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An Overview ofPrecast Prestressed

♦ Segmental Bridges

Walter Podolny, Jr.Bridge DivisionOffice of EngineeringFederal Highway AdministrationU.S. Department of TransportationWashington, D.C.

The seventies will be recorded byengineering historians as the de-

cade in which prestressed concretesegmental bridge construction came ofage in North America. Segmental boxgirder bridges have attracted the at-tention and captured the imaginationof bridge engineers and designersacross the continent.

Because of practical limitations ofhandling and shipping, the precastprestressed I-girder type of bridgeconstruction is limited to an approxi-mate range of 120 to 150-ft (37 to 46m) spans. Beyond this range of span,post-tensioned cast-in-place box gir-ders on falsework are more attractive.However, in certain instances the ex-tensive use of falsework can prove tobe an economic disadvantage. Wheredeep ravines or navigable waterwaysmust be crossed, extensive formworkmay be impractical.

Construction in this manner mayalso have a serious impact upon envi-ronment and ecology. Prestressedsegmental construction has extendedthe practical span of concrete bridgesto approximately 800 ft (244 m).Where segmental construction is usedin conjunction with the cable-staybridge concept, the span range can beextended to 1300 ft (400 m) andperhaps longer.'

Because construction of the super-structure is executed from above, i.e.,at deck level, the use of extensivefalsework is avoided. Thus, there is noeffect upon navigation clearance fromfalsework during construction and thecost of extensive formwork is elimi-nated. Segmental viaduct type bridgesprovide a method whereby the impactof highway construction through en-vironmentally sensitive areas can beminimized.

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Utilization of an elevated viaducttype structure requires only a rela-tively narrow path along the align-ment to provide access for pier con-struction. Once the piers have beenconstructed, all construction activity isfrom above. Thus, the impact on theenvironment is minimized. Also, be-cause the structure is elevated, as op-posed to an at-grade highway, there isno interference with wild life migra-tory habits.

Prestressed concrete segmentalbridges have proven to be estheticallyappealing and, because various con-struction methods can be used, thestructures are cost effective and en-vironmentally adaptable.

Evolution ofSegmental Bridges

Before discussing the various facetsand variants of precast segmental boxgirder bridges, it may enhance theunderstanding of this type of con-struction to briefly trace the historical

evolution of prestressed concretebridges to this point in the state-of-the-art and to present a few basic de-finitions.

Precasting of elements or membersof a structure implies that the concreteis cast in forms at some location otherthan the final position of the member.The member may be cast at a perma-nent precasting plant at some locationother than the construction site; thentransported by truck, rail, or barge tothe site; and eventually erected to itsfinal position. The member may alsobe cast at some location in closeproximity to the construction siteeliminating the transportation fromprecasting plant to construction site.In either situation the member is castat a location other than its final posi-tion in the structure.

Segmental construction has beendefined as "... a method of construc-tion ... in which primary load carry-ing members are composed of indi-vidual segments post-tensioned to-gether."2

As early as 1948, Eugene Freyssi-

PCI JOURNAL/January-February 1979ҟ 57

Fig. 1. Marne River Bridge near Paris, France. (Courtesy: Figg and MullerEngineers, Inc., Tallahassee, Florida.)

net, the great French prestressingpioneer, used prestressed concrete forthe construction of five bridges overthe Marne River near Paris, withspans of 240 ft (73 m) having an ex-ceptionally light appearance (Fig. 1).Construction of these bridges, as indi-cated in Fig. 2, utilized precast seg-ments which were post-tensioned to-gether. Thus , by definition, these fivestructures can be called precast pre-stressed segmental bridges.

Prestressing of bridges in NorthAmerica did not start until about1949.* The first prestressed bridge inthe United States was built in Madi-son County, Tennessee. This bridge

*An interesting historical account of the early prestressedbridges in America is given by Charles C. Zollman in"Reflections on the Beginnings of Prestressed Concretein America—Part 1: Magnel's Impact on the Advent ofPrestressed Concrete; Part 2: Dynamic American En-gineers Sustain Magnel's Momentum," PCI JOURNAL,V. 23, Nos. 3 and 4, May-June and July-August 1978, pp.22-48 and pp. 30-67. See also Ross Bryan's article on"Prestressed Concrete Innovations in Tennessee," pub-lished in the current PCI JOURNAL, pp. 14-31.

was made using a series of machine-made blocks (strung like beads on astring) which were prestressed to-gether to form a beam.

The construction method (althoughvery crude by modern standards) issimilar, in principle at least, to today'sprecast prestressed segmental bridges.

The Tennessee prestressed blockbeam bridge was followed veryshortly by the famed Walnut LaneBridge in Philadelphia, Pennsylvania,in 1950. The 160-ft (48.8 m) longbeams were cast-in-place and post-tensioned.

Soon thereafter, precast preten-sioned bridge girders evolved result-ing from inherent economies andquality control of plant fabricatedelements. With few exceptions, duringthe fifties and early sixties, mostmulti-span precast prestressed bridgesbuilt in the United States were de-signed as a series of simple spans.

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They were designed with standardAASHTO-PCI girders of various crosssections in spans ranging up to about100 ft (30.5 m), but more commonlyfor spans of 40 to 80 ft (12 to 24 m).The advantages of a continuous cast-in-place structure were abandoned infavor of the more economical con-struction offered by plant producedstandardized units.

During the middle sixties a growingconcern with regard for safety of thehighways asserted itself. An AASHTOTraffic Safety Committee report in1967 called for:

"Adoption and use of two-spanbridges for overpasses crossing di-vided highways ... to eliminatethe bridge piers normally placedadjacent to the shoulders."

