment in the event of a de-railment. Therefore, the superstructure was de-signed to withstand the removal of pier c by an ac-cident. Six untensioned but anchored Macallovtendons in certain segments were added so as topreclude ultimate collapse with no live load on thebridge and pier c removed.7*H

Normally, in this type of construction, the cast-ing bed is of sufficient length to accommodate atleast two and sometimes three segment lengths,such that the bottom flange may be cast separatelyin advance of the webs and top flange. In this proj-ect, with restricted space for the casting bed, it wasdecided to cast one complete segment in one pour.


‘we,. h n,ns 00. - a ohllk rmll

Dbnwula h mWumb*.

FIGURE 7.50. Shepherds House Bridge, west elevation, from reference 7 (courtesy ofThe Concrete Society, London).

A maximum of three weeks was allowed for con-struction and launching of a segment. This timewas later reduced to two weeks except for thosesegments with a diaphragm.’ A typical cross sectionof the box girder segment is shown in Figure 7.51.

The launching sequence is shown in Figure 7.52.The steel launching truss nose was first erectedusing a temporary intermediate support. The firstsegment was cast against the launching nose andpost-tensioned by Macalloy bars, some of whichwere used to connect the launching nose to the firstsegment. The launching nose, in position, beforethe launching of the first segment is shown in Fig-u r e 7 . 5 3 . A f t e r t h e f i r s t s e g m e n t h a d b e e nlaunched forward, the next segment was cast andpost-tensioned to the previous one. This proce-dure was repeated until the completed bridge was

launched to the north abutment. The launchingnose passing over pier c is shown in Figure 7.54.Arrival of the launching nose at pier b is shown inFigure 7.55. The launching nose was removedafter the concrete superstructure arrived at pier b,Figure 7.56.

The superstructure was launched over tempo-rary bearings, which consisted of high-grade con-crete pads with a +Z in. (1 mm) thick stainless steelplate clamped and tensioned across the top sur-face. Lateral guide bearings were also provided tokeep the superstructure on line. Upon completionof launching the superstructure was jacked in apredetermined s e q u e n c e a n d t h e t e m p o r a r ybearings were replaced with permanent bearings8

The jacking force for launching was provided bytwo jacks pulling on a set of nine 0.6 in. (15 mm)

FIGURE 7.51. Shepherds House Bridge, girder cross section, from refer.ence 8 (courtesy of The Institution of Civil Engineers).


Stage 1: Cast first unit andconnect to launching nose

Stage 2: Launch to pier CStages 3-5: Launch over tracks

Stage 6: Launch to per BStage 7: Conttnue launch

Stage 8: Reach pw 9 and remove “018Stages 9 and 10: Complete launch

FIGURE 7.52. Shepherds House Bridge, sequence ofincremental launching, from reference 8 (courtesy ofThe Institution of Civil Engineers).

FIGURE 7.53. Shepherds House Bridge, launchingnose in position before launching, from reference 7(courtesy of The Concrete Society, London).

diameter cables passing under the casting bed andanchored to the front of the abutment. The loadwas applied to a fabricated bracket secured to therear of the segment by bolts coupling with theprojecting ends of the Macalloy bar tendons inthe top and bottom flanges of the segment, Fig-ure 7.57. The two jacks were operated in tandemby a single pump. This system required 30 secondsfor jacking and 30 seconds for retracting for each10 in. (254 mm) str0ke.s

FIGURE 7.54. Shepherds House Bridge, launchingnose passing over pier c, from reference 7 (courtesy ofThe Concrete Societv. London).

FIGURE 7.55. Shepherds House Bridge, launchingnose at pier b, from reference 7 (courtesy of The Con-crete Society, London).

FIGURE 7.56. Shepherds House Bridge, superstruc-ture launched to pier b and launching nose removed,from reference 7 (courtesy of The Concrete Society,London).

Design of Incrementally Launched Bridges 343

The dimensions for typical cross sections pre-sented in Section 4.5.4 remain valid for the webthickness, but the top flange and bottom flangethickness may have to be increased, depending onthe type of prestressing layout adopted (see Section7.9.4).

FIGURE 7.57. Shqhtwls 1 lowc~ Bridge, segmentbeing launched from f’ormwork, from reference 7(courtesy of’ The Concrete Society, London).

7 . 9 Design of Incrementally Launched Bridges

7.9.1 BRIDGE ALIGNMENT REQUIREMENTS

The designer must always remember that in orderto construct incrementally launched bridges, thehorizontal and vertical alignment must be eitherstraight or constantly curved or twisted. This isgenerally not the case, as road planners are notbridge builders. As a matter of fact, it is the soffit of-the bridge deck that has to be designed with a con-stant radius of curvature; the transverse cantileverof the deck flange can be varied to accommodatepossible small deviations.

7.9.2 TYPE, SHAPE AND DIMENSIONS OFSUPERSTRUCTURE

This method of construction requires a cross sec-tion with a constant depth, since the designer hasto insure the resistance of the superstructure,under its own weight, at all sections as the launch-ing proceeds. Economic considerations dictate aconstant moment of inertia.

Two types of cross section have been used todate: the box girder and the double T. The boxgirder provides a better stiffness and resistance totorsion and at the same time an easier placement ofthe prestressing tendons in the cross section. Thedepth of the box is usually one-twelfth to one-sixteenth of the longest span, the first value ap-plying to larger and the second to smaller spans.Table 7.1 summarizes the characteristics of severalincrementally launched bridges.

7.9.3 SPAN ARRANGEME,VT AND RELATEDPRI,VCIPLE OF CONSTRUCTION

The constant-depth requirement limits the eco-nomical use of this construction method to spansnot longer than 160 to 200 ft (50 to 60 m). It isadvantageous if all the spans are equal in length.However, much longer spans have been built byutilizing special techniques in conjunction with thebasic principle of incremental launching.

A three-span construction may be launchedfrom both sides. In this way the center span can betwice the length of the edge spans without increaseof the stresses in the deck. The span configurationthen becomes: L-2L-L (see Figure 7.58).Champigny Bridge near Paris was the first struc-ture of this type. Longer bridges are oftenlaunched from one side only (the record length isthat of Olifant’s River Bridge in South Africa, inexcess of 3300 ft). Auxiliary temporary devices areused to reduce the bending moments in the frontportion of the deck (launching nose or tower stays)

FIGURE 7.58. Three-span symmetrical incrementallylaunched bridge.

TABLE 7.1. Characteristics of Incrementally Launched Bridges

Name Year Cross Section1‘) pical ~I‘otal Launched Vertical HorizontalSpan Length Weight (t) Curve Curve

(t’t) (W

Nuel Viaduct,France

BorriglioneViaduct,France

KimonkroBridge,Ivory Coast

Tet Viaduct,France

Luc Viaduct,France

PaillonBridge,France

Oli Viaduct,France

MarollesBridge,France

Creil Bridge,France

344

1976

1976

1978

1976

1976

1972

1978

135 807 6,000 Slope 6% R = 2,460 ft

135 807 6,000 Slope 5.5% R = 2,460 ft

118 709 3,600 Straight

141 660

135 915 7,900 Slope 3.8% Straight

135 1 ,151

135 2,018 15,000 Slope 5.85% R = 6,712 ft

131 345

194 1,102

Slope 1.3% Curve

Design of Incrementally Launched Bridges

TABLE 7.1. (Continued)

345

.\ ‘II11C l’eal-

l‘otal Launched Vertical HorizontalLength Weight (t) Curve Curve

(it)

GronachtalBridge,Gerlnan!

Var Viaduct,France

Inn Bridge,Kufstein,German\

Koches Valle)Bridge,Gerlnan\

Querlin GuenBridge.German\

AbeouAqueduct,France

IngolstadtBridge,DanubeBridge,Gertnant

1978

1976

1 9 6 5

1 9 6 7

1978

t-46.3’

1

\L17.5’

\

262 1,732 13,000 Slope 0.7% R = 7,217 ft

1 3 8 1,107 9,700 Straight

335 1,476

1 6 9 1,562

1 3 8 1,398

1 0 8 4 6 9

6 spans

197 to377

2 x1,246

as previously indicated in some of the examples de-scribed in this chapter.

When the spans become too large, intermediatetemporary bents are used. This was done for thefirst bridge over the Caroni River in Venezuela.The record span length for incrementallylaunched bridges was obtained by a structure overthe Danube River designed by Prof. Leonhardt,the originator of the method, Figure 7.59. The costof the temporary bents depends greatly ox the

foundation conditions; it may be prohibitive if thebent height is greater than 100 ft (30 m) and soilconditions require deep piling.

For very long bridges, intermediate expansionjoints are needed, much the same as for cantileverbridges. The expansion joints are temporarilyfixed by prestressing during launching and are re-leased at the end of construction to allow for ther-mal expansion in the structure during service. Avery ingenious variation of this principle was de-


FIGURE 7.59. Ih~ltrlx Ki\-et. B r idge, .-\ustria.

veloped for the Basra Bridge in Iraq, where a con-crete swing span was launched together with theapproach spans as a single unit and later arrangedto serve its purpose as a movable bridge over thenavigation channel, Figure 7.60.

7.9.4 DESIGN OF LOlVGITUDINAL MEMBERS FORFLEXURE AND TENDON PROFILE

During launching, the superstructure is subjectedto continually alternating bending moments, sothat any one section is subjected to a continualvariation of bending moments, both positive and

negative, as shown in Figures 7.61 and 7.62. Thesebending moments are balanced by internal uni-form axial prestressing.

In the final stage, additional tendons are re-quired to supplement the uniform axial prestress-ing in order to carry the service loads. Conven-tional solutions are applied to this problem, and inthe present discussion we need only enlarge uponthe specific problem of the axial prestressing. Forthis prestressing, tendons are so arranged that thecompressive stresses are the same over the entirecross-sectional area. The required tendons areplaced in the top and bottom flanges of the boxsection. They are usually straight, tensioned beforelaunching, so couplers are needed at each jointbetween successive segments.

Segment length may vary from 50 ft (15 m) to100 ft (30 m). As noted in our discussion of- theprogressive construction method, there are limita-tions to the deck’s capacity to carry its own weightduring launching when the front part is in can-tilever beyond a typical pier. To keep bendingmoments and stresses within allowable values, it isusually necessary to use a launching nose, a lightsteel member placed in front of the concretestructure to allow support from the next pier,rather than launching the concrete deck all the waywith no support. Numerical values are given inFigures 7.61 and 7.62 for the critical maximumpositive and negative moments during launching.

Assuming the unit weight of the launching noseto be 10% of the weight of the concrete deck (avalue somewhat lower than average), the critical

FIGURE 7.61. Critical negative moments during launching with nose. M, =(W’L2/12)[6a’ + 6y(l - &)I. Multiplier: WL2/12. For y = 0.10:

N P M”

0.20 0.80 0.820.30 0.70 1.090.40 0.60 1.460.50 0.50 1.95

1 .oo 0.00 6.00

k yo/rp,n .&

FIGURE 7.62. Critical positive moment during launching with nose. M, =(WL”/12)(0.933 - 2.96#*). Multiplier = WL’l12. For y = 0.10:

a P M,

0.20 0.80 0.740.30 0.50 0.790.40 0.60 0.830.50 0.50 0.86

1.00 0.00 0.93

347

3 4 8 Incrementally Launched Bridges

moments are as follows for various lengths of thelaunching nose:

Nose Length, Maximum MomentsPercent ofTypical Span Support OKJ Span (Ml) M&f,

5 0 1.95 0.86 2.276 0 1.46 0.83 1.767 0 1.09 0.79 1.388 0 0.82 0.74 1.11

Moment factor is WL2/12

(W = weight of concrete per unit length and L =span length)

Technologically, the uniform axial prestress maybe installed in the superstructure in several differ-ent ways:

1 . Straight tendons running through the top andbottom flange of each segment, joined bycouplers at the joints between segments.

2. Straight tendons running through the top andbottom flanges, anchored in block-outs insidethe box girder, Figure 7.63.

3. Temporary curved tendons may be used tobalance the final continuity tendons duringconstruction. These tendons are outside theconcrete section between supports, Figure7.64. This method has been used for severallarge projects.

Figure 7.65 shows the Sathorn Bridge in Bangkok,Thailand, with the temporary tendons installed

FIGURE 7.63. Lapped prestressing tendons.

TEMPORARY PRESTRESSING SUPPORT5

I F I N A L PRES’RESSINGI

FIGURE 7.64. Temporary external prestressing sys-tem.

FIGURE 7.65. Sathorn Hr idge, Thailand.

above the concrete deck with steel deviation sad-dles at intermediate joints.

The three solutions above have their relativemerits and disadvantages:

1. The first solution may require local thick-ening of the concrete flanges for placement ofthe couplers. However, it is often preferred to in-crease the thickness of the flanges over the entirebridge length to simplify casting of the segments.Axial prestressing tendons are permanent andcannot be removed. They must be incorporated inthe final prestressing layout. The joints betweensegments have to be carefullv designed, owing tothe presence of couplers and concrete voids thatmay significantly weaken the section.

2. The main advantage of the second solutionpertains to the removal and reuse of those tendonsnot required in the final prestressing layout. How-ever, the cost and difficulty of providing a largenumber of block-outs offsets a significant part ofthe advantage of removing the temporary tendons.In order to obtain a satisfactory shear resistancefrom the webs, particularly during launching withalternating shear and bending stresses, theconfiguration of the box section and location of theupper and lower blisters must be carefully consid-ered. This problem was mentioned in Chapter 4 aspresenting potential difficulties. A satisfactory so-lution is shown in Figure 7.66, where upper andlower blisters are not in the same vertical plane. Asufficient amount of vertical prestress will insurethe resistance of webs against shear during all con-struction stages.

3. The third solution is theoretically a satisfac-tory one, allowing the permanent prestress to beinstalled during construction and the temporaryprestress to be designed only to counteract the un-


FIGURE 7.66. Offset lapped prestressing tendons.

desired effects of the former during ‘moment re-versals created by the successive launching stages.In practice, installation of the tendons passingfrom the inside to the outside of the box section isnot particularly simple. An attempt should bemade to reuse these temporary tendons to reducethe investment in nonproductive materials.

A comparative analysis between the first twomethods of temporary prestressing has been madefor a typical railway bridge. Solution 2 requires19% more conventional reinforcement than solu-tion 1 because of the many blisters and more elabo-rate tendon layout. The total cost of materials(concrete prestress and reinforcement) is 9%higher for solution 2 than for solution 1. These re-sults may be significantly different for highwaybridges, where the ratio between girder load andsuperimposed dead and live loads is very different.

7.9.5 CASTING AREA ANDLAC’,VCHING METHODS

The precasting area is located behind one abut-ment and has a length usually equal to that of twoor three segments. T h e r e a r e t w o d i f f e r e n tlaunching methods:

1. The launching force is transmitted from thejacks bearing against the abutment face to thebridge by pulling tendons or steel rods an-chored in the bridge soffit.

2. A launching device consisting of horizontaland vertical jacks is placed over the abutment.The vertical jack rests on a sliding surface andhas a special friction gripping element at thetop. The vertical jack lifts the superstructurefor launching, and the horizontal jack pushes ithorizontallv.

The designer should be concerned with the fol-lowing items:

The first launching method applies high localforces to the concrete soffit where the pulling de-vice is anchored. Careful design of the passive

reinforcement must be made in an area alreadydensely prestressed.

The second launching method requires sufficientvertical reaction on the vertical jack. This could becritical at the end of launching, when the requiredlaunching force reaches its maximum with a corre-sponding small vertical reaction.

A very precise geometry control is required duringlaunching. The possibility of foundation settle-ment must be considered in the design. Whicheverlaunching method is used, after completion of thelaunching procedure the deck must be raised suc-cessively at each pier so that the permanent bear-ings may be installed. This phase also calls for care-ful analysis.

7.9.6 LAUNCHING NOSE ANDTEMPORARY STAYS

The large cantilever moments occurring in thefront part of the superstructure that is beinglaunched from pier to pier inevitably call for spe-cial provisions to keep the bending stresses and thetemporary prestress within allowable and eco-nomically acceptable limits. Two methods havebeen used together and separately, as previouslymentioned:

Launching nose: A steel member made either ofplate girders or of trusses is temporarily pre-stressed into the end diaphragm of the concretebridge, which is the front section of the deck dur-ing launching.

Tower and stays: This method was described inChapter 6 for progressive construction. Its appli-cation to incremental launching, however, needs aspecial approach, because the relative position ofthe tower and the stays changes constantly with re-gard to the permanent piers.

The advantage of the launching nose to reducecantilever moments in the concrete superstructurewas discussed in Section 7.9.4. It is important notonly to select the proper dimensions of thelaunching nose but also to take into proper accountthe actual flexibility of the steel nose in comparisonto that of the concrete span. This relative flexibilitymay be characterized by the following dimension-less coefficient:

++c c


where E, and E, refer to steel and concrete moduli,and I, and I, are the moments of inertia of the steelnose and concrete superstructure. Figure 7.67 pre-sents the results of a study analyzing the variationof the maximum support moment in the concretedeck for different launching stages with the rela-tive stiffness K. This chart confirms the obviousfact that a flexible nose has only a limited efficiencyin reducing the moments in the concrete deck. Thefollowing table gives the characteristics of severalstructures using a launching nose and serves as areference for preliminary investigations of the op-timum launching method.

To allow the method to be effective in alllaunching stages, it is necessary to constantly con-trol the reaction of the tower applied to the con-crete deck. When the tower is above one pier, it istotally efficient. When launching has proceededfor another half-span length, the tower and staysproduce additional positive moments at midspan,exactly contrary to the desired effect. For this rea-son the tower may be equipped with jacks betweenthe concrete deck and the tower legs, and the towerreaction may be constantly adjusted to optimize thestresses in the concrete superstructure. Figure 7.68shows a device being successfully used for the firsttime in the construction of the Boivre Viaduct,near Poitiers, France.

Bridge

Launching Weight o fNose Leng th Launching

[ft (Ml Nose (tons) Stays

Wabash River 56 (17) 30 N oOli River 59 (18) 36 YesSaone 93.5 (28.5) 65 N oRoche 124.5 (38) 90 N o

For longer spans the launching nose is not neces-sarily the optimum solution, while temporary bentsmay also be expensive. A tower-and-stay systemhas been successfully used either alone or in con-junction with a launching nose to reduce the can-tilever moments in the front part of the super-structure.

FIGURE 7.67. Variation of the maximum supportmoment.

7.9.7 PIERS AND FOUNDATIONS

The loads applied to the piers and foundationsduring the incremental launching procedure arevery different from those appearing during ser-vice. The static configuration of the piers is also

FIGURE 7.68. Boivre Viaduct. nwr I’oiliers. France.


different. During construction, the bridge slidesover the pier tops and the buckling length of thepier is larger than that during service. The hori-zontal force applied to the pier top is also higherthan during service, thus requiring a close study ofthis construction phase.

Lou& <4cting on the Piers The various systems ofhorizontal forces that may act on the piers dependon the following:

Longitudinal profile of the superstructure

Direction of’ launching

E‘riction coef‘ficient of sliding bearings

Notation:

H=

4=R =

angle ot bridge superstructure lvith respect tothe horizontal; tan 0 = r

angle of’ f’riction of sliding bearings; tan C$ = p

total reaction of the superstructure on thepiel-: \,ertical and horizontal components Vand H, normal and tangential components A:and 7

The f’ollowing four cases will be considered (seeFigure 7.69):

1. H > 4, upulard launching: Sliding starts on thebearings \vhen the inclination of the reaction R\\,ith respect to the vertical is:

cY=t)++, H = V tan (0 + 4)

For small values of 0 and 4:

H = (r + p)V

2. H > 4, downward launching: Sliding startsLvhen cy = 8 - 4. The horizontal force on thepier acts in the direction opposite to that ofmovement irith a value:

H = V tan (0 - 4)

For small values of the angles:

H = (I - p)V

Because p varies with environmental condi-tions (cleanness of the plates in particular), thelaunching equipment and the pier will be de-signed for H = 4’. The downward movementof’ the bridge is controlled by a restrainingjacking force:

FIGURE 7.69. Reactions on piers during launching.(a) upward launching. (b) downward launching.

F=N(tan8-tan+) o r F=N(r-p)

For the same reasons as above, the safe valueof F is equal to Nr.

3. 0 < $, upward launching: As above, the hori-zontal load applied to the pier is:

H = (r + p)V

4. 0 < 4, downward launching: In this case thehorizontal load on the pier is applied in the di-rection of the movement with a value of‘:

H = (r - p)V

Because of the possible variation in the angleof friction, it is safer to provide a braking sys-tem to control the movement of the bridge.

Pier Cap Detailing The pier caps must be care-fully detailed in order to provide room for the fol-lowing devices:

Temporary sliding bearings

Vertical jacks to lift the bridge after launching toinstall the permanent bearings

Horizontal guiding devices during launching

3 5 2 Incrementally Launched Bridges

Adjusting jacks for correction of the relative dis-placements between piers and deck

Moreover, to reduce the pier bending momentsinduced by launching, the sliding bearings areoften eccentric. However, it is possible to reduce orbalance this horizontal force by installing ties an-chored in the ground. If the piers are very high,the horizontal force can be eliminated by usingjacking equipment directly installed on the piers.

7.10 DemoEition of a Structure byIncremental Launching

We close this chapter with an unusual applicationshowing the interesting potential of incrementallaunching. An overpass structure over the A-lmotorwav north of Paris needed to be demolishedfor replacement by another structure as part of ahighway relocation program. I‘he limited head-roonl between the existing bridge soffit and theclearance diagram, together with the considerabletraffic on the major motorway providing perma-nent access from Paris to Charles de Gaulle Air-port, made all conventional methods of demolitionextremely difficult and unadapted.

A ver! simple scheme was devised whereby thedeck was launched away from the traffic onto theapproach embankment to be conventionallv de-molished at leisure. The dimensions of the bridge

and the principle of the method are shown in Fig-ure 7.70. The 900-ton structure had a width of 26ft and the following spans: 46, 55, 55, 46 ft.

The existing reinforcing did not provide the nec-essary strength to resist superstructure dead loadduring launching. Therefore, a rear launching-outtail 26 ft long was installed at the end opposite thedirection of launching, while exterior post-ten-sioning tendons were placed above the deck tostrengthen the structure.

The bridge was lifted off its bearings 7 in. to in-stall sliding bearings and lateral guiding devices inpreparation f’or the operation. The whole opera-tion was performed in 54 weeks as f’ollo\vs:

Design and preparation of the contract

Mobilization and purchase of equipmentLaunching

2

21;-5;

rraffic \vas interrupted for only f’our nights be-tween 10 P.SI. and 6 .a.~. The operation turned outto be a complete success in spite of its originality.

L4UNWlt4G

I 46’I

1 55’ 1 55’ : 46’T t

PROCEDURE

I/ LIFT TOTAL BRIOSC 7’

2) PLACE ROLLERS OVER PIERS

A N D 48lJlMCNl5

3) INSTALL APPROACH FILL AND

C O N C R E T E BEAM5

A) PLACE P R O V I S I O N A L P/l AND

A REAR NOW 26 FT. LONG

TOTAL WEICUT soot

SCHEDULE TOTAL 5’/2 W E E K S

_ DESIGN & CONTRACT : 2

.MOB. PURCUAsLS : 2

_ LAUNCHING : IV!?

5 k

TRAFFIC INTERRUPTION :

(IO PM. TO 6 A.M.) 4 N;OUTs

FIGURE 7.70. Bridge over A-1, launching out.

References 353

2. :~non.. “First Incrementally Launched Post-Ten-sioned Box Girder Bridge to Be Built in the UnitedSwtes.” Bridge Report, December 1976, Post-Ten-sioning Institute, Phoenix, Ariz.

3. .ir\ icl (;I.d1it. “Increment;il Launching of ConcreteStn~cturcs.” Jorrmnl of thr .-lvwriccl~r Courwtp Imtltutr,\‘()I. T”. s o . 8. .-\ug”st 19i5.

4 . .4IlOII.. “\‘a1 Restel Viaduct tol- the Provincial RoadSo . 89 .Se;rr Ko\ereto. .I‘rento,” Prr.clrr.c,wd Couovtr.Strrlttrrtfs I)/ I/n/y 1970/l 974, .-\ssociarioIle Itdli;~na(:c.IllcIlto .-\llllatc, E: l’l~ec.oIllpl~esM~ (AIC.-\I’) and

.\ ssoc-id/ione It~rliamr ~cononica Del Cement0(.\I IX(:). Rome 1971.

5 . .-h~Il., “Segmental Box Girder Bridges \lake the Big‘I‘ime in U.S..” Engiuuwiug .\‘~!\-RPcoM/. \Iarch 2.1 9 7 8 .

6. Xnon., “Wabash Rive]- Bridge. Covingtot). I ndian;l.”Por t land Cement .-\ssociation, Bridge Repot“,SR201 .Ol E, lYi8, Skokie. 111.

i. Xl. .\Iaddison, “Crossing the Cutting with Segments atSonning,” Coucwtp, 7%~ Jou,-r~u/ of tha Corlo.rtr Socirt!

(Lot~rlor~j, Yol. 12. S o . 2, Februar\ 19iH.8. K. H. Best, R. H. Kingston, and 11. J. \Vhatle\, “ln-

cremental Launching at Shepherd House Bridge,”Pwcfwfirrgc, Instztution of Cnfil Eugrnrfm, \‘ol. 64. PartI, Fehruar\ 1978.

8Concrete Segmental Arches,

Rigid Frames, and Truss Bridges

8.1 INTRODUCTION8.2 SEGMENTAL PRECAST BRIDGES OVER THE

MARNE RIVER, FRANCE8.3 CARACAS VIADUCTS, VENEZUELA8.4 GLADESVILLE BRIDGE, AUSTRALIA8.5 ARCHES BUILT IN CANTILEVER

8.5.1 Review of Concept ; Summary of Structures wi thTemporary Stays

8 .5 .2 Neckarburg Br idge , Germany8.5 .3 Niesenbach Br idge , Austr ia8 .5 .4 Kirk Br idges , Yugos lav ia

8.1 Introduction

An arch bridge, in a proper setting, is an elegantand graref‘ul structure with aesthetic appeal. In-stinctivelv, a layman relates to an arch bridge as aform that follows its function. Long before pre-stressed concrete was developed as a technology,concrete arches were used for long spans, takingadvantage ot the compressive stress induced b\gravitational- forces into a curved tnetnbet- much asearlier generations of builders had done withniasotirv arches.

Three bridges designed and built by EugeneFreyssinet between 1907 and 1910 in centralFrance were to become a tnajor landmark in thedevelopment of concrete structures. In the \‘eut--dre Bridge, Figure 8.1, the three hinged rein-forced concrete arches had a clear span of 238 ft(72.50 m) and an unusual rise-to-span ratio of l/15dictated by the topography of the site and the sud-den floods of the Allier River. The \‘enture Fvas anunqualified success both during load testing andafter opening to traffic. As Freyssinet wrote in hismemoirs:

354

8.6 RIGID-FRAME BRIDGES

8.6.1 Saint Michel Bridge in Toulouse, France

8 .6 .2 Br ies le Maas Br idge , Nether lands8 .6 .3 Bonhomme Br idge , France8.6.4 Motorway Overpasses in the Middle East

8 .7 TRUSS BRIDGES

8.7.1 Retrospect on Concepts for Concrete TrussBridges

8 . 7 . 2 Mangfall Br idge , Aus tr ia8 .7 .3 Rip Br idge , Aus t ra l i a

8.7.4 Concept for a Cross ing of the Engl ish ChannelREFERENCES

Lord testing um (I triumph. 0~ the Gght bank, (1 hilloz~erlookirrg the bricige site UYS occupied by .\e-c~ewlthou,wd spectators do had trrken thei?- plclce c~lretrd~ crtdnulrl to ulatch the j<lilure of‘ the bricl<ge predicted by n10~~1 riea$mper .cold to some ur~happ~ competitor. Thesehopes were deceiz~ed, c~rrd ule had (I -corltirruom lnrle ojhenry .cteclm rollers trm~eling the bridge brick CIH~ for-thquite unable to produce ar+hing more th(crl the corn&tede(n.rtic de$ections.

Between 1907 and 191 1, however. fears de-veloped in Freyssinet’s mind. It seemed that thehand rails, which had been properly aligned at thetime of the load test, were showing some convexit!toward the skv at the nodes of the cro\vn hinges. Brthe spring of 191 1 the crown had moved do~vn-w a r d a s m u c h a s 5 i n . ( 0 . 1 3 m), a n d cot-t-e-spondingly the springings had raised appreciablv.Without telling anyone, Freyssinet mobilized ateam of four devoted tnen and placed hydraulicratns at the arch crowns to raise the bridge spans totheir original profile; he then replaced the hingeby a rigid concrete connection between the trvoabutting half-arches. This near-disaster \v;ts the

Introduction 355

FIGURE 8.1. Veurdre Bridge.

first consequence seen in a structure of a phenom-enon theretofore completely ignored: long-termconcrete creep.

Other beautiful concrete arches were also con-structed in the same period. The VilleneuveBridge over the Lot River in southwestern France,Figure 8.2, is an interesting example. The twinarch ribs are of plain concrete with a clear span of316 ft (96 m) and a rise of 47 ft 4 in. (14.5 m). Eachrib has a solid section 10 ft (3 m) wide and 4 ft 9 in.(1.45 m) deep built in at both ends into the con-crete abutments. The reinforced concrete deckrests upon the arch ribs through a series of thinspandrel columns, faced with red brick.

Construction began shortly before World War Iand was interrupted for four years, fortunately notbefore the concrete arch ribs could be cast on awooden falsework, Figure 8.3. Immediately uponcompletion, hydraulic rams were used at themidspan section to lift the concrete arches off thefalsework and actively create the compressive stressin them, a technique from Freyssinet’s fertile mindthat already contained the germ of the idea of pre-stressing.

FIGURE 8.2. \~illcncu\c HI itigc O\~I chc Lot Ki\cr.

The bridge was completed in 1919 and kept theworld’s record for long-span concrete structuresfor several years. The photograph appearing inFigure 8.2 was taken by one of the authors in thesummer of 1980; it shows that beautiful structurein a remarkable state after sixtv vears of continu-Ious operation under constant urban traffic.

Another Freyssinet design, the Tonneins Bridgeover the Garonne River, was built at the same time,and he considered it to be one of his nicest bridgestructures, Figure 8.4.

The Plougastel Bridge in Brittany, Figure 1.38,reached for longer spans with concrete arches. Forthe first time a box section was employed, callingon an ingenious method of construction in which awooden falsework was floated into position and re-used several times for the various arch ribs. Di-mensions of the structure and typical details of thearches are shown in Figure 8.5, which is a facsimileof a document published in 1930.

The three arches have a span length of 611 ft(186.40 m) and carry a single-track railroad and atwo-lane highway. The reinforced concrete trusseddouble deck accommodates the train track on itslower level and the highway on the upper. Nearthe arch crown in each span, the train passesthrough the arch rib.

The arch ribs were only slightly reinforced andthe quantity of steel was 39 lb/y&’ (23 kg/m’{), inspite of the relatively thin walls used for the boxsection.

The three arch ribs were constructed one afterthe other on a temporary wooden arch built onshore and floated into position for each of thethree concrete arches, Figures 8.6 ,and 8.7. Thiswooden arch was 490 ft (150 m) long and weighed550 tons (500 mt), including the two reinforcedconcrete end sections, which allowed the thrustcreated by the concrete arch ribs to be transferred

.-

-- ~. --.,.. ,I,. r

Segmental Precast Bridges Over the Marne River, France 357

know it today. It incorporated so many innovationsin a single structure that it would not be out ofplace in today’s modern bridge technology.

The single-span structure, Figure 8.8, is adouble-hinged arch with a distance between hingesof 180 ft (55 m) and a very tight clearance diagramfor river navigation that allowed only 4 ft 3 in.(1.30 m) below the finished grade of the roadway.Consequently, not only is the bridge structure veryshallow, 4.16 ft (1.27 m), at midspan, but the rise-to-span ratio of the arch is unusual: l/23. Thebridge consists of three parallel box sections madeup of precast segments 8 ft (2.44 m) long, con-nected after placement in the structure by precastslab sections at both top and bottom flanges, Figure8.9.

The bridge is prestressed in three directions:

to the arch springings completed earlier on thefoundation caissons.

Two barges and a temporary steel tie slightlyabove the water level, with the help of the largetidal range, allowed the transfer of this falseworkfrom the construction area to the three positions ofuse and its final return after completion of the con-crete structure.

As this outstanding undertaking neared com-pletion in 1930 after five years of uninterruptedeffort, Freyssinet expressed his thoughts as fol-lows:

In Brittany light is like a fairy who constantly plays atcovering nature with [many] changing coats, now oflead, noul of silver or of pearls, or of something immate-rial and radmnt.

Toward the evening oj the load testing of the bridge, shehad spread her most sumptuous treasures on the roadsteadand each line of the work, changed into a long rosary ofunreal light, added another touch of beauty to the mar-vellous whole, proving in this way that the Fairy of theRoadstead had already adopted the child that men hadimposed on her and had known how to weave for himgarments magn$cent enough to hide all the imperfectionsof the work.

8.2 Segmental Precast Bridges over theMarne River, France

Located some 30 miles (50 km) east of Paris, theLuzancy Bridge represents probably the first ap-plication of truly segmental construction as we

The 4 in. (0.10 m) webs are vertically prestressed toresist shear.

The longitudinal box girders are then prestressedto connect the precast segments and resist bending.The negative-moment prestressing tendons at thetop flange level over the arch springings are lo-cated in grooves provided at the top surface of theprecast segment upper flange and are ultimatelyembedded in a 2 in. (50 mm) concrete topping.This dense, high-quality concrete pavement pro-vides the sole protection for the high-tensile steelwires and also serves as the sole roadway wearingcourse. In spite of the excellent behavior of thisstructure after more than 34 years of operation, itwould probably be difficult to envisage duplicatingit today.

Transverse connection between the box girdersand the connecting slabs is achieved by prestress-ing.

There was no conventional reinforcing steel inthe bridge superstructure except in local areas,such as the Freyssinet concrete hinges at the archspringings. The erection was just as remarkable asthe conception of the bridge. Each box girder con-sisted of 22 segments, which were cast in a centralyard at the rate of one a day (little progress hasbeen achieved after thirty years). Afterward theywere carefully aligned on concrete blocks to takethe profile of the finished structure with properprovision for camber. The 2 in. (20 mm) wide jointswere dry packed to allow segment assembly by pre-stressing. In fact, the 22 segments of each boxgirder were assembled at this stage in three units:two side units made up of three segments each, andthe center unit incorporating the remaining 16

L E GENIE CIVIL - - .FONT A.LOUPPE,EN BQTONARMG, SUR L'ELORN,PRlj:S DEPLOUGASTEL (FINIST~RE)

Fig 3 Coupe par a a

re du tabher

Fi

Fig 8 Coupe’de kc montrantla dqositmn des armatures

Ali #,.,,,.,, Iy.I DIl4.L 1.1.1/ 0 ,.~,.swn.CU*o”~rUn*ar *.ms

I

FIGURE 8.5. Plougastel Bridge, dimensions of the structure and details of the arches, afacsimile of a document published in 1930.

Segmental Precast Bridges Over the Mame River, France 359

segments with a length of 170 ft (52 m) and amaximum weight of 134 tons (122 mt). All threeunits were assembled on the bridge centerline im-mediately behind one abutment, while the delta-shaped sections representing the arch springingswere cast in place over the abutment in their finallocation in the structure.

A special aerial cableway made up of two steeltowers resting on both banks and properly an-chored to the rear, a system of suspended winches,and a unique elliptical drum allowed the transferof the precast girder units from their assembly po- FIGURE 8.8. Luzancy Blitlgc.

P 1ou re midlane - Demo coupe dans he

Demo-coupe i l a cli Bern/. coupe i 24 “ho de la c/i

FIGURE 8.9. Luzancy Bridge, concrete dimensions.

360 Concrete Segmental Arches, Rigid Frames, and Truss Bridges

sition on the banks to their final location in thestructure. In spite of a seemingly involved concept,the operations were carried out safely and rapidly;a center beam was placed in only eight hours and acomplete arch including all preparatory andfinishing operations was assembled in 120 hours,Figure 8.10.

Another interesting feature of this structure wasthe incorporation at both arch springings of Freys-sinet flat jacks and reinforced concrete wedgesbetween the arch inclined legs and the abutmentsills, to adjust and control the arch thrust and thebending moments at midspan.

The bridge was opened to traffic in May 1946after successfully proving its structural adequacythrough a comprehensive series of static anddynamic load tests, following a custom still in usetoday in several European countries. Figure 8.11gives a view of the finished structure.

This first precast segmental arch bridge was fol-lowed a few years later by a series of five otherstructures, all of the same type and in the samegeographical area, the valley of the Marne River,

FIGURE 8.10. Luzancy Bridge, erection of centralsection.

FIGURE 8.11. Luzancy Bridge, view shmving flat archrise.

The concrete was vibrated with high-frequencyexternal vibrators, then compressed for maximum

FIGURE 8.12. One of the five hlarne River Bridges:Esbly, Anet, Char@, ‘Trilbardou, and Ussy.

Figure 8.12, at the following locations: Esbly, Anet,Changis, Trilbardou, and Ussy. All five bridgeshave the geometric dimensions shown in Figure8.13:

Distance between hinges: 243 ft (74 m)Rise of the central axis at the crown over the abut-ment hinge: 16.3 ft (4.96 m)Depth at crown: 2.82 ft (0.86 m)Deck width: 27.5 ft (8.40 m)

The deck structure is made up of six precast gir-ders, each consisting of:

Two precast delta-shaped sections at thespringings

Thirty-two precast segments 6.8 ft (2.07 m) longand weighing from 2 to 4.2 tons (1.8 to 3.8 mt).

The same design and construction principlesused at the Luzancy Bridge were repeated for thisseries of five bridges, except for some improve-ments commensurate to the experience gainedfrom the first structure and taking into account theimportance of the project. Precasting of the 960segments was achieved in a factory completely en-closed and using the most modern concrete man-ufacturing techniques of that period.

Each segment was fabricated in two stages inheavy steel forms. Top and bottom flanges werecast first, with high-strength steel stirrups em-bedded in both units. After strength was achieved,a set of steel forms equipped with jacks was placedbetween the flanges, which were jacked apart tostress the web pretensioned stirrups. Then the webwas cast between the flanges. There was no needfor any conventional reinforcing steel in the pre-cast segments.

FIGURE 8.13. Marne River Bridges, typical longitudinal and CTOSS sections.


compaction and steam cured for a fast reuse of theforms. The equivalent 2%day cylinder strengthwas in excess of 6500 psi.

Near the precast factory, an assembly yard al-lowed the segments to be carefully aligned and as-sembled by temporary prestressing into sections,which were transferred into barges to be floated tothe various bridge sites. Each longitudinal girderwas thus made up of six sections:

The two delta springing sections

Two intermediate five-segment sections

Two center ten-segment sections

Handling of these various sections was performedby the Luzancy cableway properly rearranged forthe purpose.

The stability of the side sections, at both ends,was obtained by temporary cantilever cables an-chored in the abutments, while the two center sec-tions were suspended to the cableway until castingof the wet joints was completed and longitudinalprestressing installed to allow the arches to supporttheir own weight. Figures 8.14 through 8.16 showthe various sequences of the arch construction,while one of the finished bridges is shown in Figure8.17.

The quantities of materials for the superstruc-ture were very low, considering the span lengthand the slenderness of the structure:

Precast concrete: 353 yd:’ (270 m3)

Reinforcing steel: 13.2 tons (12 mt)

Prestressing steel: 13.2 tons (12 mt)

For a deck area of 6540 ft2, the quantities persquare foot were:

FIGURE 8.14. YI,II IIC Ki\ (‘1 RI iclga, Ed ectetl end scc-tion.

FIGURE 8.15. ,tIanre Kiwx Rridgm, L’IWJ ion ot’ ccn-tral section.

FIGURE 8.16. 11~1 nc Kixcl RI idgcs, t‘~ cc tton of (cn-tral section.

Precast concrete: 1.46 ft 3/ft 2

Reinforcing steel: 4.0 lb/ft2

Prestressing steel: 4.0 lb/ft2

As in the Luzancy Bridge, the high-density con-crete placed over the exposed longitudinal pre-stressing tendons was also used for the roadway

Caracas Viaducts, Venezuela 363

FIGURE 8.17. Marne River Bridges, completed strut-ture. FIGURE 8.19. C;lr-atas Viadutr\, Britlgcs 2 ,mct 3.

wearing course. The behavior of these bridges hasbeen excellent f’or thirty years.

8.3 Caracas Viaducts, Venezuela

In Venezuela in 1952 a highway was being con-structed between Caracas and La Guaira airport.Alignment of this highway necessitated crossing agorge at three locations with relatively largebridges. These structures were designed and con-structed under the direction of Eugene Freyssinet.’

Although the three bridges are similar in ap-pearance, Figures 8.18 and 8.19, they vary in

length as shown in Table 8.1 .2 Preliminary investi-gations indicated that adequate soil material wouldprobably be found irregularly at great depths.Construction of abutments to resist large bendingmoments under these conditions would be difficultif not impossible. The decision was therefore madethat the abutments would resist only the centeredthrust of the arches and that the bending momentsapplied to the abutment would be reduced, as faras practical, to zero. This required that hinges belocated as near as possible to the points of origin ofthe arches. Because of consideration of long-termcreep deformation on buckling of the arch andpossible consequences of abutment displacementas might be caused by an earthquake, the decisionwas made to eliminate a crown hinge, thus result-ing in two hinged arches.’

Although the bridges vary considerably in di-mensions, they are quite similar in appearance. Be-cause of the valley profile, it was possible to use thesame basic design for all three structures. All weredesigned for AASHO H20-44 loading. Whereverpossible, the elements were standardized in order tominimize design and maximize precasting and pre-fabrication.

FIGURE 8.18. ~&acas Viaducts, Bridge 1.

Pilasters were placed at each end of the arch inBridge 1 so as to avoid an unpleasant appearanceof a change without transition from the mainstructure to the approach viaducts.

Bridge

123

TABLE 8.1. Caracas Viaduct Arches

Height fromTotal Length Bed of Gorge

1013 ft (308.8 m) 230 ft (70.1 m)830 i’t (253 m) 240 ft (73.2 m)700 ft (213.4 m) 170 ft (51.8 m)

Main Span

498 it (151.8 m)478 it (145.7 Ill)453 tt (138.1 m)


FIGURE 8.20. Caracas Viaducts, elevation of Bridge 1, from reference 1 (courtesy ofCivil Engineering-AXE)

An elevation of Bridge 1, Figure 8.20, shows theprincipal dimensions and foundations of the arch.The three bridges have identical cross sections,Figure 8.2 1. The poured-in-place concrete decktopping varies in thickness from 2 in. (50 mm) atthe edges to 7$ in. (190 mm) at the center to pro-vide a transverse slope of 1.5% for drainage. Eachdeck span, except at the crown, consists of eightprecast prestressed I girders. Variations in spanlength of the deck girders are accommodated byadding or removing standard form units. Identicaltransversely prestressed precast stay-in-place deckslabs span transversely between the deck girders.Continuity of the deck girders is accomplished bylongitudinal tendons placed in a groove in the topof the top flange of the girders.’

Approach piers and spandrel columns over thearches consist of three I-shaped columns of astandard cross section shown in Figure 8.21. Afive-segment precast cap beam on the columns re-

ceives the eight deck I girders. A perspective of thedeck over the piers is shown in Figure 8.22. Theprecast deck girders, cap beams, and slab are sup-ported on the cast-in-place piers, and the whole as-sembly is prestressed vertically, transversely, andlongitudinally.

The center span consists of three paralleldouble-hinged arch ribs 27 ft 6 in. (8.4 m) oncenter, Figure 8.21. Each arch rib is a box with awidth of 10 ft 6 in. (3.2 m) and a slightly varyingdepth from 9 ft 6 in. (2.9 m) to 10 ft (3.05 m) at thesupporting points of the deck. To provide in-creased capacity to resist end moments developedby horizontal loads, the width of the ribs is in-creased to 17 ft (5.18 m) at the spring lines. The 5in. by 5 in. (127 mm x 127 mm) fillets provided ateach inside corner of the box are to reduce theconcentration of torsion stresses. Thickness of thebottom f lange of the box r ib was kept to aminimum to reduce weight on the falsework. The

C r o s s s e c t i o n o f p i e r A - A FCross section of arcqly’ 1 7”

5’3” 4 itkA

FIGURE 8.21. Caracas Viaducts, typical cross section, from reference 1 (courtesyof Civil Engineering-ASCE).

Caracas Viaducts, Venezuela 365

FIGURE 8.22. Caracas Viaducts, perspective of deck over piers, from reference1 (courtesy of Civil Engineering-ASCE)

thicker top flange provides the box rib with the re-quired area and moment of inertia for resistingthrust and live-load moments.

Design of these structures considered a designwind pressure of 50 psf (2.4 kN/m*). The arch ribscarry part of the wind pressure to which they aredirectly subjected; the remainder is transmitted tothe deck structure by bending of the spandrel col-umns and the connection of the arch rib to thedeck at the crown. The arches were assumed to betransversely fixed in the foundations, the end mo-ment developed in the springings resulting in aslight transverse displacement of the pressureline.*

Thus, the deck structure was chosen as the prin-cipal member to resist wind loads, requiring theexclusion of all joints in the deck from abutment toabutment. The condition of deck continuity led tothe attachment of the deck to the arch on bothsides of the arch crown. This was accomplished byprestressing the continuous cables provided overthe top flange of the girders and anchoring theminto the arch. Six girders were connected to thearch in this manner: the two intermediate girderst h a t d o n o t r e s t d i r e c t l y o n t h e a r c h w e r elengthened to the crown, Figure 8.21.*

an approximate length of 1000 ft (305 m), de-veloping approximately symmetrically on bothsides of the arch crown. Free movement of thedeck structure over the pilasters was accommo-dated by providing two concrete rockers over eachtransverse wall of a pilaster. The rockers consistedof a 3 ft 6 in. (1.07 m) high continuous wallthroughout the width of the bridge with a continu-ous Freyssinet-type concrete hinge at both the topand bottom. Approach piers were fixed in the deckat the top and hinged at their footings. Because oftheir height, these piers have sufficient flexibility toallow movement of the deck without developingappreciable bending moments, the exception beingthe short stiff piers next to the abutment, whichwere hinged both top and bottom.*

We shall describe the construction procedure forthe superstructure of Bridge 1, which was alsoused for the other two bridges. Because the cable-way did not have the capacity to transport the deckgirders across the canyon, precasting operationswere established at both ends of the bridge. Duringconstruction of the foundations, precasting opera-tions were started at both sites at either end of thebridge.

During construction, an open joint was providedat the crown. In this joint Freyssinet flat jacksstaggered with concrete wedges were inserted,acting as a hinge for the arches to adjust the pres-sure line during different phases of construction.

Expansion and contraction of the deck due totemperature, creep, and shrinkage take place over

When the foundations for the approach pierswere completed, the cableway transported and po-sitioned the precast Freyssinet pier hinges to theirrespective locations, where they were grouted totheir respective foundations. Pouring of the piersthen commenced, using special steel forms at-tached to the hinge blocks. Two sets of forms wereused in leap-frog fashion to maintain a pouring


rate of 5 ft (1.52 m) per day. Because of the hingeat the base of each pier column, the piers requiredtemporary support until the deck girders could beplaced. The first 25 ft (7.62 m) lift of each columnin each pier was supported by a light steel scaf-folding that surrounded each column; the scaf-foldings, in turn, were braced together. Succeed-ing 25 ft (7.62 m) lifts were braced to the previouslift by light timber trusses. As the columns in thepiers rose, steel reinforcement was placed: at thesame time, holes for vertical prestressing tendonswere cast in the concrete by the insertion of l+ in.(38 mm) steel tubes, which were withdrawn lflio~~t-s after concrete placenlent.3

Upon completion of the three columns of an ap-proach pie r, precast segments of the cap beamwere placed atop the columns and prestressedvertically to them as indicated in Figure 8.22. Thetwo intermediate cap beam segments were placedby the cableway and temporaril!; held in positionby steel brackets. Four prestresslng tendons werethen placed through the cap beam segments andthe four vertical 14 in. (38 mm) joints between thesegments were packed with a rich mortar. Aftereight to ten hours the longitudinal tendons in thecap beam \vere stressed and anchored to completea pier bent, which was then readv to receive thedeck girders and slabs. The 137 ft (41.75 m) highpilasters at each end of the arch are four-celledhollow boses 20 by 80 ft (6.1 s 24.4 m) in plan withall walls 4: in. (120.65 mm) thick. They were con-structed in lifts with special steel forms that wereleap-f‘rogged. ‘l‘en vertical prestressing tendonsanchored into the foundation provided stabilit\against wind forces.3

Upon completion of the abutments and the firstapproach piers, erection of the bridge deck girdersand slabs commenced. It was accomplished with a126 ft (38.4 m) long structural steel lattice girdergantry, 60 f’t (18.3 m) of which extended as a can-tilever. One 48 ft (14.6 m) span, consisting of eightprecast beams and 112 precast slabs, required nineworking days and a crew of 16 men. When the ap-proach viaduct decks were in place, they were pre-stressed longitudinally by prestressing tendonsplaced in the grooves of the top flange of the deckgirders, which were anchored at one end into theabutment and at the other end over the arch pilas-ters.

The three arch ribs of the main span were cast inplace on a light wooden falsework, which was re-used almost in its entirety for the two otherbridges. Basically, the system adopted was to erectthe timber formwork for casting the arch ribs by

the cantilever method, this formwork being placedby the overhead cableway and held in place by asystem of cable stays. Thus, the arch rib was essen-tially constructed to the quarter-points. The centerhalf-span formwork was constructed as a lightwooden trussed arch assembled at the bottom ofthe canyon and winched into position from theends of the quarter-span cantilevers. .I‘he timberfalsework truss was wedged against the concretearch ribs already erected. It acted as an arch underthe weight of the bottom flange concrete, trans-mitting its thrust to the cantilevered arch sectionspreviously erected. Later the timber falseworkacted compositely with the hardened bottom flangeconcrete to support the webs and top Hange of thehollowbox arch ribs when they were placed.’

The following discussion describes the erectionsequence of the center-span arch ribs.” The firstfalsework unit in the quarter-span for each archrib consisted of a timber platform 31 ft (9.45 m) inlength with a width of 27 ft 8 in. (8.43 m) at thespring line and a width of 17 ft 2 in. (5.23 m) at theopposite end, Figure 8.23 (Phase 1). This platformwas constructed of 3 x 10 in. (76.2 x 254 mm) tim-bers on edge at l@ in. (267 mm) centers coveredon the upper face with 1 in. (12.7 mm) thickplywood. It provided the form for the bottom ofthe arch rib. For the first section of the quarter-span, three of these units (one for each rib) wereplaced by the cableway, supported by cable stays Aand B, and their position adjusted by hydraulicjacks at the ends of the anchor cable stays. Nextfour precast Freyssinet hinge blocks were posi-tioned at the spring line and assembled into onehinge block by prestressing them together. Formswere then erected on the falsework for the webs ofthe arch rib, and placement of concrete com-menced, Figure 8.23 (Phase 2). As the weight ofeach increment of concrete came onto the forms,the cable stays elongated and the geometry of thearch-rib soffit had to be carefully adjusted by thehydraulic jacks.

Upon completion of the concreting for the firstsection of the quarter-span, falsework section 2 wasattached to it and supported by two more cablestays, C and D. After geometry adjustment, con-creting continued, Figures 8.23 (Phase 3) and 8.24.As a result of the position of the cable stays and theconcreting sequence, angular deformations werepossible between falsework sections 1 and 2.Therefore, a temporary concrete hinge was placedin the lower flange of the arch rib, which wouldallow angular deformation but transmit the thrustto maintain equilibrium. When the concreting of

/’/ /

/

/

3As.u

-. -.-._c

i’/.

,//I/

PHASF3

;rF---_‘\(

FIGURE 8.23. Caracas Viaducts, erection and construction sequence, from refet-ence 3(courtesy of Civil Engineering-ASCE).

367


FIGURE 8.24. Caxcas Viaducts, comtruction of wchspringings on suspended scaffolding.

the second portion of arch rib was completed andgeometry adjustment made, the temporary hingewas blocked and the two sections were prestressedtogether. In the same manner, temporary hingeswere used for the remaining sections of thequarter-span arch rib and at each end of the cen-tral half-span arch section.

The first two sections of arch rib thus became acontinuous member supported at the outer end bycable stays, and during construction of the rest ofthe arch its geometric position was adjusted bycable stay D.

The next operation was the erection of the thirdfalsework unit consisting of a trusswork. Its weightwas such that it could not be accommodated by thecableway, Therefore, it was assembled at the bot-tom of the canyon below its position in the arch.The outer end was lifted by the cableway and theinner end by a winch located at the end of the pre-viously concreted section of the arch, Stay cables Epassing over the pilaster were attached, and thebottom flange of the new arch rib section was cast,Figures 8.23 (Phase 4) and 8.25,

In like manner the next section of trussedfalsework was positioned and supported by cablestay F. Next, concrete for the bottom flange of therib was placed, including small concrete brackets

which protruded below the bottom flange to takethe thrust of the 267 ft (81.4 m) central falseworkafter its positioning, Figure 8.23 (Phase 5).

In the last phase of the quarter-span concreting,the vertical webs were formed and concreted, aswell as a few narrow strips across the top to providestiffness to the arch-rib members, which at thisstage had a U-shaped cross section, Figure 8.23(Phase 6). The anchor stay cables were again ad-justed to bring the 125 ft (38 m) quarter-span intoits proper position.

The central 267 ft (81.4 m) falsework span hadbeen assembled at the bottom of the canyon belowits final position in the arch, Figure 8.26. The endsof the timber falsework arches were tied togetherby steel cables acting as ties to keep the archfalsework rigid. The whole central falsework washoisted into position by winches located at the endsof the cantilevered quarter-span units, Figure 8.27.

Once the central falsework was in place and thelocation of the crown exactly positioned, cementmortar was packed in the gap between the endsof the central falsework and the quarter-spanfalsework, and extra-flat sand boxes were em-bedded in the joint for subsequent stripping of thecentral falsework.

After two days, the steel tie cables on the centralfalsework were released and the winches support-

GENERAL ELEVATION OF FALSEWORK

I A’ ._--,/ -

n II\-a,,, \

DETAIL OF JOlNT OF TOP MEMBERAND DIAGONALS

Concrete Segmental Arches, Rigid Frames, and Truss Bridges

FIGURE 8.27. Caracas Viaducts, lifting centerfalse\\x)rk.

ing the section were loosened. At this point thecombination of the central trussed falsework andthe concreted quarter-span units acted as a com-plete arch from abutment to abutment.

Next, the bottom flanges of the arch ribs wereconcreted, in a previously arranged sequence, upto the crown on each side, and temporary crownhinge blocks were placed. The other temporaryhinges between elements of the quarter span wereblocked and the cable stays up to stay D removed.‘rhe combination of timber falsework and partlybuilt concrete arch ribs continued to be held in po-sition by stays D, E, and F, with a temporary hingeat F onlv.

The vertical webs of the arch ribs over the cen-tral section were then concreted up to the crownhinge; cable stav D was released; crown concretewas completed; the remaining construction jointswere tied with prestressing tendons; and the lastcable stays E and F were released. At this point the

FIGURE 8.28. Caracas Viaducts, lowering centerfalsework. FIGURE 8.29. Caracas Viaducts, finished Viaduct 1.

concrete arch ribs, less the top flange over thecenter 260 ft (79.25 m) section, carried themselvesas well as the dead load of the entire falsework.

Next, the cement joints at the ends of thefalsework were destroyed, sand boxes emptied,and, after the steel cable ties had been retightened,the central section of falsework was lowered, Fig-ure 8.28. Falsework elements in the quarter-spanswere lowered by hand winches.

