State of the Art for Long Span Prestressed Concrete Bridges of Segmental Construction

STATE OF THE ART FOR LONG SPAN PRESTRESSED CONCRETE BRIDGES OF SEGMENTAL CONSTRUCTION

Segmental prestressed concrete bridges are described in terms of cross-sectional shape, layout of tendons, casting procedures, jointing techniques, and design details. Techniques of analysis for structures of this type are reviewed. Prospects for use of this type of construction in the United States are discussed and current work outlined.

Geoffrey C. Lacey John E. Breen Ned H. Burns University of New South Wales The University of Texas The University of Texas Sydney, Australia Austin, Texas Austin, Texas

In highway bridge construction access and minimize obstruction. there is an increasing trend toward With stream crossings, even longer the use of longer spans. This trend is spans in the 300 ft. (90 m) range will the result of a number of different sometimes be necessary. When all requirements relating to safety, factors are considered the trend to- economy, function and esthetics. . ward long span bridges seems irre- The February 1967 report(38> of versible. the special AASHO Traffic Safety Precast I-girders, of the type now Committee calls for the "adoption widely used for spans up to 120 ft. and use of two-span bridges for over- (37 m), will not be adequate for passes crossing divided highways .. . these longer spans. It was pro- to eliminate the bridge piers normal- posed(48) that AASHO Type VII- ly placed adjacent to the outside girders might be used for simple shoulders." To comply with these spans up to 140 ft. (43 m) and con- safety criteria, two-span, three-span, tinuous spans up to 160 ft. (49 m) and four-span overpasses will be re- (where precast lengths of 80 ft. are quired with spans up to 180 ft. joined together by splicing). To ob- (55 m). tain greater spans than this, the use In the case of elevated urban ex- of haunched sections or inclined pressways, long spans will facilitate piers was also proposed.

September-October 1971 53 Table 1. Segmental precast, post-tensioned box girder bridges

Cells Spans No. of Per b b Bridge and Location Year ft. Boxes Box ft. ft. Australia Silverwater Bridge, Sydney 1962 120-20 -120 2 1 —— Commonwealth Avenue Bridge, 1963 185-210-240-210-185 1 3 40 40 Canberra Taren Point Bridge, Sydney 1964 2 @ 235-250-2 @ 235 4 1 21 11 Austria Traun Bridge, Linz 1961 246-30 -246 4 1 22 7.9 Ager Bridge 1963 238-278-278-117 1 1 46 17.7 Canada Lievre River Bridge, Quebec 1967 130-26 -130 1 2 33 22 Czechoslovakia Ondava Bridge, Sirnik 1964 98-197-98 2 1 18 7.9 Kosicke Hamre Bridge 1965 126-25 -126 — - Railway Bridge, Margecany 1966 100-180-100 1 1 18.4 - England Hammersmith Flyover, London 1961 11 @ 140 1 3 61 10

Mancunian Way, Manchester 1966 28 @ 105 1 1 30 9 Western Avenue Viaduct, 1968 [Several @ 115 (approx.) 1 3 62 — London 1Several @ 204 (approx.) 1 3 94 - France Choisy-Le-Roi Bridge, Paris 1965 123-180-123 2 1 22 12 Bridge on the Rhone at 1184-276-184 — 2 1 27 11.5 Pierre Benite 1965 164-246-246-164 Oleron Viaduct 1965 26 @ 259 1 1 35 18 Courbevoie Bridge, Paris 1966 131-197-131 4 1 29 - St. Denis Viaduct, Paris 1966 6 @ 157 2 2 47 23.1 Pont Aval, Paris 1967 221-301-267-234 2 1 26 11.5 Japan Kakio Viaduct 1964 69-3 @ 122 1 1 23 13.1 Kamiosaki Viaduct 88102-88—— 2 1 24 9.8 196 { 75-129-75 Konoshima Bridge 1968 138-282-138 1 1 27 13.1 Tama Bridge 1969 164-165-165-164 2 1 20 - Mexico Bridge in Veracruz State 1965 20-131-20 1 1 14 7 Netherlands Oosterschelde Bridge 1965 52 @ 312 1 1 39 22 Hartelkanaal Bridge 1967 220-375-220 2 1 28 .Poland Bridge near Bomberg 1966 59-141-59 — —— - Russia Autosawodbridg 1960 119-487-119 — —— Ojat Bridge 1961 105-210-105 ——— Irtysch Bridge 1961 361 3 — — - Schelnicha Bridge, Moscow 1964 198-420-198 — — 48 - Don Bridge, Rostow 1964 260-455-260 — —— - Venezuela Caroni Bridge — 157-4 @ 315-157 1 1 34 13.1

Notes: See Fig. 1 for dimension designations in columns 6 to 9. 1. C3 = 3 in. concrete joint; E = epoxy joint; D = dry joint. 2. FT = falsework trusses; F = falsework; FG = falsework girders; C = cantilever construction; A = assembly on shore.

54 PC[ Journal

L Table 1. (Cont.)

