Podolny and Muller - Construction and Design of Pre Stressed Concrete Segmental Bridges

Construction and Design of Prestressed Concrete Segmental Bridges

Walter Podolny, Jr., Ph.D., P.E. Bridge Division Office of Engineering Federal Highway Administration U.S. Department of Transportation

Jean M. Muller Chairman of the Board Figg and Muller Engineers, Inc.

1982 A Wiley-Interscience Publication

John Wiley &? Sons New

York

Chichester

Brisbane

Toronto

Singapore

Series Preface J

The Wiley Series of Practical Construction Guides provides the Ivorking constructor \vith up-to-date information that can help to increase the job profit margin. These guidebooks, ivhich are scaled mainly for practice, but include the necessary theory and design, should aid a construction contractor in approaching \+vork problems with more knolvledgeable confidence. The guides should be useful also to engineers, architects, planners, specification tvriters, project managers, superintendents. materials and equipment manufacturers and. the source of all these callings, instructors and their students. Construction in the United States alone will reach $250 billion a year in the early 1980s. In all nations. the business of building will continue to grow at a phenomenal rate, because the population proliferation demands new living, lvorking, and recreational facilities. This construction will have to be more substantial, thus demanding a more

professional performance from the contractor. Before science and technology had seriously affected the ideas, job plans, financing, and erection of structures. most contractors developed their knolv-holy by field trial-and-error. Wheels, small and large. jvere constantly being reinvented in all sectors, because there was no interchange of knolvledge. The current complexity of construction, even in more rural areas, has revealed a clear need for more proficient, professional methods and tools in both practice and learning. Because construction is highly competitive, some practical technology is necessarily proprietary. But most practical day-to-day problems are common to the Fvhole construction industry. These are the subjects for the Wiley Practical Construction Guides. M. D. MORRIS , P.E.

Preface J

Prestressed concrete segmental bridge construction has evolved, in the natural course of events, from the combining of the concepts of prestressing, box girder design, and the cantilever method of bridge construction. It arose from a need to overcome construction difficulties in spanning deep valleys and river crossings without the use of conventional falsework, which in some instances may be impractical, economically prohibitive, or detrimental to environment and ecology. Contemporary prestressed, box girder, segmental bridges began in Western Europe in the 1950s. Ulrich Finsterwalder in 1950, for a crossing of the Lahn River in Balduinstein, Germany, was the first to apply cast-in-place segmental construction to a bridge. In 1962 in France the first application of precast, segmental, box girder construction was made by Jean Muller to the ChoisyLe-Roi Bridge crossing the Seine River. Since then the concept of segmental bridge construction has been improved and refined and has spread from Europe throughout most of the world. The first application of segmental bridge construction in North America was a cast-in-place segmental bridge on the Laurentian Autoroute near Ste. Adele, Quebec, in 1964. This was followed in 1967 by a precast segmental bridge crossing the Lievre River near Notre Dame du Laus, Quebec. In 1973 the first U.S. precast segmental bridge was opened to traffic in Corpus Christi, Texas, followed a year later by the cast-in-place segmental Pine Valley Bridge near San Diego, California. As of this date (1981) in the United States more than eighty segmental bridges are completed, in construction, in design, or under consideration. Prestressed concrete segmental bridges may be identified as precast or cast in place and categorized by method of construction as balanced cantilever, span-by-span, progressive placement, or incremental launching. This type of bridge has

extended the practical and competitive economic span range of concrete bridges. It is adaptable to almost any conceivable site condition. The objective of this book is to summarize in one volume the current state of the art of design and construction methods for all types of segmental bridges as a ready reference source for engineering faculties, practicing engineers, contractors, and local, state, and federal bridge engineers. Chapter 1 is a quick review of the historical evolution to the current state of the art. It offers the student an appreciation of the way in which segmental construction of bridges developed, the factors that influenced its development, and the various techniques used in constructing segmental bridges. Chapters 2 and 3 present case studies of the predominant methodology of constructing segmental bridges by balanced cantilever in both cast-in-place and precast concrete. Conception and design of the superstructure and piers, respectively, are discussed in Chapters 4 and 5. The other three basic methods of constructing segmental bridgesprogressive placement, span-by-span, and incremental launching-are presented in Chapters 6 and 7. Chapters 2 through 7 deal essentially with girder type bridges. However, segmental construction may also be applied to bridges of other types. Chapter 8 discusses application of the segmental concept to arch, rigid frame, and truss bridges. Chapter 9 deals with the cable-stayed type of bridge and Chapter 10 with railroad bridges. The practical aspects of fabrication, handling, and erection of segments are discnssed in Chapter 11. In selected a bridge type for a particular site, one of the more important parameters is economics. Economics, competitive bidding, and contractual aspects of segmental construction are discussed in Chapter 12. Most of the material presented in this book is not vii

Preface

original: Although acknowledgment of all the many.source$&. not possible, full credit is given wherever the specific so;rce can be identified. Every effort has been. made to eliminate errors; the authors will appreciate notification from the reader ‘of any that remain. The authors are indebted to numerous publications, organizations, and individuals for their assistance and permission to reproduce photo-

graphs, tables, and other data. Wherever possible, credit is given in the text. WALTER PODOLNY, JEAN M. MUILEK Burke, Virginia Par%, Francr Jarmar? 1982

JK.

Contents 1

Prestressed Concrete Bridges and Segmental Construction 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10

1.11

2

Introduction, 1 Development of Cantilever Construction, 2 Evolution of Prestressed Concrete, 4 Evolution of Prestressed Concrete Bridges, 5 Long-Span Bridges with Conventional Precast Girders, 8 Segmental Construction, 10 Various Types of Structures, 12 Cast-in-Place and Precast Segmental Construction, 17 Various Methods of Construction, 18 Applications of Segmental Construction in the United States, 26 Applicability and Advantages of Segmental Construction, 28 References, 30

Cast-In-Place Balanced Cantilever Girder Bridges 2.1 2.2 2.3 2.4 2.5 2.6 2.7

Introduction, 3 1 Bendorf Bridge, Germany, 35 Saint Adele Bridge, Canada, 37 Bouguen Bridge in Brest and Lacroix Falgarde Bridge, France, 38 Saint Jean Bridge over the Garonne River at Bordeaux, France, 4 1 Siegtal and Kochertal Bridges, Germany, 43 Pine Valley Creek Bridge, U.S.A., 46

2.8 2.9 2.10 2.11 2.12

1

2.13 2.14 2.15 2.16

3

Precast Balanced Cantilever Girder Bridges 3.1 3.2 3.3 3.4

31

Gennevilliers Bridge, France, 52 Grand’Mere Bridge, Canada, 55 Arnhem Bridge, Holland, 58 Napa River Bridge, U.S.A., 59 Koror-Babelthuap, U.S. Pacific Trust Territory, 61 Vejle Fjord Bridge, Denmark, 63 Houston Ship Channel Bridge, U.S.A., 68 Other Notable Structures, 71 Conclusion, 8 1 References, 8 1

3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16

82

Introduction, 82 Choisy Le Roi Bridge and Other Structures in Greater Paris, France, 83 Pierre Benite Bridges near Lyons, France, 89 Other Precast Segmental Bridges in Paris, 91 Oleron Viaduct, France, 96 Chillon Viaduct, Switzerland, 99 Hartel Bridge, Holland, 103 Rio-Niteroi Bridge, Brazil, 106 Bear River Bridge, Canada, 108 JFK Memorial Causeway, U.S.A., 109 Saint Andre de Cubzac Bridges, France, 113 Saint Cloud Bridge, France, 114 Sallingsund Bridge, Denmark, 122 B-3 South Viaducts, France, 124 Alpine Motorway Structures, France, 129 Bridge over the Eastern Scheldt, Holland, 134 ix

X

3.17 Captain Cook Bridge, Australia, 136 3.18 Other Notable Structures, 1 3 9 References, 147 4

Design of Segmental Bridges 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19

5

5.4

5.6 5.7

Introduction, 225 Loads Applied to the Piers, 2 3 0 Suggestions on Aesthetics of Piers and Abutments, 232 Moment-Resisting Piers and Their Foundations, 234

5.8 5.9

148

Introduction, 148 Live Load Requirements, 149 Span Arrangement and Related Principle of Construction, 149 Deck Expansion, Hinges, and Continuity, 15 1 Type, Shape and Dimensions of the Superstructure, 159 Transverse Distribution of Loads Between Box Girders in Multibox Girders, 164 Effect of Temperature Gradients in Bridge Superstructures, 170 Design of Longitudinal Members for Flexure and Tendon Profiles, 173 Ultimate Bending Capacity of Longitudinal Members, 190 Shear and Design of Cross Section, 193 Joints Between Match-Cast Segments, 199 Design of Superstructure Cross Section, 202 Special Problems in Superstructure Design, 203 Deflections of Cantilever Bridges and Camber Design, 205 Fatigue in Segmental Bridges, 2 10 Provisions for Future Prestressing, 2 12 Design Example, 2 12 Quantities of Materials, 219 Potential Problem Areas, 220 References, 224

Foundations, Piers, and Abutments 5.1 5.2 5.3

5.5

Piers with Double Elastomeric Bearings, 24 1 Piers with Twin Flexible Legs, 253 Flexible Piers and Their Stability During Construction, 263 Abutments, 27 1 Effect of Differential Settlements on Continuous Decks, 276 References, 280

6 Progressive and Span-by-Span Construction of Segmental Bridges 6.1 6.2 6.3 6.4 6.5 6.6

Introduction, 281 Progressive Cast-in-Place Bridges, 283 Progressive Precast Bridges, 289 Span-by-Span Cast-in-Place Bridges, 293 Span-by-Span Precast Bridges, 308 Design Aspects of Segmental Progressive Construction, 3 14 References, 3 19

7 Incrementally Launched Bridges 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10

8 225

8.3 8.4 8.5 8.6

32

Introduction, 32 1 Rio Caroni, Venezuela, 323 Val Restel Viaduct, Italy, 327 Ravensbosch Valley Bridge, Holland, 329 Olifant’s River Bridge, South Africa, 33 1 Various Bridges in France, 333 Wabash River Bridge, U.S.A., 335 Other Notable Bridges, 338 Design of Incrementally Launched Bridges, 343 Demolition of a Structure by Incremental Launching, 352 References, 352

Concrete Segmental Arches, Rigid Frames, and Truss Bridges 8.1 8.2

2,

Introduction, 354 Segmental Precast Bridges over the Marne River, France, 357 Caracas Viaducts, Venezuela, 363 Gladesville Bridge, Australia, 37 1 Arches Built in Cantilever, 374 Rigid Frame Bridges, 382

35

xi

Contents 8.7

Truss Bridges, 392 References, 399

11

11.1 11.2

9 Concrete Segmental Cable-Stayed Bridges 400 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10

Introduction, 400 Lake Maracaibo Bridge, Venezuela, 405 Wadi Kuf Bridge, Libya, 407 Chaco/Corrientes Bridge, Argentina, 408 Mainbrticke, Germany, 410 Tie1 Bridge, Netherlands, 412 Pasco-Kennewick Bridge, U.S.A., 418 Brotonne Bridge, France, 419 Danube Canal Bridge, Austria, 427 Notable Examples of Concepts, 430 References, 439

10 Segmental Railway Bridges 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8

10.9 10.10 10.11

Introduction to Particular Aspects of Railway Bridges and Field of Application, 44 1 La Voulte Bridge over the Rhone River, France, 442 Morand Bridge in Lyons, France, 442 Cergy Pontoise Bridge near Paris, France, 444 Marne La Vallee and Torcy Bridges for the New Express Line near Paris, France, 444 Clichy Bridge near Paris, France, 449 Olifant’s Bridge, South Africa, 452 Incrementally Launched Railway Bridges for the High-Speed Line, Paris to Lyons, France, 453 Segmental Railway Bridges in Japan, 457 Special Design Aspects of Segmental Railway Bridges, 458 Proposed Concepts for Future Segmental Railway Bridges, 464

Technology and Construction of Segmental Bridges

11.3 1.1.4

11.5 11.6 11.7 11.8

441

12

Scope and Introduction, 465 Concrete and Formwork for Segmental Construction, 466 Post-tensioning Materials and Operations, 470 Segment Fabrication for Cast-In-Place Cantilever Construction, 475 Characteristics of Precast Segments and Match-Cast Epoxy Joints, 485 Manufacture of Precast Segments, 493 Handling and Temporary Assembly of Precast Segments, 507 Placing Precast Segments, 509 References, 5 17

Economics and Contractual Aspects of Segmental Construction 12.1 12.2 12.3

13.4 13.5 13.6

Index Index Index Index

518

Bidding Procedures, 5 18 Examples of Some Interesting Biddings and Costs, 523 Increase in Efficiency in Concrete Bridges, 528 References, 535

13 Future Trends and Develofnnents 13.1 13.2 13.3

465

536

Introduction, 536 Materials, 536 Segmental Application to Bridge Decks, 542 Segmental Bridge Piers and Substructures, 543 Application to Existing or New Eridge Types, 544 Summary, 548 References, 549 of Bridges of Personal Names of Firms and Organizations of Subjects

551 555 557 559

Construction and Design of Prestressed Concrete Segmental Bridges

1 Prestressed Concrete Bridges and Segmental Construction

1.1 INTRODUCI’ION 1.2 DEVELOPMENT OF CANTILEVER CONSTRUCITON 1.3 EVOLUTION OF PRESTRESSED CONCRETE 1.4 EVOLUTION OF PRESTRESSED CONCRETE BRIDGES 1.5 LONGSPAN BRIDGES WITH CONVENTIONAL PRECAST GIRDERS 1.6 SEGMENTAL CONSTRUCTION 1.7 VARIOUS TYPES OF STRUCl-URFS 1.7.1 Girder Bridges 1.7.2 Trusses 1.7.3 Frames with Slant Legs 1.7.4 Concrete Arch Bridges 1.7.5 Concrete CabkStayed Bridges 1.8 CAST-IN-PLACE AND PRECAST SEGMENTAL CONSTRUCTION

