Prestressed Concrete

657 Pages·2022·14.101 MB·English

by  Warner Foster, Kilpatrick Gravina

PRESTRESSED CONCRETE
FIFTH EDITION
Robert Warner Stephen Foster Andrew Kilpatrick Rebecca Gravina
Copyright © 2022 Pearson Australia (a division of Pearson Australia Group Pty Ltd) 9780655706397 Prestressed Concrete 5e
Prestressed Concrete
FIFTH EDITION
(cid:1)
Warner Foster Kilpatrick Gravina
(cid:1)
(cid:1)
Copyright © 2022 Pearson Australia (a division of Pearson Australia Group Pty Ltd) 9780655706397 Prestressed Concrete 5e
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Copyright © 2022 Pearson Australia (a division of Pearson Australia Group Pty Ltd) 9780655706397 Prestressed Concrete 5e
Table of Contents
CHAPTER 1 Introduction ........................................ 1
Prestressed concrete ......................................................................... 1
Prestressing as a design option ....................................................... 10
Use of high-strength tendons and cables ........................................ 12
Methods of prestressing .................................................................. 15
Anchorage and bond of tendons ..................................................... 19
Cable profile and level of prestress ................................................ 21
References ...................................................................................... 23
CHAPTER 2 Properties of materials .................... 25
Introduction .................................................................................... 25
Properties of prestressing steel ....................................................... 26
Properties of reinforcing steel ........................................................ 32
Strength properties of concrete ....................................................... 33
Short-term deformation of concrete ............................................... 36
Shrinkage of concrete ..................................................................... 39
Creep of concrete under constant stress ......................................... 45
Concrete creep under varying stress ............................................... 53
References ...................................................................................... 58
CHAPTER 3 Methods of design and analysis .... 61
The structural design process ......................................................... 61
Design objectives and design criteria for prestressed concrete ...... 62
Design criteria and structural reliability ......................................... 65
AS3600 design checks for prestressed concrete ............................ 66
The critical stress method of design ............................................... 72
Methods of analysis ........................................................................ 72
Strut-and-tie modelling and stress-fields ........................................ 74
References ...................................................................................... 80
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CHAPTER 4 Flexural behaviour of uncracked
members ........................................... 83
Introduction .................................................................................... 83
Short-term behaviour of uncracked beams ..................................... 83
Equivalent load concept ................................................................. 91
Load balancing ............................................................................. 100
Creep and shrinkage effects in beams .......................................... 104
Analysis of creep and shrinkage effects ....................................... 107
Deflections of uncracked beams ................................................... 109
References .................................................................................... 135
CHAPTER 5 Flexural behaviour in the post-
cracking range ................................ 137
Cracking moment ......................................................................... 137
Post-cracking flexural behaviour .................................................. 141
Elastic analysis for a rectangular cracked section ....................... 145
The effect of prior creep and shrinkage ........................................ 157
Cracked section analysis: general trial-and-error method ........... 157
Non-linear analysis at high overload ............................................ 159
Moment-curvature and stress-moment relationships .................... 160
Deflection calculations ................................................................. 165
Crack control ................................................................................ 186
References .................................................................................... 194
CHAPTER 6 Flexural strength analysis ............. 195
Overload behaviour and ultimate strength ................................... 195
Assumptions for ultimate strength analysis .................................. 198
Rectangular section: calculation of ultimate moment .................. 201
T- and I-sections: calculation of ultimate moment ....................... 208
Moment capacity with some steel not at yield ............................. 214
Effect of incomplete bond ............................................................ 219
General analysis by trial strain distributions ................................ 221
Stress in bonded tendons at ultimate ............................................ 229
Design considerations ................................................................... 232
References .................................................................................... 242
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CHAPTER 7 Shear and torsion .......................... 243
Shear and torsion in prestressed concrete ..................................... 243
Overload behaviour in shear and bending .................................... 244
Web reinforcement behaviour in the post-cracking range ............ 248
Effect of prestress on behaviour in shear ..................................... 252
Web-shear cracking load for prestressed members ...................... 254
Strength in shear ........................................................................... 264
Design for shear according to AS3600 ........................................ 278
Analysis and design for torsion ................................................... 294
References .................................................................................... 317
CHAPTER 8 Anchorage ...................................... 319
Introduction .................................................................................. 319
Simplified design approach for post-tensioned beams ................. 322
Anchorage of pretensioning tendons ............................................ 353
Design of end blocks using strut-and-tie modelling ..................... 357
References .................................................................................... 386
CHAPTER 9 Loss of prestress ........................... 389
Types of losses .............................................................................. 389
Elastic loss .................................................................................... 390
Duct friction loss .......................................................................... 392
Anchorage slip .............................................................................. 394
Stress relaxation ............................................................................ 396
AS3600 calculation of deferred losses ........................................ 397
Analytic methods for evaluating deferred losses ......................... 405
References .................................................................................... 410
CHAPTER 10 Design procedures for statically
determinate beams ........................ 411
Structural design ........................................................................... 411
Choosing the type of construction ................................................ 412
Choosing the cross-section .......................................................... 413
Choosing the prestressing details ................................................. 417
