An Overview of Precast Prestressed ♦ Segmental

Walter Podolny, Jr. Division Office of Engineering Federal Highway Administration U.S. Department of Transportation Washington, D.C.

he seventies will be recorded by Construction in this manner may T engineering historians as the de- also have a serious impact upon envi- cade in which ronment and ecology. Prestressed segmental bridge construction came of segmental construction has extended age in North America. Segmental box the practical span of concrete bridges girder bridges have attracted the at- to approximately 800 ft (244 m). tention and captured the imagination Where segmental construction is used of bridge engineers and designers in conjunction with the cable-stay across the continent. bridge concept, the span range can be Because of practical limitations of extended to 1300 ft (400 m) and handling and shipping, the precast perhaps longer.' prestressed I-girder type of bridge Because construction of the super- construction is limited to an approxi- structure is executed from above, i.e., mate range of 120 to 150-ft (37 to 46 at deck level, the use of extensive m) spans. Beyond this range of span, falsework is avoided. Thus, there is no post-tensioned cast-in-place box gir- effect upon navigation clearance from ders on falsework are more attractive. falsework during construction and the However, in certain instances the ex- cost of extensive formwork is elimi- tensive use of falsework can prove to nated. Segmental type bridges be an economic disadvantage. Where provide a method whereby the impact deep ravines or navigable waterways of highway construction through en- must be crossed, extensive formwork vironmentally sensitive areas can be may be impractical. minimized.

56 Utilization of an elevated viaduct evolution of prestressed concrete type structure requires only a rela- bridges to this point in the state-of- tively narrow path along the align- the-art and to present a few basic de- ment to provide access for pier con- finitions. struction. Once the piers have been Precasting of elements or members constructed, all construction activity is of a structure implies that the concrete from above. Thus, the impact on the is cast in forms at some location other environment is minimized. Also, be- than the final position of the member. cause the structure is elevated, as op- The member may be cast at a perma- posed to an at-grade highway, there is nent precasting plant at some location no interference with wild life migra- other than the construction site; then tory habits. transported by truck, rail, or barge to Prestressed concrete segmental the site; and eventually erected to its bridges have proven to be esthetically final position. The member may also appealing and, because various con- be cast at some location in close struction methods can be used, the proximity to the construction site structures are cost effective and en- eliminating the transportation from vironmentally adaptable. precasting plant to construction site. In either situation the member is cast at a location other than its final posi- Evolution of tion in the structure. Segmental Bridges Segmental construction has been defined as "... a method of construc- Before discussing the various facets tion ... in which primary load carry- and variants of precast segmental box ing members are composed of indi- girder bridges, it may enhance the vidual segments post-tensioned to- understanding of this type of con- gether."2 struction to briefly trace the historical As early as 1948, Eugene Freyssi-

PCI JOURNAL/January-February 1979 ҟ 57 Fig. 1. Marne River Bridge near Paris, . (Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

net, the great French prestressing was made using a series of machine- pioneer, used prestressed concrete for made blocks (strung like beads on a the construction of five bridges over string) which were prestressed to- the Marne River near Paris, with gether to form a beam. spans of 240 ft (73 m) having an ex- The construction method (although ceptionally light appearance (Fig. 1). very crude by modern standards) is Construction of these bridges, as indi- similar, in principle at least, to today's cated in Fig. 2, utilized precast seg- precast prestressed segmental bridges. ments which were post-tensioned to- The Tennessee prestressed block gether. Thus, by definition, these five was followed very structures can be called precast pre- stressed segmental bridges. shortly by the famed Walnut Lane Bridge in Philadelphia, Pennsylvania, Prestressing of bridges in North America did not start until about in 1950. The 160-ft (48.8 m) long 1949.* The first prestressed bridge in beams were cast-in-place and post- tensioned. the United States was built in Madi- son County, Tennessee. This bridge Soon thereafter, precast preten- sioned bridge girders evolved result- *An interesting historical account of the early prestressed ing from inherent economies and bridges in America is given by Charles C. Zollman in "Reflections on the Beginnings of Prestressed Concrete quality control of plant fabricated in America—Part 1: Magnel's Impact on the Advent of elements. With few exceptions, during Prestressed Concrete; Part 2: Dynamic American En- gineers Sustain Magnel's Momentum," PCI JOURNAL, the fifties and early sixties, most V. 23, Nos. 3 and 4, May-June and July-August 1978, pp. multi-span precast prestressed bridges 22-48 and pp. 30-67. See also Ross Bryan's article on "Prestressed Concrete Innovations in Tennessee," pub- built in the United States were de- lished in the current PCI JOURNAL, pp. 14-31. signed as a series of simple spans.

