:imbined strength ·elds are

f ASTM s. These rocesses. id build­: carbon imit this :d use in to 5 in.

ans and 1posilion 1stant in s, by in-

kations. :rease in

in. thick

1ich pre­n is that ncreased .dability. tructural

.perature content,

:e up the

,as good ~his fact, e to A-7, is rapid­steel will

General Discussion of Recent Ohio River Bridges Design Concepts

FRANK B. WYLIE, JR. , Principal Design Engineer

Hazelet & Erda!, Consulting Engineers

The title of tl1is presentation requires some definition of the term "recent." For the purpose of this paper let us use five years and limit the number of bridges to three. These three will be those of which .the author has some personal and in­timate knowledge. They have been designed by the firm of Hazelet & Erda!, con­sulting engineers to the States of Kentucky and Indiana.

The three bridges lie across the Ohio River between the Commonwealth of Ken­tucky and the State of Indiana. This illustration ( Slide No. 1) shows the loca­tions. In the order of construction, first is the Sherman Minton Bridge between Louisville, Kentucky and New Albany, Indiana on the National Defense Highway designated Interstate 64 . This bridge was completed and opened to traffic in De­cember, 1961.

The second is the new John F. Kennedy Memorial Bridge which was dedicated and opened to traffic on December 6, 1963. This is the bridge between Louisville, Kentucky and Jeffersonville, Indiana on Interstate 65 .

The third bridge which is now under construction and scheduled for completion in 1965 is on US-41 between Henderson, Kentucky and Evansville, Indiana.

Indianapolis \ O H I O

N D A N A

L L I N O I

' <. r I- ! '--- -

- ·- ·- ·---'

T E N N E

Nashville

C K Y

______ ______ ______ _,,

s s E E

SLI DE NO. I

83

It is beyond the scope of this paper to give the historical background for route locations, bridge site studies', traffic need and numerous other factors which deter· mined the bridge locations . Numerous studies of all these factors were made in each instance. In the case of the Henderson-Evansville Bridge, the location of the new structure is 150 feet downstream from and parallel to the existing bridge. When completed, the new bridge will serve the southbound roadway and the old will serve the northbound for an improved dual .roadway US-41.

SPAN LENGTHS

This map of the Falls Cities Kentuckiana area shows the definite locations of the proposed Interstate Highways and Expressway system in that vicinity (Slide No. 2 ). The two bridge sites on I-64 and I-65 are circled. In the crossing of any navigable stream, the most important single factor in selecting the length and loca­tion of the main span is the satisfactory accommodation of navigation. This has been recognized by the laws of our nation in the requirement that all bridges over navigable waters shall be approved by the U. S. Army Corps of Engineers insofar as location and horizontal and vertical clearances for navigation are concerned.

Please note the location of the Sherman Minton Bridge in the bend of the Ohio River downstream from the McAlpine Dam and its locks. The level of'this lower pool is subject to wider variations in water level than any other part of the Ohio River. For these reasons two navigable channels are required at this bridge site. These two channels made two 800-foot spans necessary for this structure.

At the upstream site of the Kennedy Bridge, water level fluctuation is restricted by the dam to periods of flood . However, the pool is wide and navigation uses both sides of the river except when directed toward the Portland Canal. This bridge lies between the Big Four Railroad Bridge and the Clark Memorial Highway Bridge both of which provide two navigation channels. Local traffic on the river uses the space between the two navigation channels. These features virtually dictated two 700-foot spans separated by a SOO-foot span for the Kennedy Bridge.

84

give of u Offi)

stat< !1

50,0 six I con~ latei app: stru, Brid Ken rive1 acce sligl nedi

T carr.

\\ the I

omy or c foun arch are I

F, datic occu coul, the t

Si the t

con ti cost! simp and pens com1 syst( reasc arch, steel was little

w supe nedy wide

Jr route h deter­in each the new ~- When old will

lions of y (Slide

of any 1d loca­'his has ;es over insofar

1eerned. he Ohio is lower he Ohio lge site.

estricted on uses , bridge :ighway he river dictated

/

TYPES OF SPANS

The factors which usually govern the selection of the type of structure for any given bridge span are, in the order of decreasing importance: economy, amount of traffic, economy, foundation requirements , economy, ease of construction, econ­omy aesthetics, economy and designers' preference. (This facetious listing merely states economy is the most important factor).

