Contenido The Design of Prestressed Concrete Bridges Concepts and Principles

Examining the fundamental differences between design and analysis, Robert Benaim explores the close relationship between aesthetic and technical creativity and the importance of the intuitive, more imaginative qualities of design that every designer should employ when designing a structure.

Aiding designers of concrete bridges in developing an intuitive understanding of structural action, this book encourages innovation and the development of engineering architecture. Simple, relevant calculation techniques that should precede any detailed analysis are summarized. Construction methods used to build concrete bridge decks and substructures are detailed and direct guidance on the choice and the sizing of different types of concrete bridge deck is given. In addition guidance is provided on solving recurring difficult problems of detailed design and realistic examples of the design process are provided.

This book enables concrete bridge designers to broaden their scope in design and provides an analysis of the necessary calculations and methods.

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Acknowledgements
Disclaimer

Introduction

1 The nature of design

1.1 Design and analysis
1.2 A personal view of the design process
1.3 Teamwork in design
1.4 The specialisation of designers
1.5 Qualities required by a bridge designer
1.6 Economy and beauty in design
1.7 Expressive design
1.8 Bridges as sculpture
1.9 Engineering as an art form

2 Basic concepts

2.1 Introduction
2.2 Units
2.3 Loads on bridge decks
2.4 Bending moments, shear force and torque
2.5 Limit states
2.6 Statical determinacy and indeterminacy

3 Reinforced concrete

3.1 General
3.2 The historical development of reinforced concrete
3.3 General principles of reinforced concrete
3.4 Reinforced concrete in bending
3.5 The cracking of reinforced concrete
3.6 The exothermic reaction
3.7 The ductility of reinforced concrete
3.8 Imposed loads and imposed defl ections
3.9 Creep and relaxation of concrete
3.10 Truss analogy
3.11 Strut-and-tie analogy
3.12 Continuity between the concepts of bending and arching action

4 Prestressed concrete

4.1 Introduction
4.2 A comparison between reinforced concrete and prestressed concrete
4.3 Pre-tensioning and post-tensioning
4.4 Conclusion

5 Prestressing for statically determinate beams

5.1 General
5.2 Materials employed for the example
5.3 Section properties
5.4 Central kern and section efficiency
5.5 Loads
5.6 Bending moments, bending stresses and shear force
5.7 Centre of pressure
5.8 Calculation of the prestress force
5.9 Table of stresses
5.10 Non-zero stress limits
5.11 Compressive stress limits
5.12 Sign convention
5.13 Arrangement of tendons at mid-span
5.14 Cable zone
5.15 The technology of prestressing
5.16 Cable profile
5.17 Losses of prestress
5.18 The concept of equivalent load
5.19 Internal and external loads
5.20 Prestress effect on shear force
5.21 Anchoring the shear force
5.22 Defl ections
5.23 The shortening of prestressed members
5.24 Forces applied by prestress anchorages
5.25 Following steel
5.26 The introduction of prestress forces
5.27 Bonded and unbonded cables

6 Prestressing for continuous beams

6.1 General
6.2 The nature of prestress parasitic moments
6.3 Parasitic moments at the ULS
6.4 The effect of parasitic moments on the beam reactions
6.5 Concordant cables
6.6 Straight cables in built-in beams
6.7 Cable transformations
6.8 Control of prestress parasitic moments
6.9 Details of the sample bridge deck
6.10 Section properties
6.11 Comment on the accuracy of calculations
6.12 Dead and live loads
6.13 Bending moments
6.14 Considerations on the choice of tendon size
6.15 Calculating the prestress force
6.16 Prestress scheme
6.18 Non-zero stress limits
6.19 Very eccentric cross sections
6.20 Design of the parasitic moments
6.21 Modifi cation of bending moments due to creep
6.22 Modifi cation of bending stresses due to creep following change of cross section
6.23 Bursting out of tendons
6.24 The anchorage of tendons in blisters
6.25 Checks at the ULS

7 Articulation of bridges and the design of substructure

7.1 General
7.2 Design parameters
7.3 Bearings: general design considerations
7.4 Mechanical bearings
7.5 Elastomeric bearings
7.6 Concrete hinges
7.7 Design of foundations
7.8 The design of piers
7.9 The articulation of decks with mechanical bearings
7.10 Deck on laminated rubber bearings
7.11 Piers built into the deck
7.12 Split piers
7.13 Integral bridges
7.14 Continuity versus statical determinacy
7.15 Examples of bridge articulation

8 The general principles of concrete deck design

8.1 General
8.2 Transverse bending
8.3 Transverse distribution of live loads
8.4 Material quantities and costs
8.5 Choice of most economical span

9 The design of bridge deck components

9.1 General
9.2 Side cantilevers
9.3 Top slabs
9.4 Bottom slabs
9.5 Webs
9.6 Diaphragms
9.7 Deck drainage
9.8 Waterproofi ng
9.10 Expansion joints

10 Precast beams

10.1 General
10.2 Standard precast beams
10.3 Customised precast beams
11 Solid slabs, voided slabs and multi-cell box girders
11.1 Slab bridges, general
11.2 Reinforced concrete slab bridges
11.3 Prestressed concrete slab bridges
11.4 Solid slab portal bridges
11.5 Voided slabs
11.6 Case history: River Nene Bridge
11.7 Multi-cell box girders

12 Ribbed slabs

12.1 General
12.2 Behaviour of twin rib decks
12.3 The use of diaphragms
12.4 Proportioning of twin rib decks
12.5 Ribbed slabs and skew bridges
12.6 Heat of hydration effects on twin rib decks
12.7 Prestress layout
12.8 Substructure for twin rib bridges
12.9 Construction technology
12.10 The development of ribbed slabs

13 Box girders

13.1 General
13.2 Cast-in-situ construction of boxes
13.3 Evolution towards the box form
13.4 Shape and appearance of boxes
13.5 The number of webs per box
13.6 Number of boxes in the deck cross section

14 Counter-cast technology for box section decks

14.1 General
14.2 Long line casting
14.3 Short line casting

15 The construction of girder bridges

15.1 General
15.2 Cast-in-situ span-by-span construction of continuous beams
15.3 Precast segmental span-by-span erection
15.4 Cast-in-situ balanced cantilever construction
15.5 Precast segmental balanced cantilever construction
15.6 Progressive erection of precast segmental decks
15.7 Construction programme for precast segmental decks
15.8 Incremental launching
15.9 Prefabrication of complete spans

16 The effect of scale on the method of construction

16.1 General
16.2 A bridge length of 130 m on four spans
16.3 A bridge length of 130 m on three spans
16.4 The bridge is 500 m long
16.5 A series of short bridges totalling typically 1,000 m
16.6 The bridge is 1,000 m long
16.7 The bridge is 2,000 m long
16.8 The bridge is 10,000 m long

17 The design and construction of arches

17.1 General
17.2 Line of thrust
17.3 Unreinforced concrete and masonry arches
17.4 Flat arches
17.5 Reinforced concrete arches
17.6 Short-span reinforced concrete arches with earth fi ll
17.7 Longer span reinforced concrete arches supporting bridge decks
17.8 Construction of arches
17.9 Progressive collapse of multi-span arch bridges
17.10 Tied arches

18 Cable-supported decks

18.1 General
18.2 Extradosed bridge decks
18.3 Undertrussed bridges
18.4 Cable-stayed bridges
18.5 Stressed ribbon bridges
18.6 Steel cable catenary bridges
18.7 Flat suspension bridges

Appendix
References
Index