58 They were designed with standard 100 to 120 ft (30.5 to 36.6 m) in length AASHTO-PCI girders of various cross depending upon local regulations. sections in spans ranging up to about As a result of longer span require- 100 ft (30.5 m), but more commonly ments, a study was conducted by the for spans of 40 to 80 ft (12 to 24 m). Prestressed Concrete Institute in The advantages of a continuous cast- cooperation with the Portland Cement in-place structure were abandoned in Association. 4 This study proposed favor of the more economical con- simple spans up to 140 ft (42.7 m) and struction offered by plant produced continuous spans up to 160 ft (48.8 m) standardized units. be constructed of standard precast During the middle sixties a growing girders up to 80 ft (24 m) in length concern with regard for safety of the joined together by splicing and post- highways asserted itself. An AASHTO tensioning. To obtain longer spans the Traffic Safety Committee report in use of inclined or haunched piers was 1967 called for: proposed. In general, these concepts "Adoption and use of two-span utilized precast I- or box girders with bridges for overpasses crossing di- field splices and post-tensioning for vided highways ... to eliminate continuity. the bridge piers normally placed This type of construction, using adjacent to the shoulders." long standard precast prestressed It soon became apparent that the units never quite achieved the popu- conventional precast pretensioned larity that it merited. Despite some AASHTO-PCI girders were limited by limitations, the method is adaptable their transportable length and weight. for spans up to 200 ft (61 m). Transportation over the highways The concepts developed by the limits the precast girder to a range of PCI-PCA studies fall into the defini-

Fig. 2. Marne River Bridge near Paris, France. (Courtesy: Figg and Muller Engineers, 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 construction the first to apply cast-in-place seg- and might be described as "longitudi- mental prestressed construction in a nal" segmental construction. The in- balanced sequence to a bridge cross- dividual elements are long with re- ing the Lahn River at Balduinstein, spect to their width. Germany. This system of cantilever As spans increased, designers segmental construction rapidly gained turned toward utilization of post- acceptance in Germany, especially tensioned cast-in-place box girder after the successful completion of a construction. The Division of High- bridge crossing the Rhine River at ways, State of , including Worms in 1952.5 Since then, the con- several other states, have been quite cept has spread across the entire successful using cast-in-place, multi- world. cell, post-tensioned box girder con- Concurrently, precast segmental struction for multi-span structures construction was evolving during this with spans of 300 ft (91.5 m) and period. In 1952, a single span county longer. However, this type of con- bridge located near Sheldon, New struction has its disadvantages; it re- York, was designed by the Freyssinet quires extensive formwork during Company. Although this bridge was casting with its undesirable impact constructed using longitudinal seg- upon the environment and/or ecology. ments, rather than transverse seg- Meanwhile in Europe, segmental ments, as was being done in Europe, construction proceeded slightly dif- the structure represents the first prac- ferently in conjunction with box gir- tical application of match casting. This der design. Segments were cast-in- technique has become an important place or precast in relatively short development in precast segmental lengths, providing full roadway width construction. and depth. Today, "segmental con- The bridge girders were divided struction" is generally recognized as into three longitudinal segments that having been pioneered in Europe. were cast end to end. The center seg- Ulrich Finsterwalder, in 1950, was ment was cast first and the end seg- 60 Fig. 4. JFK Memorial Causeway, Corpus Christi, . ments were cast directly against the was built in 1967. The Bear River center segment. Keys were cast at the Bridge, Digby, Nova Scotia, followed joints so that the three precast ele- in 1972 with six interior spans of 265 ments could be joined together at the ft (80.8 m) and end spans of 203.75 ft site in the same position they had in (62.1 m). the precasting yard. Upon shipment to The JFK Memorial Causeway, Cor- the job site, the three elements of a pus Christi, Texas (Fig. 4) represents girder were post-tensioned together the first precast prestressed segmental with cold joints.6'7 bridge completed in the United The first major application of match States. It was opened to traffic in cast, precast, segmental construction 1973. Designed by the Bridge Divi- was not realized until 10 years later, sion of the Texas Highway Depart- in 1962, in France. This structure, de- ment, this structure has a center span signed by Jean Muller,* was the of 200 ft (61 m) with end spans of 100 Choisy-Le-Roi Bridge located south of ft (30.5 m). Paris crossing the Seine River (Fig. 3). In the United States, currently Since then the concept has been re- (1979), the author is aware of at least fined and has spread from France to 24 precast segmental bridge projects many other countries. that are either completed, in con- The first precast segmental bridge struction, or in design and planning to be built in North America was the stages (see Table 1). There are un- Lievre River Bridge located on High- doubtedly many more. way 35, 8 miles (13 km) north of Notre *Jean Muller, formerly chief engineer with Entreprises Dame du Laus, Quebec. The bridge, Campenon Bernard, Paris, France, is currently in partnership with Figg and Muller Engineers, Inc., with which had a center span of 260 ft (79.2 offices in Tallahassee, Florida, Washington, D.C., and m) and end spans of 130 ft (39.6 m), Paris, France.

PCI JOURNAL/January-February 1979 ҟ 61 Table 1. Precast Segmental Concrete Bridges in North America.