Span/ Segment Joints Erection depth Length Method2 ratio dmas. drain. L ft. ft. drain. ft. Support System and Special Features

--- - C 3 F T Deck cast in place 9 9 27 10 C 3 F Roller bearings on piers - 10.5 24 9 C 3 F T Cantilever-suspendedҟspan system- box section and slab cast separately 13.4 13.4 23 13 C F 14 14 22 30 C F 14.8 5.8 - 9.5 E C Bridge and segments are skewed 10 4.6 - 9.8 C 1.2 C Structure forms a 3-span frame with a hinge in the middle-deck slab be- - -- 9.8 C 1.2 C tween boxes cast separately 13 7.1 25 9.8 C C 9 6.5 21 10 C 3 F Girders rigidly connected to columns -superstructure includes box section and "coathanger" units 4.3 4.3 25 7.5 C 3 F "Rotaflon" sliding bearings on columns 5.5 5.5 21 7.7 C 4 F G Sliding bearings on columns 10.25 10.25 20 7.8 C4 FG Superstructure forms a portal with the 8.2 8.2 22 8.2 E C piers and is simply supported on the abutments 14 11.8 23 9.8 E C Girders are made continuous with the caissons 14.8 8.2 - 10.8 E C Semirigid support from neoprene pads 7.5 7.5 26 12.5 E C on the piers 6.6 6.6 24 9.8 E F Deck slab projections cast separately 18 11.1 29 12.5 E C -bridgeҟis curved-simple support from neoprene pads on the piers 6.0 6.0 20 10.6 C 14 F 4.9 4.9 26 8.2 E C 14.1 6.6 - 9.8 E C 8.8 8.8 19 11 E C 7.2 7.2 18 3 C C 19 7 - 42 C 16 C Girders continuous with piers-dow- elled expansion joints at span centers 17.3 4.9 ------9.8 D C - -- - C8 C -- - 7.2 D C - - - 10.7 C 0.8 C - -- 9.8 E C - -- 9.8 E C 18.4 18.4 17 - - A

September-October 1971ҟ 915 a

(a) SINGLE CELL BOX GIRDER

v \ I

(b) SINGLE CELL BOXES CONNECTED BY UPPER SLAB

bҟJ

(c ) TWO-CELL BOX GIRDER

Fig. 1. Types of segmental box girder cross sections

56ҟ PCI Journal ASPHALT SURFACE IN SITU EDGE BEAM

61-0

CAST ROAD SLABS

PRE(

ESSING CABLES

TRANSVERSE PRESTRESSII BARS

Fig. 2. Hammersmith Flyover, London, England

A substantial number of long span When construction of large num- bridges have been constructed bers of bridges is envisaged, as in a. throughout the world utilizing pre- highway department, precasting has stressed concrete box girders. This a number of advantages over cast-in- type results in a very compact struc- place construction: tural member, which combines high 1. Mass production of standard- flexural strength with high torsional ized girder units is possible, strength. The box girders may be ei- such as is presently done with. ther cast-in-place or precast in seg- precast I-girders for shorter ments. Their suitability for very long spans. spans can be seen from the Bendorf 2. High quality control can be at- Bridge in West Germany, which was tained through plant produc- cast-in-place and has a span of 682 tion and inspection. ft. (208 m). In the United States, 3. Greater economy of production cast-in-place box girder bridges are is possible by precasting girder being widely used by the California units at a plant rather than Division of Highways, as well as by casting them in place. several other states; precast, segmen- 4. Speed of erection can be much tal box girder bridges are now under greater which is very important construction in Nova Scotia and when construction interferes Texas. with existing traffic and is par-

September-October 1971ҟ 57 ticularly critical in an urban en- vironment. This paper will examine in detail one means of achieving long spans in bridge structures, namely, segmental z precast box girder construction. The o reason for casting short segments is that box girders, unlike I-girders which have narrow width, cannot be readily transported in long sections. In addition, the short units are suited to fairly simple methods of assembly and post-tensioning to form the completed structure. The length and weight of the segments are chosen so as to be most suitable for transporta- tion and erection. U-

+^. TYPES OF CROSS SECTION AND E PRESTRESSING SYSTEMS Dimensions and details of a num- a)E ber of segmental, prestressed concrete box girder bridges are sum- marized in Table 1 and the cross sections of many of them are shown in o Figs. 1 to 15. With the exception of the Hammersmith Flyover, the superstructures of these bridges generally conform to three main types: 1. the single cell box girder; 2. a pair of v single cell box girders connected by T a deck slab; 3. the multi-cell box girder (see Fig. 1). The prestressing M systems used depend partly on the i^. type of cross section, the structural system, and the method of construction, but vary greatly from bridge to bridge. Several of the bridges included in Table 1 are described in detail in the following sections. Hammersmith Flyover. The Ham- mersmithFlyover in London(l"2'6) is of unique construction (see Fig. 2). ° The main girder element is a three- cell hollow box, 26 ft. (7.9 m) wide, cast in segments 8 ft. 6 in. (2.6 m) long. These alternate with 1 ft. (0.3 m) thick, precast cantilever "coat hanger" sections 60 ft. (18.3 m) wide.

58 PCI Journal ,.ҟ24.- 0,. 0 ҟ24- 0"

IN-SITU MEDIAN STRIP

Fig. 4. Mancunian Way, Manchester, England

The sections are joined by 3 in. (7.6 lapping groups, each group passing cm) of cast-in-place concrete. Pre- through two successive spans and cast concrete slabs form the deck of overlapping the next group by one the structure. The cantilever sections span length (see Fig. 3). Both ends act as diaphragms for the box girder are anchored in the top flange of the and also support the outer deck slab box girder after passing over a col- units. The girders are rigidly con- umn. The cables are kept in position nected to their supporting columns, by steel saddles over the columns which in turn rest on roller bearings and at points 25 ft. (7.6 m) on either at their bases. side of midspan; cable profiles are The Gifford-Udall system is used linear between saddles. for longitudinal prestressing. The girder segments over the col- Stranded cables, Pk-in. (2.86 cm) in umns are prestressed transversely diameter, are arranged in four clus- through the top flange and are tied ters of 16 each, one cluster on either to the columns with vertical pre- side of each inner web of the girder. stressing. At midspan, each cluster passes through a 10-in. (25.4 cm) diameter Single cell box girders. The follow- duct in the lower flange. The cables ing bridges are of this type: Ager are arranged longitudinally in over- (Austria), Margecany (Czechoslova-

