Prestressed Concrete design and practice

PREFACE v
1 INTRODUCTION 1-1
1.1 THE BASIC IDEA OF PRESTRESSED CONCRETE 1-1
1.2 EFFECTS OF PRESTRESSING 1-3
1.3 GENERAL PRINCIPLES 1-5
1.4 BASIC DEFINITIONS 1-10
1.5 PRESTRESSED VERSUS REINFORCED CONCRETE 1-12
1.6 HISTORY OF PRESTRESSED CONCRETE 1-13
1.7 REFERENCES 1-15
2 MATERIAL PROPERTIES 2-1
2.1 CONCRETE 2-1
2.1.1 Compressive strength 2-1
2.1.2 Stress-strain relationship 2-5
2.1.3 Modulus of elasticity 2-7
2.1.4 Tensile strength 2-10
2.1.5 Time-dependent behaviour 2-13
2.1.6 Thermal properties of concrete 2-20
2.1.7 Poisson’s ratio 2-20
2.1.8 Fatigue 2-20
2.2 STEEL REINFORCEMENT 2-20
2.2.1 Non-prestressed reinforcement 2-21
2.2.2 Prestressed reinforcement 2-25
2.2.3 Relaxation of prestressing steel 2-31
2.2.4 Fatigue characteristics of reinforcement 2-35
2.2.5 Thermal properties of reinforcement 2-37
2.3 REFERENCES 2-37
3 PRESTRESSING SYSTEMS AND PROCEDURES 3-1
3.1 INTRODUCTION 3-1
3.2 PRETENSIONING SYSTEMS AND PROCEDURES 3-1
3.2.1 Basic principle and procedure 3-1
3.2.2 Stressing beds 3-7
3.2.3 Structural frames 3-9
3.3 POST-TENSIONING SYSTEMS AND PROCEDURES 3-10
3.3.1 Basic principle and procedure 3-10
3.3.2 Post-tensioning systems 3-12
3.3.3 Post-tensioning operations 3-20
3.3.4 Ducting for bonded construction 3-23
3.3.5 Grouting 3-25
3.4 PRETENSIONING VERSUS POST-TENSIONING 3-28
3.5 REFERENCES 3-29
4 DESIGN FOR FLEXURE 4-1
4.1 INTRODUCTION 4-1
4.2 SIGN CONVENTION 4-1
4.3 ANALYSIS 4-2
4.3.1 Basic assumptions 4-2
4.3.2 Flexural response 4-5
4.3.3 Analysis of the uncracked section 4-7
4.3.4 Cracking moment 4-11
4.3.5 Ultimate moment: Sections with bonded tendons 4-12
4.3.6 Analysis of beams with unbonded tendons 4-31
4.3.7 Flexural analysis of composite sections 4-36
4.4 DESIGN 4-51
4.4.1 Limit states design 4-51
4.4.2 Design for the serviceability limit state 4-54
4.4.3 Design for the ultimate limit state 4-69
4.4.4 Limits on steel content 4-74
4.4.5 Flexural design of composite sections 4-75
4.4.6 Partial prestressing 4-82
4.5 REFERENCES 4-87
5 PRESTRESS LOSSES 5-1
5.1 INTRODUCTION 5-1
5.2 METHODS FOR CALCULATING PRESTRESSING LOSSES 5-1
5.2.1 Total loss in pretensioned members 5-2
5.2.2 Total loss in post-tensioned members 5-3
5.2.3 Methods for calculating prestress losses 5-3
5.3 ELASTIC SHORTENING OF THE CONCRETE 5-5
5.3.1 Pretensioned concrete 5-5
5.3.2 Post-tensioned concrete 5-7
5.4 TIME-DEPENDENT LOSSES 5-8
5.4.1 Loss due to relaxation of the steel 5-8
5.4.2 Loss due to shrinkage of the concrete 5-9
5.4.3 Loss due to creep of the concrete 5-10
5.5 LOSSES DURING POST-TENSIONING 5-28
5.5.1 Friction losses 5-28
5.5.2 Anchorage seating losses 5-35
5.6 REFERENCES 5-40
6 EFFECTS OF CONTINUITY 6-1
6.1 INTRODUCTION 6-1
6.2 ELASTIC ANALYSIS 6-1
6.2.1 Eccentricity of prestressing force 6-2
6.2.2 Force (flexibility) method 6-4
6.2.3 Fixed-end moments 6-9