1 . l Zntroduction, The conception, development, and worldwide acceptance of,segmental construction in the field of prestressed concrete bridges represents one of the most interesting and important achievements in civil engineering during the past thirty years. Recognized today in all countries and particularly in the United States as a safe, practical, and economic construction method, the segmental concept probably owes its rapid growth and acceptance to its founding, from the beginning, on sound construction principles such as cantilever construction. Using this method, a bridge structure is made up of concrete elements usually called segments (either precast or cast in place in their final position in the structure) assembled by post-tensioning. If the bridge is cast in place, Figure 1.1, travelers are used to allow the various segments to be constructed in successive increments and progressively

1.8.1 1.8.2 1.8.3 1.9

1.10 1.11

Characteristics of Cast-in-Place Segments Characteristics of Precast Segfnents Choice between Cast-in-Place and Precast Construction VARIOUS METHODS OF CONSTRUCTION 1.9.1 Cast-in-Place Balanced Cantilever 1.9.2 Precast Balanced Cantilever 1.9.3 Span-by-Span Construction 1.9.4 Progressive Placement Construction 1.9.5 Incremental Launching or Push-Out Construction APPLICATIONS OF SEGMENTAL CONSTRUCTION IN THE UNITED STATES APPLICABILITY AND ADVANTAGES OF SEGMENTAL CONSTRUCI’ION REFERENCES

prestressed together. If the bridge is precast, segments are manufactured in a special casting yard or factory, transported to their final position, and placed in the structure by various types of launch-

FIGURE 1.1 Cast-in place form traveler. 1

Prestressed

Concrete Stidges ad Segmental Constrt4ction

FIGURE 1.2. Oleron Viaduct, segmental construction in progress. One typical precast segment placed in the Oleron Viaduct.

ing equipment, Figure 1.2, while prestressing achieves the assembly and provides the structural strength. Most early segmental bridges were built as cantilevers, where construction proceeds in a symmetrical fashion from the bridge piers in successive increments to complete each span and finally the entire superstructure, Figure 1.3. Later, other construction methods appeared in conjunction with

______ Llzcr---/.#-------. ,% --------------/-------l-r -77 -------------.------3-r

FIGURE 1.3. Cantilever construction applied to prestressed concrete bridges.

the segmental concept to further its field of application. 1.2

Development of Cantilever Construction

The idea of cantilever construction is ancient in the Orient. Shogun’s Bridge located in the city of Nikko, Japan, is the earliest recorded cantilever bridge and dates back to the fourth century. The Wandipore Bridge, Figure 1.4, was built in the

seventeenth century in Bhutan, between India and Tibet. It is constructed from great timbers that are corbeled out toward each other from massive abutments and the narrowed interval finally capped with a light beam.’

FIGURE 1.4. Wandipore Bridge.

Develofwnent

of Cantilever Construction

3

That half an arc should stand upon the ground Without support while building, or a rest; This caus’d the theorist’s rage and sceptic’s jest. Prefabrication techniques were successfully combined with cantilever construction in many bridges near the end of the nineteenth century, as exemplified by such notable structures as the Firth of Forth Bridge, Figure 1.6, and later the Quebec Bridge, Figure 1.7, over the Saint Lawrence River. These structures bear witness to the engineering genius of an earlier’ generation. Built more recently, the Greater New Orleans Bridge over the Mississippi River, Figure 1.8, represents modern contemporary long-span steel cantilever construction. Because the properties and behavior of prestressed concrete are related more closely to those of structural steel than those of conventional reinforced concrete, the application of this material to cantilever construction was a logical step in the continuing development of bridge engineering.

FIGURE 1.7. Quebec Bridge.

FIGURE 1.8. Greater New Orleans Bridge.

Prestressed Concrete Bridges and Segmental Construction

4

This application has evolved over many years by the successive development of many concepts and innovations. In order to see how the present state of the art has been reached, let us briefly trace the development of prestressed concrete and in particular its application to bridge construction.

1.3

Evolution

of

Prestressed

Concrete

The invention of reinforced concrete stirred the imagination of engineers in many countries. They envisioned that a tremendous advantage could be achieved, if the steel could be tensioned to put the structure in a permanent state of compression greater than any tensile stresses generated by the applied loads. The present state of the art of prestressed concrete has evolved from the effort and experience of many engineers and scientists over the past ninety years. However, the concept of prestressing is centuries old. Swiss investigators have shown that as early as 2700 B.C. the ancient Egyptians prestressed their seagoing vessels longitudinally. This has been determined from pictorial representations found in Fifth Dynasty tombs. The basic principle of prestressing was used in the craft of cooperage when the cooper wound ropes or metal bands around wooden staves to form barrels.3 When the bands were tightened, they were under tensile prestress, which created compression between the staves and enabled them to resist hoop tension produced by internal liquid pressure. In other words, the bands and staves were both prestressed before they were subjected to any service loads. The wooden cartwheel with its shrunk-on iron rim is another example of prestressed construction. The first attempt to introduce internal stresses in reinforced concrete members by tensioning the steel reinforcement was made about 1886 when P. H. Jackson, an engineer in San Francisco, obtained a United States patent for tightening steel rods in concrete members serving as floor slabs. In l&S, C. E. W. DGhring of Berlin secured a patent for the manufacture of slabs, battens, and small beams for structural engineering purposes by embedding tensioned wire in concrete in order to reduce cracking. This was the first attempt to provide precast concrete units with a tensioned reinforcement. Several structures were constructed using these concepts; however, only mild steel reinforcement was available at the time. These structures at first behaved according to predictions, but because so little prestress force could be induced in the mild

steel, they lost their properties because of the creep and shrinkage of the concrete. In order to recover some of the losses, the possibility of retightening the reinforcing rods after some shrinkage and creep of the concrete had taken place was suggested in 1908 by C. R. Steiner of the United States. Steiner proposed that the bond of embedded steel bars be destroyed by lightly tensioning the bars while the concrete was still young and then tensioning them to a higher stress when the concrete had hardened. Steiner was also the first to suggest the use of curved tendons. In 1925, R. E. Dill of Nebraska took a further step toward freeing concrete beams of any tensile stresses by tensioning high-tensile steel wires after the concrete had hardened. Bonding was to be prevented by suitably coating the wires. He explicitly mentioned the advantage of using steel with a high elastic limit and high strength as compared to ordinary reinforcing bars. In 1928, E. Freyssinet of France, who is credited with the modern development of prestressed concrete, started using high-strength steel wires for prestressing. Although Freyssinet also tried the method of pretensioning, where the steel was bonded to the concrete without end anchorages, the first practical application of this method was made by E. Hoyer about 1938. Wide application of the prestressing technique was not possible until reliable and economical methods of tensioning and end anchorage were devised. From approximately 1939 on, E. Freyssinet, Magnel, and others developed different methods and procedures. Prestress began to gain some importance about 1945, while alternative prestressing methods were being devised by engineers in various countries. During the past thirty years, prestressed concrete in the United States has grown from a brand-new idea into an accepted method of concrete construction. This growth, a result of a new application of existing materials and theories, is in itself phenomenal. In Europe the shortage of materials and the enforced economies in construction gave prestressed concrete a substantial start. Development in the United States, however, was slower to get underway. Designers and contractors hesitated mainly because of their lack of experience and a reluctance to abandon more familiar methods of construction. Contractors, therefore, bid the first prestressed concrete work conservatively. Moreover, the equipment available for prestressing and related techniques was essentially new and makeshift. However, experience was gained rapidly, the quality of the work improved,

Evolution

of

Prestressed

Concrete

Bridges

5

FIGURE 1.9. Freyssinet’s Esblv Bridge on the Marne River.

and prestressed concrete became more and more competitive with other materials.

1.4

Evolution of Prestressed Concrete Bridges

Although France took the lead in the development of prestressed concrete, many European countries such as Belgium, England, Germany, Switzerland, and Holland quickly showed interest. As early as 1948, Freyssinet used prestressed concrete for the construction of five bridges over the Marne River near Paris, with 240 ft (74 m) spans of an exceptionally light appearance, Figure 1.9. A survey made in Germany showed that between 1949 and 1953, out of 500 bridges built, 350 were prestressed.

FIGURE 1.10 W a l n u t L a n e B r i d g e , Phil,~dcll~hia (courtesy of the Portland Cement Association).

Prestressing in the United States followed a different course. Instead of linear prestressing, circular prestressing as applied to storage tanks took the lead. Linear prestressing as applied to beams did not start until 1949. The first structure of this type was a bridge in Madison County, Tennessee, followed in 1950 by the well-known 160 ft (48.80 m) span Walnut Lane Bridge in Philadelphia, Figure 1.10. By the middle of 1951 it was estimated that 175 bridges and 50 buildings had been constructed in Europe and no more than 10 structures in the United States. In 1952 the Portland Cement Association conducted a survey in this country showing 100 or more structures completed or

FIGURE 1.11. AASHTO-PC1 I-girder cross sections.

6

Prestressed

Concrete

Bridges

under construction. In 1953 it was estimated that there were 75 bridges in Pennsylvania alone. After the Walnut Lane Bridge, which was cast in place and post-tensioned, precast pretensioned bridge girders evolved, taking advantage of the inherent economies and quality control achievable with shop-fabricated members. With few exceptions, during the 1950s and early 196Os, most multispan precast prestressed bridges built in the United States were designed as a series of simple spans. T h e y w e r e d e s i g n e d w i t h s t a n d a r d AASHTO-PCI* girders of various cross sections, Figure 1.11, for spans of approximately 100 ft (30.5 m), but more commonly for spans of 40 to 80 ft (12 to 24 m). The advantages of a continuous cast-in-place structure were abandoned in favor of t h e s i m p l e r c o n s t r u c t i o n o f f e r e d b y plantproduced standardized units. At this time, precast pretensioned members found an outstanding application in the Lake Pontchartrain crossing north of New Orleans, Louisiana. The crossing consisted of more than 2200 identical 56 ft (17 m) spans, Figures 1.12 through 1.14. Each span was made of a single 200 ton monolith with pretensioned longitudinal gird*American Association of State Highway and Transportation Officials (previously known as AASHO, American Association of State Highway Officials) and Prestressed Concrete Institute.

and

Segmental

Construction

FIGURE 1.12. Lake Pontchartrain Bridge, U.S.A.

ers and a reinforced concrete deck cast integrally, resting in turn on a precast cap and two prestressed spun piles. The speed of erection was incredible, often more than eight complete spans placed in a single day. In the middle 1960s a growing concern was shown about the safety of highways. The AASHTO Traffic Safety Committee called in a 1967 report 4 for the “ . . . adoption and use of twospan bridges for overpasses crossing divided highways . . . to eliminate the bridge piers normally placed adjacent to the shoulders,” Figure 1.15. Interstate highways today require overpasses with two, three, and four spans of up to 180 ft (54.9 m) or longer. In the case of river or stream crossings,

FIGURE 1.13. Lake Pontchartrain Bridge, U.S.A.

33'4

18'4'

I

I

I (b)

FIGURE 1.14. verse section.

Lake Pontchartrain Bridge, U.S.A. (a) Longitudinal section. (b) Trans7

-

bestressed Concrete Bridges and Segmental Construction

8

STANMRD 4-SPAN INTERSTATE CROSSING I

tg

177’ 250’

FIGURE 1.15. Standard four-span interstate crossing (courtesv of the Portland Cement Association). longer spans in the range of 300 ft (91.5 m) or longer may be required, and there is a very distinct trend toward longer-span bridges. It soon became apparent that the conventional precast pretensioned AASHTO-PC1 girders were limited by their transportable length and weight. Transportation over the highways limits the precast girder to a length of 100 to 120 ft (30.5 to 36.6), depending upon local regulations.

I .5

Long-Span Bridges with Precast Girders

Conventional

As a result of longer span requirements a study was conducted by the Prestressed Concrete Institute (PCI) in cooperation with the Portland Cement Association (PCA).S This study proposed that simple spans up to 140 ft (42.7 m) and continuous spans up to 160 ft (48.8 m) be constructed of standard precast girders up to 80 ft (24 m) in length joined by splicing. To obtain longer spans the use of inclined or haunched piers was proposed. The following discussion and illustrations are based on the grade-separation studies conducted by PC1 and PCA. Actual structures will be illus-

trated, where possible, to emphasize the particular design concepts. The design study illustrated in Figure 1.16 uses cast-in-place or precast end-span sections and a two-span unit with AASHTO I girders.6 Narrow median piers are maintained in this design, but the abutments are extended into the spans by as much as 40 ft (12 m) using a precast or cast-in-place frame in lieu of a closed or gravity abutment. When site conditions warrant, an attractive type of bridge can be built with extended abutments. A similar span-reducing concept is developed in Figure 1.17, using either reinforced or prestressed concrete for cantilever abutments. An aesthetic abutment design in reinforced concrete was developed for a grade-separation structure on the Trans-Canada Highway near Drummondville in the Province of Quebec, Figure 1.18. This provided a 324 ft (9.9 m) span reduction that led to the use of type IV Standard AASHTO I girders to span 974 ft (29.7 m) to a simple, narrow median pier. A cast-in-place reinforced concrete frame with outward-sloping legs provides a stable, center supporting structure that reduces span length by 29 ft (8.8 m), Figure 1.19. This enables either standard box sections or I sections 84 ft (25.6 m) long to be used in the two main spans. This layout was used for the Hobbema Bridge in Alberta, B.C., Canada, shown in Figure 1.20. This bridge was built with precast channel girder sections, but could be built with AASHTO I girders or box sections. The median frame with inclined legs was cast in place. The schematic and photograph in Figures 1.21 and 1.22 show the Ardrossan Overpass in Alberta. It is similar to the Hobbema Bridge except that the spans are longer and, with the exception of a cast-in-place footing, the median frame is made up of precast units post-tensioned together, Figure 1.21. The finished bridge, Figure 1.23, has a

Carl-in-place Froma

SECTION

A-A

FIGURE 1.16. Extended abutments (courtesy of the Prestressed Concrete Institute, from ref. 6).