34.8

Fig. 5. Oleron Viaduct, France September-October 1971 ҟ 59 Fig. 6. Superstructure of the Oosterschelde Bridge, Netherlands

kia), Mancunian Way (England), 01- prestressing cables. There are 16 ca- eron (France), Kakio and Konoshima bles through each section with two (Japan), Oosterschelde (Nether- layers of four in each web. Each lands), and Caroni (Venezuela). span contains two sets of cables, The Mancunian Way, Manches- each set being two spans long, over- terM26'39 , comprises a pair of single lapping the next set by one span cell box girders, joined by a cast-in- length, and anchored near the quar- place median strip (see Fig. 4). The ter points of the spans. The girders upper slab of each box is cantilev- are supported by Rotaflon sliding ered to accommodate the roadway bearings on the columns. width. The precast segments are 7 ft. Oleron Viaduct in France(20,24.42) 3 in. (2.2 m) long, with 3-in. (7.6 cm) is a single cell box girder bridge, concrete joints between. The vertical with the upper deck slab cantilev- webs of the box girders are made ered out to a total width of 35 ft. thick enough to accommodate all the (10.7 m) (see Fig. 5). The precast seg-

Fig. 7. Ager Bridge, Austria 60ҟ PCI Journal c.

Fig. 8. Choisy-Ie-Roi Bridge, Paris, France

ments are 10.8 ft (3.3 m) long. The long with cantilevered upper slabs girders are prestressed in both the and a constant depth of 14 ft. (4.3 longitudinal and transverse direc- m). The prestressing cables are ex- tions and are elastically fixed to each ternal to the section within the cell pier through four neoprene bearing but bonded to the web by concrete pads. encasement and held by stirrups an- The Oosterschelde Bridge in the chored in the web. Netherlands(21,31) is a single cell box girder with cantilevered upper Parallel single cell boxes connected slab (see Fig. 6). The precast seg- by a deck slab. This type includes ments are about 41 ft. (12.5 m) long the following bridges: Ondava and vary in depth from 19 ft. (5.8 m) (Czechoslovakia), Choisy-le-Roi, at the piers to 7 ft. (2.1 m) at mid- Pierre Benite, Courbevoie, and Pont span. The structure is not continuous Aval (France), Kamiosaki and Tama but consists of a series of double (Japan), and Hartelkanaal (Nether- cantilevers rigidly supported at the lands). piers and separated by open joints at The Choisy-le-Roi Bridge, Paris, midspan. To restrict vertical move- France "16'33 ), consists of two identi- ment while accommodating expan- cal half bridges (see Fig. 8). These sion between the cantilever ends, are connected by a 4 ft. (1.2 m) wide dowels and shock absorbers were in- concrete slab with a longitudinal stalled at the midspan joints. Longi- hinge joint on either side, and are tudinal prestressing consists of tied together with transverse post- Freyssinet cables in the deck with a tensioning. The three-span continu- few in the lower slab near midspan. ous girders form a portal frame with Segment walls are stressed vertically the two piers and are simply sup- with unbonded bars and laterally ported at the abutments. with Freyssinet tendons. Each half bridge, 44 ft. (13.4 m) in The Ager Bridge in Austria(9,23) width, consists of two box girders, (Fig. 7) consists of a pair of indepen- 8.2 ft. (2.5 m) in depth and cast sep- dent, single cell box girders made up arately in 8.2 ft. long segments. The of precast segments 30 ft. (9.2 m) top slab of each box is cantilevered

September-October 1971ҟ 61 out in both directions. After erection and longitudinal post-tensioning, the two girders are connected rigidly with a concrete joint and transverse post-tensioning. At the piers the two box girders are braced together with a transverse box, the vertical faces of which also function as girder diaphragms, one over each wall of the V-shaped pier. There are single diaphragms at the abutments, both in- ternally and externally (i.e., between the two box girders) but no intermediate diaphragms. ao There are two sets of longitudinal prestressing cables (see Fig. 9). The m primary function of one set is to 0 withstand the negative moments during construction (by the cantilev-

7.U, er method). Some of these cables, of 0 varying length, run horizontally in

0 the deck slab; the remainder have

0 4- draped profiles with anchorage in aD the girder web. The second set of w0 cables is located in the lower slab for 0 positive moment near midspan with C) most of them draped and anchored

U in the deck slab. The bridge on the Rhone at Pierre c Benite(34 > (Fig. 10) consists of a pair

to of single cell box girders with pro- c jecting upper slabs, rigidly con- 0 nected after erection. The depth is o; 11.8 ft. (3.6 m), except near the sup- ab ports where it increases to approxi- U- mately 14 ft. (4.3 m). Each box is cast in segments 9.8 ft. (3.0 m) long. The superstructure is continuous over the intermediate supporting caissons, to which it is rigidly connected, and it rests on neoprene pads at the abutments. Two diaphragms at each cais- son are extended to form a transverse box section bracing the two box girders. There are single diaphragms at the abutments but no intermediate diaphragms. The girder segments and the diaphragms at the caissons and abutments are cast in

62ҟ PCI Journal c. R,

Fig. 10. Rhone River bridge at Pierre Benite, France

place, because of the skew of the girders, with upper slabs rigidly con- bridge, whereas all other segments nected by an 8-in. (20.3 cm) cast-in- are prefabricated. place joint and transverse post-ten- As in the-case of the Choisy-le-Roi sioning. Overall width is 52 ft. (15.9 Bridge, there are two sets of longitu- m); girder depths are 11.1 ft. (3.4 m) dinal prestressing cables for negative over the central portions increasing and positive moments, respectively. to 18 ft. (5.5 m) at the supports. The After erection and longitudinal post- precast segments are 12.5 ft. (3.8 m) tensioning, the two boxes are con- long. The bridge has four continuous ',' nected by a 3.6 ft. (1.1 m) wide slab spans and is supported on neoprene and transverse post-tensioning is ap- pads. The layout of the longitudinal plied. prestressing cables is similar to that The superstructure of the Pont of the Choisy-le-Roi Bridge. Aval in Paris(41'52) is similar to that of Pierre Benite (see Fig. 11). It con- Multi-cell box girders. The following sists of a pair of single cell box bridges are of this type: Common-

