The crossing that has been designed to replace the Pearl Harbor Memorial

Bridge, in New Haven, Connecticut, has the appearance of a cable-stayed

bridge with unusually short towers and a deep deck. In reality, the structure

is an extradosed prestressed bridge, the first application of this innovative

bridge design in the United States. By Steven L. Stroh, P.E., William R. Stark,

and Joseph E. Chilstrom, P.E.

First of Its Kind

54 0885-7024-/03-0008-0054/$18.00 per article Civil Engineering August 2003 August 2003 Civil Engineering 55

The new Pearl Harbor Memorial Bridge, right, will be the centerpiece ofthe Interstate 95 New Haven Harbor Crossing Corridor Improvement Pro-gram. The structure, an extradosed prestressed bridge, will look much likea cable-stayed bridge, but will have shorter towers and a relatively deepdeck, below. Simple, clean lines in keeping with the structure’s role as awar memorial figure prominently in the final form of the bridge, opposite.

The centerpiece of the Interstate 95 New HavenHarbor Crossing Corridor Improvement Pro-gram—which includes the reconstruction ofapproximately 7 mi (11 km) of I-95 in New Haven,

East Haven, and Branford, Connecticut—is the replacement ofthe bridge that carries the interstate over New Haven Harbor atthe confluence of the Quinnipiac and Mill rivers. This newbridge will be a signature structure for the New Haven area andis intended to live up to the name it will inherit from its prede-cessor, the Pearl Harbor Memorial Bridge.

The design of the new Pearl Harbor Memorial Bridgeincludes plate girder approaches and a three-span main cross-ing that will be built as an extradosed prestressed bridge.Twoalternative bridge designs are being fully developed for com-petitive bidding: a concrete extradosed prestressed bridge anda steel composite extradosed bridge.The latter is believed tobe the first design of its type in the world.

In an extradosed prestressed bridge, external prestressingcables are installed above the bridge deck and are deviated by

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The cast-in-place concrete superstructure is designedto be constructed via the balanced-cantilever methodusing a form traveler. It is anticipated that the schedulewill require the use of four travelers so that the cantileveroperations can proceed from both towers simultaneous-ly.The depth of the section is nominally 11.5 ft (3.5 m),deepening to 16.4 ft (5.0 m) over the supports.The sec-tion is longitudinally posttensioned with tendons inter-nal to the concrete, and the deck slab is transversely post-tensioned. Moreover, there are transverse externaltendons at the stay locations that anchor in the edgegirder and are deflected through the two central webs.

The stay cables are anchored in 3.3 ft (1.0 m) thickedge beams. A concrete diaphragm is provided in theouter tr iangular cell at each stay cable location.Diaphragms are provided in the inner cells only at thesupports.

The concrete superstructure has modular expansionjoints at the anchor pier locations. Pot bearings are usedat all supports, and the northbound and southboundstructures are each supported by three bearings at eachsupport. At tower 3 the center bearing is fixed and theouter bearings are guided transversely. At tower 2 and the anchor piers the center bearing is guided longitudi-nally and the outer bearings are free to translate in all directions. The maximum bear ing reaction is 12,140 kips (54,000 kN) for the center bearing at eachtower.

In the steel alternative, the main longitudinal systemfor the superstructure is composed of three main steelbox girders with vertical webs.These girders each have a9.5 ft (2.9 m) deep web and are constant in depth.Thestay cables are anchored in steel edge girders that are tiedto the main steel box girders by a lateral bracing system

in the plane of the girder top flange and by heavy verti-cal cross frames.The vertical component of the stay cableforce is carried by the cross frames, and the horizontalcomponent of the force is distributed into the systemthrough the lateral bracing system.

The web is 0.8 in. (20 mm) thick and is stiffened longi-tudinally. The top flanges vary from 16 by 1 in. (400 by 25 mm) to 24 by 4 in. (600 by 100 mm); the bottom flangeis 150 in.(3,800 mm) wide and varies in thickness from 1 to2 in. (25 to 60 mm).The bottom flange is longitudinallystiffened with two T stiffeners.

The edge girders each take the form of a box sectionbuilt up from two fabricated channel sections that are lacedtogether by bolted plates on both top and bottom.The crossframes and lateral bracing are built up from standard chan-nel and angle sections.

The deck slab in the steel alternative is cast-in-placeconcrete with an 11 in. (280 mm) depth spanning up to19.0 ft (5.8 m) between the box flanges.The final ridingsurface is a 2.6 in. (65 mm) asphalt overlay with a water-proof membrane.