Long-Span

APPROX.

Bridges with

36’ Its’-0”

Conventional

ELEVATION r;

Precast

Girders

9

A P P R O X . *I’-

IS’-0”

T Y P E lx A A S H O OlROtR OIROER

SECTION

FIGURE 1.1’7. Cantilevered abutments (courtesy of the Prestressed Concrete Institute, from ref. 6). \\,\_ \ \\\ \\\\ \ ,, \ \\\ \\ \ \

\

FIGURE 1.18. Drummondville Bridge (courtesy of the Portland Cement Association).

pleasing appearance. The standard units were channel-shaped stringers 64 in. wide and 41 in. deep (1.6 m by 1.04 m). The use of precast units allowed erection of the entire superstructure, ineluding the median frame, in only three weeks. The bridge was opened to traffic just eleven weeks after construction began in the early summer of 1966. By use of temporary bents, Figure 1.24, standard units 60 ft (18.3 m) long can be placed over the median pier and connected to main span units with cast-in-place reinforced concrete splices located near the point of dead-load contraflexure.

ELEVATION

SECTIONS A -A

FIGURE 1.19. Median frame cast in place (courtesy of the Prestressed Concrete Institute, from ref. 6).

10

Prestressed

Concrete

Bridges

and

Segmental

Construction

from the side pier over the main pier to the hingesupport for the suspended span. The type of construction that uses long, standard, precast, prestressed units never quite achieved the recognition it deserved. As spans increased, designers turned toward post-tensioned cast-in-place box girder construction. The California Division of Highways, for example, has been quite successful with cast-in-place, multicell, posttensioned box girder construction for multispan structures with spans of 300 ft (91.5 m) and even longer. However, this type of construction has its own limitations. The extensive formwork u s e d during casting often has undesirable effects on the environment or the ecology.

FIGURE 1.20. Hobbema Bridge, completed structure (courtesy of the Portland Cement Association).

1.6 Segmental Construction This design is slightly more expensive than previ-

ous ones but it provides the most open type twospan structure. The structural arrangement of the Sebastian Inlet Bridge in Florida consists of a three-span unit over the main channel, Figure 1.25. The end span of this three-span unit is 100 ft (30.5 m) long and cantilevers 30 ft (9 m) beyond the piers to support a 120 ft (36.6 m) precast prestressed drop-in span, Figure 1.26. The end-span section was built in two segments with a cast-in-place splice with the help of a falsework bent. The Napa River Bridge at Vallejo, California (not to be confused with the Napa River Bridge described in Section 2.1 l), used a precast concrete cantilever-suspended span concept similar to the Sebastian Inlet Bridge, at about the same time. The only difference was that the cantilever girder was a single girder extending

ELE

V A

Segmental construction has been defined’ as a method of construction in which primary loadsupporting members are composed of individual members called segments post-tensioned together. The concepts developed in the PCI-PCA studies and described in the preceding section come under this definition, and we might call them “longitudinal” segmental construction because the individual elements are long with respect to their width. In Europe, meanwhile, segmental construction proceeded in a slightly different manner in conjunction with box girder design. Segments were cast in place in relatively short lengths but in fullrpadway width and depth. Today segmental construction is usually understood to be the type developed in Europe. However, as will be shown later, the segments need not be of full-roadway

T

I O N

81p-40 AASHO-PCI BOX SECTION

3’-6”

6’-6*

b’-6”

&X-IONS A - A

FIGURE

1.21.

Median frame precast (courtesy of the Prestressed Cot xrete Institute, from ref. 6).

Segmental Construction

FIGURE 1.22. Ardrossan Overpass precast median frame (courtesy of the Portland Cement Association).

width and can become rather long in the longitudinal direction of the bridge, depending on the construction system utilized. Eugene Freyssinet, in 1945 to 1948, was the first to use precast segmental construction for prestressed concrete bridges. A bridge at Luzancy over the Marne River about 30 miles east of Paris, Figure 1.27, was followed by a group of five precast bridges over that river. Shortly thereafter, Ulrich Finsterwalder applied cast-in-place segmental prestressed construction in a balanced cantilever fashion to a bridge crossing the Lahn River at Balduinstein, Germany. This system of cantilever segmental construction rapidly gained wide acceptance in Germany, after construction of a bridge crossing the Rhine at Worms in 1952, as shown in Figure 1.28,s with three spans of 330, 371, and 340 ft (100, 113, and 104 m). More than 300 such structures, with spans in excess of 250 ft (76 m), were constructed between 1950 and 1965

SECflON

FIGURE 1.23. Completed Ardrossan o\crpass (courtesy of the Portland Cement Association).

in Europe.s Since then the concept has spread throughout the world.’ Precast segmental construction also was evolving during this period. In 1952 a single-span county bridge near Sheldon, New York, was designed by the Freyssinet Company. Although this bridge was constructed of longitudinal rather than the European transverse segments, it represents the first practical application of match casting. The bridge girders were divided into three longitudinal segments that were cast end-to-end. The center segment was cast first and then the end segments were cast directly against it. Keys were cast at the joints so that the three precast elements could be joined at the site in the same position they hid in the precasting yard. Upon shipment to the job site the three elements of a girder were post-tensioned together with cold joints. l”,ll The first major application of match-cast, precast segmental construction was not consummated

A-A

FIGURE 1.24. Field spike for continuity (courtesy of the Prestressed Concrete Institute, from ref. 6).

12

Prestressed

Concrete

Bridges

and

Segmental

Construction

1.

FIGURE 1.25. Sebastian Inlet Bridge (courtesy of the Portland Cement Association). until 1962. This structure, designed by Jean Muller and built by Entreprises Campenon Bernard, was the Choisy-le-Roi Bridge over the Seine River south of Paris, Figure 1.29. This concept has been refined and has spread from France to all parts of the world. The technology of cast-in-place or precast segmental bridges has advanced rapidly in the last decade. During its initial phase the balanced cantilever method of construction was used. Currently, other techniques such as span-by-span, incremental launching, or progressive placement also are available. Any of these construction methods may call on either cast-in-place or precast segments or a combination of both. Consequently, a variety of design concepts and construction methods are now available to economically produce segmental bridges for almost any site condition. Segmental bridges may be classified broadly by four criteria:

The ultimate use of the bridge-that is, highway or railway structure or combination thereof. Although many problems are common to these two categories, the considerable increase of live loading in a railway bridge poses special problems that call for specific solutions. 2. The type of structure in terms of statical scheme and shape of the main bending members. Many segmental bridges are box girder bridges, but other types such as arches or cable-stayed bridges show a wide variety in shape of the supporting members. 3. The use of cast-in-place or precast segments or a combination thereof. 4. The method of construction. The sections that follow will deal briefly with the last three classifications.

1.7

Various Types of Structures

From the point of view of their statical scheme, there are essentially five categories of structures: (1) girders, (2) trusses, (3) rigid frames, (4) arch frames, and (5) cable-stayed bridges. 1.7.1 GIRDER BRIDGES

Box girders in the majority of cases are the most efficient and economical design for a bridge. When constructed in balanced cantilever, box girder decks were initially made integral with the piers while a special expansion joint was provided at the center of each span (or every other span) to allow

Conventional

\

Section A-A

FIGURE 1.26. Sebastian Inlet Bridge (courtesy of the Prestressed Concrete Institute, from ref. 6).

13

Various Types of Structures

FIGURE 1.29. Choisy-le-Roi FIGURE 1.27.

I,uzanc~ Bridge over the Marne River.

FIGURE 1.28. & LVidmann).

b’ornx Bridge (courtesy of Dyckerhoff

CF

6lb’

E N D PIEI

176’-0’

MAIN

for volume changes and to control differential deflections between individual cantilever arms. It is now recognized that continuity of the deck is desirable, and most structures are now continuous over several spans, bearings being provided between deck and piers for expansion. Today, the longest box girder bridge structure that has been built in place in cantilever is the Koror Babelthuap crossing in the Pacific Trust territories with a center span of 790 ft (241 m), Figure 1.30.r2 A box girder bridge has been proposed for

PIER

f-

I_

1

L \

FIGURE 1.30.

Bridge.

/J 12%

._

176’-0“

I

I

12/-O”

Koror-Babelthuap Bridge, elevation and cross section (ref. 12).

14

Prestressed

Longitudmal

Concrete Bridges and Segmental Construction

section

r

1

G-r-r

Typical sections at span and over main piers

center

IF-4

FIGURE

FIGURE 1.31. The Great Belt Project.

the Great Belt Project in Denmark with a 1070 ft (326 m) clear main span, Figure 1.31. The box girder design has been applied with equal success to the construction of difficult and spectacular structures such as the Saint Cloud Bridge over the Seine River near Paris, Figure 1.32, or to the construction of elevated structures in very congested urban areas such as the B-3 Viaducts near Paris, Figure 1.33.

1.33.

R-3 Viaciuc t\. FI ‘111~ e.

The cantilever method has potential applications between the optimum span lengths of typical box girders for the low ranges and of stayed bridges for the high ranges. 1.7.3 FRAMES WITH SLANT LEGS

When the configuration of the site allows, the use of inclined legs reduces the effective span length.

1.7.2 TRUSSES

When span length increases, the typical box girder becomes heavy and difficult to build. For the purpose of reducing dead weight while simplifying casting of very deep web sections, a truss with open webs is a very satisfactory type that can be conveniently built in cantilever, Figure 1.34. The technological limitations lie in the complication of connections b e t w e e n p r e s t r e s s e d d i a g o n a l s a n d chords. An outstanding example is the Rip Bridge in Brisbane, Australia, Figure 1.35.

FIGURE

1.32. Saint Cloud Bridge, France.

FIGURE 1.34. Long-span concrete trusses.

FIGURE

1.35.

Rip Bridge, BI ishne, Xu\tl

nli,l

Various Types of Structures

15

FIGURE 1.36. Long-span frame.

Provisional back stays or a temporary pier are needed to permit construction in cantilever, Figure 1.36. This requirement may sometimes present difficulty. An interesting example of such a scheme is the Bonhomme Bridge over the Blavet River in France, Figure 1.37. The scheme is a transition between the box girder with vertical piers and the true arch, where the load is carried by the arch ribs along the pressure line with minimum bending while the deck is supported by spandrel columns.

FIGURE 1.37. Bonhomme

Bridge.

1.7.4 CONCRETE ARCH BRIDGES

Concrete arches are an economical way to transfer loads to the ground where foundation conditions are adequate to resist horizontal loads. Eugene Freyssinet prepared a design for a 1000 meter (3280 ft) clear span 40 years ago. Because of construction difficulties, however, the maximum span built to date (1979) has been no more than 1000 ft (300 m). Construction on falsework is made difficult and risky by the effect of strong winds during construction. The first outstanding concrete arch was built at Plougastel by Freyssinet in 1928 with three 600 ft (183 m) spans, Figure 1.38. Real progress was achieved only when free cantilever and provisional stay methods were applied to arch construction, Figure 1.39. The world record is presently the Kirk Bridge in Yugoslavia, built in cantilever and com-

FIGURE 1.38. Plougastel Bridge, France.

16

Prestressed Concrete Bridges and Segmental Construction

I FIGURE 1.39. Concrete arches.

,,,)

.

.

.

\

,.

.

.

,,~

\

pleted in 1979 with a clear span of 1280 ft (390 m), Figure 1.40.

,_

i

1.7.5 CONCRETE CABLE-STAYED BRIDGES’”

FIGURE 1.40. Kirk Bridges, Yugoslavia.

When a span is beyond the reach of a conventional girder bridge, a logical step is to suspend the deck by a system of pylons and stays. Applied to steel structures for the last twenty years, this approach gained immediate acceptance in the field of concrete bridges when construction became possible

FIGURE 1.41. Long-span concrete cable-stayed bridges.

an m dr th m 1. al

Cast-in-Place and Precast Segmental

Construction

17

the structure’s deformability, particularly during construction. Deflections of a typical cast-in-place cantilever are often two or three times those of the same cantilever made of precast segments. The local effects of concentrated forces behind the anchors of prestress tendons in a young concrete (two or four days old) are always a potential source of concern and difficulties. I.82 CHARACTERISTICS OF PRECAST SEGMENTS

FIGURE 1.42. Krotonne Bridge, France.

and economical in balanced cantilever with a large number of stays uniformly distributed along the deck, Figure 1.41, The longest span of this type is the Brotonne Bridge in France with a 1050 ft (320 m) clear main span over the Seine River, Figure 1.42. Single pylons and one line of stays are located along the centerline of the bridge.