It soon became apparent that theconventional precast pretensionedAASHTO-PCI girders were limited bytheir transportable length and weight.Transportation over the highwayslimits the precast girder to a range of

100 to 120 ft (30.5 to 36.6 m) in lengthdepending upon local regulations.

As a result of longer span require-ments, a study was conducted by thePrestressed Concrete Institute incooperation with the Portland CementAssociation. 4 This study proposedsimple spans up to 140 ft (42.7 m) andcontinuous spans up to 160 ft (48.8 m)be constructed of standard precastgirders up to 80 ft (24 m) in lengthjoined together by splicing and post-tensioning. To obtain longer spans theuse of inclined or haunched piers wasproposed. In general, these conceptsutilized precast I- or box girders withfield splices and post-tensioning forcontinuity.

This type of construction, usinglong standard precast prestressedunits never quite achieved the popu-larity that it merited. Despite somelimitations, the method is adaptablefor spans up to 200 ft (61 m).

The concepts developed by thePCI-PCA studies fall into the defini-

Fig. 2. Marne River Bridge near Paris, France. (Courtesy: Figg and MullerEngineers, Inc., Tallahassee, Florida.)

PCI JOURNAUJanuary-February 1979 59

rig. s. unoisey-Le-Roi Bridge over the Seine River south of Paris, France.(Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

tion of precast segmental constructionand might be described as "longitudi-nal" segmental construction. The in-dividual elements are long with re-spect to their width.

As spans increased, designersturned toward utilization of post-tensioned cast-in-place box girderconstruction. The Division of High-ways, State of California, includingseveral other states, have been quitesuccessful using cast-in-place, multi-cell, post-tensioned box girder con-struction for multi-span structureswith spans of 300 ft (91.5 m) andlonger. However, this type of con-struction has its disadvantages; it re-quires extensive formwork duringcasting with its undesirable impactupon the environment and/or ecology.

Meanwhile in Europe, segmentalconstruction proceeded slightly dif-ferently in conjunction with box gir-der design. Segments were cast-in-place or precast in relatively shortlengths, providing full roadway widthand depth. Today, "segmental con-struction" is generally recognized ashaving been pioneered in Europe.

Ulrich Finsterwalder, in 1950, was

the first to apply cast-in-place seg-mental prestressed construction in abalanced sequence to a bridge cross-ing the Lahn River at Balduinstein,Germany. This system of cantileversegmental construction rapidly gainedacceptance in Germany, especiallyafter the successful completion of abridge crossing the Rhine River atWorms in 1952.5 Since then, the con-cept has spread across the entireworld.

Concurrently, precast segmentalconstruction was evolving during thisperiod. In 1952, a single span countybridge located near Sheldon, NewYork, was designed by the FreyssinetCompany. Although this bridge wasconstructed using longitudinal seg-ments, rather than transverse seg-ments, as was being done in Europe,the structure represents the first prac-tical application of match casting. Thistechnique has become an importantdevelopment in precast segmentalconstruction.

The bridge girders were dividedinto three longitudinal segments thatwere cast end to end. The center seg-ment was cast first and the end seg-

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Fig. 4. JFK Memorial Causeway, Corpus Christi, Texas.

ments were cast directly against thecenter segment. Keys were cast at thejoints so that the three precast ele-ments could be joined together at thesite in the same position they had inthe precasting yard. Upon shipment tothe job site, the three elements of agirder were post-tensioned togetherwith cold joints.6'7

The first major application of matchcast, precast, segmental constructionwas not realized until 10 years later,in 1962, in France. This structure, de-signed by Jean Muller,* was theChoisy-Le-Roi Bridge located south ofParis crossing the Seine River (Fig. 3).Since then the concept has been re-fined and has spread from France tomany other countries.

The first precast segmental bridgeto be built in North America was theLievre River Bridge located on High-way 35, 8 miles (13 km) north of NotreDame du Laus, Quebec. The bridge,which had a center span of 260 ft (79.2m) and end spans of 130 ft (39.6 m),

was built in 1967. The Bear RiverBridge, Digby, Nova Scotia, followedin 1972 with six interior spans of 265ft (80.8 m) and end spans of 203.75 ft(62.1 m).

The JFK Memorial Causeway, Cor-pus Christi, Texas (Fig. 4) representsthe first precast prestressed segmentalbridge completed in the UnitedStates. It was opened to traffic in1973. Designed by the Bridge Divi-sion of the Texas Highway Depart-ment, this structure has a center spanof 200 ft (61 m) with end spans of 100ft (30.5 m).

In the United States, currently(1979), the author is aware of at least24 precast segmental bridge projectsthat are either completed, in con-struction, or in design and planningstages (see Table 1). There are un-doubtedly many more.

*Jean Muller, formerly chief engineer with EntreprisesCampenon Bernard, Paris, France, is currently inpartnership with Figg and Muller Engineers, Inc., withoffices in Tallahassee, Florida, Washington, D.C., andParis, France.


Table 1. Precast Segmental Concrete Bridges in North America.

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Advantages of PrecastSegmental Construction

In many instances where pre-stressed concrete segmental bridgedesign alternates have competedagainst structural steel designs theyhave proven to be cost effective. Aspreviously indicated, when comparedto more conventional methods of con-crete construction, prestressed con-crete segmental construction has ex-tended the span range for concretebridges and is competitive in the in-termediate and long span range. Themethod eliminates the need for costlyfalsework and minimizes its impact onthe environment.

In general, the economic feasibilityof cast-in-place or precast segmentswill be determined by site conditions,site accessibility, available erectionequipment, time to construct and/orerect the segments, and the relativeeconomic trade-off in transporting afinished segment as opposed to trans-porting constituent materials.