·' In the case of both the I-64 and I-65 bridges, estimated traffic counts exceed 50,000 vehicles daily and 3,600 vehicles for the Design Hour Volume. Hence six lanes must be provided for each bridge. For more than four lanes, double deck construction is nearly always cheaper for long span bridges because of the shorter lateral bracing and lloorbeams and the narrower piers. More often, the complicated approach construction for the double deck bridge overshadows the cheaper con­struction for the main spans. This was not the case for the Sherman Minton Bridge, therefore it is a double deck structure. The opposite was the case for the Kennedy Bridge; in fact, with limited room for the approaches on both sides of the river it was almost impossible to bring the grades down from the upper deck to the access and exit ramp levels at grade. This factor together with an estimated cost slightly favoring single deck construction made that the type selected for the Ken­nedy Bridge.

There was no other choice for the new .Henderson-Evansville Bridge. It is to carry only two lanes of traffic.

With number and lengths of spans and number of lanes and decks selected, the next determination is the type of superstructure. Here again the subject of econ­omy becomes most important. Which will be cheapter - simple spans, continuous or cantilever; trusses , girders, suspension or arches; steel or concrete? Of course, foundation conditions must be considered carefully for suspension bridges and true arches. In this country with relatively cheap steel, bridge spans over 400 feet long are usually built cheaper with steel trusses.

For both the sites of the Sherman Minton and Kennedy Bridges, rock for foun­dations is relatively accessible with cofferdam construction, although problems do occur as Mr. Whitaker's paper will show. Since the piers for these two bridges could be founded on rock, foundation conditions were not a determining factor in the type of superstructure.

Since two 800-foot spans were reyuired at the site of the Sherman Minton bridge, the type of superstructure is very nearly limited to two choices: either a two-span continuous or two simple spans. The two-span continuous bridge is usually less costly tlian two simple spans but it is not ordinarily a thing of beauty. Ordinary simple spans are not very pretty either. The tied arch is externally a sin1ple span and it can be a nice looking structure, but in the past it has been relatively ex­pensive to construct because of extensive falsework and extra steel required in the completed structu11e for erection. Because of its location over a part of the park system of Louisvill e, it was felt that the structure should be attractive and that a reasonably small increased cost to achieve that end could be justified. The twin tied arches shown in Slide No. 3 were the answer. Happily, with the use of high-s trength steel a11d modern erection eyuipment, oi'1ly 8 to11's of ad1itional steel for erection was added to the original design. Probably the final cost of this structure is very little different from that of the more prosaic two-span continuous bridge.

Where more than two long spans are necessary, continuous or cantilever type superstructures usually afford the best construction . This was the case for the Ken­nedy Bridge. Since the normal pool of the river at this site is nearly a half mile wide and two 700-foot spans separated by 500 feet were necessary, it was ea~y

85

SLIDE NO. 3 SHERMAN MINTON BRIDGE

to fit these req uirements with a five span multiple cantilever 2 ,500 feet long. ( Slide No. 4) The middle 500-foot span has double cantilevers over the two middle piers and the end spans are cantilevered over th e two outer river piers. The center 350 feet of both the 700-foot spans are su~pended spans.

The new Henderson-Evansville Bridge of necessity has the same spans as the older bridge. These are an unsymmetrical multiple cantilver arrangement. ( Slide No. 5) The first span from the south is 540 feet long made up of a 360-foot semi­suspended span and a 180-foot cantilever from the second span. This latter is 600 feet long, and is the anchor for a double cantilever. The fourth and northerly span is a 432-foot anchor span for the other cantilever in the third span. Finally, the center 360 feet of this third span is susp ended from the two 180-foot cantilevers.