1.8

Cast-in-Place and Precast Segmental Construction

1.8.1 CHARACTERISTICS OF CAST-IN-PLACE SEGMENTS

In cast-in-place construction, segments are cast one after another in their final location in the structure. Special equipment is used for this purpose, such as travelers (for cantilever construction) or formwork units moved along a supporting gantry (for spanby-span construction). Each segment is reinforced with conventional untensioned steel and sometimes by transverse or vertical prestressing or both, while the assembly of segments is achieved by longitudinal post-tensioning. Because the segments are cast end-to-end, it is not difficult to place longitudinal reinforcing steel across the joints between segments if the design calls for continuous reinforcement. Joints may be treated as required for safe transfer of all bending and shear stresses and for water tightness in aggressive climates. Connection between individual lengths of longitudinal post-tensioning ducts may be made easily at each joint and for each tendon. The method’s essential limitation is that the strength of the concrete is always on the critical path of construction and it also influences greatly

In precast segmental construction, segments are manufactured in a plant or near the job site, then transported to their final position for assembly. Initially, joints between segments were of conventional type: either concrete poured wet joints or dry mortar packed joints. Modern segmental construction calls for the match-casting technique, as used for the Choisy-le-Roi Bridge and further developed and refined, whereby the segments are precast against each other, preferably in the same relative order they will have in the final structure. No adjustment is therefore necessary between segments before assembly. The joints are either left dry (in areas where climate permits) or made of a very thin film of epoxy resin or mineral complex, which does not alter the match-casting properties. There is no need for any waiting period for joint cure, and final assembly of segments by prestressing may proceed as fast as practicable. Because the joints are of negligible thickness, there is usually no mechanical connection between the individual lengths of tendon ducts at the joint. Usually no attempt is made to obtain continuity of the longitudinal conventional steel through the joints, although several methods are available and have been applied successfully (as in the Pasco Kennewick cable-stayed bridge, for example). Segments may be precast long enough in advance of their assembly in the structure to reach sufficient strength and maturity and to minimize both the deflections during construction and the effects of concrete shrinkage and creep in the final structure. If erection of precast segments is to proceed smoothly, a high degree of geometry control is required during match casting to ensure accuracy. 1.8.3

CHOICE BETWEEN CAST-IN-PLACE AND PRECAST CONSTRUCTION

Both cast-in-place methods and precast methods have been successfully used and produce substan-

18

Prestressed Concrete Bridges and Segmental Construction

tially the same final structure. The choice depends on local conditions, including size of the project, time allowed for construction, restrictions on access and environment, and the equipment available to the successful contractor. Some items of interest are listed below: 1. Speed of Construction Basically, cast-in-place cantilever construction proceeds at the rate of one pair of segments 10 to 20 ft (3 to 6 m) long ever) four to seven days. On the average, one pair of travelers permits the completion of 150 ft (46 m) of bridge deck per month, excluding the transfer from pier to pier and fabrication of the pier table. On the other hand, precast segmental construction allows a considerably faster erection schedule. a . For the Oleron Viaduct, the average speed of completion of the deck was 750 ft (228 m) per month for more than a year. b. For both the B-3 Viaducts in Paris and the Long Key Bridge in Florida, a typical 100 to 150 ft (30 to 45 m) span was erected in two working days, representing a construction of 1300 ft (400 m) offinished bridge per month, c. Saint Cloud Bridge near Paris, despite the exceptional difficulty of its geometry and design scheme, was constructed in exactly one year, its total area amounting to 250,000 sq ft (23,600 sq m). It is evident, then, that cast-in-place cantilever construction is basically a slow process, while precast segmental with matching joints is among the fastest. 2. Investment in Special Equipment Here the situation is usually reversed. Cast-in-place requires usually a lower investment, which makes it competitive on short structures with long spans [for example, a typical three-span structure with a center span in excess of approximately 350 ft (100

Ml.

In long, repetitive structures precast segmental may be more economical than cast-in-place. For the Chillon Viaducts with twin structures 7000 ft (2 134 m) long in a difficult environment, a detailed comparative estimate showed the cast-in-place method to be 10% more expensive than the precast. 3. Size and Weight of Segments Precast segmental is limited by the capacity of transportation and placing equipment. Segments exceeding 250 tons are seldom economical. Cast-in-place construction does not have the same limitation, al-

though the weight and cost of the travelers are directly proportional to the weight of the heaviest segment. 4. Environment Restrictions Both precast and cast-in-place segmental permit all work to be performed from the top. Precast, however, adjusts more easily to restrictions such as allowing work to proceed over traffic or allowing access of workmen and materials to the various piers. 1.9

Various

Methods

of

Construction

Probably the most significant classification of segmental bridges is by method of construction .41though construction methods may be as varied as the ingenuity of the designers and contractors, they fall into four basic categories: (1) balanced cantilever, (2) span-by-span construction, (3) progressive placement construction, and (4) incremental launching or push-out construction. 1.9.1 CAST-I.\‘-PL4CE

BAL,-I,VCED C.4.iTILEC’ER

The balanced or free cantilever construction concept was originally developed to eliminate falsework. Temporary shoring not only is expensive but can be a hazard in the case of sudden floods, as confirmed by many failures. Over navigable waterways or traveled highways or railways, falsework is either not allowed or severely restricted.’ Cantilever construction, whether cast in place or precast, eliminates such difficulties: construction may proceed from the permanent piers, and the structure is self-supporting at all stages. The basic principle of the method was outlined in Section 1.1 (Figure 1.3). In cast-in-place construction the formwork is supported from a movable form carrier, Figure 1.1. Details of the form travelers are shown in Figure 1.43. The form traveler moves forward on rails attached to the deck of the completed structure and is anchored to the deck at the rear. With the form traveler in place, a new segment is formed, cast, and stressed to the previously constructed segment. In some instances a covering may be provided on the form carrier so that work may proceed during inclement weather, Figure 1.44. The operation sequence in cast-in-place balanced cantilever construction is as follows: 1.

Setting up and adjusting carrier.

2.

Setting up and aligning forms.

Various Methods of Construction

CENTERJACK

FORM TRAVELLER

8,i-J?i,! -Lu ,.

! I

i-HUN I AL WORKING PLATFORM

ADDITIONAL

REAR GANG-BOARD

FIGURE

\BOTTOM FRAME WORK

~ONTAL LOWER WORKING PLATFORM

1.43. Form traveler (courtesy of Dyckerhoff & Widmann).

3. 4. 5.

Placing reinforcement and tendon ducts. Concreting. Inserting prestress tendons in the segment and stressing. 6. Removing the formwork. 7. Moving the form carrier to the next position and starting a new cycle. Initially, the normal construction time for a segment was one week per formwork unit. Advances in precast segmental construction have been applied recently to the cast-in-place method in order to reduce the cycle of operations and increase the efficiency of the travelers. With today’s technology it does not seem possible to reduce the

FIGURE 1.44. Bendorf Bridge form traveler (courtesy of Dyckerhoff & Widmann).

construction time for a full cycle below two working days, and this only for a very simple structure with constant cross section and a moderate amount of reinforcing and prestress. For a structure with variable depth and longer spans, say above 250 ft (75 m), the typical cycle is more realistically three to four working days. Where a long viaduct type structure is to be constructed of cast-in-place segments, an auxiliary steel girder may be used to support the formwork, Figure 1.45, as on the Siegtal Bridge. This equip-

1.45. Siegtal Bridge, use of an auxiliary truss in cast-in-place construction.

FIGURE

20

Prestressed

Concrete Bridges and Segmental Construction

ment may also be used to stabilize the free-standing pier by the anchoring of the auxiliary steel girder to the completed portion of the structure. Normally, in construction using the form traveler previously described, a portion of the end spans (near the abutments) must be cast on falsework. If the auxiliary steel girder is used, this operation may be eliminated. As soon as a double typical cantilever is completed, the auxiliary steel girder is advanced to the next pier. Obviously, the economic justification for use of an auxiliary steel girder is a function of the number of spans and the span length. I-9.2. PRECAST BALANCED CANTILEVER

For the first precast segmental bridges in Paris (Choisy-le-Roi, Courbevoie, and so on, 1961 to 1965) a floating crane was used to transfer the precast segments from the casting yard to the barges that transported them to the project site and was used again to place the segments in the structure. The concept of self-operating launching gantries was developed shortly thereafter for the construction of the Oleron Viaduct (1964 to 1966). Further refined and extended in its potential, this concept has been used in many large structures. The erection options available can be adapted to almost all construction sites. 1. Crane Placing Truck or crawler cranes are used on land where feasible; floating cranes may be used for a bridge over navigable water, Figure 1.46. Where site conditions allow, a portal crane may be used on the full length of the deck, preferably with a casting yard aligned with the deck near

one abutment to minimize the number of handling operations, Figure 1.47. 2. Beam and Winch Method If access by land or water is available under the bridge deck, or at least around all permanent piers, segments may be lifted into place by hoists secured atop the previously placed segments, Figure 1.48. At first this method did not permit the installation of precast pier segments upon the bridge piers, but it has been improved to solve this problem, as will be explained later. 3. Launching Gantries There are essentially two families of launching gantries, the details of which will be discussed in a later chapter. Here we briefly outline their use. In the first family developed for the Oleron Viaduct, Figures 1.49 and 1.50, the launching gantry is slightly more than the typical span length, and the gantry’s rear support reaction is applied near the far end of the last completed cantilever. All segments are brought onto the finished deck and placed by the launching gantry in balanced cantilever; after completion of a cantilever, after placing the precast segment over the new pier, the launching gantry launches itself to the next span to start a new cycle of operations. In the second family, developed for the Deventer Bridge in Holland and for the Rio Niteroi Bridge in Brazil, the launching gantry has a length approximately twice the typical span, and the reaction of the legs is always applied above the permanent concrete piers, Figures 1.51 and 1.52. Placing segments with a launching gantry is now in most cases the most elegant and efficient method, allowing the least disturbance to the environment. 1.9.3 SPAN-BY-SPAN CONSTRUCTION

FIGURE 1.46. Segment erection by barge-mounted crane, Capt. Cook Bridge, Australia (courtesy of G. Beloff, Main Roads Department, Brisbane, Australia).

The balanced cantilever construction method was developed primarily for long spans, so that construction activity for the superstructure could be accomplished at deck level without the use of extensive falsework. A similar need in the case of long viaduct structures with relatively shorter spans has been filled by the development of a span-by-span methodology using a form traveler. The following discussion explains this methodol13.14.15.16 %Y* In long viaduct structures a segmental span-byspan construction may be particularly advantageous. The superstructure is executed in one direc-

Various Methods of Construction

COUPE

21

TRANSVERSALE

FIGURE 1.47. Mirabeau Bridge at Tours, France.

tion, span by span, by means of a form traveler, Figure 1.53, with construction joints or hinges located at the point of contraflexure. The form carrier in effect provides a type of factory operation transplanted to the job site. It has many of the ad: . .

the field. The form traveler may be supported on the piers, or from the edge of the previously completed construction, at the joint location, and at the forward pier. In some instances, as in the approaches of Rheinbrticke, Dusseldorf-Flehe, the movable formwork may be supported from the ground, Figure 1.54. The form traveler consists of a steel superstructure, which is moved from the completed portion of the structure to the next span to be cast. For an above-deck carrier, large formwork elements are suspended from steel rods during concreting. After concreting and post-tensioning, the forms are released and rolled forward by means of the structural steel outriggers on both sides of the form traveler’s superstructure. For a below-deck carrier, a similar procedure is followed. Many long bridges of this type have been built in Germany, France, and other countries. Typical construction time for a 100 ft (30 m) span superstructure is five to eight working days, depending upon the complexity of the structure. Deck configuration for this type of construction is usually a monolithic slab and girder (T beam or double T), box girder, or a mushroom cross sec-

Prestressed

22

J-I

52.00 m

Concrete Bridges and Segmental Construction

170ft 54.OOm _ 1 0 6 . 0 0 Ill 3 5 0 ff

180 ft

(6)

4

80.00

m

260 f t

c

FIGURE 1.51. Second family of launching gantries, Rio Niteroi Bridge.

J

1 0 6 . 0 0 Ill 3 5 0 ft

I

Cc)

FIGURE

1.49.

First family of launching gantries (Ole-

ron Viaduct). tion. This method has been used recently in the United States on the Denny Creek project in the state of Washington. In its initial form, as described above, the spanby-span method is a cast-in-place technique. The same principle has been applied in conjunction with precast segmental construction for two very large structures in the Florida Keys: Long Key Bridge and Seven Mile Bridge, with spans of 118 ft (36 m) and 135 ft (40 m), respectively. Segments are assembled on a steel truss to make a complete

FIGURE 1.50. Placing precast segments on the Oleron Viaduct.

span. Prestressing tendons then assure the assembly of the various segments in one span while achieving full continuity with the preceding span, Figures 1.55 and 1.56. The floating crane used to place the segments over the truss also moves the truss from span to span. The contractor for the Seven Mile Bridge modified the erection scheme from that used for Long Key Bridge by suspending a span of segments from an overhead falsework truss. This is the first application of a method that seems to have a great potential for trestle structures in terms of speed of construction and economy. 1.9.4

PROGRESSIVE

PLACEMENT

CONSTRUCTION

Progressive placement is similar to the span-byspan method in that construction starts at one end of the structure and proceeds continuously to the

FIGURE 1.52. Rio Niteroi launching girder.

i of Construction

23

FIGURE 1.56.

Placing segments on assembly truss for Long Key Bridge.