Ballast concrete at the ends of the bridge within thebox girder cells counteracts uplift forces and eliminatesthe need for mechanical hold-down devices.This con-crete extends 6.9 ft (2.1 m) into the span at anchor pier1 and 14.1 ft (4.3 m) into the span at anchor pier 4.

The alternative steel superstructure has modularexpansion joints at the anchor pier locations. Three potbearings are used at the tower supports and two neoprenebearings and a steel shear lock are used at the anchor piers.At tower 3 the center bearing is fixed and the outer bear-ings are guided transversely.At tower 2 the center bearingis guided longitudinally and the outer bearings are free totranslate in all directions.At the anchor piers the neoprene

August 2003 Civil Engineering 5756 Civil Engineering August 2003

short columns above the piers. Typically this type ofbridge utilizes concrete box girder construction. Theresulting structure looks like a cable-stayed bridge with alow tower and a relatively deep deck. Structurally, how-ever, this system behaves very differently from a cable-stayed bridge.

The basic role of the stay cables in a cable-stayedbridge is to provide an elastic vertical support that carriesmost of the permanent and live loads. The cables aretherefore subject to substantial fatigue loading.The basicrole of the cables in an extradosed prestressed bridge is toimpart horizontal prestressing to the deck,while the decksystem provides the primary resistance to permanent andlive loads. Because the prestressing cables are inclined,they also provide additional resistance to shear, but theamount is less than in a true cable-stayed bridge. Thisarrangement results in relatively low fatigue stress in thecables and allows them to be stressed to levels close tothose in traditional prestressing.The designer of an extra-dosed prestressed bridge is free to apportion the perma-nent and live loads between the cables and the girderbased on cable and tower geometry, cable stiffness, anddeck stiffness.This freedom in selecting the load distribu-tion is the fundamental distinguishing feature of an extra-dosed prestressed bridge.

The extradosed prestressed bridge concept is general-ly attributed to Jacques Mathivat.The world’s first extra-dosed prestressed bridge is reported to be the OdawaraPort Bridge, which was completed in Japan in 1994.Some 25 extradosed prestressed bridges either have beencompleted or are currently under construction aroundthe world (see table on page 64). Twenty of these arelocated in Japan. The Japanese experience with thisbridge type, which serves as a transitional type betweengirder bridges and true cable-stayed bridges, is that it canbe quite economical for spans ranging in length from 400to 600 ft (120 to 180 m).

The selection of the extradosed prestressed bridgetype for the New Haven Harbor crossing was the out-come of a detailed study that also considered cost andappearance. The existing bridge at this site has a 387 ft(118 m) main span. It was desirable to increase that spanto 515 ft (157 m) to improve navigation, but a plate gird-er structure would not have been able to attain thatlength because of the structure depth limitations imposedby the approach grades, which in turn are dictated by theadjacent interchanges. A cable-stayed structure was con-sidered but was ruled out because of tower height limita-tions imposed by an adjacent airport. An extradosedbridge, however, could be designed with tower heightswithin the limits set by the Federal Aviation Administra-tion. The estimated cost of the extradosed bridge was

within 10 to 15 percent of that of the plate girder option,and it had the advantage of achieving the desired spanlength. Moreover its appearance would go far in meetingthe aesthetic desideratum of a functioning structure thatalso serves as a war memorial. In the end the Connecti-cut Department of Transportation, which owns thebridge, and the Federal Highway Administration, whichprovided project funding and oversight, determined thatthe extradosed prestressed bridge type best met thedesign conditions.

The concrete and steel alternatives are identical in lay-out, each having a 515.1 ft (157.0 m) long main span andtwo 248.9 ft (75.9 m) long side spans.The span layout wasselected to provide the necessary horizontal navigationaldistance and to minimize any uplift on the side span pierswhile keeping the extradosed prestressed spans out of thecurved alignment of the adjacent approach spans. Thebridge provides 62.0 ft (18.9 m) of vertical clearance fornavigation.

The bridge was designed in accordance with the Stan-dard Specifications for Highway Bridges, issued by the Amer-ican Association of State Highway and TransportationOfficials (aashto). Additionally, the CEB-FIP Model Codefor Concrete Structures, published by the International Fed-eration for Structural Concrete, based in Switzerland, wasused for the analysis of shrinkage and creep; the Recom-mendations for Stay Cable Design, Testing, and Installation,issued by the Post-Tensioning Institute (pti), of Phoenix,were used for the stay cable design; and the AASHTO LRFD

Bridge Design Specifications were used for strut-tie analysis.Concrete members were designed for service load

stresses and checked for ultimate strength. Steel memberswere designed using the load factor method and checkedfor overload and deflection under service conditions.