MEMBER SELECTION AND DESIGN

Early in the preparation of preliminary design and plans for the Sherman Min­ton and the Kennedy Bridges, a conference of represen tatives of the States of Ken­tucky and Indiana, the Bureau of Public Roads, and the Consulting Engineers de­cided major criteria for the design of these bridges. There were:

1. the new heat treated, low-alloy, high strength weldable steel would be used where economical;

'2. the assembly of built-up members would be shop welded; 3. the field connections wo uld be ma de with high strength bolts; 4. the decks of the Sherm an Minton bridge would be susp ended from the arch

trusses with high strength wire rope or bridge strand; and 5. the consulting engineers would prepare and submit for approval special design

specifications incorporating these features.

DESIGN SPECIFICATIONS

The accepted design specifications for highway bridges in this country are the "Standard Specifications for Highway Bridges" of the American Association of State Highway Officials. Their scope is limited to spans of about 400 feet, however. The 1957 edition of those ·specifications was used as the basic design specification. For the design of welded bridges, the AASHO specification refers to the American Welding Society Specifications for Welded Highway a nd Railway Bridges and the 1956 edition of these specificiations was used. Both these specifications were modi· ficd by the design specifications for these specific projects as considered necessary to accommodate the longer spans and the newer materials.

The design live loading for th ese three bridges is the AASHO H20-Sl6, with the reduction fac tors for multi-lane lo adings where applicable. Research by a number of states has shown th a t live loadings of this intensity have never been experienced by medium and long span bridges. Furthermore, for spans of the range here dis· cussed, the dead load stresses in the chords and more highly stressed web members is from eighty to nin ety percent of the maximum stress. Fluctu ations of stress due to live load a nd impact in such members are quite small. With these observations,

86

~ I 1, ,dl!'TI I I I D J!

I m /Mr..w;,jk,-....+-i~-d :- (Slide · Ile piers 1ter 350 ,

I • s as the I i

t. ( Slide -- --1-ot semi· H~=,;;!;tilliil' r is 600 · ·ly span • ~ :. ;illy, the ~

.tilevers.

rn Min­of Ken·

,~:'.,'. I ill I \ J J J , tll!U,:; ~l ~

/"-1 1, 'I 11 ! I I I I I ""i 111 I I

~i the arch I ~

l design

are the ation of 10wever . .fication.

m~·~,, I a and the .,

re modi· ~ ~

!~ ssary to .,

..!:,.__

~ I~ -1 ~ ' ' ,:t

with the d

illUJ z

number . w ,erienced

. Cl

here dis· : :J (/)

~

11embers Iess due :vations,

I 87

LO

d z w Cl

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it was decided th at the permissible stresses for dead load would be increased ap­proximately ten percent as compared to the usual permissible stresses. These usual permissible stresses of the AASHO specifications for the plain carbon steels (ASTM A7 and A373) and the low alloy medium strength steels ( ASTM A242, A440 and A441) were retained for live load siresses. Refer to Slide No. 6. There are excep­tions to the application of the increased permissible stresses for dead load. These a re members which are stressed directly by application of live lo ad; such as, string­ers, lloorbeams and hangers; and members subject to large fluctuations or re­versals of stress under different positions of the live load; such as the chords in the anchor span of a double cantilevered truss.

Permissible stresses for the heat treated alloy steels of 90,000 and 100,000 psi yield strength are not covered by the Standard Specifications. These .steels were first used in major bridge .construction by California in the second Carquinez Straits Bridge. Drawing heavily on the experiences of that state with that bridge, it was decided to use a safety factor of 2 .5 based on the yield strength in tension fo r the basic permissible live load stress. In accordance with the policy adopted for the other steels, the basic permissible dead load stress was increased about ten per­cent. An AASHO Committee on High Strength Steels for Bridges has subsequently suggested the use of approximately the same safety factor for this material as that given for other steels by the Standard Specifications. This recommended stress is plotted as the dotted-line bar in the figure.

Permissible stresses for ASTM A36 steel are shown on the chart but this mate­rial was not used in the design of any built-up sections for these three projects be­cause it was not accepted as a fully weldable steel until late in 1962 . The fabricator for the new Henderson bridge is using this material as a substitute for tl1e A373 steel with no change in member areas.