52.0

mr _

11.5

26.2

Fig. 11. Pont Aval, Paris, France

September-October 1971 63 I

ING PANEL

4NDS

Fig. 12. Commonwealth Avenue Bridge, Canberra, Australia

wealth Avenue (Australia), Lievre Both three-cell units, with projecting (Canada), Western Avenue (En- deck slabs, were cast in full-width gland), and St. Denis (France). segments (see Fig. 14). One unit has Commonwealth Avenue Bridge, a width of 62 ft. (18.9 m) and the Canberra, Australia( lo.11 >, is a three- girder spans approximately 115 ft. cell box girder consisting of precast (35.0 m). The other unit is 94 ft. (28.7 segments 9 ft. (2.7 m) high, 10 ft. (3.0 m) wide and is post-tensioned longi- m) long, and 40 ft. (12.2 m) wide (see tudinally, transversely and vertical- Fig. 12). Diaphragms are included at ly; the average girder span is 204 ft. the piers and near the third points in (62 m). In both cases the continuous each span, where a change in direc- superstructure is seated on sliding tion of the longitudinal prestressing bearings on the columns. cables occurs. The girder is sup- The St. Denis Viaduct, Paris, ported on roller bearings seated on France(24), shown in Fig. 15, com- the piers. The bridge is post-ten- prises two half bridges, each a two- sioned from end to end, using 1%-in. cell box girder with projecting deck (2.86 cm) diameter tendons placed slab. on either side of the four webs of the box girders. The tendon profile is METHODS OF PRECASTING shown in Fig. 13. Vertical post-ten- The methods of precasting used sioning was applied to the webs of with segmental box girder bridges the box girder segments adjacent to will be largely dependent on the and at the piers and transverse post- procedures selected for erection and tensioning to all diaphragms. jointing. General precasting advan- The Western Avenue Viaduct in tages have been outlined by Ger- London(49 >, includes two different wick(12). Precasting operations gen- wide, three-cell box girder bridges. erally follow normal procedures and

B4 PCI Journal segments have been cast in many different types of forms and posi- tions. The box girder segments and cantilever units for the Hammersmith Flyover were cast on end (i.e., on a face that later would be in contact with a cast-in-place joint after erection) using steel forms. Both types of

units contained normal reinforce- LL

ment and 6000-psi (420 kg/cm2) z concrete, and they were stripped 18 a LL hours after casting. 4) M In the French bridges, special C v techniques were developed to fabri- U-LL ` d N cate segments with ends suitable for z C epoxy resin jointing( 24 ,28 ). In order 00 to minimize the joint thickness it was C4 necessary to obtain a perfect fit between the mating ends of adjacent Co

segments. This was achieved by cast- C 0 ing each segment against the end w E face of the preceding one and later 0 E z 0 erecting the segments in the same J U order they were cast. U- 0 0 4- For the Choisy-le-Roi Bridge, the a, UI seg ments of a box girderg were cast in 0 0 z a line, using a single steel form assem- a> bly riding on rails. The rails were set I- .Q U) to the required profile of the under- 0 side of the bridge, allowing for cam- C ber. After each segment had set, the C ends were sprayed with a bond- I bo breaking resin and the next segment C z 0 cast against it. The line of assembled w J n units was then dismantled and reas- r, sembled in the same order during an erection. An important advantage of L this system is that it guarantees alignment of the span. However, the cost and difficulty increase with span length, and it is hard to provide for variation in cross section. In the case of Pierre Benite another procedure was adopted. The forms were fixed in position and after each casting the segment was re- ' moved, first to the position of "coun- ter-form" for the next segment and

September-October 1971ҟ 65 0I. - 4••

(a) 94-ft. WIDE SECTION.

62- 0"

(b) 62-ft. WIDE SECTION

Fig. 14. Western Avenue Viaduct, London, England

then to storage. The form assembly setting of the epoxy. Generally, the included an adjustment for variation flanges were also keyed. in depth. With this procedure pre- cautions must be taken to ensure ERECTION METHODS proper alignment of the fabricated Most of the bridges studied have bridge girder. Pont Aval was fabri- been erected by one of the following cated in a similar manner with the three methods: 1. erection on false- alignment of each pair of segments work, 2. assembly on shore, and 3. checked on fabrication and any error the cantilever technique. There may compensated for in the next seg- be considerable variation in each ment. The segments for the St. Denis method from bridge to bridge. For Viaduct were cast on end instead of example, falsework may have short in the normal horizontal position. spans with closely spaced supports, In all cases the ends of the webs as in the case of a viaduct not pass- of the box girder segments were ing over existing roads, or may con- keyed to prevent vertical slip before sist of large trusses or girders span-