62 Disadvantages Advantages of Precast Segmental Construction The disadvantages of precast seg- mental construction are: • Necessity for a high degree of In many instances where pre- geometry control during fabrica- stressed concrete segmental bridge tion and erection of segments. design alternates have competed • Temperature and weather limi- against structural steel designs they tations regarding mixing and have proven to be cost effective. As placing epoxy joint material. previously indicated, when compared • Lack of mild steel reinforcement to more conventional methods of con- across the joint and therefore a crete construction, prestressed con- limitation of tension stress across crete segmental construction has ex- the joint. tended the span range for concrete bridges and is competitive in the in- It should be noted that for large- termediate and long span range. The sized projects, it is no longer difficult method eliminates the need for costly to set-up fully mechanized concrete falsework and minimizes its impact on site mixing equipment. With today's the environment. technology, it is possible to produce a In general, the economic feasibility high quality concrete at the site. of cast-in-place or precast segments Therefore, for large projects, it is will be determined by site conditions, doubtful whether factory produced site accessibility, available erection concrete has an advantage over site equipment, time to construct and/or produced concrete except for the im- erect the segments, and the relative portant aspect that loads and pre- economic trade-off in transporting a stressing forces are applied at a later finished segment as opposed to trans- age on a more mature concrete. porting constituent materials.

Advantages Types of Precast The often cited advantages of pre- Segmental Construction cast segmental construction are: • Fabrication of the segments can be accomplished while the sub- It has been observed' that the structure is under construction, technology for constructing segmental and thus, erection of the super- bridges has rapidly advanced in the structure is speeded up. last decade. During the initial de- • By virtue of precasting and velopment of segmental bridges they maturity of the concrete at the were constructed by the balanced time of erection, the time re- cantilever method. quired for strength gain of the Currently, such techniques as concrete is removed from the span-by-span construction, incremen- construction critical path. tal launching, and progressive placing • As a result of the maturity of the are also being utilized. Thus, there are concrete at the time of erection, now a variety of design concepts and the effects of concrete shrinkage construction methods which may be and creep are minimized. used to economically produce seg- • Quality control of factory pro- mental bridges for almost all site con- duced precast concrete. ditions.

PCI JOURNAL/January-February 1979ҟ 63 Fig. 5. Sallingsund Bridge, Denmark, showing balanced cantilever construction.

Balanced Cantilever Construction tilever from the preceding pier (Fig. The balanced cantilever method of 5). This procedure is then repeated construction, sometimes referred to as until the structure is completed.l,s the free cantilever method, was de- Unless symmetrical segments are veloped out of a need to eliminate simultaneously erected, the pier will falsework. Not only is falsework ex- be out of balance by one segment. pensive, but it is a temporary structure The moment caused by this imbalance and, as such, is designed with small can be accommodated by a moment margins of safety, as has been indi- resistant pier. Where the pier is not cated by some falsework failures. monolithic with the superstructure, a In waterways that are subject to temporary moment resistance may be spring flash floods, falsework can be provided by temporarily "clamping" washed away resulting in potential the superstructure to the pier, pro- damage to the structure, lost con- vided the pier is designed to take the struction time, and possible financial temporary moment. Where feasible, ruin. In navigable waterways, false- temporary bracing may be provided work is either not allowed or is se- (Fig. 6). Obviously, the imbalance verely restricted. With cantilever con- must be maintained on the side of the struction, falsework is eliminated be- pier where the bracing is located. cause precast segments are erected This concept utilizes a dual system and supported from the pier or the al- of prestressing tendons. Cantilever ready completed portion of the struc- (negative moment) tendons are re- ture. quired at the top of the segments for In this method of construction seg- dead load cantilever stresses [Fig. ments are simply cantilevered from 7(a)] and then after closure, at the preceding pier in a balanced se- midspan, continuity (positive mo- quence on each side until midspan is ment) tendons [Fig. 7(b)] are installed reached. Then a closure placement is to accommodate the positive moment made with a previous half-span can- in the continuous structure. Because

64 of the high cantilever moments during construction, which are reduced by moment redistribution in the final structure, a slightly larger amount of prestressing is required compared to a structure supported on falsework. In continuous structures the final stresses in the completed structure are substantially different from what they were initially during cantilever con- struction. However, subsequent con- crete creep and steel relaxation will tend to make the initial and final stresses approach each other. This means that there will be a redistribu- tion in the moments and stresses of the structure. In general, the negative moments over the piers will decrease while the positive moments at midspan will increase by a corre- sponding amount. This redistribution of moments must be accommodated in the design. Normally in precast balanced can- Fig. 6. Konoshima Ohashi Bridge, Japan.

diaphragm closure pour

R cantilever 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).

PCI JOURNAL/January-February 1979 ҟ 65 tilever construction, tendons are of the strand type. However, in the Kish- waukee Bridge (Figs. 8a and 8b) lo- cated near Rockford, Illinois, tendons were of the Dywidag thread bar type. In so far as the author is aware, this is the first time that Dywidag bars have been used in conjunction with precast segmental construction. The bar type tendon was allowed in the specifica- tions issued by the Illinois Depart- ment of Transportation to encourage competition.