In 1973, twenty-one years after the constructionof these arches, they were reevaluated to see howthey would now be designed and constructed. Fig-ures 8.30 and 8.3 1 compare the actual project con-structed in 1952 with the structure as it would have

Spandrel columns were constructed next. Then,following a carefully worked out sequence, the topflanges of arch ribs over the central section were

been designed in 1970 (two boxes) and in 1973

concreted. Upon completion of the arch ribs thedeck beams and slabs were placed, in the manner

(single box). The three-arch-rib and eight-beam

previously described for the approach viaducts, ina symmetrical and simultaneous manner on both

superstructure would be replaced by a variable-

sides of the crown. After the deck had been pre-stressed transversely, it was prestressed longitudi-

depth box section (cantilever construction using

nally in the same manner as the approach viaducts.Finished Viaduct 1 is shown in Figure 8.29.

precast segments) supported on slip-formed piers.The arch remains an appealing and aesthetic

structure and might still prove to be competitive;but perhaps the construction technique suggestedin the Neckarburg Bridge (Section 8.5.2) mightbe more appropriate today, either cast in place orprecast.

Gladesville Bridge, Australia 371

As constructed in 1952

Possible alternative in 1973FIGURE 8.30. Caracas Viaducts, comparison of longitudinal sections.

8.4 Gladesville Bridge, Australia

This precast segmental arch bridge, completed in1964, spans the Parramatta River between Glades-ville and Drummoyne and serves a large section ofthe northern area of the Sydney Metropolis, Fig-ure 8.32.

After award of contract the contractors submit-ted an alternative design. They proposed that thearch be built on fixed falsework, whereas in theoriginal design part of the arch was to be built onfloating falsework and towed into position. Theoriginal design called for an arch span of 910 ft(277.4 m). The alternate design increased the clearspan of the arch to 1000 ft (305 m) and eliminatedthe necessity for deep-water excavation for thearch foundations on the Gladesville, or northern,side of the river.4

Total bridge length between abutments is 1901ft 6 in. (579.6 m). The 1000 ft (305 m) clear spanarch consists of four arch ribs, Figure 8.33, sup-ported on massive concrete blocks, known as“thrust blocks,” founded on sandstone on each sideof the river. Roadway width is 72 ft (22 m) with 6 ft(1.8 m) wide sidewalks on each side. The roadwayhas a grade of 6% at each end, and the grades areconnected by a vertical curve 300 ft (91.4 m) in

ngth over the center portion of the structure.he arch has a maximum clearance, at the crown,

of 134 ft (40.8 m) above the water and not less than120 ft (36.6 m) above water level for a width of 200ft (61 m) in the center of the river.

Construction of the bridge involved the follow-ing main operations4:1. Excavation for foundation of:

a. Arch thrust blocks on each side of the riverat the shoreline and partly below water.

b. Abutments at the ends of the bridge.C. Shore pier columns of the approach spans

on each side of the river.2.

3.

4.

5.

Concreting of the arch thrust blocks, theabutments and columns.

Driving of falsework piles in the river anderection of steel falsework to support the hol-low concrete blocks and diaphragms formingeach of the four arch ribs.

Casting of the box-section segments of the archand diaphragms and the erection of the fourarch ribs one at a time.Jacking each rib to raise and lift it off thefalsework.

6. Casting of concrete deck beams on each side ofthe river.

7.

8.

Erection of the deck beams to form the road-way over the arch.

Paving of the concrete roadway and final com-pletion of the structure.

As constructed in 1952

-t--2 0 . 5 0

--wftI

1II I R

-.-

Possible alternative in 1970

-20.50

Possible alternative in 1973

FIGURE 8.31. Caracas Viaducts, comparison of cross sections.

372

FIGURE 8.32. Gladesville Bridge, aerial view, fromreference 4.

The roadway deck is supported on pairs of pre-stressed concrete columns, Figure 8.33. The wallthickness is 2 ft (0.6 m), except in the tall columnsabove the arch foundation where the wall thicknessis increased by 6 in. (152 mm). At the top of eachpair of columns there is a reinforced concrete capbeam to support the deck girders.

During construction it was necessary to providefalsework to support the box segments and dia-phragms that make up each of the four arch ribsin the arch. The falsework was made up of steeltubular columns on steel tubular pile trestles car-rying spans of steel beams 60 ft (18.3 m) long and asteel truss span of 220 ft (67 m) over a navigationopening in the Gladesville (northern) half of the

FIGURE 8.34. Gladesville Bridge, arch rib falseworkand positioning of arch rib segment, from reference 4.

falsework. These falsework units were tied to-gether and anchored at each end to the thrustblocks, Figure 8.34. Piling was taken down to rockin the river bed.

Steel columns, braced together, formed a towerextending transversely the full width of the bridgeat the center of the falsework. Transverse mem-

FIGURE 8.33. Gladesville Bridge, schematic of four arch ribs, col-umns, and deck, from reference 4.

3 7 4 Concrete Segmental Arches, Rigid Frames, and Truss Bridges

bers, extending the full width of the bridge, abovethe waterline connected the pile trestles, Figure8.34. The balance of the falsework was of sufficientwidth to support one arch rib. Upon completion oferection of an arch rib, the falsework was movedtransversely on rails on the transverse members ofthe pile trestle to a position to enable erection ofthe adjacent arch rib, until all arch ribs wereerected.

Equipment installed on the central tower liftedthe arch box segments and diaphragms from waterlevel and positioned them. The tower also servedas a lateral bent to stabilize the individual arch ribsafter they were self-supporting and until they weretied together. 4

The hollow-box segments and diaphragms werecast 3 miles (4.8 km) downstream from the bridgesite. The casting yard was laid out to accommodatethe manufacture of one arch rib at a time. Eacharch rib consists of 108 box segments and 19 dia-phragms. Each arch-rib box segment is 20 ft (6 m)wide, with depths decreasing from 23 ft (7 m) atthe thrust block to 14 ft (4.3 m) at the crown of thearch, measured at right angles to the axis of thea r c h . T h e l e n g t h o f t h e b o x s e g m e n t s a l o n gthe arch varies from 7 ft 9 in. (2.36 m) to 9 ft 3 in.(2.82 m). After the box units were manufactured,they were loaded on barges and transported to thebridge site. The box segments and diaphragmswere lifted from the barges to the crown of thearch falsework and winched down to their properposition, Figure 8.34. Diaphragms are spaced atintervals of 50 ft (15.24 m), serving not only tosupport the slender columns that support theroadway above but also to tie the four arch ribs to-gether.

When the units were located in position on thefalsework, a 3 in. (76 mm) joint between the pre-cast segments was cast in place. At two points ineach rib, four layers of Freyssinet flat-jacks wereinserted, with 56 jacks in each layer. The rib wasthen jacked longitudinally by inflating the jackswith oil one layer at a time, the oil being replacedby grout and allowed to set before the next layerwas inflated. Inflation of the jacks increased thedistance between the edges of the segments adja-cent to the jacks and thus the overall length of thearch along its centerline. In this manner a camberwas induced into the arch rib, causing it to lift offthe supporting falsework. The falsework was thenshifted laterally into position to support the adja-cent arch rib and repeat the cycle. Figure 8.35 is aview of the completed four arch ribs, and Figure8.36 shows the completed bridge.

FIGURE 8.35. Gladesville Bridge, complctrd fourarch ribs, from reference 4.

8.5 Arches Built in Cantilever

Until the appearance of the concrete cable-staybridge starting in 1962 (see Chapter 9), long-spanconcrete bridges were the domain of the archtype of structure. Until 1977, with the completionof the Brotonne Cable-Stay Bridge in France with aspan of 1050 ft (320 m), the record length for aconcrete bridge had always been held by an arch-type bridge. When the Kirk Bridges in Yugoslaviawere completed in 1980, the larger arch with aspan of 1280 ft (390 m) once again regained for thearch the record of longest concrete span.

FIGURE 8.36. Gladesville Bridge, \ ICI\ of completedbridge.

Arches Built in Cantilever 375

Here is a brief chronology of record concretearch spans up to 1964:

1930, Plougastel Bridge, France: three spans of611.5 ft (186.40 m)

1939, Rio Esla, Spain: 631 ft (192.4 m) span

1943, Sando, Sweden: 866 ft (264 m) span

1963, Arrabida, Portugal: 886 ft (270 m) span

1964, Iguacu, River Parana, Brazil: 951 ft (290 m)span

1964, Gladesville, Sydney, Australia: 1000 ft (305m) span

The concrete arch bridge does not enjoy thefavor it once did. Modern methods of bridge con-struction utilizing prestressing, cable stays, andsegmental construction have all but eliminated itfrom contention as a economical bridge type.However, with the application of these modernmethods to the older form, and given the propersite conditions, concrete arches may regain some oftheir lost popularity.

8.5.1 REVIEW OF COSCEPT; SUMMARY OFSTRUCTURES WITH TEAZIPORARY STz4YS

The use of temporary stays to facilitate the con-struction of arch bridges began, perhaps, with thePlougastel Bridge. Temporary prestress tendonswere used to provide stability to the short archcantilever sections emanating from the arch foun-dations (see Figure 8.5). Prestressing tendons wereused to support the f-alsework of the Rio EslaBridge and were incorporated into the structure.However, the more novel method, which is thebirth of today’s technology, was employed in theconstruction of the Saint Clair Viaduct at Lyon,France, by M. Esquillan. The stability of precastsegments was obtained by the use of temporarystays.

fc)FIGURE 8.37. Concrete arches built in cantilever withtemporary stays. (n) With stays and pvlons. (h) With stays.spandrel columns, and pylons. (c) With spandrel col-unins, tie diagonals and stay’s.

In the construction of the Caracas Viaduct,Freyssinet extended this concept by using tempo-rary stays to support the falsework and construct amuch longer cantilever section of the arch. Thissame stay system was then used to accommodatethe forces produced by lifting the center arch sec-tion falsework (see Section 8.3). This concept waspartially recaptured for the construction of theIguacu Bridge in Brazil, where the falsework of thecentral portion of the arch was supported by tem-porary stays.

arch by temporary stays is the Sibenik Bridge inYugoslavia. Falsework f-or an approximate lengthof 88.6 ft (27 m) was supported on Bailey trusses,which were in turn supported by temporary stays,Figure 8.376, consisting of a combination of cablesand structural steel rolled shapes. This arch wasconstructed in nine sections, four on each side andthe central closure section. A modification of thisconcept was used for a second Yugoslav bridge atPag with a 634 ft (193.2 m) span constructed inseven sections. A further modification was used forthe Van Staden Bridge in South Africa, Figure8.37a, with a span of 656 ft (200 m).

A somewhat different concept is where, with theassistance of spandrel columns, the stays act astemporary diagonals during construction, Figure8.37~. In this manner, the structure is built as avariable-depth Pratt truss. This concept was usedfor the Kirk Bridges in Yugoslavia. In some in-stances these temporary diagonal stays may be in-corporated into permanent diagonals such that inthe final configuration the structure is a truss andnot an arch (see Section 8.7.3).

The first arch bridge to be constructed using the In summarizing the construction methods usingconcept of supporting segmental sections of the temporary cable stays, we find two basic categories:

I II II I

i I iI ’ I

__~


(a)

Erection scheme

3 7 6

a-a b-bat approaches at arch

Cross-sections

Cc)

Arches Built in Cantilever 377

FIGURE 8.38. (Opposite) Neckarburg Bridge, erec-tion scheme and sections, from reference 5. (a) Lon-gitudinal section. (h) Erection scheme. (c) Cross section.

Where the arch is supported directly by the tempo-rary stays

Where the temporary stays act as diagonals of aPratt truss during construction

Characteristics of the arch bridges using this con-cept of temporary stays during construction arepresented in Table 8.2.

8.5.2 NECKARBURG BRIDGE, GERMANY

This unique and contemporary arch-supportedstructure, some 50 miles (80 km) southwest ofStuttgart, crosses the Neckar River near Rottweil,Germany. It is a part of the federal expresswayA-81 from Stuttgart to the west of Bodensee with aconnection to Zurich, Switzerland.

The original scheme proposed by German au-thorities consisted of a steel girder structure sup-ported on tall piers. Designer-contractor Ed. Zub-lin, Stuttgart, developed an alternative designconsisting of twin concrete arches to support theroadway. The proposal was to construct the archessegmentally by the cantilever method and con-struct the twin single-cell trapezoidal box girdersfor the roadway by the incremental launchingtechnique (see Chapter 7). The Austrian methodcalled the Mayreder system was used to constructthe arches without scaffolding.5,6

The roadway of this 1197 ft (364.98 m) longstructure is approximately 310 ft (94.7 m) above theNeckar River, Figure 8.38. The 507 ft (154.4 m)arch span, Figure 8.39, has a rise of 164 ft (49.85m). Total roadway width is 102 ft (31.0 m). The

FIGURE 8.39. Neckarburg Bridge, completed arch(courtesy of Willhelm Zellner).

FIGURE 8.40. Neckarburg Bridge, arch just beforeclosure (courtesy of Willhelm Zellner).

structure is constructed as two independent paral-lel structures with a 1.8 ft (0.54 m) gap in the me-dian. Roadway spans are 98 ft (30 m) in the ap-proach sections and 72.6 ft (22.14 m) over the arch.

Each independent arch rib is a two-cell box. Thearch ribs were constructed in symmetrical halves,Figure 8.40. The cuEved formwork was 43 ft (13.1m) long, the first 23.3 ft (7.1 m) of the formclamped to the previously constructed arch seg-ment and the remaining 19.7 ft (6 m) remained tocast the next segment increment. The first 23.3 ft(7.1 m) of arch segment at the arch foundation wasconstructed by conventional forming methods.There are 14 segments on each side of an arch riband a closure segment at the crown of each arch.The exterior dimensions of each two-cell arch ribare 21.3 ft (6.5 m) wide by 9.8 ft (3.0 m) deep. Ex-terior webs vary in thickness from 10 to 11 in. (260to 280 mm), and the interior web is 6.3 in. (160mm) thick. The arch rib was cast in two operations-first the bottom flange and second the webs andtop flanges.”

Piers supported by the arch or independentfoundations are of a constant section and slip-formed by conventional methods. Sliding bearingsare used at the abutments and the short stiff piers 1and 13. The remaining piers are hinged to thesuperstructure deck such that the elastic piers canfollow the superstructure movement.5’6

During construction, as each half-rib was can-tilevered out from its foundation, it was supportedby a temporary system of Dywidag bar stays, Fig-ures 8.38, 8.41, and 8.42. After completion of thearch, the temporary stays were removed, exceptthose required to stabilize the arch during the in-cremental launching of the superstructure deck.Dywidag bar stays were anchored either to a pierfoundation or to Dywidag rock anchors in the sideof the valley.5

Name

TABLE 8.2 Characteristics of Arch Bridges Constructed with Cable Stays

Year 01 Span, It. Arch(:onwuctlon (In) Stiay Mrthod C~,tlSt~U~tlOtl Arc II Type De< k ‘I’ypc

StaicArch Scheme Remarks

Vat1 Statlen

Sib&k Yugfelavia I Y64-66 x07

(246)

I Y66-67 6 3 4

( 1 9 3 . 2 )

‘I‘hrer stay\Iormed fromrolled \trelshape\ and cables,auxiliary pylon,the longer stqbeing addttxmallysu}q”“ted on toI-UrnllS

Nine wction\ onlalsework of X8.6and Y5 It (27 and2Y 111)

I brce-cell ICC 1611-gulnr box

Simple ,,rrCa\tglrders ol 76.4 tt(23.30 Ill) spat,rmde continuott9

Possibility 01 car-I-ertmg the thrustat the crown by abattery 01 hy-draulic jacks

Pos5ibiltty 01 car-recting the thrustat the c~owtt by abattery ol hy-draulic jacks

South Al&a About I970 6 5 6

( 2 0 0 )

Niesenbachbrucke Austria

Hvkawaru Japan

I Y73 3 9 4

( 120)

1973-74 55x( 170)

Multif~le stayswpporting thearch dire< tly withthe aid of an aux-iliary pykm

Segment\ 19.6 It( 2 0 m) long

Mobile formspet-mittinK thrsuccessive construction of 21 11( 6 . 5 1x1) tong seg-

“,e”tS

Simple precastgirders 01 55 tt(16.8 m) spanmnde ~OIIIIIIUOU\

Continuousdouble-T \pan 0165.6 It (20 111)

Fixed

Fixed Horinmtal curva-ture of deck is R =

1092 It (332.8 m)

Formwo~-k par-ttally tufq>orted bya stay for- the firs1SC< lion betweenthe abutment andthe hrst Fpandrelcolumn. Alter-ward, ~onstru-tion by successivec antilevers by\cgments 01 I I I t(3.4 111) Ienfgh.

Rectangular two-cell box. Near thespringings, thewidth increasesItnearly from 26 to52 It (X to I6 m) to,mprwe the tat-era1 stahdttv

Hollow slab of 2 It( 0 . 6 0 m) thtc k-nes5; 5 0 I t ( I5 m)continuous span\< r,nstru<ted ,,I a\pan-by-spanmovable lalwwork

Hmgrd ‘it the twoqwingmgs of thra r c h

Schwar/waswhrtrke Switzerland 1977-79 374(114)

Akayagwa JZ3ptl 197R 4 I 3(126)

K i r k Bridge(smaller arch)

Yugoslavia 197x x00(244)

Krummharhbr-ilrke Switxrland 1976-77 407(124)

Constructrd I”

segmentc rd 20.5tt (6.25 m) length

Neckarhurg (&many I977 507( 154.4)

(:onstrurted of I’wo p”‘“llelwccessive seg- arches. each <on-ments 19.7 It (6.0 +Isting of a rectawrn) In length gular twwell box

‘fwo parallelarches. dla-phragm at thecolumns. t:acharch IS a solidr-e< tangular rib 3 6x 6.6 It (1.1 x 2.0m)

Succesive curl-tilever segments16.4 to 17.7 It (5to 5.4 m) 111 length

Constructed withmohile l.orms suchthat a completepanfzl was cast, in-

c tuding the arch.the column, andthe de< k

Rectangular \lah

Arch c onsistc of arectangular thinslab between twoCOlUmtIS

st‘lys uwtl ‘ISdiagonals ot aPratt tn,s\

ue< t‘rnp I‘Nthree-cell box

Rectanpdarthree-cell box

Double ‘I’ wthcontinuous cpnsvarymg between32.8 ‘I”1 65.6 II( IO to 20 111)

Fixed

IGxed

E‘ixed Railroad bridge

rwr,-<ell box Fixed Railroad bridge

Fixed: posslhltityot correcting thethrust at thecrown hy a hatteryot hydraulic jacks

(Same as ;tbove.for smaller arch)

FIGURE 8.41. TSecharburg Bridge, temporaq Dvwi-dag bar stays supporting cantilevered arch rib (cour-tesy of Willhelm Zellner).

FIGURE 8.42. Neckarburg Bridge, temporary Dywi-dag bar stays supporting cantilevered arch rib (cour-tesy of Willhelm Zeliner).

The trapezoidal box girders of the superstruc-ture deck were constructed behind the Singenabutment and incrementally launched “downhill”toward the Stuttgart abutment, Figure 8.43. Aclose-up of the launching nose is shown in Figure8.44. Overall girder width is 48.8 ft (14.9 m) with aconstant depth of 7.5 ft (2.3 m). Girder segmentswere cast in lengths of 65.6 ft (20 m). The lift andpush combination of hydraulic jacks (see Chapter7) launched the girder in 10 in. (0.25 m) incre-ments. To maintain deformations of the arch and

FIGURE 8.43. Neckahur-g Bridge, hudling of’ deckgirder.

FIGURE 8.44. Neckarburg Bridge, close-up oflaunching nose.

piers, resulting from the horizontal forces of theincremental launching operations, within allowablelimits, the tops of the piers were tied back to theabutments and the arch was tied back by the tem-porary stays used during the arch construction. Aninnovation introduced by Zublin on this projectwas the use of bearings for the incrementallaunching that remained as permanent bearings.Prior procedure had employed a system of tempo-rary bearings for the incremental launching andthen a transfer to permanent bearings5

8.5.3 NIESENBACK BRIDGE, AUSTRIA

This is a two-rib arch structure utilizing the freecantilever construction method for each half-arch,Figure 8.45. The arch has a span of 394 ft (120 m)with a rise of 123 ft (37.5 m). Each arch rib is atwo-cell box with exterior dimensions of 16.4 ft (5m) wide by 8.2 ft (2.5 m) deep. The roadway con-sists of a concrete slab and girder system with anoverall width of 57.7 ft (17.6 m). Although the lon-gitudinal axis of the arch is in a straight line, the

Arches Built in Cantilever

Structure during construction

Hll‘SPYlO”I Final structure

I

WJO - 590 != s&m cl

FIGURE 8.45. Niesenback Bridge, elevation, plan, and cross section, from reference 7.

roadwav it supports has a centerline radius, inplan, of 1092 ft (332.8 m).

The curved roadway structure has spans of 65.6ft (20 m) over the arch and is supported by two 3.3ft (1.0 m) square piers, one on each arch rib. Atthe arch foundations, roadway support is by a wallpier with dimensions of 4.6 ft (1.4 m) by 33.8 ft(10.3 m).

Each two-cell box arch rib is constructed by thecantilever method, using a 41 ft (12.5 m) longtraveling form. The form clamps to the precedingconstruction such that a 19.7 ft (6.0 m) segmentcan be cast. A crew of seven men was able to cast asegment on a weekly cycle.

To keep moments in the cantilevering arch to aminimum during construction, the cantilevered


portion of the arch was supported by a system ofDywidag bar stays, Figure 8.45. Stay stresses aremonitored at each stage of construction to main-tain a nearly moment-free condition in the arch.Dywidag bars used in the stays were 1 in. (26.5mm) diameter and were used because they wereeasily coupled and could be reused.’

8.5.4 KIRK BRIDGES, YUGOSLAVIA

These structures connect the mainland with theIsland of Kirk in the Adriatic Sea. In between is asmall rocky outcropping known as St. Mark, suchthat from the mainland to St. Mark is the world’slongest concrete arch with a span of 1280 ft (390m) and from St. Mark to Kirk is the seventh longestconcrete arch with a span of 800 ft (244 m), Figures1.40 and 8.46.

Because the distance between the shores of themainland and St. Mark is 1509 ft (460 m), the archsupport is partially founded in the sea, Figure 8.47.The arch reaction of approximately 15,400 tons(14,000 mt) is accommodated by the inclined pierin the sea, which takes 9900 tons (9000 mt) to therock, while the nearlv horizontal box structure

1/3.00 !

Section 1

above sea level takes the other reaction componentof 6600 tons (6000 mt).

A system of temporary stavs was used to supportthe arch as it was progressively cantilevered outfrom the springings, Figure 8.48. These temporar)stays were used as the top chord and diagonals of atemporary variable-depth Pratt truss during con-struction, Figures 8.48 and 8.49. The arch rib con-sists of a three-cell rectangular precast box, whichwas cast in segment lengths of 16.4 ft (5 m) andassembled with cast-in-place joints, Figure 8.48. .4view of the completed arch with spandrel columnsis given in Figure 8.50.

8.6 Rigid-Frame Bridges

Another bridge type that lends itself to the con-temporary segmental concept is the rigid-framebridge. Unfortunately, segmental construction hasnot often been applied to this type of structure.The reason is probably that the segmental conceptis associated with the conventional girder typebridge, and designers have given little considera-tion to applying this method to the rigid-framebridge. Hopefully, the few examples that followwill stimulate thinking about this type of structure.

Section 2

ELEVATION

FIGURE 8.46. Kirk Bridges, elevation and sections.

1 390m L I /

300 t

0 0 00~ -

, -'lo. 00

33 50 1 33 50

, 0 00- -

, -19OQ

FIGURE 8.47. Kirk Bridge, foundation detail.

383

FIGURE 8.48. Kirk Bridge, erection of first arch sec-tion.

FIGURE 8.49. Kil k Bridge, erection apploarhingcrown.

7L’O’

FIGURE 8.50. Kirk Bridge, completed arch.

FIGURE 8.51. Saint Xlichael 131 itigc, LI~‘M ot the com-pleted structure.

_- - __- _-__. .-- I-.--“.. --_ 2Tr;LO’--- --.

FIGURE 8.52. Saint Michael Bridge, partial longitudinal section

8.6.1 SAINT MICHEL BRIDGE IN TOULOUSE,FRANCE

This beautiful structure, Figure 8.51, appears as asuccession of arches with inclined legs, crossing thetwo branches of the Garonne River in the southerncity of Toulouse, France. Typical dimensions of arigid frame are presented in Figures 8.52 and 8.53.

Because the bridge replaced an obsolete struc-ture resting on masonry piers, it was possible to

construct the inclined legs on suspended scaffold-ing using temporary ties anchored to the masonrypiers before they were demolished, Figure 8.54.The longitudinal girders were cast in place be-tween the legs to complete the rigid frame. Overeach pier an expansion joint with laminated bear-ings is provided in the roadway slab, Figure 8.54.

Another view of the finished bridge is pre-sented in Figure 8.55.

FIGURE 8.53. Saint Michael Bridge, typical section.

49 4 4@oprmc bearing Q Q

‘...

‘AExtcling moaonry pier

FIGURE 8.541. Saint Michael Bridge, construction sequence at typical pier.

FIGURE 8.55. Saint Michael Bridge, finished struc- FIGURE 8.56. Briesle Maas Bridge, general view.ture.


8.6.2 BRIESLE MAAS BRIDGE, NETHERLANDS

The Briesle Maas Bridge near Rotterdam, com-pleted in 1969, is a distinctive structure with itsV-shaped piers, Figure 8.56. This bridge, crossingthe Meuse River, is situated in an area reserved forpleasure boating and recreational purposes. It wastherefore considered essential to maintain a highdegree of bridge aesthetics. Although the design isperhaps not the most economical, it was chosen tomeet the aesthetic requirements.

in this project, however, as the additional weight inthe pier segments would have increased intolera-bly. Shear stresses were maintained at an accept-able level by increased web thickness and by triaxialprestressing.

The three-span superstructure consists of a 369ft (112.5 m) center span with end spans of 264 ft(80.5 m). Transversely, the superstructure consistsof three precast single-cell boxes, joined at theirflange tips by a longitudinal closure pour andtransversely prestressed, Figure 8.57. The hollowinclined legs of the V piers are structurally con-nected to the deck structure by post-tensioning, andthe V pier is supported at its base through neo-prene bearing pads on the pile cap foundation, Fig-ures 8.58 and 8.59. The superstructure, with theexception of a few cast-in-place closure joints, iscomposed of precast segments.

At the moment that the midspan closure pour ofthe center span is consummated, the bending mo-ment at this joint is zero. With time this momentincreases, as a result of creep, to a significant per-centage of what would occur if the bridge werebuilt as a continuous structure on falsework. Pre-stressing to accommodate both conditions cannotbe given maximum eccentricity, and it becomesboth difficult to execute and expensive. .4 consid-erable amount of prestressing was saved byeliminating the condition of zero stress at closureand therefore preventing creep. This was accom-plished by inducing an upward reaction undersegments 7 and 72, Figure 8.59, after joint closure.Simultaneously with the increase of these reactionforces, prestressing tendons in the central spanwere stressed. Upon completion of the end spansthe induced forces were released automatically byprestressing the end spans.

Shear forces, mainly concentrated in the webs, Segments were produced at an existing castingnormally are transferred to piers or columns by a yard 68 miles (110 km) from the bridge site. Adiaphragm. Prefabrication prevented this solution long-line precasting bed (see Figure 11.37) was

as-25 485 3525 i 485 Lc.75 /

C R O S S S E C T I O N

FIGURE 8.57. Briesle Maas Bridge, transverse cross section.

LONGITUDINAL SECTION WITH CABLE PROFILE

FIGURE 8.58. Briesle Maas Bridge, longitudinal section with tendon profile.

A= Steel frameB= JacksC= Rubber bearing padsD= lolntsE = Counter weight

F = JointG = Temporary supportH = ScaffoldingJ = Joint

Rigid-Frame Bridges 387

FIGURE 8.59. Briesle Maas Bridge, erection sequence.

used with a length equal to a half-span-that is,one cantilever. Three sets of segment forms wereemployed to cast a total of 234 segments, averaging78 reuses. Segments were transported to thebridge site by barge.

The various stages of erection are indicated inFigure 8.59. A special structural steel frame wasused to position the inclined precast hollow-boxlegs of the piers and to support the seven precastroadway girder segments before casting the jointsat the corners of the delta pier portion of thestructure. This frame was also utilized to balancethe pier during erection of the remainder of theroadway girder segments and to adjust, by meansof jacks, the loads in the inclined legs of the pierduring various stages of erection.

Upon completion of the balanced cantilevererection about both piers, temporary supportswere placed under segments 7 and 72 (the extremeend segments of the partially completed end spans)so that the temporary steel frames under the pierscould be removed. At this point both halves of thestructure were in an unstable equilibrium condition,therefore, counterweights were placed over thesupported segments, Figure 8.59, to prevent thehalf-structures from toppling over.

Jacks atop the temporary supports were used toadjust the position of the bridge halves with respectto one another and to induce the upward verticalreaction forces previously discussed. Also, dif-ferences in elevation between the three box girders

were adjusted by these jacks. After casting thecenter-span closure joint and stressing in thecenter span, the remaining segments in the endspans were placed on falsework, Figure 8.60; clo-sure joints were cast; and longitudinal and trans-verse prestressing was completed.

All segments in the balanced cantilever portionof the structure were placed by a floating crane.Because of the crane’s small reach, it could notplace the last five segments needed to complete theend span. Therefore, it placed them on a smalldolly installed on top of the falsework, whichwould roll them into their final positions. To avoiddismantling the falsework after completing onegirder and reinstalling it under the next, it wasconstructed so that it could be lowered and movedtransversely into position, Figure 8.60.

A close-up of the piers of the finished structureis shown in Figure 8.61.

8.6.3 BONHOMME BRIDGE, FRA.VCE

The Bonhomme Bridge over the Blavet River inBrittany, France, was designed and built between1972 and 1974, Figure 8.62. This three-spanslant-leg portal-frame bridge has a center span of481 ft (146.7 m) and end spans of 223 ft (67.95 m),Figure 8.63. The span between the foundations ofthe slant legs is 611 ft (186.25 m). A tubular steelframework was used to support the slant legs tem-porarily until closure at midspan, Figures 8.64 and

Concrete Segmental Arches, Rigid Frames, and Truss Bridges

I -k--J smcu A-.

FIGURE 8.60. Briesle Maas Bridge, erection falsework for last five segments in the endspan.

8.65. This structure was built by the cast-in-placebalanced cantilever method.

For adjusting the geometry of the bridge, flatjacks were placed under the legs and at midspan. Adetail of the adjusting jacks placed on top of thetemporary support is shown in Figure 8.66. Flatjacks and sand boxes were used both to adjustthe geometry of the bridge before closure wasachieved at midspan and later to release the energystored in the legs of the temporary supports, whichwere loaded with the full weight of the bridge.

FIGURE 8.61. Briesle Maas Bridge, close-up \iew ofV piers.

FIGURE 8.62. Ronhomme Bridge over Blavet River.

& O R I E N T

L 282.60KERVIGNA&

N 67.95 146.70 67.95

/

FIGURE 8.63. Bonhomme Bridge, elevation.

TW'FII FRS FOR CIP CONSTRUCTlONA

FIGURE 8.64. Bonhomme Bridge, construction stages.

+ + + + + + +

\

+ ++ + +

++ +i

FIGURE 8.65. Bonhomme Bridge, temporary support389


CONI’RFTF CAF

_. ,.;

13'- 5 'i

FIGURE 8.65. (Continued)

The scheme is a very satisfactory one in terms ofboth the aesthetics of the finished structure andsimplicity of construction. However, it may be usedonly when site conditions allow the foundations ofthe temporary supports to be established safely at areasonable cost. Figure 8.67 shows the temporarysupports during the balanced cantilever construc-tion of the bridge.

8.6.4 MOTORWAY OVERPASSES IN THEMIDDLE EAST

The use of precast segmental construction for theAlpine Motorways in southern France was de-scribed in Section 3.15. It was shown how massproduction could be applied to the construction ofa large number of similar overpasses.

This experience was repeated recently in a mid-dle eastern country for the construction of 17overpass structures over an existing freeway, Fig-ure 8.68. To minimize disturbance of freewaytraffic, it was felt that a three-span rigid-framestructure with inclined legs would be an attractivesolution.

Dimensions are shown in Figures 8.69 and 8.70.The total deck length of 252 ft 3 in. (77 m) is di-vided into 32 precast segments for each of the twinbox girders. Deck width of the overpasses is either36 ft (11 m) or 46 ft (14 m). The same box section isused for all structures, and the cast-in-place lon-gitudinal closure strip varies as required.

The slant legs are precast in the same plantwhere the deck segments are produced. The typi-cal erection sequence is shown in Figure 8.71. Atemporary bent founded at the edge line of thenew freeway is used to place and adjust the precastlegs on either side of the bridge. Segments areplaced in balanced cantilever from the special seg-ment located atop the slant legs. A light temporarybent in the short side spans is used to reduce thebending moment in the slant legs during construc-tion.

After completion of the deck and removal of alltemporary supports, the structure is in effect atwo-hinged arch with vertical restraints at bothends. The bridges were analyzed for earthquakeand large thermal variation loads (seasonal varia-tion of 120°F and temperature gradient betweentop and bottom flange of 18°F).

Figure 8.72 shows a detailed view of the inclinedlegs and the temporary support during construc-tion.

b. ,h

FIGURE 8.66. Bonhomme Bridge,details of bearing of concrete can-tilever on temporary support.


FIGURE 8.67. Honl~ornrne Bridge, during cantileverconstruction.

FIGURE 8.68. Motorway Overpass Frames, generalview.

8.7 Truss Bridges

As with rigid frames, segmental construction hasseldom been applied to truss bridges. Once againthe designer must realize that the principles ofsegmental construction, together with imagination,can be applied to bridge structures other than theconventional girder bridge.

+----- I I--- B: : ‘--:

I / //j,/ : r] ;-y $1

j / 1Plain

c o n c r e t e, 19’-0” ,9’-0”

FIGURE 8.70. Motorway Overpass Frames, cross sec-tion and elevation of inclined legs.

8.7.1 RETROSPECT ON CONCEPTS FOR CONCRETETRUSS BRIDGES

Trusses were used in all long-span cantilever steelbridges, and it was logical to conceive of the appli-cation of this type of structure to prestressed con-crete. An interesting example of such an approachis presented in Figure 8.73, in which an origi-nal sketch made in 1948 by Eugene Freyssinet forthe design of a precast prestressed concrete trussis reproduced. The studies were applied to twospecific examples:

149.3I 51’-6” A

3Segments-8’0” I “: II I

FIGURE 8.69. Motorway Overpass Frames, longitudinal section.

Truss Bridges 393

FIGURE 8.71. Motorway Overpass Frames, erection sequence.(a) Stage 1. (b) Stage 2. (c) Stage 3. (d) Stage 4.

6

FIGURE 8.72. Motorway Overpass Frames, detail ofinclined leg and temporary support.

A bridge over the Hanach River near Algiers,Algeria, with a clear span of 400 ft (123 m), Figures8.74 and 8.75.A major crossing of the Rhine River at Pfaffen-dorf, Germany, with a main span of 600 ft (180 m)

These studies were very encouraging from theviewpoints of both economy of materials andsimplicity of construction. The deck was to be en-tirely precast, with members assembled by pre-stressing. Construction would proceed in balancedcantilever from the main piers until reachingmidspan closure, where adjustment of the deckgeometry and loads in the members was providedby jacks.

FIGURE 8.73. Original sketch of E. Freyssinet for a concept of prestressed precastconcrete truss (1948).

__ ELEVATION -

FIGURE 8.74. Concept of a truss bridge.

l/2 COUPE A-A l/2 COUPE B-B

FIGURE 8.75. Concept of a truss bridge.

The use of I girders at 7 ft (2 m) spacing for theprecast deck would not be considered today as theoptimum design. One of the authors, who was in-volved in the studies with E. Freyssinet, remembersalso that many technological problems such as theconnection details between diagonals and chordswere not completely solved.

Neither of these two designs reached the con-struction stage, and the concept was rapidly for-gotten before its potential could be objectively as-certained.

Oddly enough, the designers of steel structuresfollowed a similar path. Abandoning prematurelythe concept of truss structures, which had allowedsuch outstanding structures as the Firth of ForthBridge to be built all over the world, they turned toweb girder structures and closed box sections withall the critical problems they entailed, such as elas-tic stability. Perhaps it is time to reassess somemajor design approaches in both steel and concretefor very long spans.

8.7.2 MANGFALL BRIDGE, AUSTRIA

The Mangfallbriicke in Austria, Figure 8.76, onthe autobahn between Munich and Salzburg wasconstructed in 1959. This structure is perhaps bestdescribed as a large box girder with the webs beinga trusswork. Total length is 945 ft (288 m) fromabutment to abutment; the center span is 354 ft(108 m) with side spans of 295.5 ft (90 m). It wasconstructed as cast-in-place segmental using thefree cantilever method. However, it, was not bal-

anced cantilever, as construction started at oneabutment and proceeded to the opposite abutmentby progressive placement. Temporary interme-diate piers were used as required to reduce thecantilever stresses.

Figure 8.77 shows an interior view. The lowerflange is used as a walkway for pedestrians and forbicycles. The railing in the center surrounds anopening in the bottom flange where stress condi-tions do not require the concrete area. Figure 8.78is an interior view looking through one of the flooropenings, and Figure 8.79 is another interior view.

8.73 RIP BRIDGE, AUSTRALJA

The recently completed Rip Bridge, Figure 8.80,north of Sydney, Australia, has a center span of

FIGURE 8.76. Mangfallbriicke, general view.


FIGURE 8.77. hl;~t~gf;llIbt.ucke, interim view showingtrusswork.

FIGURE 8.78. Mangfallbl.iicke, interior view lookingthrough floor opening.

FIGURE 8.79. M,tngfallbrticke, general intertor view.

FIGURE 8.80. Rip Bridge, general view.

600 ft (182.88 m). The identical cantilever trusses,which sit symmetrically on either side of the cross-ing, reach out 240 ft (73.56 m) toward each otherto support a 122 ft (37 m) drop-in simple span attheir extremities, Figure 8.8 1.

The erection scheme is illustrated in Figure 8.82.Note that cable stays were used as diagonal mem-bers during construction to support the arch seg-ments. Temporary falsework bents were used ateach panel point of the truss on the landward sideof the main piers. Precast concrete elements weredelivered from a precasting plant some 80 miles(130 km) from the site.

Each panel of the lower chords of the truss wasassembled from five precast I-shaped elementswith a 1 ft (0.3 m) longitudinal pour strip betweenthe flange tips. Similarly, the upper chord was as-sembled from five rectangular two-cell precastmembers. Erection of one of the lower chordmembers is shown in Figure 8.83. The exterior twoI-shaped lower chord members are supported bythe diagonal stays, while the interior three ele-ments of the lower chord are supported by a trans-verse beam arrangement from the exterior twoduring construction.

Each diagonal member was assembled from lon-gitudinally split halves, which, when brought to-gether, encase the diagonal prestress tendon stays,incorporating them into the structure by concretepoured in place between the two halves. The upperchord or deck members are erected after the verti-cal members along with temporary falsework tosupport the deck panels, while the cast-in-placeconcrete is placed between the deck elements andtransversely prestressed.

Truss Bridges 397

FIGURE 8.81. Rip Bridge, elevation and cross sections.

Prestress cable tosupport lower member

fAbutment

I. ,

Locat ion of

<- ggri.n

FIGURE 8.83. Rip Bridge, erection of knver chord.

The deck performs as a prestressed concretetension member. As construction proceeds, addi-tional prestress is progressively added to ensurethat the deck remains in compression.

8.7.4 CONCEPT FOR A CROSSING OF THEENGLISH CHANNEL

Certain projects for crossings, such as of the Eng-lish Channel between France and Great Britain,the Straits of Messina, and even the Straits of Gi-braltar, have exerted a powerful fascination on theminds of the great engineers of this century.

FIGURE 8.82. Rip Bridge, erection sequence.

FIGURE 8.84 . E‘t-eyssinet’h c-oncept of‘ preconfinetl concrete at-ch crossing the EnglishChannel with a set-ies of‘ 2000 f’t (612 111) slxtns.

Refmences 399

Eugene Freyssinet was no exception, and hespent the last years of his long professional careerstudying the crossing of the English Channel with aseries of 2000 ft (612 m) long prestressed concretespans. The many worthwhile ideas contained inthis concept are not likely to be developed soon, oreven by the turn of the century.

Figure 8.84 presents an elevation of a typical2000 ft (612 m) span, which was contemplated as aprestressed concrete composite truss. Major mem-bers of the truss were not of conventional pre-stressed concrete, because such high stresses had tobe accepted to keep the weight of the span withinacceptable limits. A new material to be used forthat purpose had occupied Freyssinet’s mind forseveral years and had even been laboratory testedfor confirmation of the concept. When a concretemember is completely confined in an envelope thatcreates permanently biaxial transverse compressivestress, it will resist safely much higher stress than ifsubjected to a monoaxial stress or reinforced con-ventionally with untensioned transverse reinforc-ing (such as spirals in a circular column).

From a technological point of view, the perma-nent active restraint creating the biaxial transversecompressio:l is easily achieved in a member thathas a circular cross section by confining it in ahigh-strength steel pipe or within a continuous spi-ral of prestressing steel wires, which are pre-stressed at the time the concrete is cast.

This material, which could be called “pre-confined concrete,” has extraordinary propertiessuch as total absence of brittleness and a capability

to sustain several times as much longitudinal com-pressive stress as a reinforced concrete memberwithout excessive strains, provided it is initiallyloaded to offset the initial strain.

Such a project and such a material could not bedeveloped in a short period of time. They arementioned here at the close of this chapter as aconceptual heritage, which it is our duty to makefunctional.

References

1. E. Freyssinet, “Largest Concrete Spans of theAmericas-Three Monumental Bridges Built inVenezuela,” Cizd Engineering-ASCE, March 1953.

2 . J e a n Muller, “ L a r g e s t C o n c r e t e S p a n s o f t h eAmericas-How the Three Bridges Were De-

signed,” Civil Engineering-ASCE, March 1953.

3 . Robert Shama, “Largest Concrete Spans of the.Americas-How They Were Built.” C/zlil Et/g/tff’f’r-

rng--AXE, March 1953.

4. Anon., “New Bridge over Parramatta River atGladesville,” Main Roaak, Journal of the Department

of Main Roads, New South Wales, December 1964.

.

5. Anon., “Talbriicke Rottweil-Neckarburg,” Zublin-Rundschau, Heft 7/8, Dezember 1976, Stuttgart,Germany.

6. “Arch Slipformer Shuns Ground Support to CrossValley,” Engineering LXrews-Record, June 1, 1978.

7. Anon., “Niesenbachbriicke, Bogen im Freien Vor-

bau,” Austria 1970-74, FIP Congress 1974, New

York.

9Concrete Segmental Cable-Stayed Bridges

9.1 INTRODUCTION

9.1.1 Historical Review

9.1.2 Advantages of Concrete Cable-Stayed Bridges9.1.3 Structural Style and Arrangement

9.2 LAKE MARACAIBO BRIDGE, VENEZUELA

9.3 WAD1 KUF BRIDGE, LIBYA

9.4 CHACOlCORRIENTE.5 BRIDGE, ARGENTINA9.5 MAINBRiiCKE, GERMANY

9.6 TIEL BRIDGE, NETHERLANDS

9.1 Introduction

The concept of supporting a beam or bridge by in-clined cable stays is not new, and the historicalevolution of this type of structure has been dis-cussed in the literature.‘-‘j Although the modernrenaissance of cable-staved bridges is said to havebegun in 1955, with steel as the favored material,in the last two decades a number of cable-stayedbridges have been constructed using a reinforcedor prestressed concrete deck system. In recentyears several concrete cable-stayed bridges havebeen built in the long-span range. In at least fourcurrent projects, alternative designs in concreteand steel have been prepared for competitive bid-ding. Cable-stayed bridges are extending the com-petitive span range of concrete bridge constructionto dimensions that had previously been consideredimpossible and reserved for structural steel. Todate, approximately 2 1 concrete cable-stayedbridges have been constructed, and others areeither in design or under construction. A tabularsummary of concrete cable-stayed bridges is pre-sented in Tables 9.1 and 9.2.

4 0 0

9.7 PASCO-KENNEWICK BRIDGE, U.S.A.

9.8 BROTONNE BRIDGE, FRANCE9.9 DANUBE CANAL BRIDGE, AUSTRIA9.10 NOTABLE EXAMPLES OF CONCEPTS

9.10.1 Proposed Great Belt Bridge, Denmark

9.10.2 Proposed Dame Point Bridge, U.S.A.9.10.3 Proposed Rock-A-Chucky Bridge, U.S.A.

REFERENCES

9.1.1 HISTORICAL REVIEW

Since the beginning of the cable-stay renaissance in1955, whether for technical or other reasons,structural steel has been the preferred construc-tion material. In 1957, however, considerable ex-citement was generated when Prof. RiccardoMorandi’s prize-winning design of a prestressedconcrete 1312 ft (400 m) center span cable-stayedbridge for the Lake Maracaibo crossing was an-nounced. Regrettably the Lake Maracaibo Bridgewas not constructed as originally conceived. Themodified structure, built in 1962, is generally con-sidered to be the first modern cable-stayed bridge.However, the Lake Maracaibo Bridge was pre-ceded by two little-known concrete cable-stayedstructures.

The first concrete structure to use cable stays wasthe Tempul Aqueduct crossing the GuadaleteRiver in Spain. ’ Designed by the famous Spanishengineer, Prof. Torroja, who has introduced manyoriginal concepts in prestressed concrete, thisstructure has a classical three-span symmetricalcable-stayed bridge configuration with two pylons.

89

1 0111 21 31 41 51 6171 81 9202 122232425262728

Zntroduction

TABLE 9.1. Concrete Cable-Stayed Bridges-General Data

401

Bridge Location Type Spans (ft)d Year Completed

Tempul Guadalete River, SpainBenton City Yakima River, Wash., U.S.A.Lake Maracaibo VenezuelaDnieper River Kiev, U.S.S.R.Canal du Centre Obourg, BelgiumPolcevera Viaduct Genoa, ItalyMagliana R o m e , I t a l yDanish Great Belr DenmarkDanish Great Belt” DenmarkPretor ia Pretoria, S. AfricaBarwon River Geelong, AustraliaMount Street Perth, AustraliaWadi Kuf LibyaRichard Foyle Londonderry, N. IrelandMainbrticke Hoechst, West GermanyChacolCorrientes Parana River, ArgentinaRiver Waal Tiel, HollandBarranquilla Barranquilla, ColumbiaDanube Canal Vienna, AustriaKwang Fu TaiwanPont de Brotonne Normandy, FranceCarpineto Province Poetenza, ItalyPasco-Kennewick State of Wash., U.S.A.M-25 Overpass Chertsey, EnglandRuck-A-Chucky’ Auburn, California, U.S.A.Dame Poinr Jacksonville, Florida, U.S.A.East Huntington” East Huntington, W.Va., U.S.A.Weirton-Steubenville’ Weirton, W.Va., U.S.A.

Aqueduct 66- 198-66 1925Highway [email protected]@57.5 1957Highway 525-5@771-525 1962Highway 216.5-472-2 16.5 1963Pedestrian 2@220 1966Highway 282-664-689-460 1967Highway 476-176 1967Highway & rail multispans 1132 Delayed by fundingHighway & rail multispans 1148 Delayed by fundingPipe 2@93 1968Pedestrian 180-270-180 1969Pedestrian 2e116.8 1969Highway 320-925-320 1971Highway 230-689 Project abandonedHighway & rail 485.6-308 1972Highway 537-803.8-537 1973Highway 312-876-312 1974Highway 228-459-228 1974Highway 182.7-390-182.7 1974Highway 220-440-440-220 1977Highway 471-1050-471 1977Highway 100-594-100 1977Highway 406.5-981-406.5 1978Rail 2e180.5 1978Highway 1300 Design completedHighway 650-1300-650 Design completedHighway 158-300-900-608 Under constt-uctionHighway 820-688 In design

“Design by White Young and Partners.bDesign by Ulrich Finsterwalder.“Alternative design with structural steel.1 ft = 0.305 m.

The stays were introduced to replace two piers thatwere found to be too difficult to construct in deepwater. Thus, the stays were introduced to provideintermediate support in the main span.

On July 5, 1957, a stayed structure crossing theYakima River at Benton City, Washington, wasopened to traffic. Designed by Homer M. Hadley,the structure has a total length of 400 ft (122 m)with a center span of 170 ft (51.9 m) flanked oneach side by two continuous spans of 57.5 ft (17.53m) each. A 60 ft (18.3 m) central drop-in span of 33in. (0.84 m) deep steel beams is supported bytransverse concrete beams, supported in turn bystructural steel wide-flange stays. Continuous lon-gitudinal concrete beams comprise the remainderof the structure and receive support at their ex-tremity, in the center span, from the transverseconcrete beams and steel stays.4*8

In the more than half-century that has elapsedsince Torroja’s Tempul Aqueduct, 2 1 cable-stayedbridges have been constructed (Table 9.1). Thir-teen, or 62%, of these structures have been con-

strutted in the past decade. In the last five yearsnine have been completed, representing 43% ofthe total. Within the last three years the span of1000 ft (300 m) has been exceeded, and a currentdesign contemplates a span of 1300 ft (400 m). Ithas taken almost a quarter-century to reach a spancontemplated by Prof. Morandi in his original de-sign concept for the Lake Maracaibo Bridge. Bethat as it may, it is obvious from the statistics that inrecent years the concrete cable-stayed bridge hasbeen accepted as a viable structure.

9.1.2 ADVANTAGES OF CONCRETE CABLE-STAYEDB R I D G E S

As engineers, we are aware that no particular con-cept or bridge type can suit all environments, con-siderations, problems, or site conditions. Theselection of the proper type for a given site and setof circumstances must take into account manyparameters. The choice of material, in addition to

4 0 2 Concrete Segmental Cable-Stayed Bridges

TABLE 9.2. Concrete Cable-Stayed Bridges-Dimensional Parameters

Bridge

P)hlHeight Pylon Span-Above Height- Deck Girder to- Girder

Stay No. stay Deck to-Span Width Depth Depth ConstructionPlanes Stays Arrangement (f0 R a t i o ’ cf.0 (ft) Ratio” Typed

I T e m p u l 2 12 Benton City 2 13 Lake Maracaibo 2 14 Dnieper River 2 35 Canal du Centre 2 46 Polcevera Viaduct 2 17 Magliana 2 18 Danish Great Belt” 3 29 Danish Great Belt” 2 1 6

1 0 Pretor ia 2 2I1 Barwon R i v e r 2 21 2 Mount Street 1 2I3 Wadi K u f 2 11 4 River Foyle 1 21 5 Mainbrticke 2 1 31 6 Chaco/Corrientes 2 21 7 River Waal 2 21 8 Barranquilla 2 119 Danube Canal 2 120 Kwang Fu 2 221 Pont de Brotonne 1 2 122 Carpineto 2 123 Pasco-Kennewick 2 1 824 M-25 Overpass 2 225 Ruck-A-Chuck) 2 2026 Dame Point 2 2 127 East Huntington 2 1511628 WeIrton-Steubenville 2 24

1 4 . 1 0.07

RadiatingRadiating

-

139.49565.6

148111.5

0.180.200.300.210.23

RadiatingHarpRadiatingFan

-

HarpHarpRadiatingRadiating

315 0.2741 0.4443 0.1649 0.42

177.5 0.19360 0.52172 0.38155 0.19151.8 0.17

-

RadiatingFan

-

0.15

RadiatingFan

52.5-

23194.75

2207 1

-

0.220.160.220.39

Harp 302 0.23Radiating 279.4 0.31Radiating 333.2 0.41

57-

5.87597951.75’461 5 . 86

15.7542.598

101.547

1 0 13751.8676341.3’79.83954

105.7541

103.5

6.9 28.73.25 52.3

16.4 46.74.8 98.751.94 113

1 5 469.8-13.2 3623.5 48

2.95 3903 3 17 38.52 58.4

11.5-23 7011.5 608.5 57

11.5 7011.5 761 0 469.2 42.5

12.5 8411.5 52

7 1409 208.5 153

5 - 6 2605 1808.5 96.5

CIPCIPCIP/PC d-i-sP CP CCIP/PC d-i-sCIP/PC d-i-sPC segmentsCIP segmentsCIPCIPCIPCIPiPC d-i-sPC segmentsCIPPC/CIP d-i-sPC and CIPCIP segmentsPC and CIPP CPC and CIPCIPPC segmentsCIPPC segmentsCIP and PCCompositeComposite

“Design by White Young and Partners.hDesign by Ulrich Finsterwalder.( See Table 9.1 for major span dimensions.“CIP = cast-in-place, PC = precast, d-i-s = drop-in-span.’ Form hyperbolic paraboloid in space.‘Per single-cell box.1 ft = 0.305 m.

material properties, depends on availability and 2.the prevailing economics at a particular time aswell as the specific location of the site. The processof weighting and evaluating these parameters forvarious types of bridges under consideration is 3.certainly more an art than a science.

In evaluating a concrete cable-stayed bridge, thedesigner should be aware of the following advan-tages:

1. The main girder can be very shallow with re-spect to the span. Span-to-girder-depth ratios 4.vary from 45 to 100. With proper aerodynamicstreamlining and multistays the deck structurecan be slim, having span-to-depth ratios of 150to 400, and not convey a massive visual impres- 5 .sion.

Concrete deck structures, by virtue of theirmass and because concrete has inherentlyfavorable damping characteristics, are not assusceptible to aerodynamic vibrations.The horizontal component of cable-stay force,which causes compression with bending in thedeck structure, favors a concrete deck struc-ture. The stay forces produce a prestress forcein the concrete, and concrete is at its best incompression.The amount of steel required in the stays iscomparatively small. A proper choice of heightof pylon with respect to span can yield an op-timum solution.gLive-load deflections are small because of thelive-load-to-dead-load ratio, and therefore

Introduction 403

concrete cable-stayed bridges are applicable torailroad or mass-transit loadings.

6. Erection of the superstructure and cable staysis relatively easy with today’s technology ofprestressing, prefabrication; and seg&&talcantilever construction.

9.1.3 STRUCTURAL STYLE AND ARRANGEMENT

Many of the concrete cable-stayed bridges havebeen designed by Morandi or have been stronglyinfluenced by his style. Commencing with the LakeMaracaibo Bridge, of the 12 bridges constructed,excluding pedestrian and pipe bridges (see Table9.1), six have been designed by Morandi, Figures9.1 through 9.6. A third prize winner in the 1967Danish Great Belt Bridge Competition was theMorandi-style design proposed by the English con-sulting firm of White Young and Partners, Figure9.7. The ChacoKorrientes Bridge, Figure 9.8, verymuch resembles the Morandi style.

FIGURE 9.1. Lake Maracaibo Bridge, general view,from reference 11 (courtesy of Julius Berger-BauboagAktiengesellschaft).

FIGURE 9.2. Polcevera Creek Bridge, general view.

FIGURE 9.3. Magliana Viaduct (courtesy of L’Indus-tria Italiana de1 Cemento).

FIGURE 9.4. Wadi Kuf Bridge, general consrructionview (courtesy of Prof. R. Morandi). ’

FIGURE 9.5. Barranquilla Bridge (courtesy of L. AGarrido).

404 Concrete Segmental Cable-Stayed Bridges

FIGURE 9.6. Carpineto Viaduct (courtesy of L’In-dustria Italiana de1 Cemento).

FIGURE 9.7. Danish Great Belt Bridge, artist’s rend-ering (courtesy of White Young and Partners).