AdvantagesThe often cited advantages of pre-

cast segmental construction are:• Fabrication of the segments can

be accomplished while the sub-structure is under construction,and thus, erection of the super-structure is speeded up.

• By virtue of precasting andmaturity of the concrete at thetime of erection, the time re-quired for strength gain of theconcrete is removed from theconstruction critical path.

• As a result of the maturity of theconcrete at the time of erection,the effects of concrete shrinkageand creep are minimized.

• Quality control of factory pro-duced precast concrete.

Disadvantages

The disadvantages of precast seg-mental construction are:

• Necessity for a high degree ofgeometry control during fabrica-tion and erection of segments.

• Temperature and weather limi-tations regarding mixing andplacing epoxy joint material.

• Lack of mild steel reinforcementacross the joint and therefore alimitation of tension stress acrossthe joint.

It should be noted that for large-sized projects, it is no longer difficultto set-up fully mechanized concretesite mixing equipment. With today'stechnology, it is possible to produce ahigh quality concrete at the site.Therefore, for large projects, it isdoubtful whether factory producedconcrete has an advantage over siteproduced concrete except for the im-portant aspect that loads and pre-stressing forces are applied at a laterage on a more mature concrete.

Types of PrecastSegmental Construction

It has been observed' that thetechnology for constructing segmentalbridges has rapidly advanced in thelast decade. During the initial de-velopment of segmental bridges theywere constructed by the balancedcantilever method.

Currently, such techniques asspan-by-span construction, incremen-tal launching, and progressive placingare also being utilized. Thus, there arenow a variety of design concepts andconstruction methods which may beused to economically produce seg-mental bridges for almost all site con-ditions.


Fig. 5. Sallingsund Bridge, Denmark, showing balanced cantilever construction.

Balanced Cantilever Construction

The balanced cantilever method ofconstruction, sometimes referred to asthe free cantilever method, was de-veloped out of a need to eliminatefalsework. Not only is falsework ex-pensive, but it is a temporary structureand, as such, is designed with smallmargins of safety, as has been indi-cated by some falsework failures.

In waterways that are subject tospring flash floods, falsework can bewashed away resulting in potentialdamage to the structure, lost con-struction time, and possible financialruin. In navigable waterways, false-work is either not allowed or is se-verely restricted. With cantilever con-struction, falsework is eliminated be-cause precast segments are erectedand supported from the pier or the al-ready completed portion of the struc-ture.

In this method of construction seg-ments are simply cantilevered fromthe preceding pier in a balanced se-quence on each side until midspan isreached. Then a closure placement ismade with a previous half-span can-

tilever from the preceding pier (Fig.5). This procedure is then repeateduntil the structure is completed.l,s

Unless symmetrical segments aresimultaneously erected, the pier willbe out of balance by one segment.The moment caused by this imbalancecan be accommodated by a momentresistant pier. Where the pier is notmonolithic with the superstructure, atemporary moment resistance may beprovided by temporarily "clamping"the superstructure to the pier, pro-vided the pier is designed to take thetemporary moment. Where feasible,temporary bracing may be provided(Fig. 6). Obviously, the imbalancemust be maintained on the side of thepier where the bracing is located.

This concept utilizes a dual systemof prestressing tendons. Cantilever(negative moment) tendons are re-quired at the top of the segments fordead load cantilever stresses [Fig.7(a)] and then after closure, atmidspan, continuity (positive mo-ment) tendons [Fig. 7(b)] are installedto accommodate the positive momentin the continuous structure. Because

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of the high cantilever moments duringconstruction, which are reduced bymoment redistribution in the finalstructure, a slightly larger amount ofprestressing is required compared to astructure supported on falsework.

In continuous structures the finalstresses in the completed structure aresubstantially different from what theywere initially during cantilever con-struction. However, subsequent con-crete creep and steel relaxation willtend to make the initial and finalstresses approach each other. Thismeans that there will be a redistribu-tion in the moments and stresses ofthe structure. In general, the negativemoments over the piers will decreasewhile the positive moments atmidspan will increase by a corre-sponding amount. This redistributionof moments must be accommodatedin the design.

Normally in precast balanced can- Fig. 6. Konoshima Ohashi Bridge, Japan.

diaphragm closure pour

Rcantilever tendons

main pier central span

100 ft (30.48 m)

(a)

Fig. 7. Balanced cantilever method, system of prestressing tendons(JFK Memorial Causeway, Corpus Christi, Texas).


Fig. 8a. Kishwaukee River Bridge nearRockford, Illinois.

tilever construction, tendons are of thestrand type. However, in the Kish-waukee Bridge (Figs. 8a and 8b) lo-cated near Rockford, Illinois, tendonswere of the Dywidag thread bar type.In so far as the author is aware, this isthe first time that Dywidag bars havebeen used in conjunction with precastsegmental construction. The bar typetendon was allowed in the specifica-tions issued by the Illinois Depart-ment of Transportation to encouragecompetition.

Span-by-Span ConstructionThe balanced cantilever construc-

tion method was developed primarilyfor long spans, such that constructionactivity for the superstructure couldbe accomplished at deck level withoutthe use of extensive falsework. Asimilar need exists for long viaductstructures with relatively shorterspans. The German firm of Dyckerhoff& Widmann pioneered the develop-ment of a system whereby the super-structure is executed in one direction,span-by-span, by means of a moveableform carrier.

Although the span-by-span methodhas been used for cast-in-place con-struction, a method for precast span-

Hg. 8b. Precast segments for Kishwaukee River Bridge near Rockford, Illinois.