Span-by-Span Construction The balanced cantilever construc- tion method was developed primarily for long spans, such that construction activity for the superstructure could be accomplished at deck level without the use of extensive falsework. A similar need exists for long viaduct structures with relatively shorter spans. 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 moveable form carrier. Although the span-by-span method Fig. 8a. Kishwaukee River Bridge near has been used for cast-in-place con- Rockford, Illinois. struction, a method for precast span-

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

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

by-span construction has been pro- tilever concept. In this method the posed as a successful alternative for precast segments are placed continu- the Long Key Bridge project (currently ously from one end of the structure to being built in the State of Florida). A the other in successive cantilevers on structural steel trusswork (Fig. 9) is the same side of the various piers used to support the precast segments rather than by balanced cantilevers on which are installed progressively from each side of the pier. one end of the structure to the other in Currently, this construction method span increments. appears to be practical in span ranges The steel trusswork has a length from 100 to 200 ft (30 to 60 m)? Be- equivalent to the span of each identi- cause of the length of cantilever (one cal interior span. It is placed by the span) in relation to construction same floating crane that handles all depth, the stresses become excessive precast segments and further adjusted and a moveable temporary stay ar- by a system of hydraulic jacks with re- rangement must be used to limit the gard to the piers. Upon completion of cantilever stresses to a reasonable a span, the trusswork is released and level. moved over to the next span to start a The erection procedure is illus- new cycle of operations. As a conse- trated in Fig. 10. Segments are trans- quence, in this method of construction ported over the completed portion of prestressing requirements are very the deck to the tip of the cantilever similar to those of a cast-in-place span under construction where they structure. are positioned by a swivel crane that Interesting variations from normal proceeds from one segment to the precast segmental construction on the next. Approximately one-third of the Long Key project are that dry joints span from the pier may be erected by will he used between the segments, the free cantilever method, the seg- i.e., no epoxy; and the longitudinal ments being held in position by ex- prestressing tendons are external, terior ties and final prestressing ca- namely, inside the box. bles. In the balance of the span, each Progressive Placing segment is temporarily held in posi- Progressive placing is similar to the tion by external temporary ties and by span-by-span method described above two stays from a moveable tower lo- whereby construction starts at one end cated over the preceding pier. The of the structure and proceeds continu- two stays are -continuous through the ously to the other end of the structure. tower and anchored in the previously The progressive placing method de- completed span deck. The stays are rives its origin from the balanced can- anchored to the top flange of the box

PCI JOURNAL/January-February 1979 ҟ 67 Fig. 10. Progressive placing erection (Reference 7).

girder segments such that the tendons in the stays can be adjusted by light jacks. This type of construction has been used for the Rombas Viaduct (Fig. 11) constructed by Campenon Bernard in eastern France. The bridge, located in an urban area, is a dual structure of nine continuous spans ranging from 82 to 148 ft (25 to 45 m) in length. The single cell box sections have a con- stant depth of 8.2 ft (2.5 m). A view of the swivel crane picking up the seg- ments from the transport dolly is shown in Fig. 12.

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

68 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, . (Courtesy of Region 15, Federal Highway Administration.)

PCI JOURNAL/January-February 1979 ҟ 69 Fig. 14. Rendering of the Linn Cove Viaduct at Blue Ridge Parkway, North Carolina. (Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

A progressive placing scheme is stays was impractical. Temporary proposed for the Linn Cove Viaduct bents at midspan will be used to re- on the Blue Ridge Parkway in North duce cantilever and torsional stresses Carolina (Figs. 13-14). Because of the during construction to acceptable environmental sensitivity of the area, levels. Erection of the temporary access to some of the piers is not bents will be accomplished in the available. Therefore, the piers will be same manner as the permanent piers, constructed from the tip of a can- utilizing the swivel crane at the end of tilever span, with men and equipment the completed cantilevered portions being lowered down to construct the of the structure. When temporary foundation and pier. The piers are bents are no longer required, they will precast segments stacked vertically be dismantled and removed by and post-tensioned to the foundation. equipment located on the completed Because of the extreme curvature of portion of the bridge deck. Consulting the alignment, the use of temporary Engineers for this structure are Figg