FIGURE 9.8. ChacoiCorr ientes Bridge, general \iew,from reference 13 (courtesy of Normer Gray).

These structures, with the exception of the Ma-gliana, Barranquilla, and Carpineto bridges, aretypified by the A-frame pylon positioned in theplane of the stays and an auxiliary X frame or in-clined struts to support the deck structure at thepylon. They are statically determinate systems so asto preclude any possible damage from differen-tial settlements of the bridge piers and pylons orfrom light seismic shocks.

A simple schematic of the structural scheme isshown in Figure 9.9, which consists of a series ofindependent balanced systems, each carried by anindividual pier and pylon. These systems are thenconnected by drop-in girders, which are simplespan girders spanning between independent sys-tems.‘O The cantilever girder is supported at twopoints (C and D) by a pier system and elasticaflysupported at two points (B and E) by the cablestays, thus producing a three-span girder withcantilevers on each side. The stays are supportedby a pylon portal frame that is independent of thepier system supporting the girder.

Another entry in the 1967 Danish Great BeltCompetition by Ulrich Finsterwalder, of the Ger-man firm Dyckerhoff 8c Widmann, deviated fromthe Morandi style and was awarded a second prize.Finsterwalder’s design proposed a multiple-span,multistay system using Dywidag bars for the stays,Figure 9.10. The deck was envisioned as being con-structed by the cast-in-place balanced cantilever

FIGURE 9.9. Schematic of Morandi-style structuralscheme, from reference 10 (courtesy of the AmericanConcrete Institute).

FIGURE 9.10. Da&h Gre,lr Belt Bridge, .I1 list’\ rrnd-ering (courtesy of Ulrich Finsterwalder).

Lake Maracaibo Bridge, Venezuela 405

segmental method, each segment being supportedby a set of stays. This concept was later to be con-summated in the Main Bridge and in the design ofthe Dame Point Bridge.

The choice of geometrical configuration andnumber of stays in a cable-stayed bridge system issubject to a wide variety of considerations. If cablestays are few, they result in large stay forces, whichrequire massive anchorage systems. A relativelydeep girder is required to span the large distancebetween stays, producing span-to-depth ratios vary-ing from 45 to 100 (see Table 9.2). Dependingupon the location of the longitudinal main girderswith respect to the cable-stay planes, large trans-verse cross girders may be required to transfer thestay force to the main girder.

A large number of cable stays, approaching acontinuous supporting elastic media, simplifies theanchorage and distribution of forces to the girderand permits the use of a shallower girder, withspan-to-depth ratio varying from 150 to 400 (seeTable 9.2). The construction of the deck can beerected roadway-width by free cantilever methodsfrom stay to stay without auxiliary methods orstays. If the depth of the roadway girder can bekept at a minimum, the deck becomes, more orless, the bottom chord of a large cantileveringtruss; it needs almost no bending stiffness becausethe inclined stays do not allow any large deflectionsunder concentrated loads.”

In the 55 years since Torroja’s Tempul Aque-duct the concrete cable-stayed bridge has evolvedfrom basically a statically determinate structurewith one stay on each side of the pylon to ahighly indeterminate system with multistays. Asdemonstrated by the Danish Great Belt BridgeCompetition, the Pasco-Kennewick Bridge, andthe Pont de Brotonne, spans of approximately1000 ft (300 m) are practical and have been ac-complished. The practicality of spans of 1300 ft(400 m) is demonstrated by the Dame PointBridge, and spans approaching 1600 ft (500 m) areconsidered technically feasible. Leonhardt” hasprojected that with an aerodynamically shapedcomposite concrete and steel deck a span of 2300 ft(1500 m) can be achieved. With today’s technologyof prefabrication, prestressing, and segmentalcantilever construction, it is obvious that cable-stayed bridges are extending the competitive spanrange of concrete bridges to dimensions that hadpreviously been considered impossible and int.o arange that had previously been the domain ofstructural steel. This technological means exist;they only require implementation.

9.2 Lake Maracaibo Bridge, Venezuela

This bridge, Figure 9.1, has a total length of 5.4miles (8.7 km). Five main navigation openings con-sist of prestressed concrete cable-stayed structureswith suspended spans totaling 771 ft (235 m). Thecantilever span is supported on four parallel Xframes, while the cable stays are supported on twoA frames with a portal member at the top. There isno connection anywhere between the X and Aframes, Figure 9.11. The continuous cantilevergirder is a three-cell box girder 16.4 ft deep by 46.7ft wide (5 m by 14.22 m). An axial prestress force isinduced into the girder as a result of the horizontalcomponent of cable force, thus, for the most part,only conventional reinforcement is required. Ad-ditional prestress tendons are required for nega-tive moment above the X-frame support and thetransverse cable-stay anchorage beams. l1

The pier cap consists of the three-cell box girderwith the X frames continued up into the girder toact as transverse diaphragms, Figures 9.12 and9.13. After completion of the pier, service girderswere raised into position to be used in the con-struction of the cantilever arm. Owing to the addi-tional moment, produced during this constructionstage by the service girder and weight of the can-tilever arm, additional concentric prestressing wasrequired in the pier cap, Figure 9.13. To avoidoverstressing of the X frames during this opera-tion, temporary horizontal ties were installed andtensioned by hydraulic jacks, Figures 9.13 and9.14.

FIGURE 9.11. Lake Maracaibo Bridge, pier cap withX frames, from reference 11 (courtesy of JuliusBerger-Bauboag Aktiengesellschaft).

IL I I II

FIGURE 9.12. Lake Maracaibo Bridge, main span tower and X-f’rames, fromreference 11 (courtesy of Julius Berger-Bauboag Aktiengesellschaft).

II---,

Worklnq ’ \ \ /I I I

Service qirder for

FIGURE 9.13. Lake Maracaibo Bridge, pier cap of a main span and servicegirder, from reference 11 (courtesv of Julius Berger-Bauboag Aktiengesell-shaft).

406

Wadi Kuf Bridge, Libya 407

FIGURE 9.14. Lake Maracaibo Bridge, brace mern-bers bear against X frames after being tensioned by hy-draulic ,jacks, from ref‘e rence 11 (courtesv of’ JuliusBerger-Bauboag Aktiengesellschaft).

In the construction of the cantilever arms, spe-cial steel trusses (service girders) were used forformwork. They were supported at one end by thecompleted pier cap and at the other end by aux-iliary piers and foundations, as shown in Figure9.15.

The anchorages for the cable stays are located ina 73.8 ft (22.5 m) long prestressed inclined trans-verse girder. The reinforcing cages for thesemembers were fabricated on shore in a positioncorresponding to the inclination of the stays. They

FIGURE 9.15. Lake Maracaibo Bridge, placing ser-vice girder for forming cantilever girders, from refer-ence 11 (courtesy of Julius Berger-Bauboag Ak-tiengesellschaft).

weighed 60 tons and contained 70 prestressingtendons, Figure 9.16. The cable stays are housed inthick-walled steel pipes, Figure 9.1’7, which werewelded to steel plates at their extremities and wereencased in the anchorage beam. A special steelspreader beam was used to erect the fabricatedcage in its proper orientation. The suspendedspans are composed of four prestressed T sections.

9.3 Wadi Kuf Bridge, Libya

The Wadi Kuf Bridge in Libya, designed by Prof.Morandi, consists of two independent balanced

FIGURE 9.16. Lake >fal-acaibo Bridge, fabrication of anchorage beam, from reierence11 (courtesy of Julius Berger-Bauboag Aktiengesellschaft).


FIGURE 9.17. L&e hla~.rc&o BI idge, bousing forcable stays, from reference 11 (courtesy of JuliusBerger-Bauboag Aktiengesellschaft).

cable-stay systems having their ends anchored tothe abutment by a short hinge strut. The cable-staysystems are connected by a simply supporteddrop-in span, Figure 9.4.

This structure consists of only three spans. Thecenter span is 925 ft (280 m) long and the two endspans are each 320 ft (97.5 m), for a total length of1565 ft (475 m). The simply supported drop-incenter portion of the main span consists of threedouble-T beams 180 ft (55 m) in length; each beamweighs approximately 220 tons (200 mt).12

The A-frame towers are 459 ft and 400 ft (140and 122 m) high and the roadway deck is 597 (182m) above the lowest point of the valley beneath thestructure. l2 The superstructure is a single-cell boxgirder that varies from 13 ft (4.0 m) to 23 ft (7.0 m)at the pylons. The single-cell box is 24 ft (7.4 m)wide and with cantilever flanges forms a 42.7 ft (13m) deck.

The contractor made good use of travelingforms to construct the box girder and deck, usingthe balanced cantilever technique to build on bothsides of the pylons at the same time. Travelingforms were used because extreme height anddifficult terrain made other conventional con-struction methods impossible or too costly. Thedeck was constructed by progressive cast-in-placesegments, attached to the previously completedsegments by means of temporary prestress ties andsubsequent permanent post-tensioning Dywidagbars. The procedure adopted required temporarycable stays to support the cantilever arms duringthe construction sequence as the superstructureprogressed in both directions from the pylon.When the superstructure extended sufficiently, thepermanent stays were installed, and the structurewas completed in the same manner.

9.4 ChacolCorrientes Bridge, Argentina

The ChacoKorrientes Bridge (also referred to asthe General Manuel Belgrano Bridge) crosses theParana River between the provinces of Chaco andCorrientes in northeast Argentina and is an im-portant link in one of the highways between Braziland Argentina, Figure 9.8. It has a center naviga-tion span of 803 ft 10 in. (245 m), side spans of 537ft (163.7 m), and a number of 271 ft (82.6 m) ap-proach spans on both the Chaco and Corrientessides of the river. The vertical clearance in themain spans above flood level is 115 ft (35 m).i3.14

The superstructure of this bridge consists of twocast-in-place concrete A-frame pylons, which sup-port a deck of precast segmental post-tensionedconcrete. The pylons are flanked by concretestruts, which reduce the unsupported length of thedeck, Figure 9.18. Although the pier cap section ofthe deck (between inclined struts) is cast in place,the cantilever portion consists of precast segments.The drop-in spans are cast in place.

The deck structure consists of two longitudinalhollow boxes 8 ft 2% in. (2.5 m) wide and with aconstant depth of 11 ft 6 in. (3.5 m), which supportprecast roadway deck elements, Figure 9.19. Theprecast girder elements were match-cast on theriver bank in lengths of 13 ft 1% in. (4.0 m), withthe exception of shorter units at the point of stayattachment, which contain an inclined transverseanchorage beam, Figure 9.20. Units were cast bythe long-line method on a concrete foundationwith the proper camber built in. Each unit was castwith three alignment keys, one in each web andone in the top flange. The units were erected asbalanced cantilevers with respect to the pylon tominimize erection stresses. After a unit was hoisted,an epoxy joint material was placed over all of thebutting area; then the unit was placed against thealready erected unit and tensioned.13

To eliminate the need for falsework, the tnclmedstruts and pylon legs were supported by horizontalties at successive levels as construction proceeded,Figure 9.21. The legs were poured in segments bycantilevering the formwork from previously con-structed segments. When deck level was reached,the girder section between the extremities of theinclined ties was cast on formwork. To further stif-fen the pylon structure, a slab was cast between boxgirders at the level of the girder bottom flanges.This slab is within the limits of the cast-in-place boxgirders and inclined struts and serves as an addi-tional element to accept the horizontal thrust fromthe cable stays. The upper portion of the pylon was

ChacolCorrientes Bridge, Argentina 409

Precast constructionk- --+I-Cast-irt-place 4f Precast construction +

369ft 1 in.(112.50m)

=I=

369 ft 1 in. (112.50 ml -4

~803 ft 10 in (245.00 m) 537 ft 0 in. (163.70 rn)M

Center span Side span

FIGURE 9.18. Chaco/Corrientes Bridge, longitudinal geometry, from refer-ence 14 (courtesy of Civil Engineering-ASCE).

8; I”. 9 ft 2: in 27 ft 3 in. 9 ft 2f in. 8: i n .I I

(22cm) ’n

(2.80 m) (8.30 m) Cast-w-place (2.8Om) ’I nl

(22 cm1concrete7

i i n . . ’

Ii ’

; 11 ft 5; in.

( 3 .50 ml

/+8 ft 2f in.&-11 ft 3: in. 11 ft 3: in. -& 8 ft 2f in.4 (25-30 c m )

(2.50 m) (3.45 ml (3.45 m) (2.50 m)

FIGURE 9.19. Chaco/Corrientes Bridge, deck cross section, from reference14 (courtesy of Civil Engineering-AXE).

1 each rade of cable

4 ,n. anchor bolt

.,:.-:.

.,i.,...,.:,.. : ‘.. . . :.:..,;.;y..,,. . Box girder -i: . . .! ‘.

,;. . . . ,?.:..: . ..*.,. .._ .., . ,. :. 2, T.‘..

FIGURE 9.20. ChacoKorrientes Bridge, cable an-chorage at girder, from reference 14 (courtesy of CivilEngineering-AXE).

then completed, using horizontal struts to bracethe legs until they were connected at the apex, Fig-ure 9.21.r3*14

The precast box girder units, with the exceptionof those at the cable-stay anchorage, were cast 13 ft1% in. (4 m) in length by the long-line, match-castprocedure. The soffit bed of the casting form hadthe required camber built in. Alignment keys werecast into both webs and the top flange. Match cast-ing and alignment keys were required to ensure aprecise fit during erection. Each 44 ton (40 mt) unitwas transported by barge to the construction siteand erected by a traveling crane operating on theerected portion of the deck. Since each box waslifted by a balance beam, four heavy vertical boltshad to be cast into the top flange of each box. Thelifting crane at deck level allowed longitudinal


1 2

P---

FIGURE 9.21. ChacoiCorrientes Bridge, erection se-quence of pylon, front reference 14 (courtesy of CivilEngineering-ASCE).

movement of the suspended box. Upon erection tothe proper elevation, the unit was held to within 6in. (150 mm) of the mating unit while epoxy jointmaterial was’applied. Bearing surfaces of the unitwere sand-blasted and water-soaked before erec-tion. The water film was removed before erectionand application of the epoxy joint material. Thetraveling deck crane held the unit in positionagainst its mating unit until it could be post-ten-sioned into position. The crane was slacked offwithout waiting for the joint material to cure.13*14

To minimize overturning forces and stresses inthe pylon, it was necessary to erect the precast boxunits by a balanced cantilever method on both sidesof the centerline of the pylon. The erection sched-ule demanded simultaneous erection at eachpylon, although the pylons are independent ofeach other. When four precast box units wereerected in the cantilever on each side of the pylon,temporary stays were installed from the top of thepylon to their respective connections at deck level.After installation of the temporary stays, cantilevererection proceeded to the positions of the perma-nent stays, and the procedure was repeated tocompletion of the installation of the precast boxunits.13

The erection sequence may be outlined as fol-lows:

1. Erect precast boxes and post-tension succes-sively.

2. Erect diaphragms between lines of boxes andpost-tension.

3. Place temporary and permanent stays as erec-tion proceeds.

4. Remove temporary stays.5. Remove temporary post-tensioning in the can-

tilever sections.6. Place precast deck slabs between box girders.7. Concrete the three 65 ft 8 in. (20 m) drop-in

spans.8. Place asphalt pavement, curbs, and railings.

9.5 Mainbriicke, Germany

The Main Bridge near Hoechst, a suburb ofFrankfort, constructed in 1971 is a prestressed,cast-in-place, segmental, cable-stayed structurethat connects the Fabwerke Hoechst’s chemical in-dustrial complex on both sides of the River Mainin West Germany, Figure 9.22. It carries twothree-lane roads separated by a railway track andpipelines. This structure, a successor to Finster-walder’s Danish Great Belt Bridge proposal, repre-sents the first practical application of the Dywidagbar stay. l5

The bridge spans the river at a skew of 70” fromthe high northern bank to the southern bank,which is 23 ft (7 m) lower. The center navigationspan is 486 ft (148.23 m) with a northern ap-proach span of 86 ft (26.17m) and southern ap-proach spans of 55, 84, 95, and 129 ft (16.91,25.65, 29, and 39.35 m), Figure 9.23.

Railroad track and pipelines are in the medianbetween the two cantilever pylon shafts and aresupported on an 8.7 ft (2.66 m) deep torsionallystiff box girder, Figure 9.24. The centerline of the

FIGURE 9.22. .1Ltinbt nuke, from reference 16.

Mainbriicke, Germany 4 1 1

: . . . ._\ . ~ ..\\.\~; \\_ LIP ~:FIGURE 9.23. Mainbriicke, elevation and plan, from reference 16.

FIGURE 9.24. Ll;ti~~l~l-iicke, cl-ass sections, f’rotl~ rcf’evellcc\ l(i.

longitudinal webs of the box girder coincides withthe centerline of the individual cantilever pylons,and they are 26.25 ft (8 m) apart. Transverse crossbeams at 9.8 ft (3 m) centers form diaphragms forthe box and cantilevers, which extend 39 ft (11.95m) on one side and 36 ft (11 m) on the other side ofthe central box to support the two roadways, Figure9.25.

The cross section of the towers consists of an an-choring web in the center, sandwiched by two flat-plate flange elements, Figure 9.26. In a transverseelevation of the pylons, the width of the pylon in-creases from the top to just below the transversestrut, where it decreases to accommodate clearancerequirements for both modes of traffic, Figure9.26. The stay cables (Dywidag bars) are in pairs,horizontal to each other in the main span and ver-tical in the side span, thus simplifying the anchor-age detail at the pylon, Figure 9.26.1fi

FIGURE 9.25. Mainbriicke, view of deck at pylon(courtesy of Richard Heinen).

FIGURE 9.26. Mainbticke, pylon and cable configuration, from refer-ence 16.

_

Construction of the bridge superstructure wasby the cast-in-place segmental method, Figure9.27. Segments in the river span were 20.7 ft (6.3 m)in length, corresponding to the spacing of thestays. Segments in the anchor span were 19 ft (5.8m) in length. Segments in the anchor span wereconcreted before the corresponding segment inthe river span to maintain stability. The pylonsegments were associated with the superstruc-ture segments, and each pylon segment was slip-formed.

Figure 9.28 shows the partially completedstructure and the falsework necessary to install thestays. Each stay is composed of twenty-five 16 mm(5/s in.) diameter Dywidag bars encased in a metalduct, which is grouted for corrosion protectionsimilar to post-tensioned prestressed concrete con-struction.

FIGURE 9.27, Mainbriicke, casting of deck segments(courtesy of Dyckerhoff & Widmann).

Ii] VERANKERUNG DERSCHR;LiGSEILE IM PYLON

9.6 Tie1 Bridge, The Netherlands

The Tie1 Bridge, l7 Figures 9.29 and 9.30, crossesthe Waal River, which, together with the Maas andthe Rhine, flowing east to west, divides the

FIGURE 9.28. Mainbticke, parCall\ compleredstructure (courtesy of Richard Heinen).

APPROACH VIADUCT OUVRAGE PRINCIPAL MAIN BRIDGEVIADUC D’ACCF5

FIGURE 9.29. ‘l‘iel Bridge, general layout.


FIGURE 9.30. l‘iel Hriclgc, main splls.

Netherlands into northern and southern parts.This structure provides a needed traffic link be-tween the town of Tie1 and the south of the coun-try and is a major north-south route.

The structure has an overall length of 4656 ft(1419 m) and consists of a 2644 ft (806 m) curvedviaduct on a 19,685 ft (6000 m) radius, which in-cludes ten continuous 258 ft (78.5 m) long spansand a 2008 ft (612 m) straight main structure com-prising three stayed spans of 3 12, 876, and 3 12 ft(95, 267, and 95 m) and two 254 ft (77.5 m) sidespans.

The cross section consists of two precast concreteboxes, each supporting two vehicular and one bicy-cle lane. The total width of the superstructure,which is 89 ft (27.2 m) in the access viaduct, Figure9.31, is enlarged to 103 ft (31.5 m) over the mainstructure so as to accommodate the pylon sup-porting the stays.

The structure crosses not only the Waal River butalso a flood plain, which is under water during thewinter months. Navigation requirements dictate ahorizontal clearance of 853 ft (260 m) and a verti-cal clearance of 30 ft (9.1 m).

The ten-span 2648 ft (806 m) long access viaductis continuous over its entire length. The super-structure is supported on the piers by slidingteflon bearings, except at the three center pierswhere it is supported on neoprene bearings, hav-ing a thickness such that they ftx the viaduct atthese piers. Expansion joints are located at piers 1and 11. The superstructure in the access viaductconsists of two precast rectangular boxes of a con-stant depth of 11.5 ft (3.5 m) and width of 21 ft 8in. (6.6 m). The top flange including cantileveroverhangs has a width of 44 ft (13.44 m). Theoverall width of the approach viaduct deck is 89 ft3 in. (27.2 m), including a longitudinal pour strip.The viaduct was constructed by the precast bal-anced cantilever method with cast-in-place closurepours at the midspans. To accommodate the can-tilever compressive stresses in the bottom flangeover the piers, the thickness of the bottom flange islinearly increased from a minimum of 8 in. (200mm) to 24 in. (600 mm) over a length of 33 ft (10m) on each side of the pier. Each pier segmentcontains a diaphragm.

Because of the potential flooding of the riverfrom April through December and the consequentloss or damage of falsework and loss of time, it wasdecided to build the access viaduct utilizing precastsegments in the balanced or “free” cantilever con-struction. The segments could be cast duringflooding and placed in storage. Erection of thesegments, which would take less time than thecasting, could be accomplished after the flood hadsubsided.

The precast segments, weighing 132 tons (120mt), were cast in movable forms on a casting bedhaving the length of one span (by the long-linemethod, see Section 11.6.2). Segments were storedby and parallel to the casting bed and handled by a130 ft (40 m) span gantry crane, Figure 9.32. Theywere transported to the site (access viaduct abut-ment) by means of a 132 ton (120 mt) capacitytrolley and then placed in the structure by the samegantry crane used in the precasting yard for han-dling, Figure 9.33; The trolley was used to trans-port the segments because the gantry was usuallyengaged in the precasting yard or in placing seg-ments in the viaduct. The gantry crane was suchthat it spanned over the twin boxes in the super-structure and the trolleyway used to transport thesegments.

Segment joints are of the epoxy-bonded type(see Section 11.5). Cantilever imbalance is accom-modated by a temporary support ad.jacent to thepier, Figure 9.33. Five temporary prestress bars

Tie1 Bridge, The Netherlands 415

FIGURE 9.32. Precasting plant. (1) Casting bed, (2)I-e-bar storage, (3) segment storage, (4) concrete batchplant, (5) office, (6) gantry crane, (7) bridge approach.

are used as provisional prestressing to hold thesegments in position until permanent prestresstendons can be threaded into the ducts andstressed.

T h e s y m m e t r i c a l b o x g i r d e r m a i n s t r u c t u r econsists of a 254 ft (77.5 m) side span, a 312 ft (95m) side stayed span, and a 33 1 ft (101 m) section ofstayed center span cantilevering toward the centerof the bridge. The center section between thestayed cantilever ends is made up of four 213 ft (65m) suspended lightweight concrete girders.

Two alternatives were considered for the cable-stay pylons: a single pylon located on the lon-gitudinal centerline of the bridge or a portal-typepylon. To simplify the project, the portal-typepylon was selected. The portal pylon is fixed to thepier and passes freely through the superstructure,Figure 9.34. The superstructure is fixed at thepylon piers except for rotation. It is allowed tomove longitudinally at succeeding piers.

Two alternatives were also considered for thestay system: a multiple stay system supporting thedeck almost continuously and a system consistingof a few large stays. As prestressed concrete stayshad been selected, the second solution becamesomewhat mandatory. Construction of prestressed

FIGURE 9.34. Free passage of pylon through deck.

concrete stays is a costly operation requiring exten-sive high scaffolding, Figure 9.35; thus it is advan-tageous to reduce the number of stays.

The short stays of the bridge have a slope of 1: 1and the long stays a slope of 1:2. Their points ofanchorage to the deck are respectively at 156 ft(47.5 m) and 3 12 ft (95 m) on both sides of a pylon.The long stays have a cross section of 3 by 3.3 ft(0.9 by 1 .O m) and are prestressed by 36 tendons onthe bank side and by 40 tendons on the river side,because of the larger load on that side, Figure9.36a. The effect of the different loads on the staysintroduces a flexural moment into the pylon. Theshort stays have a cross section of 2.13 by 3.3 ft(0.65 by 1.0 m) and are prestressed by 16 tendons

FIGURE 9.33. Placing of segments by gantry crane.


FIGURE 9.35. Falsework fbr stay construction.

on the bank side and 20 tendons on the river side,Figure 9.366.

The concrete of the stays has a 2%day strengthof approximately 8700 psi (60 MPa). Its function isnot only to protect the tendons, but also to increasethe rigidity of the stays, which is four times that ofthe tendons alone.

Long stays40/36 cables

E?!l

Short stays20/16 cables

65 t8,:I

(b)

FIGURE 9.36. Cross section of stays.

Three loading conditions were considered forthe stays from a statics point of view:

1 . For the self-weight of the stays and dead loadof the superstructure, the deck is considered assupported on nonyielding supports, which arethe stay anchorage points, and the load in thestays results from the reactions at these points.

2. For design live load, the deck is considered assupported on yielding supports, the rigidity ofwhich is determined by the rigidity of the pre-stressed stays.

3. The prestress of the stays was calculated with asafety factor against cracking of 1 .l for deadload and 1.3 for live load, without allowing anytension in the concrete. The ultimate loadsafety factor is 1.8. For the load condition be-tween cracking and collapse the stay rigidity isreduced to the rigidity of the tendons alone.Their excessive elongation, in case theyyielded, would lead to an excessive deflectionof the box girder and a premature collapse be-fore the proposed safety limit. Therefore, itwas necessary to reduce the initial stress of thetendons to 40 to 45% of their ultimate strengthin order to keep them in the elastic range up toultimate load determined by the safety factorof the structure as a whole.

The sag of the long stay is 2.3 ft (0.70 m) in alength of 328 ft (100 m) under dead load. Underlive load the sag is reduced to 1.8 ft (0.55 m). Thecross section of the stays at their extremities is in-creased slightly to resist bending stresses. Thesestresses were calculated by the method of finite dif-ferences.

In the longitudinal direction the girders areprestressed primarily by the horizontal componentsof the stay forces. The unstayed end spans are pre-stressed with 54 tendons. In the other spans addi-tional prestressing is provided by 10 tendons thatoverlap each other at the supports. These tendonswere required until such time as the stay forceswere applied and, at completion, to provide safetyagainst cracking and collapse. The deck slab is pre-stressed transversely by tendons spaced at 12 to 17in. (0.30 to 0.44 m).

The suspended 213 ft (65 m) span is composedof four precast lightweight concrete girders with a6500 psi (45 MPa) concrete. The cast-in-place deckslab is increased from a thickness of 9.8 in. (250mm) in the box girders to 12.6 in. (320 mm), owingto the smaller restraint of the slab in the one webgirders.

Tie1 Bridge, The Netherlands 417

The following restraints and conditions wereconsidered in the determination of the construc-tion procedure for the main spans of the structure:

1. The exclusion of falsework from the river be-cause of ndvigation requirements.

2. The potential for flooding.3. The presence of the precasting plant on the

north bank.4. The possibility of adjusting the attachment

points of the stay to the deck.

Construction was executed in increments limitedby the attachment points of the stays to the deck.The stays were prestressed progressively, by in-creasing the number of stressed tendons as theload in the stays increased. However, during cer-tain construction phases when the load in the staysdecreased, some of the tendons were detensionedor slacked off.

Using the north side (access viaduct side) as anexample, the construction was divided into thefollowing phases, Figure 9.37:

Phme 1: Construction oj the outer spans-that is, thestay-supported side span andjanking spana . Superstructure from pier 11 to pier

12 and a 72 ft (22 m) cantilever intothe next span

b. Extension up to temporary support1 2 A

c. Extension up to pier 13 with a 26 ft(8 m) cantilever into the center span;simultaneous construction of thepylon

Phase 2: Construction qf the$rst section over the riverand the shortfbrestay.

Phase 3: Construction of the second section ouer theri-iw a11d the long,fowstay.

The external spans on the north side were con-structed on falsework during the dry season.Utilizing the precast plant on the north side, pre-cast segments 16.7 ft (5.10 m) long weighing 132tons (120 mt) were assembled on the falsework.Segments were joined by f in. (5 mm) cast-in-placejoints. Placing of the segments was carried out bythe same gantry crane as for the access viaduct. Onthe south bank, where there was no precastingplant, the external spans were cast in place onfalsework.

The cantilever river spans were built on 157 ft(48 m) long steel falsework, consisting of four 10 ft

P H A S E 1

PHASES DE CONSTRUCTION DEL’OUVRAGE PRINCIPAL

MAIN BRIDGELONSTRUCTION P H A S E S

FIGURE 9.37. Main bridge construction phases.

(3 m) deep girders on 23 ft (7.10 m) centers. Thisfalsework was suspended at one end by prestress-ing strands from the top of the pylons. At thelower end, the temporary support strands were an-chored in a cross beam that supported the steelfalsework by four 350 ton (315 mt) jacks. The 3 ft(1 .O m) stroke of the jacks allowed adjustment ofthe level of the suspension points, and the jackswere used also to release the temporary prestresssuspension strands when the final stays were in-stalled. At the opposite end, the steel falsework washinged. The horizontal force component on thesehinges was transmitted directly to the completedpart of the deck, and the vertical component wastaken by 1 in. (26 mm) bars.

In Phase 3, the temporary stays were deflectedby means of 95 ft (29 m) booms. This provided theadvantage of maintaining the angles at the lowerconnection equal to that of Phase 2 and keepingapproximately the same force level in the tempo-rary stay.

The falsework used in Phases 2 and 3 was car-ried on a barge; it was positioned by two derrickslocated on the completed part of the deck and by afloating crane. After the box girders were cast, thelevel of the falsework was adjusted, the last joint


was cast, and the concrete was prestressed. Thenext steps were constructing the stays, prestressingthem, releasing the temporary stays, and removingthe falsework.

In order to reduce creep and shrinkage, thestays were made of 17 ft (5.15 m) long segmentswith protruding reinforcement and 16 in. (0.4 m)cast-in-place joints. The building of the falseworkfor the stays and the handling of the precast seg-ments were carried out with the help of a 16 ton(15 mt) tower crane 2 13 ft (65 m) high, running onthe deck.

The precast 213 ft (65 m) suspended span gird-ers weighed 468 tons (425 mt) and were trans-ported by barge.

9.7 Pasco-Kennewick Bridge, U.S.A.

The first cable-stayed bridge with a segmental con-crete superstructure to be constructed in theUnited States is the Pasco-Kennewick IntercityBridge crossing the Columbia River in the state ofWashington, Figure 9.38. Construction began inAugust 1975 and was completed in May 1978. Theoverall length of this structure is 2503 ft (763 m).The center cable-stayed span is 981 ft (299 m), andthe stayed flanking spans are 406.5 ft (124 m). ThePasco approach is a single span of 126 ft (38.4 m),

FIGURE 9.38. Pasco-Kennewick Intercity Bridge(courtesy of Arvid Grant).

while the Kennewick approach is one span at 124 ft(37.8 m) and three spans at 148 ft (45.1 m).4*15*18,1s

The girder is continuous without expansionjoints from abutment to abutment, being fixed atthe Pasco (north) end and having an expansionjoint at the Kennewick (south) abutment. The con-crete bridge girder is of uniform cross section, ofconstant 7 ft (2 m) depth along its entire length and79 ft 10 in. (24.3 m) width. The shallow girder andthe long main spans are necessary in order to re-duce roadway grades to a minimum, to provide thegreatest possible navigation clearance below, andto reduce the number of piers in the 70 ft (21.3 m)deep river.

The bridge is not symmetrical. The Pasco pylonis approximately 6 ft (1.8 m) shorter than the Ken-newick pylon, and the girder has a 2000 ft (610 m)vertical curve that is not symmetrical with the mainspan. Therefore, the cable-stay pairs are not ofequal length, the longest being 506.43 ft (154 m).‘s

There is no attachment of the girder at the py-lons, except for vertical neoprene-teflon bearingsto accommodate transverse loads. The girder issupported only by the stay cables. There are, ofcourse, vertical bearings at the approach piers andabutments. It is estimated that the natural fre-quency of the girder, where it will respond todynamic acceleration (i.e., earthquake), is 2 cyclesper second. If the situation occurs where the lon-gitudinal acceleration exceeds this value, the ver-tical restraint at the Pasco (north) abutment is de-signed to fail in direct shear, thus changing thestructure frequency to 0.1 cycles per second, whichrenders the system insensitive to dynamic excita-tion. The three main spans were assembled fromprecast, prestressed concrete segments, while theapproach spans were cast in place on falsework,Figures 9.39 and 9.40.

Deck segments were precast about 2 miles (3.2km) downstream from the bridge site. Each seg-ment weighs about 300 tons (272 mt) and is 27 ft(8.2 m) long, Figure 9.41. The segment has an 8 in.(0.2 m) thick roadway slab, supported by 9 in. (0.22m) thick transverse beams on 9 ft (2.7 m) centers,and is joined along the exterior girder edges by atriangular box which serves the function of cableanchorage stress distribution through the girderbody, Figure 9.42. 6 Each match-cast segment re-quired approximately 145 yd3 (11 lm3) of concrete,continuously placed in a previously adopted se-quence within six hours. After initial curing in theforms, the girder segments were wet cured for twoweeks in the storage yard, air cured for an ad-ditional six months, prestressed transversely,

Brotonne Bridge, France 419

F I G U R E 9 . 3 9 . l’r~w~-K~~~~w~ I& Intu Lit\ HI ldge,precast segments in main spans (courtesy of ArvidGrant).

FIGURE 9.40. Paaco-Kenne\\ic 1, Intel city Bridge, ap-preach spans cast in place on falsework (courtesy ofWalter Bryant, FHWA Region 10).

FIGURE 9.41. Pasco-Kennewick Intercity Bridge,precast segments in casting yard (courtesy of ArvidGrant).

cleaned, repaired, completed, loaded on a barge,and transported to the structure site for installa-tion in their final location. For possible unpredicteddevelopments a shimming process was held in re-se rve for main ta in ing the assembled g i rdergeometry correctness, but it was not used. Thereare no sh ims in the segmenta l ly assembled ,epoxy-joined prestressed concrete girder.‘“+18*‘”The sections were barged directly beneath theirplace in the bridge and hoisted into position, Figure9.43. Fifty-eight precast bridge girder segmentswere required for the project.

The stays are arranged in two parallel planeswith 72 stays in each plane-that is, 18 stays oneach side of a pylon in each plane. They are held ateach pylon top, 180 ft (55 m) above the bridgeroadway, in a steel weldment, Figure 9.44. Stay an-chorages in the bridge deck are spaced at 27 ft (8.2m) to correspond with the segment length. Thestays are composed of + in. (6 mm) diameter parallelhigh-strength steel wires of the BBR type. Theprefabricated stays, manufactured by The PrestonCorporation, arrived on the job site on reels, Fig-ure 9.45, and contained from 73 to 283 wires, de-pending upon their location in the structure. Theywere covered with a # in. (10 mm) thick poly-ethylene pipe, and after installation and finaladjustment were protected against corrosion bypressure-injected cement grout. The outside di-ameter of the pipe covering varies from 5 to 7 in.(0.12 to 0.17 m). Design stress level for the stays is109 ksi (751.5 MPa). Stay anchorages are of theepoxy-steel ball (HiAmp) fatigue type produced byThe Preston Corporation.

This structure was designed by Arvid Grant andAssociates, Inc., of Olympia, Washington, in pro-fessional collaboration with Leonhardt and Andraof Stuttgart, Germany.

9.8 Brotonne Bridge, France

The Pont de Brotonne, designed and built byCampenon Bernard of Paris, crosses the SeineRiver downstream from Rouen in France. Becauseof increased navigation traffic in the area, a secondcrossing over the Seine River was urgently neededbetween the two harbors of Le Havre and Rouen.The first one, the steel suspension bridge of Tan-carville, was opened to traffic in 1959. The second,the Brotonne Bridge, the world’s largest cable-stayed prestressed concrete bridge, was opened totraffic in June 1977. 2o A model of the structure is

II-

22 .50 m7

cl CROSS -SECTION OF CONCRETE

SECTION. ELEVATION B - BFIGURE 9.42. Pasco-Kennewick Intercity Rridge,cables (courtesy of Prof. Fritz Leonhardt).

BRIDGE/

eoprene sleeve

S E C T I O N A - Across section and anchorage of sta?

FIGURE 9.43. Pasco-Kennewick Intercity Bridge,erection of precast segments from barge (courtesy ofArvid Grant).

FIGURE 9.44. I’asco-Kennewick lntercity Bridge,pylon and stay attachment steel weldment at top (cour-tesy of Arvid Grant).

Brotonne Bridge, France 4 2 1

FIGURE 9.45. l’asco-E;enne~~,ick Intcrcity Bridge,prefr~bricated cable stay on reel.

shown in Figure 9.46 and the general layout in Fig-ures 9.47 and 9.48. The box girder carries fourlanes and replaces ferry service between two majorhighways that run north and south of the Seine.Because large ships use this section of the river toapproach the inland port of Rouen 22 miles (35km) to the east, vertical navigation clearance is164 ft (50 m) above water level, which results in a6.5% grade for its longer approach.15*21

Total length of structure is 4194 ft (1,278.4 m),consisting of the main bridge and two approachviaducts. The main crossing has a span of 1050 ft(320 m). On the right bank, the transition betweenthe main span and the ground is quite short be-cause of a favorable topography where limestonestrata slope upward to a relatively steep cliff. Onthe left bank, the terrain is flat and occupied bymeadows. With an allowable maximum grade of6.5% and a maximum height of fill of 50 ft (15 m),a nine-span viaduct was required to reach the mainbridge. In a structural sense, the bridge is dividedinto two sections separated by an expansion joint ata point of contraflexure in the left-bank viaductspan adjacent to the cable-stayed side span, Figure9.48.‘O

FIGURE 9.46. Model of the Pant dc Rrotonne.

FIGURE 9.47. Artist’s rendering of the Pont deBrotonne.

The prestressed segmental concrete deck con-sists of a single-cell trapezoidal box girder withinterior stiffening struts, Figures 9.49 and 9.50. Inthe approach spans, web thickness is increasedfrom 8 in. (200 mm) to 16 in. (400 mm) near thepiers, and the bottom flange thickness is increasedto a maximum thickness of 17 in. (430 mm). Theonly portion of the segment that was precast is itssloping webs, Figure 9.51, which were precast atthe site. The other portions of the cross section,including top and bottom flanges, interior stiffen-ing struts, and cable-stay anchorages (in the mainstructure only), were cast in place. Each segment is9.8 ft (3 m) long.

Extensive use of prestressing was made in thedeck to provide adequate strength to this lightstructure. To resist the extreme shear stresses itwas decided to place vertical prestressing in thewebs. Pretensioned units were stressed on a castingbed, Figure 9.52, and equipped with specially de-signed button heads, thus producing a combina-tion of pretensioning and anchorage plates. Thissystem has the advantage of ensuring a perfectcentering of the prestressing force together with avery rapid transfer of this force at both ends. In-tensive rupture tests proved that an extremelyhigh resistance to shear was created by this sys-tem.20

Finally, prestressing was also used as follows,Figure 9.53:20

1. Transversely in the top flange to provideflexural strength to the thin 8 in. (200 mm)slab.

2. In the inclined internal stiffeners, to accom-modate tensile forces created by the transferof loads from the box girder to the stays.

-+s_s_sO,s8>~_+ 5850 1 5850 1 5850 4 5850 1 5850 i 5850 (5850 i

_ _ _ _ _

32000

6 9 7 5 0

127840

FIGURE 9.48. General layout of Brotonne Bridge.

b sl tI

1.50,, ., 6.50 I 1.60 1.60 6.50 1.50. . , *-’ (5’) - (5’) (5’) _ 1 (5’)

I

I I5.60 1 4.00 I 4.00 1 5.60 I

(18’) (13’) (13’) (18’)

FIGURE 9.49. Cross section of Brotonne Bridge.

FIGURE 9.50. Interior view of deck, BrotonneBridge.

FIGURE 9.51. Precast webs, Hrotonnc 131 ItlgC.

coupler for tensioning jack36 am dia tension

distribution beam

Dyuidag mat- -..

FIGURE 9.52. Casting bed for pretensioned webs.

FIGURE 9.53. Various prestressing systems in the box girder.

3. Transversely in the bottom flange, to coun-teract tensile forces created by the stiffeners.

4. Longitudinally near the center of the mainspan, to allow for a reasonable margin of theorder of 300 psi (2 MPa) of compressive stressin view of creep and secondary tensile stresses.

Before erection of the superstructure, thebridge’s 12 approach piers were slip-formed, nineon the left bank and three on the right. The piershafts have an octagonal curvilinear cross sectioninscribed inside a 13 by 29 ft (4.0 by 8.75 m) rec-tangle, Figure 9.54. The same section was used forall the approach-span piers, whose height variedfrom 40 to 160 ft (12 to 49 m). The shape of thepiers did not substantially increase costs but did in-crease the aesthetic appeal of the piers. The piersbear through a reinforced concrete footing on fourrectangular slurry trench walls used as piles with amaximum length of 60 ft (18 m), Figure 5.17.

The pylon pier shafts also have an octagonalcurvilinear shape inscribed inside a 30 ft (9.2 m)square to produce equal bending resistance aboutboth principal axes. They are supported on foun-dation shafts having a diameter of 35 ft (10.86 m)with a maximum wall thickness of 6 ft 8 in. (2.03m). The foundation shafts transfer the loads to alimestone stratum at a depth of 115 ft (35 m) belowground level. Foundation shafts were built insidea circular slurry trench wall, which was used as acofferdam for dewatering.*”

When slip-forming of the piers reached decklevel, the piers were prestressed to their founda-tion so as to stabilize them for erection of the decksegments. As the precast deck units were erected,

/.

!IJ*

FIGURE 9.54. Pier and foundation of approachspans.

c wlI

1.50 ,, 6.50 , 1 . 6 0 ,. 1 . 6 0 A 6 . 5 0 ; 1 . 5 0

*I (5’) T _ (5’) - (5’) (21’)ROADWAY 1 (d

I

FIGURE 9.49. Cross section of Brotonne Bridge.

FIGURE 9.50. Interior view of deck, BrotonneBridge.

FIGURE 9.51. Precast webs, Brotonnc Hr~tlgc.

bulkhead coupler for tensioning jack dlatributiw bean_-.-- . . ___-- ___i.. __.a-__--_ - .--._

steel formai.., tcnaion rods

,-- ___.i- - -:’36 am dia tendon rodr;_- - -. _ ._--.- . .

adjustable_-- -bracketa

11-36 IUS Rwidag preatrcrsin~ tendons soffit--.- ..--- i _ _ _ __ __ ._-._ -- ..__ -tenrion bars

FIGURE 9.52. Casting bed for pretensioned webs.

FIGURE 9.53. Various prestressing systems in the box girder.

3. Transversely in the bottom flange, to coun-teract tensile forces created by the stiffeners.

4. Longitudinally near the center of the mainspan, to allow for a reasonable margin of theorder of 300 psi (2 MPa) of compressive stressin view of creep and secondary tensile stresses.

Before erection of the superstructure, thebridge’s 12 approach piers were slip-formed, nineon the left bank and three on the right. The piershafts have an octagonal curvilinear cross sectioninscribed inside a 13 by 29 ft (4.0 by 8.75 m) rec-tangle, Figure 9.54. The same section was used forall the approach-span piers, whose height variedfrom 40 to 160 ft ( 12 to 49 m). The shape of thepiers did not substantially increase costs but did in-crease the aesthetic appeal of the piers. The piersbear through a reinforced concrete footing on fourrectangular slurry trench walls used as piles with amaximum length of 60 ft (18 m), Figure 5.17.

The pylon pier shafts also have an octagonalcurvilinear shape inscribed inside a 30 ft (9.2 m)square to produce equal bending resistance aboutboth principal axes. They are supported on foun-dation shafts having a diameter of 35 ft (10.86 m)with a maximum wall thickness of 6 ft 8 in. (2.03m). The foundation shafts transfer the loads to alimestone stratum at a depth of 115 ft (35 m) belowground level. Foundation shafts were built insidea circular slurry trench wall, which was used as acofferdam for dewatering.2u

When slip-forming of the piers reached decklevel, the piers were prestressed to their founda-tion so as to stabilize them for erection of the decksegments. As the precast deck units were erected,

FIGURE 9.54. Pier and foundation of approachspans.

Bccticm D-D

Lalgitullim1bctic0A-AFIGURE 9.55. Half center span and pylon.

longitudinal rection

cocaectioaktweea Pyloncrdl Plcr------c

I

c

I

__ . . . _ - 2* w . i

l O N ._ � + .i. - .._.. Pzo. _ . . -. . . . .

FIGURE 9.56. Connection between pylon, deck, and pier.

the pylon was constructed by convent ionalmethods.

Two single-shaft pylons carry a system of 21stays located on the longitudinal axis of the struc-ture, Figure 9.55. The reinforced concrete pylonsrequired limited cross-sectional dimensions to pre-clude an unnecessary increase of the deck widthwhile providing sufficient dimension to accommo-date bending stresses from a transverse wind di-rection. Total pylon height above the deck is 23 1 ft(70.5 m). Construction of the pylon required Ieap-frog forms with 10 ft (3 m) lifts. An interestingfeature is the total fixity of the pylon with the boxgirder deck. Because the bending capacity of thepylon pier and foundation had to be such as to ac-commodate unsymmetrical loads due to the can-tilever construction, a decision was made to takeadvantage of this requirement in the final structureto reduce the effect of live load in the deck. There-fore, the pylon was constructed integral with thedeck at its base, both pylon and deck being sepa-rated from the pier by a ring of neoprene bearings,Figure 9.56.20

FIGURE 9.57. C.;;rl,lc-SI;I> mhor;1gc.

All deck loads are carried to the pylon piers by21 stays on each pylon. Each stay consists of 39 to60-0.6 in. (15 mm) strands encased in a steel pipe,which is grouted after final tensioning. Stay lengthvaries from 275 to 1115 ft (84 to 340 m). Anchor-age spacing of the stays at deck level is every 19.7 ft(6 m), every other segment, where the inclined stif-feners in the deck segments converge, Figures 9.53and 9.57. A special deck anchorage block was de-signed to accommodate the variable number ofstrands in the stay as well as to allow full adjust-ment of the tension in the stays by a simple an-choring nut, Figure 9.58. The anchorage of thestays is such that it is possible at any time duringthe life of the structure to either readjust the ten-sion in the stay or replace it without interruptingtraffic on the bridge. Permanent jacks are incorpo-rated into the anchorage, Figure 9.59, such that bytensioning the stay the adjusting nut can be slackedoff . Stays are cont inuous through the pylonwhere they transfer load to the pylon by a steelsaddle. The pipe wall thickness is increased nearthe anchorage points and near the pylon so as toimprove fatigue resistance of the stays with regardto bending reversaIs.20

In constructing the deck girder, the operationwas to extend the bottom flange form from atraveling form at the completed segment, placingthe precast web units that form the basic shape andact as a guide for the remaining traveling form.After placement of the precast webs the interiorsteel form was jacked forward to cast the bottomflange struts and the top flange. Tower cranes atthe pylon placed, as far as they could reach in bothdirections, the precast webs, Figure 9.60. Beyondthe range of the tower cranes, gantry cranes run-ning on rails on the top flange and extending 9.8 ft

FIGURE 9.58. Jacking of stay.

FIGURE 9.59. Permanent stay anchorage.

Danube Canal Bridge, Austria 4 2 7

FIGURE 9.6 1. Stnrt of mnill \pdn Loll$tructiotl. flomreference 20.

FIGURE 9.62. &fore closure of mn111 SP;III, f 1 oln Ed-erence 20

FIGURE 9.60. llZain pier, pylon, anti deck during FIGURE 9.63. Aerial view of the Hroronne Hrldge,construction, from reference 20. from reference 20.

(3 m) beyond the end of the completed sectionwere used to place new elements.

The structure is shown at the start of main spanconstruction in Figure 9.61, before closure of themain span in Figure 9.62, and completed in Figure9.63.20

9.9 Danube Canal Bridge, Austria

This structure is located on the West Motorway(Vienna Airport Motorway) and crosses theDanube Canal at a skew of 45”. It has a 390 ft (119m) center span and 182.7 ft (55.7 m) side spans,


182.7 ft 390 ft 182.7 ft* I

5 5 . 7 m 110m 55.7 m

FIGURE 9.64. Elevation of the Danube Canal Bridge.

Figure 9.64. It is unique because of its constructiontechnique. Because construction was not allowed tointerfere with navigation on the canal, the struc-ture was built in two 360.8 ft (110 m) halves oneach bank and parallel to the canal, Figure 9.65.Upon completion the two halves were rotated into

FIGURE 9.65. Construction of half-bridge on bank ofcanal .

final position and a cast-in-place closure joint wasmade, Figures 9.66 through 9.69. In other words,each half was constructed as a one-time swing span.

The bridge superstructure is a 5 1.8 ft (15.8 m)wide trapezoidal three-cell box girder, Figure 9.70.The central box was cast in 25 ft (7.6 m) long seg-ments on falsework, Figure 9.7 1. After the precastinclined web segments were placed, Figure 9.72,the top slab was cast.

Each half-structure has two cantilever pylonsfixed in a heavily prestressed trapezoidal crossheadprotruding under the deck with a two-point bear-ing on the pier, Figure 9.73. At the deck level thestays attach to steel brackets connected to pre-stressed crossbeams, Figures 9.74 and 9.75.

Each stay consists of eight cables, two horizontalby four vertical. At the top of the pylons each cableis seated in a cast-iron saddle. The cable saddles arestacked four high, Figure 9.76, and are fixed toeach other as well as to those in the adjacent plane.The cables were first laid out on the deck, fixed to asaddle, and then lifted by a crane for placement atthe top of the pylon. The cables were then pulled

FIGURE 9.66. Plan of Danube Canal Bridge during construction and final state.

Danube Canal Bridge, Austria 429

FIGURE 9.67. Danube Canal Bridge during rotation.

FIGURE 9.69. Closure joint, Danube Canal Bridge.

FIGURE 9.68. Ihnubc Canal Bridge during rotation.

FIGURE 9.70. Cross section, Danube Canal Bridge.

at each extremity by a winch rope to their attach- tion the structure was lowered to permanentment point at the deck level. bearings by emptying the sand box.

During rotation of the two half-bridges, the deck At the canal-bank end the deck had a concreteand pylon sat on a bearing consisting of five wall on its underside, bearing on a circular con-epoxy-glued circular steel plates. The top plate was Crete sliding track, Figure 9.77. The bearing be-coated with teflon, sitting in turn on a reinforced tween the wall and the track was effected by twoconcrete block that sat on a sand box. After rota- concrete blocks clad with steel plates, under which


FIGURE 9.71. Con~tl llctiotl OII htnk, I),~nubc C,~nnlBridge.

FIGURE 9.73. ‘Trapezoidal crosshead, Danube CanalBridge.

FIGURE 9.72. P~t.c,~st \jcbr, Danube Canal Bridge.

teflon-coated neoprene pads were introducedduring the rotation movement (similar to the in-cremental launching method). The pivoting was ac-complished by means of a jack pulling on a cableanchored in a block located near the sliding-trackend.

After rotation the two halves of the structurewere connected by a cast-in-place closure joint, andcontinuity tendons were placed and stressed.22 Thefinal structure is shown in Figure 9.78.

9.10 Notable Examples of ConceptsFIGURE 9.74. Jacking of stays, Danube Canal Rridge.

9.10.1 PROPOSED GREAT BELT BRIDGE,DENMARK

The competition for a suitable bridge design inDenmark produced many new concepts and ar-chitectural styles. The design requirements spec-ified three lanes for vehicular traffic in each direc-tion and a single railway line in each direction.

The rail traffic was based on speeds of 100 mph(161 km/hr).23 Navigational requirements stipu-lated that the bridge deck be 220 ft (67 m) abovewater level, and the clear width of the channel wasto be 1130 ft (345 m).

A third prize winner in this competition was theMorandi-style design proposed by the English con-sulting firm of White Young and Partners, Figure

Notable Examples of Concepts 431

FIGURE 9.75. Cable-stay attachment, Danube CanalBridge.

FIGURE 9.76. Stay saddles at pylon, Danube CanalBridge.

9.7. This design embodied the principles of acable-stayed bridge combined with conventionalapproaches of girders and piers with normal spans.

The principal feature of this bridge design is thethree-plane alignment of cable stays. This featuremay become more important in urban areas, wheretrends in the future may dictate multimodal trans-portation requirements and an increase in the

FIGURE 9.77. Circular concrete sliding track, Dan-ube Canal Bridge.

FIGURE 9.78. Completed Danube Canal Bridge.

number of automobile traffic lanes. The deck con-sists of two parallel single-cell prestressed concretebox’girder segments, Figure 9.79. The rail traffic issupported within the box on the bottom flangeand the road traffic is carried on the surface of thetop flange.

The box girder contemplated a depth of 23.5 ft(7.2 m) and width of 27.75 ft (8.45 m) with thetop flange cantilevered out 12 ft (3.7 m) on eachside. The piers and towers were to be cast-in-placeconstruction to support the deck segments, whichwere to be precast at various locations on shore andfloated to the bridge site for erection. Themaximum weight of a single box segment was es-timated at 2200 tons (2000 mt). All segments ofthe superstructure were to be of reinforced andprestressed concrete.

Up to this point in time, when the competitionfor this structt.re was conducted, all the concretecable-stayed bridges had been either designed by

432

-e--- 3.675 m

Concrete Segmental Cable-Stayed Bridges

b ’ < 8.45 m

Morandi (Lake Maracaibo, Wadi Kuf, and so on) between pylons of 1148 ft (350 m) and a spacing ofor strongly influenced by his style (Chaco/ the stays at deck level of 32.8 ft (10 m). PylonCorrientes). They were typified, for the most part, height above water level was 520 ft (158.5 m). In aby the transverse A-frame pylon with auxiliary transverse cross section the deck was 146 (44.5X-frame support for the girder. However, an entry m) wide with two centrally located vertical stayin the Danish Great Belt Competition by Ulrich planes 39 ft 4 in. (12 m) apart to accommodate theFinsterwalder of the German firm of Dyckerhoff two rail traffic lanes, and three automobile traffic& Widmann deviated from this style and was lanes in each direction outboard of the stay planes,awarded a second prize. Figure 9.80.

Finsterwalder proposed a multiple span, multi- The solid concrete deck had a thickness of 3 ftstay system using Dywidag bars for the stays, Fig- (0.9 m) in the transverse center portion, under theure 9.10. This proposal contemplated a spacing rail traffic, and tapered to a 1.3 ft (0.4 m) thickness

-k! 58,M

i

22,50

f 0.00

- 175.w-j- 350,oo / 175,oo -J ‘,. ;p2,50

-_-_-_--------_-__- _______r____

/ r ________,/__ ------ Ir _ _ . r ____ - -----‘-‘-, -------,

j lu~+~

‘-----:- -.--- 7 --__ -_,_ _ _Bahn

1Ir ; !

1n ..I’ !L.

-q-i-’ (

~ ‘C

’ ONsam& :o,llo

- - - - - - - - - - ------_-- ----______ _15,25 ------&2,00?c--- 10,00------+2,00- 15,25 - - -

k MO

FIGURE 9.80. Danish Great Belt Bridge, elevation and cross section (coultesv ofDyckerhof’f’ & Widmann).

Notable Examples of Concepts 4 3 3

at the edges. The deck was to be constructed by thecast-in-place balanced cantilever segmentalmethod, each segment being supported by a set ofS&F s.

