An Overview ofPrestressed SegmentalConcrete BridgesDonald J. WardPresidentDywidag Systems International, USA, Inc.Lincoln Park, New JerseyFree cantilever construction waspioneered by Dr. Ulrich Finsterwalder of Dyckerhoff and Widman, AG(DYWIDAG) in Germany during theearly 1950's. During the last three decades, hundreds of segmental concretebridges have been built throughout theworld.The word "segmental," althoughsupposedly defining a specific type ofconstruction, actually covers a widerange of different construction techniques. The most appropriate andeconomical technique for a particularsite depends on many factors.Some of the more significant factorsare as follows:1. Availability and cost of labor andmaterials.2. Availability of specialized and/orheavy equipment.3. Allowable construction time.4. Environmental restrictions.5. Accessibility of the work areas.6. Soil conditions.The above conditions change withevery project. Therefore, when thesevariations are combined with the constantly emerging new technology, itoften makes the selection of a particularconstruction technique very difficult.The design consultant, in most cases, iscalled upon to predict the most120

Fig. 1. Pine Valley Creek Bridge, San Diego, California.economical solution and then design itbased on today's factors. Unfortunately,the actual construction may not takeplace for several years. For this reason,the design must be as uncomplicatedand as flexible as possible in order toaccommodate all these variables andtake into account state-of-the-artchanges.The following segmental projects illustrate this point in that they employseveral different construction techniques, ranging from cast in place onfalsework and cantilever to precastcantilever. In most cases, the contractoremployed alternate designs and/ortechniques from those originally designed.its kind in the United States and onlythe second in North America. Thebridge was free cantilevered from thepiers, with sliding forms on falseworkused for a portion of the end spans.This project was redesigned under avalue engineering proposal. The original design called for the closure of thecenter span 90 days prior to closure ofthe adjacent spans. This aspect of thedesign was intended to compensate forcreep and shrinkage and their effect onthe piers.The value engineering proposalcalled for the bridge to be built fromone end. Vertical jacking at the closureswas used to adjust initial moments andmeet the original intents.Pine Valley Creek Bridge(Fig. 1)Note: This paper is based on a presentationgiven at the Segmental Concrete Bridge Conference in Kansas City, Missouri, March 9-10, 1982.The Conference was sponsored by the AssociatedReinforcing Bar Producers — CRSI, FederalHighway Administration, Portland Cement Association, Post-Tensioning Institute, and PrestressedConcrete Institute.This classical free cantilever cast-inplace segmental box girder bridge inSan Diego, California, was the first ofPCI JOURNAUMarch-April 1983121

Fig. 2. Eel River Bridge, California.Eel River Bridge (Fig. 2)The Eel River Bridge in Californiawas originally designed as a cast-inplace continuous prestressed concretebox girder built on falsework. The contractor made a value engineering proposal to construct the bridge segmentally, using sliding forms. Only a portion of the bridge was falseworked, including bottom slab soffit, at any onetime.The segments were then cast inlengths varying between 40 and 75 ft(12.2 and 22.9 m) with the use of slidingforms, and post-tensioned as the workprogressed. The total length of falsework required at any one time was approximately 25 percent of the totallength of bridge. The formwork required was approximately 3 percent ofthe total contact form surface.The method selected provided economy by allowing repetitive uses of thesame falsework and forming material. Italso allowed the first few spans to be122constructed and stressed before falsework was removed during the winterand spring high water seasons.Kipapa Stream Bridge(Fig. 3)The Kipapa Stream Bridge in Honolulu, Hawaii, was originally designedas a cast-in-place continuous prestressed concrete box girder built onfalsework. This 12 million bridge wasvalue engineered at considerable savings and built by the free cantilevermethod.The twin superstructures, providing aroadway approximately 120 ft (36.6 m)wide and 2000 ft (609.6 m) long, wereconstructed using a combination ofform travelers and .falsework. One interesting aspect of the design whichalso facilitated the construction was theabsence of transverse expansion jointsexcept at each abutment.