70 Casting bed and ---0 etnlinnnry fnrmc Direction of launching

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

and Muller Engineers, Inc., working lengths of 33 to 100 ft (10 to 30 m) for Region 15 of the Federal Highway (Fig. 15). After a segment reaches suf- Administration and the Park Services. ficient strength, it is post-tensioned to the previous segment and the entire superstructure is pushed out lon- Incremental Launching gitudinally one increment length. The Another variant of the segmental succeeding segment is then cast concept, which is new to American against its predecessor. Normally, a bridge engineers and contractors, has work cycle of one week is required to evolved in Germany and is called cast and launch a segment, irrespec- "Taktschiebeverfahren." Literally tive of its length. Operations are translated taktschiebeverfahren means scheduled such that the concrete can "phased shoving concept." In North attain sufficient strength over a America it is refered to as incremental weekend to allow launching at the launching or push-out construction. beginning of the next week (Fig. 16). This concept was first implemented in Bridge alignment in this type of 1962/63 on the Rio Caroni Bridge in construction is either straight or on a Venezuela, built by its originators curve; however, the curve must be of Willi Baur and Dr. Fritz Leonhardt of constant radius. This requirement of the consulting firm Leonhardt and constant rate of curvature applies to Adra, Stuttgart, West Germany.'°' n both horizontal and vertical curvature. The bridge superstructure is con- The Val Ristel Bridge in Italy which structed in an on-site factory in sta- was incrementally launched on a tionary forms behind the abutment in radius of 500 ft (150 m) is illustrated in

PCI JOURNAL/January-February 1979 ҟ 71 bearings are made of teflon (PTFE) faced steel-reinforced neoprene pads which slide on polished stainless steel plates (Fig. 18). There are two methods of launch- ing. The method used on the Rio Ca- roni Bridge has the jack bearing on an abutment face and pulling on a steel rod, which is attached to the last seg- ment cast by launching shoes. The second and more current method con- sists of a horizontal and vertical jack (Fig. 19). The vertical jack slides with a teflon plate at its base on a stainless steel plate and has a friction element at the top to engage the superstructure. The vertical jack lifts the superstructure approximately 3/1 6 in. (5 mm) for launching. The horizontal jack then moves the superstructure longitudi- nally. After the vertical jack has

Fig. 16. Schematic drawing of incremental launching sequence. (Courtesy: Fritz Leonhardt, Stuttgart, West Germany.)

Fig. 17. This then implies that road- way geometry is dictated by construc- tion rather than the present practice in the United States, where geometry dictates construction. To counteract the varying bending moments that occur during the launching operation, the superstruc- ture is concentrically prestessed. In addition, a launching nose (Fig. 16) is provided 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 increments by means of hydraulic jacks. To ac- commodate the movements of the su- Fig. 17. Val Ristel Bridge, Italy. perstructure, temporary sliding bear- (Courtesy: Fritz Leonhardt, Stuttgart, ings are installed on the piers. These West Germany.)

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

moved forward one stroke of the hori- centric prestress must resist the vary- zontal jack, the vertical jack is lowered ing moments which occur as the su- and the horizontal jack is retracted to perstructure is pushed over the piers restart the cycle 11 to its final position. After launching is completed, when The incremental launching tech- the opposite abutment has been nique has been used for spans up reached, additional prestressing is to 200 ft (60 m) without the use of added to accommodate moments in temporary falsework bents. Spans up the final structure. The original con- to 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. segmental bridge constructed entirely Girders are of a constant depth and on falsework that the author is aware usually with a depth of 1/12 to lhs of the of is the Pennsylvania DOT test longest span. This construction structure constructed at the Pennsyl- technique has been used for the first vania State University test track facil- time in the United States for con- ity; however, this structure was spe- structing the Wabash River Bridge at cifically specified as precast segmen- Covington, Indiana. tal for research purposes. Since the segments are cast behind The Long Key Bridge in Florida the abutments and relocated in the might be considered as segmental on final structure, this construction falsework; however, in this case the method, by definition, may be clas- falsework is portable, i.e., mounted on sified as precast. Most precast produc- barges and relocated from span to ers would consider this to be a fine span and therefore is not falsework in line of distinction; however, depend- the conventional sense. ing upon constraints at a particular site, the segments could be precast and match-cast at a precasting plant, transported to the site, positioned, post-tensioned, and launched. There Segment Erection would have to be some modification The method of erecting precast in design to accommodate the lack of segments is dependent upon a mild steel reinforcement continuity number of parameters. The size and across the joint. weight of the unit will determine, or be determined by, the erection equipment available. The height of Construction on Falsework the bridge above existing terrain, or Segmental construction on false- navigational clearance, will determine work, although negating a major if the units can be erected by truck, advantage of segmental construction, crawler, or barge mounted cranes. under certain circumstances is ad- In some instances, precast units vantageous. Generally, the end span may be lifted up from a barge or truck of a bridge will be slightly longer than by a jacking mechanism located on the half the span of the first interior span. pier or completed portion of the Thus, there will be a short length of structure (Fig. 6). On the other hand, end span near the abutment that will if the height of the structure is such not be accommodated by the balanced that truck or barge cranes are not cantilever concept. Segments in this practicable, if access for trucks at short portion of the structure will gen- existing grade is not feasible, or if the erally be placed on falsework sup- structure is a long viaduct, a moveable ported at grade. launching gantry such as that shown Where simple span structures are in Fig. 5, or a swivel crane (Fig. 12), contemplated or where the height of may be necessary and economically the bridge from existing terrain is not justifiable. excessive and falsework is not en- The moveable launching gantry can vironmentally objectionable, it is be more readily justified economically doubtful whether segmental con- for a long viaduct. Usually, launching struction would be economically gantries are used for the balanced competitive with conventional in-situ cantilever type of construction and type of construction, unless it were a only require repositioning upon com- long viaduct type structure. The only pletion of two half-span cantilevers. 74 Fig. 20. Pasco-Kennewick Bridge over Columbia River in the State of Washington nearing completion. (Courtesy: Arvid Grant, Olympia, Washington.)