The proposed Dame Point Bridge over the St.Johns River in Jacksonville, Florida, as designedb) the firm of Howard Needles Tammen &Bergendoff, is a cable-staved structure with a con-crete and a steel alternative. .4n artist’s renderingof the concrete cable-staved bridge alternative isshown in Figure 9.81. Navigation requirementsdictate a 1250 ft (381 m) minimum horizontalopening and a vertical clearance of 152 ft (46.3 m)above mean high water at the centerline of theclear opening. I‘he proposed concrete cable-stayedmain structure will have a 1300 ft (396 m) central

FIGURE 9.81. lhmc Point l3ritigc , artist’s rendering(cotll-tc’sv of’ Ho\vxcl Needles I‘a~nrncn ,Y- Bergendoff).

span with 650 ft (198 m) flanking spans. The layoutof the main structure is shown in Figure 9.82.‘4

Structural arrangement of the bridge deck isshown in Figure 9.83. The bridge deck, which willcarry three lanes of traffic in each direction, willspan between longitudinal edge girders on eachside. The longitudinal edge girder is in turn sup-ported by a vertical plane of stays arranged in aharp configuration. The concrete deck and edgegirders take local and overall bending from deadand live load in addition to the horizontal thrustfrom the stavs.25 The stav cables are anchored inmassive vertical concrete pvlons, two at each mainpier, which carry all loads to the foundations, Fig-ure 9.84.

In the center span, at each edge of the deck, thestavs are in a single plane spaced 30 in. (0.76 m)vertically, Figures 9.84 and 9.85. Stavs in the sidespans, along each edge, are in two planes spaced 30in. (0.76 m) transversely. Spacing of pairs of stavsalong the edge beam is approximately 30 ft (9.1 m).Preliminary design contemplates 7 to 9 Dlwidagbars per stay, li in. (31.75 mm) in diameter, thenumber of bars per stay being a function of stressin the stay. The Dywidag bars are to be encased in ametal duct. During erection the fabricated lengthof duct is left uncoupled. After final adjustmentthe lengths of duct are coupled and pressure-grouted. Thus, the steel encasing tube will then becomposite for live load and secondary dead load.‘”

Construction proceeds bv conventional methodsfrom the top of the pier bases at elevation 15.0 ft(4.6 m) to the level of the roadway at elevation144.6 ft (44 m). At this point, a fixed formtable issecured and the first elements of the pylon andedge girders are cast. Erection of the deck is bv the

FIGURE 9.82. Dame Point Bridge, concrete cable-stayed alternative, from reference23 (courtesy of Howard Needles ‘l‘ammen & Bergendoff).

105’-10” (32 3m)

Cast-in-situ Beam.Precast T B e a m

FIGURE 9.83. Dame Point Bridge, structural arrangement of bridge deck. fromreference 24 (cowtesy of Howard Needles I‘ammen & Bergendoff).

Tower -.,

SIDE V I E W F R O N T V I E W

FIGURE 9.84. Dame Point Bridge, pylon arrangment, from reference 24(courtesv of Howard Needles Tammen & Bergendoff).

434

;OMETRIC VIEW OF ERECTION SEQUENCE PLATE 17,’ ,?x /

*’ 15,/’ / <,,de’, 15


balanced cantilever method. Two pairs of traveling horizontal. Two existing roads parallel the canyonforms are then used for sequential casting of 17.5 faces; a straight bridge across the river would re-ft (5.3 m) lengths of edge girders on each side of quire extensive cuts into the rock faces of the can-the pylon. The bridge deck consists of single-T yon to provide the necessary turning radius at theprecast floor beams spanning between longitudi- bridge approaches. This would be not only expen-nal edge girders and a cast-in-place topping. The sive but would also be damaging to the environment.precast T’s are pretensioned for erection loads. Conventional piers in the river provide prohibitiveAfter erection the entire deck is post-tensioned to design constraints, not only because of the 450 ftprovide positive precompression between edge (137 m) water depth, but also because of the seis-girders under all conditions of loading, Figure micity of the area. The hydroseismic (seiche effect)9.85.24*25 forces provide a formidable design load.

A hinge expansion joint is provided at the cen-terline of the main span to allow for changes ofsuperstructure length due to temperature, creep,and shrinkage. Similar joints are provided at theend piers, and link connections are used to preventvertical movement of the superstructure.

After extensive studies, the proposed final solu-tion was that of a hanging arc, Figures 9.87 and9.88. The geometric configuration of this structureis such that the stays are tensioned to control thestresses and strains, in order to balance all the deadload with zero deflection; the curved girder carriesthe traffic and absorbs the horizontal componentof the stays as axial compression. The stays are an-chored on the slope according to the design forma-tion to control the line of pressure in the girder.Thus, an ideal stress condition is achieved withalmost no bending or torsional moments. Afternumerous studies and trade-offs a final radius ofcurvature was selected at 1500 ft (457 m).26

9.10.3 PROPOSED RUCK-A-MUCKYBRIDGE, U.S.A.

The site for the proposed Ruck-A-Chucky Bridgedesigned by T. Y. Lin International, Figure 9.86, isapproximately 10 miles (16 km) north of the pro-posed Auburn Dam and about 35 miles (56 km)northeast of Sacramento, California, crossing themiddle fork of the American River. The river atthis location is about 30 ft (9 m) deep and 100 ft(30.5 m) wide; however, upon impounding of thewater behind the proposed dam, the river will be-come 450 ft (137 m) deep and 1100 ft (335 m)wide.26

In order to provide a 50 ft (15 m) vertical clear-ance above high reservoir water level, a bridgelength of 1300 ft (396 m) will be required betweenthe hillsides, which rise at a 40” angle from the

Two alternative designs have been prepared forthis structure, one with a steel box girder and onewith a lightweight concrete box girder. The con-crete box girder, Figure 9.89, is fixed at the abut-ments and has no hinges or expansion joints in the1300 ft (396 m) span. Depth of this box girder is8.5 ft (2.6 m), so as to provide vertical stiffness andto distribute live load and construction loads on thedeck to a sufficient number of adjoining cables.Stay anchorage at the girder is at 30 ft (9 m) inter-vals, based on construction and aesthetic consider-ations. 26

FIGURE 9.86. Ruck-A-Chucky Bridge, artiht‘s rend-ering (courtesy of T. Y. Lin).

/ ) I LAY CAe‘ES L /+\TAY CANESsourn 0U%5l0h

PEDESTALSSOUTH INSlOE

FIGURE 9.87. Kuck-A-Chucky Bridge, plan of bridge with concrete alternate, fromreference 26.

.

ABtJWENT

FIGURE 9.88. Ruck-A-Chucky Bridge, elevation of bridge with concrete alternative,from reference 26.

References

54’-0”

FIGURE 9 .89 . Ruck-A-Chuckv Bridge, cross section of concrete box girder alternative,from reference 26

References 10.

1. A. Feige, ” The Evolution of German Cable-StayedBridges-An Overal l Survey,” Acier-Stahl-Steel, N o .12, December 1966 (reprinted in AISC Engineering

Journal, July 1967). 11.2. H. Thul, ‘Cable-Stayed Bridges in Germany,” Pro-

ceedings, Conzerence on Structural Steelwork, InstitutionoJ Civil Engineer.s, September 26 to 28, 1966, London.

3. W. Podolny, Jr., and J. F. Fleming, “Historical De-velopment of Cable-Stayed Bridges,” Journal of theStructural Division, ASCE, Vol. 98, No. ST9, Sep-tember 1972.

12.

13.

4. W. Podolny, Jr., and J. B. Scalzi, ‘Construction andDesign of Cable-Stayed Bridges,” John Wiley &Sons, Inc., New York, 1976.

5. M. S. Troitskp, “Cable-Stayed Bridges-Theory andDesign,‘* Crosby Lockwood Staples, London, 1977.

6 . F . Leonhardt , “Latest Developments of Cable-S t a y e d B r i d g e s f o r L o n g S p a n s , ” Saetryk ufBygoningsstatzske Meddelelser, Vol. 45, No. 4 , 1974Denmark).

14.

15.

7. E. Torroja, Philosophy of Structures, English versionby J. J. Polivka and Milos Polivka, University ofCalifornia Pt-ess, Bet-kelev and Los Angeles, 1958.

8 . H. M. Hadley, “Tied-Canti lever Bridge-PioneerStructure in U.S.,” Civil Engineering, ASCE, January1958.

16.

9. F. Leonhardt and W. Zellner, “Vergleiche zwischenHangbrucken und Schragkabelbrucken fur Spann-w.eiten iiber 600 111,” International Association forBridge and Structural Engineering, Vol. 32, 1972.

17.

18.

R. Morandi, “Some Types of Tied Bridges in Pre-stressed Concrete,” First International Symposium,Concrete Bridge Design, AC1 Publication SP23,Paper 23-25, American Concrete Institute, Detroit,1969.

.Anon.. The Bridge Spanning Lake ,21aracn1bo in VU-ezurla, W i e s b a d e n . B e r l i n . Bauverlag (;mbH..1963.

Anon., “Longest Concrete Cable-Stayed Span Can-t i levered over Tough Terrain,” Engineering ‘Vews-Record, July 15, 1971.

N. Gray, “ChacoiCorrientes Br idge in .4rgentina,”Municipal Engineers Journal, Paper No. 380, Vol. 59,Fourth Quarter , 19i3.

H. B. Rothman, and F. K. Chang, “Longest Precast-Concrete Box-Girder Bridge in Western Hemi-sphere,” Civil Engineering, ASCE, March 1974.

W. Podolny, Jr., “Concrete Cable-Stayed Bridges,”Transportation Research Record 665, Bridge En-gineering, Vol. 2, Proceedings, Transportation ResearchBoard Conference, September 25-27, 1978, St. Louis,MO . , National Academy of Sciences, Washington,D.C.

H. Schambeck, “The Construction of the MainBridge-Hoechst to the Design of the 365 m SpanRhein Bridge Dusseldorf-Flehe,” Cable-StayedBridges, Structural Engineering Series No. 4, June1978, Bridge Division, Federal Highway Adminis-tration, Washington, D.C.

Anon. , “Tie1 Bridge,” Freyssinet International, STUPBulletin, March-April 1973.

Arvid Grant, “Pasco-Kennewick Bridge-The


Longest Cable-Stayed Bridge in North America,”Civil Engineting, AXE, Vol. 47, No. 8 , August1977.

19. Arvid Grant, “Intercity Bridge: A Concrete Ribbonover the Columbia River , Washington,” Cable-Stayed Bridges, Structural Engineering Series No.4 , June 1978, Br idge Divis ion, Federal HighwayAdministration, Washington, D.C.

20. C. Lenglet, “Brotonne Bridge: Longest PrestressedConcrete Cable Stayed Bridge,” Cable-StayedBridges, Structural Engineering Series No. 4, June1978, Bridge Division, Federal Highway Adminis-tration, Washington, D.C.

2 1. Anon., “Cable-Stayed Bridge Goes to a Record withHvbrid Girder Des ign,” Engznwring Nrw.+R~cod.October 28, 1976.

22 . Anon. , “The Danube Canal Bridge (Austr ia) ,”

Freyssinet International, STUP Bulletin, May-June,1975.

23. Anon., “Morandi-Stvle Design Allows Constant Sus-pended Spans ,” C’otr~wlting Enginret ( L o n d o n ) .

March 1967.

24 . H. J . Graham, “Dame Point Bridge,” Cable-StayedBridges, Structural Engineering Series No. 4, June1978, Bridge Division, Federal Highway Adminis-tration, Washington, D.C.

25 . Anon. , “Dame Point Bridge,” Design Report, How-ard Needles Tammen SC Bergendoff , November1976.

26. T. Y. Lin, Y. C. Yang, H. K. Lu, and C. M. Redfield,“Design of Ruck-A-Chucky Bridge,” Cable-StayedBridges, Structural Engineering Series No. 4, June1978, Bridge Division, Federal Highway Adminis-tration, Washington, D.C.

1 0Segmental Railway Bridges

1 0 . 1

10.2

10.3

10.4

10.5

10.6

10.7

10 .1

INTRODUCTION TO PARTICULAR ASPECTS OFRAILWAY BRIDGES AND FIELD OF APPLICA-TION

LA VOULTE BRIDGE OVER THE RHONE RIVER,FRANCE

MORAND BRIDGE IN LYONS, FRANCE

CERGY PONTOISE BRIDGE NEAR PARIS,FRANCE

MARNE LA VALLEE AND TORCY BRIDGES FORTHE NEW EXPRESS LINE NEAR PARIS, FRANCE

CLICHY RAILWAY BRIDGE NEAR PARIS,FRANCE

OLIFANT’S RIVER BRIDGE, SOUTH AFRICA

Zntroduction to Particular Aspects of RailwayBridges and Field of Application

Construction of segmental post-tensioned bridgesfor railway structures started in France in 1952with a bridge crossing the Rhone River at LaVoulte, Figure 10.1. It has been used extensivelysince that time in many countries. Precast seg-mental construction was introduced in railwaystructures in France with the Marne la Vallee Via-duct and in Japan with the Kakogawa Bridge,while incremental launching was adopted for sev-eral large railway crossings including the world’slongest bridge of this type: the Olifant’s RiverBridge in South Africa (see Section 7.5).

The major characteristic distinguishing railwaybridges from highway bridges is the magnitudeand application of loading. Live loading on a rail-way structure is two to four times larger than thatapplied to a highway bridge of comparable size.Every time a train crosses a railway bridge, the ac-tual load applied to the structure is much closer todesign live load than for a highway bridge, whereeven dense truck traffic usually represents only a

10.8

10.910.10

10.11

INCREMENTALLY LAUNCHED RAILWAYBRIDGES FOR THE HIGH-SPEED LINE, PARISTO LYONS, FRANCESEGMENTAL RAILWAY BRIDGES IN JAPANSPECIAL DESIGN ASPECTS OF SEGMENTALRAILWAY BRIDGES

10.10.1 Magnitude of Vertical Loads10.10.2 Horizontal Forces10.10.3 Bearings10.10.4 Stray Currents10.10.5 Durability of the Structure10.10.6 ConclusionPROPOSED CONCEPTS FOR FUTURE SEGMEN-TAL RAILWAY BRIDGES

moderate proportion of the design load. Fatigueand durability of railway structures, therefore, areessential problems and need careful consideration,particularly in view of the fact that maintenanceand repair of railway structures under permanent

FIGURE 10.1. La Voulte Bridge. view of the com-pleted structure.

441

Segmental Railway Bridges

traffic is a very critical operation that can lead tounacceptable disturbance in a railway network.

10.2 La Voulte Bridge over the Rhone River,France

This first segmental prestressed concrete railwaybridge is a notable structure and a landmark in thedevelopment of prestressed concrete. Constructedin 1952, it carries one railway track over the RhoneRiver near la Voulte, 80 miles (128 km) south ofLyons, in the southeastern part of France.

The structure has five spans, each 164 ft (50 m)long. Each pier is made up of two inclined legs, andeach span is an independent frame supported byan inclined leg at each end. Between the inclinedlegs on each pier, the deck is supported by a smallbeam resting on simple bearings.

Construction proceeded using the cantileverscheme, with poured-in-place segments. The formtravelers were supported by a temporary steel trussbridge, Figure 10.2. The cantilevers were builtsymmetrically in one span, the unbalancedmoments being taken care of by temporarypost-tensioning connecting the two inclined legsand the independent beam on one pier. The seg-ments were 9 ft (2.75 m) long. The bending mo-ments of each completed frame were adjusted byjacks placed at midspan and by continuity post-tensioning tendons, Figure 10.3.

10.3 Morand Bridge in Lyons, France

This structure is a combined highway and mass-transit bridge over the Rhone River in Lyons,

FIGURE 10.2. La Voulte Bridge, aerial view of thedeck under construction.

FIGURE 10.3. L,a Voulte Bridge, cantllcver- deck con-struction in progress.

France’s third largest city. It is a three-span con-tinuous structure with span lengths of 160, 292,and 160 ft (49, 89, and 49 m), resting on two riverpiers and two end abutments, which allow the tran-sition of highway and railway traffic on both banks.The deck is made up of two parallel box girderscarrying at the upper level three lanes of highwaytraffic including sidewalks. Inside each box girderis a railway track for the mass-transit system, Fig-ure 10.4.

This final scheme proved to be significantly lessexpensive and more efhcient in terms of the layoutof the railway system than did the initial proposal,which contemplated a submerged tunnel for therailway crossing and a separate bridge for thehighivay traffic.

Dimensions of the structure in cross section areshown in Figure 10.5. The railway clearance of 13ft 5 in. (4.12 m), including ballast and rail, calls fora 15 ft (4.56 m) structural height in excess of thenormal requirements for a maximum span lengthof 292 ft (89 m). A constant-depth girder couldthus be maintained throughout the river crossingexcept in the vicinity of the river piers, where shortstraight haunches allow the depth to be increasedto 22 ft 7 in. (6.90 m). Over the piers a strongtransverse diaphragm connects the two boxgirders, and the additional height over the pierallows the continuity of the diaphragm over theheight of the haunch while the full clearance ofthe trains is maintained inside the box girders.

The deck was built in balanced cantilever with 10ft (3.0 m) long cast-in-place segments using onepair of travelers on a typical one-week cycle, Fig-ures 10.6 and 10.7.

Typical quantities of materials are as follows forthe deck alone:

Mot-and Bridge in Lyons, France 443

FIGURE 10.4. Morand Bridge, perspective view of the structure.

ON PIER AT MID-SPAN

FIGURE 10.5. Mm-and Bridge, typical cross section.

Deck area 31,200 ft* 2,900 m2Concrete 3,100 yd” 2,400 m3

Reinforcing steel 618,000 lb 280,000 kgPrestressing steel 256,000 lb 116,000 kg

(longitudinal andtransverse)

FIGURE 10.6. Mm-and Bridge, construction of thesuperstructure.

Both concrete and reinforcing steel quantities farexceed those required for a typical highway be-cause of the very important increase of loads dueto the railway lines in the box girders.

The s tructure was completed and opened totraffic in 1977.

Segmental Railway Bridges

single box carries the twin tracks, with the depthvarying between 13.6 ft (4.15 m) and 17.9 ft (5.45m) for the maximum span length of 280 ft (85 m)as shown in Figures 10.9 and 10.10. The segmentaldeck was cast in place, with travelers working in theconventional balanced cantilever fashion.

FIGURE 10.7. MOI and Bridge, (onstl uction o fsuperstructure. Note pier segment for second parallelbox girder.

10.4 Cergy-Pontoise Bridge near Paris, France

A new railway line was completed in 1977 betweenParis and the new satellite town of Cergy-Pontoise.A major prestressed concrete structure carries thisline over several obstacles, including an inter-change between two expressways (A-86 and A-14)and two branches of the Seine River.

The trestle structures have a solid slab deck withspans varying between 65 ft (20 m) and 117 ft(35.60 m). Typical dimensions of the two mainbridges over the Seine are shown in Figure 10.8. A

10.5 Mane la Vallee and Torcy Bridges for theNew Express Line near Paris, France

The extension of the Paris mass-transit system inthe highly populated southeastern suburbs was theoccasion for building a long elevated segmentalprestressed concrete railway structure in a sensitiveurban environment, Figure 10.11. This structure,located in the city of Marne la Vallee, includes abridge over the Marne River and a long viaductcarrying two parallel railway tracks. Near the tran-sition between the river bridge and the viaduct apassenger station is carried by the bridge structure.

Three major considerations guided the choice ofthe structure:

Maintain maximum clearance at ground level, notonly to reduce the visual disturbance to theneighboring population, but also to allow all piersof the new structure to be fully compatible with thelayout of all existing and future roads.

Elevation

(a)

Typical cross section

(b)

FIGURE 10.8. Cergy-Pontoise Bridge, dimensions. (a) Elevation. (b) Typical crosssection.

Marne la Vallee and Torcy Bridges near Paris, France 4 4 5

FIGURE 10.9. Ccrg!-Pontoise Bridge, cantilever con-s t ruc t i on .

FIGURE 10.10. Ckrgy-Ponroise Bridge, main spanclosure .

Produce a structure that is aesthetically pleasingwhen seen constantly from nearby.

Protect the neighboring population from unac-ceptable noise aggression.

Basically, the structure is a single box of constantdepth built of precast segments assembled by pre-stress into a continuous beam; the beam rests uponvertical piers provided with an architectural shapeand regularly distributed at distances of 90 ft (27m) to 120 ft (36 m), Figure 10.12.

Both parallel tracks are laid on the transverselyprestressed deck slab of the box girder and on acrushed-stone bed retained sideways by three con-tinuous reinforced concrete walls. A central noisebarrier separates the two opposite tracks and pre-vents the noise of a train riding one track to travelacross to the other. At the edge of the concrete boxgirder, precast concrete panels manufactured withspecial white cement improve the appearance ofthe structure while providing the outside soundbarriers.

FIGURE 10.11. Marne la Vallee Bridge, ae~i,~l Liewof the completed structure.

FIGURE 10.12. Mane la Vailee Bridge, view offinished structure from ground level.

In plan, the structure is laid out on a curve with aminimum radius of curvature of 1640 ft (500 m),Figure 10.11. Characteristic dimensions of theMarne la Vallee Viaduct are shown in Figures10.13 and 10.14 and are summarized as follows:

1 . Bridge over the Marne River:a. Total length, 528 ft (161 m).b. Three-span continuous bridge with spans

of 157,246, and 125 ft (48,75, and 38 m).c. Cross section: constant-depth box section

with depth of 12.8 ft (3.90 m), web thick-ness varying from 20 to 35 in. (0.50 to 0.90m) and bottom flange thickness from 7 in.(0.18 m) at midspan to 5 1 in. (1.30 m) overthe river piers. Length of precast segments5.6 ft (1.71 m).

d. Two river piers are founded on large-diameter bored piles and support thesuperstructure through special teflonbearings.

nI

t

ALLUVIUM DEPOSITS

LIMESTONE

S A N DFIGURE 10.13. Mar-ne la Vallee Bridge, typical sections of deck and piers.

446

Marne la Vallee and Torcy Bridges near Paris, France 447

f. All bearings in the viaduct are standardlaminated elastomeric pads.

c- 4~70 250- ~~~km-- - I I 00

12 CROSS 12 M I D S P A NSECTION ON P IER C R O S S S E C T I O N

(0)

g. Piers are made of twin columns locatedunder the webs of the box girder and con-nected at ground level by a common foot-ing, which transfers the loads to deepslurry trenched walls anchored in lime-stone. The number and position of thesebearing walls under each pier has beendetermined in relation to the magnitudeof the transverse and longitudinal hori-zontal loads transferred by the superstruc-ture, particularly in the curved portion ofthe viaduct.

(b)

FIGURE 10.14. Xlarne la Vallee and .Torcy Viaduct,topical deck sections. (0) I\larne la Vallee trestle andI‘orq Viaduct cross section. (h) klarne la Vallee Bridge

over the Llarne River.

2. Elevated viaduct:a . Total length, 4482 ft (1367 m).

b. The viaduct is divided into 11 sectionsseparated by expansion joints, allowingcompatibility of thermal stress between thecontinuous welded rails and the concretesuperstructure. The typical section is 412ft (126 m) long with four spans of 88, 118,118, and 88 ft (27, 36, 36, and 27 m).

c. The two south viaduct sections adjacent tothe main river crossing carry the passen-ger station and have shorter spans 69and 92 ft (21 and 28 m).

d. Typical cross section is a single box carry-ing the two tracks with two main verticalwebs 35 in. (0.90 m) thick and two sharplyinclined facia webs used essentially for ar-chitectural purposes to reduce the appar-ent structural depth of the box and focusthe eye on the high parapet wall.

e . Average length of precast segments 7.5 ft(2.30 m).

The entire project was predicated on the use ofprecast segments with match casting and epoxyjoints. A precasting yard on the south bank of theMarne, using four casting machines, produced the690 segments with a maximum weight of 60 tons(55 mt) in eleven months. Segments were trans-ported with a tire-mounted self-propelled carrierover the finished portion of the deck and placed inthe structure with a launching gantry, Figure10.15, in balanced cantilever. The gantry used onthat project was that designed and built earlier forthe B-3 Viaducts project.

The gantry allowed all operations to be per-formed from the top in complete independencefrom the ground and all its related constraints.Placing of all segments was performed in a periodof nine months between March and December of1976, including the three spans of the main bridgeand the fortv-four spans of the viaduct. The entireproject was’completed in 24 months (includingpreparation of the final design), for a total deckarea of 190,000 ft* (17,600 m’). Figure 10.16 shows

FIGURE 10.15. Marne la Vallee Bridge, precast seg-ments placed with the launching gantry.

FIGURE 10.16. l\larne la \‘allee Bridge, crossing theMarne River and elevated passenger station.

FIGURE 10.17. Marne la Vallee Bridge, aerial view ofthe river crossing, a passenger station, and the elevatedviaduct.

the northern span of the river crossing and the ele-vated passenger station. Figure 10.17 is an aerialview of the overall project.

In view of the success of this first application ofsegmental construction in urban railway elevatedstructures, the Paris Mass-Transit Authority de-cided to extend the same concept to construct an-other large structure a few miles eastward: theTorcy Viaduct. Fortunately, the precasting yardfor the first bridge was still available and all seg-ments could be manufactured there and trucked tothe second bridge site, Figure 10.18.

Dimensions of this new bridge are as follows:

Cross section: exactly the same as for the Marne laVallee elevated viaduct.Distribution of spans: 17 spans with typical spanlength of 115 ft (35 m).

FIGURE 10.18. Torcy Viaduct, segment transporta-tion from Marne la Vallee to Torcy.

The total length of 1870 ft (570 m) is divided intothree separate sections: one four-span unit, onenine-span unit, and one four-span unit.

Precast segments were placed in the structurewith an overhead launching gantry of a typeslightly different from the one used previously,although calling on the same sequence of move-ments. Two parallel longitudinal trusses makethe track for a transverse overhead portal cranecarrying and placing the segments between thetrusses. Figures 10.19 and 10.20 show the generalview of the gantry and the detail of one segmentplacing. The overall view of the finished bridgeappears in Figure 10.21.

FIGURE 10.19. ~l‘orcy Viaduct, precast segment plac-ing with launching gantry.

Clichy Railway Bridge near Paris, France 4 4 9

vated metro. It crosses the Seine River adjacent to anew highway bridge between the cities of Clichyand Asnieres, as shown in Figure 10.22. Layoutand principal dimensions appear in Figures 10.23and 10.24.

The prestressed concrete segmental structure is1350 ft (412 m) long with a 280 ft (85 m) main spanover the river with a deck of variable depth. Theriver piers of the two railway and highway bridgesmatch exactly to minimize water flow and bargetraffic disturbance. A provision is made for a sec-ond future highway bridge at the other side of therailway bridge, as seen clearly in Figure 10.25~.

The restricted transverse clearances between thethree structures and their corresponding trafficexplains the special shape of the piers for thecenter railway bridge, which was carefully studiedarchitecturally to enhance the appearance of theproject. Foundations were very close to one an-other but could be maintained structurally inde-pendent to better control settlement and avoid vi-bration interference between bridges and in theground.

FIGURE 10.20. I’orcy V iaduc t , de t a i l o f s egmen thandling between twin trusses of launching gantry.

To carry the two railway tracks, the deck has atypical cross section consisting of three precastwebs connected by a bottom slab, which forms es-sentially the compression flange over the piers, andan intermediate slab, which receives the ballast,Figures 10.25b and 10.26. The depression thusrealized between the web top flange and the trackshas several advantages, including providing fullsafety against derailing on one track and reducingthe noise level.

Construction of the superstructure includedmatch casting of all webs in a yard near the projectsite. The webs were placed in balanced cantileverwith a light portal crane carried by the finished

FIGURE 10.21. Torcy Viaduct, view of the completedstructure.

10.6 Clichy Railway Bridge near Paris, France

At about the same time the two structures de-scribed above were built, a large and innovativerailway bridge was constructed in the northeasternsuburb of Paris for another extension of the reno-

FIGURE 10.22. Clichy Railway Bridge, view of thecompleted structure.

450 Segmental Railway Bridges

Lot 4 SW_ 76s~ .I1 +L o t 3 sur 4 1 1 . 7 0 m

9!i 32

j+?i3 rl,

FIGURE 10.23. Clichy Railway Bridge, layout and elevation of the structure. (n) Planview. (h ) E leva t ion .

cf!mfy~-~4 . 5ElNE RIVER~_~~~ ~~-~~ ~(kg C-7) (rps) cps) P/a, (?& 6%fJ m-g

FIGURE 10.24. Clichy Railway Bridge, main dimensions of segmental structure.

portion of the deck, Figure 10.27. Maximum twin slab sections were poured in place between theweight of precast webs was 19 tons (17 mt), webs in balanced cantilever on very simple travel-whereas segments that included the full three-web ers. Web segments were 7.3 ft (2.22 m) long for thebox (or even a more conventional single box for constant-depth part of the deck and 4.8 ft (1.48 m)the equivalent span length) would have weighed in for the variable-depth part. In fact, the slabs wereexcess of 66 tons (60 mt). After assembly of precast cast in place between the three webs in two or threewebs with longitudinal post-tensioning, the two increments of that length respectively (a length of

451Clichy Railway Bridge near Paris, France

LEGENDE

FIGURE 10.25. Clichy Railway Bridge, typical sec-tions of piers and deck. (a) Elevation of land and riverpiers. (b) Dimensions of the deck cross section.

14.6 or 4.44 m) to reduce the number of site oper-ations. A three-day cycle of operations could beconstantly maintained, including some overtimework for the larger segments near the river piers.Overall, construction in cantilever of the totalsuperstructure took one year between September1977 and September 1978.

A special design aspect, specific to railwaybridges, was the transfer of horizontal loads (in-

(a)

FIGURE 10.26. Clichv Railway Bridge, pier segnrentand cantilever constr&ion.

duced through braking or starting of the trainsover the bridge), to the piers and foundations. Asingle fixed bearing was provided over pier P6, thefoundation of which was designed to transfer to

4 5 2 Segmental Railway Bridges

FIGURE 10.27. Clichy Kailway Hrtdge, plar~ng pre-cast webs for cantilever construction.

the limestone stratum the total maximum hori-zontal load of 660 tons (600 mt) applied to thebridge. There are three pot bearings between thedeck and the pier shaft, each capable of safelytransferring half of the maximum horizontal load.Each bearing can thus be changed under trafficwithout reducing the capacity of the structure.

Special provisions were also included at the de-sign stage, Figure 10.28, to allow additional pre-stressing to be incorporated in the structure should

fb)

FIGURE 10.28. Clichy Railway Bridge. (a) View ofad.jacent highway and railway bridges crossing the SeineRiver. (b) Provisions for future additional p&tress.

the need arise in the future. Two families of ten-dons could be added:

Above the lower slab in the two voids of the boxsection, anchors being provided in blisters alreadybuilt in the structure.

Atop the center precast web and on the outsideface of the two facia webs, anchor blocks and de-viation saddles being prestressed by high-strengthbolts to the precast webs.

The large precast architectural panels on bothsides of the deck could be temporarily removed toallow this work of additional prestresstng to be per-formed. Upon completion, all additional tendonswould be fully protected and concealed behind thepanels.

The new line has been open to traffic since May1980, and the first months of operation confirmthat the precautions taken to reduce noise and vi-bration disturbance through welded continuousrails and sound-barrier panels make such elevatedstructures an acceptable solution for mass-transitlines in urbanized areas.

10.7 Olifant’s River Bridge, South Africa

This structure is part of a line carrying iron ore onspecial heavy trains 7500 ft (2300 m) long made upof 200 cars with a total weight of 19,000 tons(17,000 mt) to connect the Sishen mines to the har-bour of Saldanha 110 miles north of Capetown.Olifant’s River Viaduct is today the world’s longestincrementally launched prestressed concretestructure (refer to Chapter 7) with a total length of3400 ft (1035 m) and 23 spans of 148 ft (45 m),Figure 10.29.

Shown in cross section in Figure 10.29, the singlebox girder deck accommodates only one track onballast. The equivalent uniform live load of the 33ton (30 mt) axles is 7.1 kips/lineal ft (10.5 mt/lm),which is increased by an impact factor of 1.29.

The 23 spans are divided into two 1 l-span sec-tions, each anchored to the end abutment, and onesingle transition span at the center. This schemeallows all horizontal loads to be transferred to theabutments. The maximum horizontal reaction in-cluding all thermal effects is in excess of 1200 tons(1100 mt). The piers, which vary between 80 ft (25m) and 150 ft (55 m) in height, are extremely flexi-ble and do not, therefore, have an important effecton the horizontal restraint of the structure, exceptduring construction. The pier shafts have an I-

Incrementally Launched Railway Bridges 453

I L 3.10 ;I

5 50m c

(b)

-I

51nl--L

FIGURE 10.29. Olifant’s River Viaduct. (a) Generalview of the structure. (b) ‘T‘ypical cross section.

shaped cross section with longitudinally taperedfaces. Neoprene bearings are used for the piersnear the abutments and teflon sliding bearings inthe center of the structure.

The deck was entirely constructed behind oneabutment (see schematic view in Figure 7.29) andincrementally launched in one direction. Construc-tion time for the superstructure was nine months,with a theoretical cycle of 10 working days for atypical 148 ft (45 m) span realized after 10 spans; itwas further reduced to seven days with two shiftstoward the end of the project. The total weight ofthe superstructure of 14,500 tons (13,000 mt)called for two 200 ton jacks for the push-out oper-ations in increments of 3.5 ft (1 .OO m). A 60 ft (18 m)long launching nose was used in front of the firstspan to reduce the variation of bending stresses inthe superstructure during the successive stages ofconstruction, Figure 10.30. The bridge nearingcompletion is shown in Figure 10.3 1; it was openedto iron ore trains in 1976.

10.8 Incrementally Launched Railway Bridges forthe High-Speed Line, Paris to Lyons, France

To meet increased competition by domestic air-lines, the French National Railways decided to

FIGURE 10.30. Olifant’s River Viaduct, launchingnose reaching beyond a high pier.

build some new very-high-speed train lines (safemaximum speed of 200 mph or 320 km/hr) andstarted the construction of the first such line be-tween Paris and Lyons, which included an entirelynew structure over a distance of 250 miles (400km) with proper connections to the existing met-ropolitan track and station system.

The new project required 400 bridges includingnine large viaducts, such as the structure shown inFigure 10.32. A very comprehensive optimizationstudy followed, and a set of guidelines and struc-tural standards were prepared for the French Na-tional Railways by a team of engineers headed byone of the authors. Results of the preliminary in-vestigations and of this optimization study can besummarized as follows:

1. Track alignment is chosen to keep the curva-ture in plan more than 10,500 ft (3200 m) andpreferably more than 13,000 ft (4000 m). The

FIGURE 10.31. Olifant’s River Viaduct, view of thestructure nearing completion.

FIGURE 10.32. Railwq Viaducts for Paris-Lyonshigh-speed line, view of the viaduct over the SaoneRiver.

corresponding cross fall between rails is 7 in.(180 mm).

2. All rails are to be continuously welded andplaced on a ballast bed with a minimum thick-ness of 14 in. (0.35 m).

3. Maximum rigidity of the structures is obtainedby using a continuous box section with slen-derness rat io of l/14. The corresponding

4.

5.

6.

maximum deflection under design load istherefore l/2000 of the span, whereas conven-tional specifications for normal-speed linesallow up to l/800.Adopt as much as possible single box girderdecks for the two parallel tracks with minimumweb thickness of 14 in. (0.35 m) and aminimum top slab thickness of 10 in. (0.25 m).

The optimum span length is between 150 and170 ft (45 to 50 m), which leaves the construc-tion method open to various solutions (can-tilever, span-by-span or incremental launch-ing).

The horizontal loads should be transferred toone abutment equipped with a special fixedbearing, allowing all piers to be relieved of anyappreciable longitudinal bending. A typicalH-sect ion was adopted as the most appro-priate except for certain specific locationswhere a box section might be required.

Because many of the viaducts were located in en-vironmentally sensitive areas, an overall architec-tural study was also conducted to establish a unityof appearance for all bridges in terms of the shapesof deck and piers, parapet or guard rails, abut-ments and approach fills.

Of the nine viaducts, two were finally con-structed with conventional methods and the re-maining seven were incrementally launched. Thismethod proved economical in view of the moder-ate span lengths, the depth of the box section avail-able, and especial ly because the superimposeddead and live loads were so much more importantthan for a highway bridge that the increaseddead-load moments during construction were inproportion of much less significance.

Table 10.1 gives the essential characteristics ofthe seven segmental viaducts, including principalquantities of materials for the superstructure. Ele-vations of five bridges appear in Figure 10.33.

As an example of the construction method, somedetails are given for the bridge over the SaoneRiver, where a launching nose 93 ft (28.50 m) longand weighing 71 tons (65 mt) was used in front ofthe first span to reduce the stress variations in thesuperstructure during launching, Figure 10.34.

The bridge superstructure was cast in successiveincrements in a fixed location behind the rightbank abutment in the length of a half-span,Figure 10.35. A typical sequence of operations isshown schematically in Figure 10.36. Eachsuperstructure section is in fact cast in two stages

BridgeLocationand Span Lengths

[ft @)I"

Table 10.1. Characteristics of Segmental Viaducts on the Paris-Lyons High-Speed Line

Dimensions of Deck Quantities of

[ft or in. (m)) D e c k

H.T. Reinf.Flange Thick. C0ncr. S t e e l S t e e l

Total B O X Web Pier YearBridge Bridge Width Height W i d t h Thick. TOP Bottom Height [ftvf? [Ib/yd3 [Ib/yd3 Corn-Layout Length (ft) (W (f0 (in.) (in.) (in.) lft WI WWI (kg/m?1 (kg/&)1 pleted

@J Saulieu115-3@ 144- 115(35 - 3 @ 44 - 35)

Q Serein

6 6 2

115-3@ 1 4 4 - 1 1 5

(35 - 3 @ 44 - 35)0 SamRium155 ~ 5 (a: 164 - 137

(47.2 - 5 6 50 - 41.8)

hong. grade: 1.3%Radius in plan:20,000 ft (6000 m)Lrmg. grade: 0.95%

Radius in plan:26,000 ft (8000 m)Circular profilein elevation:R = 130,000 ft(40,000 m)

41.0 1 0 . 8 1 8 . 0

(202) (12.50) (3.30) (5.50)

6 6 2 41.0 1 0 . 8 1 8 . 0

w-w (12.50) (3.30) (5.50)

40.3(12.30)

@ figtine109-8@ 144- 1 0 9(33.4 - 8 @ 44 - 33.4)@I Rochc

39.0(11.90)

108-7@149-108(33.1 - 7 I@ 45.5 - 33.1)0 Seine River114-ZOl- 114(34.8 - 61.4 - 34.8)Q cmler Cad (length)85 - 105 - 85(26 - 32 - 27)

39.0(11.90)

1 1 1 2

(339)

Long. grade: 2.5% 1 3 7 0

Straight in plan (419)Long. grade: 3.5%

Radius in plan: 1 2 6 010,600 ft (3250 m) (385)

Long. grade: 0.55% 429Straight in plan (131)

Long. grade: 0.2% 279Straight in plan (85)

“Structures are numbered with increasing numbers from Paris to Lyons.

41.0(12.50)

40.0(12.10)

1 1 . 5(3.51)

1 0 . 8

(3.30)

1 0 . 8(3.30)

1 3 . 1(4.00)

7 . 8(2.37)

1 8 . 0(5.50)

1 8 . 0

(5.50)

1 8 . 0(5.50)

1 9 . 0(5.80)

1 9 . 0(5.80)

18/49 11(0.45/1.25) (0.275)

18/49(0.45/1.25)

1 1(0.275)

2 0(0.50)

1 2 . 5(0.32)

2 4(0.60)

1 2 . 5(0.32)

2 4(0.60)

1 2 . 5(0.32)

24135(0.60/0.90)

11(0.28)

1 2(0.30)

1 0(0.25)

I O 461121(0.25) (14137)

I O 661148

(0.25) (20/45)

1 2 . 5 4 6(0.32) (14)

1 4 43/105(0.35) ( 13/32)

1 4 43/l 15

(0.35) (I 3135)

12120 3 6(0.30/0.50) (11)

8 4 3(0.20) (13)

2 .52(0.77)

2 .52(0.77)

2.46(0.75)

2.30(0.70)

2.30(0.70)

7 8

(46)

7 8

(46)

8 4

(50)

8 4

(50)

8 4

(50)

8 4

(50)

-

2 4 0

(140)

2 4 0

(140)

2 1 0

(125)

2 5 0

(150)

2 5 0

(150)

1 9 0

(110)

1978

1 9 7 9

1 9 7 9

1 9 7 8

1 9 7 8

1 9 8 0

1 9 7 8

Viaduc du Serrein

FIGURE 10.33. Elevation of five segmental bridges for Paris-Lyons line.

456

Segmental Railway Bridges in Japan 457

FIGURE 10.34. S;IO~C Kivcl- Bridge, launching noseapproachtng pier.

FIGURE 10.35. Saone Kivcr Bridge, xrial 1 ie\\ withcasting vard in behind abutment in foreground.

TEMPORARY SUPPORTF O R PUSHN;

(bottom slab during the first stage, webs and topslab during the second stage). The typical con-struction cycle allowed casting a half-span everyweek-that is, constructing two spans per month.

The launching operation proper called for avery efficient system, developed and perfectedpreviously in Germany, including under each webof the box section:

One vertical jack with sliding plateTwo coupled horizontal jacks for actual launching,allowing movements in 3 ft increments

Typically, launching of an 80 ft section took threeto three and a half hours, despite the large weightof the concrete superstructure, reaching 9000 tons(8000 mt) at the end of construction.

Figure 10.37 shows a completed structure, andFigure 10.38 shows another aspect of the con-struction of these seven viaducts.

10.9 Segmental Railway Bridges in Japan

Many railroad bridges have been built in Japanusing the segmental construction technique. Thesketches shown in Figures 10.39 through 10.42 de-pict the elevation and the cross section of the fol-lowing cast-in-place segmental bridges:

Kyobashigawa BridgeNatorigawa Bridge

APPROACH_^-wAN~PRECAST Y A R D eSLIDING PACE

* .~~ - - - - -~

SITUATION DURING FABRICATION OF SEGMENT 7,2r550~25~0 7Q5 0 0-%!!L

SITUATION AFTER PUSHING OF SEGMENT 7

GENERAL PRINCIPLE OF THE CONSTRUCTION METHOD BY PUSHING

FIGURE 16.36. Saone River Bridge, typical construction stages of incre-mental launching.

FIGURE 10.37. Saone River Bridge, view of‘ the completed structure.

FIGURE 10.38. Digoine Bridge, incremental launch-ing over high piers.

Kisogawa Bridge

Ashidagawa Bridge

Figure 10.43 shows the Kakogawa Bridge duringconstruction. The superstructure is made of twinconstant-depth box girders, one box girder carry-ing one railway track. The total length of thebridge is 1640 ft (500 m), with typical span lengthof 180 ft (55 m). Each box is 13 ft (4 m) wide and11.5 ft (.3.50 m) deep. The precast segments werehandled by a launching gantry and assembled bylongitudinal post-tensioning tendons. The erectionused the balanced cantilever system.

The most outstanding prestressed concrete rail-way structure, however, is the Akayagawa arch

bridge shown in Figure 10.44. Total length is 980ft (298 m) and the center arch span is 410 ft (126m). The 13 ft (4.00 m) deep box girder carryingtwo railway tracks is continued throughout be-tween abutments and rests over the center gorgeon a very flat arch rib through ten spandrel col-umns. The respective proportions are such that thedeck carries all bending moments and the arch ribcarries the normal load induced by its curvature.The erection scheme was unique and called forcantilever construction starting from both sides.

A very strong back stay made up of a prestressedconcrete member with a prestress force of 5300tons (4800 mt) was installed diagonally between thetop of the main transition piers between the archstructure and the approaches on one hand, and thefoundation of the adjacent piers in the approachstructures on the other hand.

While erection progressed, high-strength steelbars were placed diagonally between the verticalmembers, forming a temporary truss structureuntil the crown was reached from both ends. Con-trol of tensioning of those steel bars was very criti-cal and complicated. Finally, all steel bars and thetwo temporary back stays were removed after clo-sure of the arch at midspan.

10.10 Special Design Aspects of SegmentalRailway Bridges

10.10.1 MAGNITUDE OF VERTICAL LOADS

Most bridges carry tracks laid on ballast with aminimum thickness of 10 to 14 in. (0.25 to 0.35 m).

Special Design Aspects of Segmental Railway Bridges 459

SHIN OSAKA199 8Om

-L 33.90 66.00 66.00 33.90HAKATA

ELEVATION

p-s- 61 51 / j 2 so 2.70 '---+I IO 5 90 92 m i24,

CROSS SECTION

FIGURE 10.39. Hyobashigalva Bridge, Japan

Live loading used in design of railway bridgesvaries between countries-Cooper loading forAnglo-Saxon countries, new UIC loading for mostEuropean countries-and also according to the na-ture of the structure: mass-transit lines are usuallydesigned for much lighter loads than normal trainlines. The heaviest loadings are for ore freighttrains.

To exemplify the basic difference between ahighway and a railway bridge, Figure 10.45 com-pares a typical 150 ft span and a 36 ft wide decknormally designed for three highway lanes oftraffic or two railway tracks. The total superim-posed dead and live load is 3.6 times greater forthe railway bridge. In addition, the weight of bal-last (representing 40% of the total load) must beconsidered as a live load to cover the cases wherethe ballast is removed from the deck or has not yetbeen placed on a new bridge.

10.10.2 HORIZONTAL FORCES

Railway bridges have to carry very important hori-zontal forces, between five and ten times the hori-zontal forces carried by a highway bridge of similarsize. The standard current practice for long via-ducts is to have a fixed bearing on one abutment ifthe bridge length is less than 1500 ft (450 m), andon both abutments and on intermediate specialbents if it is greater. The order of magnitude ofthis horizontal force on the abutments carrying thefixed bearings is often 1000 tons for a two-trackviaduct.

The various forces involved are described below:

Longitudinal Forces

Braking and acceleration forces


TOKYO MORIOKA/ 524.90 m ,A

ELEVATION

C R O S S S E C T I O N

FIGURE 10.40. Natorigawa Bridge, Japan.

Forces due to box girder deformations: creep,shrinkage, and temperature variationsLoads induced by the length variations of longwelded rails under temperature variationsLongitudinal component of wind forces

Braking and acceleration forces are one-seventh of the total weight of live loads, with aceiling of 285 tons for braking and 53 tons for ac-celeration (French regulations).

Forces due to longitudinal deformations of thebox girder vary because of creep, shrinkage, andtemperature variations. The bearing displace-ments induce horizontal loads by distortion orfriction.

Transuerse Horizontal Forces Centrifugal horizorltalforce can be very important f-or high-speed trains.For the 200 mph train from Paris to Lyons thisforce is more than 400 tons for some viaducts 1200ft (380 m) long with two tracks and radius of cur-vature of 10,500 ft (3200 m). The lateral accelera-tion is more than 20% of that of gravity.

Transverse wind force is described in theAASHTO standards (50 lb/f?).

10.10.3 BEARINGS

Length variations of the long welded rails due to In order to gain complete control of these ver)temperature variations create a horizontal force large horizontal forces, the bearings are speciallyparallel to the rail. This force can be estimated at designed to take care of the vertical loads and ro-50 tons per rail (length of rail more than 100 me- tation of the box girder and simultaneously to pro-ters). For a two-track bridge it is 2 x 2 x 50 = 200 vide all possible horizontal restraints (fixed bear-tons. ing, bearing free lengthwise or crosswise, or both).

Longitudinal component of wind forces are de-scribed in the AASHTO specifications for bridges.

Special Design Aspects of Segmental Railway Bridges 461

ELEVATION

CROSS SECTIONFIGURE 10.41. Kisogawa Bridge, Japan.

These bearings are specially manufactured for thistvpe of structure, Figures 10.46 and 10.47. Thesliding parts consist of a teflon-coated plate restingon a stainless steel plate, and the restraints are pro-vided by steel keys.

ference of potential with the ground may be mea-sured at regular intervals, and a permanent con-nection with the ground may be decided on as aresult.

10.10.~ DURABILITY OF THE STRUCTURE

10.10.4 STRAY CURRENTS

For structures carrying electrified railways there issome uncertainty about the long-term effect ofstray currents generated near the power lines. Inorder to preclude electrolytic corrosion of rein-forcing steel and prestressing steel, the followingprecautions are now taken in prestressed concretestructures:

The deck is electrically isolated from the ground,piers, and abutments by elastomeric plates.The reinforcing and prestressing steel systems ofthe entire deck are interconnected by mild steelbars to equalize the electric potential. The dif-

Because very difficult problems of train trafficwould arise during repairs to these bridges, theirdurability needs special attention. The followingprovisions were established for the high-speedbridges between Paris and Lyons:

Under the worst service loads the concrete mustremain under a 140 psi minimum compression.For continuous bridges, the design shall bechecked by weighing the dead-load vertical forceon the bearings.The stressing force of the post-tensioning tendonsshall be less than 80% of the ultimate strength ofthe tendons.

NAGOYA-


317.00 m

ELEVATION

---e-J

I ‘!I53 2.30 ./. 2.70 / 1

2.61 1 5.90 L 2.41I

10 .92 m

CROSS SECTIONCROSS SECTIONFIGURE 10.42. Ashidagawa Bridge, Japan.FIGURE 10.42. Ashidagawa Bridge, Japan.

fy FJL. ‘i r’.

FIGURE 10.43. Kakogawa Railway Bridge, placingprecas t segments wi th launching gantry.

The ultimate strength of the structure should becapable of supporting the service loads increasedby 30%, if 30% of the post-tensioning steel weremissing.Provisions shall be made for installing additionaltendons while the structure is under traffic. Theadditional post-tensioning force shall be 15% ofthe designed force minimum.It shall be possible to replace all the bearings.

10.10.6 CONCLUSION

This review of specific design problems of railwaybridges should raise no doubts whatsoever aboutthe advantages of prestressed concrete and seg-mental construction’in this field. Prestressed con-crete is the safest material known today to resistindefinitely the large variations of loads such asthose applied to a railway bridge.

The problem of fatigue has been covered brieflyin Chapter 4, and the results mentioned thereapply particularly well to railway bridges. Themain objective in the design and construction ofprestressed concrete bridges should be to minimizeand even eliminate concrete cracking, which is al-ways a source of weakness in a structure subject tocyclic loading.

The use of the provisions laid down in Section10.10.5 should result in practically crack-freestructures with an expected life free of majormaintenance.

978

I

184’ , 98’ , 4 1 4 ’ , 98’_,_ 184I I I

I

(b)

FIGURE 10.44. Akayagalva Rail\\av Bridge, general dimensions. ((0 Ele-vation. (1~) l‘vpical cross section .4-A.

55 k 55 k 55 k 55 k5.4 k/cF (25tl 125t1 (25d (25d

(8 t/ml) (8 t/ml1

V Y V v

5 .2 ’ 5 .2 ’ 5 .2 ’ 2 .6 ’+I----

Descr ip t ion

Span lengthDeck widthNumber of lanes or tracksSuperimposed dead load:

Bal las tCurb, pavement, etc.Total S.L.

Live loads :Equivalent uniform

loadImpact factorTotal L.L.

Total (S.L. + L.L.)

Highway Bridge

150 ft (45 m)36ft (11 m)

Three lanes

- -1.5 kips/ft

1.5 kips/ft

2.4 kips/ft

1 8 %2.8 kips/ft

4.3 kips/ft

Railway Bridge

150 ft (45 m)36ft(ll m)Two tracks

6.5 kips/ft0.5 kips/ft

7.0 kips/ft

6.8 kips/ft

30%8.8 kips/ft

15.8 kips/ft

FIGURE 10.45. Vertical loading on railway bridges. (a) Typical UIC - track loading.(b) Comparison of superimposed dead and live loading on highway and railway bridges.

463

4 6 4 Segmental Railway Bridges

FIGURE 10.46. Detail of pot bearing with unidirec-tional horizontal movement.

FIGURE 10.47. Detail of fixed bearing.

10.11 Proposed Concepts for Future SegmentalRailway Bridges

We should note that many types of structures de-scribed for highway bridges are equally appropriatefor railway bridges: the structures described in thischapter were essentially girder or arch bridgesbuilt in cantilever or incrementally launched.

Today, many design projects are based on stayedbridges. As an example, Figure 10.48 shows a pro-posed crossing of the Caroni River in Venzuela forheavy iron ore freight trains.

FIGURE 10.48. Proposed crossing of Rio Caroni foriron ore railway line.

11Technology and Construction

of Segmental Bridges

11.1 SCOPE AND INTRODUCTION11.2 CONCRETE AND FORMWORK FOR SEGMENTAL

CONSTRUCTION

11.2.1 Concrete Design and Properties11.2.2 Concrete Heat Curing11.2.3 Dimensional Tolerances11.2.4 Formwork for Segmental Construction

11.3 POST-TENSIONING MATERIALS AND OPERATIONS

11.3.1 General11.3 .2 Ducts11.3.3 Tendon Anchors

11.3.4 Tendon Layout11.3.5 Friction Losses in Prestressing Tendons11.3.6 Grouting

11.3.7 Unbended Tendons11.4 SEGMENT FABRICATION FOR CAST-IN-PLACE

CANTILEVER CONSTRUCIION

11.4.1 Conventional Travelers

11.4.2 Self-Supporting Mobile Formwork11.4.3 Tw&tage Casting11.4 .4 Combination of Precast Webs with Cast-in-Place

Flanges11.4.5 Practical Problems in Cast-in-Place Construction

Camber Control

11.5 CHARACTERISTICS OF PRECAST SEGMENTS ANDMATCH-CAST EPOXY JOINTS

1 I .l Scope and Introduction

Certain problems are common to all types of seg-mental construction-for example, the selectionand control of materials, prestressing operations,and choice of bearings, joints, and wearing surface.Other- problems are specific to a particular con-struction method. The use of form travelers incast-in-place cantilever construction and the cast-ing and handling of segments in precast cantileverconstruction are two such examples. This chaptercovers these various topics in the following order:

11.5.1 First-Generation Segments11.5.2 Second-Generation Segments11.5.3 Epoxy for Joints

11.6 MANUFACTURE OF PRECAST SEGMENTS

11.6.1 Introduction

11.6.2 Long-Line Casting11.6.3 Short-Line Horizontal Casting11.6.4 Short-Line Vertical Casting11.6.5 Geometry and Survey Control

Segment Precasting in a Casting MachineSegment Cast ing ParametersSurvey Control During Precasting Operations

Survey Control During ConstructionConclusion

11.6.6 Precasting Yard and Factories11.7 HANDLING AND TEMPORARY ASSEMBLY OF PRE-

CAST SEGMENTS11.8 PLACING PRECAST SEGMENTS

11.8.1 Independent Lifting Equipment11.8.2 The Beam-and-Winch Method

11.8.3 Launching GirdersLaunching Girders Slightly Longer Than the Span

hn%hLaunching Girders Slightly Longer Than Twicethe Typical Span

REFERENCES

1 . Problems common to all segmental bridges

2. Problems specific to cast-in-place cantileverconstruction

3. Problems specific to match-cast segmentalbridges with particular emphasis on cantileverconstruction, which is the most widely usedmethod.

In designing segmental bridges, it is importantto pay attention to certain details at the time ofconception, in order to keep the project as simpleas possible and thereby achieve economy and effi-

465

466 Technology and Construction of Segmental Bridges

ciency during construction. The following guide-lines apply to both cast-in-place and precast con-struction:

1 .

2.

3.

4.

5 .

6.

7 .

8 .

Keep the length of the segments equal, andkeep the segments straight even for curvedstructures (chord elements).

Maintain constant cross-section dimensions asmuch as possible. Variations of cross-sectiondimensions should be limited to change ofdepth of webs and thickness of bottom slab.

Corners should be beveled to facilitate casting.Segment proportions (shear keys, for example)should be such as to allow easy form stripping.

Avoid as much as possible surface discon-tinuities on webs and flanges caused by anchorblocks, inserts, and so on.Use a repetitive layout for tendons and an-chors, if possible.