At the time design and plans for the Sherman Minton Bridge were completed, the specified medium strength steel was a modified ASTM A242 . At that time, ASTM Specifications for A440 a~d A44 1 had not been developed and adopted. >

The material actually used and which met the requirements for the modified A242

100 100

90 ~ 90

~ ,,

80 " BO

,n ~ " \ 70

UN IT 60 ~ " ,.· 60

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MATERIAL A373 A36 -SLIDE. N0.6

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r/ "' TO 514" OV[" 3/411 OVtlll 1-1/l"

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88

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TO l • l/l" OVUI t-1/r TO•"

HEAT TREATED

of ti actu , COOlf

the p cond: e~ ua· men1 slide.

tsed ap­;e usual (ASTM AO and e excep-1. These , string­s or re­s in the

000 psi ere first : Straits :, it was . for the

for the ten per­!quently as th at

stress is

is mate­jects be­bricator 1e A373

npleted, .at time, 1dopted. :d A242

designation was a proprietary formula which meets the later A441 designation. Permissible stresses for compression members for plain carbon and low a lloy

steels are given by parabolic formulas in the Standard Specifications. These were used for live load stresses and increased by about ten percent for dead load in accordance with the provisions for tension. The secant formula was selected for tl1e. determination of permissible compression stresses for the heat treated, high­strength steel. Factors of 0.25 for inherent crookedness and eccentricity and three­fourths the point to point length because of bolted end connections were applied in the eccentricity term of the formula. All the column formulas were plotted in grap h form to make design work eas ier. (Refer to Slide No. 7).

36 - ...........

' ' 34

\ \

30 Mox.. HT- ·'\

28

26

12

10

\

ASTM A7, A373, A242, A440, A441

\ I I

a HT

I I I I I I

\

.:: 26

{24 ~ 22 0 3 20

' IB ..:

16

14

12

10

HEAT TREATED ALLOY STEEL

L • TOTAL LENGTH OF MEMBER

COMPRESSION MEMBER FORMULAS SLIDE NO. 7

f, • 1.000 1bs./ sq in.

Surely the reader has noted that the dual permissible stress system is extremely cumbersome in application. There are other ways to achieve the same eni:I . This author would favor the use of a modified live load for long span truss members rather than tampering with the dead load stresses or using arbitrarily modified permissible stresses.

Compression members are made up of "box" sections which will be illustrated later. For the component plates of such members, the Standard Specifications pre­scribe fixed width to thickness ratios for a given position of the plate in the mem­ber. Had these fLxed ratios been applied for these projects in which the range of compressive stress is quite wide, some of the more hig hly stressed members might have been composed of thin plates and subject to local buckling. Conversely some of the nominal members with low stresses would have had plates thicker than actually required to resist buckling. Accord ingly , thickness to width ratios were computed from the theoretical equation for critical buckling stress in plates for the plates making up compression members. Suitable safety factors for the various conditions of edge restraint were selected. The resulting dat.a computed from these e~uations gave safe width to thickness ratios as a function of working stress in the member. The data were plotted and the curv.es are shown at the right on this slide.(No.7)

89

The wind load was also modified by the special d esign specifications. The pres­sure specified by the Standard Specifications is based on a wind velocity of 100 miles per hour. The maximum recorded velocity at Louisville is 68 miles per hour. Thus, for the long spans the wind pressure for application to the trusses was re­duced by one-third which gives an equivalent design velocity of 82 miles per hour. This was considered reasonable.

TRUSS MEMBER SECTIONS

The double plane truss members are composed entirely of plates which are welded together. All the compression members and some of the tension members are " box" sections. The major compression members are double " boxes;" that is, they are made up of five plates as shown for the chords of the Sherman Minton Bridge. ( Slide No. 8) Minor compression members such as web members and major tension members are single " box" sections. Other tension members are made up of three plates weld ed into "I"or"H" sections.