66ҟ PCI Journal ping from bridge pier to bridge pier the succeeding span and was in- or even longer. serted and stressed after erection of There is also considerable varia- this span. All cables were stressed tion in lifting and placing tech- from both ends simultaneously, and niques, especially with cantilever were finally grouted in the ducts in erection. Lifting devices may be sup- the flange and bound to the webs ported either on or below the with mortar casing. Lifting hooks bridge; . segments can be brought in cast into the segments were burned from below or transported along the off after erection. top of the partially completed On Mancunian Way, the segments bridge. . were hoisted into place on the false- The erection method used for work with a truck crane, utilizing each bridge is indicated in Table 1. temporary lifting hooks cast into the webs. The joints were concreted and Erection on falsework. A number of the prestressing cables threaded segmental precast bridges, especially through the ducts. Each span con- viaducts built over land, have been tained two sets of cables, each set constructed on falsework. On the being two spans long and overlap- Hammersmith Flyover, the segments ping the next by one span length. As were lifted onto the falsework by a each span was erected, one set of gantry crane riding on rails on top of cables was stressed sufficiently to the previously placed segments. take the dead load. Falsework was They were then adjusted in position removed and taken forward to an- by means of jacks. The 3-in. (7.6 cm) other span. Finally, the partially joints were filled with concrete and, stressed span received its second set after design strength was reached, of cables and was fully stressed. The the longitudinal prestressing was ap- cables were again tensioned from plied. The prestressing cables were both ends at the same time. arranged longitudinally in overlap- On the Commonwealth Avenue ping groups, as described on page Bridge, the precast elements were 59, so that each newly erected span lifted into position on timber false- had only one group of cables in it, work by an overhead traveling gan- thus receiving initially only half the try crane and shifted into their exact total prestressing force. The second location by hydraulic jacks. The pre- group of cables lapped forward into stressing cables, running the full

23.1

Fig. 15. Saint Denis Viaduct, Paris, France September-October 1971ҟ 67 length of the bridge, were tensioned may then be positioned by means of from both ends. As the strands barges, as in the case of a number of stretched several feet during stress- Russian bridges(12), or by launching ing, the load had to be applied in over the piers, as on the Caroni stages, each stage being limited by Bridge in Venezuela(5). the stroke of the jack, anchored tem- Cantilever construction. A number porarily, and the jack moved for- of long-span bridges, especially ward and reset. After stressing, the cables were encased in concrete those constructed over water, have been erected without falsework by bonded to the webs of the box gird- 28.29). This er. the cantilever technique( involves placing the precast seg- In the case of the Western Avenue ments, two at a time, symmetrically Viaduct, a pair of large steel girders, on either side of a pier. Resistance longer than the bridge spans, was mounted on steel falsework around against the increasing negative the columns. The tops of these gird- bending moment is provided at each stage of construction by adding pre- ers were set at the same height as the stressing cables of increasing length bottom of the box girder elements. in the top chord of the girder. The Mobile cranes set the segments for pier must be designed for possible one span on top of the steel girders, unbalanced moment loadings or sup- leaving 4-in. (10.2 cm) gaps between plemental struts or ties may be pro- segments. After concreting of the vided. joints, the prestressing cables were In the case of the Choisy-le-Roi threaded through the ducts and Bridge, the segments were trans- post-tensioned. ported by water and lifted into place Movable falsework trusses have with a floating crane. Steel jigs set been used to construct bridges over inside the cantilever arms were used water. In the Silverwater( 3,12> and Taren Point(14,15) bridges in Austra- for exact positioning. As each pair of segments was placed, the prestress- lia, the trusses were supported on ing cables were threaded through ledges at the piers. The segments the ducts, the abutting faces were were assembled on them, the 3-in. coated with epoxy and brought into (7.6 cm) joints concreted, the pre- contact and the cables were ten- stressing cables placed and tensioned. This balanced erection pro- sioned, and the trusses moved for- cedure was continued at both piers ward. A number of bridges in Japan until the symmetrical cantilever have been constructed over existing arms were completed. The gap at highways using steel erection trusses the center of the main span was then to minimize interference with traffic. closed with a 16.4 ft. (5.0 m) long The trusses are set below, alongside closing segment. A longitudinal com- or above the bridge superstructure, pressive force was applied at the depending on head-room require- joints by means of a Freyssinet flat ments. jack, inserted at the top of the box Assembly on shore. Another method girder webs, in order to compensate of erection for river bridges is to as- for shrinkage and prestressing short- semble the precast elements on ening effects and to create an initial falsework on the shore. The joints positive moment. The closing joints are then concreted and the prestress- were then concreted and finally the ing applied. The assembled girders longitudinal prestressing was corn-