Swivel cranes have only been used, The material presented herein indi- thus far, for the progressive placing cates only the adaptation of segmental method of construction and require construction; it is not within the scope relocation for erection of each seg- of this paper to present specific design ment. considerations for the various types of bridges. The reader should consult other literature* for design informa- tion relative to a specific type of Types of structure. Segmental Bridges Cable-Stayed Bridges Up to this point the documentation The first cable-stayed bridge with a of prestressed concrete segmental segmental concrete superstructure to bridges has been concerned with what be built in the United States is the might be classified as girder type Pasco-Kennewick Intercity Bridge bridges. However, segmental con- crossing the Columbia River in the struction is a versatile type of con- State of Washington (Fig. 20). The struction applicable to other types of overall length of this structure is 2503 bridge construction and as such ft (763 m). The center cable-stay span should not be stereotyped to girder bridges only. As with any new con- cept the innovative engineer should *An informative design manual on segmental construc- tion titled Precast Segmental Manual be able to apply the concept to other (1978) is available from the Prestressed Concrete Insti- types of construction. tute, Chicago, Illinois.

PCI JOURNAUJanuary-February 1979 75 Fig. 21. Giant precast segment in casting yard for Pasco-Kennewick Bridge over Columbia River in the State of Washington. (Courtesy: Arvid Grant, Olympia, Washington.)

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

76 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- required. The segments are match- ing spans are 406.5 ft (124 m). The cast, prestressed, cured and then three main spans are assembled from transferred to the bridge, and erected precast prestressed concrete seg- symmetrically about the two main ments, while the approach spans are bridge towers, epoxy joined, lon- cast-in-place on falsework. gitudinally prestressed against the previously erected ones, and sus- The segments are precast about 1 pended to the bridge stays. A large mile (1.6 km) downstream from the part of the longitudinal prestressing bridge site (Fig. 21). Each segment is force is provided by the compression 27 ft (8.2 m) long and consists of three resulting from the horizontal compo- transverse girders and a roadway slab nent of stay-cable forces. joined along the segment edges with a hollow triangular box and weighs Another interesting cable-stay about 300 tons (272 mt). The segment structure is the Danube Canal Bridge has a constant depth of 7 ft (2 m) and located on the Vienna Airport Motor- is 79 ft 10 in. (24.3 m) wide. way and crossing the Danube Canal at Segments are barged directly be- an angle of 45 deg. It has a 390-ft (119 neath their place in the bridge and m) center span with 182.7-ft (55.7 m) hoisted into position (Fig. 22). It re- side spans (Fig. 23). The structure is quires approximately 6 hours to lift unique insofar as its construction each segment into position. Fifty- technique is concerned. Because con- eight precast, transversely prestressed struction was not allowed to interfere concrete bridge girder segments are with navigation on the canal, the

PCI JOURNAL/January-February 1979ҟ 77 Fig. 24. Plan for Danube Canal Bridge on Vienna Airport Motorway in Austria.

structure was built in two 364-ft (111 was constructed as a one-time swing m) halves on each bank and parallel to span.12 the canal (Fig. 24). Upon completion, the two halves of The bridge superstructure is a the span were swung into final posi- 51.8-ft (15.8 m) wide trapezoidal tion and a cast-in-place closure joint three-cell box girder. An interesting was made. In other words, each half variation in this structure is that the

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

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

central box is cast in 25-ft (7.6 m) long The Brotonne Bridge crosses the segments on falsework; after the pre- Seine River downstream from Rouen cast inclined web segments are in France. An aerial view (Fig. 26) placed, the top slab is cast (Fig. 25). shows the general configuration of the Thus, the system uses a combination bridge. Fig. 27 shows an isometric of both precast and cast-in-place seg- view of a segment and the orientation mental construction. of prestressing and stay.13

main sta transverse post-tensioning

web

strut pos t- longitudinal post-tensioning /transverse post -tension Fig. 27. Isometric view of precast segment of Pont de Brotonne near Rouen, France. (Courtesy: Figg and Muller Engineers, Inc., Tallahassee, Florida.)