L zr

SLIDE NQ. 8

TYPICAL CHORD SECTIONS

75 TO 226 3 SQ IN EFFECTIVE GROSS AREA

TYPICAL VERTICALS ANO DIAGONALS 26 7 TO 70 8 SO IN

EFFE CTIVE GROSS AREA

T'*l

TYPICAL TIE SECTION Htiol - Tttoltd Hi41h ·St ren9lh StHI

NET AREA 125 3 SQ IN

TYPICAL DIAGONAL BRACING

800' TRUSS SPAN OHIO RIVER BRiOGE LOUISVILLE - NEW ALBANY

c:.~:.~ ..... "~:::~

Formerly, the top chord members of cantilever trusses which carry high tensile stress were pin connected -eye-bars. The tension members are "H" shapes and con· nected with high strength bolts. The only pin connections in these trusses are those conn ecting the hangers for the suspended spans and connecting the chord members for ro tation or expansion at the ends of the suspended spans. Since the hangers and gusset plates are made of heat treated high strength plates, the pins are high strength forgings.

Refer to the detail of the tie section for the Sherman Minton Bridge. ( Slide No.8). Note that thicker plates than those of the main section have been welded In at the ends to make up for the reduction in area at the bolt holes. This one feature ac· co unts for a very large saving in material as compared to the riveted type of ten· sion member.

The sizes of the fillet welds joining the component parts of the members are governed by the plate of greater thickness. Since these welds do not transfer stress except in a secondary way, there is no other criteria for selecting the size. This

90

rais 1

The dilfe the The Not, long ofil plat• cro11

arr a essa strin dept 8001

n wou angl pect, load

Fe 10 ) cent< web ners The, rial : are COlllJ

high the t

was Pl

era! tl1e left o

\~ arch, simp force cons, ment of th 10-in floor perm

A1 deck:

he pres­, of 100 er hour. was re­

er hour.

hich are ·hers are ' that is,

Minton >ers and re made

ON ilnl

;QNAL

SPAN BRiOGE ALBANY .....

~h tensile and con· are those members

: hangers are high

ie No.8 ). in at the

!ature ac· pe of ten·

nbers are ,fer stress size. This

weld metal must be sound and as fully ductile as the base metal, however, because it participates in all the deformation of the stressed member throughout the length. The welds were all made continuous to seal the member and to eliminate stress raising craters at the ends of intermittent welds.

The floorbeam girders for all three bridges are single web welded construction. The lloorbeams for the two larger bridges offer a wide contrast because of the difference between single deck and double deck construction. The floorbeams for the Kennedy Bridge span 97 ft.-6 in. center to center of the trusses. (Slide No . 9). These are sizable girders by any standard. The depth at the center is over 9 feet. Note that the flanges are tapered in width from a straight center section 24 feet long. This arrangement permits design of the simple span with variable moment of inertia witho ut changing flange thickness and the resulting butt welds joining plates of different thickness. Note also that the top flange is sloped parallel to the crown slope of the deck. The stringers are continuous over the girders; thus, this arrangement eliminates large fill plates under the stringers, a lthough fil ls are nec­essary to accommodate the changing grade and vertical web alignment of the stringers. The floorbeams are vertical. A horizontal stiffener is placed one-fifth the depth of web below the top flange to permit minimum thickness of web. These floorbeam girders are designed of A441 steel.

Because the dead load deflection of these girders is sizable and the end rotations would produce secondary bending in the vertical truss members, the end connection angles were set and reamed with rotation opposite to the deflection. This was ex­pected to keep the end connections and the truss verticals truly .vertical under dead load.

For contrast refer to the floorbeams for the Sherman Minton Bridge ( Slide No . 10) shown in the "Typical Section." Here the trusses are 51 ft.-6 in. center to center. Beca use of the double deck construction, the floorbeams are actually single

1 web rigid frames. They are hung from the wire strand hangers at the upper cor­ners. The ties of the arches are supported in the " cut-outs " in the bottom corners. These frames are fabricated of A242 steel, but as was pointed out earl ier the mate­rial actually used is the saine as A441. The webs are 3/ 8-il;ch thick and the flanges are 14 inches wide and of varying thicknesses. There frames were designed to be completely shop welded but because of possible shipping size limitations, optional high strength bolted splices were designed at the approx im ate inflection points of the two girders. The optional sp lices were used by the Contractor because shipment was by rail.

Please note that these frames are supported laterally at the bottoms by the lat­eral bracing truss at the plane of the ties and the bottom flange. This bracing and ~1e end anchorages are shown schematically in the " Plan ·at Tie" at the upper left of the illustration.