Minimize the number of diaphragms and stif-feners.Avoid dowels passing through formwork, ifpossible.

11.2 Concrete and Formwork for SegmentalConstruction

11.2.1 CONCRETE DESIGLV A,VD PROPERTIES

Uniform quality of concrete is essential for seg-mental construction. Procedures for obtaininghigh-quality concrete are covered in PC1 and AC1publications.‘** Both normal weight and light-weight concrete can be made consistent and uni-form by means of proper mix proportioning andproduction controls.

Corrosive admixtures such as calcium chlorideshould never be used, since they can have a det-rimental effect on hardened concrete and cancause corrosion of reinforcement and prestressingsteel. Water-reducing admixtures and also air-entraining admixtures that improve concrete re-sistance to environmental effects, such as de-icingsalts and freeze and thaw actions, are highly desir-able. Very careful control at the batching stage isrequired, however, since the advantages of air-entrained concrete cannot be relied upon unlessthe quantity of entrained air is within specifiedlimits.

Ideal concrete will have a slump as low as prac-ticable, notwithstanding the possible use of specialplacing equipment such as pumps, and a 28-daystrength greater than the minimum specified bystructural design. It is recommended that statisticalmethods be used to evaluate uniformity of con-crete mixes.

The cement, fine aggregate, coarse aggregate,water, and admixture should be combined to pro-duce a homogeneous concrete mixture of a qualitvthat will conform to the minimum held-test andstructural design requirements. Care is necessaryin proportioning concrete mixes to insure that the\meet specified criteria. Reliable data on the poten-tial of the mix in terms of strength gain, creep, andshrinkage performance should be developed toserve as the basis for improved design parameters.

The methods and procedures used to obtain theconcrete characteristics required by the design mayvary somewhat, depending on whether the seg-ments are cast in the field or in a plant. The resultswill be affected by curing temperature and type ofcuring. Liquid or steam curing or electric heatcuring may be used.

Proper vibration should be used to permit theuse of low-slump concrete and to allow for the op-timum consolidation of the concrete.

11.2.2 CONCRETE HEAT ClJRI,\‘G

In temperate climates and where curing is car- An early concrete strength usually is required toried out in an isothermal enclosure, only small ad- reduce the cycle of operations and to maintain the

ditions of heat are required to maintain the curingtemperature, full advantage being taken of theheat of hydration generated by the fresh concrete.In this case heat demand will be a function of theambient temperature, more heat being required inwinter and little or no additional heat during hotsummer weather.

Where segment production rate is not critical, itmay be possible to do without accelerated curingand simply use a normal curing period of a fewdays, during which the concrete is well protectedagainst excessive temperature variations and allexposed surfaces are kept moist.

A sufficient number of trial mixes must be madeto assure uniformity of strength and modulus ofelasticity at all important phases of construction.Careful selection of aggregates, cement, admix-tures, and water will improve strength and mod-ulus of elasticity and will also reduce shrinkage andcreep. Soft aggregates and poor sands must beavoided. Creep and shrinkage data for the con-crete mixes should be determined bv tests.

Concrete and Formwork for Segmental Construction 4 6 7

efficiency of the special equipment used either incast-in-place or in precast construction. Twomethods may be used for this purpose, either sepa-rately or together: (a) preheating the fresh con-crete, before placing it in the forms or in the cast-ing machines, (b) heat curing the concrete afterconsolidation in the forms.

In the first case the concrete is preheated toabout 85 to 90°F (30 to 35°C). This operation isachieved in several ways:

1. Steam heating the aggregates-a simple solu-tion that presents the disadvantage of chang-ing the aggregate water content

2. Heating the water-a solution that has limitedefficiency, owing to the small proportion ofwater in comparison with the other compo-nents (water at 140°F raises the concrete tem-perature by only 20°F).

3. Direct heating of the concrete mix by injectingsteam into the mixer itself-the best solutionand the one most easily controlled.

To avoid heat loss, the forms are generally in-sulated and some source of radiant heat is installedinside the segment (radiators or infrared ele-ments).

In the second case, the concrete is heated in itsmold inside a container in which low-pressuresteam is circulated. In this way it is relatively easy toobtain the strength required for prestressing oper-ations [3500 to 4000 psi (25 to 28 MPa)] after oneor two days, even in winter. If however, tensioningoperations are to be performed earlier, after 24hours for example, modifications must be made tothe concrete in the anchorage zone.

Electrical resistances may be embedded in theconcrete, or precast end-blocks may be used. Pre-cast end-blocks were used notably for the Issy-les-Moulineaux, Clichy, and Gennevilliers Bridges.For the Gennevilliers Bridge, despite the excep-tional dimensions of the box girder deck, twosegments were cast each week through an earlystressing of the prestress tendons.

In the case of precast segments, the acceleratedcuring of the concrete must attain two apparentlycontradictory objectives:

1 . Accelerated curing to permit rapid stripping.2. Final compressive strength as near as possible

to that of the design concrete.

Several curing systems may be considered:

1. Conventional kilns.2. Direct heating of forms with electric resis-

tances.3. Direct heating of forms with low-pressure

steam.

The use of a conventional kiln entails severalprecautions. First, a constant temperature must bemaintained in the kiln. Second, the segment sec-tions of varying thickness are all heated to the sametemperature, which may produce unacceptablelocal thermal gradients and cracking if heat curingis excessive. Finally, the heated segment may besubjected to a thermal shock when removed fromthe kiln, if the difference between the ambienttemperature and the kiln temperature is greaterthan 60°F. However, kiln curing is a simple solu-tion and is acceptable for long curing cycles-forexample, of 10 to 14 hours.

Form heating by means of electrical resistances isperfectly adapted to long curing cycles. This sys-tem permits a wide range of adjustment per zone,varying the temperature between the thick andthin sections of the segment and thereby minimiz-ing thermal gradients and eliminating the risk ofpermanent damage to the concrete at the begin-ning of its solidifying phase.

The heating of forms with low-pressure steam ispreferable for short curing cycles lasting less thanfive hours, as it permits the distribution of a largequantity of calories over a short period, causing arise in the internal temperature of the concrete ofthe order of 20 to 30°F (10 to 15°C) per hour. Thissystem, however, requires a complex regulator toensure an equal temperature in all the form panelenclosures, at all times during the treatment, what-ever their thermal inertia and the externalinfluences to which they are subjected, Figure 11.1.

FIGURE 11.1. Heat-curing control system (B-3 SouthViaducts).


The different systems (kiln, electrical resistances,and low-pressure steam) have all been applied suc-cessfully to segmental bridges. The segments forthe Choisy-le-Roi and Courbevoie bridges werekiln cured. Electric heating was adopted for theconstruction of the upstream and downstreambridges on the Paris Ring Road and the BloisBridge, among others. Form heating using low-pressure steam was used for the Pierre BeniteBridges, the Oleron Viaduct, and the B-3 SouthViaducts.

Whether forms are heated by electricity or b)steam, it is relatively easy to produce a long curingcycle, and the desired final concrete strength iseasily obtained. A short curing cycle, on the otherhand, requires a great deal of caution and meticu-lous preliminary calculations. Particular attentionmust be given to:

1 . Choosing a cement, the performance of whichis adapted to the accelerated curing of concrete(preferred is artificial Portland cement with:C,,A s 11% and C,,SIC,S 2 3).

2. Consistently manufacturing concrete with aminimum water content and a maximum tem-perature of 95°F (35°C) at the time of pouring.

3. Using sufficiently rigid forms to resist thethermal expansion of the concrete in its plasticstate while heating.

In order to avoid a drop in the long-term me-chanical properties of the concrete, the tempera-ture curve during the heat curing must necessaril\include, see Figure 11.2:

An initial curing period of two to three hours,during which the concrete is kept at the ambienttemperature

,411 increase in temperature at a low rate of lessthan 36°F (20°C) per hour

A period (depending upon the concrete strengthto be attained) during which the temperature isheld constant and below 150°F (65T)

A period during which the concrete is cooled at arate similar to that used for the temperature in-crease

‘The loss of strength in the long term will begreater:

If the initial curing period is short

If the temperature increase is rapid

If the maximum temperature is high

As an example, the short-cycle treatment usedfor the B-3 Viaduct segments was the follo\~ing,see Figure 11.3:

Initial period of 14 hour at 95°F (35°C) (mixingtemperature)

212

i

PREHEATING ALTERNATIVE

I

FORM STRIPPING

I I I I I

2 to 3H tti-Y-Jw\-

piNI;; TEMPERATURE CONSTANT C O O L I N G

I N C R E A S E TEMPERATUREP E R I O D

FIGURE 11.2. Heat-treatlnent c-~c-le.

Concrete and Formwork for Segmental Construction 469

SHORT CYCLE

LONG CYCLE

Temperature increase of 27°F (15°C) per hour for2 hours

.-\ constant temperature of 150°F (65°C) for lfhours

Figure 11.3 shows an example of- tong-cycle heattreatment, the Conflans Bridge, which had a totalheat-treatment duration of 19 hours.

11.2.3 DI,~lESSIO,\-‘4L TOLERrllVCES

Formwork that produces tvpical bridge box girdersegments within the following tolerances is consid-ered to be of good quality3.4:

1 I .2.4 FORMWORK FOR SEGMENTALCO,\5 TR UCTIO,V

Formwork along with its supports and foundationsmust be designed to safely support all loads thatmight be applied without undesired deformationsor settlements. Soil stabilization of the foundationmav be required.

Since economical production of cast-in-place orprecast segments is based on repetitive use of thesame forms as much as possible, the formworkmust be sturdy and special attention must be givento construction details. Where formwork is to beassembled by persons other than the manufactureror his representatives, particular care must betaken with erection details and assembly instruc-tions. All elements of the formwork must be easy tohandle. 1-Z

Formwork for structures of variable geometrywill need to be relatively flexible in order to allowadaptation at the various joints. Both external andinternal forms are usually retractable in order toleave a free working space for placing reinforcingsteel and prestressing ducts3

Special consideration must be given to thoseparts of the forms that have variable dimensions.To facilitate alignment or adjustment, specialequipment such as turnbuckles, prefitted wedges,screws, or hydraulic jacks should be provided.

Tendon anchors and inserts must be designed insuch a way that they remain rigidly in positionduring casting. Projecting anchorage blocks orother such irregularities should be detailed topermit easy form stripping.3

If accelerated steam curing with temperatures ofthe order of 130°F (55°C) is to be used, then thedeformations of the forms caused by heating andcooling must be considered in order to preventcracking of the young concrete.

In general, internal vibration using needle vi-brators should always be applied. External vibra-tors, if used, must be attached at locations that will

Width of web 2; in. (+ 10 mm)

Depth of bottom slab +f in. to 0 in. (+lO mm to 0 mm)

Depth of top slab k+ in. (55 mm)

Overall depth of segment ?& of depth (5 mm min.)

with f in. min.

Overall width of segment ?h of width (5 mm min.)

with f in. min.

Length of match-cast segment *a in. (25 mm)

Diaphragm dimensions ki in. (210 mm)


achieve maximum efficiency of consolidation andpermit easy replacement in the case of a break-down during casting operations. External vibrationmay lead to fatigue failure in welded joints, andregular inspection should be made to help preventany sudden failure of this kind.3

Paste leakage through formwork joints must beprevented by suitable design of joint seals. Nor-mally this can be achieved by using a flexible seal-ing material. This is particularly important at thejoint face with the matching segment, where loss ofcement paste can lead to poorly formed joint sur-faces and subsequent spalling and loss of matching,requiring repair. Special attention must be given tothe junction of tendon sheathing with the forms.3l4All form surfaces, especially welded joints in con-tact with the concrete, must be perfectly smoothand free from reentrant areas, pitting, or otherdiscontinuities, which could entrap small volumesof concrete and lead to spalling during form strip-ping.3

I I .3 Post-Tensioning Materials and Operations

1 1 3 . 1 GE,\‘ERAL

Technical details relating to the different methodsavailable are described in the various post-tensioning manuals5g6 and in the specific docu-ments issued by suppliers.

113.2 DUCTS

Ducts are used to form the holes or enclose thespace in which the prestressing tendons are lo-cated. The ducts may be located inside or outsidethe concrete section.

Although in some instances the tendons areplaced in the ducts before concreting (cast-in-placeand span-by-span construction), post-tensioningtendons will normally be threaded into the ductsaf-ter erection of the segments. The duct crosssection must, therefore, be adequate to allowproper threading; and in general it will be about fin. (5 mm) larger in any direction than for ducts inwhich the tendons are placed before concreting.

The duct dimension must allow not only the in-stallation of the tendons but also free passage ofgrout materials after stressing. The ratio or pro-portion of cross-sectional area of the duct with re-spect to the net area of prestressing steel shouldconform to appropriate specifications or codes.4 Aminimum value of 2 usually leads to satisfactory re-sults.

Ducts must have sufficient grouting inlets, shut-off valves, and drains to allow proper grouting andto avoid accumulation of water during storage.Vent pipes should not be spaced more than ap-proximately 400 ft (120 m) apart.’ This spacingmay have to be reduced, depending upon the ex-pertise of the personnel performing the grouting.

Particular attention must be paid to the qualit!of duct connections at the joints between segments.At the joints, accurate placing is mandator\. ~I‘hemethod of duct connection depends on the type ofjoint3:

Telescopic sleeves pushed over projecting ducts-wide joints

Screw-on type sleeves-wide joints

Internal rubber or plastic sleeves-match-castjoints

Gaskets or other special seals-match-cast joints

No special provisions: clean ducts with a torpedoafter jointing to remove penetrated epoxv ifanv-match-cast joints

Connection tightness is essential in order to pre-vent penetration of joint material, water, or otherliquids or solids into the ducts, which would intro-duce a risk of blockage, and also to prevent leakageat the joint during tendon grouting operations.3

1 1 . 3 3 TE,VDO.V ASCHORS

Tendon anchors usually consist of a bearing plateand an anchorage device either in combination oras separate units. Shape and dimensions of the an-chors must conform with the applicable specifica-tions, particularly insofar as bearing stresses areconcerned.

Choice of anchor positions in the segmentsshould take into account the following considera-tions3:

Tendon layout requirements and installation se-quences.

Stresses generated around the anchors.

Ease of tendon threading and stressing.

Ease of formwork preparation, stripping and con-crete placing.

Certain anchorage positions, such as the anchorageblock on a thin slab shown in Figure 11.4, shouldbe avoided. If this type of detail cannot be avoided,then particular care must be taken in design andconstruction of the zone concerned.3

Post-Tensioning Materials and Operations 471

Tendonanchorageblocks

FIGURE 11.4. .Anchor-qr block position to he;I\ aided.

Bearing plates are usually embedded in the seg-ment at the time of casting. In certain cases theyare installed against the hardened surface of theconcrete with a dry mortar bed or a suitable cush-ioning material such as asbestos cement or syn-thetic resin.

This subject has been covered in Chapter 4 relatingto design. The choice of tendon layout must betreated carefully, with special attention paid to thefollowing factors:

Construction sequence with respect to tendonplacing, segment casting (or erection), and otherconstruction imperatives

Standardization and repetition of essential fea-tures, especialla duct and anchor positions at joints(in order to facilitate formwork design)

Various loading conditions throughout the con-struction period and in service

When using large tendons, it is not advisable touse couplers or crossed splices, for reasons of con-gestion and formwork complication. Also, couplersand splices should not be located in areas wherevielding mav occur under ultimate load condi-tions.3

In order to limit friction losses, and to facilitatetendon threading, excessively curved tendonsshould be avoided if possible.

11.3.5 FRICTIOS LOSSES IS PRESTRESSISGTESDO,VS

Segmental construction usually calls for prestress-ing tendons to be installed through a succession ofshort duct lengths coupled to one another at thejoints between segments, these being at approxi-mately 8 to 30 ft (2.5 to 10 m) intervals.

The friction factors (for curvature and wobble)usually accepted for long tendons in cast-in-placestructures may not be realistic for this type of con-

struction under ordinary working conditions andsupervision. The actual results obtained in a seg-mental bridge built in Europe are given below byway of example for the benefit of future projectdesigners.

Cantilever tendons were placed along a straightprofile in the roadway slab and anchored either onthe segment face or tn a block-out inside the boxgirder. Continuity tendons were either anchoredin a block-out at the bottom slab level or drapedupward in the webs and anchored in the sameblock-out of the cantilever tendons. All tendonswere made up of twelve 0.6 in. diameter strands.Soluble oil for reducing friction in the ducts wasnot allowed by the consultant. The calculationswere carried out using the following values forcurvature and wobble friction coefficients:

/..l = 0.20, K = O.OOf/ft = 0.0021/m

The Young’s modulus of the tendon samplestested in the factory or in the laboratory variedbetween 28,000 and 29,000 ksi, and the variationbetween various heats over the whole structure wasvery low. According to direct tests carried out onsite, and a systematic analysis of all results of ten-don elongations recorded during the stressing op-eration, the actual Young’s modulus of a (twelve0.6 in. diameter strand) tendon at first tensioningvaried between 25,000 and 26,000 ksi, which isonly 90% of the value recorded during factory andlaboratory tests.

Figures 11.5 and 11.6 show values of the wobblefriction coefficient K measured for all the tendonsin the structure’s 18 cantilevers. All the tendons areshown in Figure 11.5, while Figure 11.6 shows onlythose tendons in the spans without hinges, andseparates the tendons anchored on the segmentface from those anchored in block-outs (the ten-dons had the same layout except a rather severecurvature at the end). It is obvious that:

As construction proceeded and the quality ofmanufacture and supervision improved, theresults got better.

At the beginning of the job, the effect of thecurved ends of certain tendons was lost in thegenerally mediocre results. As these results gotbetter (value of K equal to that used in calcula-tion from cantilever 11 on), this effect becamepreponderant, counteracting that of the im-proved standard of work.

As the site staff became accustomed to thework and the effort and supervision dropped,the results became gradually worse (comparecantilevers 13 and 17, for example).

472

dK,

1O’K

Technology and Construction of Segmental Bridges

2 3 k 5 6 7 8 9 1 0 1 1 1 2 1 3 lk 1 5 1 6 1 7 18M

CANTILEVER n ”

FIGURE 11.5. Prestressing in a cantilever bridge. Variation of uobble 1.1.ic tioncoefficient for cantilever tendons in each of the structure’s 18 spans.

A N C H O R E D I N

BLOCK - OUTS

TENDONS ANCHORED A T

T H E S E G M E N T

2 3 5 7 9 1 1 1 3 is 1 7 18w

CANTILEVER

FIGURE 11.6. Prestressing in a cantilever bridge. Wobble friction coefficient for C;LII-tilever tendons in the 10 spans without hinges.

As an example, a straight tendon in the top slab cage as the concrete is poured (when the tendon isfillet between slab and web was isolated. The wob- in the slab rather than in the fillet, the accidentalble friction coefficient depends on the care exer- deviations are much smaller). For the first sevencised in fastening the duct to the reinforcing steel cantilevers (see Figure 11.7) the wobble coefficient

Post-Tensioning Materials and Operations 473

F L E X I B L E

1 L L::!!::!: :-

2 3 4 5 6 + 8 9 10 11 12 0 U 15 16 17 M

FIGURE 11.7. Prestressing in a cantilever bridge.straight tendon located in the upper fillet.

Wobble friction coefficient for a

reached up to six times the assumed value used inthe calculations, and yet very careful constructionwill enable this assumed value to be reached or atleast approached closely to obtain the desired pre-stress with little room for uncertainty.

The presence of hinged segments not only com-plicates the tendon profile and the constructionphases, but introduces uncertainty about obtaining

the required prestress force. Owing to the techni-cal restrictions imposed by the consultant, the tra-ditional prestress layout employed in earlierbridges could not be used. Consequently, long ten-dons stressed only at the opposite end had to beaccepted. It was thought that a realistic value of thefinal force for each of the tendons (twelve 0.6 in.diameter strand) would be 350 kips (160 mt). It is


fortunate that a direct check was made at the site,which revealed the actual initial load at transfer tobe the following for the four tendons under con-sideration: 130 kips (60 mt), 210 kips (96 mt), 130kips (60 mt), and 200 kips (90 mt). The averageinitial prestress load per tendon was therefore 170kips (78 mt), and the probable final force wouldhave been 150 kips (70 mt) as compared to the as-sumed value of 350 kips (160 mt). Fortunately, thesituation could be easily corrected and remedialmeasures put into effect as follows:

1. The reinforcing steel and local prestressingtendons allowed for a certain margin of safety.

2 . It was possible to restress two of the four cablesin the first cantilever and then to change theprofile and method of placing segments inorder to stress all the tendons at both ends forthe rest of- the cantilevers.

The above results, quoted rigorously so as to il-lustrate several important aspects of friction losses,must not lead the reader to suppose that the safetvof the structure was at any time compromised. Thkforce in a tendon varies much more slowly thananv changes in the friction coefficients for ordinar)

tendon stressed at both ends, if the frictioncoefficients are multiplied by 4, the minimum forcein the tendon is reduced bv only 16%.

It is interesting to examine the results for theactual prestress obtained in cantilevers 2 and 3 (theones having the worst results) shown in Figure 11.8for each section, compared with the prestress usedin the calculations. The lack of prestress, mostmarked at midspan, was compensated by addi-tional tendons to bring the force back up to thatrequired by the calculations in the first two spans.Afterward, the originally calculated prestress wasalwavs sufficient.

To summarize, the authors wish to underline thefollowing points:

1. Bench tests should be performed on site todetermine a realistic value of the modulus ofelasticity of the tendons to be used to computethe theoretical tendon elongations.

2 . Realistic values of curvature and wobble fric-tion coefficients should be used in the designand further controlled on site. Direct frictiontests should be made together with a statisticalanalvsis of the measured elongations for all

tendon profiles. For example, in a 270 ft (80 m) tendons.

5UPPORT5UPPORT

l.ax,l.ax,

SUPPORTSUPPORT

MIDMID -- 5PAN5PAN%f-%f-

hh1.W1.W

- EFECTIVE PRESTRESS IN 5PAN5 2AND3 -

FIGURE 11.8. Prestressing in a cantilever bridge. Effective prestress in spans 2 and 3

Segment Fabrication for Cast-in-Place Cantilever Construction 475

3. Provisions should be made at the design stagefor additional prestress to compensate for anyunexpected reduction in the design prestressforce due to excessive friction. This may bedone as follows:a.

b .

C .

By adding additional ducts over and abovethe number required by design calcula-tions; if this method is used, the unusedducts at the end of construction must begrouted to prevent water from seeping in-side and subsequently freezing with disas-trous effects on the structure.By using larger than required sizes forsome of the ducts, so as to allow the use oflarger-capacity tendons if required.By providing anchor blocks and possibledeviation saddles so as to allow the instal-lation of external tendons located insidethe box girder but outside the concretesection.

If the correct approach is taken at the concep-tion stage, perf-ect control of this aspect of prestressmav be obtained and verv satisfactorv structurescan be built that give maintenance-free long-termperformance.

I I .3.h GROC’TI,\‘G

As in conventional post-tensioned structures, seg-mental construction requires the grouting of pre-stressing tendons after tensioning to provide cor-rosion protection and to develop bond between thetendon and the surrounding concrete. Currentrecommendations and provisions of good practiceare therefore applicable to segmental bridges.However, several important points need to be ex-amined.

Grouting must not be carried out if the temper-ature in the ducts is less than 35°F (2°C) or if thesurrounding concrete temperature is less than32°F (2°C). This requirement virtually precludesgrouting operations during the winter months inthe northern and middle western United States,unless very special winter precautions are used. Itis preferable to postpone all grouting operationsuntil the following spring, even though some ten-dons may be left tensioned and ungrouted for along period. Attention must then be given to cor-rosion protection of the high-tensile steel bars orstrands. Satisfactory protection is obtained by seal-ing all tendon ducts at both ends after blowing outwith cool compressed air. Hot air should not be

used because it increases the moisture content ofthe air and reduces the natural corrosion protec-tion.

Another important and sometimes acute prob-lem relates to potential grout leakage at segmentjoints, which can lead to the passing of grout fromone duct to another. For this reason ducts must bewell connected and sealed at joints. To check thegrout tightness of the joints and to avoid blockages,it is advisable to flush the ducts with water underpressure before grouting. Any leakage points thusdetected may then be sealed. If communication isdiscovered between tendon ducts, the tendongroups affected should be grouted in one opera-tion after threading and stressing of all the tendonsinvolved. 3

If couplers are being used (notably for single-bartendons), precautions tnust be taken to limit therisk of grout blockage at the coupling points.Couplers must be housed in special enlarged en-closures with two essential features3:

I. Clear cross-sectional area for the passage ofgrout equal to or greater than that for the restof the tendon.

2. Independent grout inlets and vent pipes.

I1 3.7 UNBONDED TENDONS

Unbonded tendons may be used in segmental con-struction provided that the performance require-ments of the post-tensioning steel are also met bythe tendon anchorage, notably with respect tofatigue characteristics. In unbonded post-ten-sioning a corrosion protection system must beprovided to guarantee at least the same degree ofcorrosion protection as for bonded tensioning.This may be achieved by enclosing the tendons inflexible ducts (such as polyethylene pipes) and bycement grouting after tensioning.

I I .4 Segment Fabrication for Cast-in-PlaceCantilever Construction

11.4.1 CONVENTIONAL TRAVELERS

The conventional form traveler supports theweight of fresh concrete of the new segment bymeans of longitudinal beams extending out in can-tilever from the last segment in order to supportthe forms and service walkways.

Form Travelers with Top Main Beam (Figure2.83) The longitudinal main beams or girders areusually located above the segment to be concreted,in line with the webs. The outside forms, the bot-tom forms, the work floor, and the service walk-ways are hung from the main beams with the helpof cross beams. The inside forms are supported ona trolley, which travels inside the deck.

The main beams are anchored to the previoussegment. In order to maintain stability during thepouring operation a counterweight is sometimesused to reduce the uplift forces applied to the con-crete section. When the traveler is transported toits new position ready for the next segment, thecounterweight keeps it in balance between two suc-cessive anchoring positions. The main beams thatsupport the load due to concrete, forms, walkways,and so on are often subject to large deflections,which can give rise to transverse cracking along thejoints between segments. These cracks appear atthe upper face of the bottom slab and at the con-nection between web and top slab. This undesir-able condition can be avoided by using a rigidstructure; the weight of the traveler is increasedtogether with the prestress required in the can-tilevers. The form traveler used for the OisselBridge weighed 120 tons (110 mt) and may be con-sidered as a heavy form traveler.

If the travelers are light, care must be taken tocompensate deflections during concreting by ad-justing jacks. This type of traveler weighs (exclud-ing counterweight) a little less than half themaximum concrete segment weight. An exampleof a light form traveler is shown in Figure 11.9 forthe Tourville Bridge. Each traveler weighs 33 tons(30 mt).

Form Travelers with Lateral Main Beams (Figure11.10) Travelers with their main beams above thebridge deck present the disadvantage of hinderingthe construction operation concerning the upperpart of the segment. For this reason certain formtravelers have their main beams disposed laterallyparallel to the outside webs, underneath the bridgedeck. This solution leaves a clear working surfaceand allows easy access to all surfaces to be formed,reinforced, and concreted. In this way, the tech-nology originally developed for precast segmentalconstruction can be applied to cast-in-place can-tilever methods, resulting in shorter constructioncycles. The Moulin-les-Metz Bridge in easternFrance, Figure 11.11, was constructed using thistype of form traveler.

FIGURE 11.9. I‘ourville-la-Kwiere Bridge form trav-eler .

1 I .4.2 SELF-SUPPORTING MOBILE FORMWORK

In the case of traditional form travelers, the re-sulting deflections seen during construction arealmost entirely due to the main beams. Theformwork as such usually acts only as a mold anddoes not support any part of the total load, eventhough it comprises very stiff walls.

In several recent bridges the traveler concept hasbeen modified so as to use the rigid formwork asthe weight-carrying member, thus producing aself-supporting rigid mold. Several advantages aregained with this concept:

Surveying control and correction of bridge deckgeometry are easily obtained.Cracking near the joints caused by the deflection ofconventional travelers is completely eliminated.The work area is maintained completely free andallows prefabricated reinforcing steel cages to beused as in precast segmental construction.

This type of mobile formwork was first used forconstant-inertia bridge decks such as the KennedyBridge, Dijon, and the Canadians Interchange inParis, Figure 11.12.

During the concreting operations, the mobileformwork is prestressed to the existing deck. Theexact positioning of the formwork is obtained by

Segment Fabrication for Cast-in-Place Cantilever Construction

1 a CONCRETING PHASE

2, LAUNCHING PtlASE

FIGURE 11.10. Typical for.rn traveler with later .a1 main beams.

FIGURE 11.11. Moulins-les-Metz form traveler.

means of adjusting pins located at the rear in res- while pouring the segment. Figure I 1.13 shows theervations provided in the previously poured seg- arrangement for the Canadians Viaduct in Paris,ments. The formwork is transported to its new po- France. Monostrands located in the webs are provi-sition, ready for the next segment, on an overhead sionally anchored to the front of the traveler andtrolley, which travels along short steel girders can- embedded in the webs of the concrete segments totilevered out from the existing hardened concrete be incorporated in the reinforcement of the per-in line with the webs. manent structure.

A further refinement was to use pretensionedreinforcing to add to the stability of the traveler

The use of the self-supporting mobile formworkwas later extended to variable-depth bridge decks

FIGURE 11.12. Canadians Viaduct (Paris), view ofform traveler in operation.


S&le S t r a n d s 1 tic R e a r Fixation’ ’ I(4x0 6”)

iA i.E S E C T I O N B . BSECTION A.A U er Fixations

/-=-7

\ Sinqle S t r a n d s \ ’ Lower Fixations

FIGURE 11.13. Canadians Viaduct (Paris), details of the self-supporting form traveler.

as well as three-web cross sections, as in the Clichy,Orleans, and Gennevilliers Bridges.

The structural members of the mobile formworkare therefore the side forms of the exterior face ofthe outside webs and the bottom forms of theunderside of the bottom slab, both of which arestiffened transversely by front and rear framesbraced together for additional rigidity, Figure11.14. In this manner a rigid box is formed, whichis prestressed to the existing deck. The change ofsection height is achieved by vertical displacementof the bottom forms, which are fastened to thefront stiffening framework and bottom slab of thelast segment.

The stability of the self-supporting mobile formsof the Gennevilliers Bridge was ensured by (Figure11.15):

1 . Two steel pins fixed to the top of the outsideforms and matching imprints provided on theoutside face of the previous segment, the con-nection being assured by high-strength barsgoing through each web.

2. Two steel pins fixed to the upper surface of thebottom forms and matching the correspondingimprints provided in the last segment bottomslab, again held by prestress bars.

The self-weight of the mobile forms and the freshconcrete creates an overturning moment, which is

balanced by two forces F sustained by the previ-ously described locating pins. Practically all theshear force is taken by the upper pins. Because ofthe large forces transmitted through the top pinsto the concrete, precast concrete elements are usedto avoid the transmission of high stresses to youngconcrete, Figure 11.16. These forces are transmit-ted by friction between pin and concrete, and thisdetermines the necessary prestress force.

11.4.3 TWO-STAGE CASTING

The method of two-stage casting involves, first, thefabrication of the bottom slab and the webs to-gether with a small part of the top slab in order tocreate a flange in which all or some of the can-tilever tendons can be located. This operation, car-ried out using a conventional form traveler, pro-duces either a U-shaped or a W-shaped section,depending on the number of webs, Figure 11.17.After the cantilever tendons are stressed the formtraveler is moved to the next position, the top ispoured using a mobile formwork of relatively sim-ple design. This second stage usually follows thefirst with a minimum interval of two or three seg-ments, and concrete can be placed in a simple pourover the length of several segments.

This method has the advantage of reducing theconcrete volume to be supported by the formtraveler, thus reducing the weight of the traveler.


bunt a n d rrar stiffrncrs

!

‘B0tt0m f0rms ’

Mob/h t r u s s

\Bottom f o r m s

FIGURE 11.14. Self-supporting mobile forms for variable-depth bridge decks.Concreting. (b) Moving f&ward.-

In addition, the second stage is independent withrespect to the first and so is no longer on the criticalpath of concreting operations.

The bridge decks of the Saint Isidore and Mag-nan Viaducts on the Nizza A-8 bypass were con-structed using this method. All of the 130 ft (40 m)spans of the Saint Isidore Viaduct were completedfor stage one only, including closure to the pre-ceding span, before the second stage was com-pleted, using mobile formwork which rolled alongthe bottom slab from one abutment to the other.As regards the Magnan Viaduct, the second stagefollowed the first with an interval of three seg-

(a)

ments, because of the long spans in this structure.The same procedure was used for the Clichy, Join-ville, and Woippy Bridges, Figure 11.18.

11.4.4 COMBINATION OF PRECAST WEBS WITHCAST-IN-PLACE FLANGES

The preceding methods allowed a considerable re-duction in the construction cycle. Two pairs ofsegments could thus be completed every week, cor-responding to an average rate of construction of 7to 10 ft (2 to 3 m) per working day.

MOBILE FORM STABILITY

Prestressina b a r s

FIGURE 11.15. Stability of the Genne~illiers Bridge self-supporting mobile forms.

_ PRECAST JOINT _

Pin

FIGURE 11.16. Precast gusset for Genne\illiers Bridge

FIGURE 11.17. Two-stage construction of a two-web bridge deck.

Segment Fabrication for Cast-in-Place Cantilever Construction

. I. . ” ” .,y’ .1. .(r+.“.r.,

--,.. x -,___-_ i. j‘1. .‘.W *&e “,~..,‘?C~~:r^~.y’~.~~ **v.,; ;a -3 - _, _ ,

FIGURE 11.18. \Voippy Viaduct, France. Detail of theself supporting form traveler and two-stage casting.

The main obstacle preventing further reductionin the construction cycle and therefore a closer ap-proach to the speed of precast segmental construc-tion is the lack of strength of young concrete andthe consequent interference with stressing opera-tions. Apart from several other methods alreadydiscussed, the problem can be partially overcomeby using precast end blocks or precast webs orboth. This was first tried for the construction of theBrotonne Viaduct approach spans, Figure 11.19.The webs, which were rather thin and heavily in-clined, were precast in pairs and pretensioned,Figure 11.20.

FIGURE 11.19. Brotonne Bridge, mobile form car-rier.

match-cast or cast in place. The second phase con-sisted of casting the rest of the segment inside theform traveler, which was now suspended from thenewly stressed webs.

The deck Was cantilevered out from the piers This procedure, which requires partial prefabri-using 10 ft (3 m) long segments assembled in two cation of the segments using light casting equip-phases. In the first phase, the precast webs weigh- ment, enables a considerable simplification of theing up to 18 tons ( 16 mt) were placed inside the form traveling equipment, the limitation of totalform traveler, previously adjusted to the bridge weight to 39 tons (35 mt), and a reduction in theprofile including the desired camber. The webs construction cycle such as to produce, even for awere then prestressed to the preceding segment cable-stayed bridge, as many as four segments perwith provisional prestress bars, the joint being week for each pair of form travelers.

TENSION RODS

STEEL FORMS

COUPLER FOR TENSIONING JACKTENSION RODS

36 mm dia TENSION RODS

A D J U S T A B L E A D J U S T A B L E

B R A C K E T S

11-36 mm dia TENSION RODS T E N D O N SCASTING BED

BED FOR PRETENSIONED WEBS

FIGURE 11.20. Brotonne Bridge, precasting of webs.


During construction of the Brotonne cable-stayed bridge, the precast webs were placed bytower crane traveling parallel to the bridge deckabove the river banks and by an overhead gantrycrane above the Seine River.

Another example of the use of precast webs isfound in the Clichy Bridge carrying the met-ropolitan line over the Seine in the northwest ofParis. The bridge deck with a 280 ft (85 m)maximum span consists of a three-web box girderwithout cantilever flanges and with the deck sup-porting the live loads as low as possible in order toreduce the length of the access ramps to the struc-ture. The 8 ft (2.5 m) long segments were also con-structed in two stages, Figure 11.2 1.

The precast webs, with epoxy match-cast joints,are placed with the aid of a mobile handling systemrolling along the webs of the previously placedsegments. They are then prestressed to the existingstructure before the top and bottom slabs arepoured in place on the length of two segments.

11.4.5 PRACTICAL PROBLEMS IN CAST-IN-PLACEC O N S T R U C T I O N C A M B E R C O N T R O L

Before proceeding with the cantilever constructionproper, a starting base must first be completed onthe various piers. This first special segment, calleda pier segment or a pier table, is generally con-structed on a temporary platform anchored by

FIGURE 11.21. Precast web placing equipment forClichy Bridge carrying the metropolitan line over theSeine River.

SECTION ELEVATION

Rotressinq b a n /

I I

FIGURE 11.22. Construction of the pier segment fora cast-in-place cantilever deck.

prestressing the pier top, Figure 11.22. This spe-cial segment may either be given the minimumlength to insure adequate connection to the pierfor the stability of the future cantilever or else be ofsuch length as to allow both travelers to be installedsimultaneously, Figure 11.23.

Another important problem relates to the safetyof the travelers during construction. Chapter 4 de-scribed the difficulties of ensuring pier safety inthe event a form traveler fell during transfer fromone position to the next. The difficulties wouldeven be greater in the event of an accident duringthe casting operation. Consequently, all precau-tions must be taken both at the design stage andduring construction to eliminate this potentialhazard. The load-carrying members of the travelermust be carefully inspected and Ray even be loadtested before use so as to practically eliminate thedanger of structural failure.

The most critical areas are in the safety of thesuspension rods and the transfer of the travelerreactions to the concrete. Preferably all suspensionrods and anchor bars should be doubled. Also, theprestressing tendons must have an adequate mar-gin of safety. Use of a single strand or a single barin each web of the box should be avoided. Rather amultistrand tendon with individual anchors foreach strand or two prestress bars should be used.

Worldwide use of cast-in-place cantilever con-struction has established an extremely good safetyrecord, much better than that for cast-in-place con-struction on fabework. Accidents are very few andfar between; however, designers and constructorsmust always be safety conscious.


FIGURE 11.23. Stal-t of cantilever construction fromthe piel- segment. (n) Short pier segment - successiveinst;illation of travelers. (6) Long pier segment-simultaneous installation of travelers.

The most critical practical problem of cast-in-place construction is deflection control, partic-ularly for long-span structures. There are fivecategories of deflections (or space geometricalmovements of the structure) during constructionand after completion:

1 . Deflection of the travelers under the weight ofthe concrete segment. This value is given bythe manufacturer or may be computed andchecked at the site during the first operations.

2. Deflection of the concrete cantilever armsduring construction. For each casting of a pairof segments, the weight of the concrete seg-ments and the corresponding cantilever pre-

stress forces impose upon the cantilever a newdeflection curve.

3. Deflections of the various cantilever arms afterconstruction and after removal of the travelersbefore continuity is achieved with the otherparts of the deck.

4. Short- and long-term deflections of the con-tinuous structure, including the effect ofsuperimposed dead loads (curbs, railings,pavements, utilities, and so on) and live loads.

5. Short- and long-term pier shortenings andfoundation settlements.

Using the data available on concrete propertiesand foundation conditions, the designer shouldcompute the various deflections mentioned underitems 3, 4, and 5 above, assuming the bridge un-loaded for foundation settlements and long-termconcrete deflections and half the design live loadfor computation of the short-term concrete deflec-tions.

The sum of the various deflection values ob-tained in the successive sections of the deck allowsthe construction of a camber diagram, whichshould be added to the theoretical longitudinalprofile of the bridge to determine for each can-tilever arm an adequate casting curve. This castingcurve is the goal toward which construction pro-ceeds during cantilever casting. The essentialdifficulty is that no absolute coordinates are avail-able in a system where everything changes at eachconstruction stage (transfer of traveler, concretecasting, or cantilever prestressing).

A very simple example may illustrate the solu-tion of the problem of accommodating the deflec-tions described under item 2 above. For simplicity,assume only a four-segment cantilever arm, forwhich a horizontal longitudinal profile is required,Figure 11.24.

As outlined in Chapter 4 and summarized brieflyabove, the designer analyzes the various deflectioncurves for each construction step (casting segmentand precasting). The typical results are shown inFigure 11.24. The cumulative deflection curve isimmediately obtained together with the camber dia-gram, Figure 11.25. The use of the camber diagramfor determining the adequate deflection at each con-struction stage is simple; however, it is much lesssimple to use in a proper manner in the field, andexperienced surveyors have often made mistakes.

When properly used, the camber diagram allowsthe determination at each joint, of offset valuessuch as yle2, yzm3, and y3.4 at each point, which will


IELEVATION OF TYPICAL CANTILEVER

Downward deflection IS posltlve

I

CASTING ANDPRESTRESSING

VERTICAL DEFLECTIONS (in mm)

SEGMENT& &J @

0 1 - 5 (-11) (-17) (-23)

0 2 1 5 (9) 1131

0 3 5 1 0 2 0 (30)

0 4 8 1 6 2 9 4 9

I TOTALDEFLECTION +9 +22 4 1 6 9

FIGURE 11.24. Partial deflections due to girder weight and prestressing at each ~011.struction stage.

bring the traveler in the proper position to realizethe desired final geometry. The sketch and table inFigure 11.26 show how to use the camber diagramproperly. It is very important to realize that at noconstruction stage does the profile of the cantilevercoincide with either the final deflection curve orthe camber diagram.

The natural tendency would be to build up thetraveler to the required offset to make its nose fall

exactly on the camber diagram. The results of thisimproper procedure are shown in detail in Figure11.27. The bridge is built with an undesired doublecurvature, particularly undesirable toward the endof the cantilever. When the mistake is discovered, itis usually too late to put into effect any remedialmeasures, because the final shape of a cantileverdepends essentially upon the accuracy of thegeometry near the piers, where the deck is sub-

Characteristics of Precast Segments and Match-Cast Epoxy Joints 4 8 5

/Camber curve

-69

.-

Yr9

.'/‘ 6 0

41,’

/’

LY,-;-~

( a s s u m e polygonailme 1

FIGURE 11.25. Cumulati\-e deflection curve and choice ofcamber.

jetted to the highest moments and where itsdeflections have the greatest effect at midspan.

I I .5 Characteristics of Precast Segments andMatch-Cast Epoxy Joints

Developed originally to allow a rapid and safe as-sembly of precast segments at the construction site,the technique of match casting was progressivelyrefined as experience was gained. We shall de-scribe the characteristics of segments in the earlystructures to further highlight the latest improve-ments and variations of the original concept.

11.5.1 FIRST-GE~VERATIOS SEGME.VTS

In those early structures the epoxy resin playedseveral important roles:

1. During assembly before hardening:a. To lubricate the mating surfaces while

final positioning took place.

b. To compensate for minor imperfections inthe match-cast surfaces.

2. In the finished structure after hardening:a. To ensure the watertightness of the joints,

especially in the top slab.

b. To participate in the structural resistanceby transmitting compression and shearforces. However, before hardening of theepoxy resin, the joints present no shear re-sistance whatsoever, because the epoxybehaves like a perfect lubricant. It wastherefore necessary to provide shear keysin each web in order to ensure the shear-force transfer between segments. Thesekeys, as well as those situated in the topslab, also allowed a very accurate assemblyof one segment with respect to another.

During assembly of the deck, some sort of tem-porary fixation, either mechanical or by means ofprestress bars, allowed the placing equipment(launching girder, crane, and so on) to be quickly

4 8 6 Technology and Construction of Segmental Bridges

I

1

FIGURE 11.26. Follow-up of deflections with proper use ofcamber diagram.

unloaded without waiting for the cantilever ten-dons to be stressed.

Figure 11.28 shows how a typical first-generationsegment can be assembled to the existing structureusing a temporary apparatus located on the topand bottom slabs, which is used to create forces F,and F, which ensure the equilibrium of the newsegment at the joint.

These two forces, combined with the weight Wof the segment, give the resultant force R, which isinclined with respect to the joint. Because of thevery small coefficient of friction of the epoxy, theshearing component of R produced by W canbe balanced only by the vertical component of thereaction C, which exists normal to the bottom faceof the web shear keys, Figure 11.28. The resultantR is composed, therefore, of the oblique reaction Csupported by the shear keys and a horizontal reac-tion N, which is responsible for securing the joint.

The axial stress distribution at the joint crosssection differs in this case from what would be ob-

tained by ordinary calculations. It is obvious that Nis smaller than F (the sum of forces F, and FJ. Let(Y be the angle of the key support faces with respectto the horizontal; then F - N = W tan (Y, and for atypical case of tan (Y = 0.50, F - N = W/2. Considera segment weighing 50 tons (45 mt), temporarilyassembled by a prestress force of 100 tons (90 mt)located in the top slab; the axial force reduction is25 tons (23 mt)-that is, 25% of the total appliedprestress force.

If the rate of erection of the precast segments issufficient to ensure the positioning of four seg-ments before the resin in the first joint has set, thenthe reduction in the effective axial force in thisjoint will be 100 tons (90 mt), which more or lesscorresponds to one tendon of twelve f in. diameterstrands. The same conclusion would be valid whenthe permanent prestressing was used to ensure thetemporary stability of the cantilever.

In conclusion, it is recommended that this re-duction of the effective prestress force be taken

Characteristics of Precast Segments and Match-Cast Epoxy Joints 487

( 13).-~*-~ .~~.-~~ -

i-21) C-25)

FIGURE 11.27. Follow-up of deflections with improper use ofcamber diagram.

TEMPORARY SEGMENT ASSEMBLY JOINT EPUILIBRIUM

Fl

(J)lb)

(a)

FIGURE 11.28. Temporary assembly. (a) Elevation of temporary assembly. (6) Jointequilibrium.

into account while verifying the cantilever resis- It is also preferable to choose the intensity andtance and stability. Failure to do so may result in the point of application of the forces F, and F, suchtemporary joint opening, which is undesirable alas to allow the axial force N to be as close as possi-though not dangerous for stability. ble to the section centroidal axis, thus ensuring a


nearly uniform axial stress distribution over thetotal height and hence a resin film of constantthickness.

Permanent Assembly: Structural Importance of EpoxyResins As regards the final prestress tendon pro-files, it was shown in Chapter 4 how the resistanceof the different cantilevers is ensured by a firstgroup of tendons, known as cantilever tendons,which may be straight or curved in profile and an-chored on the various segment faces. The stressingoperations remain in the critical path of construc-tion because a new pair of segments cannot beplaced before the last pair has been stressed to theexisting cantilever, Figure 11.29.

The second group of tendons joins the differentcantilevers together and makes the structure COII-

tinuous. They are anchored either in block-outs inthe bottom slab or in the fillets at the junction be-tween the top slab and the webs after upward de-viation to top slab level.

The service shear forces that act upon the jointsvary according to the type and characteristics ofthe structure. In variable-depth bridge decks withdraped prestressing tendons the shear stress acrossthe joints is usually low. In a long-span, constant-depth bridge deck with straight tendons, however,the shear stresses at the joints can exceed 600 psi (4MPa), as was the case in several structures men-tioned in Chapter 4. A bad choice, or improperuse, of the epoxy resin can be a critical factor con-cerning the shear resistance of the joints, and forthis reason joints of this type require strict qualitycontrol.

In general, the different types of epoxy resinsavailable have final strengths substantially exceed-ing that of concrete, so they do not constitute aweak point in themselves. Several conditions must

FINAL SEGMENT ASSEMBLY

DETAIL A

FIGURE 11.29. Final segment assembly.

be satisfied, however, in order that the resin cureproperly.

1. Mixing the constituents in their correct pro-portions.

2. Eliminating any solvents that have a fatal effecton the propertles of the resin.

3. Avoiding any flexible additives, such asthiokol, that greatly increase the deformabilit)of the epoxy.

4. Mixing and applying carefully.

With respect to the last point, the surfaces to bejoined must be specially treated if the best resultsare to be obtained. Comparative tests have shownthat sand blasting gives the most satisfactorv I-e-suits, the surfaces being kept clean. dry, and freefrom grease during placing. In damp or rain!weather alcohol is burnt on the joint surfaces toeliminate surface moisture. The water present inthe concrete itself has no detrimental effect on theperformance of the resin.

It has also been established that rapid placing otsuccessive segments has a favorable effect on theproperties of the resin. The additional compressivestress applied to an epoxy joint under polymeriLa-tion when the next segment is prestressed im-proves the resin’s ultimate mechanical properties.

Finally, note that in variable-height structuresthe joint detailing is such that the joint plane isnot normal to the principal stress, especially at thebottom slab level. The epoxy joint is then subjectedto shear forces that may be quite large and that cancause failure of the bottom slab in the event ofnonpolymerization of the epoxy resin.

In addition to the precautions taken to ensurecorrect curing, one may provide against the risk ofbad results by including shear keys in the bottomslab.

1 I S.2 SECOND-GE,\‘EKA TI0.V SEC;.LlE.VTS

Although the characteristics and performance ofthe first structures built with match-cast joints arenot in doubt, it seems a good idea to investigatenew types of joints allowing the transmission ofshear forces without relying on the strength ofepoxy resins.

Second-generation segments do just this, beingequipped with interlocking keys in the top andbottom slabs and in most of the height of the webs.This configuration of shear keys at regular inter-vals, which improves the behavior of joints bv re-lieving the epoxy of its structural role, has the


advantages of simplicity and safety. This type ofsegment has been used with success in severalbridges, notably the Alpine Motorways, the SaintAndre de Cubzac Bridge, and the SallingsundBridge, and more recently in several structuresin the United States such as the Long Key andSeven Mile bridges in Florida.

Ribs and Interior Anchorage B1ock.s Anchorageblocks (blisters) or stiffening ribs are currentlyused inside the segments for the final longitudinalprestress anchors. The tendons, ensuring the sta-bilit\, and resistance of the cantilever and placedprogressively as construction proceeds, can be an-chored away from the joint faces, thereby render-ing the stressing operations and the segment-placing operations independent of one another.The ribs and anchorage blocks are generally usedto house the temporary prestress that ensures theprovisional stability of the cantilever, thus leavingthe top slab completely free.

Bolted Ribs Despite the tensile strength of theepoxy resin at a glued joint, no tensile resistance isusually considered, as precast segmental structuresare nearly always totally prestressed and so no ten-sile stresses can develop across the joint. However,we can further improve epoxied match-cast jointsby giving them a certain resistance to tension byusing bolted ribs, which ensure the continuity ofthe longitudinal reinforcing steel, Figure 11.30.

11.5.3 EPOXY FOR JOAVTS

The structural importance of the thin layer ofepoxy resin forming the joint between two adjacentprecast segments was discussed in Section 11.5.1.We now take a closer look at the physical and me-chanical properties of these resins and the variousprecautions to be taken to ensure satisfactory andconsistent results.

-.Epoxy Types Epoxy resin glues are made up

from two components: the epoxy resin and thehardener. Mixing these two components in thecorrect proportions gives a thermostable product

with properties that depend upon the type of resinand hardener used. Three grades of epoxy resinare commonly used, depending upon the ambienttemperature range under which the resin is to beapplied:

40 to 60°F (5 to 15°C)60 to 75°F (15 to 25°C)

Fast-reacting epoxyMedium-fast-reacting

epoxy75 to 105°F (25 to 40°C) Slow-reacting epoxy

1. Color The resin and the hardener must beof clearly contrasting colors thus avoiding any con-fusion. When properly mixed, the final product isto be a homogeneous gray color similar to that ofconcrete.

2. Shelf life of components Both componentsmay be stored for up to one year, provided that thestorage temperature is kept between 50 and 70°F(10 and 20°C). After three months’ storage it isnecessary to check that the epoxy resin shows nosign of becoming crystalline. If it does, then specialtreatment must be given to the resin, followed bytests, before use.

3. Pot Life of the Mixed Glue The pot life of anepoxy resin is a measure of the time interval be-tween the mixing of the components together andthe moment when the glue becomes no longerworkable. The workability of the glue is deter-mined by its internal temperature, dependingupon the grade of epoxy resin employed. For a 10lb (5 kg) mix used on site, mixed under isothermicconditions until an even color of mix is obtained,the following results are required:

WorkabilityLimit

Epoxy Grade Temperature

5 to 15°C 40°C ( 104°F)

15 to 25°C 40°C ( 104°F)

25 to 40°C 55 to 60°C(131 to 140°F)

The pot life must be approximately:

Ambient Temperature

Epoxy Grade41°F 50°F 59°F 68°F 86°F 95°F(5°C) ( 10%) ( 15°C) (20°C) (30°C) (35°C)

5 t o 1 5 ° C 40 min. 15 min.1 5 t o 25°C 2 0 min. 1 5 min.25 t o 40°C 2 5 min. 1 8 min.


BOLTED RIB JOINTS

FIGURE 11.30.

On site, each 10 lb (5 kg) mix of epoxy resin mustbe applied to the concrete surface within the pot-life period as specified above.

4. Open Time of the Applied Epoxy Glue Theopen time of the glue is defined as the period be-tween its application to the concrete surface andthe moment when it reaches its workability limittemperature. Because of the much greater heatdissipation from the thin layer [& to a in. (1 to 3mm)] on the concrete surface, the applied gluetakes much longer to reach the workability limittemperature than the mix in the pot.

The open time must never be less than onehour, regardless of the grade used. One measur-ing device used to determine open time is theVicat’s needle shown in Figure 11.3 1. A 1 mm layerof epoxy glue is spread onto a steel plate, and thestopwatch is started. The time lapsed before theneedle will penetrate only 0.5 trim into the gluelayer is defined as the open time.

5. Thixotropy This characteristic gives an in-dication of the epoxy resin’s ability to be applied tovertical surfaces with relative ease and yet with sub-sequent running. Thixotropy may be measuredusing Daniel’s gauge, Figure 11.32. The gauge isplaced on a level surface with the gutter sectionhorizontal. The gutter is then filled with freshlymixed resin and hardener and abruptly turned tothe upright position, as shown in the diagram. Theflow time relationship is recorded. The test shouldbe carried out at the maximum temperature forwhich the resin is specified. A resin that flows lessthan 30 mm in 10 minutes-is suitable for applica-tion to vertical concrete surfaces. Other testingmethods are available such as the sag flow ap-paratus according to ASTM D2730-68.

I

Bolted rib joints.

Other characteristics of the epoxy glue that maybe tested on site are:

The angle of internalfriction: The ease with whichthe excess resin may be squeezed out of the jointwhen subject to uniform pressure.

FIGURE 11.31. Open-time testing-Vicat’s needle.


/100 mm

FIGURE 11.32. .I‘hisotropy testing-Daniel’s gauge.

Shrinkngp: Must be practically nil.Water absorption rate and solubility in water:Maximum permissible true water absorption-12%. Maximum permissible quantity of epoxy sol-uble in water at 25°C (i7”F)--4%.Hen t resista rice: Minimum required value accord-ing to Mostens (DIN 53458) on week-old 10 x 15x 120 mm test rods is 50°C (122°F).

,Mechu rricnl p)-opertie.)

1. Shenr resistance The shear resistance of themixed epoxy glue is determined on rectangularconcrete test specimens with the following dimen-sions: 1.6 x 1.6 x 6.3 in. (4 x 4 x 16 cm) with aresin interface at 17” to the vertical, Figure 11.33.The concrete test pieces are made from a high-quality concrete comparable to that used in precastsegment manufacture and are cured under waterseven days f-rom time of casting.

After removal from the water the pieces are dab-dried and the surfaces to be assembled are pre-pared by shot blasting, wire brushing, or othersimilar methods to remove laitance. The test piecesare then resubmerged in water for three hours,after which they are removed and dabbed dry witha clean cloth. The resin is then applied in a layer of& in. (2 mm) on one surface and the test beamclamped in an assembly that maintains a normalpressure on the interface of 2 1 psi (0.15 MPa). Theassembly is stored for seven days at a temperaturerepresentative of the desired working conditions,and then the test is carried out. The minimum ac-

FIGURE 11.33.

,4X4cm,

s’

Shear-resistance test

ceptable ultimate shear stress at the interface is1400 psi (10 MPa).