Fig. 3. Kipapa Stream Bridge, Honolulu, Hawaii.Fig. 4. Koror-Babelthaup Bridge, near the Philippines.PCI JOURNAUMarch-April 1983123

Vail Pass Bridges.(Fig. 5)Fig. 5. Vail Pass Bridges, Colorado.Koror- Babeithaup Bridge(Fig. 4)The Koror-Babelthaup Bridge, located in the Palau District of Micronesia near the Philippines, is theworld's longest concrete box girderspan. The 790 ft (240.8 m) main spanlinks the two islands from which thebridge gets its name.Due to deep, swift water in the channel, it was decided to maximize themain span, allowing the pier foundations to be built on dry ground. Theend spans, built totally over the approach causeway, serve only to counter-balance the main span. For this reason, the spans were shortened significantly and filled with rock and concreteballast. The end spans were built segmentally on falsework concurrentlywith free cantilevering in the mainspan.124The Vail Pass Bridges in Colorado,with spans varying from 140 to 260 ft(42.7 to 79.2 m), were originally designed as precast segmental cantilevers.All four structures were eventuallybuilt by cast-in-place cantilever construction.The concept was different from freecantilever in that the bridges were notconstructed as balanced cantilevers justfrom the piers. The form travelers wereset up at the abutments and movedthrough the spans, past the piers andthrough the next span. Fig. 5 shows themethod of construction.Temporary towers were installedperiodically to support the structure,control the reactions, and balance thebridge. With the help of superplasticizers, extremely high early concretestrengths, and staggered shifts, a2½-day casting cycle was achieved. Asa result, the four bridges were constructed using five form travelers in oneconstruction season.Bedford Bypass Bridges(Figs. 6 and 7)The Bedford Bypass #1 and BedfordBypass #2 Bridges in Bedford, NovaScotia, are examples of bids which included , alternate designs. Bedford Bypass #2 provided the contractors with achoice of (1) a combination of cast-inplace reinforced concrete and precastprestressed I girders vs. (2) a cast-inplace prestressed concrete double teeconstructed span by span on the falsework.Bedford Bypass #1 was bid as: (1)structural steel with concrete deck vs.(2) a cast-in-place span-by-span designsimilar to Bedford Bypass #2. In bothcases, the cast-in-place span-by-spansolution was successful.

Fig. 6. Bedford Bypass Bridge No. 2, Bedford, Nova Scotia.Fig. 7. Bedford Bypass Bridge No. 1, Bedford, Nova Scotia.PCI JOURNAL/March-April 1983125

Fig. 8. Grand Mere Bridge, St. Maurice, Quebec.Fig. 9. Shubenacadie River Bridge, Nova Scotia.Grand Mere Bridge (Fig. 8)T h e G r a n d Mere Bridge i n St.Maurice, Quebec, with a 595 ft (181.4m) main span, was a similar but smallerversion of the Koror-Babelthaup Bridge.T h e shortened ballasted e n d spanswere also built on falsework. However,in this particular case they were constructed prior to and not concurrentlywith the main span.Shubenacadie River Bridge(Fig. 9)The Shubenacadie River Bridge inNova Scotia has a 700 ft (213.4 m) mainspan flanked by 375 ft (114.3 m) sidespans. Single temporary falseworkbents were used in the side spans. Thebents reduced the unbalanced deadload moment and allowed the total sidespan to be built with form travelers.

Fig. 10. Parrots Ferry Creek Bridge, Vallecito, California.Parrots Ferry Creek Bridge(Fig. 10)The Parrots Ferry Creek Bridge inVallecito, California, was also a castin-place cantilever segmental boxgirder. It was the first bridge of its kindto be built in the United States, usinglightweight concrete while also employing the classical free cantilevermethod with form travelers.Kishwaukee River Bridges(Figs. 11 and 12)The Kishwaukee River Bridges inWinnebago County, Illinois, consist oftwo structures: two single cell box girders, each with five spans [170-3 at 250 170 ft (51.8 - 3 at 76.2 - 51.8 m)] ; The Illinois Department of Transporation developed plans for a precast box superstructure. Cast-in-place alternative designs were encouraged. Five of theseven bids submitted were for the precast scheme. Two alternate designsusing cast-in-place techniques completed the bid tabulation. The successful bidder chose the precastscheme, with post-bid modifications byDSI.PCI JOURNAL/March-April 1983A significant factor in the economy ofthe contractor's proposal was a uniqueredesign which used larger segmentsand eliminated the need for temporarypost-tensioning. The use of Dywidaghigh tensile bars both transversely andlongitudinally allowed the initial longitudinal post-tensioning required forerection of the segments to be incorporated into the permanent post-tensioning required for the final structure.The above provided economy oferection time in addition to savings inmaterials and labor. This was evidenced by the record pace of erection(up to seven segments per day). Thefact that the post-tensioning tendonswere all straight and completely contained within the top or bottom slabalso produced a significant economy.The bridge superstructures wereerected by free cantilever constructionusing an overhead launching truss.During cantilever erection the trusswas supported on the preceding cantilever and pier segment of the cantilevers being erected. A portion of theend spans adjacent to the abutmentswas erected on falsework.A detailed report on the KishwaukeeRiver Bridges appeared in the November-December 1982 PCI JOURNAL,pp. 22-47.127