Design steps .................................................................................. 420
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Discussion of key steps ................................................................ 421
Design criteria for serviceability .................................................. 426
Design examples ........................................................................... 428
References .................................................................................... 446
CHAPTER 11 Continuous beams ......................... 449
Advantages of continuous construction ........................................ 449
Effects of prestress in continuous beams ...................................... 450
Calculating the effects of prestress by the equivalent load method 454
Cable profiles for continuous post-tensioned beams .................... 462
Service load behaviour of continuous beams ............................... 466
Deflection calculations for continuous beams .............................. 468
Overload behaviour and flexural strength .................................... 472
Design procedure for continuous beams ...................................... 475
References .................................................................................... 491
CHAPTER 12 Slab systems .................................. 493
Introduction .................................................................................. 493
Effects of prestress ........................................................................ 495
Effects of prestress plus service load ............................................ 503
Cracking ....................................................................................... 508
Deflections .................................................................................... 512
Ultimate strength analysis ............................................................ 515
Design steps for prestressed slabs ................................................ 517
References .................................................................................... 554
APPENDIX A Analysis of uncracked sections ... 555
Uncracked post-tensioned section with reinforcement ................ 555
Uncracked pretensioned section with reinforcement ................... 563
APPENDIX B Creep and shrinkage in uncracked
flexural members ........................... 565
Introductory note .......................................................................... 565
Order-of-magnitude estimates of long-term deformations and
prestress losses .............................................................................. 565
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One-step analysis with age-adjusted effective modulus ............... 569
Step-by-step analysis .................................................................... 593
Approximate closed form equations for losses and deformations .. 604
Non-uniform shrinkage and creep ................................................ 621
References .................................................................................... 624
APPENDIX C Effects of prior creep and
shrinkage on flexural strength ..... 627
Introduction .................................................................................. 627
Short-term service load application .............................................. 628
Effect on flexural strength ........................................................... 635
Concluding remarks ..................................................................... 636
APPENDIX D Elastic deflections and end
rotations for single-span beams .. 639
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Preface
Preface to the Fifth Edition
The prime purpose of this new edition of Prestressed Concrete is to take
account of important changes that have been made in the new edition of the
Australian Standard for Concrete Structures, which appeared in 2018 and
Amendment 2 in 2021. Changes include modifications to the rectangular
stress-block parameters for flexural strength calculations, modifications to
the design clauses for shear and torsion, and changes in the safety coefficients
for ultimate strength design which result in a slight reduction in the overall
safety margins for design. We have also taken the opportunity to correct
minor errors and to rearrange the material in Appendix B, which deals with
the effects of creep and shrinkage in prestressed flexural members, to make it
more directly applicable to the design process.
Robert Warner Stephen Foster Andrew Kilpatrick Rebecca Gravina
Adelaide Sydney Bendigo Melbourne
November, 2021
Preface to the Fourth Edition
Following the death of Ken Faulkes, who was an original co-author of
previous editions of this book, Rebecca Gravina has joined the team of
co-authors in the preparation of the fourth edition of Prestressed Con-
crete. In this new edition we have taken the opportunity to make cor-
rections to the text and to extend and improve the treatment of creep
and shrinkage effects in Appendix B.
Robert Warner Stephen Foster Rebecca Gravina
Adelaide Sydney Melbourne
December, 2016
Preface to the Third Edition
When the first edition of this book appeared, more than thirty years ago, pre-
stressed concrete and reinforced concrete were considered to be separate and
distinct materials of construction. In Australia, different design standards had
to be used for the two materials. At that time, prestressed concrete was
Prestressed concrete ix
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designed to remain uncracked under full working load, using elastic analysis
and allowable stress concepts. The apparent gulf between reinforced concrete
and prestressed concrete was exaggerated by severe restrictions that were
placed on the use of partial prestressing by the then-current prestressed con-
crete standard, AS1481. One of the main aims of the first edition of this book
was to present a rational and unified approach to the analysis and design of
prestressed concrete, and hence to encourage designers to choose freely from
the full range of design options, including reinforced concrete and any appro-
priate level of prestress. A further aim of the book was to present rational
ways of selecting prestress levels that would optimise service load behaviour
and economy. This aim was reflected in its full title: Prestressed Concrete:
1
with emphasis on partial prestressing .
Today, the Australian Concrete Structures Standard, AS3600, adopts a uni-
fied, performance-based approach to design for all reinforced concrete struc-
tures and members, irrespective of whether or not prestress is used. This
integrated approach has removed unnecessary restrictions on design and has
provided significant advantages to innovative designers. This in turn has
resulted in partial prestressing becoming the design norm, and the term pre-
stressed concrete now means, simply, structural concrete with prestress.
The world-wide developments that occurred in the field of concrete structures
also made possible a more elegant, unified treatment of the underlying theory.
Structural concrete members may contain any mix of reinforcing and pre-
stressing steel, with reinforced concrete members being at one end of this
continuum. Such a unified approach to analysis and design was adopted in a
2
previous text book, titled Concrete Structures .
Nevertheless, when we consider the processes of teaching and learning today,
we find that many students and lecturers prefer to deal first with the basics of
reinforced concrete before going on to consider the concepts of prestressed
concrete. Furthermore, it is now usual for many undergraduate course pro-
grams in structural engineering to cover reinforced concrete but not pre-
stressed concrete. Although used widely in practice, prestressed concrete has
become an option for undergraduate students, and hence a subject to be stud-
ied by postgraduates and practising engineers. For these reasons, we have
1. Warner, R. F. and Faulkes, K. A., 1979, Prestressed Concrete: with emphasis on partial pre-
stressing, Pitman Publishing, Melbourne.
2. Warner, R. F., Rangan, B. V., Hall, A. S. and Faulkes, K. A., 1998, Concrete Structures,
Longman-Cheshire, Melbourne.
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