2. Shear Modulus The instantaneous shearmodulus (Ci) must be greater than 220,000 psi(1500 MPa) at:

15°C (59°F) for grade 5 to 15°C25°C (77°F) for grade 15 to 25°C40°C (104°F) for grade 25 to 40°C

The long-term shear modulus must be greaterthan 14,500 psi (1000 MPa) after 28 days at thesame temperatures as above. Solid cylindrical testpieces are used for measuring these values in con-junction with the easily made test apparatus shownin Figure 11.34.

Certain epoxy resins show an excessive sensitiv-ity to high temperatures that makes them unac-ceptable in warm climates. Figure 11.35 showscomparative results of ten different resins testedfor the Rio Niteroi Bridge. It is obvious that aproduct that becomes practically plastic with noshear modulus at 60°C is completely unacceptable.

3. Tensile Bending Strength A three-pointbending test is carried out on a pair of glued con-crete cubes with a compressive strength of 5700 psi(400 kg/cm2), Figure 11.36. The faces to be gluedare shot blasted, or bush hammered, so as to re-move laitance. The cubes are then submerged inwater for 72 hours. When taken out of the waterthe surfaces to be glued are dried simply by dab-bing with a clean cloth. Immediately after the dab


Dial gauge,

G (M.&)

2500

2000

1500

1000

500

0

View X-X

FIGURE

I Ix1

View from one side

11.34. Shear=nioclulus test.

t (‘Cl20 30 40 50 60 m

FIGURE 11.35. Variation of’ shear ~nodulus G with temperature.

drying the glue is applied in a layer of & in. (1.5mm) to one of the prepared faces. The corre-sponding face of the other cube is placed againstthe glue layer, and the two cubes are clamped to-gether with a clamping force of 300 lb (150 kg).The assembly is then wrapped in a damp cloth,which must be kept wet until the three-pointbending test is carried out.

4. Compressive Strength The compressivestrength is determined according to DIN 1164 on 4cm (14 in.) cubes of cured epoxy glue. After 24hours (from the time of preparing the samples) atthe maximum temperatures for each grade thecompressive strength must be not less than 12,000psi (80 MPa). The loading rate is to be approxi-mately 3600 psi (25 MPa) per minute.

5. Elastic modulus in compression The instan-taneous modulus (Ei) is determined on cubes ofpure epoxy after curing for seven days at the

maximum group temperature. These cubes are thesame size as those used for the compressive-strength determinations. The modulus must not beless than 1,140,OOO psi (7850 MPa)

Practical Use of Epoxy in Match-Cast Joint.\ Inregard to the use of the resin, the two compo-nents should be mixed carefully and quickly asnear as possible to the surfaces to be coated. Underno circumstances should oil or grease be allowed tocome into contact with surfaces that are to beglued. Most standard demolding agents are suita-ble for use, but care should be taken to ensure thatno oil-based demolders are used. Exposure toweather during the storage period is oftensufficient to remove the demolding agent. For bestresults, surface laitance should be removed by shotblasting or bush hammering. This treatment isnormally carried out in the storage yard. With theuse of multiple keys, the structural role of the

Manufacture of Precast Segments

, ,L o a d amlied h e r e ,

p--j-~ -___

FIGURE 11.36. Tensile bending-strength test.

epoxy is considerably reduced and a special prepa-ration of the surface is not a mandatory feature.

Immediately before the glue is applied, the sur-faces are to be cleaned to remove traces of dirt,grease or oil, and dust.

Under normal climatic conditions it will not al-wavs be possible to avoid dampness on the surfacesto be glued. If the surfaces do show signs of mois-ture, they must be dab dried with a clean cloth, andno gluing may proceed until all free water has beeneliminated.

The thickness of the glue layer should be abouth in. (1.5 mm). As soon as possible after the resinhas been applied, the surfaces must be brought to-gether. Pressure must be applied before the opentime of the epox) resin expires. The pressureapplied by either temporary or final prestressshould not be less than 30 psi (0.2 MPa).

11.6 Manufacture of Precast Segments

11.6.1 1,VTRODUCTION

The various methods used until now for precastingsegments fall into two basic categories:

1. Long-line casting, where all segments to makeup either half or a full cantilever are manufac-tured on a fixed bed with the formwork mov-

ing along the bed for the successive casting op-erations.

2. Short-line casting (with either horizontal orvertical casting), where segments are man-ufactured in a step-by-step procedure with theforms maintained at a stationary position.

For match-cast joint structures, the accuracy ofthe segment geometry is an absolute priority. Ade-quate surveying methods and equipment must beused to ensure an accurate follow-up of thegeometry and an independent verification of allmeasurements and adjustments.

Immediately after the manufacture of a segmentthe as-cast geometry should be controlled andcompared to the theoretical geometry to allow anynecessary adjustment to be incorporated in sub-sequent casting operations. This aspect of matchcasting is particularly important for the short-linemethod and will be covered later in this chapter.

11 h.2 LONG-LINE CASTLX’G

In this method all the segments are cast, in theircorrect relative position, on a casting bed thatexactly reproduces the profile of the structure withallowance for camber. One or more formworkunits travel along this line and are guided by apreadjusted soffit. With this method the joint sur-faces are invariably cast in a vertical position.


Figure 11.37 shows the casting sequence.3 Thepier segment (3) is cast first, then the segments oneither side of the pier segment (1) and (2). If a pairof forms is used, then the symmetrical segments oneach side of the pier segment can be cast simul-taneously, thus saving casting time. As segmentcasting progresses, the initial segments may be re-moved for storage, leaving the center portion ofthe casting bed free. If enough forms are available,then the casting of a second pair of cantilevers mayproceed even though the first pair is not com-pletely cast.

Figure 11.38 shows the typical cross section of along-line casting bed with the formwork in opera-tion. The method was initially developed forconstant-depth box girders (Choisy-le-Roi andCourbevoie Bridges). It was later extended to thecase of variable-depth decks such as the OleronViaduct (the two sketches of Figures 11.37 and11.38 refer to this structure) and also adopted inother countries (Hartel Bridge in Holland).

The important advantages of the long-line cast-ing method are:

It is easy to set out and control the deck geometry.

After form stripping, it is not necessary to im-mediately transfer the segments to the storage areain order to continue casting.

The disadvantages are:

Substantial space may be required. The minimumlength is usually slightly more than half the lengthof the longest span of the structure, but it dependsupon the geometry and the svmmetrv of thestructure.

The casting bed must be built on a firm foundationthat will not settle or deflect under the weight ofthe segments. If the structure is curved, the longline must accommodate this curvature.

All equipment necessary for casting, curing, and soon must be mobile.

11.6.3 SHORT-LIIVE HORIZOh’TAL CASTI.YG

The short-line casting method requires all seg-ments to be cast in the same place, using stationaryforms, and against the previously cast segment inorder to obtain a match-cast joint. After castingand initial curing, the previously cast segment is

Segments being cast Segments completed.

FIGURE 11.37. Typical long-line precasting bed.

Travellingcrane leg

I I

Mobile outsider formwork

Telescopic insidef-form work

FIGURE 11.38. Typical cross section of long-line casting bed with formwork.

Manufacture of Precast Segments 495

removed for storage and the freshly cast segment ismoved into its place. The casting cycle is then re-peated. This operation is illustrated in Figures11.39 and 1 1.40.“*4

B L A N K E N DT O S T O R A G E

/

FIGURE 11.39. ‘I‘ypical short-line precasting opera-t i on.

It is important that the reader fully comprehendthe principle of the method insofar as building adeck of a given geometry is concerned. When astraight box is desired, Figure 11.41, the matchmarking mate segment (n - 1) is moved from thecasting position to the match-cast position along astraight line, and this is usually verified by takingmeasurements on four elevation bolts (a) em-bedded in the concrete roadway slab and twoalignment stirrups (b) located along the box cen-terline. A pure translation of each segment be-tween the cast and match-cast positions thereforeresults in the construction of a perfectly straightbridge (both in elevation and in plan view), withinthe accuracy of the measurements made at thecasting site.

To obtain a bridge with a vertical curve, thematch-cast segment (n - 1) must first be translatedfrom its original position and then give a small ro-tation in the vertical plane (angle CY shown in Fig-ure 11.42). Usually the bulkhead is left in a fixedposition, and all segments have in elevation theshape of a rectangular trapezoid with the taperedface along the match-catch segment. It is thereforeonly necessary to adjust the soffit of the cast seg-ment during the adjustment operations.

A curve in the horizontal plane is obtained in thesame fashion, Figure 11.43, by first moving thematch-cast segment (n - 1) to its position by a puretranslation followed by a rotation of a small angle pin plan to realize the desired curvature.

T O S T O R A G E 4 /,

FIGURE 11.40. Formwork used in casting segments.

ELEVATION TRANSVERSE SECTION

STRAIGHT BRIDGE

P L A N V I E W

FIGURE 11.41. Straight bridge.

ELEVATION

_------- m-e-----

e-------A- 1-------;

P L A N V I E W

FIGURE 11.42.

TRANSVERSE SECTION

BRIDGE WITHV E R T I C A L C U R V E

Bridge with vel-tical curve.

496



BRIDGE WITHHORIZONTAL CURVE

P L A N V I E W

FIGURE 11.43. Bridge with horizontal curve.

Change in the superelevation of the bridge mayalso be achieved with a short-line casting; however,the principle is a little more difficult to properlygrasp, Figures 11.44 and 11.45. A constant trans-verse fall of the bridge does not need to be re-peated in the casting machine. Segments may becast with soffit and roadwav slab both horizontaland placed at their proper attitude in the bridge byoffsetting the bearing elevation under the webs toobtain the desired cross fall. Only a variablesuperelevation must be accounted for in the cast-ing operation, and this is the normal case inbridges with reverse curves and in transition areasbetween curves and straight alignments. In such acase match-cast segment (n - 1) needs to be ro-tated by a small angle such as y around the bridgecenterline. Because the bridge geometry is usuallydefined at roadway level and not at soffit level, therotation given to the match-cast segment results ina slight horizontal displacement of the soffit in thecasting machine, which must be accounted for.Also all surfaces of the box segment (top slab,soffit, and webs) are no longer true planes but areslightly warped. To allow the formwork panels toadjust to this change of shape, it is absolutely man-datory to eliminate all restraints such as closed tor-sionally stiff members.

The basic advantages of the short-line castingmethod are therefore the relatively small space re-quired and the fact that all equipment andformwork remain at a stationary position. Themobility of equipment necessary for the long-linemethod is no longer needed. Also, horizontal andvertical curves as well as variable superelevationare obtained with short-line casting without themajor change in soffit configuration that would berequired in the long-line casting method. How-ever, success will depend upon the accuracy of ad-justment of the match-cast segments, and precisesurvey and control procedures must be initiated(Section 11.6.5). This last aspect represents themajor potential disadvantage as a direct conse-quence of the intrinsic potential of the method.

11.6.4 SHORT-LINE VERTICAL CASTING

Normally, for both the long- and short-linemethods, the segments are cast in a horizontal po-sition. A variation in the short-line method is thatused for the Alpine Motorways near Lyons,France, where the segments were cast in a verticalposition (cast on end) as shown in Figure 3.100.The procedure is as follows: after the first segmentis cast, the forms are removed and moved upward



BRIDGE WITH VARIABLESUPER ELEVATION

P L A N V I E WFIGURE 11.44. Short-line casting-bridge with variable super-elevation.

\ END BULKHEAD

FIGURE 11.45. Short-line casting-isometric view of segment casting with variablesuperelevation.

so that each succeeding segment can be cast above claimed for vertical match casting include easierthe previous one. After a segment is cast and placing and vibration of the concrete. However,cured, the segment beneath it is transferred to special handling equipment and procedures arestorage and the one removed from the forms is required to rotate the segment from the vertical tomoved down, to rest on the floor. The advantages its final horizontal position.


11.6.5 GEOMETRY AND SURVEY CONTROL

Segment Precasting in a Casting Machine

The principles described in this section apply toshort-line horizontal casting but may be easily ex-tended to vertical casting. The apparatus used toform the concrete segment is usually referred to asa casting machine and is made up essentially of fivecomponents:

1. The bulkhead that forms the front section ofthe segment.

2. The match-cast segment, properly coated atthe front end section with a suitable demoldingagent and used to form the back end section ofthe newly cast segment.

3 . The mold bottom (or soffit).4. The side forms, properly hinged for stripping

and firmly sealed to the bulkhead and thematch-cast segment during casting. The insideforms, which pivot and retract for stripping.

5. The inside forms, which piv.ot and retract forstripping.

The relationship between an individual segmentand the finished structure is established by meansof three different systems of reference:

1. The final system of reference, which is the refer-ence for the finished geometry of the struc-ture. In this system each segment is describedby its basic geometry.

2. The auxilia? system of reference, which corre-sponds to the precasting machine and is at-tached thereto.

3. The elementa reference system, which is attachedto each segment and would be the equivalentof intrinsic coordinates in space geometry.

The principle of the precasting method is asfollows. During the casting of segment A (segmentB being in the match-cast position) the elementaryreference system of A is identical with the auxiliaryreference system, that of the casting machine.

To position B with respect to A becomes simply amatter of positioning B with respect to the pre-casting machine. It is the task of the design office toprovide the theoretical geometric information nec-essary for positioning. The values are computedfrom the basic geometry with the addition of therelevant compensatory values for deflections. Thedefinitions of these reference systems are pre-sented below.

FIGURE 11.46. Auxiliary reference system (casting-machine reference).

The auxiliary reference system refers to thecasting machine and is defined in Figure 11.46.The plane of the bulkhead is perfectly vertical.The upper edge of the bulkhead is a horizontal inthis plane except when segments do not have pla-nar top surfaces. The x, y and z axes refer to thecasting-machine reference system, whereas XA, yA9and z,., refer to the elementary system of reference.The elementary system of reference is materializedon each segment in the following manner:

1

2.

3.

The x, axis: This axis is represented by marks(such as saw cuts) made on two steel stirrupsanchored in the top slab as near as possible tothe joints.The origin 0,: The origin o, is located at thepoint where the x, axis intersects the plane ofthe joint at the bulkhead.Theplunex,,o,,y,: This plane may be definedby three fixed leveling points, the position ofeach point with respect to the plane x, o, y beingarbitrary but invariable. For practical reasons,four leveling points are used and materializedby bolts anchored in the top surface of thesegment above the webs and as close as possibleto the joints.

Now that the elementary system of reference hasbeen established (all measurements and readingsbeing made while the segment is in the castingmachine before the forms are removed), the seg-ment can be positioned with respect to the aux-iliary reference system, so that it can be placed inthe correct countercasting position according tothe calculations supplied by the design office.


In order to correctly position the countercastingsegment, information is needed about the finalgeometry of the structure. The overall geometry ofa bridge structure is normally defined by thegeometry of the roadway. From this roadwaygeometry it is necessary to determine the geometryof the concrete structure itself.

The longitudinal reference line to which all thenecessary parameters are related is known as thebox girder line (BGL). This line may coincide withthe top concrete surface of the box girder, but itmay also be a fictitious line of reference if the boxgirder top slab shape is not regular.

The box girder line is usually described usingtwo curves, Figure 11.47:

One curve (a) in a horizontal plane, which gives yas a function of x for each point where the boxgirder line intersects a joint plane between seg-ments and also the center points of supports (abut-ments or piers); this curve is simply the projectionof the true space box girder line onto a horizontalplane and is sometimes referred to as the “bgl”(small letters).One curve (5) in a developed vertical plane giving zas a function of c for the same points mentionedabove. Thiss curve is the real box girder line, BGL.

To complete the definition of the segment posi-tion in space-at each joint line and at supportcenters-we must define the transverse slope ofthe theoretical extrados line.

It is important for both the bgl and the BGL tocalculate the m and s parameters, respectively, inorder to obtain an accurate determination of pro-jected and real span lengths.

The calculations and structural drawings refer tonominal segment lengths and span lengths. Usu-ally these lengths refer to the projection on a hori-

Box girder line

Horizontal pqcctionof box girder linel bgl’

FIGURE 11.47. Box girder line curves.

zontal plane and follow the curvilinear abscissas.The segment lengths chosen on this basis may beretained, but in calculating the real lengths ofcast-in-place closure joints and three-dimensional scurve must be used.

Because of the way a casting machine works, thesegment joint at the bulkhead end is invariablyperpendicular to the axis of the segment. There-fore, in plan view, the segments are generally oftrapezoidal shape, except for segments over thepiers which are rectangular in order to provide aconstant starting point for each cantilever, Figure11.48.

Segment Casting Parameters

All measurements on a segment are made whenthe segment is still in the casting machine.Readings must be taken when the concrete hashardened and before formwork stripping, Figure11.49. Horizontal alignment readings give the dis-tance of the segment axes as marked on the stir-rups from the casting-machine reference line.Longitudinal profile level readings are given by thefour bolt elevations relative to the horizontal refer-ence plane.

Readings must be taken on the segment just castand also on the match-cast segment. Correctionsare applied to allow for the geometric defects inthe preceding segment, Figure 11.50, and are usedas “theoretical values for adjustment.”

Survqr Control During Precasting Operations

The surveyor in charge of the operations mustcomplete a data sheet for each segment containingessentially:

1. Theoretical basic data supplied by the designoffice, allowing the preparation of the hori-zontal alignment and the two parallel boltlines.

2 . Corrected values defined either graphically orby computer.

3. Survey control readings.4. Linear measurements on the segments.5. Schematic representation of the segment to

rapidly verify the relative positions of the seg-ment axes.

6. A level check to pick up any gross error in levelreadings on the same segment.

7 . Comments on the casting operations.


Segment over pier

Pier\f

( Segment ax is / Hj+vi*3

- BOX girder line “bgl*or Q ( sigma ) curve

FIGURE 11.48. Short-line casting-position of segment joints in plan view.

Ewi’dw

?--

!- L

Esw1dsw

. A!

r L3

FIGURE 11.49. Casting-machine orientation and segmentmeasurements.

As an example, Figure 11.5 1 shows the typicalsurvey control made on the first four segments of atypical cantilever. Control of alignment and levelsmay be followed graphically or numerically bycomputer, using the basic geometric data obtainedin the casting machine and shown in Figure 11.52.

In order to avoid any significant deviation fromthe theoretical geometry, it is necessary to provide

for corrections when casting the next segment.Figure 11.53 shows how this would be done for theplan alignment. Similar corrections are made forthe longitudinal profile on the two parallel boltlines. It is essential not only to follow carefully thetrajectory of the two bolt lines separately but also tocheck for each segment that the superelevation(given by the crosswise difference in level between


FIGURE 11.50. Plan view of’ casting operation-readings using survev instruments.

FIGURE 11.51. Casting operation-topical survey control

the two bolt lines) varies regularly according to thetheoretical geometry. Failure to do so has resultedin important geometric imperfections on certainprojects.

Suruey Control During Construction

The nature of match-cast segmental construction issuch that the structure is really “built” in the pre-casting yard. Although corrections can be made inthe field, such corrections are undesirable and al-ways a source of additional expense and delays.Close control of precasting is far more efficient. Itis nevertheless important to check the evolution ofthe structural geometry during segment placing:

1. To compare actual deflections with computedvalues,

2. To ensure that no major errors have escapedthe control in the precast yard or factorv.

Such checks at the site should include:

1 . Pier positions, height and in plan.2 . Bearing positions, level and orientation.3 . Pier segments, level and orientation.4. Cantilevers proper, every third segment, in-

cluding levels, superelevation, and orientation.5. Overall geometry of the structure after con-

tinuity is achieved between the individual can-tilevers.

Conclukon

The principles of geometry and survey control aremore complicated to explain than to use, once the


THEORETICAL AX15 OFO, THEORETICALAXIS OFO,

cAsTI Nt M~CI~NE

IHG MACHINE BULKHEAD

SEGMCNTO ’ QGMENT~

TUEORETltnL LEVEL FUR 1t

_ _ -;--- -.--~~Z?-~ +L;W’: ;R yyoE;;= .

THEORETICnL,

LEVEL FOR 0REAL LEVELFOR 055TING M A C H I N E EUJLKHMD

SEGMENT 0 sEGMENTI

FIGURE 11.52. Survey control-horizontal alignment and longitudinal profile results.((I) Horizontal alignment. (h) Longitudinal profile.

REAL AXIS OF 1

TUE ORETICAL AXISOF 0 (2 REAL AXIS)

FIGURE 11.53. Typical alignment corrections during casting operations.

basic principles of a casting machine are thor- are the Chillon and St. Cloud Viaducts in Europeoughly understood. The short-line method has and Linn Cove Viaduct in the United States. Atgreat potential to construct segments for bridges, Saint Cloud, 120- to 140-ton segments were casteven those with very complicated trajectories, on a one-day cycle, and the final geometry of therapidly and economically. Outstanding examples bridge was obtained with no on-site adjustment.


On the other hand, a loose approach togeometry control at the casting yard may lead toserious difficulties at the project site.

11.66 PRECASTING YARD AND FACTORIES

The precasting operations are usually carried outin a yard or even a factory if the size of the projectallows the corresponding investment. All opera-tions, such as:

Preparation of the reinforcing steel cages andducts for post-tensioning tendons

Manufacture of concrete

Manufacture of segments including heat curing

Storage of segments including finishing and qual-ity control are performed in a repetitive fashionunder factory conditions.

As an example of typical precasting-yard lay-outs, Figures 11.54 and 11.55 show views of:

The Saint Cloud Viaduct precasting yard withshort-line casting

The Oleron Viaduct precasting yard with long-linecasting

The typical precasting cycle (with either thelong-line or the short-line method) is of one seg-ment per formwork per day with a one-day workshift, concrete hardening taking place during thenight (at least 14 hours between the completion ofconcrete placing in the evening and the strippingof forms the next morning). Shorter constructioncycles may be obtained by reducing the time ofconcrete hardening, but quality may decline if allthe operations are not kept under very strict con-trol.

Heat curing of the concrete to reduce the con-struction cycle and accelerate the rotation of thecasting machines is perfectly acceptable. Its im-proper use, however, may alter the accuracy ofjoint matching between segments, as shown in Fig-ure 11.56. This effect would be particularlysignificant for wide but short segments.

Typical segments usually have the following di-mensions:

Width 30 to 40 ft (9 to 12 m)Length 10 to 12 ft (3 to 3.6 m)Ratio width/length 3 to 3.5

In the case of wide decks or long spans, where thesegment length is reduced to reduce the unitweight, the usual geometric proportions may varyconsiderably; such is the case for two notablestructures:

St. Cloud width 70 ft. length 7 ft,ratio 10

St. Andre de Cubzac width 58 ft, length 5.8 ft.ratio 10

For such segments, heat curing is more likely tocreate small changes in the segment shape, whichmay build up progressively and so alter the ef-fectiveness of joint matching. This is due to thedevelopment of a temperature gradient in thematch-cast segment, which is in contact on oneside with the newly cast heated segment and onthe other side with the lower outside temperature.

The problem may be completely eliminated byalways heat curing both segments simultaneouslyso as to avoid any temperature gradient. Experi-ence has proved the method totally efficient.

When the project involving segment precastingis of sufficient magnitude or where climatic condi-tions are adverse, precasting factories are a logicalextrapolation from the short-line method per-formed in an open precasting yard. Segment man-ufacture takes place in a completely enclosedbuilding with a better use of personnel and a moreconsistent quality of products.

An interesting example is afforded by the B-3South Viaducts, requiring production of 2200 pre-cast segments weighing between 28 and 58 tons (25to 53 mt). The precasting site was installed close tothe project and included four main areas:

1 . An assembly workshop, where the reinforcingsteel cages were prepared and the prestressingducts positioned. The finished cages werehandled by a 5 ton tower crane.

2. A concrete mixing plant.

3. A precasting factory where the segments werecast and cured.

4. A storage area where the finished segmentswere left to cure adequately. These segmentswere handled by a traveling portal crane.

The precasting factory was equipped with fourprecasting machines, all of which were entirelyprotected from the outside environment. Twomachines were reserved for the manufacture of 15to 20 ft (4.5 to 6 m) segments and two for the 20 to

1 .

2

3.

4.

5

6.

I.

8

PRECASTING YARD

S c a l e 11500

Launching track for tr,irder

a n d trolle!y

A c c e s s r a m p .

Loading point for s e g m e n t s

Launching g\ rdet assemblyzone

Segment storage.

Travelllng crane t r a c k

hlauld bot tom

r’rPstress1ng steel sturaqe

10 Rplnforcernent asspmbty

17 F u t u r e carriagewayalignment

\ ,’ ’ _/’

0

\ I/ ’ /’/ ‘_ 27 ,’ ,/’0% “\ ‘\ ,A’

J:‘i

FIGURE 11.54. St. Cloud Viaduct, precasting yard layout. (1) Launching track forgirder and trolley. (2) Access ramp. (3) Loading point for segments. (4) Launching-girder assembly zone. (5) Segment storage. (6) Traveling crane track. (7) Mold bottom.(8) Prestressing steel storage. (9) Tower crane track. (10) Reinforcement assembly. (11)Concrete plant. (12) Precast elements. (13) Prestress tendon manufacture. (14) Offices.(15) General services. (16) Toll gate position. (17). Future carriageway alignment.

506 Technology and Construction of Segmental Bedges

Staff quarters

Launching girder assembly

Retnforcement

i D u c t s t o r a g e a r e a L OffIce

FIGURE 11.55. Oberon \‘iatiuct, precasting yard layout.

SEGMENT CONJUGATE

L-lL E N G T H E&CT OF IMPROPER CURING OF SEGMENTSL IN SHORT LINE CASTING

FIGURE 11.56. Effect of improper curing of segments in short-line casting.

31 ft. (6 to 9.5 m) segments, Figures 11.57 and 11.58. The production of the different segments in-Each casting machine was made up of a mobile volved the following operations:form, an end form or bulkhead, two hinged out-side forms, and a telescopic inside form, Figure 1. Assembly of the steel cages in a template.

11.59. Handling of concrete and reinforcing steel 2. Steel-cage storage.inside the factory was performed by two 10 ton 3. Final steel-cage preparation and duct installa-travel cranes. tion.

Handling and Temporary Assembly of Precast Segments 507

FIGURE 11.57. R-3 Sot~rh Viaducts, inside view of the precasting f’acto~~~.

Casting machine Concrete Plant Control System

/

FIGURE 11.58. B-3 South Viaducts, plan view of the precasting factory.

Inside formworkt

Outside formwork Bottom formwork

FIGURE 11.59. B-3 South Viaducts, detail of a castingmachine.

4. Positioning of steel cage inside the formwork.

5 . Adjus tment o f cas t ing machine , inc lud ingalignment of match-cast segment and sealingof all form panels.

6. Concrete casting and finishing.

7. Steam curing.8. Formwork stripping; followed by transfer of

the match-cast segment to the storage yard and

of the newly cast segment to the match-cast po-sition by means of an independent motorizedtrolley.

1 I .7 Handling and Tempera y Assemblyof Precast Segments

In either long- or short-line casting, segments can-not be handled before the concrete has reached asufficient strength to prevent:

Spalling of edges and keys

Cracking of the parts of the segment subjected toappreciable bending stresses due to self-weight

Inelastic deformations that would ultimately im-pair proper matching of the segments

Critical sections in a typical single-cell box segmentare, Figure 11.60:


IFIGURE 11.60. Critical sections in a typical segment at time of formwork stripping.

Section A where the side cantilevers are attached tothe webs

Sections B and C at midspan of the top and bottomslab

Section A is almost always the most critical. SectionB is usually subjected to moderate tensile stress be-cause the top slab is built-in on the web when theinner formwork is stripped. Section C is criticalonly on long-line casting when the casting bed doesnot have a continuous soffit and when the span ofthe bottom slab is larger than 16 to 20 ft (5 to 6 m).

Experience has shown that at the time of formstripping and before any handling of the segmentis allowed, the tensile cracking strength of the con-crete should be at least equal to the bending stressdue to the segment weight in the most critical sec-tions (A, B, and C). Practically, the correspondingcompressive strength is:

f:i = 3000 to 4000 psi (21 to 28 MPa)

In the casting yard, segments are usually handledby a portal crane traveling on rails or on steeringwheels for added mobility. A typical portal crane inthe Oleron Viaduct precasting yard is shown inFigure 11.61.

Proper handling of the segment requires properpick-up points to keep the stresses in the sectionwithin the allowable limits. A typical example ofhandling three different shapes of box girders isshown in Figure 11.62.

For the conventional single box, inserts or throughholes are provided near the web in the roadwayslab, allowing lifting to be accomplished by a simplespreader beam.

FIGURE 11.61. Oleron Viaduct, portal crane in pre-casting yard.

For the twin-box, three-web section, a four-pointpick-up is usually necessary to eliminate excessivetransverse bending of the top and bottom slab. Atriple spreader-beam arrangement allows the loadtransfer from the four pick-up points to the singlelifting hook.

For a triple-box, four-web section (such as used inthe Saint Cloud Bridge), temporary ties are pro-vided in the outer cells to transfer the reaction ofthe outside webs to the center webs. A simplespreader beam is then sufficient to lift the segment.

Segments must be stored in a manner designedto eliminate warping or secondary stresses. Con-crete beams installed at ground level provide agood bearing for the segments, which must besupported under the web or very close thereto. Ifstacking is required to save storage space, precau-tions must be taken to transfer weight from the

Placing Precast Segments 509

Slmnle spreader beam

FIGURE 11.62. Handling precast segments. (a) Two-web segment. (6) Three-web seg-ment. (c) Four-web segment.

upper to the lower layers of segments without ex-cessive bending of the slab.

11.8 Placing Precast Segments

Transportation and placement of segments may beperformed by one of several methods, dependingon the site location and the general characteristicsof the structure. These methods can be dividedinto three main categories:

1. Transportation by land or water and place-tnent by an independent lifting apparatus.

2. Transportation by land or water and place-ment with the help of a beam and winch carriedby the bridge deck itself.

3. Transportation by land, water, or along thebridge deck already constructed and place-ment with the help of a launching girder.

There are tnethods that fall into none of these cat-egories, such as the use of a cableway, but their useis limited.

11.8.1 INDEPENDENT LIFTING EQUIPMENT

This method, where feasible, is the simplest andleast expensive. It was used for the Choisy-le-Roi,Courbevoie, Juvisy, and Conflans bridges, wherethe navigable stretch of water lent itself to the use

of a barge-mounted crane, ensuring the collectionof segments from the precasting site and their po-sitioning in the final structure. A terrestrial cranewas employed for the Gardon, Bourg-Saint An-deal, and Bonpas Bridges. The same crane, ma-neuvering either on land or over water (on abarge), assured the positioning of all the segmentsused to construct the upstream and downstreambridges of the Paris Ring Road.

When site conditions are suitable, the same lift-ing crane may be used both to serve the precastingyard and to transport the segments to their finalposition in the structure (Hartel Bridge, Holland).This principle was enlarged successfully during theconstruction of the bridges over the Loire River atTours (Motorway Bridge and Mirabeau Bridge),where the segments were placed with the aid of amobile portal frame. The portal frame is placedastride the bridge deck and moves along a tracksupported by two bailey bridges, one either side ofthe structure. The track length is approximatelytwice that of the typical span, and the track itself ismoved forward progressively as construction pro-ceeds. The bailey bridges are supported on tempo-rary piers driven into the river bed. The segmentsare first brought to the bridge deck and then takenby the mobile portal frame, which transports themto their final position in the finished structure, Fig-ure 1.47.

Where a mobile truck or crawler crane is usedfor placement, there are often difficulties in the


positioning of the key segments at midspan, be-cause the finished structure on either side of thekey segment prevents the crane from maneuveringproperly and hinders the positioning of the seg-ment, which may be carried out only from the sideof the structure. For the B-3 Motorway Bridges aspecial apparatus was designed to place those seg-ments in the cantilever arm to be constructed in thedirection of the completed structure, Figure 3.95.Two longitudinal girders are braced together andrested on the pier head of the cantilever to be con-structed at the front, and on the existing structureat the rear. The apparatus consists of a mobilewinch-trolley, ensuring the hoisting and position-ing of the segments, and an advancing trolleysituated at the rear and equipped with a translationmotor. The front and rear supports are conceivedin such a manner as to transmit the vertical loadsthrough the segment webs.

The segments on the other side of the cantileverare easily placed by the mobile crane. This beammay easily be used to ensure cantilever stabilityduring construction when the piers are notsufficiently rigid to support unsymmetrical load-ing. The cantilever is rigidly fixed to the girders byclamping bars capable of resisting both tension andcompression. The crane and the girders, used to-gether, will allow a 130 ft (40 m) span to be erectedin four working days.

Placement of segments with a mobile crane hasfound another application in the construction ofsmall-span structures such as three-span motorwayoverpasses (see the discussion of the AlpineMotorway, Section 3.15, and Figure 3.103). Thesegments are precast in a central factory, trans-ported to the various sites by road and positionedby a mobile crane according to the erectionscheme, which consists essentially of the following:

Two temporary adjustable props, easily dismount-able, placed at the one-fourth and three-fourthspoints of the central span.

Temporary supports with jacks allowing cantileverconstruction

Temporary prestress to tie the segments togetherbefore stressing the final prestress

Elimination of the classic cast-in-place closure jointby direct junction of the two cantilever arms face toface.

Final prestress by continuous tendons instead ofcantilever-type layout.

The total construction time for such an overpass,including the piers, usually does not exceed twoweeks, of which less than one week is spent on thebridge superstructure itself. This method has beenused with great success for the Rhone-Alps motor-way overpasses, with spans varying between 60 ft(18 m) and 100 ft (30 m).

11.8.2 THE BEL4iM-ASD- WI,VCH .klETHOD

The beam-and-winch method of placing precastsegments was conceived for the construction of thePierre-Benite Bridges over the Rhone River. Thisconstruction method requires a fairly simple ap-paratus rolling along the already constructed partof the cantilever and ensuring the lifting, transla-tion, and positioning of all the segments. The ap-paratus is shown diagrammatically in Figure 11.63.It consists of the lifting gear B carried by the trolle)C rolling along the bridge deck on tracks D. Thesegment A is brought, bv land or water, beneaththe pier in question, where it is lifted bv theequipment. It is then transported to two launchingbeams E that cantilever out from the bridge deck,upon which it continues to advance until reachingits final position, whereupon it is lifted to its finallevel next to the previous segment, Figure 11.64.This system can, of course, be simplified if thesegment can be brought by some independentmeans to a location vertically below its final posi-tion in the structure.

As originally conceived, this system was notcompletely independent: another constructionprocedure was required to erect the pier segment.The pier segment was cast in place in the Pierre-Benite Bridges. It was precast and placed by acrane for the Ampel Bridge in Holland and by afloating barge crane for the Bayonne Bridge overthe river Adour. This weakness was eliminated inthe construction of the Saint-Andre-de-CubzacBridge. For this structure, the pier segments,which form the starting point for each cantilever,were placed by the same equipment that placed thetypical span segments, Figure 3.72. The equipmentwas hung, with the help of cables, to an auxiliarymast fixed to a lateral pier face. The pier segmentwas brought in from the opposite side, lifted andplaced by the mobile equipment’s winches. In thesame position the following segment was locatedand the auxiliary mast removed, Figure 3.73. Atthis point it was a simple matter to reposition themobile lifting equipment in order to place the typi-cal span segments, Figure 3.70.

recast Segments 511

GMFNTS NFAR RIGHT RANK

PPARATUS T R A N S F E R T R O L L E Y

P I E R B L O C K

4ENT P O N T O O N

,tream Bridge, placing apparatus.

evolved and how the original concept has beenmodified.

Launching Girders Slightly Longer Thanthe Span Length

We first consider the construction method of theOleron Viaduct Bridge superstructure, Figure3.32. The segments were brought along the topslab until they reached the launching girder, thenlifted by the latter, transported to their final posi-tion, lowered so as to come into contact with theprevious segment erected, and prestressed to thecantilever. The launching girder itself, slightlylonger than the span length, was made up of a steeltrellis beam with an entirely welded rectangularsection weighing 124 tons (113 mt) and measuring312 ft (95 m). The maximum span length of thebridge was 260 ft (79 m).

The launching-girder system consists of twofixed supports, called tunnel legs, allowing thesegments to pass between them, one at the rear ofthe girder and the other at the center. At the frontend is a mobile prop enabling the girder to findsupport on the next pier. The bottom chords of thegirder are used for the rolling track that supportsthe segment trolley, which can move the segmenthorizontally and vertically and rotate it a quar-


~23~~118’~141’--ll6’-7”4

Placlng center segment

118’i141”259’A

Movmg gantry to next pier

Placing segments in doudle cantilever

FIGURE 11.65. Oleron Viaduct, launching-girderoperations. (A) Rear support, (B) center support, (C)temporary front prop, (D) prop support, (E) pier seg-ment, (F) temporary support.

ter-turn. Three phases are clearly distinguishablein the construction of a cantilever, Figure 11.65:

Phase 1: Placing the pier segmentThe launching girder rests on three supports-therear support, the center support near the end ofthe newly constructed cantilever, and the frontprop, which is attached to the front of the next pierwith the help of a temporary prop support.

Phase 2: Moving the launching girder forwardThe girder rolls along on the rear support and thesegment trolley, which is rigidly attached to a metalframework known as the temporary translationsupport, which is fixed to the pier segment. Therear and central supports are equipped with bogiesand roll along a track fixed to the bridge deck whilethe girder is being moved forward.

Phase 3: Placing typical segmentsThe launching girder rests on two supports, thecentral support anchored to the pier segment andthe rear support tied with prestressing bars to theend of the previously constructed cantilever.

A support adjustment was carried out with thehelp of hydraulic jacks when the girder was restingon the rear and central supports and the tempo-rary front prop, before installing the pier segment.The purpose of this adjustment was to obtain theoptimal distribution of the launching girder self-weight among the three supports. While the fi-ontprop is being installed, the central support rests onthe end of the previous cantilever in the same po-sition in which the rear support will be during theerection of the typical segments. In this phase thelaunching girder rests on two supports and istherefore statically determinate; nothing can bedone to change the rear-support reaction. Whilethe pier segment is being placed, however, thegirder is resting on three supports and is staticallyindeterminate. It is therefore necessary to ensurethat the reaction at the central support is less thanor equal to that which will be produced by the rearsupport during the next construction stage, in-cluding the weight of the trolley and the tractorplaced in the near vicinity. Several other structureshave been built with launching girders of the samegeneration as the one used for the Oleron Viaduct.

The Chillon Viaduct, Figures 3.43, 11.66, and11.67, along the bank of Lake Leman used a 400 ft(122 m) launching girder weighing 253 tons (230mt). The maximum span length was 34 1 ft ( 104 m).The launching girder, of constant rectangular sec-tion, was of the suspension type, being suspendedat the one-quarter points by cable stays anchored atthe central mast, which extended above the level ofthe launching girder. The supports were hy-draulically adjustable, allowing the girder to copewith different angles of superelevation, Figure

FIGURE 11.66. Chillon Viaduct, launching-girder inoperation.

D3


4th &ageGirder lauchmg

FIGURE 11.67. (:hillon Viaduct, launching-girder movements.

FIGURE 11.68. Chillon Viaduct, launching-girderadjustments.

11.68. The launching girder included three meansof adjustment:

Adjustment Dl: Lateral movement of the trolley inorder to place eccentric segments

Adjustment 02: Lateral translation of the centralsupport in order to cope withhorizontal curvature of thestructure

[email protected] 03: Vertical adjustment of bogies totake up the superelevation and sokeep the central support vertical.

In order to follow the horizontal curves thelaunching girder rotated about the rear supportwhile moving sideways across the central support,Figure 11.69. The mobile temporary front propwas conceived in the same way as the other sup-ports so as to allow the passage of the first segmentsto either side of the pier segment.

The Blois Bridge on the Loire River in Francehad a 367 ft (112 m) long launching girder weigh-ing 135 tons (123 mt), Figure 11.70. Themaximum span length was 300 ft (91 m). Thelaunching girder, of constant triangular section,could be dismantled and transported by road. Allof the girder components were assembled withhigh-strength bolts, ensuring the transmission of


C O N S T R U C T I O N O F HOlzIZ0rifA~ CURVC ( STAGE 1. )

C O N S T R U C T I O N O F UORIZONTAL C U R V E ( STAGE 2 )

FIGURE 11.69. Chillon Viaduct, curved span con-struction.

FIGURE 11.70. Blois Bridge, launching girder.

forces by friction between adjoining plates, Figure FIGURE 11.71. Blois Bridge, launching-girder as-11.71. sembly detail.

The use of a very light structural steelframework carried with it the risk of large deflec-tions. These were reduced and controlled by twosets of cable stays, passive and prestressed, whichcame successively into play during maneuvering ofa segment (upper passive stays) and during thelaunching-girder advancement (lower prestressedstays). This launching girder was later used for theerection of two other structures: the AramonBridge on the Rhone River, Figure 11.72, and the2950 ft (900 m) long Seudre Viaduct.

The Saint Cloud Bridge on the Seine, Figure3.78, is a recent example of the use of a largelaunching girder. The girder could place segmentsweighing up to 143 tons (130 mt) in spans of up to335 ft (102 m) with a minimal radius of curvaturein plan of 1080 ft (330 m), Figure 3.79. The weightof the launching girder was 260 tons (235 mt) andits total length was equal to 400 ft (122 m).

FIGURE 11.72. Aramon Bridge over the RhoneRiver.

The adjustments adopted were similar to thoseused for the Oleron, Blois, and Chillon bridges.The launching girder, which used upper passivestays and lower prestressed stays, was constructed

with a constant triangular section made up of indi-vidual elements assembled by prestressing. Thislaunching girder is notable, apart from its assemblyby prestress, for its ability to follow extremely tightcurves. The movements used for the Chillon Via-

ELEVATION

SFCTION A


duct were, of course, used for this purpose. How-ever, in the Saint Cloud Bridge it was necessaryalso for the launching girder to take up several in-termediate positions during the erection of a givencantilever so as to bring each segment to its finalposition in the structure. The total lateral transla-tion reached 19.7 ft (6 m) at its maximum. Con-struction speed of the bridge deck was 130 ft (40m) per week, including all launching-girder ma-neuvers. Two other structures erected with thehelp of the Saint Cloud launching girder were theAngers Bridge and the Sallingsund Viaduct.

The launching girder used for the AlpineMotorway network was conceived for spans andsegment weights of more modest dimensions; it istypical of lightweight universal equipment that canbe easily dismantled for reuse in another structure,Figure 11.73. This girder allowed the handling ofsegments weighing up to 55 tons (50 mt) overspans up to 200 ft (60 m).

Reflecting on the launching girders mentionedabove, we note that their evolution centers on twomajor characteristics: the structural conception ofthe girder and the assembly method (connectiontypes, number of elements, and so on).

Launching girders tend more and more to be ofthe lightweight type, relying on exterior forces tocope with different loadings. These exterior forcesare provided by the external active cable stays,which allow the structure to be placed in a condi-tion ensuring a favorable behavior under a givenloading. This approach to launching-girder designprovides more optimal use of materials than didthe first-generation girders of variable cross sec-tion.

Another advantage of a constant cross section isthat it facilitates the construction of standard sec-

tions that can be interchanged and assembled onsite. In this way the girder length can be varied ac-cording to the span length and the weight of thesegments. Connections are made with tensionedbolts, Figure 11.74, which reduce considerably thenumber required and consequently the t imeneeded to assemble or dismantle the structure.These connections have recently replaced thosemade with high-strength bolts and fishplates, nota-ble on such structures as the Deventer Bridge andthe B-3 Viaducts.

Means of erection adjustments also have im-proved, tending to reduce the forces applied to thedeck itself by ensuring that the girder supports arelocated over the piers or at least in the very nearvicinity.

This natural evolution leads us toward a newtype of launching girder, one whose total length isslightly greater than twice the typical span length,allowing the simultaneous placing of the typicalsegments of cantilever N and the pier segment ofcantilever N + 1.

Launching Girders Slightly Longer Than Twice theTypical Span

The first launching girders of this type were usedon the following bridges: Rio Niteroi in Brazil; De-venter in Holland, Figure 3.50; and B-3 SouthViaducts in the eastern suburbs of Paris, Figure3.93.

The Rio Niteroi Bridge (Section 3.8), linking thecity of Rio de Janeiro with Niteroi, consists of 10miles (16 km) of bridge deck constructed by fouridentical launching girders, Figures 3.55 and 3.56.Each 545 ft (166 m) long girder could be com-pletely dismantled. The constant triangular sec-

FIGURE 11.73. Alpine Motorway launching girder. FIGURE 11.74. Prestressed connections.


tion, weighing 440 tons (400 mt), could cope withspans of up to 260 ft (80 m). The connections wereidentical in principle to those used for the Bloisgirder. Each installation was equipped with threesupports of nontunnel type, one fixed and theother two retractable.

The erection sequence was as follows, Figure1.51:

Phase 1: Segment placingThe girder rests on three supports, each one over apier. Two segments are erected simultaneously,one on either side of the double cantilever underconstruction. The pier segment of the next can-tilever is also placed with the launching girder inthis position.

Phase 2: Moving the launching gder forwardThe girder rolls on two temporary translation sup-ports, one placed above the pier of the finishedcantilever and the other above the pier of the can-tilever to be constructed. These temporary sup-ports are attached to the trolleys; the launchinggirder is lifted, thus freeing the permanent sup-ports; and the trolleys are engaged, enabling thetranslation of the launching girder to a position toerect the next cantilever. The temporary transla-tion supports are equipped with a mechanism al-lowing transverse movements, as the structure in-cludes a certain amount of horizontal curvature.

The Rio Niteroi girder was equipped with threesets of active stays: lateral stays, central stavs, andlaunching stays. The lateral stays, positioned onthe underside of the two spans and constantlyunder tension, ensure the resistance of the girderwhile the load (segment) passes near midspan. Thecentral stays strengthen the girder in the vicinity ofthe central support. The launching stays, undertension while maneuvering the girder, transfer thefront and rear reactions to the central support.

Owing to the length of the bridge and the pres-ence of a large stretch of water beneath the struc-ture, the segments were brought to the launchinggirder on barges. The cantilever stability of thebridge was assured by the launching girder itself,and ties and props were positioned as constructionproceeded.

The launching girder used for the DeventerBridge in Holland, Figures 3.49 and 3.50, werealso capable of being entirelv dismantled and oftriangular section. Its total length was 5 12 ft (156m) f o r a w e i g h t o f 1 9 8 t o n s ( 1 8 0 m t ) . T h emaximum span length was 243 ft (74 m).

Assembly of the launching-girder elements wasconsummated by prestress bars normal to thejoints. It was supported by the fixed supports, of.which the rear and the central allowed the passageof a segment, and two sets of cable stavs: centralstays and launching stays. The translation opera-tions were identical to those of the Rio NiteroiBridge, even though only one segment could belowered into place at a time.

What was peculiar about this launching girderwas its abilitv to raise itself to its working level bv itsown means, and this from the ground level whereit was assembled. This was made possible bv thecentral suspension mast, which acted as a liftingjack.

In the case of the B-3 South Viaducts, Figure3.92, the constantly varying structure supported b\200 piers, crossing five railway tracks, the OurcqCanal, and several urban roadwavs, was masteredby a highly mechanized launching girder. Thesimultaneous placing of two segments of the samecantilever, each weighing between 33 and 55 tons(30 and 50 mt) either side of the pier, is controlledby a radio-controlled servo mechanism that syn-chronizes the loading at each end of the girder.Again the length of the launching girder wasslightly greater than twice the typical span length,

FIGURE 11.75. B-3 South Viaduct launching girder. general la\o11t.

T Y P I C A L

CROSSw8ECTION

References 517

FIGURE 11.76. B-3 Sourh Viaduct, segment trans-port tractor.

which varied between 100 and 164 ft (30 and 50m), Figure 11.75. The girder support reactionswere thus applied in the region of the piers, andthe cantilever stability was ensured by the launch-ing girder itself. This stabilizing device can be seento the left of the central support in Figure 11.75.

The segments were supplied by a special eight-wheeled tractor moving along the top slab, Figure11.76. A special device used to unload and storethe segments brought by the tractor freed the lat-ter and removed the supply of segments from theerection critical path. The cycle of segment place-ment and girder advancement is represented inFigure 3.93. The next pier segment was placedduring the same phase as the typical segments.About two spans were constructed each week-

that is, between four and six segments per day.The average construct ion speed, includinglaunching-girder maneuvers, was therefore 200 ft(60 m) per week.

The B-3 launching girder was recently reusedfor the Marne-la-Vallee Viaduct, which carrieshigh-speed suburban rail for the Paris transportauthority.

References

1. Anon. , Manual for Quality Control for Plants and Pro-duction of Precast Prestressed Concrete Products, MNL-116-70, Prestressed Concrete Institute, Chicago,1970.

2 . Anon. , ACI Manual of Concrete Practice, Part I, Ameri-can Concrete Institute, Detroit, 1973.

3. “Proposed Recommendations for Segmental Con-struction in Prestressed Concrete,” FIP Commis-sion-prefabrication, 3d Draft, September 1977.

4. “Recommended Practice for Segmental Constructionin Prestressed Concrete,” Report by Committee onSegmental Construction, Journal of the PrestressedConcrete Institute, Vol. 20, No. 2, March-April 1975.

5. Anon. , PCI Post-Tensioning Manual, Pres t ressed Con-crete Institute, Chicago, 1972.

6. Anon. , PTI Post-Tensioning Manual, Pos t -Tens ion ingInstitute, Phoenix, Arizona, 1976.

7. T. J. Bezouska, Field Inspection of Grouted Post-Tensioning Tendow, Post-Tensioning Institute,Phoenix, Arizona, March 1977.

12Economics and Contractual Aspects

Of Segmental Construction

12.1 BIDDING PROCEDURES 12.2.5 Zilwaukee Bridge, Michigan

12.1.1 Single Design 12.2.6 Cline Avenue Bridge, Indiana

12.1.2 Design and Build 12.2.7 Napa River Bridge, California

12.1.3 Value Engineering 12.2 .8 Red River Bridge, Arkansirs

12.1.4 Alternate Designs 12.2.9 North Main Street Viaduct, Ohio

12.1.5 Summary Remarks on Bidding Procedures 12.2.10 Summary of California’s Experience

12 .2 EXAMPLES OF SOME INTERESTINti BIDDINGS AND 12.3 INCREASE IN EFFICIENCY IN CONCRETX BRIDGEScDsrs

12.2 .1 Pine Valley Creek Bridge, California12.2.2 Vail Pass Bridges, Colorado12.2.3 Long Key Bridge, Florida12.2.4 Seven Mile Bridge, Florida

12 .3 .1 Redesign of Chacas Viaducts, Venezuela12 .3 .2 Comparison between Tancarville and Brotonne Bridges,

France

REFERENCES

12.1 Bidding Procedures

A bridge design should on principle be economicaland as a practical matter must fall within budgetaryrestrictions of a particular project. The economic“moment of truth” for a given bridge design occurswhen bids are received and evaluated.

In a basically stable economy where material andlabor costs are predictable within relatively smallfluctuations, the selection of structure type andmaterials is relatively straightforward. This situa-tion prevails when the time required for the designis relatively short and thus is not affected by eco-nomic cycles, or, if the design time is relativelylong, the economic cycles are mild. In an inflation-ary economy there is no economic stability, and de-signers are hard put to make rational choices, asthey have no control over economic parametersthat can influence their design decisions. In short,the problem is whether economic assumptionsmade during the course of design are valid at thetime of bidding.

Obviously, the design and the bidding (tender-ing) of a project are closely related. Contractualbidding procedures vary from country to country,and current economic pressures are leading tochanges in these procedures. The various biddingmethods used in various countries can be broadlycategorized (with some possible variations) as fol-lows: (1) single design, (2) design and build, (3)value engineering, and (4) alternate designs.

12.1.1 SISGLE DESIGl\

Heretofore, single design was the major methodused in North America and Great Britain. In thismethod, in general, design drawings prepared forbid are very detailed, to the extent that even thelength and other dimensions of every reinforcingbar may be given. The bidding period is followedby a tight construction schedule. The contractorbids and executes the project in strict accordancewith the bidding documents. No variation from thedocuments is allowed unless an error in design is

518

Bidding Procedures 5 1 9

discovered, or a specific detail proves impractical toconsummate, or geological perturbations are dis-covered that differ from what was assumed in de-sign and delineated in the contract documents.These changes are authorized by a change order,and if there is an increase in cost the contractor ispaid an “extra.”

This system worked well for many vears whenthe economy was fairly stable and predictable andwhen economic changes were gradual over an ex-tended period. Its disadvantage is its lack of flexi-bility to accommodate an inflationary economy,sudden price changes in materials, a rapidly ad-vancing technology, and the current emergence ofspecialtv contractors with unique equipment orskills, proprietarv designs, and patented construc-tion methods. Its biggest advantages are ease inadministering the contract and absolute controlover the final design.

In some European countries, by contrast, biddocuments are prepared with the intention thatthe contractor will prepare and submit his owndetailed design for the prqject. Thus, bid plans willbe more general and, for a bridge, may show onlyspan lengths, profile, and typical sections. Thecontractor may then refine the original design orsubmit an alternate design of his own choice, theresponsibilitv for producing the final design anddetails being his rather than the engineer’s, Thisprocedure allows the contractor to use any specialequipment or technique he may have at his dis-posal. For example, a cast-in-place concrete boxmav be substituted for a steel superstructure wherethe contractor has special know-how in concreteconstruction, or the change may be less drastic andinvolve only a reduction in the number of webs in abox girder.

Verification of the adequacy of the contractor’sfinal design is generally carried out by a “proof en-gineer” who is retained by the owner or is on theowner’s engineering staff. In order to minimizedisagreements between the contractor and theproof engineer, European codes have been madevery specific. As a result, European contractorsusually maintain large in-house engineering staffs,although they may also use outside consultants.The outcome apparently is a savings in construc-tion cost, achieved by the investment of more de-sign time and effort than in the single-designmethod.

The advantage of the design-and-build methodis that in an atmosphere of engineering competi-tion, innovative designs and construction practicesadvance very rapidly. The state of the art of de-signing and constructing bridges advances in re-sponse to the need for greater productivity. Thedisadvantage is the lack of control over the selec-tion of the type of structure and its design. There issome concern, too, that quality of construction maysuffer as a consequence of overemphasis on pro-ductivity and initial cost. However, the contractoris usually required to produce a bond and guaran-tee his work over some period of time, and any de-fects that surface during this period have to be re-paired at his expense. Whether such a system couldbe adopted in the United States is debatable.

1 2 . 1 3 VALUE E.\‘GI.~EERI,~G

Value engineering is defined by the Society ofAmerican Value Engineering as “the systematicapplication of recognized techniques which iden-tify the function of a product or service, establish avalue for that function, and provide the necessaryfunction reliability at the lowest overall cost. In allinstances the required function should be achievedat the lowest possible life-cycle cost consistent withrequirements for performance, maintainability,safety, and esthetics.“’

In 1962 the concept of value engineering be-came mandatory in all U.S. Department of Defensearmed services procurement regulations (ASPR).Before this time value engineering had beenapplied to materials, equipment, and systems. Theadvent of ASPR provisions introduced value en-gineering concepts to two of the largest construc-tion agencies in the United States-the U.S. ArmyCorps of Engineers and the U.S. Navy Bureau ofYards and Docks. Soon thereafter the U.S. Bureauof Reclamation and the General Services Adminis-tration (GSA) adopted and inserted value en-gineering clauses in their construction contracts,and the U.S. Department of Transportation estab-lished a value engineering incentive clause to beused by its agencies.

Several value engineering clauses (or’ incentiveclauses) are in use today by many agencies. In gen-eral, they all have the following features’:

1 . A paragraph that defines the requirements ofa proposal: (a) it must require a change to thecontract and (b) it must reduce the cost of thecontract without impairing essential functions.