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Fig. 9. Span-by-span erection (Long Key Bridge, Florida).

by-span construction has been pro-posed as a successful alternative forthe Long Key Bridge project (currentlybeing built in the State of Florida). Astructural steel trusswork (Fig. 9) isused to support the precast segmentswhich are installed progressively fromone end of the structure to the other inspan increments.

The steel trusswork has a lengthequivalent to the span of each identi-cal interior span. It is placed by thesame floating crane that handles allprecast segments and further adjustedby a system of hydraulic jacks with re-gard to the piers. Upon completion ofa span, the trusswork is released andmoved over to the next span to start anew cycle of operations. As a conse-quence, in this method of constructionprestressing requirements are verysimilar to those of a cast-in-placestructure.

Interesting variations from normalprecast segmental construction on theLong Key project are that dry jointswill he used between the segments,i.e., no epoxy; and the longitudinalprestressing tendons are external,namely, inside the box.

Progressive PlacingProgressive placing is similar to the

span-by-span method described abovewhereby construction starts at one endof the structure and proceeds continu-ously to the other end of the structure.The progressive placing method de-rives its origin from the balanced can-

tilever concept. In this method theprecast segments are placed continu-ously from one end of the structure tothe other in successive cantilevers onthe same side of the various piersrather than by balanced cantilevers oneach side of the pier.

Currently, this construction methodappears to be practical in span rangesfrom 100 to 200 ft (30 to 60 m)? Be-cause of the length of cantilever (onespan) in relation to constructiondepth, the stresses become excessiveand a moveable temporary stay ar-rangement must be used to limit thecantilever stresses to a reasonablelevel.

The erection procedure is illus-trated in Fig. 10. Segments are trans-ported over the completed portion ofthe deck to the tip of the cantileverspan under construction where theyare positioned by a swivel crane thatproceeds from one segment to thenext. Approximately one-third of thespan from the pier may be erected bythe free cantilever method, the seg-ments being held in position by ex-terior ties and final prestressing ca-bles.

In the balance of the span, eachsegment is temporarily held in posi-tion by external temporary ties and bytwo stays from a moveable tower lo-cated over the preceding pier. Thetwo stays are -continuous through thetower and anchored in the previouslycompleted span deck. The stays areanchored to the top flange of the box


Fig. 10. Progressive placing erection (Reference 7).

girder segments such that the tendonsin the stays can be adjusted by lightjacks.

This type of construction has beenused for the Rombas Viaduct (Fig. 11)constructed by Campenon Bernard ineastern France. The bridge, located inan urban area, is a dual structure ofnine continuous spans ranging from82 to 148 ft (25 to 45 m) in length. Thesingle cell box sections have a con-stant depth of 8.2 ft (2.5 m). A view ofthe swivel crane picking up the seg-ments from the transport dolly isshown in Fig. 12.

Fig. 11. Rombas Viaduct underconstruction in eastern France.(Courtesy: Figg and Muller Engineers,Inc., Tallahassee, Florida.)

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Fig. 12. Lifting of precast segment for Rombas Viaduct in eastern France.(Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

Fig. 13. Photomontage of the Linn Cove Viaduct at Blue Ridge Parkway, NorthCarolina. (Courtesy of Region 15, Federal Highway Administration.)


Fig. 14. Rendering of the Linn Cove Viaduct at Blue Ridge Parkway, NorthCarolina. (Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

A progressive placing scheme isproposed for the Linn Cove Viaducton the Blue Ridge Parkway in NorthCarolina (Figs. 13-14). Because of theenvironmental sensitivity of the area,access to some of the piers is notavailable. Therefore, the piers will beconstructed from the tip of a can-tilever span, with men and equipmentbeing lowered down to construct thefoundation and pier. The piers areprecast segments stacked verticallyand post-tensioned to the foundation.

Because of the extreme curvature ofthe alignment, the use of temporary

stays was impractical. Temporarybents at midspan will be used to re-duce cantilever and torsional stressesduring construction to acceptablelevels. Erection of the temporarybents will be accomplished in thesame manner as the permanent piers,utilizing the swivel crane at the end ofthe completed cantilevered portionsof the structure. When temporarybents are no longer required, they willbe dismantled and removed byequipment located on the completedportion of the bridge deck. ConsultingEngineers for this structure are Figg

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Casting bed andetnlinnnry fnrmc Direction of launching ---0

Fig. 15. Incremental launching, casting bed and launching arrangement.(Courtesy: Fritz Leonhardt, Stuttgart, West Germany.)

and Muller Engineers, Inc., workingfor Region 15 of the Federal HighwayAdministration and the Park Services.

Incremental LaunchingAnother variant of the segmental

concept, which is new to Americanbridge engineers and contractors, hasevolved in Germany and is called"Taktschiebeverfahren." Literallytranslated taktschiebeverfahren means"phased shoving concept." In NorthAmerica it is refered to as incrementallaunching or push-out construction.This concept was first implemented in1962/63 on the Rio Caroni Bridge inVenezuela, built by its originatorsWilli Baur and Dr. Fritz Leonhardt ofthe consulting firm Leonhardt andAdra, Stuttgart, West Germany.'°' n

The bridge superstructure is con-structed in an on-site factory in sta-tionary forms behind the abutment in

lengths of 33 to 100 ft (10 to 30 m)(Fig. 15). After a segment reaches suf-ficient strength, it is post-tensioned tothe previous segment and the entiresuperstructure is pushed out lon-gitudinally one increment length. Thesucceeding segment is then castagainst its predecessor. Normally, awork cycle of one week is required tocast and launch a segment, irrespec-tive of its length. Operations arescheduled such that the concrete canattain sufficient strength over aweekend to allow launching at thebeginning of the next week (Fig. 16).