FIGURE 1.55. Span-by-span assembly of precast segments.

other end. It derives its origin, however, from the cantilever concept. In progressive placement the precast segments are placed from one end of the structure to the other in successive cantilevers on the same side of the various piers rather than by balanced cantilevers on each side of a pier. At present, this method appears practicable and economical in spans ranging from 100 to 300 ft (30 to 90 m). Because of the length of cantilever (one span) in relation to construction depth, a movable temporary stay arrangement must be used to limit the cantilever stresses during construction to a reasonable level. The erection procedure is illustrated in Figure 1.57. Segments are transported over the completed portion of the deck to the tip of the cantilever span under construction, where they are positioned by a swivel crane that proceeds from one segment to the next. Approximately one-third of the span from the pier may be erected by the free cantilever method, the segments being held in position by exterior temporary ties and final prestressing tendons. For the remaining two-thirds of the span, each segment is held in position by temporary external ties and by two stays passing through a tower located over the preceding piers. All stays are continuous through the tower and anchored in the previously completed deck structure. The stays are anchored to the top flange of the box girder segments so that the tension in the stays can be adjusted by light jacks. Used for the first time in France on several structures, Figure 1.58, progressive placement is being applied in the United States for the construction of the Linn Cove Viaduct in North Carolina. In this bridge the precast pier construction proceeds also from the deck to solve a difhcult problem of environmental restrictions.

24

Prestressed Concrete Bridges and Segmental Construction

FIGURE 1.57. Progressive placement erection procedure.

The progressive placement method may also be applied to cast-in-place construction. 1.9.5. INCREMENTAL LAUNCHING OR PUSH-OUT CONSTRUCTION

This concept was first implemented on the Rio Caroni Bridge in Venezuela, built in 1962 and 1963 by its originators, Willi Baur and Dr. Fritz Leonhardt of the consulting firm of Leonhardt and Andra (Stuttgart, Germany).”

Segments of the bridge superstructure are cast in place in lengths of 30 to 100 ft ( 10 to 30 m) in stationary forms located behind the abutment(s), Figure 1.59. Each unit is cast directly against the previous unit. After sufficient concrete strength is reached, the new unit is post-tensioned to the previous one. The assembly of units is pushed forward in a stepwise manner to permit casting of the succeeding segments, Figure 1.60. Normally a work cycle of one week is required to cast and launch a segment, regardless of its length. Operations are

Various Methods of Construction

FIGURE 1.60. Incremental launching (courtesy of Prof. Fritz Leonhardt).

25

sequence

superstructure under its own weight at all stages of launching and in all sections. Four methods for this purpose are used in conjunction with one another. 1.

A first-stage prestress is applied concentrically to the entire cross section and in successive increments over the entire length of the superstructure. 2. To reduce the large negative bending moments in the front (particularly just before the superstructure reaches a new pier) a fabricated structural steel launching nose is attached to the lead segment, Figure 1.62. 3. Long spans may be subdivided by means of temporary piers to keep bending moments to a reasonable magnitude. This construction technique has been applied to spans up to 200 ft (60 m) without the use of temporary falsework bents. Spans up to 330 ft (100 m) have been built using temporary supporting bents. The girders must have a constant depth, which is usually one-twelfth to one-sixteenth of the longest span. 4. Another method has been used successfully in France to control bending moments in the

26

Prestressed

FIGURE 1.61. Incremental launching (courtesy of Prof. Fritz Leonhardt).

Concrete

Bridges

and

Segmental

Construction

o n J GUI ve ‘FIGURE 1.62. Steel launching nose (courtesy of Prof. Fritz Leonhardt).

deck in the forward part of the superstructure. A system using a tower and provisional stays is attached to the front part of the superstructure. The tension of the stays and the corresponding reaction of the tower on the deck are controlled automatically and continuously during all launching operations to optimize the stress distribution in the deck, Figure 1.63.

ft (1035 m). The incremental launching technique was used successfully for the first time in the United States for the construction of the Wabash River Bridge at Covington, Indiana.

After launching is complete, and the opposite abutment has been reached, additional prestressing is added to accommodate moments in the final structure, while the original uniform prestress must resist the varying moments that occur as the superstructure is pushed over the piers to its final position. Today, the longest incrementally launched clear span is over the River Danube near Worth, Germany, with a maximum span length of 550 ft (168 m). Two temporary piers were used in the river for launching. The longest bridge of this type is the Olifant’s River railway viaduct in South Africa with 23 spans of 147 ft (45 m) and a total length of 3400

The state of the art of designing and constructing prestressed concrete segmental bridges has advanced greatly in recent years. A wide variety of structural concepts and prestressing methods are used, and at least a thousand segmental bridges have been built throughout the world. We may conclude that segmental prestressed concrete construction is a viable method for building highway bridges. There are currently no known major problems that should inhibit utilization of segmental prestressed concrete bridges in the United States. They have been successfully consummated in other countries and are increasingly being employed in the United States.

1 .I 0

Applications of Segmental Construction in the United States

27

Applications of Segmental Construction in the United States

fbJ

FIGURE 1.64. ‘Three Sisters Bridge.

Cd)

FIGURE 1.63. Incremental launching with provi-

sional tower and stays.

One of the earliest projects for which segmental construction was considered was the proposed Interstate I-266 Potomac River Crossing in Washington, D.C., Figure 1.64, otherwise known as the Three Sisters Bridge. This structure contemplated a 750 ft (229 m) center span with side spans of 440 ft (134 m) on reverse five-degree curves, built with cast-in-place segmental construction. Because of environmental objections, this project never reached fruition. The JFK Memorial Causeway (Intracoastal Waterway), Corpus Christi, Texas, Figure 1.65, represents the first precast, prestressed, segmental, balanced cantilever construction completed in the United States. It was opened to traffic in 1973. Designed by the Bridge Division of the Texas Highway Department, it has a center span of 200 ft (61 m) with end spans of 100 ft (30.5 m). The first cast-in-place, segmental, balanced cantilever, prestressed concrete bridge constructed in the United States is the Pine Valley Bridge in California, on Interstate I-8 about 40 miles (64 km) east of San Diego. Designed by the California Department of Transportation, .the dual structure, Figure 1.66, has a total length of 1716 ft (53.6 m)

FIGURE 1.65. JFK hlcnwr ial Causewav.

Corpus

FIGURE 1.66. Pine Valley Bridge (courtesy CALTRANS).

of

Christi, Texas.

Pt-estressed

Concrete Bridges and Segmental Construction

of

Houston

with spans of 270, 340, 450, 380, and 276 ft (82.3, 103.6, 137.2, 115.8, and 84.1 m). As indicated previously, numerous segmental bridge projects have been constructed or are contemplated in the United States. Many of them will be discussed in detail in the following chapters. Among the most significant are the Houston Ship Channel Bridge with a clear span of 750 ft (228 m), which will be the longest concrete span in the Americas, Figure 1.67, and the Seven Mile Bridge, which will be the longest segmental bridge in North America, Figure 1.68.

1 .I 1

FIGURE

1.67.

Rendering

FIGURE 1.68. Rendering of’ Seven Mile Bridge.

Ship

Channel

Bridge.

Applicability and Advantages of Segmental Construction

Segmental construction has extended the practical range of span lengths for concrete bridges. Practical considerations of handling and shipping limit the prestressed I-girder type of bridge construction to spans of about 120 to 150 ft (37 to 46 m). Beyond this range, post-tensioned cast-in-place box girders on falsework are the only viable concrete alternative. At many sites, however, falsework is not practical or even feasible, as when crossing deep ravines or large navigable waterways. Falsework construction also has a serious impact upon environment and ecology. Prestressed concrete segmental construction has been developed to solve these problems while extending the practical span of concrete bridges to about 800 ft (250 m) or even 1000 ft (300 m). With cable-stayed structures the span range can be extended to 1300 ft (400 m) and perhaps longer with the materials available today.13 Table 1.1 summarizes the range of application of various forms of construction by span lengths. Although the design and construction of verylong-span concrete segmental structures pose an important challenge, segmental techniques may

Applicability TABLE 1.1

and

Advantages

of

Segmental

Construction

29

Range of Application of Bridge Type by Span Lengthsa

Span

Bridge Types

o- 150 ft loo- 300 ft loo- 300 ft 250- 600 ft 200- 1000 ft 800-1500 ft

I-type pretensioned girder Cast-in-place post-tensioned box girder Precast balanced cantilever segmental, constant depth Precast balanced cantilever segmental, variable depth Cast-in-place cantilever segmental Cable-stay with balanced cantilever segmental

“1 fi = 0.3048 tn.

find even more important applications in moderate span lengths and less spectacular structures. Especially in difficult urban areas or ecology-sensitive sites, segmental structures have proven to be a valuable asset. Today most sites for new bridges can be adapted for segmental concrete construction. The principal advantages of segmental construction may be summarized as follows: 1. Segmental construction is an efficient and economical method for a large range of span lengths and types of structure. Structures with sharp curves and variable superelevation may be easily accommodated. 2. Concrete segmental construction often provides for the lowest investment cost. Savings of 10 to 20% over conventional methods have been realized by competitive bidding on alternate designs or by realistic cost comparisons. 3. Segmental construction permits a reduction of construction time. This is particularly true for precast methods, where segments may be manufactured while substructure work proceeds and be assembled rapidly thereafter. Further cost savings ensue from the lessening of the influence of inflation on total construction costs. 4. Segmental construction protects the environment. Segmental viaduct-type bridges can minimize the impact of highway construction through environmentally sensitive areas. Whereas conventional cut-and-fill type highway construction can scar the environment and impede wildlife migration, an elevated viaduct-type structure requires only a relatively narrow path along the alignment to provide access for pier construction. Once the piers have been constructed, all construction activity proceeds from above. Thus, the impact on the environment is minimized. 5. Interference with existing traffic during construction is significantly reduced, and expensive detours can be eliminated. Figure 1.69 indi-

cates how precast segments may be handled while traffic is maintained with a minimum disturbance. 6. Segmental construction contributes toward aesthetically pleasing structures in many different sites. A long approach viaduct (Brotonne, Figure 1.70), a curved bridge over a river (Saint Cloud, Figure 1.7 l), or an impressive viaduct over a deep valley (Pine Valley, Figure 1.66) are some examples where nature accepts human endeavor in spite of its imperfections. 7. Materials and labor are usually available locally for segmental construction. The overall labor requirement is less than for conventional construction methods. For the precast option a major part of the work force on site is replaced by plant labor. 8. As a consequence, quality control is easier to perform and high-quality work may be expected. 9. Segmental bridges when properly designed and when constructed by competent contractors under proper supervision will prove to be practically free of maintenance for many years. Only bearings and expansion joints (usually very few for continuous decks) need to be controlled at regular intervals.

FIGURE 1.69. Saint Cloud Bridge, segments placed

over

traffic.

Prestressed

30

Concrete

Bridges

FIGURE 1.70. Brotonne Bridge approach.

10. During construction, the technique shows an exceptionally high record of safety. Precast segmental construction today is competitive in a wide range of applications with other materials and construction methods, while it adds a further refinement to the recognized advantages of prestressed concrete.

FIGURE 1.71. Saint bridge over a river.

Cloud

Bridge, France, curved

References 1 . H. G. Tyrrell, History of Bridge Engineeting, Henry G. Tyrrell, Chicago, 1911. 2. Elizabeth B. Mock, The Architecture of Bridges, The Museum of Modern Art, New York, 1949. 3. T. Y. Lin, Design of Prestressed Concrete Structures, John Wiley & Sons, Inc., New York, 1958. 4. Anon., “Highway Design and Operational Practices Related to Highway Safety,” Report of the Special AASHO Traffic Safety Committee, February 1967. 5 . Anon., Prestressed Concrete for Long Span Bridges, Prestressed Concrete Institute, Chicago, 1968.

and

Segmental

Construction

6. Anon., “Long Spans with Standard Bridge Girders,” PC1 Bridge Bulletin, March-April 1967, Prestressed Concrete Institute, Chicago. 7. “Recommended Practice for Segmental Construction in Prestressed Concrete,” Report by PC1 Committee on Segmental Construction, Journal of the Prestressed Concrete Instztute, Vol. 20, No. 2, MarchApril 1975. 8. Ulrich Finsterwalder, “Prestressed Concrete Bridge Construction,” Journal oj the Amerzcan Concrete Instztute, Vol. 62, No. 9, September 1965. 9. F. Leonhardt, “Long Span Prestressed Concrete Bridges in Europe,” Journal of the Pre.,tressed Concrete Institute, Vol. 10, No. 1, February 1965. 10. Jean Muller, “Long-Span Precast Prestressed Concrete Bridges Built in Cantilever,” Fzrst International Symposium, Concrete Bridge Design, AC1 P u b l i c a t i o n SP-23, Paper 23-40, American Concrete Institute, Detroit, 1969. 11. Jean Muller, “Ten Years of Experience in Precast Segmental Construction,” Journal of the Prestressed Concrete Instatute, Vol. 20, No. 1, January-February 1975. 12. Man-Chung Tang, “Koror-Babelthuap Bridge-A World Record Span,” Preprint Paper 3441, ASCE Convention, Chicago, October 16-20, 1978. 13. C. A. Ballinger, W. Podolny, Jr., and M. J. Abrahams, “A Report on the Design and Construction of Segmental Prestressed Concrete Bridges in Western Europe- 1977,” International Road Federation, Washington, D.C., June 1978. (Also available from Federal Highway Administration, Offices of Research and Development, Washington, D.C., Report No. FHWA-RD-78-44.) 14. Ulrich Finsterwalder, “New Developments in Prestressing Methods and Concrete Bridge Construction,” Dywzdag-Berzchte, 4-1967, September 1967, Dyckerhoff & Widmann KG, Munich, Germany. 15. Ulrich Finsterwalder, “Free-Cantilever Construction of Prestressed Concrete Bridges and MushroomShaped Bridges,” First International Symposaum, Concrete Bridge Deszgn, AC1 Publication SP-23, Paper SP 23-26, American Concrete Institute, Detroit, 1969. 16. C. A. Ballinger and W. Podolny, Jr., “Segmental Construction in Western Europe-Impressions of an IRF Study Team,” Proceedings, Conference conducted by Transportation Research Board, National Academy of Sciences, Washington, D.C., TRR 665, Vol. 2, September 1978. 17. Willi Baur, “Bridge Erection by Launching is Fast, Safe, and Efficient,” Czvzl Engineerzng-AXE, Vol. 47, No. 3, March 1977. 18. Walter Podolny, Jr., and J. B. Scalzi, “Construction and Design of Cable-Stayed Bridges,” John Wiley & Sons, Inc., New York, 1976.