520 Economics and Contractual Aspects of Segmental Construction

2. A “documentation” paragraph that itemizesthe information the contractor should furnishwith each proposal. It should be comprehen-sive enough to ensure quick and accurateevaluations, detailed enough to reflect thecontractor’s confidence in its practicability, andrefined to the point where implementation willnot cause undue delay in construction opera-tions. Careful development of this paragraphand meticulous adherence to its requirementswill preclude scatter-shot proposals by thecontractor and burdensome review by theagency.

3 . A paragraph on “submission.” This paragraphdetails the procedure for submittal.

4. A paragraph on “acceptance,” which outlinesthe right of the agency to accept or reject allproposals, the notification a contractor mayexpect to receive, and appropriate reference toproprietary rights of accepted proposals.

5 . A paragraph on “sharing,” which contains theformula for determining the contract priceadjustment if the proposal is accepted and setsforth the percentage of savings a contractormay expect to receive.

As generally practiced by highway agencies inthe United States, a value engineering proposalmust indicate a “substantial” cost savings. This is topreclude minor changes such that the cost of pro-cessing offsets the savings to be gained. Some otherreasons for which a value engineering proposalmay be denied are as follows:

Technical noncompliance.

Delay in construction such that the cost savingswould be substantially nullified.

Proposed change would require resubmission ofthe project for any number of various permits,such as environmental impact statement, wetlandspermit, and navigation requirements. Resubmis-sion would in all probability delay construction andnullify any cost savings.

Savings resulting from a value engineering pro-posal are generally shared equally by the agencyand the contractor, after an allowance for the con-tractor’s development cost, the agency’s cost inprocessing the proposal, or both. As practiced inthe United States, all contractors must bid on thedesign contained in the bid documents, and onlythe low bidder on the base bid is allowed to submit

a value engineering proposal. This is, of course,value engineering’s biggest disadvantage. An)number of contractors may have more cost-effective proposals that they are not allowed tosubmit because they were not low bidder on thebase bid. Its advantage is that to some degree it al-lows contractor innovation to be introduced.

Alternate designs, as it is developing in the UnitedStates, basicallv is an attempt to produce a hvbridsystem consisiing of the best elements oi thesingle-design and the design-and-build methods. Itattempts to accomplish the following:

Retain for the authorizing agency control over the“type selection” of the structure and its design

Provide increased competition between materials(structural steel versus concrete or prestressingstrand versus bars) or construction procedures(cast-in-place versus precast segmental or balancedcantilever versus incremental launching, and so04Provide contractor flexibility (construction proce-dures, methods, and/or expertise)

This method has developed, with encouragementfrom the Federal Highway t\dIninistratiorl, as an

anti-inflationary measure to combat dramatic in-creases in highway construction costs. A technicalAdvisory2 published by the Federal Highway Ad-ministration states:

Because qf.fluctuating economic conditions, it isfelt thaton multiple repetitive spans, long spans or major bridges,or where there is an extended period qf‘design from con-ception of the project to a release for bds, there can be noassurance of price stability fbr n particular material orconstruction methodoloCg. With alternate de.siLgns, nomatter how the economy changes, more designs are ctzlail-able at the time of biddt’ng that are likely to be suited to theprevailing economic conditions.

General recommendations regarding alternatedesigns from the same document’ are as follows:

1 . To receive the most economical constructionbetween basic structural materials, consistentwith geographic, environmental, ecologicalor other site restrictions, there should bemaximum opportunity for competition be-tween structural steel and concrete.

Bidding Procedures 521

2. Within environmental, aesthetic, site, andother constraints, the plans and bid docu-ments should show or otherwise indicate whatalternative types of structures will be allowedor considered. The contractor should be al-lowed the option to bid any designated alter-native design that is consistent with the con-tractor’s expertise, available equipment, andso on.

3 . Bid documents and the contract plans shouldclearly indicate the design criteria and whattvpe of alternative designs and/or contractoroptions will be acceptable. Determination ofpractical and economical alternatives and/orcontractor options should be developed in thepreliminary design.

4. Bid documents should be considered as“open” documents in regard to constructionmethod, erection systems, and prestressingsvstems.

5 . Consistent design criteria should be used foralternatives; for example, if load factor de-sign is used, it should be used for all alterna-tives.

6. Span lengths should be identified on thecontract plans. However, other than wherepier locations are constrained by physical andgeological conditions at the site, considerationshould be given to allowing a tolerance in pierlocation to avoid placing a particular alterna-tive at an economic disadvantage. For exam-ple, in a typical three-span structure, the sidespan should be approximately 80 percent ofthe center span for structural steel, 70 per-cent for conventional cast-in-place concreteon falsework, and 65 to 70 percent in seg-mental balanced cantilever construction.

7 . To avoid an economic disadvantage to a par-ticular superstructure alternative, alternativesubstructure designs may be required. Limi-tations on the substructure, such as allowableaxial load and moment, should be clearlyidentified on the contract plans.

8. Where specific design requirements are notcovered by the American Association of StateHighway and Transportation Officials(AASHTO) Bridge Specifications, the con-tractor should be allowed to use other recog-nized codes and standards where applicable.However, the alternative design shoulddocument where these provisions are to beused, why the AASHTO requirements do not

9.

10.

1 1 .

apply, and which articles of the substitutedcode or standard are to be used. Such provi-sions should be subject to approval by the en-gineer and appropriate agencies.Prebid conferences are to be encouraged as ameans of communication between the en-gineer, highway agencies, and contractors.

In order to allow a contractor adequate timeto investigate the various alternatives andprepare plans, it is recommended that theadvertising time be commensurate with thesize and complexity of the project with aminimum of 60 days.

In order to allow adequate review andchecking of the low bidder’s proposal, awardof contract should be extended commensu-rate with the size of project.

Specific recommendations* regarding prestressedconcrete alternates are as follows:

1 . To increase the competition in post-tensionedconcrete construction, it is recommended thatplans and other bid documents allow conven-tional cast-in-place on falsework, precast pre-stressed span units, and segmental construc-tion or combinations thereof.

2. Segmental construction should allow the fol-lowing at the contractor’s option:a. Precast or cast-in-place segmental con-

struction.b. Any of the post-tensioning systems-that

is, strand, wire, or bars or combinationsthereof.

c. Any of the following constructionmethods: balanced cantilever, span-by-span, progressive placing, incrementallaunching, or combinations thereof.

d. Exterior dimensions of the cross sectionshould be fixed. At the contractor’s option,the thickness of webs and flanges may bevaried to accommodate proposed con-struction and erection methods andpost-tensioning systems, providing thatany changes in the dead weight, shear, andso on are accommodated in the design.

3 . T h e c o n t r a c t plans should indicate themaximum and minimun final prestressing force(P,) and moment (Pr x e) required, after alllosses, for the final condition of the structure-that is, dead, live, impact, and all superim-posed loads. Any increase in prestressing force


requirements as a result of the method of con-struction, erection, or type of tendon systemshould be evaluated at the shop drawing stage.

4. Changes in eccentricity of prestress should beaccompanied with appropriate changes in pre-stress force to produce the same minimumcompressive stress due to prestress.

5 . The minimum prestress force should be suchthat under any loading condition, both duringand after construction, stresses will be withinallowable limits. Consideration should be givento secondary moments due to prestress, redis-tributed moments due to creep, and stressesresulting from thermal gradient (between thetop and bottom of the girder and between theinside and outside of webs).

6. Contractor revisions to contract plans, withsupporting calculations, should be submittedto the engineer for approval.

12.1.5 SU,MMARY REtMARKS OlV BIDDIiVGP R O C E D U R E S

All of the bidding procedures described abovehave one thing in common: they all attempt toproduce the lowest initial cost by competition inconstruction and/or design. All of the last threeapproaches (design-and-build, value engineering,and alternate designs) require decisions based oncomparisons of basic structural materials, structuretypes, construction methods, and so on. This im-plies that the basic premise in the selection processis equivalency-comparable service, performance,and life-cycle cost of the facility.

Life-cycle costs refer not only to initial cost, butalso to maintenance and any rehabilitation costsduring the life of the structure. True cost of theproject must be considered. What may be initiallyleast expensive may in the long run, when futurecosts are accounted for, be actually most expensive.Some newer structure types and designs are at thefringe of the state of the art and have only beenused in the United States within the last decade orless. Thus, an adequate background of experienceis unavailable to evaluate life-cycle costs. The esti-mation of life-cycle costs may be difficult in manycases, such as for new and progressive bridge de-signs. Functionally, alternative structures are de-signed to the same criteria. Only years of opera-tional experience can provide the data base forreasonably estimating life-cycle costs and therebytrue equivalency in design insofar as cost is in-

volved. However, the problem of adequacy of datadoes not diminish the importance of the questionand the need to attempt to answer it.

Another anti-inflationary measure used in recentyears is that of stage construction. This conceptmay take one of two forms. Major structures, be-cause of their size, lend themselves to stageconstruction-that is, separate substructure andsuperstructure contracts. Usually several years willelapse between bidding and awarding of the sub-structure contract and the superstructure contract.The economic superstructure span range for dif-ferent alternative types and materials is a variable.In this form of stage construction the substructureis let first; thus the spans for the superstructure de-sign become fixed. This may or may not impose aneconomic disadvantage to specific superstructurealternates. The substructure must be designed forthe largest self-weight superstructure alternative,which may or may not be the successful super-structure alternative. It appears that this formof stage construction may be to some extent self-canceling or counterproductive to cost savings.With a total alternative design package, the sub-structure (foundation, piers, span arrangement)can also have alternatives commensurate with thesuperstructure alternatives.

The other form of stage construction concerns alarge project, containing many bridges, that is sub-divided for bidding purposes into a number ofsmaller projects. Its primary purpose is to encour-age small contractors bv providing prqjects ofmanageable size, thus Increasing competition.However, certain construction techniques, by vir-tue of the investment in sophisticated casting orerection equipment, require a certain volume ofwork to amortize the equipment and be competi-tive. Depending upon the size of the subdividedcontract, this form of stage construction in someinstances may also become counterproductive.

The value engineering concept can be dividedinto two major areas of application: during designand during construction. Value engineering pro-cedures in the design stage may result in veryspecific recommendations based on a certain set ofassumptions at a particular point in time for thedesign. If conditions change during the intervalbetween the design decision and the actual con-struction, which can be several years, conditions onwhich the assumptions were based may havechanged. Such changes could make the originalvalue engineering decision incorrect. The alterna-tive design concept, on the other hand, does notmake all such specific design decisions at an early

stage but retains some options in order to allow alater response to changed conditions. Therefore,there is an apparent incompatibility between theapplication of value engineering principles in thedesign stage and the concept of alternative designsfor bidding purposes. However, the concept ofvalue engineering is a powerful tool and can bemade compatible with the concept of alternativedesigns if its principles are used to determinewhether a given project should require alternativedesigns and, if so, what structure types should beconsidered as equivalent alternates.

Examples of Some Interesting Biddings and Costs 523

the contractor was faced with a difficult and costlyerection procedure. At least one cableway span-ning the entire valley would have been required totransport men and material to appropriate loca-tions during the construction procedure. Completesite installations on both sides of the valley wouldhave been required, which were accessible onlywith a great deal of difficulty.

12.2 Examples of Some InterestingBiddings and Costs

12.2.1 PI.L’E VALLEY CREEK BRIDGE, C‘4LIFORNlA

The superstructure design alternative submittedunder this proposal employed the Dywidag system,which included the following: (1) use of thethreaded-bar system especially suited to segmentalconstruction, (2) increased prestress-force eccen-tricities, since most longitudinal prestressing barscould be placed and anchored in the slab, (3)diagonal prestressing in the webs to cater to theshear stresses, and (4) a modification in construc-tion sequence so as to work from piers 5, 4, 3, and2, Figure 2.44.

The Pine Valley Creek Bridge (Section 2.7) was thefirst segmental bridge in the United States to in-corporate the concept of value engineering (cost-reduction incentive proposal) in the biddingdocuments. The original design assumed cast-in-place balanced cantilever construction with theprestressing force (P,) and moment (Pr x e) basedon strand capabilities.

Changes proposed under the value engineeringclause are summarizied in Table 12.1. Total sav-ings as a consequence amounted to $382,000.3

12.22 VAIL PASS BRIDGES, COLORADO

Project plans developed by CALTRANS re-quired construction of the cantilevered sections atpiers 3 and 4 before those at piers 2 and 5 (refer toFigure 2.40). Because of rigid specification re-quirements for the protection of the valley slopes,

The Vail Pass structures are part of Interstate I-70near Vail, Colorado, in an environmentally sensi-tive area. Environmental considerations played adominant role in the selection of the bridge typesand the design thereof. Another factor consideredwas the relatively short construction season at thehigh elevations of the sites.

TABLE 12.1. Pine Valley Creek Bridge, Value Engineering Proposal

SavingsOriginal CRIP estimated

Constructionsequence

Structuralsvstem

Concrete stresses:ConstructionTension

Concrete shear

Slab designs

H i n g e Two diaphragms

Long cantilevers beforeshort to minimizecreep AsCantilever for D.L.,continuous for L.L.+ added D.L.No Redistribution

AASHTO loads, methodand distribution reinf.

Reverse to facilitateconstr. from abutment

$ 88,000

Continuous forall loads

Full redistribution

0.55fi

3*Principal stressesdiagonal prestressAASHTO loads with“Homberg” graphs, nodistribution reinf.No diaphragms

$228,00022,000

22,000

22,000

$382,000


Of the 21 bridge structures in this project, 17were designed and bid on the basis of alternativedesigns. One alternative design consideredtrapezoidal steel box girders composite with a con-crete roadway flange. The other alternative designwas for precast concrete segmental box girder de-sign, with the Federal Highway Administration re-quiring that the contractor be given the option ofcast-in-place segmental construction.

At two locations, the site constraints were suchthat they were bid without alternatives as steel boxgirders. Two other locations required 80 ft (24 m)long simple-span underpass structures to providefor wildlife migration. These structures were builtof cast-in-place concrete box girder construction.The remaining 17 structures were completely de-signed and detailed for the two alternatives, one instructural steel and the other in precast concretesegmental (with a contractor option of providing acast-in-place segmental design). Spans varied innumber from two to five and in length from 30 to260 ft (9 to 79 m).

Table 12.2 tabulates the five contracts that in-volved the 17 bridges bid on the basis of alternativedesigns and lists them in the order in which theywere bid.4 Approximately a year elapsed betweenthe letting of the first and last contracts. Althoughconsiderable differences in bid prices are shown inindividual projects, for the total project there is lessthan $80,000 difference out of an approximatetotal cost of- $17 million, or less than 0.5% dif-

ference in bid prices for the alternatives. Precastsegmental was the low bid on project 1 and cast-in-place segmental was the low bid on project 4.Based upon length (width was constant), the seg-mental concept was successful in approximately60% of the total project.

The consultants, International EngineeringCompany, Inc., estimated that the additional costto produce alternative designs was about 2.5% ofconstruction cost. It is difficult to estimate whatsavings were achieved by bidding alternative de-signs rather than a single design; however, overallsavings of 7 to 10% of the construction costs arenot unreasonable.4

12.2.3 LO.VG KEY BRIDGE, FLORID.4

The Long Key Bridge in the Florida Keys was bidutilizing the concept of alternate designs. Fourcomplete sets of contract plans were prepared forthe alternative construction schemes indicated inTable 12.3. Plans for the AASHTO precast, pre-tensioned I girders were prepared by the FloridaDepartment of Transportation. Plans for the threebasic precast segmental schemes were prepared bythe state’s consultant, Figg and Muller Engineers,Inc.

In the preliminary design stage three methodsof segmental construction were considered forthis project: balanced cantile\.er, span-by-span,and 1,rogressk.e placing. ‘l‘he progressi\,e placing

TABLE 12.2. Results of Alternative Bids, Vail Pass Bridges

Proj.N o .

BridgeN o .

N o .Spans

Length(ft)

TotalLength

(ft)Low Steel

BidCost/F?.

SteelLOW Concrete

BidCostiFr’,Concrete

2

3

4

1 F-l l-AXF-l l-AWF-l 1-AVF-l l-AUF-12-AKF-12-AMF-12-ANF-12.A0F- 12-APF-l I-APF-l l-A0F-l l-ANF-l l-AMF-l l-ALF-l l-AK

5 F-12-ATF-12-AS

Totals

45443233332444344

727880690668 2965 $5,992,155 $48.12 f5,527,3 18 s44.39220240350368600 1778 $3,777.549 $50.59 $4,111,170 $55.05310222 532 $994,347 $44.50 $1,053,364 $47.14740744514450 2448 $4,257,77 1 $4 1.4 1 $4,108,057 $39.96726726 1452 $2,298,409 $37.69 $2.598.938 $42.62

9175 $17,320,23 1 $44.95 $17,398,847 545.15

Examples of Some Interesting Biddings and Costs

TABLE 12.3. Long Key Bridge, Alternatives

Substructure

525

Superstructure

Precast girders, AASHTO

Segmental:Span by span, V piers

Span by span, vertical piers

Cantilever, vertical piersFirst option, slab reinforcing

Second option, barrier curbs

Precast Piles Drilled Shafts

A B

C D

E F

G H

R/C epoxy coated

PretensioningCast-in-place conventional

Precast (never integral)

method was discarded because it was felt to be (atthe time) too new for acceptance in U.S. practice. Itwas later introduced on the Linn Cove Bridge inNorth Carolina. The basic difference in the twospan-by-span alternatives for the Long Key Bridgeis in the pier configuration: V piers or verticalpiers.

Aside from the construction alternatives andpier types, the contractor was offered the optionon all segmental alternatives of transversely rein-forcing the top flange either with epoxy-coatedconventional reinforcing steel or by transverselypretensioning with 4 in. (12.7 mm) diameterstrand. Further, he had the option on all segmentalalternatives of either precasting or casting in placethe traffic barriers.

The contractor also had the option of casting thesegments rightside up or upside down. Casting thesegments upside down was intended to facilitatetransversely pretensioning the top flange. How-ever, since no waterproof membrane or wearingsurface was specified, the top flange surface of thedeck was required to have a grooved or tined sur-face for skid resistance. If the segment were castupside down, then, the form would be required toproduce the desired texture. Specifications wereleft open such that strand or bar prestressing ten-dons could be bid. All conventional steel rein-forcement was required to be epoxy coated in allalternatives.

The eight basic alternatives for this project pro-duced bids from eight contractors, as indicated inTable 12.4. Note that there were six bids for thespan-by-span method, one for the balanced can-tilever method, and one for the precast preten-sioned AASHTO I girders.

The low bid in precast segmental was $2.6 mil-lion less than the AASHTO I-girder bid. Low bidwas for the span-by-span alternative with precast V

TABLE 12.4. Long Key Bridge, Bid Tabulation

Bid Rank Alternative Chosen Relative Bid

1 D 1.0000

2 F 1.0225

3 F 1.05394 F 1.0963

5 B 1.1731

6 F 1.1844

7 F 1.2557

8 H 1.3063

piers and drilled shaft foundations. The contractorelected to precast the segments near the project siteand cast the segments rightside up, using trans-verse prestressing in the top flange. He slip-formed the cast-in-place barriers after segmenterection. Further, he elected to move the scaffold-ing trusswork from span to span by using abarge-mounted crane as opposed to having thefalsework trusses mounted on barges.

Table 12.5 presents a cost analysis of the low bidas compared with the AASHTO pretensioned I-girder alternative.5

TABLE 12.5. Long Key Bridge, Cost Analysis of theLow Bid and the AASHTO I-Girder Bid

Span-by-Span Precast AASHTO

Segmental I Girder

Total cost” $26.63/ft2 $30.95/ftZ

Superstructure $21.43/ft2 $23.59/f@

costSubstructure cost $ 5.20/f? $ 7.36/f?

Segments erected $19.16/ft2Total bid $15,307,375.91 $17,956,538.75

Total area 468,301 ft2 470,277 ft*

“The mobilization bid items were proportioned to the structuralitems in all cases. The Florida Department of Transportationestimate was $14,550,000.


TABLE 12.6. Seven Mile Bridge, Alternatives

Substructure

Superstructure Precast Piles Drilled Shafts

Precast AASHTO I-girdersSegmental:

Span-by-span, vertical piersCantilever, vertical piersFirst option, slab reinforcing

Second option, barrier curbs

Third option, box piers

A A

C DE F

R/C epoxy coatedPretensioningCast-in-place conventionalPrecast (never integral)Cast-in-place conventionalPrecast

12.2.4 SEVE,\’ MILE BRIDGE, FLORIDA 12.2.5 ZILWz4CTKEE BRIDGE. ,MICHIG,4.\

Seven Mile Bridge in the Florida Keys had thesame basic alternatives as Long Key Bridge, exceptthat the span-by-span with V piers was eliminatedand the contractor had the further option for thevertical piers of casting in place conventionally orprecasting, Table 12.6.

Six bids were received, with all bidders se-lecting alternative D, Table 12.7. Low bid was$44,986,942.3 ! 1 here were no bids for theAASHTO I-gil,ders. The low bidder optioned toreinforce the top slab with conventional reinforce-ment, epoxy coated; to cast the barrier curb inplace; and to precast segmental box piers. The lowbid included $5,128,600 for waterline, roadwayapproaches, and navigational requirements. Anal-ysis of the bid items revealed a superstructure costof $23.22/ft2 and a substructure cost of $5.68/ft2,resulting in a $28.90/ft2 total cost. The FloridaDepartment of Transportation estimate was $52million ($7 million higher than the low bid).

TABLE 12.7. Seven Mile Bridge, Bid Tabulation

Bid Rank Alternative Chosen Relative Bid

1 D 1.00002 D 1.02143 D 1.07684 D 1.14045 D 1.22976 D 1.2556

This structure was designed with alternatives ofsteel plate girders and precast segmental concretebox girder. Bids were first taken in November1978, Table 12.8. The engineer’s estimate for theconcrete alternative was $60,609,614.30 and forthe steel alternative $71,3 16,854.90. On the basisthat the low bid of $80,999,445.50 was 33% higherthan the estimate, the bids were rejected.

The design underwent revision, and the biddocuments allowed the contractor to make designand prestressing system changes under a “cost re-duction incentive,” and an escalation clause wasintroduced. The project was rebid in August 1979(nine months later), Table 12.9. The engineer’s es-timate was $7 1,645,661.50 for the concrete alter-native and $7 1,965,5 16.70 for the steel alternative.The low bid of $76,787,252.65 was 7% over theestimate-5% below the previous low bid. By re-bidding the project (after nine months of inflation)a savings of $4.2 million was achieved.

TABLE 12.8. Zilwaukee Bridge, Ranking ofFirst Bids

Bid Rank Relative Bid Alternative

1 .oooo1.01151.05621.08161.10711.1375

ConcreteConcreteSteelConcreteSteelSteel

Examples of Some Znteresting Biddings and Costs 527

TABLE 12.9. Zilwaukee Bridge, Ranking ofSecond Bids

Bid Rank Relative Bid

1 1 .oooo2 1.07983 1 .08294 1.12315 1.1501

Alternative

ConcreteConcreteConcreteSteelSteel

12.2.6 CLINE AVENUE BRIDGE, INDIANA

The Cline Avenue bid documents were very liberaltoward redesign, with the bidder only having to in-form the state of the intention to redesign at bidopening. As designed, the plans and specificationsprovided the option of a steel plate girder or pre-cast segmental box girder structure. The structurewas redesigned as cast-in-place on falsework, pre-stressed concrete box girder, except for the mainchannel spans which are cast-in-place segmental.The steel option was a composite load factor de-sign. The low concrete bid was for $53,545,770.55with the engineer’s estimate being $53,560,259.78.Relative bids are listed in Table 12.10.

12.2.7 NAPA RIVER BRIDGE, CALIFORNIA

The Napa River Bridge (Section 2.11) is anotherexample of the use of alternative designs. For thisproject, because the lower structure height madefalsework feasible, bid documents were preparedfor three alternative schemes:

A: Conventional continuous cast-in-place boxgirder bridge

B: Trapezoidal continuous structural steel boxgirder bridge

C: Cantilever prestressed segmental concretebridge with either precast or cast-in-placesegments, and erection either by the balancedcantilever method or on falsework

Because of poor foundation material and areadily available aggregate supply, all alternativesused lightweight concrete in their superstructures.

TABLE 12.10. Cline Avenue Bridge, Rankingof Bids

Bid Rank

123

Relative Bid

1 .oooo1.02521.0596

Alternative

ConcreteSteelSteel

Alternative C used a transverse prestressed deck inorder to reduce the number of girders. Strongcompetition was expected from the steel industry,as this site is readily accessible by water from theyards of two major fabricators. However, the lowbidder, G. F. Atkinson Company, selected alterna-tive C and cast the bridge generally in half-spansegments on falsework to the ground as a series ofbalanced T’s. About 60 ft (18 m) of the 250 ft (76m) span over the navigation channel was con-structed in three segments on falsework suspendedfrom the cantilevered boxes on each side.‘j

There were six other bidders, of which only onebid the steel alternative and none bid alternative A.Relative bids are listed in Table 12.11. The first sixbids were for alternative C, and the last and highestwas for alternative B.

122.8 RED RIVER BRIDGE, ARKANSAS

This is a seven-span structure with five interiorspans of 210 ft (64 m), end spans of 135 ft (41 m),and a roadway width of 32 ft (9.75 m). Estimatedcost was $3.3 million. Eight bids were received, sixin structural steel and two for concrete segmental.Bids ranged from $3.22 to $4.89 million. The con-crete segmental was completely open as to themethod of construction (both concrete bids werebased on the incremental launching method). Rel-ative bids are listed in Table 12.12.

TABLE 12.11. Napa River Bridge, Ranking of Bids

Bid Rank Relative Bid

1 1 .00002 1.0928

3 1 .12184 1.18375 1.2765

6 1.43057 1 .5210

TABLE 12.12. Red River Bridge, Ranking of Bids

Bid Rank Relative Bid Alternative

1 1 .oooo Steel2 1 .1437 Steel3 1 .2685 Steel4 1 .2800 Steel5 1 .3099 Concrete

6 1.3229 Concrete7 1 .4267 Steel8 1 .5175 Steel


Structural steel prices varied from a low of$0.65/1b to a high of $0.93/1b with an average of$0.78/1b. Structural steel prices in Arkansas for thistype of construction had previously been in therange of $0.80 to $0.85/1b. The low bid price of$0.65/lb represents a reduction of approximately19 to 23%. All steel prices were for domestic steel.

Note that the bid prices included the demolitionof the existing bridge. If this item were deleted, thebidding would be rearranged as indicated in Table12.13.

The lump-sum price for the concrete super-structure was, for the low concrete bidder, $3 1.37/ft2, which compares favorably with the Keysbridges in Florida. However, this price was notcompetitive. Undoubtedly there are numerousreasons why. One may be that there was no pre-casting plant within sufficient distance of the site,and thus the cost of shipping the segments mayhave been prohibitive. The project was not largeenough to attract contractors with the expertise toset up a precasting operation at the site. The twoconcrete segmental bids received were based on in-cremental launching, and evidently the project wasnot large enough to adequately amortize the cost ofthe casting bed and launching equipment on thisproject to make the method competitive.

12.2.9 NORTH Md4I,\’ STREET VIADUCT, OHIO

The low bid on this project was $25,715,733.00,as compared with the engineer’s estimate of$29,200,000. Probably a major reason why the lowbid was 12% under the engineer’s estimate was thecompetition offered by the two plan alternative de-signs in concrete and structural steel, resulting in aminimum savings of at least $3,500,000. The com-petitive situation was further enhanced by allowingbidders to propose additional optional designs.Although no additional steel optional designs were

TABLE 12.13. Red River Bridge, Reranking of Bids

Bid Rank” Relative Bid Alternative

1 1 .oooo Steel4 1 .1147 Steel2 1 .1620 Steel8 1.2841 Steel3 1 .3379 Steel5 1 .3919 Concrete6 1.4054 Concrete7 1 .5276 Steel

“Ranking corresponds with that presented in Table 12.12.

submitted, three optional concrete redesigns werebid.

As designed, the plans and specifications pro-vided the option of a steel plate girder or precastsegmental box girder structure. Bid documentswere quite liberal for redesign but required quite abit of detail with the bid documents. The winningbid was steel girders, as designed, priced at about$87/f? without one abutment, which was to be con-structed under another contract.

T h e s t e e l g i r d e r s w e r e a n o n c o m p o s i t e ,working-stress design. The approximate]\ 15 mil-lion pounds of A588 structural steel was bid at$0.75/1b. It should be noted that additional savingsin steel could have been accomplished with a com-posite design. Table 12.14 is a relative summary ofthe eight bids.

Note that the low concrete bid was only 3.7%above the low bid, which indicates the competitive-ness.

12.2.10 SU,ZI,M,4RY OF CALIFORSIA’S EXPERIE.VCE

California’s experience with a cost reduction in-centive proposal (CRIP) (value engineering) andalternative designs for projects involving segmen-tal construction is summarized in Table 12.1 5.s

1 2 . 3 Increase in Efjciency in Concrete Bridges

As stated in previous chapters, prestressed con-crete segmental bridges have extended the prac-tical and competitive economic span range ofconcrete bridges. An interesting comparativeexercise is to look back at bridges built in thepast and evaluate them in the light of present-day developments.

TABLE 12.14. North Main Street Viaduct,Ranking of Bids

BidRank

RelativeBid Alternative

1 1 .0000 Steel alternative as per plan2 1.0370 Redesign concrete alternative3 1.0401 Steel alternative as per plan4 1.0579 Concrete alternative as per plan5 1.0884 Steel alternative as per plan6 1.1128 Steel alternative as per plan7 1 .1508 Redesign concrete alternative8 1.4099 Redesign concrete alternative

TABLE 12.15. Summary of California’s Segmental Prestressed Bridge Experience

DateBid Bridge

Length/Max.span (ft)

Cost-Bridge Design AlternativesWork Only Provided Remarks

2/72 P i n e \‘alle>Creek

17001450 $14.2 M = $69/f-? A .

Y/72 .Stani.slausKiter at NewMelones

225oi550 $12.0 M = $127/f? (inch. A .prov. for future widening)

B.

.3/73 Eel River Br. 13871310 $5.0 M = $37/t?and Overhead

1 1174 Napa RiteI- at 22301250Napa

Y/i5 Colomdo 27501220Ri\er at \‘uma

12176 GuadalupeRiver at SanJose

1009/155

.5/76 San JoaquinRiver at Anti-och

94041460

$8.9 M = $54/f?

7.4 M = $34/ft2

$2.6 M = $28/f?

$33.4 M = $79/f?

A .

A .

B .

C .

A .

A .

0.

A .

B .

C .

Cantilever prestressedconcrete segmentalbox girder witheither:1. Prestressed rock

anchor footings”2. Mined rock shaft

foundationCantilever prestressedconcrete segmentalbox girderStructural steel boxgirder”Both with either:1. Prestressed rock

anchor footings2. Mined shaft

foundations”Conventional twintwo-cell cast-in-placeprestressed concretebox girders

Conventional six-cellcast-in-place pre-stressed box girderStructural steel boxgirderCantilever prestressedconcrete segmentaltwo-cell box girder”Segmental pre-stressed concretesingle cell box withcriteria provided toconvert to cantilever

Conventional seven-cell prestressed con-crete box”A four-cell pre-stressed box designedfor segmental con-structionPrestressed concretewith three main spansdesigned for can-tilever segmental con-struction and 20 300ft approach spans de-signed for segmentalconstruction withprovisions to modifyto cantileverStructural steelwelded plate girders(unpainted A-588)with 29 200 ft ap-proach spans”Same as A with 200 ftapproach spans

CRIP by contractor re-vised superstructure de-sign and construction se-quence. Savings to state,$191,000.

Seven contractors bid steeland two bid concrete 1.6%separated low steel andlow concrete.

CRIP modified design tosegmental single-cellboxes. Max. falseworkheight 92 ft +. Savings tostate, $112,824.Six of seven bidders choseC. Falsework heights var-ied from 64 to 132 ft.

Cantilever constructionconsidered by contractorbut not used because con-tractor owned adequatesupply of falsework. Max.f.alsework height 70 ft i_.Maximum falseworkheight 40 ft over a season-ally dry river. Contractorinexperienced in segmen-tal construction.

AH five bidders chose steel.Lower-than-anticipated(foreign) steel prices pre-vailed.

5 2 9


TABLE 12.15. (Continued)

Date Length/Max. Cost-Bridge Design Alternatives

Bid Bridge Span (ft) Work Only Provided Remarks

l/78 San Francisco 46501150 $24.3 M = $59/ft2 A. Precast delta girders” Much bidder interest in all

Bay at Dum- B. Twin single-cell pre- choices during prebid

barton (ap- stressed box girders stage. Final results: seven

preach spans) designed for seg- chose A, one chose C.mental construction Some uncertainties aboutwith criteria for rede- criteria provided in B.sign for cantileveringor launching

C. Structural steel boxgirder

“Selected by low bidder.

12.3.1 REDESIGN OF CARACAS VIADUCTS,VENEZUELA

The Caracas Viaducts in Venezuela (Chapter 8)were completed in 1952, approximately thirtyyears ago. If these viaducts were built today, thechosen structure would probably be very differ-ent from that chosen at the time after exhaustivefeasibility studies. In 1973 these structures werereevaluated in terms of the more conventionalbalanced cantilever method of girder construc-tion. Figures 8.30 and 8.31 compare the actualproject constructed in 1952 with possible alter-native designs in 1973 and 1975. The three-arch-rib and eight-beam superstructure would be re-placed by a variable-depth twin box section(cantilever construction using precast segments)supported on slip-formed piers.

Today, with the same span arrangement consid-ered in 1973, possible alternatives might be a singletwo-cell box similar to that used in the KipapaStream Bridge, or a ribbed single-cell box as in theVejle Fjord Bridge, Figures 4.24 and 4.22, respec-tively. This approach would require only singleshaft piers.

\\12.3.2 COMPARISON BETWEEN TANCARVILLE

AND BROTONNE BRIDGES, FRANCE

Progress is made slowly through accumulated ex-perience, and it is worthwhile to look back pe-riodically and try to measure such progress. Withthis in mind, and as a conclusion to this chapter, acomparison is offered between two similar con-crete structures separated in time by seventeenyears.

As mentioned in Section 9.8, the Seine Riverbetween the maritime inland harbor of Rouen andthe English Channel is now crossed twice by twooutstanding structures:

Tancarville Bridge designed in 1956 incorporatinga 2000 ft (610 m) span steel suspension bridgeBrotonne Bridge designed in 1973 incorporating a1050 ft (320 m) span concrete stayed bridge

These two structures are ohly 20 miles (32 km)apart and are located in very similar surroundingstopographically and geotechnically (see Figures12.1 and 12.2).

On the left bank, a flat expanse of meadows andfields requires a long approach viaduct to reach thedesired altitude of the main crossing above thenavigation channel, while a deep formation of softsoil overlying the load-bearing strata requires deeppile foundations. On the right bank, the limestonecliff extends close to the river bank and calls foronly a short transition between the main river spanand the approach highway. The comparison pre-sented here pertains only to the left-bank approachviaduct of each structure, although interestingcomments could be made also on the relative char-acteristics of their other parts.

The Tancarville approach viaduct has eight 164ft (50 m) spans, having five 140 ton (127 mt), 10 ft

FIGURE 12.1. ‘I‘ancarville Bridge, set-ial v i e w from

the southwest showing left bank approach viaduct.

fFIGURE 12.2. Brotonne Bridge, aerial view from the southwest showing left bank ap-proach viaduct.

(3 m) deep precast girders in each span, Figures12.3 and 12.4. Piers are founded on precast con-crete piles and were cast in place with a box section.When the design was prepared, it represented themost advanced technology in terms of use of mate-rials. The elastic stability of these very long, slenderprecast girders was even the occasion of interestinginnovative studies. Construction methods were alsofar from conventional.

All girders were prefabricated in a yard locatedat the original ground level. Moving and lifting op-erations for one girder (see Figure 12.5) included:

Placing girder on dollies, moving in two perpen-dicular directions to bring it at the foot of the sup-porting piers

Hoisting girder along the piers with special steelrigs, Figure 12.6

Placing girder on top of the pier with the rotatingarm of the special rig, Figure 12.7

Transverse displacement of girder to its final posi-tion

Suspension of the girder at both ends was achievedby the means of special cantilevers to provide thehighest safety against lateral buckling during lift-ing operations of such slender girders, Figure 12.8.The project was carried out smoothly and com-pleted successfully a long time ahead of the othercontracts for the entire crossing.

Fifteen years later, the same problem of safelyand economically building an aesthetically pleasing

FIGURE 12.3. Tancarville Bridge, elevation of approach spans.


IL 11'-4" I: 11'-4" *'-o"

I 1 1'4" 1 l'-4"

FIGURE 12.4. Tancarville Bridge, typical cross section of approach spans.

approach viaduct for the Brotonne crossing wassolved with very different methods, both of designand construction. The light single box section se-lected for the stayed structure was also used for theapproach spans. Precast piles were replaced in thefoundations by cast-in-place slurry load-bearingwalls. Box piers were slip-formed instead of incre-mentally cast in successive lifts. The superstructurewas cast in place in balanced cantilever with travel-ers, Figure 12.9. Today precast segments wouldprobably be preferred, although the characteristicsof the deck would remain substantially unchanged.

_ _ _ _ _ A comparison between quantities of materialsFIGURE 12.5. f‘ancarville Bridge, lif ring one prec<rst per square foot of deck appears in Table 12.16.girder for the approach spans. The savings in concrete volume of Brotonne over

TABLE 12.16. Cost Comparison Between Tancarville and Brotonne Approach Viaducts

Tancarville, 1956(Adjusted 1973) Brotonne, 1973

1. Quantities (per ft”)(super- and substructure)Concrete (yd3)Reinforcing steel (lb)Prestressing steel (lb)

2. Labor (hr/ftz)3. Cost ($/ftZ)

LaborMaterialsEquipment, plant, and job overheadSubcontractsDesign, overhead and fee

4. Total

0.14 0.111 1 146.4 3.14.1 1.6

14.20 5.606.90 6.30

15.70 5.003.70 4.20

12.90 4.20

$53.40 $25.30

Increase in ESJiciency in Concrete Bridges 533

FIGURE 12.6. I‘ancarville Bridge, equipment for lifting precast girders in approachspans.

P~nc~no GIRDER or-i P E R

Tancarville is justified only by the fact thatminimum weight was vital for the concrete stayedbridge and was maintained in the approach spans.Weight of prestressing steel is approximately halfbecause the deck is continuous at Brotonne and thebox section is more efficient than the I-girder sec-tion.

More important, however, is the comparison ofcosts and the components thereof, Table 12.16 andFigure 12.10. One is struck by the total labor re-quirements for both sub- and superstructure:

TancarvilleBrotonne

4.1 hr/fP1.6 hr/ft*

In the 15 years that elapsed between the two proj-ects, the combination of design improvements andmore efficient construction methods allowed thelabor to be divided by 2.5.

A similar trend has been observed in other fields.FIGURE 12.7. Placing precast girder over pier cap. For example, a complete survey of all hydroelectric

Economics and Contractual Aspects of Segmental Construction

LATERAL SA D D L E S----IQIRDCR

DETAIL O F GIRDER SUSPWISIO~

FIGURE 12.8. Lifting device at precast girder ends.

FIGURE 12.9. Brotonne Bridge, cantilever construc-tion of superstructure of approach spans.

projects carried out by French Electricity between1950 and 1970 showed that the annual value of in-vestment for each worker was multiplied by 2without allowance for inflation and by 3 includinginflation, Figure 12.11. Costwise the true gainwould be somewhat less significant, because labor

6 0

5 0

c 4 08ii* 3 0.r::ho

10

0

$53.40

Tancarville Brotonne(readjusted 1973) (1973)

FIGURE 12.10. Cost comparison between Iancarvilleand Brotonne approach viaducts. (5) Design overheadand fee, (4) subcontracts, (3) equipment, plant, and siteoverhead, (2) materials, (1) labor.

-I-----19% 1I

I I IK5 1 9 6 0 1965 1970 YEAR

FIGURE 12.11. Increase of productivity on powerprojects in France.

rates have constantly increased faster than materialrates.

The comparison between other items of the costbreakdown of Tancarville and Brotonne is equallyinstructive. Material costs are almost equal, in-cluding the value of subcontracts (pile foundations

References

and roadway work in both projects). The essentialdifferences are seen in the two following areas:

Equipment , plant , and job overheads: reducedfrom $15.70 at Tancarville to $5 at Brotonne. Thisdifference is due essentially to increased efficiencyin management but also to a climate of fierce com-petition.

Design, overheads and fees: reduced from $12.90for Tancarville to $4.20 for Brotonne. The sametwo reasons explain this drastic reduction, whichalso reflects the change in the overall operation ofl a r g e c o n s t r u c t i o n c o m p a n i e s d u r i n g t h e l a s ttwenty years from family-owned or controlledcraftsmen such as building contractors to modernmanagement industrial companies.

When Eugene Freyssinet designed his PlougastelBridge masterpiece (see Chapter 8), he was per-sonally involved in the project for more thanthree years and probably involved in little else. Onegeneration later, an experienced engineer wouldhave to control or at least participate in many dif-ferent projects during the same period.

In summary, the comparison of costs betweenTancarville and Brotonne approach viaducts withprices of both projects reduced to 1973 levels is:

Tancarville $53.40/f?

Brotonne $25.30/ftZ

Both projects were bid completely on a design-and-build basis and awarded to the lowest bidder.The above costs are a true picture of the technol-

ogy and of the level of prices for the two respectiveperiods.

To estimate both projects at the level of today’sprices (1980) it would be necessary to multiply thelabor rates by 2.3 and the materials and equipmentrates by 1.7.

References1. “Guidelines for Value Engineering (VE),” prepared

by Task Force 19, Subcommittee on New HighwayMaterials, AASHTO-AGC-ARTBA Joint Coopera-tive Committee.

2. “Alternate Bridge Designs,” FHWA Technical Advi-sory T5140.12, December 4, 1979, Federal HighwayAdministration, Washington, D.C.

3. Richard A. Dokken, “CALTRANS Experience inSegmental Bridge Design,” Bridge Notes, Division ofStructures, Department of Transportation, State ofCalifornia, Vol. XVII, No. 1, March 1975.

4. A. B. Milhollin, and C. L. Benson, “Structure Designand Construction on the Vail Pass Project,” Trans-portation Research Record 7 17, Transportation Re-search Board, National Academy of Sciences,Washington, D.C., 1979.

5. James M. Barker, “North American State of the ArtCurrent Practices,” Prestressed Concrete SegmentalBridges, Structural Engineering Series No. 6, Fed-eral Highway Administration, Washington, D.C.,August 1979.

6. Donald W. Alden, “California’s Experience with CostSaving Contracting Techniques,” Prestressed Concrete

Segmental Bridges, Structural Engineering Series No.6, Federal Highway Administration, Washington,D.C., August 1979.

13Future Trends and Developmenti

1 3 . 1 INTRODUCTION 1 3 . 51 3 . 2 MATERL4IS

13.2.1 Prestressiq Tendons13.2.2 High Strength Concrete13.2.3 Fiber Reinforced Concrete13.2.4 Pdymer Concre&13.2.5 Composite Concrete Materials13.2.6 Material Limitations

1 3 . 3 SEGMENTAL APPLICATION TO BRIDGE DECKS 1 3 . 61 3 . 4 SEGMENTAL BRIDGE PIERS AND SUBSIXUClVRES

APPLICATION TO EXISTING OR NEW BRIDGETYPES13.5.1 Overpass Strut13.5.2 Arches, Trusses, Rigid Frames13.5.3 Wichert Truss13.5.4 Stress Ribbon Bridges13.5.5 !3pwe F- Bridges

S U M M A R YREFERENCES

13.1 Introduction

As observed in previous chapters, prestressed con-crete segmental bridges have extended the practi-cal and competitive economic span range of con-crete bridges. The Bendorf Bridge in Germany(Section 2.2) constructed in 1964 with a navigationspan of 682 ft (208 m) was a monumental achieve-ment. Because of economic differences betweenEurope and the United States (primarily the ratioof labor cost to material cost) it was not until theearly 1970s with the JFK Memorial Causeway(Section 3.10) with a span of 200 ft (61 m) andshortly therafter the Pine Valley Creek Bridge(Section 2.7) with a span of 450 ft (137 m) thatsegmental construction was introduced in theUnited States. Today these spans are somewhatcommonplace when one considers the Three Sis-ters Bridge (Section 1. lo), the Koror-BabelthuapBridge (Section 2.12), and the Houston ShipChannel Bridge (Section 2.14), with spans of 750 ft(229 m), 790 ft (241 m), and 750 ft (229 m), re-spectively. When combined with the cable-stayconcept, spans increase to 981 ft (299 m) for thePasco-Kennewick Bridge, 1050 ft (320 m) for theBrotonne Bridge, and 1300 ft (396 m) for theDame Point and Ruck-A-Chucky Bridges.

536

In earlier years these spans for concrete bridgeswould have been considered incomprehensible andcertainly not economical. The fact that they havebecome achievable, only within the last decade,stands as a testimonial to rapid technological ad-vances and to the courage and vision of those engi-neers who participated in this development.

In the United States as of November 1980, 19segmental bridges had been completed and therewere 16 under construction, 22 in design, and 29under study-a total of 86 bridges. We may con-clude that segmental prestressed concrete con-struction is a viable concept for highway bridgesand that there are no known major problems toinhibit its use. What, then, is the potential for seg-mental bridge construction in the 198Os? Thischapter will look at this potential in terms of new orimproved materials, potential application in bridgedecks, piers, and substructure, and application toexisting or new bridge superstructure types.

Z3.2 Materials

During the nineteenth century timber, stone, andmasonry were the common materials for bridgeconstruction. Then iron, steel, concrete, and rein-

Material 537

forced concrete emerged successively as favoritematerials, culminating in the twentieth centurywith prestressed concrete. The present materialsused in bridge construction have some or all of thefollowing disadvantages: weight, cost, or inherentweaknesses in one form or another. In the recentpast,‘development of improved bridge systems hasevolved primarily by more exact methods of cal-culation made feasible by the electronic computeror by innovative bridge systems such as the cable-stayed and segmental types of bridges. Intensivedevelopment of the materials themselves hasbarely begun.

13.2.1 PRESTRESSING TENDONS

Until recently, corrosion of prestressing tendonshas caused few problems and little concern. How-ever, with the advent of segmental constructionand transverse prestressing on the top flange, anincreasing concern has been expressed about thepotential deterioration of the tendons resultingfrom their closeness to the deck surface and expo-sure to the action of de-icing chemicals. Currentmethods of alleviating this concern are the use ofpolyethylene ducts or the possibility of epoxy coat-ing the duct, epoxy coating post-tensioning bartendons, and possibly epoxy coating the prestress-ing strand. A research effort is required to deter-mine the production feasibility and cost; the effect,if any, that nonmetallic coatings might have on thebond of strand to concrete; and the compatibilityof strains between the coating and the tendon. An-other potential method uses individual unbondedstrands with successive coatings of teflon, a corro-sion inhibitor, and polypropylene, Figure 13.1.

An old idea that may need to be resurrected isthat of using glass fibers for prestressing. Thismaterial was being investigated in the 195Os,’ butfor either technical or economic reasons it neverreached fruition. There were problems of chemicalreaction of the glass fibers with the cement; how-

ever, Owens-Corning Fiberglass Corp. has de-ve loped a coa t ing fo r g lass f ibe r s fo r fiber-reinforced concrete. Perhaps this coating could beused for a glass fiber prestressing strand. An ulti-mate strength of 400 ksi (2758 MPa) and a lowmodulus of elasticity ranging from 6000 to 10,000psi (41 to 69 MPa) might be expected. The highstrength and low modulus would indicate a lowpercentage of prestress losses-a decided advan-tage. The high strength would produce, for a givenrequired prestress force, fewer or smaller tendons,thus reducing congestion. Smaller tendon sizeswould reduce web thickness, thus reducing deadweight and prestress force requirements, and soon. Obviously, suitable end anchorages would haveto be developed.

13.2.2 HIGH-STRENGTH CONCRETE

Early prestressed concrete designs were based on3000 psi (20.7 MPa) strength concrete. As knowl-edge of concrete properties and quality control in-creased, it became more feasible to use a 6000 psi(41.4 MPa) strength concrete for many prestressedconcrete structures. In the Pacific Northwest an8 0 0 0 p s i ( 5 5 . 2 MPa) s t r eng th i s r ead i ly androutinely available. Use of such concrete has per-mitted the design of longer-span, lighter-weightconcrete structures.

Within the past few years it has been found thatstrengths of 10,000 psi (68.9 MPa) and higher canbe obtained where special attention is given to (1)selecting the constituent materials, (2) propor-tioning the concrete mix, and (3) handling, plac-ing, and curing the concrete.

It has recently been demonstrated that the appli-cation of ultrahigh-strength concrete is not onlypractical but also economically feasible. High-strength concrete, 9000 to 11,000 psi (62 to 75.8MPa), has been used in the columns of five high-rise buildings in Chicago. The concrete was pro-duced in a local ready-mix plant and trucked to the

7 Wire prestressing

Bonded low frlctlonpolymer (Teflon) Corrosion

/

I n h i b i t o r

’ Polyproplylenecover ing

FIGURE 13.1. Corrosion-resistant strand tendon.

538 Future Trends and Developments

project site. An economic study for a short tiedcolumn indicated that the cost per foot varied withthe concrete strength and steel percentage as fol-lows: $15.50 for 9000 psi (62 MPa) concrete and1% steel compared to $39 for 4000 psi (27.6 MPa)concrete and 8% steel.

Over the past five to ten years considerable re-search has been conducted on high-strength con-crete, dealing primarily with selecting materials,developing concrete mix design criteria, and de-termining basic physical properties of the con-cretes. Very little, if anything, has been doneregarding the implementation of high-strengthconcretes, especially in bridge structures.

(213.4 m) main span and 372 (113.4 m) side spans.The bridge was constructed with a 5000 psi (34.5MPa) concrete strength and used lf in. (32 mm)diameter Dywidag bars for post-tensioning. Forthe analysis, the top flange was assumed to be uni-form and 11; in. (292 mm) thick. The bottomflange was assumed to taper uniformly from itsthickest point at the support piers to 6 in. (152 mm)at midspan. The centroid of the prestressing forcewas assumed to be located 59 in. (146 mm) belowthe top of the section-that is, centered in the topflange. AASHTO HS 20-44 was used for loading,as in the actual bridge.

In an interim report,* “Applications of HighStrength Concrete for Highway Bridges,” pre-pared by Concrete Technology Corporation forthe Federal Highway Administration, a segmentalbridge segment at a pier was redesigned withhigh-strength concrete. The purpose was to de-termine to what extent the thickness of the lowerflange could be reduced, and in turn what effectthis reduction would have on the overall moments.

Prestress force was provided by la in. (32 mm)diameter Dywidag bars with a minimum yieldstress of 150 ksi (1034 MPa). These bars were as-sumed to provide 104 kips (0.46 MN) of final pre-stress force each. This assumes a jacking force of70% of the minimum yield strength and 20 ksi(137.9 MPa) losses. Maximum allowable compres-sive stress in the concrete was assumed to be O.+f“,,and an allowable tensile stress was assumed to bezero.

For purposes of this study, the Shubenacadie Significant benefits were found in the use ofBridge in Nova Scotia (Section 2.15.4) was selected high-strength concrete to reduce the thickness ofas a design example. Overall dimensions of the the lower flange. As shown in Figure 13.3, the totalbridge are shown in Figure 13.2. It has a 700 ft flexural prestress demand is reduced by approxi-

700’. 0” 372’- 0”d-

I 1I -

I

I

AJ ELEVATION

35’- 6”

SECTION B-B

I’- 6,-

+I

1’. 6”r

SECTION A-A

FIGURE 13.2. Shubenacadie Bridge.

Materials 539

36.000

‘-6”

‘7-6”

31,000 1 I I I I 1

5 6 7 a 9 1 0

Concrete strength SKI

FIGURE 13.3. Variation of prestress force with con-crete str-ength-Shubenacadie Bridge.

mately 10% as a result of the reduced dead load.The optimum lower flange thickness is about 1 ft 8in. (508 mm), obtained at 8 ksi (55 MPa) concretestrength.

13.23 FIBER-REINFORCED CONCRETE

A relatively new material that has not yet seenmuch application in structures is fiber-reinforcedconcrete. Fibers have been used to reinforce brittlematerials since ancient times; straws were used toreinforce sun-baked bricks, horsehair was used toreinforce plaster, and more recently various fibershave been used to reinforce Portland cement.3 Astate-of-the-art report4 prepared by AC1 Commit-tee 544 defined fiber-reinforced concrete as “con-crete made of hydraulic cements containing fine orfine and coarse aggregates and discontinuous dis-crete fibers.”

Deflection .

FIGURE 13.4. Schematic load-deflection diagram

Several types of fibers along with several of theirproperties are listed in Table 13. 1.3,4 As can beseen, fibers have been produced from steel, plastic,glass, and natural materials in various shapes andsizes.

Two stages of behavior in the load-deformationcurve have been generally observed when fiber-reinforced concrete specimens are loaded inflexure. The load-deformation curve may be con-sidered as approximately linear up to point A inFigure 13.4. Beyond this point the curve issignificantly nonlinear, reaching a maximum atpoint B. The load or stress corresponding to pointA has been calledjirst-crack strength, elastic limit, orproportional limit, while the stress corresponding topoint B has been termed the ultimate strength.

Two theories have been suggested for predictingthe first-crack strength of fiber-reinforced con-crete: the spacing concept and the composite-materialsconcept. The spacing concept attempts to explain ordetermine the first-crack strength by a crack-arrestmechanism derived from the field of fracturemechanics. The basic mechanism that controls the

TABLE 13.1. Typical Properties of Fibers

Type of Fiber

TensileStrength

(ksi)

Young’sModulus( lo3 ksi)

UltimateElongation

(SC)SpecificGravity

AcrylicAsbes tosCottonGlassNylon (high tenacity)Polyester (high tenacity)PolyethyleneRayon (high tenacity)Rock wool (Scandinavian)Steel

30-60 0.3 25-45 1.1so- 140 12-20 0.6 3.260-100 0.7 3-10 1.5

150-550 10 1.5-3.5 2.5110-120 0.6 16-20 1.1105-125 1.2 11-13 1.4

100 0.02-0.06 10 0.9560-90 1.0 lo-25 1.570-l 10 10-17 0.6 2.740-600 29 0.5-35 7.8


Section A-A

FIGURE 13.5. Schematic of arrest mechanism.

first-crack strength depends primarily on thespacing of the fibers.5

The crack-arrest mechanism for fiber-reinforcedconcrete, as presented by Romualdi and Batson,can best be described with the aid of Figure 13.5,which represents a mass of concrete in tension.The reinforcement consists of a rectangular arrayof rods at a spacing h and located parallel to thedirection of tension stress. At some interior loca-tion an internal flaw exists in the form of a flatdisk-shaped crack.

The basic rationale is illustrated by section A-A,which is a side view of an internal crack betweentwo fibers. In the presence of a gross stress the ex-tensional strains in the vicinity of the crack tip, byvirtue of the stress concentration, -are larger thanthe average strains. These strains, however, are re-sisted by the stiffer fiber, and there is created a setof bond forces (assuming that the bond betweenthe mortar and the steel is intact) that act to reducethe magnitude of stresses at the crack tip. Underproper conditions of fiber spacing and diameter,an internal flaw could be prevented from prop-agating to join up with other flaws into microcrackswhich then join with other microcracks to formmacrocracks. The basic philosophy is that if theinternal flaws can be locally restrained or retardedfrom extending into adjacent material, thereby re-straining crack propagation, the tensile-strengthcharacteristic of the concrete is improved.

The crack-arrest mechanism in bending may beidealized as indicated in Figure 13.6. When a criti-cal strain is reached, the beam cracks; unlike thenonreinforced beam, however, the cracks do notpropagate through the beam but are arrested bythe fibers that span the cracks.