PCI JOURNAL/January-February 1979 ҟ 79 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 is spans. At present, this structure holds 4194 ft (1278 m). The central river the record length for a cable-stayed crossing includes a 1050-ft (320 m) bridge of prestressed concrete and for center span and 471-ft (143.5 m) side any type of concrete span. The main deck structure is a built-in balanced cantilever out from the pylon piers. Dimensions of the deck segments 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 is 9.8 ft (3 m) long. Similar to the Danube Canal Bridge, the only parts of the trapezoi- dal box girder that are precast are its sloping webs. The 9.8-ft (3 m) long, 13-ft (4 m) wide precast web elements are precast at the site. The balance of the cross section, including top and bottom flanges and its interior stiff- ening struts, is cast-in-place. Final support for the deck units is provided by 21 stays continuous through the pylon which lie in a verti- cal plane along the longitudinal axis of the structure. Spacing of the stays at deck level is 19.6 ft (6 m); thus, every other segment has a stay anchor. Fig. 29 shows the arrangement of the stays and the underside of the Fig. 29. Bottom view of deck segments segments of the Pont de Brotonne of Pont de Brotonne near Rouen, France. (looking up the pylon piers).

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

Arch Bridges the barges to the crown of the arch The Gladesville Bridge in Au- falsework and winched down to their stralia, completed in 1964, is a pre- proper position (Fig. 31).' cast segmental arch bridge (Fig. 30). Diaphragms are spaced at intervals The arch has a clear span of 1000 ft of 50 ft (15.2 m) to serve not only as (305 m) and consists of four arch ribs. supports for the slender columns The hollow box units and diaphragms which support the roadway above, but were cast 3 miles (4.8 km) down- also to tie the four arch ribs together. stream from the bridge site. The cast- When the units were located in po- ing yard was laid out such that the sition on the falsework a 3-in. (76 mm) manufacture of one arch rib could be joint between the precast units was accommodated at one time. cast-in-place. At two points, in each Each arch rib consists of 108 box rib, four layers of Freyssinet flat jacks units and 19 diaphragms. Each box were inserted, with 56 jacks in each unit is 20 ft (6 m) wide with depths layer. The rib was then jacked lon- decreasing from 23 ft (7 m) at the gitudinally by inflating the jacks with thrust block to 14 ft (4.3 m) at the oil one layer at a time, the oil being crown of the arch, measured at right replaced by grout and allowed to set angles to the axis of the arch. The before the next layer was inflated. length of the box units along the arch Inflation of the jacks increased the varies from 7 ft 9 in. (2.4 m) to 9 ft 3 distance between the edges of the in. (2.8 m). units adjacent to the jacks and thus the After the box units were manufac- overall length of the arch along its tured, they were loaded on barges and center line. In this manner a camber transported to the bridge site. The box was induced into the arch rib causing units and diaphragms were lifted from it to lift off the supporting falsework.

PCI JOURNAUJanuary-February 1979ҟ 81 Fig. 31. Erection of precast Fig. 32. Completed four arch ribs of segments of Gladesville Arch Gladesville Arch Bridge, Australia Bridge, Australia (Reference 14). (Reference 14).

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

82 The falsework was then shifted lat- Each independent arch rib is a erally into position to support the ad- two-cell box. The ribs are constructed jacent arch rib and repeat the cycle. A in symmetrical cantilever halves (Fig. view of the completed four arch ribs is 34) by the cast-in-place segmental shown in Fig. 32. method. As each rib is cantilevered A unique segmental arch bridge is out from its foundation, it is tem- the Talbrucke Rottweill-Neckarburg porarily tied back to rock anchors with located 50 miles (80 km) southwest of Dywidag bars. The roadway for this Stuttgart, West Germany, and crosses structure is composed of parallel the Neckar River (Fig. 33). Although single-cell box girders which are con- the structure is constructed utilizing a structed by the incremental launching cast-in-place segmental technique, it method (see Fig. 35 on next page). could, with some modification in de- With some modification in design, sign, be constructed with precast an arch bridge of this type could be segments. constructed with precast arch rib seg- The roadway of this 1197-ft (365 m) ments. The segments could be po- long structure is approximately 310 ft sitioned perhaps with the assistance of (95 m) above the river. The 507-ft (154 a high-line, held in position with tem- m) arch span has a rise of 164 ft (50 porary prestressing until permanent m). Roadway width is 102 ft (31 m). prestressing is installed and supported The entire structure is actually con- by the back stays until closure. structed in two independent lon- gitudinal halves, which are joined to- gether along the abutting edges of the Rigid Frame Bridges roadway trapezoidal box girder The Brielse Maas Bridge, near Rot- flanges. 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 frame B= Jacks C= Rubber bearing D= Joints

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

structure with its V-shaped piers (Fig. just, by means of jacks, the loads in 36). Transversely the structure is the inclined legs of the pier during made up of three precast single-cell various erection stages (Fig. 37). The boxes which are joined together at inclined legs are connected to the their flange tips with a longitudinal deck structure by post-tensioning and closure placement and are trans- the V-pier is supported at its base versely prestressed. through neoprene bearing pads on A special structural steel frame was piers founded on piles (Fig. 37). used to position the inclined precast hollow box legs of the piers and to The Bonhomme Bridge over the support the seven precast roadway Blavet River in Morbihan, France, is a girder segments prior to casting the slant leg rigid frame of cast-in-place joints at the corners of the delta pier segments (Fig. 38). The span between portion of the structure. This frame is the foundations of the slant legs is 611 also utilized to balance the pier dur- ft (186.25 m). A tubular steel falsework. ing erection of the balance of the was used to temporarily support the roadway girder segments and to ad- slant legs until closure at midspan.