2 Cast-in-Place Balanced Cantilever Girder Bridges

2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.18

INTRODUCTION BENDORF BRIDGE, GERMANY SAINT ADELE BRIDGE, CANADA BOUGUEN BRIDGE IN BREST AND LACROIK FALGARDE BRIDGE, FRANCE SAINT JEAN BRIDGE OVER THE GARONNE RIVER AT BORDEAUX, FRANCE SIEGTAL AND KOCHERTAL BRIDGES, GERMANY PINE VALLEY CREEK BRIDGE, U.S.A. GENNEVILLIERS BRIDGE, FRANCE GRAND’MFRE BRIDGE, CANADA ARNHEM BRIDGE, HOLLAND NAPA RIVER BRIDGE, U.S.A. KOROR-BABELTHUAP, U.S. PACIFIC TRUST TERRITORY VEJLE FJORD BRIDGE, DENMARK

2.1

Introduction

Developed initially for steel structures, cantilever construction was used for reinforced concrete bridges as early as fifty years ago. In 1928, Freyssinet used the cantilever concept to construct the springings of the arch rib in the Plougastel Bridge, Figure 2.1. The reactions and overturning moments applied by the falsework to the lower part of the arch ribs were balanced by steel ties connecting the two short cantilevers. A provisional prestress was thus applied by the ties to the arch ribs with the aid of jacks and deviation saddles. The first application of balanced cantilever construction in a form closely resembling its present one is due to a Brazilian engineer, E. Baumgart, who designed and built the Herval Bridge over the Rio Peixe in Brazil in 1930. The 220 ft (68 m) center span was constructed by the cantilever method in reinforced concrete with steel rods extended at the various stages of construction by threaded couplers. Several other structures fol-

2.14 HOUSTON SHIP CHANNEL BRIDGE, U.S.A. 2.15 OTHER NOTABLE STRUCXURFS 2.15.1 Medway Bridge, U.K. 2.15.2 Rio Tocantins Bridge, Brazil ‘2.153 Pueute Del Azufre, Spain 2.15.4 Schubeuamdie Bridge, Canada 2.15.5 Inci- Bridge, Guatemala 2.15.6 !3etubal Bridge, Argentina 2.15.7 Kipapa Stream Bridge, U.S.A. 2.15.8 Parrots Ferry Bridge, U.S.A. 2.15.9 Magnan Via’duct, France 2.15.10 Puteaux Bridge, Frame 2.15.11 Tricastiu Bridge, France 2.15.12 Eschachtal Bridge, Germauy 2.16 CONCLUSION REFERENCES

lowed in various countries, particularly in France. Albert Caquot, a leading engineer of his time, built several reinforced concrete bridges in cantilever. Shown in Figures 2.2 through 2.4 is Bezons Bridge over the River Seine near Paris, with a clear center span of 310 ft (95 m), being constructed in successive cantilever segments with auxiliary trusses. This bridge design was prepared in 1942. The method was not widely used at that time, because the excessive amount of reinforcing steel

Jack,

/ Ties

f Overturning moment due to centering

FIGURE 2.1. Cantilever construction of arch springings for Plougastel Bridge, France. 31

FIGURE 2.2. Bezons Bridge over the Seine River, France, typical longitudinal and transverse sections.

33

Introduction

,w--. ---.-._ -_-..--._ z I .! I-

- _._.._- _______ _ :

:

h’ ..*gr- _ _ ._- -.__. --I .- ._-__ ____L_ --/ :: : .I

il

FIGURE 2.3. Bezons Bridge, construction procedure.

required to balance the cantilever moments produced the tendency toward cracking inherent in an overreinforced slab subject to permanent tensile stresses. The introduction of prestressing in concrete structures dramatically changed the situation.

Used successfully in 1950 and 195 1 by Finsterwalder with the German firm of Dyckerhoff & Widmann for the construction of the two bridges of Balduinstein and Neckarrews, balanced cantilever construction of prestressed concrete bridges experienced a continuous popularity in Germany

FIGURE 2.4. Bezons Bridges under construction.

34

Cast-in-Place Balanced Cantilever Girder Bridges

FIGURE 2.5. La Voulte Bridge, France.

and surrounding countries. Nicolas Esquillan designed and built a large bridge by the cantilever method over the Rhine River in France, La Voulte Bridge (J952), where an overhead truss was used during construction, Figure 2.5. Between 1950 and 1965 more than 300 such bridges were constructed in Europe alone. Initially were prestressed by high-strength all &uctures bars, and hinges were provided at the center of the

various spans. Later other prestressing methods with parallel wire or strand tendons were also used. More important, a significant improvement in structural behavior and long-term performance was made possible by the achievement of deck continuity between the various cantilever arms. The first cantilever bridges with continuous decks were designed and built in France in 1962: the Lacroix Falgarde Bridge and Bouguen Bridge, Figures 2.6 and 2.22. Subsequently, the advantages of continuity were recognized and accepted in many countries. From 1968 to 1970 cantilever construction was considered for the Three Sisters Bridge in Washington, D.C., Figure 1.64. This project never reached the construction stage. The first cast-inplace balanced cantilever segmental bridge built in the United States is the Pine Valley Creek Bridge in California (1972 to 1974), Figure 2.7. To date, all segmental bridges constructed in the United States have been either precast or cast-in-place cantilever construction, with the following exceptions: Wabash River Bridge, incrementally launched (Chapter 7) Denny Creek and Florida Keys Bridges, span-byspan construction (Chapter 6)

FIGURE 2.6. Bouguen Bridge in Brest, France. First continuous rigid-frame structure built in balanced cantilever.

35

Bendorf Bridge, Germany

FIGURE 2.8. Bendorf Bridge (courtesy of Dvckerhoff & Widmann).

FIGURE 2.7. Pine Valley Creek Bridge. Linn Cove Viaduct, progressive placement construction (Chapter 6) The balanced cantilever method of construction has already been briefly described. In this chapter we shall see how this method has been implemented on various structures before we go on to consider specific design and technological aspects.

(west) are the river spans consisting of a symmetrical seven-span continuous girder with an overall length of 1721 ft (524.7 mj. In part two (east) are the nine-span continuous approach girders with the spans ranging from 134.5 ft (41 m) to 308 ft (94 mj and having an overall length of 1657 ft (505 mj, Figures 2.9 and 2.10. The continuous, seven-span, main river structure consists of twin, independent, single-cell box girders. Total width of the bridge cross section is 101 ft (30.86 mj. Each single-cell box has a top flange width of 43.3 ft (13.2 mj, a bottom flange width of 23.6 ft (7.2 mj, and webs with a constant thickness of 1.2 ft (0.37 m). Girder depth is 34.28 ft (10.45 m) at the pier and 14.44 ft (4.4 mj at midspan representing, with respect to the main span, a depth-to-span ratio of l/20 and l/47, respectively. Girder depth of the end of this sevenspan unit reduced to 10.8 ft (3.3 mj. The main navigation span has a hinge at midspan that is deHinge

2.2 Bendorf Bridge, Germany Longitudinal

An early and outstanding example of the cast-inplace balanced cantilever bridge is the Bendorf autobahn bridge over the Rhine River about 5 miles (8 km) north of Koblenz, West Germany. Built in 1964, this structure, Figure 2.8, has a total length of 3378 ft (1029.7 mj with a navigation span of 682 ft (208 mj. The design competition allowed the competing firms to choose the material, configuration, and design of the structure. Navigation requirements on the Rhine River dictated a 328 ft (100 m) wide channel during construction and a final channel width of 672 ft (205 mj. The winning design was a dual structure of cast-inplace concrete segmental box girder construction, consummated in two distinct portions. In part one

Cross sectton river pier

at

section

Cross section at pier G

FIGURE: 2.9. Bendorf Bridge, Part one (West), longitudinal section, plan, and cross secnons at the river pier and pier G, from ref. 1 (courtesy of Beton- und Stahlbetonbauj.

36

Cast-in-Place Balanced Cantilever Girder Bridges

-~~ ss,o -L- SP.0 --L-- so0 -$A---5O$Om-

Longitudinal

-

-

~

section

Plan

FIGURE

2.10. Bendorf Bridge, Part Two (East), longitudinal section and plan, from ref. 1 (courtesy of Beton- und Stahlbetonbau).

signed to transmit shear and torsion forces only, thus allowing the superstructure to be cast monolithically with the main piers.1,2 After construction of the piers, the superstructure over the navigable portion of the Rhine was completed within one year. The repetition of the procedure in 240 segments executed one after the other offered numerous occasions to mechanize and improve the erection method.3,4 The deck slab has a longitudinally varying thickness from 11 in. (279.4 mm) at midspan to 16.5 in. (419 mm) at the piers. The bottom flange varies in thickness from 6 in. (152 mm) at midspan to 7.87 ft (2.4 m) at the piers. To reduce dead-weight bending-moment stresses in the bottom flange concrete, compression reinforcement was used extensively in regions away from the piers. Thicknesses of the various elements of the cross section are controlled partly by stress requirements and partly by clearance requirements of the tendons and anchorages. The structure is three-dimensionally prestressed: longitudinal prestressing uniformly distributed across the cross section; transverse prestressing in the top flange; and inclined prestressing in the webs. A total of 560 Dywidag bars la-in. (32 mm) in diameter resists the negative bending moment produced by a half-span, Figure 2.11.

The maximum concrete compressive stress in the bottom flange at the pier is 1800 psi (12.4 MPa). As a result of the three-dimensional prestress the tensile stresses in the concrete were negligible. The longitudinal prestressing is incrementally decreased from the pier to the hinge at midspan and to the adjacent piers; thus, shear stresses in the webs on both sides of the main piers are almost constant. Therefore, the web thickness remains constant and the diagonal prestressing remains very nearly constant. Construction began on March 1, 1962. After completion of the foundations and piers, balanced cantilever operations began from the west river pier in July 1963 and were completed at the end of that year. Segments were 12 ft (3.65 m) in length in the river span and 11.4 ft (3.48 m) in the remaining spans. Segments were cast on a weekly cycle. As the segments became shallower, the construction cvcle was advanced to two segments per week. During winter months, to protect operations from inclement weather, the form traveler was provided with an enclosure, Figure 2.12.

FIGURE

FIGURE 2.12. Bendorf‘ Bridge, protective covering

2.11. Bendorf Bridge, cross section showing tendons in the deck, ref. 2, (courtesy of the American Concrete Institute).

for form traveler (courtesy of Ulrich

Finsterwalder).

Saint Adele Bridge, Canada

FIGURE 2.13.

Ste. Adele Bridge, elevation, from ref. 5 (courtesy of

In the construction of the approach spans, the five spans from the east abutment were built in a routine manner with the assistance of falsework bents. The four spans over water were constructed by a progressive placement cantilever method (see Chapter 6), which employed a temporary cablestay arrangement to reduce the cantilever stresses.

Eng$mritzg ~V~7o.~-R~cord).

This structure, built in 1964 (the same year as the Bendorf Bridge), represents the first segmental bridge, in the contemporary sense, constructed in North America. It crosses the River of the Mules near Ste. Adele, Quebec, and is part of the Laurentian Autoroute. It is a single-cell box girder continuous three-span dual structure with a center span of 265 ft (80.8 m) and end spans of 132 ft 6 in. (40.4 m), Figure 2.13. At one end is a prestressed concrete 55 f-t (16.8 m) simple span. The bridge has a 100 ft (30.5 m) vertical clearance over the river in the canyon below.

The variable-depth girder is 16 ft 3 4 in. (4.96 m) deep at the piers and 6 ft (1.83 m) deep at midspan and its extremities, Figure 2.14. Each dual structure consists of a single-cell rectangular box 23 ft (7 m) wide with the top flange cantilevering on each side 9 ft (2.75 m) for a total width of 41 ft (12.5 m), Figure 2.15, providing three traffic lanes in each direction. Thickness of bottom flange, webs, and top flange are respectively 1 ft l# in. (0.35 m), 1 ft 6 in. (0.46 m), and 1 ft (0.3 m).5 A total of 70 prestressing tendons were required in each girder. Each tendon of the SEEE system consists of seven strands of seven 0.142 in. (3.6 mm) wires. The seven strands are splayed out through a steel ring in the anchorage and held in a circular pattern by steel wedges between each of the strands. The number of tendons anchored off at each segment end varies with the distance from the pier, increasing from an initial six tendons to eight tendons at the eighth segment, then decreasing to two tendons at the eleventh segment at midspan. There are an additional 44 positivemoment tendons in the center span located in the bottom flange.5

FIGURE 2.14. Stc. Adele HI idge, v i e w 01 variabledepth box girder (courtesy of the Portland Cement ASsociation).

FIGURE 2.15. Ste. Adele Bridge, view of end of box girder segment (courtesy of the Portland Cement Association) .