WITHOUT FIBERS

WlTH FIBERS

FIGURE 13.6. Idealized crack-arrest mechanism inhending.

The composite-materials concept hypothesizesthat the properties of fiber-reinforced concrete, in-cluding the first-crack strength, can be predictedfrom the individual properties of matrix andfibers. It assumes that fiber-reinforced concretecan be analyzed as conventional reinforced con-crete, the main difference being that the rein-forcement is shorter, thinner, and randomly dis-tributed.

Table 13.2 summarizes the improvement of theproperties of a steel-fiber-reinforced concrete ascompared to plain concrete.3

13.2.4 POLYiMER CONCRETE

Concrete produced with Portland cement and air-

entraining agents can contain approximately 13%voids, which are interconnected and distributedthroughout the mass. When this concrete is heatedto drive out the chemically unbonded moisture and

TABLE 13.2. Concrete Reinforced with U.S.S.Fibercon Steel Fiber

Properties

CompressionFlexural modulus of ruptureTensile strengthImpact strengthCrack and spa11 resistanceFatigue strength to 2 million

cyclesAbrasionShear and torsional strengthCorrosion resistanceFreeze-thawConductivity (thermal and

electrical)

Approx.Improvement over

Plain Concrete

10-30s70-300%50-300s

150-1000%70-300%

100%

30%50-300%

Good as or betterGood as or better

Conducts both

Mater ia l s 541

TABLE 13.3. Summary of Properties of Concrete-Polymer Material

Concrete with up to 6.7

Weight % Loading of

Concrete Polymethyl Methacrylate,

Control Specimen Co-60 Gamma Radiation

Property (Type II Cement) Polymerized

Compressive strength (psi) 5 ,267 20,255

Tensile strength (psi) 416 1,627

‘Modulus of elasticity (psi) 3.5 x 106 6.3 x lo6

Modulus of rupture (psi) 739 2,637

Flexural modulus of elasticity (psi) 4.3 x 10” 6.2 x 10”Coefficient of expansion (in./in. “F) 4 .02 x 1O-6 5 .36 x 1O-6

Thermal conductivity at 73°F (23°C) 1 .332 1.306

(BTU/ft-hr-“F)

Water permeability (ft/yr) 6 . 2 x lo-’ 0

Water absorption (%) 5.3 0 .29

Freeze-thaw durability:

Number of cycles 590 2,420

Percent weight loss 2 6 . 5 0 . 5

Hardness-impact (“L” hammer) 3 2 . 0 5 5 . 3

Corrosion by 15% HCl (84-day exposure), 10.4 3 . 6

% weight lossCorrosion by sulphates (300-day exposure), 0 .144 0

% expansionCorrosion by distilled water Severe attack No attack

then impregnated with a chemical monomer, suchas methyl methacrylate (MMA), and irradiatedwith gamma rays, some startling changes in itsproperties are produced, Table 13.3.’ Tensile andcompressive strength are almost quadrupled.Modulus of elasticity is increased by a factor of 1.8and modulus of rupture by more than 3.5. A com-pressive stress-strain curve for this material showscomplete linearity up to more than 75% of failureload, Figure 13.7.’

Thus far, research with this material has aimedtoward its application in bridge decks. Problems inpolymerizing large units such as bridge segmentshave yet to be solved. Practical resolution of theseproblems could offer a tremendous advantage forconcrete structures.

13.2.5 COMPOSITE CONCRETE MATERIALS

Assuming that the materials previously discussedcan be developed to a point of practical usage, whatimprovement in properties might be expected ifthese materials were combined? Sukiewicz and Vir-alas have presented flexural-load-versus-deflectiondata for concrete and composite materials, Table

14

12

-z

,” 1 0

8

2 8E

G

6

18 , , , , ( , , , , , , , y , , , ,I

Impregnated CP,6 - COnCrete 5.4 wt

% MMA Failure

UnimpregnatedCP concrete

loo0 2ooa 3000 4000

Compressive strain (microinches/inch)

FIGURE 13.7. Compressive stress-strain curve for

MMA-impregnated concrete.


TABLE 13.4. Relative Load Versus RelativeDeflection

Plain concreteSteel-fiber reinforcedPolymer impregnatedPolymer impregnated and

steel-fiber reinforced

Approx.RelativeMidspan

Approx. DeflectionRelative at Max.

Max. Load L o a d

5 518 2020 13

100 105

13.4. It is obvious that a vast improvement in be-havior and toughness can be expected.

13.2.6 AMATERIAL LIMITATIOSS

With improved material properties, not only wouldstructures become lighter but also the depth ofsuperstructure and thickness of individual ele-ments would be reduced. There are some practicallimitations, however, as to how much the thicknessof a web, for example, may be reduced. The prac-tical limitations of placing the concrete in the formsand of congestion of supplemental reinforcementand prestressing tendons must still be considered.To some extent this could be alleviated by the useof external tendons, as implemented in the LongKey Bridge in Florida, Figure 6.53. This also hasthe advantage of reducing the complexity of fabri-cation for precast segments.

Perhaps a more important limitation in usingmaterials with improved properties is that at somepoint in the design, stress no longer becomes thecontrolling criterion. Deformations, both globaland local, may govern. Because of the reducedsection required from a strength point of view,there may be more concern not only with flexibilityof the structure in a global sense but also with thepossibility of web buckling and limberness of thedeck slab.

13.3 Segmental Application to Bridge Decks

To date, there has been very little use of precast-ing, prestressing, and segmental construction forbridge decks. Transverse prestressing has beenused in the top flange of large, cast-in-place onfalsework, concrete box girders. Lately, transverse

prestressing has been used to a greater extent inthe construction of segmental bridges-to providegreater load capacity and load distribution forlarge overhanging flanges and between adjacentsingle-cell box girders.

Although a few bridge designs have includedtransverse prestressing, much greater use could bemade of it for more economical bridge structures.For replacement of the decks on existing bridges,precast prestressed concrete segmental construc-tion offers great advantages, only some of whichcan be associated with identifiable costs.

As with the segmental box girder, a full-depthsegmental panel bridge deck may be precast inshort segment lengths longitudinally and may befull deck width or partial deck width, Figure 13.8,depending on the width of deck required for aparticular application. Also, in addition to thetransverse prestressing, segmental bridge decksmay be conceived as having expoxied transversejoints and longitudinal prestressing.

A transversely prestressed segmental full-depthpanel bridge deck, Figure 13.9, has been proposedby T. Y. Lin International as an alternative designfor SR 182, Columbia River Replacement Bridge,in the state of Washington. This proposal has thefollowing features:

1. Precast full-depth panels of lightweight con-crete to reduce dead load.

2. Transverse prestressing to achieve large can-tilever overhangs and thus economies in thesuperstructure.

3 . Attachment of the panels to the superstructurewith shear studs in block-outs of the panel toachieve composite action with the superstruc-ture.

I I I

FIGURE 13.8. Deck configurations.

Segmental Bridge Piers and Substructures 543

FIGURE 13.9. SR-182 Columbia River Bridge.

4. Longitudinal prestressing of the deck tomaintain a compression across the transversejoints.

Another segmental method of constructing abridge deck is a transfer of technology from theincremental launching of segmental box-girderbridges.9~10~11 This methodology, as applied tobridge decks, has been pioneered in Switzerlandand consists of the following operations:

1 . The casting of a convenient segment length ofbridge deck behind an abutment, Figure13.10, or at midlength of the bridge, Figure13.11, whichever is more convenient. Segmentlength is normally 65 to 80 ft (20 to 25 m).

2. The jacking forward of the segment, Figure13.12, onto the flanges of the steel super-structure, Figure 13.13, thus freeing the cast-ing bed.

3 . Preparing the casting bed for concreting thenext segment.

4. Repeating the cycle until completion of thebridge deck.

The finished deck, therefore, consists of seg-ments that have been incrementally cast and lon-gitudinally launched. As in conventional structuresthe deck is attached to the superstructure and

made to act compositely by means of shear-transferdevices placed at regular intervals through block-outs cast into the deck.

To date, the incremental launching method hasbeen implemented for the construction of tenbridge decks in Switzerland.lo*ll

13.4 Segmental Bridge Piers and Substructures

Piers do not have to be massive solid cross sections;a tubular cross section may be more effective andmore economical. In the United States it is gener-ally felt to be more economical to cast a solid pier.However, for tall piers the economics of solid-piercasting should be evaluated against the cost of theadditional dead load the pier is supporting andtransferring to the foundations. It may be desira-ble to precast the pier as tubular segments that areprestressed bertically to each other as well as thefoundation.

In the Vail Pass Bridge structures the piers wereconstructed of diamond-shaped segments, stackedvertically and post-tensioned to the foundations,Figure 13.14. Footings were cast in place with ductsto allow the placing of prestressing tendons.

Other examples of segmental application topiers and substructure, previously discussed, are:

1. Linn Cove Viaduct, Section 6.3.2, Figure 6.17

2 . I-205 Columbia River Bridge, Section 5.4.3,Figures 5.25 and 5.26

3 . Sallingsund Bridge, Section 5.4.2, Figures 5.20and 5.21

The Long Key Bridge, Section 6.5.1, used precastV piers; and the Seven Mile Bridge, Section 6.5.2,used precast segments stacked vertically. It is to behoped that these concepts will be refined andutilized for future structures where applicable.

FIGURE 13.10. Incremental launching, behind abutment, from reference 10(courtesy of American Society of Civil Engineers).


FIGURE 13.11. Incremental launching, midlength of bridge, from reference10 (courtesy of American Society of Civil Engineers).

FIGURE 13.12. Incremental launching, jacking ofdeck slab.

FIGURE 13.13. Incremental launching, deck onsuperstructure.

13.5 Application to Existing or New Bridge Types

With the exception of the Pasco-Kennewick andDame Point cable-stayed bridges, the implementa-tion of the concept of segmentally constructedbridges in the United States has been limited to thegirder type of bridge. In other parts of the world,

. Prestressmg tendons

1 Precast segments

FIGURE 13.14. Vail Pass Bridges, segmental pier.

the segmental concept has been applied not only tothe cable-stayed bridge, but also to rigid frames,arches, trusses, and to a limited extent to overpassstructures. Segmental construction is versatile andshould not be stereotyped to girder bridges only; itcan be applied to other types of bridge construc-tion.

13.5.1 OVERPASS STRCrCTURES

The main application of prestressed concrete seg-mental bridge construction has been to the long orintermediate span range and to viaducts. However,

Application to Existing or New Bridge Types 545

this method of construction has been applied tohighway overpass structures, proving its versatility.Examples of overpass structures previously pre-sented are:

1. Rhone-Alps Motorway, Section 3.152 . Motorway Overpasses in the Middle East, Sec-

tion 8.6.4

The Federal Highway Administration (FHWA)in cooperation with the American Association ofHighway and Transportation Officials (AASHTO)is embarking on a study of the feasibility ofstandard sections for segmental box girderbridges. If feasible, standardization of sections,especially for overpass bridges, could provide ad-ditional economy for bridge construction.

An important and costly problem in buildingoverpass structures over heavily traveled highwaysand freeways is that of traffic control during con-struction. An idea that might minimize this prob-lem can be borrowed from the construction pro-cedure for the Vienna Motorway cable-stayedsegmental bridge. Because construction was notallowed to interfere with navigation on the canal,the structure was built in two 364 ft (111 m) halveson each bank and parallel to the canal. Upon com-pletion, the two girder halves were swung into finalposition, Figure 9.66, and a cast-in-place closurejoint was made. In other words, each half is con-structed as a one-time swing span. This conceptwas considered for a long skewed overpass in Il-linois, but the contractor elected a more conven-tional procedure.

13.5.2 ARCHES, TRUSSES, RIGID FRAMES

The adaptation of segmental concepts to arches,trusses, and rigid frames has yet to be im-plemented on the North American Continent. Asindicated in Chapter 8, there are ample examplesto indicate that segmental technology can be usedfor these types of structures. As previously notedand adequately illustrated, segmental constructionshould not be stereotyped to girder bridges only.

13.53 WKHERT TRUSS

The resurrection of the Wichert truss principle,12Figure 13.15, might yield economies in segmentalcantilever construction. This type was developedfor structural steel trusses and has the curiousproperty of providing a fixing moment while re-maining statically determinate. The fixing momentis provided as a function of the geometry of the

FIGURE 13.15. Wichert truss principle.

quadrilateral support, any desired degree of fixingmoment being obtained by arranging the geometryof that quadrilateral, with the structure remainingdeterminate. Consequently there is no danger ofcomplications from settlement of supports orparasitic moments caused by prestressing.

The Wichert truss principle has, among others,the following advantages:

1.2 .3 .4.

Economy of girder materialEconomy of foundationsElimination of intermediate hingesStresses unaffected by temperature differencebetween chords or flanges

The Smithy Wood Footbridge, Figure 13.16, inthe United Kingdom is one of three footbridgesconstructed in about 1970 over the M-l Motorwayusing the principle of the Wichert Truss.

13.5.4 STRESS RIBBON BRIDGES

Another new type of bridge, introduced relativelyrecently, is the Spannbandbriicke or stress ribbonbridge. 13~~ Its origin is obscure and can be tracedback to early societies. Basically the early versionsconsisted of wood planking supported directly onmain catenary cables. It is still used in certain partsof the world, Figure 13.17.

The first modern attempt at the implementationof this concept was in 1958, when Ulrich Finster-walder unsuccessfully entered the concept in theBosporus Bridge competition, Figure 13.18, andagain in 1961 for the Zoo Bridge at Cologne. Thefirst successful construction of a stress ribbonstructure was m 1963 and 1964 in Switzerland for aconveyor-belt bridge at the Holderbank-WildeckCement Works, with a span of 710 ft (216.4 m).The Freiburg, Germany, footbridge, Figure 13.19,constructed in 1969 and 1970 has an overall lengthof 448 ft (136.5 m) with a center span of 130 ft(39.5 m). Notice that the tops of the piers, in effect,form a large-radius saddle for the catenary cables.The deck has a width of 14.4 ft (4.40 m) and athickness of 10 in. (0.25 m). In 1971 the RhoneGenf-Lignon stress ribbon bridge, Figure 13.20,

FIGURE 13.16. Smithy Wood Footbridge,

FIGURE 13.17. Early stress ribbon bridge in theOrient. FIGURE 13.19. Freiburg Stress Ribbon Footbridge.

FIGURE 13.18. Stress ribbon concept for the Bosporus Bridge.

was constructed with a single span of 446 ft (136 m) bon bridge is safe against torsional oscillation.15 Itand a width of 10.2 ft (3.10 m). can have a relatively flat sag, such that the grade at

This type of structure has used prefabricated the abutments and piers can be kept at approxi-transverse and longitudinal prestressed precast mately 4%. Its largest disadvantage is the largesegments supported on the main catenary cables. abutments required to sustain the large tensileWind-tunnel tests have indicated that a stress rib- force in the main cables.

Application to Existing or New Bridge Types 547

FIGURE 13.20. Rhone Genf-Lignon Stress RibbonBridge.

13.5.5 SPACE FRAME BRIDGES

In 1980, one of the authors served in an advisorycapacity to the Kuwait Ministry of Public Works toevaluate responses to a request for proposals forthe Bubiyan Bridge Project. An interesting pro-posal was submitted by Bouygues, a French firm.This proposal consisted of a three-dimensionalt ru s s o r space f r ame concep t , F igu re s 13 .21through 13.23.

The concept of prestressed concrete trusses isnot a new one. Concrete trusses have been used inbuilding construction and in bridges (Chapter 8) invarious projects throughout the world. For exam-ple:

L.

3.

4.

The Mangfall Bridge in Austria (Section 8.7.2)is a three-span, cast-in-place, prestressed con-crete structure. It may be described simply as abox girder consisting of solid top and bottomflanges connected by two vertical webs, whichare trusses.The Rip Bridge in Australia (Section 8.7.3),just north of Sydney, is a three-span cantileverarch-truss structure. The upper chord (road-way slab), diagonal and vertical truss members,and lower chord are composed of precast ele-ments, which are made integral by cast-in-place concrete and post-tensioning.

At least three prestressed concrete cantileverarch-truss bridges have been constructed inYugoslavia, including the Kirk Bridge (Section8.5,4), which presently holds the record for thelongest concrete arch in the world, a 1280 ft(390 m) span.Other prestressed concrete truss bridges havebeen constructed in France, the U.S.S.R., andJapan.

FIGURE 13.21. Elevations of Bul)i)arl Bridge Pro-posal prepared by Bouygues, Paris.

FIGURE 13.22. Isometric of Bubiyan Bridge Proposalprepared by Bouygues, Paris.

FIGURE 13.23. Construction-stage model of BubiyanBridge Proposal.

All the structures mentioned above have onething in common: the prestressed concrete trussesare all oriented in a vertical plane. The concept isthe same as in conventional truss bridges con-structed of structural steel members.

The three-dimensional truss concept presentedfor the Bubiyan Bridge is essentially a multitri-angular-cell concrete box girder wherein the lon-gitudinal solid webs are replaced by an open latticesystem of trusses. Because the lattice truss webs areoriented in an inclined plane, as opposed to a ver-tical plane, adjacent trusses have common nodepoints (intersection of diagonal and vertical trussmembers with the flanges). This spatial geometrythen forms in the transverse direction anothersystem of trusses. Thus, the flanges are connectedby a system of inclined orthogonal trusses (a systemof mutually perpendicular trusses), Figure 13.24.Because the trusses are inclined to each other, withthe diagonal and vertical members intersecting atcommon node points, they form a space framecomposed of interconnecting pyramids. Thus, thestructural behavior of the bridge with regard todistribution of load resembles that of a two-wayslab in building construction.

This structural concept is new in regard to itsapplication to a bridge structure. However, theconcept of a space frame truss has been previouslyapplied to roof structures for large column-freesport facilities, auditoriums, civic centers, and thelike. These space structures have been constructedprimarily of metallic (steel or aluminum) tubularsections. There is no reason to believe that with thecurrent state of the art in prestressed concrete,segmental construction and existing concrete trussconstruction, a prestressed concrete space frame

FIGURE 13.24. Model of typical segment with topflange removed (note external post-tensioning tendons),Bubiyan Bridge Proposal.

concept cannot be consummated-in particularfor a bridge structure.

The advantage of this concept is that as a resultof the “openness” of the trellis framework oftrusses the dead or self-weight of the superstruc-ture is much less than that of conventional pre-stressed concrete construction. This comparativereduction in weight of the superstructure reducesthe dead load to be transmitted to the substructureand thus reduces the mass of the substructure,with resulting economies. Further, there is anadvantage in the manner the load is distributedthroughout the structure. That is to say, there aremany load paths. In the unforeseen event of amember failure, the load would redistribute byseeking an alternative load path. Therefore, thereis a greater degree of redundancy, which meansthat there is greater safety from a collapse failure.O r , i n o t h e r w o r d s , b y v i r t u e o f t h e s p a t i a lgeometry there is an inherent reserve capacity.

In all other respects the fabrication and erectionof the superstructure is consistent with state-of-the-art conventional prestressed, precast segmen-tal construction, including the external prestress-ing. Although the concept of a space frame struc-ture is new to bridge construction, its newness isonly in assembling existing concepts into a singleconcept.

13.6 Summary

The last decade has seen considerable changes inbridge design and construction, many of whichhave been evolving since the 1950s. As we moveinto the 198Os, we must remain aware of change.Research already underway on inproved materialsmay have dramatic impact in the indusry. Applica-tions of new systems to existing bridge types arebeing attempted along with new and improvedtypes of bridge structures. Many of the improvedmaterials and new concepts will reach practical ap-plication; others will be abandoned for technical oreconomic reasons. Unforeseen improvements inmaterials and new types of bridge structures arecertain to evolve in the next decade, which proni-ises to be one of excitement and challenge.

As engineers whose basic responsibility is thebetterment of mankind, we must be constantlyopen to new concepts and ideas that will technicallyand economically improve the structures we at-tempt to build. However, at the same time we mustanticipate a new generation of problems thatchanges in methodology are certain to bring. Of

References

prime importance, we must not fall into a trap ofoversophistication in des ign a t the expense o fsimplicity and thus economy in construction.

As we strive for longer spans and improvedmeans of constructing bridges, it would be well toremember the words of F. Stiissi, an eminent Swissengineer:

The poblem of‘ Long Spans has always fascinated thespecialist as well as the layman. The realization of abridge with a length of span hitherto unattained not onlyrequires great technical knowledge and capability, butalso intuition and creative courage; it signifies a victoryover the forces of nature and propess in the battle againsthuman insufjc&y.

This philosophy applies not only to the achieve-ment of longer spans, but also to the changingtechnology of the future.

References

1. I. A. Rubinskv and A. Rubinsky, “A Preliminary In-vestigation of the Use of Fiberglass for PrestressedConcrete,” Magazine of Concrete Research, September1 9 5 4 .

2. James E. Carpenter, “Applications of High StrengthConcrete for Highway Bridges,” Interim Report,July 1979, Concrete Technology Corporation,Contract No. DOT-FH-1 l-9510 (unpublished re-port).

3. W. Podolny, Jr., “Properties of Fiber-ReinforcedConcrete,” Highway Focus, Vol. 4, No. 5, October1972, Federal Highway Administration, Washing-ton, D.C.

4. “State-of-the-Art Report on Fiber Reinforced Con-crete,” Reported bv AC1 Committee 544,Journal ufthe .4merican Concrete Ins t i tu te , November 1973.

5 .

6 .

7 .

8 .

9 .

10.

11.

12.

13.

14.

15.

549

J. P. Romualdi and G. B. Batson, “Mechanics ofCrack Arrest in Concrete,” Proceedings o f the ASCE,Vol. 89, No. EM 3, June 1963.J. P. Romualdi and G. B. Batson, “Behavior of Rein-forced Concrete Beams with Closely Spaced Rein-forcement,“journa/ of the American Concrete Institute,

Vol. 60, Title No. 60-40, June 1963.“Polymer Concrete,” FIP ‘Votes, 38 January/February 1972, Federation Internationale de la Pre-contrainte.Jan Sulkiewicz and Juhani Virola, “Future Aspectsof Bridge Construction,” International Civil En-gineer ing Monthly , Vol. III, No. 2, 1974 (Jerusalem).G. H. Beguin, “Vergundbrticken-.4usfuhrungs-probleme beim Fahrbahn plattetr-Schiebeverfahren, Der Stahlhaum, Heft 12, Dezember 1975.G. H. Beguin, “Composite Bridge Decking b\Stage-Deck Jacking,” Journa l qf t h e S t r u c t u r a l D i v i -sion, AXE, Vol. 104, No. ST 1, January 1978.Rene Rvser, Discussion of “Composite BridgeDecking by Stage-Deck Jacking,” Journal of theStructural DiGsion, .4SCE, Vol. 104, No. ST 10,October 1978.D. B. Steinman, The Wichert Truss, Van Nostrand-Reinhold, New York, 1932.Rene Walther, “Stressed Ribbon Bridges,” Interna-tional Civil Engineering Monthly, Vol. II, No. 1,1971/1972 (Jerusalem).Heinz Nehse, “Spannbandbriicken,” in FestschriftUltih Fiwterwalder 50 Jahreftir Dywidag, Dykerhoff UWidmann, A.G., Munich, 1973.Ulrich Finsterwalder, “Free-Cantilever Constructionof Prestressed Concrete Bridges and Mushroom-Shaped Bridges,” Firs t In t e rna t iona l Sympos ium, Con-crete Bridge Design, American Concrete InstitutePublication SP-23, Detroit, 1969.

Index of Bridges

Abeou Aqueduct (France), 345

Akayagawa (Japan), 379,458,463Algiers (Algeria), 393Alpine Motorway (France), 83, 129-134, 135, 139, 390, 489,

510,515,545A-l Motorway Overpass (France), 352

Ampel (Holland), 510Anet (France), 360Angers (France), 122, 515Aramon (France), 98, 100, 5 14

Ardrossan Overpass (Canada), 8, 11Arnhem (Holland), 57-59

Arrabida (Portugal), 375Ashidagawa (Japan), 458, 462

Balduinstein, see Lahn RiverBarranquilla (Colombia), 401-404Barwon River (Australia), 401, 402

Basra (Iraq), 346Bayonne (France), 510Bear River (Canada), 83, 84, 108-l 12Bendorf (Germany), 19, 35-37, 164, 167, 283-284, 296, 536

Benton City (Washington, U.S.A.), 401, 402Bezons (France), 31-33Black Gore Creek, see Vail Pass

Blois (France), 98, 100, 233, 245, 468, 513, 514Boivre Viaduct (France), 350Bonhomme (France), 15, 387-392

Bonpas (France), 509Borriglione Viaduct (France), 344

Bospoms (Turkey), 545, 546Bouguen (France), 34, 38-40

Bourg-Saint AndCol (France), 509Briesle Maas (Netherlands), 385-388

Brotonne (France), 17, 29, 30, 198, 199, 233, 234, 236, 374,401, 405, 419-427, 481, 482, 530-535, 536

Bubiyan, Kuwait, 547-548

B-3 Viaduct (France), 14, 18, 124, 128, 139, 145, 162, 165,468, 507, 510,515, 516, 517

Calix (France), 139, 140Canadians Interchange (France), 476-478

Canal du Centre (Belgium), 401,402Capt. Cook (Australia), 20, 136-139Caracas Viaducts (Venezuela), 363-372, 375, 530Carpineto Viaduct (Italy), 401, 402, 404Center Canal (France), 455

Cergy-Pontoise (France), 444, 445Chaco/Corrientes (Argentina), 401-404, 408-410, 432Champigny (France), 173, 343

Changis (France), 360

Chillon Viaduct (Switzerland), 18, 99-103, 162,,167, 226, 254,256, 503, 512-514

Choisy-le-Roi (France), 12, 13, 17, 20, 83-88, 139, 155, 165, 169,

226, 253, 254, 255, 361,362,468,494, 509Clichy (France), 233, 234, 449-452, 478, 479, 482Cline Avenue (Indiana, U.S.A.), 527

Colorado River at Yuma (California, U.S.A.), 529Columbia River at Astoria (Oregon, U.S.A.), 238Columbia River, I-205 (Oregon, U.S.A.), 142-144, 158, 161, 162,

169, 238, 241, 543Columbia River, SR 182 (Washington, U.S.A.), 542, 543Conflans (France), 95, 96,469, 509

Corde (France), 228Courbevoie (France), 20, 88, 89, 165, 226, 254, 468, 494, 509Criel Viaduct (France), 333, 335,344

Dame Point (Florida, U.S.A.), 401, 402, 405, 433-436, 536, 544Danube Canal (Austria), 401, 402, 427-431, 545

Danube River at Worth (Germany), 26, 345, 346Dauphin Island (Alabama, U.S.A.), 256, 257, 258Denny Creek (Washington, U.S.A.), 22, 34, 304311Deventer (Holland), 20, 105, 106, 162, 515, 516

Digoine (France), 455, 456, 458Dijon (France), 476

Dnieper River (U.S.S.R.), 401, 402Drummondville (Canada), 8,9Dumbarton (San Francisco, Calif., U.S.A.), 530

Dusseldorf-Flehe (Germany), 21, 23, 303-307

Eastern Scheldt (Holland), 134136, 139East Huntington (West Virginia, U.S.A.), 401,402Elztalbrucke, (Germany), 296-300

Eel River (California, U.S.A.), 529Esbly Bridge (France), 5, 360

Eschachtal (Germany), 73, 80

Felsenau (Switzerland), 168

F-9 Freeway (Australia), 145Firth of Forth (U.K.), 3

Flying Lever Bridge, 3Fontenoy (France), 25Foyle River (N. Ireland), 401, 402

Freiburg (Germany), 545, 546

Garden (Frame), 509Gennevilliers (France), 52-55, 164, 478, 480Givers (France), 151, 152, 163Gladesville (Australia), 371-374, 375Grand’Mere (Canada), 55-58

551

552 Index of Bridges

Great Belt (Denmark), 14, 401-405, 430-433Gronachtal (Germany), 345Guadalupe River at San Jose (California, U.S.A.), 529

Guadiana Viaduct (Portugal), 300-301

Hartel (Holland), 103-105, 494, 509

Herval (Brazil), 31Hobbema (Canada), 8, 10Hokawazu (Japan), 378

Holderbank-Wildeck (Switzerland), 545Houston Ship Channel (Texas, U.S.A.), 28, 68-71, 161, 169,

212-222, 232, 238-239, 241, 536Hyobashigawa (Japan), 457, 459

Incienso (Guatemala), 71, 74, 75

Ingolstadt (Germany), 345Inn (Germany), 345Interstate I-266, Potomac River Crossing, see Three Sisters Bridge

Iquacu (Brazil), 375Islington Avenue Ext. (Canada), 84

JFK Memorial Causeway (Texas, U.S.A.), 27, 83, 84, 109, 112-

1 1 4 , 5 3 6Joinville (France), 164, 479

Juvisy (France), 95, 96, 233, 254, 509

Kakogawa (Japan), 441,462Kennedy (France), 476Kentucky River (Kentucky, U.S.A.), 84, 142, 143

Kettiger Hang (Germany), 293-294Kimonkro (Ivory Coast), 344Kipapa Stream (Hawaii, U.S.A.), 72, 76, 169, 530

Kirk (Yugoslavia), 15, 16, 374, 375, 379, 382-384, 547Kishwaukee (Illinois, U.S.A.), 84, 141, 142, 143, 169Kisogawa (Japan), 458,461Koblenz (Germany), 162, 167Kochertal (Germany), 45-46, 47, 48, 168

Koches Valley (Germany), 345Koror Babelthuap (Pacific Trust Territory), 13, 30, 61-63, 81,

536Krahnenberg (Germany), 293-295, 296Krummbachbrucke (Switzerland), 379

Kwang Fu (Taiwan), 401,402

Lacroix Falgarde (France), 34, 40-41Lahn River (Germany), 11, 33Lake Maracaibo (Venezuela), 400-403, 405-408, 432

La Voulte (France), 34, 441, 442Lievre River (Canada), 83, 84Linn Cove Viaduct (N. Carolina, U.S.A.), 23, 35, 84, 178-181,

228, 233, 282, 290-293, 308, 503, 525, 543Loisach (Germany), 301-303

Long Key (Florida, U.S.A.), 18, 22, 23, 84, 159, 169, 308-313,489, 524-525, 526, 542, 543

Luc Viaduct (France), 333-335, 344

Luzancy (France), 11, 13, 82, 357, 359, 360

Madison County (Tennessee, U.S.A.), 5Magliana (Italy), 401-404Magnan Viaduct (France), 72, 77, 256, 257, 479Mainbrucke (Germany), 401,402, 405,410-412Mangfall (Austria), 395, 396, 547

Marne la Vallee Viaduct (France), 441, 444-448, 517

Marne River Bridges (France), 5, 357, 361, 362, 363Marolles (France), 344

Medway (U.K.), 7 1Miller Creek, see Vail PassMirabeau (France), 21, 509

Morand (France), 442-444

Morlaix (France), 163Moulin a Poudre (France), 163Moulin-les-Metz (France), 476, 477

Mount Street (Australia), 401, 402M-25 Overpass (U.K.), 401, 402

Muhlbachtalbrucke (Germany), 338-339Muscatuck (Indiana, U.S.A.), 84

Napa River (Napa, California, U.S.A.), 59-61, 81, 527,

529Napa River (Vallejo, California, U.S.A.), 10

Natorigawa (Japan), 457,460

Neckarburg (Germany), 370, 376-380Neckarrews (Germany), 33New Melones (California, U.S.A.), see Stanislaus RiverNew Orleans, Greater (Louisiana, U.S.A.), 3Niesenbachbrucke (Austria), 378, 380-382

North Main Street Viaduct (Ohio, U.S.A.), 528Nuel Viaduct (France), 344

Oissel (France), 163, 476Oleron Viaduct (France), 2, 18, 20, 22, 96-99, 108, 157, 158,

165, 175, 177, 241, 243-245, 249, 468, 494, 504, 506, 508,5 1 1 , 5 1 2 , 5 1 4

Olifant’s River (South Africa), 26, 331-333, 343, 441, 452-454Oh Viaduct (France), 333-335, 344

Oosterschelde (Holland), see Eastern ScheldtOrleans (France), 478Ottmarsheim (France), 145, 165

Overstreet (Florida, U.S.A.), 145, 146Ounasioki (Finland), 281, 284-285

Pag (Yugoslavia), 375, 378Paillon (France), 344

Paris Belt, Downstream, (France), 91-94, 155, 233, 234, 263-266,468, 509, 511

Paris Belt, Upstream, (France), 94, 95, 245-248, 468, 509, 511Paris-Lyon high-speed railway line (France), 453-457Parrots Ferry (California, U.S.A.), 72, 77

Pasco-Kennewick (Washington, U.S.A.), 17, 84, 401, 402, 405,418-419, 536, 544

Penn DOT Test Track (Pennsylvania, U.S.A.), 84Pfaffendorf (Germany), 393Pierre Benite (France), 21, 89-91, 92, 468, 510Pine Valley, California (U.S.A.), 27, 29, 34, 35, 46-52, 81, 161,

169, 523, 529, 536Pleichach Viaduct (Germany), 295-296Plougastel (France), 15, 31, 355, 358, 359, 375, 535

Polcevera Viaduct (Italy), 401-403Pontchartrain (Louisiana, U.S.A.), 6, 7Pretoria (South Africa), 401, 402

Puente de1 Azufre (Spain), 7 1, 73Puteaux (France), 73, 78, 151Pyle (France), 229

Quebec (Canada), 3Querlin Guen (Germany), 345

Index of Bridges

Ravensbosch Valley (Holland), 329-331Reallon (France), 151, 153Red River (Arkansas, U.S.A.), 527, 526Rhone Genf-Lignon (Switzerland), 545, 547Richmond-San Rafael (California, U.S.A.), 238Rio Caroni (Venezuela), 24, 321-327, 345Rio Caroni railway (Venezuela), 464Rio Esla (Spain), 375Rio Niteroi (Brazil), 20, 22, 106-108, 139, 169, 176, 178, 190,

200, 201, 515, 516Rio Tocantis (Brazil), 71, 72Rip Bridge (Australia), 14, 395-397, 547Roche (France), 455, 456Rombas Viaduct (France), 282, 288-290, 317Ruck-A-Chucky (California, U.S.A.), 401, 402, 436-439, 536

Saint Adele (Canada), 37-39Saint Andre de Cubzac (France), 101, 113-116, 122, 162, 165,

489,504,510Saint Clair Viaduct (France), 375Saint Cloud (France), 14, 18, 29, 30, 114, 117-122, 139, 150,

160, 162, 165, 205, 208, 234, 503-505, 508, 514, 515Saint Isidore (France), 479Saint Jean (France), 41-44, 163, 235, 265-269Saint Michel (France), 384-385Sallingsund (Denmark), 101, 122-l 25, 158, 167, 236-238, 240,

489,5 15,543Sando, (Sweden), 375San Joaquin River at Ant&h (California, U.S.A.), 529San Mateo-Hayward (California, U.S.A.), 238Saone River (France), 454-458Sathom (Thailand), 348Saulieu (France), 455Shubenacadie (Canada), 71, 74, 81, 538,539Schwarzwasserbrucke (Switzerland), 379Sebastian Inlet (Florida, U.S.A.), 10, 12Seine River (France), 455,456Serein (France), 455, 456Setubal (Argentina], 72, 75, 76Seudre Viaduct (France), 98, 101, 165SevenMile (Florida, U.S.A.), 22, 28, 159, 169, 312-314, 489,

526, 543Sheldon (New York, U.S.A.), 11Shepherds House (U.K.), 339-343Shogun’s Bridge (Japan), 2Sibenik (Yugoslavia), 375, 378

553

Siegtal (Germany), 19, 43-45Smithy Wood Footbridge (U.K.), 545, 546Stanislaus River (California, U.S.A.), 529Sugar Creek (Indiana, U.S.A.), 84

Tancarville (France), 419, 530-535Tarento (Italy), 168Tauemautobahn (Austria), 141, 142Tempul Aqueduct (Spain), 400-402,405Tet Viaduct (France), 344Three Sisters Bridge (District of Columbia, U.S.A.), 27,34,

536Tie1 (Netherlands), 401, 402, 412-418Tonneins (France), 355Torcy Viaduct (France), 447-449Tours (France), 509Tourville (France), 476Trent Viaduct (U.K.), 140, 141Tricastin (France), 73, 79, 80, 151, 153Trilbardou (France), 360Turkey Run State Park (Indiana, U.S.A.), 84

Ussy, France, 360

Vail Pass (Colorado, U.S.A.), 84, 140, 141, 228, 285-288, 523,524,543,544

Val Ristel (Italy), 25, 327-330Van Staden (South Africa), 375, 378Var Viaduct (France), 345Vejle Fjord (Denmark), 63-67, 162, 167, 530Veurdre (France), 354, 355Villeneove (France), 355, 356Viosne (France), 164

Waal River (Holland), see Tie1Wabash River (Indiana, U.S.A.), 26, 34, 84, 324, 335-338Wadi Kuf (Libya), 401-403, 407, 408, 432Walnut Lane (Pennsylvania, U.S.A.), 5, 6Wandipore Bridge (Bhutan), 2Weirton-Steubenville (West Virginia, U.S.A.), 401, 402Woippy (France), 479, 481Worms (Germany), 11, 13

Zilwaukee (Michigan, U.S.A.), 84, 144, 145, 158, 162, 169, 526,527

Zoo (Germany), 545

Abrahams, M. J., 30, 147, 224

Index of Personal Names

Alden, Donald W., 535

Ballinger, C. A., 30, 147, 224Barker, James M., 535Batson, G. B., 540, 549Baumgart, E., 31Baur, Willi, 24, 30, 323, 352Beloff, G., 20, 138, 139Bender, Brice, 104, 105, 330, 331Benson, C. L., 535Bequin, G. H., 549Best, K. H., 353Bezouska, T. J., 5 17Bezzone, A. P., 81Bockel, Manfred, 296, 298, 302Bouchet, Andre, 147Breen, John E., 109, 112, 113, 147Brown, R. C., Jr., 147Brunei, 339Bryant, Walter, 419Bums, N. H., 147

Caquot, Albert, 31Carpenter, James E., 549Chang, F. K., 439Cooper, R. L., 147

Dill, R. E., 4Dohring, C. E. W., 4Dokken, Richard A., 81, 535Downing, Dale F., 81

Eiffel, Gustave, 41, 43Esquillan, M., 34, 375

Feige, A., 439Finsterwalder, Ulrich, 11, 23, 30, 33, 36, 81, 320, 401, 402,

404,410,432, 545,549Fleming, J. F., 439

Ereyssinet, E., 4, 5. 11, 31, 210, 226, 354, 355, 363, 375, 392,394, 398, 399,535

Gallaway, T. M., 147Garrido, L. A., 403Gerwick, Ben C., 147, 238, 280Graham, H. J., 440Grant, Arvid, 325, 326, 353, 418, 419, 420, 439,

440Gray, Normer, M., 401, 439

Hadley, Homer M., 401, 439Hale, Phil, 61Heinen, Richard, 81, 411, 412Henneberger, Wayne, 109Hoyer, E., 4

Jackson, P. H., 4

Kashima, S., 147Kingston, R. H., 353

Lacey, G. C., 147Lenglet, C., 440Leonhardt, Fritz, 24, 25, 26, 30, 149, 224, 323, 325, 345, 405,

420,439Lin, T. Y., 30,436,440Lindberg, H. A., 67Lu, H. K., 440

Macintosh, D. W., 81Maddison, M., 353Mangnel, G., 4Mathivat, J., 147, 260, 280Milhollin, A. B., 535Moth, Elizabeth B., 30Morandi, Riccardo, 400, 401, 403, 404, 407, 430, 432,

439Muller, Jean, 12, 30, 147, 224, 399

Navier, Claude Louis Marie, 83Nehse, Heinz, 549

Podolny, W., Jr., 30, 147, 224, 320, 439, 549Pope, Thomas, 3

Redfield, C. M., 440Resal, 196Romualdi, J. P., 540, 549Rothman, H. B., 439Rubinsky, A., 549Rubinsky, I. A., 549Ryser, Rene, 549

Scalai, J. B., 30, 439Schambeck, H., 320,439Schell, Herb, 3 10Shama, Robert, 399Steiner, C. R., 4Steinman, D. B., 549Sttissi, F., 549

555

556

Sulkiewicz, Jan, 541, 549

Tang, Mar&hung, 30,62, 81, 288, 319Thul, H., 81, 319, 320, 439Torroja, E., 400, 401, 405, 439Troitsky, M. S., 439Tyrrell, H. G., 30

Vatshell, J. L., 308-311Virola, Juhani, 541, 549

Index of Personal Names

Walther, Rpz, 549Whatley, M. J., 353Whitman, R. A., 81Wittfoht, Hans, 43,

282, 319

Yang, Y. c., 440

Zellner, Willhelm, 377, 380, 439Zublin, 377 ,380 , 399

Index of Firms and Organizations

American Association of State Highway and TransportationOfficials (AASHTO), formerly American Association of StateHighway Officials (AASHO), 5, 6, 8, 30, 55, 148, 149, 190,193, 199, 2.30, 243, 363, 460, 521, 524, 525, 526, 535, 538,545

American Concrete Institute (ACI), 30, 36, 81, 97, 98, 147, 193,199, 280, 295, 319, 324, 325, 326, 353, 404, 439, 466, 517,539,549

American Consulting Engineers, Inc., 335American Institute of Steel Construction (AISC), 439American Railway Engineers Association (AREA), 148, 190American Road and Transportation Builders Association

(ARTBA), 535American Society of Civil Engineers (ASCE), 30, 81, 352, 364,

365, 367, 399,409,410,439,440, 543,544, 549Arvid Grant and Associates, Inc., 419Associated General Contractors of America (AGC), 535Associazione Italiana Cement0 Armato E Precompresso (AICAP),

353Associazione Italiana Economica Del Cement0 (AITEC), 353

Beton-und-Stahlbetonbau, 35, 36, 81, 284, 320Bouygues, 547British Rail, 340Bullen and Partners, 340BVN/STS, 104,105, 330, 331

California Department of Transportation (CALTRANS), 10, 27,47, 59, 61, 81, 523, 535

California Division of Highways, see California Department ofTransportation

Concrete Society (London), The, 341, 342, 343, 353Concrete Technology Corporation, 538, 549

Der Bauingenieur, 297, 298, 299, 320DRC Consultants, Inc., 62, 288Du Pont de Nemours, 249Dyckerhoff & Widmann, 13, 19, 30, 33, 35, 62, 63, 76, 81, 284,

285,296,301, 303,307,320,404,412,432, 549

Engineering News-Record, 37, 38, 39, 81, 353, 399, 439, 440Entreprises Campenon Bernard, 12, 122, 419

Federal Highway Administration (FHWA), 30, 147, 224, 310,419,439,440,520,535,538,545,549

Federation Internationale de la Precontrainte (FIP), 224, 517,549

Federation Internationale de la Precontrainte, ComitC Europeendu Beton (FIP-cEB), 190, 193

Figg and Muller Engineers, Inc., 313, 524

Florida Department of Transportation, 524, 525, 526French National Railways, 453Freyssinet International, 11,439, 440

General Services Administration (GSA), 519G. F. Atkinson Company, 527

Heavy Construction News, 81Hensel Phelps Construction Company, 304Howard Needles Tammen & Bergendoff, 433, 434, 435, 440

Indiana State Highway Commission, 335Institution of Civil Engineers, 340, 341, 342, 353, 439International Association for Bridge and Structural Engineering

(IABSE), 149,224,319,439International Engineering Company, Inc., 524International Road Federation, 30, 147, 224

Julius Berger-Bauboag Aktiengesellschaft, 403, 405-408

Kuwait Ministry of Public Works, 547

Leonhardt and Andra, 24,323,419L’Industria Italiana de1 Cemento, 403, 404

Main Roads Department, Australia, 20, 138, 139, 147, 399Museum of Modern Art, New York, 30

Owens-Corning Fiberglass Corp., 537

Polensky-und-Zollner, 43Portland Cement Association (PCA), 5, 8, 9, 10, 11, 12, 37, 49,

50, 56, 74, 81, 135, 136, 147, 309, 320, 353Post-Tensioning Institute (PTI), 81, 320, 353, 517Preston Corporation, 419Prestressed Concrete Institute (PCI), 5, 6, 8-12, 30, 81, 110-112,

147, 224,320,466,517

Ralph Rodgers Construction Co., 335Roads and Transportation Association of Canada, 81

Siemens-Bauunion, 296Society of American Value Engineering, 5 19Structural Engineers Association of California, 190

Texas Highway, 27, 109Transportation Research Board, National Academy of Sciences,

30, 319,439,535Travaux, 147,280T. Y. Lin International, 436, 542

557

558 Index of Firms and Organizations

U.S. Army Corps of Engineers, 5 19 VSL Corporation, 308, 335U.S. Bureau of Reclamation, 5 19U.S. Coast Guard, 61 Washington Department of Transportation,U.S. Department of Defense, 519 307-311U.S. Department of Transportation, 5 19 Wayss & Fretag, 296U.S. Navy Bureau of Yards and Docks, 519 Weddle Bros. Construction Co., Inc., 335United States Steel Corporation, 540 White, Young and Partners, 401-404,430University of Texas at Austin, Center for Highway Research,

109,147 Zement and Beton, 283, 294, 295,319

Index of SubiectsJ

AASHTO-PC1 I-girders, 5, 6, 8Abutments, 8, 9, 24, 56, 132, 150, 205, 207, 232-235, 271-276,

333,336, 363Aesthetics, 232-234, 354, 424Alignment, 25Alternate designs, 29, 59, 60, 63, 114, 285, 371, 520-522Arches, 12, 15, 16, 31, 47, 354-382

frames, 12Assembly truss, see Truss, falsework

Balanced cantilever, see Cantilever constructionBallast, 62Bars:

Dywidag, 36, 52, 284, 330, 377, 380, 382, 404, 408, 411,412,432,433,538

high-strength, 34Macalloy, 340, 341, 342

Beam and winch, 20,91, 114-116, 128, 140, 510Bearings, 25, 29, 40, 41, 43, 83, 125, 132, 138, 203-205, 460,

461elastomeric, 68, 83, 96, 151, 158, 241-253, 418,426lateral guide, 325, 338, 341sliding, 326, 333, 414temporary, 325, 338, 341

Bidding procedures, 5 18-523alternate designs, 520-522design and build, 519single design, 5 18, 5 19value engineering, 5 19, 520

Box girder, 10, 12, 14, 15, 21, 35, 37, 41, 43, 47, 48, 49, 58,59, 68, 83, 88, 89, 103, 107, 109, 117, 138, 159, 160, 203,322

cast-in-place on falsework, 28, 29, 103efficiency, 159, 160torsional moments, 169, 170, 205transverse load distribution, 164, 169, 170, 202transverse moments in deck slab, 170variable depth, 37, 52, 203, 205

Box sections, see Box girder; Cross sectionBraking force, 331

Cable-stay, 12, 14, 16, 28, 400-440advantages, 401403structural style and arrangement, 403-405temporary system, 333, 349, 350

Camber, 40, 63, 71, 97, 205-210, 482-485Cantilever construction, 2-4, 11, 12, 17, 18, 23, 29, 31-146,

149cast-in-place, 17, 18, 29, 31-80

J

cast-in-place operation sequence (cycle), 18, 19, 38, 43,63

precast, 17, 18, 20, 29, 34, 82-147Casting yard and factories, 20, 103, 135, 138, 504-507Climbing forms, 45,49Competitive bidding, see Alternate designsConcrete:

composite, 541creep, 40, 62, 71, 82, 83, 151, 155-158, 206, 231, 363, 365curing, 114, 126, 466-469, 506design and properties, 466fiber-reinforced, 539, 540high-strength, 537-539lightweight, 58, 60, 72, 145polymer, 540, 541shrinkage, 17, 62, 71, 82, 83, 365shrinkage damage, 324

Construction:critical-path, 82joints, 21push-out, see Incremental launchingsegmental, see Segmental constructionsequence, see Erection sequencespeed, 18

Continuity, 34, 49, 85, 87, 158, 206Continuous superstructures, 155-158Contractual aspects, 518-535Contraflexure, 9, 21, 97, 113, 124, 150, 205Cranes:

barge (floating), 20, 22, 86, 87, 91, 109, 112, 138, 139, 237,238, 239, 311, 312

crawler, 20, 509floating, see Bargeportal, 20, 103, 105, 509swivel, 23truck, 20, 128

Creep, see ConcreteCross section, 162-169, 202, 203, 217-219

Deflections, 17, 40, 157, 158, 159, 205-210, 483Demolition, 352Depth-to-span ratio, 35, 43, 52, 69, 89, 149, 322,402, 405Design of segmental bridges, 148-223Deviation blocks, 310Diaphragms, 41, 53, 54, 57, 62, 67, 85, 90, 112, 124, 203, 204,

205, 207,332Differential settlements, 276-280Dimensional control, see Geometry controlDouble-T, 21, 322, 333

559

Zndex of Subjects

Earthquake, 49, 59, 71, 363, 390,418Ecology, 28,47, 304Economics, 5 18-535Environment, 18, 23, 27, 28, 29, 48, 99, 122, 304Epoxy, 488-493

joints, 17, 83, 87,96, 103, 112, 124, 127, 150, 199-202, 414Erection sequence, 66, 105, 127, 132, 133, 136, 341, 367, 397,

410,417Expansion joint, 12, 29, 41, 57, 68, 83, 97, 99, 107, 113, 125,

155,158, 205, 208, 303, 331, 345,414,418Expansion of long bridges, 158-159External post-tensioning, 23

Falsework bents, 25Fatigue, 210-212, 441Finger joints, 138Form traveler, 1, 17-21, 23, 36, 38, 40, 43, 50, 54, 58, 62-64,

70, 206, 302, 303, 475-478Free cantilever, see Cantilever constructionFriction, 321, 323, 330, 351Foundations, 225-280

Geometry control, 321, 322, 495-497, 499-504

Hinges, 21, 34, 35, 49, 50, 62, 124, 126, 150, 205, 208, 363Freyssinet concrete, 357, 365mid-span, 151, 155-159, 354

I-girder, 8-10, 28, 29, 525, 526Ice breaker, 124, 238, 239Incremental launching, 12, 18, 24-27, 34, 84, 321-353

alignment requirements, 343balanced casting, 322, 323casting area, 349construction principle, 343-346continuous casting, 322demolition by, 352design, 343-352launching methods, 349piers and foundations, 350-352span arrangement, 343-346superstructure type, shape and dimensions, 343-345

Investment, 18, 29

Jacking, lift-and-push, 323Jacks, Freyssinet flat, 360, 365, 374Joints, see Construction; Expansion joint; Finger joints; Hinges;

segments

Keys, 11, 112, 124, 136, 199-202,409

Launching gantries, 20, 22, 64, 67, 96, 98, 103, 105, 106, 109,117, 120-122, 124, 126-128, 134, 135, 141, 145, 511-517

Launching girder, see Launching gantriesLaunching nose, 25, 46, 322, 325, 331-333, 338, 341, 346-350,

380Launching sequence, see Erection sequenceLive load requirements, 149Long-bed, see Long-line methodLongitudinal bending, 2 12, 2 13Longitudinal closure strip, 112Long-line method, 85, 97, 103, 142, 143, 493-494

Match-cast, 11, 17, 43, 82, 83, 85, 96, 97, 117, 124, 130, 199-202.409.418

Match-cast joint, 199-202Material quantities, 219-220, 223Mayreder system, 377Median frame, 9, 11Model, 109, 112, 200, 201Mushroom girder, 21, 296, 298

Natural frequency, 418Negative moment tendons, see Cantilever construction; Prestress-

ing tendonsNeoprene bearings:

double-row, 230, 241-253influence of thickness and arrangement, 251-253properties, 245-248see also Bearings, elastomeric

Piers, 39-41, 49, 63, 68, 89, 91, 99, 100, 113, 225-280, 301, 304,308, 321,424

aesthetics, 232-234caps, 49deformation, 230, 231, 248-250, 257-261double elastomeric bearing, 241-253elastic stability with flexible legs, 261-263flexibility, 83, 158, 229, 230, 331foundation, 49, 68, 234-241for incremental launching, 350-352loads, 230-232moment-resistant, 228, 230, 234-241precast, 23, 228properties with double-row neoprene bearings, 250, 251properties with flexible legs, 257-261segmental, 543, 544stability during construction, 263-271temporary, see Temporary bentstemporary bracing, 105, 270, 27 1temporary stays, 271twin flexible legs, 228, 230, 253-263

Polyethylene pipe, 310Positive-moment tendons, see Continuity; Prestressing tendonsPrecast outrigger struts, 45, 73Precast piles, 135Prestressed concrete:

evolution, 4, 5evolution of bridges, 5-8precast girders, 8-10

Prestressing:continuity, 178, 179, 182future provisions, 212longitudinal, 69, 107, 109, 125, 213temporary, 83, 103, 132-134, 334, 348, 414three-dimensional, 36, 63, 69, 117transverse, 17, 49, 60, 61, 69, 94vertical, 17, 41, 69, 70, 125

Prestressing tendons:anchors, 470, 471cantilever, 87, 109, 114, 173continuity, 87, 109, 114, 149, 173corrosion protection, 537ducts, 470friction losses, 47 l-475glass fiber, 537

Index of Subjects 561

grouting, 475layout, 173, 174, 183, 184, 313, 471straight, 175, 176, 177, 348unbended, 475

Prestress losses, 61, 190, 206Principal stresses, 197, 198, 201, 216Problem areas, 220-222Progressive placement, 12, 18, 22-25, 35, 37, 84, 281-293

design aspects, 314-319Push-out construction, see Incremental launchingPylons, 16, 17, 408, 410, 411, 415, 418, 424, 426, 428

Railway, 26, 441-464design aspects, 458-464horizontal force, 459, 460loading, 441, 458, 459, 463

Redistribution of moments and stresses through concrete creep,183-189, 213-215

Reinforcement, compression, 36Relaxation. 155, 231Resal effect, 196, 263Rigid frames, 12, 14, 15, 382-392

Segmental bridge decks, 542, 543Segmental construction, 10-l 2, 17, 29, 30, 485-489Segments:

cast-in-place, 17, 18dimensional tolerances, 469fabrication, 82, 83, 85formwork, 469,470handling, 507-509precast, 17, 18, 22, 23size, 18, 83weight, 18, 83

Shear, 193-199, 202, 203, 215-217Short-line method, 90, 91, 109, 124, 126, 130, 494-

498Shrinkage, see ConcreteSlip-form, 43, 49, 99, 243, 298, 321, 424

Space frame bridges, 547, 548Span arrangement, 149-l 5 1Span-by-span construction, 12, 17, 18, 20-22, 34, 84, 282, 283,

293-314Span-to-depth ratio, see Depth-to-span ratioSplice, 9-11Standardized cross section, 130Stationary forms, 24Stray currents, 461Stress ribbon bridges, 545, 546Superelevation, 29, 103, 125, 302Superstructure:

cross section, see Cross sectionshape in elevation, 160, 161

Swing span, 428

T-beams, 21, 301Teflon, 49,83,132, 323, 326,338,414,418,430Temperature, 285, 302, 332, 365Temperature gradient, 170-l 73, 199Temporary bents, 323,333, 336,338,341, 345,396Thermal movement, 62, 83, 231, 345, 390Torsional moments in box girder, see Box girderTransverse load distribution, see Box girderTransverse moments in deck slab, see Box girderTransverse ribs, 67, 114Traveler, see Form travelerTruss, 12, 14, 47, 392-399

auxiliary, 31, 43, 45, 50, 52, 125, 128falsework, 22

Two-stage casting, 478, 479

Ultimate bending capacity, 190-193Uplift, 151, 204, 205

Value engineering, 143, 519-520

Wichert truss, 545Width-to-depth ratio, 149

podolny and muller - construction and design of prestressed concrete segmental bridges

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