The strength of the concrete in the concrete super-structure is 5.9 ksi (41 MPa). In the towers and piers, aswell as in the deck of the steel alternative, the concretestrength is 5.1 ksi (35 MPa).The strength of the structur-al steel is 50 ksi (345 MPa), while 70 ksi (483 MPa) steelis used for selected negative-moment regions in a homo-geneous configuration.

The northbound and the southbound traffic are carriedon separate decks separated by a 10 ft (3 m) open median.Each deck carries five lanes of traffic and has a variable-width auxiliary lane as well as two 11.8 ft (3.6 m) shoulders.The overall width of each deck varies from 94.8 to 110.6 ft(28.9 to 33.7 m).

In the concrete alternative, the superstructure iscomposed of two separate concrete box girder struc-tures supported at their edges by the stay cables. Thefinal riding surface is an asphalt overlay with a water-proof membrane.

Anchor pier 1 Anchor pier 4Tower 2 Tower 3

248.9 ft (75.9 m ) 515.1 ft (157.0 m )

1,012.8 ft (308.7 m )

248.9 ft (75.9 m )

Navigational channel

Bridge Elevation

In the design for the new Pearl Harbor MemorialBridge, the maximum fatigue stress is 3.9 ksi (27.0 MPa)for the concrete alternative and 1.7 ksi (11.7 MPa) for thesteel alternative. Based on a review of the literature fromJapan and on a correlation of the fatigue performance ofstrands at various stress levels, a conservative allowablestress level of 0.55f´s for aashto group I loading and0.6f´s for other load groups was adopted for this bridge.

In addition to the in-service load conditions, thestructure is designed for the accidental loss of any staycable under full live load or for the replacement of anystay cable under a restricted live load with appropriatelevels of safety as specified by the pti specifications.

The stay cables are provided with viscous dampers tosuppress cable vibration. The outer stay sheath is alsodetailed with a raised helical rib to help avoid excitationscaused by wind and rain.

The twin northbound and southbound structures aresupported on common towers. Each tower has threeprincipal pylon legs extending above the deck and twoadditional intermediate columns below the deck level.The center pylon leg supports the cables for both thenorthbound and the southbound deck. The spacebetween the inner surfaces of the tower legs is slightlygreater than the width of the superstructure so that

there is room for the latter. The stay cables are conse-quently slightly inclined from the vertical. The towerlegs are hollow and made of cast-in-place concrete.They are constant in cross section and elliptical inshape.

The stay cables are anchored in steel frames that areencased in the upper region of the towers. Access insidethis frame is provided for inspection and maintenance.

The foundations are 7.9 ft (2.4 m) diameter drilledshafts extending to sandstone bedrock. The rock dipssharply along the length of the bridge from east to west.At anchor pier 4 the shafts are approximately 171 ft (52 m) deep and are end bearing on rock. At the otherlocations the shafts rely on a combination of rock socketfriction and end bearings. The shafts are 121 ft (37 m),62 ft (19 m), and 56 ft (17 m) long at respectively tower2, tower 3, and anchor pier 4.

The extradosed bridge concept gives the designer theflexibility to apportion the stiffness, and consequently the load distribution, between the cables and the deck.The stay cables for an extradosed prestressed bridge,unlike those in a true cable-stayed bridge, do not need tobe proportioned to carry the full vertical load compo-nent at each stay location; rather, they can be propor-tioned for a prescribed portion of

August 2003 Civil Engineering 5958 Civil Engineering August 2003

bearings have a sliding surface of polytetrafluoroethylene(ptfe) and stainless steel that is free to translate in all direc-tions. The shear lock at the anchor piers provides lateralrestraint and unrestricted longitudinal movement.

The steel alternative is constructed to carry all of thepermanent loads noncompositely, so that the deck slabmay be replaced in the future, as in conventional steelbridges.The side spans are erected first, each girder indi-vidually, with the aid of an erection truss that spansbetween the anchor pier and tower foundations.The sidespan girders are extended into the main span approxi-mately 100 ft (30 m) by cantilevering.The central 330 ft(100 m) of the main span is preassembled on barges, float-ed into position, and lifted into its final location as a unitby strand jacks lifting off of the cantilevered girders. Atthis point the structure can support itself by the steel gridalone. Next the stay cables are installed and stressed totheir final force. Then the concrete deck slab is pouredand the barriers and overlay are constructed.