2.3

Saint Adele Bridge, Canada

38

Cast-in-Place Balanced Cantilever Girder Bridges counterweighted with 70 tons (63.5 mt) of concrete block, which was gradually diminished as construction proceeded and the depth of the segments decreased. The first pair of segments (at the pier), each with a length of 21 ft 23 in. (6.47 m), were cast on a temporary scaffolding braced to the pier, Figure 2.18, which remained fixed in position throughout the erection process.5 Construction of four segments per week, one at each end of a cantilever from two adjacent piers, was attained by the following five-day construction cycles:

FIGURE 2.16. Ste. Adele Bridge, dual structure under construction by the balanced cantilever method, from ref. 5 (courtesy of Engineering News-Record).

Forty-seven segments are required for each structure, eleven cantilevered each side of each pier, a closure segment at midspan of the center span, and a segment cast in place on each abutment. Segments cast by the form traveler were 10 ft 78 in. (3.24 m) in length.5 Four traveling forms were used on the project: one pair on each side of the pier for each of the dual structures, Figures 2.16 and 2.17. The forms were supported by a pair of 42 ft (12.8 m) long, 36 in. (914.4 mm) deep structural steel beams spaced 15 ft (5.57 m) on centers, that cantilevered beyond the completed portion of the structure. Initially the cantilevered beams were

Traveling forms moved, bottom flange First day: formed, reinforced, and cast. In the parallel span there was a one-day lag such that crews could shift back and forth between adjacent structures. Second day:

Third day: Concrete placed for webs and top

flange, cure begun. Fourth day: T e n d o n s p l a c e d a n d p r e s t r e s s i n g jacks positioned while concrete was curing. Fifth day: Prestressing accomplished. Forms stripped; preparations made to repeat cycle.

The cycle began on Monday. Since there was a lag of one day on the parallel structure, a six-day work week was required. Upon completion of the eleventh segment in each cantilever the contractor installed temporary falsework to support the abutment end and then cast the closure segment at midspan. Counterweights were installed at the abutment end to balance the weight of the closure forms and segment weight. After installation and stressing of the continuity tendons, abutment segments were cast and expansion joints installed.5

2.4

FIGURE 2.17. Ste. Adele Bridge, view of form travelers cantilevering from completed portion of the structure, from ref. 5 (courtesy of Engineering News-Record).

Reinforcement placed for webs and

top flange.

Bouguen Bridge in Brest and Lacroix Falgarde Bridge, France

The Bouguen Bridge in Brittany, West Province in France, is the first rigid-frame continuous structure built in balanced cantilever (1962 to 1963). The finished bridge is shown in Figure 2.6, while dimensions are given in Figure 2.19. It carries a three-lane highway over a valley 145 ft (44 m) deep-Le Vallon du Moulin H Poudre-and provides a link between the heart of Brest city and Le Bouguen, a new urban development. The total length of bridge is 684 ft (208 m). The main structure is a three-span rigid frame with

Bouguen Bridge in Brest

and Lacroix

Falgarde

39

Bridge, France

FIGURE 2.18. Ste. Adele Bridge, schematic of construction sequence, from ref. 5 (courtesy of Engineering News-Record).

box girder is 10 ft (3 m); web thickness also is constant throughout the deck and is equal to 9$ in. (0.24 m). Piers consist of two square box columns 10 ft by 10 ft (3 x 3 m) with wall thickness of 9$ in. (0.24 m) located under each deck girder. Two walls 84 in. (0:22 m) thick with a slight recess used for architectural purposes connect the two columns. Both piers are of conventional reinforced concrete construction, slip-formed at a speed reaching 14 ft (4.25 m) per day in one continuous operation.

piers elastically built-in on rock foundations with span lengths of 147,268, and 147 ft (45,82, and 45 m). At one end the deck rests on an existing masonry wall properly strengthened; at the other end a shorter rigid frame with a clear deck span of 87 ft (26.5 m) provides the approach to the main bridge. The deck consists of two box girders with vertical webs of variable height, varying from 15 ft 1 in. (4.6 m) at the support to 6.5 ft (2 m) at midspan and the far ends of the side spans. Width of each

Midspan

section

Pier

section

Plan section at pier

(b)

FIGURE 2.19. Bouguen Bridge, France, general dimensions. (a) Longitudinal section. (6) Cross sections.

40

Cast-in-Place Balanced Cantilever Girder Bridges

FIGURE 2.20. Bouguen Bridge, construction of east

cantilever. The superstructure box girders are connected to the pier shaft by transverse diaphragms made integral with both elements to insure a rigid connection between deck and main piers. Construction of the deck proceeded in balanced cantilever with 10 ft (3 m) long segments cast in place in form travelers with a one-week cycle, Figures 2.20 and 2.21. High-early-strength concrete was used and no steam curing was required. Concrete was allowed to harden for 60 hours before application of prestress. The following cube strengths were obtained throughout the project: 60 hours (time of prestress) 7 days 28 days 90 days

3700 psi (25.5 MPa) 5500 psi (37.9.MPa) 7000 psi (48.3 MPa) 8200 psi (56.5 MPa)

Only one pair of form travelers was used for the entire project, but each traveler could accommodate the construction of both girders at the same time.

.\’

FIGURE

2.21.

Bouguen Bridge, view of’ the traveler.

During construction of the deck, much attention was given to the control of vertical deflections. Adequate camber was given to the travelers to fully compensate for short- and long-term concrete deflections. The cumulative deflection at midspan of the first cantilever arm was 14 in. (40 mm) at time of completion. Concrete creep caused this deflection to reach 3 in. (75 mm) at the time the second cantilever arm reached the midspan section. Proper adjustment of the travelers allowed both cantilever arms to meet within t in. (3 mm) at the time continuity was achieved. Flat jacks were provided over the outer supports to allow for any further desired adjustment. The structure is prestressed longitudinallv by tendons of eight 12 mm strands: 76 tendons over the top of the pier segment, 32 tendons at the bottom of the crown section, 20 tendons in the side spans, and transversely by tendons of seven 12 mm strands. The Lacroix Falgarde Bridge over Ariege River in France, built in 1961 and 1962, is similar to the Bouguen Bridge and represents the first continuous deck built in balanced cantilever (see the photograph of the finished bridge, Figure 2.22). It consists of three continuous spans 100, 200, and 100 ft (30.5, 61, and 30.5 m). The single box girder has a depth varying between 4 ft 5 in. and 10 ft 6 in. (1.35 to 3.2 m). Dimensions are given in Figure 2.23. The superstructure rests on both piers and abutments through laminated bearing pads. The deck was cantilevered and the construction started simultaneously from the two piers with four travelers working symmetrically. During con-

FIGURE 2.22. Lacroix-Falgardc Bridge, view of’ the

structure during construction.

Saint Jean Bridge Over the Gardonne River at Bordeaux, France

FIGURE 2.23.

Lacroix-Falgarde Bridge, elevation and cross section.

struction, the deck was temporarily fixed to the piers by vertical prestress. The structure is prestressed longitudinally by tendons of twelve 8 mm strands and transversely by tendons of twelve 7 mm strands.

2.5

Saint Jean Bridge over the Garonne River at Bordeaux, France

Completed in April 1965, the Saint Jean Bridge in Bordeaux is a remarkable application of the new concepts developed at that time in cast-in-place cantilever construction. The main structure has an overall length of 1560 ft (475 m) and is continuous with expansion joints only over the abutments. The deck is f’ree to expand on neoprene bearings located on all river piers, Figure 2.24. A very efficient method of pier and foundation construction was also developed, which will be described in more detail in Chapter 5. The bridge was built in the heart of the city of Bordeaux over the Garonne River between a 175year-old multiple-arch stone structure and a 120year-old railway bridge designed by Eiffel, the engineer who designed the Eiffel Tower. The main structure includes six continuous spans. The central spans are 253 ft (77 m) long and allow a navigation clearance of 38 ft (11.60 m) above the lowest water level, while the end spans are only 222 ft (67.80 m) long. Short spans at both ends, 50 ft (15.40 m) long, provide end restraint of the side spans over the abutments. The overall width of the bridge is 88 ft (26.80 m), consisting of six traffic lanes, two walkways, and two cycle lanes. Superstructure dimensions are shown in Figure 2.25.

41

The deck consists of three box girders. The constant depth of 10.8 ft (3.30 m) has been increased to 13 ft (3.90 m) over a length of 50 ft (15 m) on each side of the piers to improve the bending capacity of the pier section and reduce the amount of cantilever prestress. No diaphragms were used except over the supports. The results of a detailed analysis performed to determine the transverse behavior of the deck confirmed this choice (see detailed description in Chapter 4). Longitudinal prestressing consists of tendons with twelve 8 mm and twelve t in. strands. Transverse prestressing consists of tendons with twelve 8 mm strands at 2.5 ft (0.75 m) intervals. Vertical prestressing is also provided in the webs near the supports. As indicated in Figure 2.26, three separate pier columns support the three deck girders. They are capped with large prestressed transverse diaphragms. The piers are founded in a gravel bed located at a depth of 45 ft (14 m) below the river level by means of a reinforced concrete circular caisson

FIGURE 2.24. Saint Jean at Bordeaux, view of the completed structure.

COUPE LONGITUDINALE CULEE R D

CVLEE NE - _ 5

FIGURE 2.25. Saint Jean ar Bordeaux. (a) Longitudinal and (6) cross sections.

FIGURE 2.26. 42

Saint Jean Bridge at Bordeaux, typical section at river piers.

Siegtal and Kochertal Bridges, Germany

FIGURE 2.27. Saint Jean Bridge at Bordeaux, work progress on piers and deck. 18.5 ft (5.60 m) in diameter and 10 ft (3 m) high, floated and sunk to the river bed and then opendredged to the gravel bed. Precast circular matchcast segments prestressed vertically make up the permanent walls of caissons, while additional segments are used temporarily as cofferdams and support for the deck during cantilever construction. A lower tremie seal allows dewatering and placing of plain concrete fill inside the caisson. The reinforced concrete footing and pier shaft are finally cast in one day. The superstructure box girders were cast in place in 10 ft (3.05 m) long segments using twelve form travelers, allowing simultaneous work on the three parallel cantilevers at two different piers. The 20 ft (6.1 m) long pier segment was cast on the temporary supports provided by the pier caissons, allowing the form travelers to be installed and cantilever construction to proceed. Six working days were necessary for a complete cycle of operations on each traveler. Work progress is shown in Figures 2.27 and 2.28. Total construction time for the entire 130,000 sq ft (12,000 m*) was approximately

FIGURE 2.28. Saint Jean Bridge at Bordeaux, cantilever construction on typical pier.

43

one year, as shown on the actual program of work summarized in graphic form in Figure 2.29. To meet the very strict construction deadline of the contract, it was necessary to bring to the project site another set of three travelers to cast the last cantilever on the left bank and achieve continuity with the southern river pier cantilever. Altogether, meeting the two-year construction schedule was recognized as an engineering achievement. Exactly one hundred years earlier, Gustave Eiffel had built the neighboring railway bridge in exactly two years-food for thought and a somewhat humbling reflection for the present generation.

2.6

Siegtal and Kochertal Bridges, Germany

The Siegtal Bridge near the town of Sieger, north of Frankfort, Germany, represents the first industrial application of cast-in-place cantilever construction with an auxiliary overhead truss. This method was initially developed by Hans Wittfoht and the firm of Polensky-und-Zollner and subsequently used for several large structures in Germany and other countries. One of the most recent and remarkable examples of this technique is the Kochertal Bridge between Ntiremberg and Heilbron, Germany. Both structures will be briefly described in this section, while a similar application in Denmark is covered in another section of this chapter. Siegtal Bridge is a twelve-span structure 3450 ft (1050 m) long resting on piers up to 330 ft (100 m) high, with maximum span lengths of 344 ft (105 m), Figure 2.30. Two separate box girders carry the three traffic lanes in each direction for a total width of 100 ft (30.5 m), Figure 2.31. Structural height of the constant-depth box girder is 19 ft (5.8 m), corresponding to a span-to-depth ratio of 18. The deck is continuous throughout its entire length, with fixed bearings provided at the three highest center piers and roller bearings of highgrade steel for all other piers and end abutments. Piers have slip-formed reinforced concrete hollow box shafts with a constant transverse width of 68 ft (20.7 m) and a variable width in elevation with a slope of 40 to 1 on both faces. The superstructure was cast in place in balanced cantilever from all piers in 33 ft (10 m) long segments with an auxiliary overhead truss supporting the two symmetrical travelers, and a cycle of one week was obtained without difficulty for the construction of two symmetrical 33 ft (10 m) long seg-

PONT USCttAMPS

I

’

em6

I

7x00

I

7200 -

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L-

n,oo

-

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I

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/

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I

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DEC JANV 2 FEV F MARS

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EWEIJVES 2 AWL 1965

FIGURE 2.29.

Saint Jean Bridge at Bordeaux, actual program of work.

Elevation t Cross section 1

‘Cross section 2 Horizontal section

FIGURE 2.30. Siegtal Bridge, general dimensions.

45

Siegtal and Kochertal Bridges, Germany Jo.M _ 2.m

_ t.7~ 1125 .n . -.fl

II 59

3s _ i

‘.IS 1so

I

L9.m I

5m ~‘

.:,

FIGURE 2.77. Vejle Fjord Bridge, pier segment with diaphragm.

FIGURE 2.78. Vejle Fjord Bridge, construction \iew, spring 1978 (courtesy of H. A. Lindberg).

\

;->, : \

I_\\

1

FIGURE 2.76. Vejle Fjord Bridge, transverse ribs. Construction progress in the spring of 1978 is illustrated in Figures 2.75 through 2.78. Figure 2.79 is an aerial view showing the structure nearing completion. To keep within the construction schedule, it was finally necessary to use two complete sets of launching girders and twin travelers working simultaneously from both ends of the bridge.