68ҟ PCI Journal pleted. segments of a segmental bridge are On the Pierre Benite Bridge, also of critical importance. They must by cantilever construction, the seg- have high strength and durability ments were transported by water and must be reasonably easy to con- and lifted into place by hoists sup- struct. Table 1 gives the joint type ported on the bridge itself. for each bridge listed. The various For Pont Aval, the segments were kinds of joints used in existing pre- lifted by cranes on both land and cast, segmental bridges are de- water. During cantilever erection, scribed in the following sections. additional temporary support for the girders was provided at a distance of Concrete joints. Reinforced concrete 8 ft. (2.4 m) from the pier centerline. joints 8 in. to 24 in. (20.3 to 60.9 cm) This was to ensure an effective rigid in width have been widely used. Re- fixity for the double cantilevers, inforcing steel left projecting from. which the narrow pier top alone the ends of the segments are usually could not provide. After closure and connected by lapping or welding. post-tensioning, the girders were High strength concrete is placed and placed on simple neoprene supports. consolidated in the joint(12). The Oleron Viaduct was con- In several of the bridges in Table structed with the help of a 300 ft. (91 1, the precast segments were con- m) long steel truss supported on top nected by cast-in-place or grouted of the superstructure. The lower joints of unreinforced concrete or chords of the truss served as twin mortar. The joint width is generally monorails for the suspended erection between 1 in. and 4 in. (2.5 and 10.0 equipment. The segments were cm), but widths up to 16 in. (40.7 transported along the deck already cm) have been used. The end faces constructed and lowered into place of the segments generally contain. with this equipment. rectangular indentations to serve as A steel truss supported on the su- shear keys between the precast ele- perstructure and extending over 2% ments and the cast-in-place concrete. spans was used in the cantilever Gerwick reports (12) that "buttered. erection of the Oosterschelde joints of mortar have generally not Bridge. The segments were brought proven successful, due to stress con- in under it by barge and hoisted into centrations from inequality of mor- place by traveling cranes mounted tar thickness. Dry packed joints of t- on the truss. The joints were con- in. (2.5 cm) width have been tried creted and prestressing applied after but it is difficult to achieve uniform- each pair of segments was erected. ly good workmanship." Using the cantilever construction method, erection speeds of the order Epoxy resin joints. In a number of of 40 ft. (12 m) per day can be bridges constructed by the cantilev- achieved with precast segmental er method, especially in France, Ja- bridges(24). This compares with a pan and Russia, the precast elements rate of 4 ft. (1.2 m) per day using were connected by a thin layer of cantilever erection for a typical cast- epoxy resin no greater than 42-in. in-place bridge. (0.8 mm) (16). These epoxy joints require perfectly matching surfaces on the ends of adjacent segments, JOINTS achieved by match casting. Shear The joints between the precast keys in the webs transmit vertical September-October 1971ҟ 69 shear forces while the resin sets and normal to the plane is governed by also serve a very useful function in the equations of biaxial plate bend- controlling alignment. ing. The Goldberg-Leve load dis- Tests to determine the strength of placement equations were utilized, thin epoxy resin joints have been in conjunction with the direct stiff- carried out in England, France, ness technique, by Scordelis(35,45) Japan, Czechoslovakia and Rus- to develop a general purpose com- sia(8'52). These tests have indicated puter program for the analysis of that it is possible to develop 94 per- continuous, prismatic box girders of cent of the flexural tensile strength arbitrary cross section. Intermediate of a comparative monolithically cast and support diaphragms were con- test specimen and approximately 75 sidered. This method has also been percent of the shear strength. Fail- utilized by Mattock and Johnston(54) ures generally occur in the concrete to compare analytical results with but not in the epoxy. The type of those from an extensive model anal- epoxy resin must be compatible with ysis with reported good correlation. damp surface conditions and have a A majority of the analytical tech- minimum pot life of 1% hours. niques fall into the thin-walled beam theory category. This approach takes Dry joints. Dry joints are those in advantage of the fact that, for the which the segments are in direct type of structures under considera- contact. They were used in the Ojat tion, longitudinal moments and asso- Bridge in Russia(32), the bridge near ciated slab shears are quite small Bomberg, Poland, and in California and can, consequently, be neglected. in the tunnel portion of the Bay Wright, et a1 050), have extended Bridge Reconstruction Project( 12). In the "generalized coordinate" tech- the latter case, chamfering of the nique of box girder analysis, origi- joint edges was found to be desirable nally presented by Vlasov, to ac- to prevent local spalling while stressing. count for anisotropic plate elements, flexible interior diaphragms and in- METHODS OF ANALYSIS termediate supports. The method The past half-decade has seen a makes further assumptions on the proliferation of publications dealing deformation of the basic plate ele- with the analysis of complete plate ment by neglecting torsional mo- assemblages, i.e., folded plates and ments and shear distortion. How- box girders(63). All of these proce- ever, the agreement reported be- dures are applicable to completed tween this method and a more bridges and do not consider segmen- refined analysis is good. tal construction problems. The Lo and Scordelis(58) have adopted most generally applicable analytical the assumption that longitudinal and methods can be categorized as: 1. torsional moments are negligible, to folded plate analysis, 2. thin-walled arrive at still another formulation beam theory, and 3. finite element falling into the thin-walled beam techniques. theory category. The technique, Folded plate analysis is the most termed "the finite segment method", exact of the three approaches. The requires division of the structure behavior of the plate element in its both transversely and longitudinally plane is governed by the plane stress into rectangular sub-regions. Each equations of elasticity, while that sub-region is assumed to behave as a

70ҟ PCt Journal beam in the longitudinal direction properties of the elements may be and a one-way slab in the transverse varied arbitrarily throughout the direction. The primary advantage is structure, and arbitrary loading may the generality of boundary and load- be considered. Numerous boundary ing conditions which may be treated. conditions, and both intermediate, Restraint from boundary and interi- shear-rigid diaphragms and dia- or supports is specified independent- phragms over supports, may be ly for each element of the cross sec- treated. The work of Meyer and tion; consequently, the structure Scordelis extends this analysis to in- may be completely free, fixed, or clude consideration of plate stiffen- something in-between at the bound- ers and flexible frame supports. The aries and supports. Both intermedi- primary disadvantage associated ate, shear-rigid diaphragms and dia- with the finite element method is the phragms over supports may be han- number of equilibrium equations dled. The noted assumptions result which must be solved, requiring vast in the minimum number of degrees computer storage and extended exe- of freedom necessary to model the cution times for even moderate size behavior of a box girder structure. problems. Scordelis(45 has com- However, they also inflict limitations pared results of the finite element upon the method, which can pro- method with those of the folded duce inaccuracies in the results plate method and reports good cor- under certain circumstances. Scor- relation. As the finite element mesh delis(45> reports that correlation be- size decreases the correlation im- tween the approximate finite seg- proves indicating convergence of his ment method and the more exact finite element analysis. folded plate method is good. The analytical techniques dis- The finite element method is the cussed above involve a large number most general of the analytical tech- of computations and, therefore, ne- niques. The structure is divided into cessitate use of a digital computer. sub-regions, the deformation pat- Wright, et al(57), and Tung(ei) terns of which are assumed. Dis- have used a technique for analysis of placement functions are assumed single cell, rectangular or trapezoid'.- such that when displacement com- al, box girders which is suitable for patibility is explicitly enforced at hand calculation. The analysis falls two element nodal points, the dis- into the thin-walled beam theory placements along the element inter- category. The analysis for the tor- face connecting the two points will sional load component is based upon be compatible. Once the displace- the analogy between the differential ment assumptions are made, the ele- equations governing the response of ment stiffness matrix may be de- a beam on an elastic foundation and rived, and the analysis is carried out that governing the response of the by the direct stiffness method. single cell to the distortional load Scordelis(45 ) and Meyer and Scor- component. The technique is quite. delis(62) have employed the finite general in that it may be applied to element method for the analysis of continuous, prismatic or haunched box girder structures. Scordelis em- girders with arbitrary end condi- ploys a rectangular element with six tions, anisotropic plate properties, degrees of freedom per nodal point. and interior rigid or flexible dia- The size, thickness, and material phragms. The disadvantage is that it