The stay cable design for both alternatives is based onseven-wire, low-relaxation posttensioning strands ofgrade 1860.The cable size is 27 strands for the steel alter-native and 48 strands for the concrete alternative; thesame number of strands is used for all cables in each alter-native. The strands are of the same type used in typical

posttensioning applications. Stay cable corrosion protec-tion is provided by an ungrouted system consisting ofgreased strands encased in individual polyethylenesheaths, then bundled into an outer polyethylene sheath.The outer sheath is coextruded with a white coating.Thestays may be jacked either at the deck level or within thetower for both alternatives.

The maximum stress level in typical stay cables is lim-ited in accordance with pti specifications to 0.45f´s, f´sbeing the ultimate strength of the strand. For conven-tional prestressing the stress level is limited to 0.7f´s peraashto.The reduction of allowable stress for stay cables isin recognition of the fatigue demands on the strands in astay cable application.

The fatigue stress range for extradosed prestressedbridges is significantly lower than for cable-stayedbridges. For example, a fatigue stress range of 5.4 ksi(37 MPa) has been reported for the Odawara PortBridge, whereas pti specifications allow a fatigue stressrange for stay cables of 16 ksi (110 MPa). In recognitionof this difference with respect to cable-stayed bridges, ahigher initial cable stress is typically allowed for extra-dosed prestressed br idges. For example, for theOdawara Port Bridge an allowable cable stress of 0.6f´swas adopted.

Extradosed Prestressed Bridges throughout the World

Number Maximum Tower Girder Depth (ft)a YearName Location of Spans Span (ft)a Width (ft)a Height (ft)a Minimum Maximum Completed

Odawara Blueway Japan 3 400 (121.9) 31.2 (9.5) 35.0 (10.7) 7.2 (2.2) 11.5 (3.5) 1994Saint-Remy France 2 172 (52.4) 34.8 (10.6) 19.3 (5.9) 7.2 (2.2) 7.2 (2.2) 1996Tsukuhara Japan 3 590 (179.8) 30.5 (9.3) 52.5 (16) 9.8 (3) 18.0 (5.5) 1998Kanisawa Japan 3 590 (179.8) 50.8 (15.5) 68.9 (21) 10.8 (3.3) 18.4 (5.6) 1998Karato (Okuyama) Japan 3 459 (189.9) 28.5 (8.7) 39.4 (12) 8.2 (2.5) 11.5 (3.5) 1998Sunniberg Switzerland 5 459 (189.9) 30.2 (9.2) 48.5 (14.8) — — 1998Shikari Japan 5 459 (189.9) 72.1 (22) 33.1 (10.1) 9.8 (3) 19.7 (6) 1999Mitanigawa Daini Japan 2 305 (92.9) 55.8 (17) 42.0 (12.8) 9.8 (3) 19.7 (6) 1999Second Mandaue-

Mactan Philippines 3 607 (185) 59.0 (18) 60.0 (18.3) 10.8 (3.3) 16.7 (5.1) 1999Miyakoda River Japan 2 436 (132.9) 54.1 (16.5) 65.6 (20) 13.1 (4) 21.3 (6.5) 2000Yukizawa Japan 3 233 (71) 41.0 (12.5) 37.1 (11.3) 6.6 (2) 11.5 (3.5) 2000Matakina (Haneji) Japan 2 359 (109.4) 26.2 (8) 86.6 (26.4) 11.5 (3.5) 19.7 (6) 2000Suriagegawa dum Japan 2 276 (84.1) 23.0 (7) 54.1 (16.5) 12.5 (3.8) 16.4 (5) 2000Nakanoike Japan 2 199 (60.6) 57.1 (17.4) 38.7 (11.8) 11.5 (3.5) 13.1 (4) 2000Sajiki Japan 3 344 (104.8) 30.5 (9.3) 40.3 (12.3) 6.9 (2.1) 10.5 (3.2) 2000Pakse Laos 3 469 (142.9) 45.3 (13.8) 49.2 (15) 9.8 (3) 21.3 (6.5) 2000Hodu Japan 6 328 (100) 47.6 (14.5) 32.8 (10) 9.2 (2.8) 9.2 (2.8) 2001Ibi River Japan 6 891 (271.5) 95.1 (29) 98.4 (30) 13.1 (4) 23.0 (7) 2001Kiso River Japan 5 902 (274.9) 95.1 (29) 98.4 (30) 13.1 (4) 23.0 (7) 2001Yubikubo Japan 2 374 (114) 26.2 (8) 72.2 (22) 10.5 (3.2) 21.3 (6.5) 2002Shinkawa Japan 5 426 (129.8) 67.2 (20.5) 42.6 (13) 7.9 (2.4) 13.1 (4) 2002Hukaura Japan 5 295 (89.9) 35.4 (10.8) 27.9 (8.5) 8.2 (2.5) 9.8 (3) 2002Himi Japan 3 590 (179.8) 31.1 (9.5) 52.5 (16) 9.8 (3) 16.4 (5) 2002Shin-Meisei Japan 3 401 (122.2) 55.2–65.6 (16.8–20) 54.1 (16.5) 11.5 (3.5) 11.5 (3.5) 2003Pearl Harbor