Wh ile reference is made to this figure some other special features of the tied arches may be mentioned. As pointed out earlier the tied arch spans are externally simple spans. Hence longitudinal force may be res isted at only one end and lateral

, forces at both ends. For an 800-foot span the lateral end rotation is sizable and the consei;uent lateral loads on the usual fixed bearings produce large torsional mo­ments in the piers. The problem was solved here by elimination. All four corners of the simple . spans are supported on rocker bearings. The spans are fixed by a 10-lnch diameter pintle and socket at the center of the fixed pier and the portal floorbeam. The lateral anchorage at the expansion end is a large shear key which perm its longitudinal motion and resists lateral forces.

Another design feature illustrated here is the hanger system for supporting the decks from the overhead trusses. The hanger at each panel point consists of two

91

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russzJ H '- 9 ' 49·.,· "4 r,uss ,,.!.,r S S"o. t!'! 8 - <f •41 ·6· .,.:,i.,.:z· S S!"'a. t!t 11._,,_ •• 41:9• ,,.._// .. ~ ~ -:1>1' I I --"' I I ·~ --------- --1---H- - :..; ' - - -

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~ FLOOR IJ(AM • FBS

SLIDE N0.9

r-------~ ---~ • --~--- -------..... ---~---0::-- - -----0---- ---~:.....::..--~------<

TYPICAL SECTION

TYPlCAL PORTAL SLIDE N0.10

800 rT TAVSS SPAN OHIO RIVER 8A10G[

LOU~Sa':lhhi ~~::1~11.\NY

2 1/2-inch diameter bridge strands. Each strand has an ultimate load capacity of 375 tons. A safety factor of 3 was used; thus, the working load per strand is 125 tons. A double socket high strength steel casting anchors the lower ends of the strand and is connected to the floorbeam frames with high-strength turned bolts. Single cast steel sockets are attached to the upper ends of the strands. These two sockets are seated in pockets in a high strength steel casting which is bolted be­tween the gusset plates at the truss panel points. This arrangement permitted shim­ming at the upper socket seats for adjusting elevations.

The construction special provisions required that two complete assemblies com­prised of two strands, the sockets, seat castings and bolts be made and tested to destruction. Both these assemblies were tested to well over 750 tons, or 3 times the working load, before failure.

Another feature which must be considered carefully in designing with high strength steels is the magnitude of deformations. The heat treated high strength steel has approximately the same Modulus of Elasticity as plain carbon steel. If the working stress in the high strength steel is double that in the plain carbon steel then the defo rmation is doubled also. This was especially disadvantageous in the case of the tied arches. These spans are 797 ft. 6 in. center to center of bearings and the ties are fabricated of the high strength steel. The elongation of the tied arch from the cambered "no-load" length to full dead load is 11 1/ 2 inches, and the elongation under live load is another 2 inches. This meant that joints n"eed be pro­vided in the deck and continuous stringers to permit adjustments as the structure elongated when load was added.

FABRICATION AND INSPECTION

At the time these projects were advertised for proposals, no standard workman­ship or inspection specifications were available for welding the A242, A441 or the heat treated, high strength steels. There still are none available for the latter. As

93

has been mentioned, California was the only state with prior experience in the use of the latter steel.

It was decided that Supplemental Specifications would modify or add to the Standard Construction Specifications of the State supervising construction. This was Indiana in the case of the Sherman Minton and the new Henderson bridges and Kentucky for the Kennedy Bridge. The specifications in these projects re(Juire an end product rather than prescribe ways and means. Of course, since these bridges have been fabricated in sequence, something has been learned from the ex· periences with each.

The most important feature in fabrication of these structures is satisfactory welding. The specifications required that the-fabricator prepare welding procedure specifications and details for each type of joint that he proposed to use in fabri· cation. Furthermore, the fabricator was required to qualify by test each of his proposed procedures. Qualification was relJuired also for all welders and automatic welding machine operators. Since the AWS specifications were written only for plain carbon steel, it was necessary to modify and supplement those specifications for their use with the medium and high strength steels. As might be expected some factors were overlooked and conferences between fabricator, inspectors, steel pro· ducers, welding material manufacturers, State and BPR representatives and con· suiting engineers have been necessary to decide on remedial procedures.