Bridge alignment in this type ofconstruction is either straight or on acurve; however, the curve must be ofconstant radius. This requirement ofconstant rate of curvature applies toboth horizontal and vertical curvature.The Val Ristel Bridge in Italy whichwas incrementally launched on aradius of 500 ft (150 m) is illustrated in


bearings are made of teflon (PTFE)faced steel-reinforced neoprene padswhich slide on polished stainless steelplates (Fig. 18).

There are two methods of launch-ing. The method used on the Rio Ca-roni Bridge has the jack bearing on anabutment face and pulling on a steelrod, which is attached to the last seg-ment cast by launching shoes. Thesecond and more current method con-sists of a horizontal and vertical jack(Fig. 19).

The vertical jack slides with a teflonplate at its base on a stainless steelplate and has a friction element at thetop to engage the superstructure. Thevertical jack lifts the superstructureapproximately 3/1 6 in. (5 mm) forlaunching. The horizontal jack thenmoves the superstructure longitudi-nally. After the vertical jack has

Fig. 16. Schematic drawing of incrementallaunching sequence. (Courtesy: FritzLeonhardt, Stuttgart, West Germany.)

Fig. 17. This then implies that road-way geometry is dictated by construc-tion rather than the present practice inthe United States, where geometrydictates construction.

To counteract the varying bendingmoments that occur during thelaunching operation, the superstruc-ture is concentrically prestessed. Inaddition, a launching nose (Fig. 16) isprovided in order to preclude the de-velopment of excessively large bend-ing moments during launching.

The concentrically prestressed su-perstructure is pushed forward lon-gitudinally in successive incrementsby means of hydraulic jacks. To ac-commodate the movements of the su-perstructure, temporary sliding bear-ings are installed on the piers. These

Fig. 17. Val Ristel Bridge, Italy.(Courtesy: Fritz Leonhardt, Stuttgart,West Germany.)

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Fig. 18. Temporary sliding bearing. (Courtesy: Arvid Grant, Olympia, Washington.)

moved forward one stroke of the hori-zontal jack, the vertical jack is loweredand the horizontal jack is retracted torestart the cycle 11

After launching is completed, whenthe opposite abutment has beenreached, additional prestressing isadded to accommodate moments inthe final structure. The original con-

centric prestress must resist the vary-ing moments which occur as the su-perstructure is pushed over the piersto its final position.

The incremental launching tech-nique has been used for spans upto 200 ft (60 m) without the use oftemporary falsework bents. Spans upto 330 ft (100 m) have been built

Fig. 19. Jacking mechanism. (Courtesy: Fritz Leonhardt, Stuttgart, West uermany.)

PCI JOURNAL/January-February 1979 73

utilizing temporary supporting bents.Girders are of a constant depth andusually with a depth of 1/12 to lhs of thelongest span. This constructiontechnique has been used for the firsttime in the United States for con-structing the Wabash River Bridge atCovington, Indiana.

Since the segments are cast behindthe abutments and relocated in thefinal structure, this constructionmethod, by definition, may be clas-sified as precast. Most precast produc-ers would consider this to be a fineline of distinction; however, depend-ing upon constraints at a particularsite, the segments could be precastand match-cast at a precasting plant,transported to the site, positioned,post-tensioned, and launched. Therewould have to be some modificationin design to accommodate the lack ofmild steel reinforcement continuityacross the joint.

Construction on FalseworkSegmental construction on false-

work, although negating a majoradvantage of segmental construction,under certain circumstances is ad-vantageous. Generally, the end spanof a bridge will be slightly longer thanhalf the span of the first interior span.Thus, there will be a short length ofend span near the abutment that willnot be accommodated by the balancedcantilever concept. Segments in thisshort portion of the structure will gen-erally be placed on falsework sup-ported at grade.

Where simple span structures arecontemplated or where the height ofthe bridge from existing terrain is notexcessive and falsework is not en-vironmentally objectionable, it isdoubtful whether segmental con-struction would be economicallycompetitive with conventional in-situtype of construction, unless it were along viaduct type structure. The only

segmental bridge constructed entirelyon falsework that the author is awareof is the Pennsylvania DOT teststructure constructed at the Pennsyl-vania State University test track facil-ity; however, this structure was spe-cifically specified as precast segmen-tal for research purposes.

The Long Key Bridge in Floridamight be considered as segmental onfalsework; however, in this case thefalsework is portable, i.e., mounted onbarges and relocated from span tospan and therefore is not falsework inthe conventional sense.

Segment Erection

The method of erecting precastsegments is dependent upon anumber of parameters. The size andweight of the unit will determine, orbe determined by, the erectionequipment available. The height ofthe bridge above existing terrain, ornavigational clearance, will determineif the units can be erected by truck,crawler, or barge mounted cranes.

In some instances, precast unitsmay be lifted up from a barge or truckby a jacking mechanism located on thepier or completed portion of thestructure (Fig. 6). On the other hand,if the height of the structure is suchthat truck or barge cranes are notpracticable, if access for trucks atexisting grade is not feasible, or if thestructure is a long viaduct, a moveablelaunching gantry such as that shownin Fig. 5, or a swivel crane (Fig. 12),may be necessary and economicallyjustifiable.

The moveable launching gantry canbe more readily justified economicallyfor a long viaduct. Usually, launchinggantries are used for the balancedcantilever type of construction andonly require repositioning upon com-pletion of two half-span cantilevers.

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Fig. 20. Pasco-Kennewick Bridge over Columbia River in the State of Washingtonnearing completion. (Courtesy: Arvid Grant, Olympia, Washington.)

Swivel cranes have only been used,thus far, for the progressive placingmethod of construction and requirerelocation for erection of each seg-ment.