-LORI ENT K ERV I GN ACS

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

PCI JOURNAL/January-February 1979ҟ 85 Closing Remarks

Precast prestressed concrete seg- The designer of a segmental bridge mental bridges have extended the must have detailed knowledge of the practical and competitive economic various alternatives, construction and span range of concrete bridges. They prestressing equipment, and site con- are adaptable to almost any conceiv- ditions. The designer must establish able site condition. This method can all major aspects of how the structure reduce environmental impact from will be constructed. Construction pro- that of conventional cast-in-place and cedures can no longer be isolated falsework type concrete construction. from design and vice versa. Although It is apparent that there are many most aspects of construction are fixed, ways in which segmental prestressed there is still leeway for both innova- concrete bridges may be constructed, tion and error in judgment. Since the using any of the four construction success of segmental construction is methods discussed in this paper. Pre- dependent upon agreement between cast concrete segments may be lifted the design assumptions and the con- by truck, crawler, or barge-mounted struction methods, it is essential that cranes or hoists secured on the top of designers and contractors interact previously placed segments. Giant during the design and construction gantry cranes may be used to span phases of the project. between bridge piers to erect the Segmental construction is a design segments. Precast segments can be in- concept that arose out of a need to corporated into a variety of bridge overcome construction difficulties. types such as cable-stay, arches and Therefore, as a concept, segmental rigid frames as well as the girder type construction's potential in general and bridge. Examples of many of these applicability to a specific project is construction procedures and equip- only limited by the innovation and ment and bridge types have been de- imagination of the designer and con- scribed in this paper. tractor.

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

86 References

1. Ballinger, C. A., Podolny, W. Jr., and 8. Finsterwalder, Ulrich, "New De- Abrahams, M. J., "A Report on the De- velopments in Prestressing Methods sign and Construction of Segmental and Concrete Bridge Construction," Prestressed Concrete Bridges in West- Dywidag-Berichte, 4-1967, September ern Europe-1977," International 1967, Dyckerhoff & Widmann KG, Road Federation, Washington, D.C., Munich, Germany. June 1978. (Also available from Fed- 9. Ballinger, C. A., and Podolny, W. Jr., eral Highway Administration, Office of "Segmental Construction in Western Research and Development, Wash- Europe, Impressions of an IRF Study ington, D.C., Report No. FHWA-RD- Team," Transportation Research Rec- 78-44.) ord 665, Bridge Engineering, V. 2, 2. PCI Committee on Segmental Con- Proceedings, Transportation Research struction, "Recommended Practice for Board Conference, September 25-27, Segmental Construction in Prestressed 1978, St. Louis, Missouri, National Concrete," PCI JOURNAL, V. 20, No. Academy of Sciences, Washington, 2, March-April 1975, pp. 22-41. D.C. 3. "Highway Design and Operational 10. Grant, Arvid, "Incremental Launching Practices Related to Highway Safety," of Concrete Structures," ACI Journal, Report of the Special AASHO Traffic V. 72, No. 8, August 1975, pp. 395-402. Safety Committee, February 1967. 11. Baur, Willi, "Bridge Erection by 4. Prestressed Concrete for Long Span Launching is Fast, Safe, and Effi- Bridges, Prestressed Concrete Insti- cient," Civil Engineering-ASCE, V. 47, tute, Chicago, Illinois, 1968. No. 3, March 1977, pp. 60-63. 5. Finsterwalder, Ulrich, "Prestressed 12. "The Danube Canal Bridge (Austria)," Concrete Bridge Construction," ACI STUP Bulletin, Freyssinet Interna- Journal, V. 62, No. 9, September 1965, tional, May-June 1975. pp. 1037-1046. 13. Lenglet, C., "Brotonne Bridge Longest 6. Muller, Jean, "Long-Span Precast Pre- Prestressed Concrete Cable Stayed stressed Concrete Bridges Built in Bridge," Cable-Stayed Bridges, Cantilever," First International Sym- Structural Engineering Series, No. 4, posium, Concrete Bridge Design, ACI June 1978, Bridge Division, Federal Publication SP-23, Paper SP 23-40, Highway Administration, Washington, American Concrete Institute; Detroit, D.C. , 1969. 14. "New Bridge over Parramatta River at 7. Muller, Jean, "Ten Years of Experi- Gladesville," Main Roads, Journal of ence in Precast Segmental Construc- the Department of Main Roads, New tion," PCI JOURNAL, V. 20, No. 1, South Wales, Australia, December January-February 1975, pp. 28-61. 1964.

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PCI JOURNAL/January-February 1979 ҟ 87