September-October 1971ҟ 71 I- 0U) U

ҟ 36ҟ32ҟ29ҟ25 24ҟ21 18

SPAN/DEPTH RATIO Fig. 16. Relation between span/depth ratio and cost

is strictly applicable to single cell way at The University of Texas is in- sections. Wright compares the re- corporating capabilities for consider- sults from the beam on elastic foun- ing arbitrary longitudinal prestress- dation analogy with results from a ing and segmental stage construction more rigorous analysis and con- into the finite segment analysis. cludes that this method predicts the These capabilities, coupled with longitudinal and transverse stresses those already a part of the analysis, resulting from torsional load compo- will result in a general purpose com- nents adequately for design pur- puter program for the analysis poses. of segmentally constructed pre- It is evident that although consid- stressed box girders at each stage of erable analytical capability is avail- erection. able for analysis of completed box girder structures, there has been lit- SUMMARY AND CONCLUSIONS tle consideration given the analysis Most of the bridges which have of segmentally constructed pre- been segmentally constructed are stressed girders. Considerations such continuous over all or several spans. as longitudinal and/or transverse Exceptions are the Oosterschelde prestressing, and the continuously Bridge, which is a double cantilever changing structural system to be an- system; Taren Point Bridge, a canti- alyzed, do not, of course, alter the lever-suspended span system; and basic problem. They do, however, the Ondava Bridge, a three-span add several additional complications frame with a hinge in the middle of heretofore not considered. the center span. A research effort presently under- Bridges having spans up to about

72 PCI Journal 250 ft. (75 m) are generally of uni- span. form depth, whereas those with In most bridges the prestressing greater spans generally vary in cables are internal, i.e., located in- depth from a maximum at the sup- side the upper and lower slabs and port to a minimum at midspan. In the webs of the box girder. How- the case of uniform depth bridges, ever, in some cases, such as the the span/depth ratio is generally in Hammersmith Flyover, the Com- the range of 20 to 27. The relation monwealth Avenue Bridge, the Ager between this ratio and cost needs in- Bridge, and the Kakio Viaduct, ex- vestigation. Esthetic factors are also ternal tendons are used. External important here since a smaller depth tendons permit the use of smaller generally has a better appearance. web thicknesses and may reduce One investigation of the relation friction Iosses, but they do not ap- between span/depth ratio and pear to be suitable for cantilever cost(22) is of a three-span continuous construction or for curved cable pro- bridge with a total length of 235 ft. files and have generally not been (72 m). The results, shown in Fig. 16, used in the more recent bridges. indicate a span/depth ratio of 25 to The superstructures of the bridges be the most economical. However, are generally supported by means of this result, based on economic condi- rigid attachment to the piers, roller tions in Germany, cannot be readily or sliding bearings, or neoprene generalized. pads. Neoprene pads, as used in All of the bridges studied have in- Pont Aval, are a very simple and ternal diaphragms at the supports to economical means of support and of- transmit the reaction from the super- fer possibilities for extensive use. structure to the bearings and to en- Erection on falsework with close- sure the rigidity of the box girder. spaced supports is the simplest External diaphragms have been method of construction when condi- found to add to the difficulty of mass tions permit. For bridges having production and it may be possible to three or more spans where interme- omit them altogether, as was done diate support is not possible, the with Pont Aval, Paris. Some of the cantilever method will probably be earlier bridges have intermediate the most suitable. There will be a diaphragms between supports, how- critical span length, however, below ever, in most bridges they were which it will be more economical to found to be unnecessary and they use a falsework truss. are omitted. For two-span bridges over an ex- In bridges which are continuous isting highway, the two main alter- over several spans and are con- natives are cantilever construction or structed on falsework, long pre- erection on a falsework truss or gird- stressing cables for two or more er. If cantilever construction is spans can be used. For bridges con- adopted, there are two possible pro- structed by the cantilever method, cedures: 1. to cantilever all the way the longitudinal prestressing always from the pier to the abutments, or 2. consists of two sets of cables—one set to cantilever from the abutments as in the deck slab designed to resist well. In the latter case, the abut-- the negative moments during con- ments would have to be designed for struction and one set in the lower this unbalanced cantilevering during slab for positive moment near mid- erection. Erection with a falsework