Types ofSegmental Bridges

Up to this point the documentationof prestressed concrete segmentalbridges has been concerned with whatmight be classified as girder typebridges. However, segmental con-struction is a versatile type of con-struction applicable to other types ofbridge construction and as suchshould not be stereotyped to girderbridges only. As with any new con-cept the innovative engineer shouldbe able to apply the concept to othertypes of construction.

The material presented herein indi-cates only the adaptation of segmentalconstruction; it is not within the scopeof this paper to present specific designconsiderations for the various types ofbridges. The reader should consultother literature* for design informa-tion relative to a specific type ofstructure.

Cable-Stayed BridgesThe first cable-stayed bridge with a

segmental concrete superstructure tobe built in the United States is thePasco-Kennewick Intercity Bridgecrossing the Columbia River in theState of Washington (Fig. 20). Theoverall length of this structure is 2503ft (763 m). The center cable-stay span

*An informative design manual on segmental construc-tion titled Precast Segmental Box Girder Bridge Manual(1978) is available from the Prestressed Concrete Insti-tute, Chicago, Illinois.

PCI JOURNAUJanuary-February 1979 75

Fig. 21. Giant precast segment in casting yard for Pasco-Kennewick Bridge overColumbia River in the State of Washington. (Courtesy: Arvid Grant, Olympia,Washington.)

Fig. 22. Precast segment erection of Pasco-Kennewick Bridge over ColumbiaRiver in the State of Washington. (Courtesy: Arvid Grant, Olympia, Washington.)

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Fig. 23. Danube Canal Bridge on Vienna Airport Motorway in Austria. (Courtesy:Figg and Muller Engineers, Inc., Tallahassee, Florida.)

is 981 ft (299 m) and the stayed flank-ing spans are 406.5 ft (124 m). Thethree main spans are assembled fromprecast prestressed concrete seg-ments, while the approach spans arecast-in-place on falsework.

The segments are precast about 1mile (1.6 km) downstream from thebridge site (Fig. 21). Each segment is27 ft (8.2 m) long and consists of threetransverse girders and a roadway slabjoined along the segment edges with ahollow triangular box and weighsabout 300 tons (272 mt). The segmenthas a constant depth of 7 ft (2 m) andis 79 ft 10 in. (24.3 m) wide.

Segments are barged directly be-neath their place in the bridge andhoisted into position (Fig. 22). It re-quires approximately 6 hours to lifteach segment into position. Fifty-eight precast, transversely prestressedconcrete bridge girder segments are

required. The segments are match-cast, prestressed, cured and thentransferred to the bridge, and erectedsymmetrically about the two mainbridge towers, epoxy joined, lon-gitudinally prestressed against thepreviously erected ones, and sus-pended to the bridge stays. A largepart of the longitudinal prestressingforce is provided by the compressionresulting from the horizontal compo-nent of stay-cable forces.

Another interesting cable-staystructure is the Danube Canal Bridgelocated on the Vienna Airport Motor-way and crossing the Danube Canal atan angle of 45 deg. It has a 390-ft (119m) center span with 182.7-ft (55.7 m)side spans (Fig. 23). The structure isunique insofar as its constructiontechnique is concerned. Because con-struction was not allowed to interferewith navigation on the canal, the


Fig. 24. Plan for Danube Canal Bridge on Vienna Airport Motorway in Austria.

structure was built in two 364-ft (111m) halves on each bank and parallel tothe canal (Fig. 24).

Upon completion, the two halves ofthe span were swung into final posi-tion and a cast-in-place closure jointwas made. In other words, each half

was constructed as a one-time swingspan.12

The bridge superstructure is a51.8-ft (15.8 m) wide trapezoidalthree-cell box girder. An interestingvariation in this structure is that the

Fig. 25. Precast inclined web segments for Danube Canal Bridge on ViennaAirport Motorway in Austria. (Courtesy: Figg and Muller Engineers, Inc.,Tallahassee, Florida.)

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Fig. 26. Aerial view of Pont de Brotonne near Rouen, France (Reference 13).

central box is cast in 25-ft (7.6 m) longsegments on falsework; after the pre-cast inclined web segments areplaced, the top slab is cast (Fig. 25).Thus, the system uses a combinationof both precast and cast-in-place seg-mental construction.

The Brotonne Bridge crosses theSeine River downstream from Rouenin France. An aerial view (Fig. 26)shows the general configuration of thebridge. Fig. 27 shows an isometricview of a segment and the orientationof prestressing and stay.13

main sta transverse post-tensioning

web

strut

longitudinal pos t-

post-tensioning /transversepost - tension

Fig. 27. Isometric view of precast segment of Pont de Brotonne near Rouen,France. (Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)


1.50ҟ6.50ҟ1.60ҟ1.60ҟ6.50ҟ1.50(5')ҟ(21')ҟ(5')ҟ(5')ҟ(21')ҟI (5')

ROADWAYҟ ROADWAY

Fig. 28. Deck cross section of Pont de Brotonne near Rouen, France (Reference 13).

The total length of the structure is4194 ft (1278 m). The central rivercrossing includes a 1050-ft (320 m)center span and 471-ft (143.5 m) side

Fig. 29. Bottom view of deck segmentsof Pont de Brotonne near Rouen, France.

spans. At present, this structure holdsthe record length for a cable-stayedbridge of prestressed concrete and forany type of concrete span.

The main deck structure is a built-inbalanced cantilever out from thepylon piers. Dimensions of the decksegments are, top flange 63 ft (19.2 m)wide, bottom flange 26 ft (8 m) wide,and a constant depth of 12.5 ft (3.8 m)as shown in Fig. 28. Each segment is9.8 ft (3 m) long.