It has been necessary to prescribe, define, review and work by trial and error to achieve sound procedures that can be qualified and used in production. The heat treated high strength steel is fully weldable but only with the proper procedure and tight control. It is especially important that the welding heating and cooling be carefully controlled to produce sound welds and prevent damage to the base metal. For this reason, inspectors are required to check the heat in the steel between weld passes with heat indicating crayons.

Then as a final welding inspection procedure, all butt welds in main material are radiographed and accepted in accordance with a standard code for such work. Some producers have been critical of the use of this code for bridge work. It is paragraph UW-51 of the ASME "Code for Unfired Pressure Vessels." It is felt, however, that this code insures sound welds and nothing less is acceptable in bridge structures. More than 25% of all the fillet welds are inspected by the magnetic particle method.

Finally, to insure proper fit of the main truss joints, the special provisions re­quired that all the holes for the high strength bolts be subpunched or subdrilled and reamed to full size while the complete joints were assembled. The splices for the continuous stringers and rigid frames were treated in a like manner.

STRUCTURAL STEEL QUANTITIES

It perhaps will be of interest to examine the i;uantities and distribution of the various types of steel in the trusses and floor sections of these three bridges. Slide No. 11 illustrates these points in the Sherman Minton Bridge. The quantities are the totals for the two tied arch spans and are taken from the final pay weights for this structure. Note that of the truss steel, the heat treated high strength type makes up 66% of the total weight.

The R. C. Mahon Company of Detroit was the contractor and fabricator for this bridge: The heat treated high strength steel in thicknesses over one inch and plates wider than 78 inches is "Tl" made by U. S. Steel Corporation and the remainder is "N-A-Xtra 100" made by the Great Lakes Steel Corporation. The erector for the contractor was the John F. Beasley Construction Company of Chicago and Dallas.

94

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I 95

Slide No. 12 is a similar illu stration for the J ohn F. Kennedy Memorial Bridge. 1 ote th at only typ ical areas of the trusses a re shown to illustra te the distribution tl11 of the ty pes of steel. Th e heat treated high strength steel ma kes up 61.5% of the ati total truss steel. It is apparent that this structure was des igned a fter th e ASTM in Designations A440 a nd A44 1 were accepted by the specify ing authorities. en

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The Allied Structural Steel Company of Chicago was the contractor. Most of the steel was fabricated a t its Hammond, Indiana pl ant. The U. S. Steel Corpor­ation "Tl " and "Tl , type A" steels a re the heat treated high strength material in this bridge. The Industrial Construction Company, a subsidiary of Allied, erected the steelwork.

The next and final slide (No. 13) shows the steels in the Henderson Bridge. Note that A36 steel was available and the stringers were designed using it. At the time of the design, it was not considered acceptable for welding as previously stated. One matter of interest is the smaller percentage of the heat treated high strength steel in these trusses - only about 48%. This could be expected, of course,

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as compared to the larger amounts in the other two bridges, because the loads carried by this two-lane bridge are much lighter than the others.

The contractor for the superstructure of this bridge is the John F. Beasley Con­struction Company of Chicago and Dallas ( the same company that erected the Sherman Minton Bridge). They will a lso erect the steelwork for this bridge. The fabricator is the Vincennes Steel Division of the Novo Industrial Corporation at Vincennes, Indiana. Again, the "Tl" and "Tl , type A" steels are being used where heat treated high strength steel is required.

As consulting engineers it is our hope that we may have an opportunity to design more structures of this nature. Most certainly, if we do, we shall probably be using not only the different types of steels in these three bridges but even newer types which even now are being developed by the producers. We trust that the in· dustry will, at the same time, develop and improve welding equipment and tech- pr, niques which can be used for these newer steels. Simultaneously, faster and less costly methods of inspection and quality control are desirable to keep pace with these techniques.

This discussion has been limited to major factors in the design of the super­structures and the use of newer steels. The substructures are a lso interesting and $Orne parts of the design presented real problems but time does not permit their consideration. The next two papers will give you the more interesting features of construction and problems involved therein.

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