September-October 1971 731 truss is probably more feasible than along these lines has been done at cantilevering. A third possibility is a The University of Texas at Austin in combination of cantilever construc- studying costs and developing an tion and use of a truss. The bridge optimization technique. It is pro- can be constructed in cantilever for posed(48> that continuous spans up some distance on either side of the to about 200 ft. (61 m) may be ob- central pier and then completed us- tained by combining AASHO Type ing falsework trusses spanning from VI I-girders with a haunched girder the ends of the cantilever arms to the or inclined piers. Bulb-T girders, an- abutments. other alternative, have been de- The most widely used joints are signed for simple spans up to 160 ft. unreinforced concrete and epoxy (49 m) and for slightly greater spans resin. For bridges constructed on in continuous bridges. However, one falsework, unreinforced concrete great advantage of precast box gird- joints have been used in nearly all ers is that they can be used for a cases. The 1 in. to 4 in. (2.5 to 10.0 much larger range of spans, includ- cm) thick joints are simple to make ing spans of 300 ft. (91 m) as re- and do not require exacting toler- quired for stream crossings. ances in the precast segments. Although detailed comparative For bridges erected by the canti- studies of precast and cast-in-place lever method, construction time de- box girder bridges are not available, pends largely on the rate of setting the factors of standardization and of the joints and epoxy resin joints, mass production, better quality con- which have a much faster rate of set- trol and greater speed of erection ting, have an obvious advantage indicate that precasting may have a over concrete joints. Dry joints, as an significant economic advantage over alternative to epoxy resin joints, cast-in-place construction. leave much to be desired and have not been used extensively. ACKNOWLEDGMENT A one-sixth scale model of a proto- This information was compiled as type segmentally constructed bridge part of the overall research program to be built near Corpus Christi, Tex- of The University of Texas Center as, is currently being tested under a for Highway Research. The work contract with the Texas Highway was sponsored jointly by the Texas Department. The completed bridge, Highway Department and the Fed- of uniform 10 ft. (3.0 m) depth, will eral Highway Administration. The span the Intercoastal Canal with a opinions, findings, and conclusions 200 ft. (61 m) main span flanked by expressed are those of the authors two 100 ft. (30.5 m) outer spans. The and not necessarily those of the Fed- construction of the scale model has eral Highway Administration. The allowed a careful study of forming project was materially aided by ef- techniques and match casting for fective liaison with the sponsors thin epoxy joints. Results from the through the project advisory contact model test will be compared with members Wayne Henneberger and the predicted performance from an- Robert Reed of the Texas Highway alysis. Department and Donald Harley of There is need to study the relative the Federal Highway Administra- advantages and economy of box tion. Special acknowledgment is girders and possible alternative made of the contribution of Robert structural elements. Some work Brown, Jr., to the section on analysis.

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R., "Analysis of Box Bautechnik, Vol. bau," 43, No. 5, May Girders with Diaphragms," Journal of 1966, pp. 180-182; No. 10, October the Structural Division, ASCE, Vol. 94, 1966, pp. 359-363. No. ST-10, October 1968, pp. 2231- 37. Thiebault, A., "Le Calcul Electronique 2256. des Ponts sur Autoroutes Francaises," 51. Carlson, C. and Ady, N., "Segmented Travaux, No. 375, April 1966, pp. 631- Posttensioned Construction," Special 646. Bibliography No. 185, March 1968, 1967 Portland Cement Association. 38. Anon., "Highway Design and Opera- 52. Coste, J. F., "Le Franchissement de la tional Practices Related to Highway Seine par le Boulevard Peripherique a Safety," Report of the Special AASHO 1'Ouest de Paris," Travaux, No. 399, Traffic Safety Committee, February June 1968, pp. 659-699. 1967. 53. Freyermuth, C. L., "Computer Pro- 39. 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76 PCI Journal Prestressed Concrete Institute, Vol. 13, ASCE Annual Meeting on Transporta- No. 3, June 1968, pp. 28-39. tion Engineering, Washington, D.C., 54. Mattock, A. H. and Johnston, S. B., July 23, 1969. "Behavior under Load of Composite 60. McManus, P. F., Hasir, G. A. and Cul- Box Girder Bridges," Journal of the ver, C. G., "Horizontally Curved Gird- Structural Division, ASCE, Vol. 94, ers—State of the Art," Journal of the No. ST-10, October 1968, pp. 2351- Structural Division, ASCE, Vol. 95, 2370. No. ST-5, May 1969. 55. Sims, F. A. and Woodhead, S., "Raw- 61. Tung, D. H. H., "Torsional Analysis cliffe Bridge in Yorkshire," Civil En- of Single Thin-Walled Trapezoidal gineering and Public Works Review, Concrete Box Girder Bridges," First April 1968. International Symposium on Concrete 56. Wright, R. N., "Design- of Box Girders Bridge Design, ACI Special Publica- of Deformable Cross Section," Univer- tion No. 23, American Concrete Insti- sity of Illinois, Department of Civil tute, Detroit, 1969. Engineering, August 1968. 57. Wright, R. N., Abdel-Samad, S. R. and 1970 Robinson, A. R., "BEF Analogy for 62. Meyer, C. and Scordelis, A. C., "Com- Analysis of Box Girders," Journal of puter Program for Prismatic Folded the Structural Division, ASCE, Vol. 94, Plates with Plate and Beam Elements," No. ST-7, July 1968, pp. 1719-1743. Report No. SESM 70-3, Department of Civil Engineering, University of 1969 California, Berkeley, February 1970. 58. Lo, K. S. and Scordelis, A. C., "Finite Segment Analysis of Folded Plates," 1971 Journal of the Structural Division, 63. "Progress Report on Steel Box Girder ASCE, Vol. 95, No. ST-5, May 1969. Bridges," Report of the Subcommittee 59. "Design of Curved Girder Bridges," on Box Girders, ASCE-AASHO Task Report of the Subcommittee on Curved Committee on Flexural Members, Girders, ASCE-AASHO Committee on Journal of the Structural Division, Flexural Members, presented at the ASCE, Vol. 97, No. ST-4, April 1971.

Discussion of this paper is invited. Please forward your comments to PCI Headquarters by Jan. 1 to permit publication in the Jan.-Feb. 1972 issue of the PCI JOURNAL. September-October 1971 77