Similar to the Danube CanalBridge, the only parts of the trapezoi-dal box girder that are precast are itssloping webs. The 9.8-ft (3 m) long,13-ft (4 m) wide precast web elementsare precast at the site. The balance ofthe cross section, including top andbottom flanges and its interior stiff-ening struts, is cast-in-place.

Final support for the deck units isprovided by 21 stays continuousthrough the pylon which lie in a verti-cal plane along the longitudinal axis ofthe structure. Spacing of the stays atdeck level is 19.6 ft (6 m); thus, everyother segment has a stay anchor.

Fig. 29 shows the arrangement ofthe stays and the underside of thesegments of the Pont de Brotonne(looking up the pylon piers).

80

Fig. 30. Aerial view of Gladesville Arch Bridge, Australia (Reference 14).

Arch BridgesThe Gladesville Bridge in Au-

stralia, completed in 1964, is a pre-cast segmental arch bridge (Fig. 30).The arch has a clear span of 1000 ft(305 m) and consists of four arch ribs.The hollow box units and diaphragmswere cast 3 miles (4.8 km) down-stream from the bridge site. The cast-ing yard was laid out such that themanufacture of one arch rib could beaccommodated at one time.

Each arch rib consists of 108 boxunits and 19 diaphragms. Each boxunit is 20 ft (6 m) wide with depthsdecreasing from 23 ft (7 m) at thethrust block to 14 ft (4.3 m) at thecrown of the arch, measured at rightangles to the axis of the arch. Thelength of the box units along the archvaries from 7 ft 9 in. (2.4 m) to 9 ft 3in. (2.8 m).

After the box units were manufac-tured, they were loaded on barges andtransported to the bridge site. The boxunits and diaphragms were lifted from

the barges to the crown of the archfalsework and winched down to theirproper position (Fig. 31).'

Diaphragms are spaced at intervalsof 50 ft (15.2 m) to serve not only assupports for the slender columnswhich support the roadway above, butalso to tie the four arch ribs together.

When the units were located in po-sition on the falsework a 3-in. (76 mm)joint between the precast units wascast-in-place. At two points, in eachrib, four layers of Freyssinet flat jackswere inserted, with 56 jacks in eachlayer. The rib was then jacked lon-gitudinally by inflating the jacks withoil one layer at a time, the oil beingreplaced by grout and allowed to setbefore the next layer was inflated.

Inflation of the jacks increased thedistance between the edges of theunits adjacent to the jacks and thus theoverall length of the arch along itscenter line. In this manner a camberwas induced into the arch rib causingit to lift off the supporting falsework.

PCI JOURNAUJanuary-February 1979ҟ 81

Fig. 31. Erection of precastsegments of Gladesville ArchBridge, Australia (Reference 14).

Fig. 32. Completed four arch ribs ofGladesville Arch Bridge, Australia(Reference 14).

rig. 33. Arch just before closure section of Talbrucke Rottweill-NeckarburgBridge southwest of Stuttgart, West Germany. (Courtesy: W. Zellner.)

82

The falsework was then shifted lat-erally into position to support the ad-jacent arch rib and repeat the cycle. Aview of the completed four arch ribs isshown in Fig. 32.

A unique segmental arch bridge isthe Talbrucke Rottweill-Neckarburglocated 50 miles (80 km) southwest ofStuttgart, West Germany, and crossesthe Neckar River (Fig. 33). Althoughthe structure is constructed utilizing acast-in-place segmental technique, itcould, with some modification in de-sign, be constructed with precastsegments.

The roadway of this 1197-ft (365 m)long structure is approximately 310 ft(95 m) above the river. The 507-ft (154m) arch span has a rise of 164 ft (50m). Roadway width is 102 ft (31 m).The entire structure is actually con-structed in two independent lon-gitudinal halves, which are joined to-gether along the abutting edges of theroadway trapezoidal box girderflanges.

Each independent arch rib is atwo-cell box. The ribs are constructedin symmetrical cantilever halves (Fig.34) by the cast-in-place segmentalmethod. As each rib is cantileveredout from its foundation, it is tem-porarily tied back to rock anchors withDywidag bars. The roadway for thisstructure is composed of parallelsingle-cell box girders which are con-structed by the incremental launchingmethod (see Fig. 35 on next page).

With some modification in design,an arch bridge of this type could beconstructed with precast arch rib seg-ments. The segments could be po-sitioned perhaps with the assistance ofa high-line, held in position with tem-porary prestressing until permanentprestressing is installed and supportedby the back stays until closure.

Rigid Frame BridgesThe Brielse Maas Bridge, near Rot-

terdam, Holland, is a distinctive

Fig. 34. Cantilever construction of Talbrucke Rottweill-Neckarburg Bridge,southwest of Stuttgart, West Germany. (Courtesy: W. Zellner.)

PCI JOURNAL/January-February 1979 83

Fig. 35. Incremental launching of deck box girder of Talbri cke Rottweill-Neckarburg Bridge, southwest of Stuttgart, West Germany.(Courtesy: W. Zellner.)

Fig. 36. General view of Brielse Maas Bridge near Rotterdam, Holland.(Courtesy: Brice Bender, BVN/STS.)

84

A = Steel frameB= JacksC= Rubber bearingD= Joints

Fig. 37. Erection frame for Brielse Maas Bridge near Rotterdam,Holland. (Courtesy: Brice Bender, BVN /STS.)

structure with its V-shaped piers (Fig.36). Transversely the structure ismade up of three precast single-cellboxes which are joined together attheir flange tips with a longitudinalclosure placement and are trans-versely prestressed.