6.2.4 Displacement (stiffness) method 6-11
6.2.5 Concept of equivalent loads 6-17
6.2.6 Effects of losses 6-23
6.2.7 Concordancy and linear transformation 6-25
6.3 DESIGN AT SERVICEABILITY LIMIT STATE 6-28
6.4 ANALYSIS AT ULTIMATE LIMIT STATE 6-29
6.4.1 Secondary moments 6-29
6.4.2 Moment redistribution 6-29
6.5 REFERENCES 6-32
7 SHEAR 7-1
7.1 INTRODUCTION 7-1
7.2 BEAMS WITHOUT WEB REINFORCEMENT 7-1
7.2.1 Cracking behaviour 7-1
7.2.2 Shear capacity of the concrete 7-3
7.3 BEAMS WITH WEB REINFORCEMENT 7-13
7.4 DESIGN PROCEDURE 7-16
7.5 COMPOSITE BEAMS 7-25
7.6 REFERENCES 7-30
8 DEFLECTIONS 8-1
8.1 INTRODUCTION 8-1
8.2 UNCRACKED BEAMS 8-2
8.2.1 Instantaneous deflections 8-2
8.2.2 Long-term deflections 8-5
8.3 CRACKED BEAMS 8-14
8.3.1 Instantaneous deflections 8-14
8.3.2 Long-term deflections 8-19
8.4 DEFLECTION LIMITATIONS 8-31
8.5 REFERENCES 8-32
9 ANCHORAGE ZONE DESIGN 9-1
9.1 INTRODUCTION 9-1
9.2 TRANSFER LENGTH 9-2
9.3 ANCHORAGE ZONE REINFORCEMENT 9-6
9.3.1 Spalling Stress Reinforcement 9-8
9.3.2 Bursting Stress Reinforcement 9-15
9.4 REFERENCES 9-21
10 PRESTRESSED CONCRETE SLABS 10-1
10.1 INTRODUCTION 10-1
10.2 EFFECTS OF PRESTRESS ON STRUCTURAL BEHAVIOUR 10-3
10.2.1 Flexural behaviour 10-4
10.2.2 Restraint to axial shortening 10-5
10.3 STRUCTURAL ANALYSIS BY THE EQUIVALENT FRAME METHOD 10-8
10.4 DESIGN 10-11
10.4.1 Design codes of practice 10-12
10.4.2 Preliminary value for the slab thickness 10-13
10.4.3 Prestressing 10-14
10.4.4 Analysis 10-19
10.4.5 Serviceability limit states 10-21
10.4.6 Ultimate limit states 10-26
10.5 DETAILING 10-30
10.5.1 Prestressed reinforcement 10-30
10.5.2 Non-prestressed reinforcement 10-31
10.5.3 Openings 10-33
10.6 DESIGN EXAMPLE 10-33
10.6.1 Material properties 10-34
10.6.2 Loadings 10-35
10.6.3 Balanced load 10-35
10.6.4 Check the preliminary value for the slab thickness 10-35
10.6.5 Minimum cover to tendons 10-35
10.6.6 Design: North-South direction 10-36
10.6.7 Design: East-West direction 10-59
10.6.8 Punching shear 10-60
10.6.9 Deflection 10-65
10.6.10 Concluding Remarks 10-71
10.7 REFERENCES 10-71
11 DETAILING 11-1
11.1 INTRODUCTION 11-1
11.2 COVER TO TENDONS 11-1
11.2.1 Considerations 11-1
11.2.2 Cover 11-6
11.3 LIMITATIONS ON PRESTRESSING STEEL CONTENT 11-6
11.3.1 Considerations 11-6
11.3.2 Minimum steel content 11-7
11.3.3 Maximum steel content 11-7
11.4 LIMITATIONS ON SPACING OF TENDONS 11-7
11.5 EFFECTS OF TENDON CURVATURE 11-8
11.5.1 In-plane normal forces 11-8
11.5.2 Out-of-plane multistrand effects 11-9
11.5.3 Minimum radius of curvature 11-11
11.5.4 Minimum tangent length 11-12
11.5.5 Code requirements 11-13
11.6 LONGITUDINAL NON-PRESTRESSED REINFORCEMENT 11-14
11.7 DRAWINGS 11-18
11.8 REFERENCES 11-19
APPENDIX A: LIST OF SYMBOLS
APPENDIX B: DRAWINGS
FLAT SLAB: REINFORCEMENT LAYOUT
TENDON LAYOUT
BRIDGE DECK: PRESTRESSING DETAILS