Fig. 11. Kishwaukee River Bridges, Winnebago County, Illinois, during construction.Fig. 12. Kishwaukee River Bridges, Winnebago County, Illinois, after completion.128

Fig. 13. Genessee River Bridge, Rochester, New York.Genessee River Bridge(Fig. 13)T h e Genessee River Bridge inRochester, New York, is a good example of the combination of two segrnental construction techniques. T h e twinstructures consist of two two-cell concrete box girders and have a combinedwidth of 120 ft (36.6 m ) and a totallength of approximately 2050 ft (624.8T h e river span a n d t w o adjacentspans [270 - 430 - 270 ft (82.3 - 131.1 82.3 m)l. - were built as free cantileversusing form travelers. T h e approachspans [seven spans varying from 140 to180 ft (42.7 to 74.9 m ) ] w e r e constructed segmentally - span by spanon falsework.For t h e cantilever vortion of thebridge, four form travelers were used,two for each structure. Segments of 16ft 3 in. (4.95 m) were cast in alternatingsequence about the centerline of thepier. The unbalanced moment aboutthe pier was taken by a temporary concrete pier supported on piling and tieddown with post-tensioned anchors. Thetemporary bearings and bents were removed after the spans were closed.Cantilever work progressed at a rateof approximately one segment per formtraveler per week [65 ft (19.8 m ) oftwo-cell box girder per week].This pace is noteworthy because considerable time was needed for the concrete to reach the required stressingstrength. Ordinarily, the use of additives and/or high early strength concrete permits stressing the second dayof the cycle (first day after concreteplacement). In this case, the concretedid not reach initial stressing strengthof 2500 psi (17.2 MPa) until the thirdday and sometimes the fourth day.The use of high early strength cem e n t could have reduced the cycletime by approximately 2 days. Whenthe concrete reached 2500 psi (17.2

MPa), longitudinal, transverse, andvertical bar tendons were stressed toallow stripping and form travelermovement. The longitudinal strandtendons were stressed at 4000 psi (27.6MPa) before casting the next segment.The approach spans were built usingconventional falsework supported bysteel piles. The box girder section wascast using mobile steel forms. The bottom slab was cast first, with webs andtop deck cast second. Transversepost-tensioning was done with bars andlongitudinal post-tensioning was donewith strand. The final closure betweenthe river portion and the approachspans was accomplished using formtravelers.structure work is progressing concurrently with superstructure work. Thissix-span structure [229 - 300 - 310 - 370- 360 - 229 ft (69.8 - 91.4 - 94.5 - 112.8 109.7 - 69.8 m)] will be constructedusing four form travelers. Temporarybents will be used in the end spans toallow the use of form travelers for theentire span.This bridge was originally designedas a precast segmental project, and wasbid against a structural steel alternate.The specifications also allowed thesubmission of contractors' alternate designs. Interestingly enough, six out ofseven bidders submitted and bid onalternate cast-in-place designs. Thehigh bidder was the only bidder on theconforming design,Red River Bridge (Figs. 14and 15)Concluding RemarksThe Red River Bridge in Boyce,Louisiana, is now under contract. Sub-Fig. 14. Red River Bridge, Boyce, Louisiana.130It should be noted that there aremany different methods of approachto segmental construction. Only a few

Fig. 15. Artist's rendering of Red River Bridge, Boyce, Louisiana.have been discussed here. Innovativeengineers and contractors are stillfinding different methods to get the jobdone efficiently and economically.Perhaps the most important point thatthe owner, engineer, and contractormust recognize is that no person has amonopoly on ideas. Flexible designand/or specifications which allow thecontractor to make use of special capa-bilities, equipment, and ingenuity havecontributed greatly to the advancementof the state-of-the-art, and have alsobeen able to save the owner (and public) considerable money in the process.Unquestionably, the many advantages afforded by segmental construction will continue to make this methoda very viable technique in bridgebuilding for many years to come.NOTE: Discussion of this paper is invited. Please submityour discussion to PCI Headquarters by Nov. 1, 1983.PCI JOURNAL/March-ApriJ 1983131

Lincoln Park, New Jersey Free cantilever construction was pioneered by Dr. Ulrich Finster-walder of Dyckerhoff and Widman, AG (DYWIDAG) in Germany during the early 1950s. During the last three de-cades, hundreds of segmental concrete bridges have been built throughout the world. The word "se