A special structural steel frame wasused to position the inclined precasthollow box legs of the piers and tosupport the seven precast roadwaygirder segments prior to casting thejoints at the corners of the delta pierportion of the structure. This frame isalso utilized to balance the pier dur-ing erection of the balance of theroadway girder segments and to ad-

just, by means of jacks, the loads inthe inclined legs of the pier duringvarious erection stages (Fig. 37). Theinclined legs are connected to thedeck structure by post-tensioning andthe V-pier is supported at its basethrough neoprene bearing pads onpiers founded on piles (Fig. 37).

The Bonhomme Bridge over theBlavet River in Morbihan, France, is aslant leg rigid frame of cast-in-placesegments (Fig. 38). The span betweenthe foundations of the slant legs is 611ft (186.25 m). A tubular steel falsework.was used to temporarily support theslant legs until closure at midspan.

-LORI ENT K ERV I GN ACS

Fig. 38. Bonhomme Bridge, Morbihan, France. (Courtesy: Figg and MullerEngineers, Inc., Tallahassee, Florida.)


Closing Remarks

Precast prestressed concrete seg-mental bridges have extended thepractical and competitive economicspan range of concrete bridges. Theyare adaptable to almost any conceiv-able site condition. This method canreduce environmental impact fromthat of conventional cast-in-place andfalsework type concrete construction.

It is apparent that there are manyways in which segmental prestressedconcrete bridges may be constructed,using any of the four constructionmethods discussed in this paper. Pre-cast concrete segments may be liftedby truck, crawler, or barge-mountedcranes or hoists secured on the top ofpreviously placed segments. Giantgantry cranes may be used to spanbetween bridge piers to erect thesegments. Precast segments can be in-corporated into a variety of bridgetypes such as cable-stay, arches andrigid frames as well as the girder typebridge. Examples of many of theseconstruction procedures and equip-ment and bridge types have been de-scribed in this paper.

The designer of a segmental bridgemust have detailed knowledge of thevarious alternatives, construction andprestressing equipment, and site con-ditions. The designer must establishall major aspects of how the structurewill be constructed. Construction pro-cedures can no longer be isolatedfrom design and vice versa. Althoughmost aspects of construction are fixed,there is still leeway for both innova-tion and error in judgment. Since thesuccess of segmental construction isdependent upon agreement betweenthe design assumptions and the con-struction methods, it is essential thatdesigners and contractors interactduring the design and constructionphases of the project.

Segmental construction is a designconcept that arose out of a need toovercome construction difficulties.Therefore, as a concept, segmentalconstruction's potential in general andapplicability to a specific project isonly limited by the innovation andimagination of the designer and con-tractor.

Discussion of this paper is invited.Please forward your comments toPCI Headquarters by July 1, 1979.

86

References

1. Ballinger, C. A., Podolny, W. Jr., andAbrahams, M. J., "A Report on the De-sign and Construction of SegmentalPrestressed Concrete Bridges in West-ern Europe-1977," InternationalRoad Federation, Washington, D.C.,June 1978. (Also available from Fed-eral Highway Administration, Office ofResearch and Development, Wash-ington, D.C., Report No. FHWA-RD-78-44.)

2. PCI Committee on Segmental Con-struction, "Recommended Practice forSegmental Construction in PrestressedConcrete," PCI JOURNAL, V. 20, No.2, March-April 1975, pp. 22-41.

3. "Highway Design and OperationalPractices Related to Highway Safety,"Report of the Special AASHO TrafficSafety Committee, February 1967.

4. Prestressed Concrete for Long SpanBridges, Prestressed Concrete Insti-tute, Chicago, Illinois, 1968.

5. Finsterwalder, Ulrich, "PrestressedConcrete Bridge Construction," ACIJournal, V. 62, No. 9, September 1965,pp. 1037-1046.

6. Muller, Jean, "Long-Span Precast Pre-stressed Concrete Bridges Built inCantilever," First International Sym-posium, Concrete Bridge Design, ACIPublication SP-23, Paper SP 23-40,American Concrete Institute; Detroit,Michigan, 1969.

7. Muller, Jean, "Ten Years of Experi-ence in Precast Segmental Construc-tion," PCI JOURNAL, V. 20, No. 1,January-February 1975, pp. 28-61.

8. Finsterwalder, Ulrich, "New De-velopments in Prestressing Methodsand Concrete Bridge Construction,"Dywidag-Berichte, 4-1967, September1967, Dyckerhoff & Widmann KG,Munich, Germany.

9. Ballinger, C. A., and Podolny, W. Jr.,"Segmental Construction in WesternEurope, Impressions of an IRF StudyTeam," Transportation Research Rec-ord 665, Bridge Engineering, V. 2,Proceedings, Transportation ResearchBoard Conference, September 25-27,1978, St. Louis, Missouri, NationalAcademy of Sciences, Washington,D .C.

10. Grant, Arvid, "Incremental Launchingof Concrete Structures," ACI Journal,V. 72, No. 8, August 1975, pp. 395-402.

11. Baur, Willi, "Bridge Erection byLaunching is Fast, Safe, and Effi-cient," Civil Engineering-ASCE, V. 47,No. 3, March 1977, pp. 60-63.

12. "The Danube Canal Bridge (Austria),"STUP Bulletin, Freyssinet Interna-tional, May-June 1975.

13. Lenglet, C., "Brotonne Bridge LongestPrestressed Concrete Cable StayedBridge," Cable-Stayed Bridges,Structural Engineering Series, No. 4,June 1978, Bridge Division, FederalHighway Administration, Washington,D .C.

14. "New Bridge over Parramatta River atGladesville," Main Roads, Journal ofthe Department of Main Roads, NewSouth Wales, Australia, December1964.

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