2.79. Vqjle Fjord Bridge. aerial view from the northwest. FIGURE

Cast-in-Place Balanced Cantilever Girder Bridges

68 2.14

Houston Ship Channel Bridge, U.S.A.

This bridge, a rendering of which is shown in Figure 1.67, includes a main structure over the Ship Channel in Houston, Texas, and two approach viaducts. The main structure is a three-span continuous box girder, cast in place in balanced cantilever. Span lengths are 375, 750, and 375 ft (114, 229, and 114 m). The navigation channel is 700 ft (213 m) wide at elevation 95 ft (29 m) and 500 f-t (752 m) wide at elevation 175 ft (53.4 m), Figure 2.80. The three-web box girder carries four traffic lanes separated by a 2 ft 3 in. (0.7 m) central barrier and has two 3 ft 9 in. (1.14 m) parapets. The box girder is fixed to the top of the main piers to make the structure a three-span rigid frame. Support for the box girder is provided by elastomeric bearings on top of the transition piers, where it is separated from the approach viaducts by expansion joints.

shrinkage, superimposed dead loads, and live loads). They are, therefore, heavilv reinforced; their dimensions are: Total height (from top of footing to bottom of pier segments): 160 ft 10 in. (49 m) Length (parallel to centerline of highway): 20 ft constant (6.1 m) Width: variable from 38 ft at the bottom to 27 ft 7 in. at the top (11.6 to 8.4 m) Pier cross section: rectangular box, with 2 ft (0.6 m) constant wall thickness

The transition piers support the last segment of the main structure side span and the last span of the approaches. The pier shaft is a rectangular box with 1 ft 4 in. (0.4 m) thick walls. Their heights are 152 ft (46 m) at one end and 164 ft (50 m) at the other end of- the bridge. The length, parallel to the centerline of the highway, varies from 18 to 8 ft (5.5 to 2.4 m); the width is 38 ft (11.6 m) constant. Atop the pier, a 6 ft 8 in. (2 m) cap carries the perFoundations The two center piers and two tranmanent elastomeric bearings and all the temporary sition piers rest on 24 in. (610 mm) diameter jacks and concrete blocks that will be used at the driven steel pipe piles. The center piers each rest time of the side-span closure pour. All four piers upon 255 piles with a unit pile capacity of 140 t are slip-formed. (127 mt). Footings are 81 ft (24.7 m) wide, 85 ft (26 Box Gzrder Superstructure Dimensions of the m) long, and 15 ft (4.6 m) deep. These footings are variable-depth box girder were dictated by verv surrounded by a sheet pile cofferdam and are stringent geometry requirements. Vertical alignpoured on a 4 ft (1.2 m) thick subfooting seal conment of the roadway was determined by the crete. The transition pier footings are 50 ft (15.2 maximum allowable grade of the approach viam) wide, 35 ft (10.7 m) long, and 5.5 ft (1.7 m) ducts and the connection thereof with the roadway thick and rest on 70 piles each of 100 t (90 mt) system on both banks. The clearance required fat bearing capacity. the ship channel left, therefore, only a structural depth of 2 1.8 ft (6.6 m) at the two points located Piers The main piers provide for the stability of 250 ft (76 m) on either side of the midspan section. the cantilevers during construction (unbalanced The soffit is given a third-degree parabolic shape construction loads and wind loads) and participate to increase the structural depth near the piers in in the capacity and behavior of the structure under order to compensate for the very lirnited height of service loads (long-term loads due to creep and

FIGURE 2.80.

Houston

Ship

Channel

Bridge,

longitudinal

section.

Houston Ship Channel Bridge, USA

the center portion of the main span. Maximum depth at the pier is 47.8 ft (14.6 m), with a spanto-depth ratio of 15.3. Minimum depth at midspan is 15 ft (4.6 m), with a span-to-depth ratio of 49. Over the 500 ft (152 m) center portion of the main span the span-to-depth ratio is 23, compared to a usual value between 17 and 20. Typical dimensions of the box section are shown in Figure 2.8 1. Posttensioning is applied to the box section in three dimensions:

69

Longitudinal prestress is provided by straightstrand tendons (twelve 0.6 in. diameter or nineteen 0.6 in. diameter strands), as shown schematically in Figure 2.82. Transversely, the top slab is post-tensioned by tendons (four 0.6 in. diameter strands) in flat ducts placed at 2 ft (0.6 m) centers. Vertically, the three webs are also post-tensioned as prescribed in the specifications to a minimum

t

k Bridge

FIGURE 2.81.

Houston Ship Channel Bridge, box section.

T r a n s v e r s e t e n d o n s 4xO.G;

Cantilever

FIGURE

prestress

over

main

piers

/

/

Tendons

( 1 2 x 06%a..ond (19xO.6’dia. I

Continuity

prestress

at

2.82.

Houston Ship Channel Bridge, longitudinal prestress.

mid

-span

70

Cast-in-Place Balanced Cantilever Girder Bridges

FIGURE

2.83.

Houston Ship Channel Bridge, details of travelers

compressive stress equal to 3Ji; that is, 230 psi (1.6 MPa) for a concrete strength J‘i = 6000 psi (41.4 MPa). Details of the form traveler are shown in Figure 2.83. Pier segments over the main piers are of unusual size and posed a very interesting design problem, arising from the transfer of the superstructure un-

balanced moments into the pier shafts. Additional vertical post-tensioning tendons are provided in the two 2 ft (0.6 m) thick pier diaphragms for this purpose. End segments over the transition piers were designed to allow either the approaches or the main structure to be completed first, as these are two separate contracts. It is possible to make an adjustment at the end piers to compensate either for differential settle-

71

Other Notable Structures

(a)

2.15.1 MEDWAY

BRIDGE, U.K.

One of the first very long-span cantilever bridges was the Medway Bridge. This structure used a series of temporary falsework bents to provide stability during construction, Figure 2.84. 2.15.2 RIO TOCANTINS

BRIDGE, BRAZIL

This structure has a center span of 460 ft (140 m) and two side spans of only 174 ft (53 m), Figures 2.85 and 2.86. 2.15.3 PUENTE FIGURE 2.84. Xlrti~av Bridge, U.K. ((I) I‘)pical struction sequence. (h) View of’ finished bridge.

COII-

ments or for any deviation of the deflections from the assumed camber diagram used for construction. Provisions have been made for unexpected additional concrete shrinkage and creep problems; empty ducts have been placed in the pier segment diaphragms and at midspan to allow for future possible installation of additional tendons located inside the box girder but outside the concrete section, should the need for such tendons arise.

DEL AZUFRE, SPAIN

This bridge is located very high over a deep canyon of the Rio Sil. Cantilever cast-in-place was the ideal answer to allow construction with a minimal contact with the environment, Figures 2.87 and 2.88. 2.15.4 SCHUBENACrlDIE

BRIDGE, CANADA

This three-span bridge with a center span of 700 ft (213 m) crosses the Schubenacadie River, near Truro, Nova Scotia. High tidal range, swift currents, ice, and adverse climatic conditions made the construction of this structure very challenging, Figures 2.89 and 2.90. 2.15.5

INCIENSO

BRIDGE,

GUATEMALA

2.15 Other Notable Structures

There are so many outstanding and interesting cast-in-place cantilever bridges in the world today that it is impossible to discuss the subject adequately in the space available here. Mention should be made, however, of several notable structures not yet covered by a detailed description.

The main three-span rigid frame structure with a center span of 400 ft (122 m) is of cast-in-place balanced cantilever construction, and the approach spans are of precast girders, Figures 2.91 and 2.92. The very severe 1977 earthquake left the center structure completely undamaged, while the usual damage took place in the approach spans.

Cast-in-Place Balanced Cantilever Girder Bridges

72

1

FIGURE 2.85.

1.72S

j6.55 1

1.725

1

Rio Tocantins Bridge, Brazil, typical elevation and cross section.

2.15.6 SETUBAL BRIDGE, ARGENTINA

This three-span structure with a main span of460 ft (140 m) rests on two main river piers with twin vertical walls and piles, with a transition footing at water elevation, Figures 2.93 and 2.94. 2.15.7 KIPAPA STREAM BRIDGE, U.S.A.

This bridge is located in the Island of Oahu in the State of Hawaii. The dual structure has an overall

width of 118 ft (36 m) to accommodate six traffic lanes, three in each direction, and consists of two double-cell box girders of constant depth with interior spans of 2.50 ft (76.2 m), Figures 2.95 and 2.96. Construction was by cast-in-place cantilever with segments 15 ft 3 in. (4.65 m) long. The bridge has pleasant lines, which blend aestheticallv with the rugged deep-valley site. 2.15.8

PARROTS FERRY BRIDGE, U.S.A.

This structure, built in California for the Corps of Engineers, represents a major application of lightweight concrete for cast-in-place cantilever construction, Figure 2.97. 2.15.9

FIGURE 2.86. Rio Tocantins Bridge, Brazil, view of the finished bridge.

MAGNAN

VIADUCT,

FRANCE

Located just off the French Riviera in Southern France, this four-span continuous structure rests on 300 ft (92 m) high twin piers of an I-shaped section. Superstructure was cast in place in two stages (first the bottom slab and webs and then the top slab) to reduce the weight and cost of travelers. Figures 2.98 and 2.99 show the principal dimensions and views of one cantilever and the finished structure, Figure 2.100.

Other Notable Structures 6S.00

130 00

73 I

*+t

cm

I I I

Ad

*

I

FIGURE

2.87.

d

Puente de1 Azufre, Spain, typical elevation and sections.

2.15.10 PUTE4UX BRIDGE, FRANCE

These are twin bridges crossing the Seine River near Paris. Because of very stringent clearance and geometry requirements, the available structural depth was only 5.9 ft (1.8 m) for the clear 275 ft (83.8 m) span and 4.8 ft (1.47 m) for the clear 214

ft (65.3 m) span, making both structures very slender, Figures 2.101 and 2.102. Stiff “V” piers in both structures help reduce the flexibility of the deck. 2.15.11 TRICASTIN BRIDGE, FRANCE

This structure spans the Rhone River with no piers in the river, which necessitates a long center span and two very short side spans anchored at both ends against uplift. The center portion of the main span is of lightweight concrete, while the two zones over the piers where stresses are high are of conventional concrete, Figures 2.103 and 2.104. 2.15.12 ESCHACHTAL BRIDGE, GERMANY

FIGURE 2.88.

Puente &%I Azuir e, Spun.

This bridge is located near Stuttgart, Germany. The superstructure consists of a large single-cell box girder with large top flange cantilevers supported by precast struts. Because of the weight involved, the central box was cast in one operation; struts were installed and flanges cast subsequently, Figures 2.105 and 2.106.

Elevation

16'~0"

1

16’4” Q I

,6,-o”

i

16’4”

Section at Midspan

II

20’~0” Section pver

4 Piers

FIGURE 2.89. Shubenacadie Bridge, elevation and sections, from ref. 16.

FIGURE 2.90. Shubenacadie Bridge, supper t avstem for unbalanced cantilever moment at pier (courtesy of the Portland Cement Association). 74

FIGURE 2.91. Incknso Bridge, Guatemala, view of the structure.

ELEVATION

@@Gp 7 50 MAIN ‘/2

SECTION ON SUPPORT

BRIDGE

‘/2

SECTION ON SPAN

FIGURE 2.92. Incienso Bridge, Guatemala, dimensions.

FIGURE 2.93. Setubal Bridge, Argentina, dimensions. 75

FIGURE bridge.

2.94.

Setubal Bridge, Argentina, view of the

Abut 2 3

2

1

29’&”

c

4 Elevation

5

-...v.&-.-.-__.

7

6

29’4”

._~ . __. i)

~~,2,, -- - FIGURE

2.95.

Kipapa Stream Bridge, elevation and cross section.

FIGURE 2.96. Kipapa Stream Bridge, construction view (courtesy of Dyckerhoff & Widmann).

FIGURE 2.97. Ferry Bridge, ref. 17.

=2?

Parrots dimensions,

COUPE LONGITUDINALE ?? 99

0 T

00

@ UC

FIGURE 2.98. Magnan Viaduct, longitudinal section.

FIGURE 2.99.

Ilagnan Viaduct, view of a cantilever.

FIGURE 2.100. Magnan Viaduct, aerial view of the completed bridge.

FIGURE

2.101.

Puteaux Bridge, aerial view of the completed bridge.

Ill1 rlnrn - Ml

h “t/ \

10.00 5 00

5.00

c

1 2 . 4 0

++-j 2 . 4 0

FIGURE 2.103. Tricastin Bridge, dimensions.

79

FIGURE 2.104. Tricastin Bridge, view of finished bridge.

FIGURE 2.105. Eschachtal Bridge, casting flange

FIGURE 2.106. Eschachtal Bridge, view of outrigger

cantilevers.

struts.

80

81

References

2.16

Conclusion

‘I‘he I~;III\~ structures described above show the versatilitv of’ cast-in-place balanced cantilever construction, particularl\~ in the field of vet-v-long-span bridges with tew repetitive spans. The design aspect 01‘ these structures will be discussed in Chapter 4 attd construction problems in Chapter 11.

References 1. H. I‘llUl, “RlYlcLentMll,”

JAIJI-g;~t~g.

Hctt 5.

Bdot/- uuct S~nhlh/e~r//~crtc, 6 1

\I;ti 1966.

2 .

L‘lt-ich Fitistrrwaldet-. “Prestressed Concrete BI-idge & the %,ex;lbcl(clty of eye