Memorial U.S. 3 515 (156.9) 95.5–107.6 (29.1–32.8) 74.3 (22.6) 11.5 (3.5) 16.4 (5) 2004b

aMeters in parentheses. bYear of bid.

11.5 to 16.4 ft(3.5 to 5.0 m)

11.8 ft (3.6 m) Minimum 5 lanes at 11.8 ft (3.6 m) 11.8 ft (3.6 m)

16.7 to 22.6 ft(5.1 to 6.9 m)

23.0 ft (7.0 m) 16.7 to 22.6 ft(5.1 to 6.9 m)

94.8 to 110.6 ft (28.9 to 33.7 m)

19.7 in. (500 mm)

94.8 to 110.6 ft (28.9 to 33.7 m)

11.5 ft (3.5 m) 11.8 ft (3.6 m) 11.8 ft (3.6 m)Minimum 5 lanes at 11.8 ft (3.6 m)

Cross Section: Steel Alternative (Top) and Concrete Alternative (Bottom)

(continued on page 87)

August 2003 Civil Engineering 87

the load at each point where thecables are introduced into the deck.

In the case of the Pearl Harbor Memorial Bridge, thedesigner’s philosophy for proportioning the structure was asfollows: For the concrete alternative, the concrete girder wasproportioned based on the transverse requirements and themaximum depth based on grade restrictions; then the maxi-mum desirable amount of internal longitudinal posttension-ing for this section was established. The remaining requiredcapacity for dead and live loads was provided by the staycables. For the steel alternative, the steel girder was propor-tioned based on the available depth (using a constant webdepth) and the maximum desirable plate sizes.The availablemoment capacities were thus established. Based on theseavailable capacities, the remaining capacity required for deadand live loads was provided by the stay cables.The stay cableswere proportioned so that the same size cable could be usedthroughout and a constant final force in the cables of 0.55f´scould be achieved.

Analysis was conducted using computer software that con-sidered the effects of shrinkage and creep of the concrete overtime in addition to the time-related effects of the construc-tion sequence for each alternative.

For both alternatives the overall construction sequencecalls for the new northbound structure to be constructedfirst while two-way traffic is maintained on the existingbridge. Two-way traffic will then be shifted temporarily tothe new northbound bridge, and the existing bridge will bedemolished.The new southbound bridge will then be con-structed in the alignment of the previously existing bridgewhile two-way traffic continues on the completed north-bound bridge. Upon completion of the southbound bridge,northbound and southbound traffic will be rerouted into thefinal configuration.

Architectural input was included in the early stages of thedesign to assist in establishing the form and details of thebridge. Simple, clean lines in keeping with the structure’s roleas a war memorial figure prominently in the final form of thebridge. Aesthetic lighting that will simply and elegantly illu-minate the main pylons is also planned. The final design isscheduled for completion in December 2003, and it isexpected that the project will be advertised for constructionin mid-2004. �

Steven L. Stroh, P.E., M.ASCE, is a vice president and deputy direc-tor of surface transportation for URS Corporation in Tampa, Florida.William R. Stark, now retired, was a principal engineer for the Con-necticut Department of Transportation. Joseph E. Chilstrom, P.E., is abridge engineer for the Federal Highway Administration in Glaston-bury, Connecticut. This paper was presented as part of the 20thannual International Bridge Conference, held in Pittsburgh June9–11, 2003.

(continued from page 59)

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