Table Of ContentConcrete Segmental Bridges
Concrete Segmental Bridges
Theory, Design, and Construction to
AASHTO LRFD Specifcations
Dongzhou Huang, Ph.D., P.E.
President, American Bridge Engineering Consultants
Chief Engineer, Atkins North America
Professor, Fuzhou University
Bo Hu, PhD., P.E., P. Eng.,
Associate Technical Director, COWI
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Dedication
The frst author is eternally grateful for his lovely wife, Yingying, without
whose patience and support this book would not have been possible.
Contents
Preface..........................................................................................................................................xxvii
Acknowledgments .........................................................................................................................xxix
Authors ..........................................................................................................................................xxxi
Unit Conversion Factors ............................................................................................................. xxxiii
Principal Notations ......................................................................................................................xxxv
Chapter 1 Introduction to Concrete Segmental Bridges ...............................................................1
1.1 Brief History and Development of Concrete Segmental Bridges ......................1
1.2 Materials ............................................................................................................9
1.2.1 Introduction ..........................................................................................9
1.2.2 Concrete ...............................................................................................9
1.2.2.1 Introduction ..........................................................................9
1.2.2.2 Compression Strength ...........................................................9
1.2.2.3 Tensile Strength .................................................................. 11
1.2.2.4 Stress-Strain Curve of Concrete and Modulus
of Elasticity.........................................................................11
1.2.2.5 Creep ................................................................................... 13
1.2.2.6 Shrinkage ............................................................................16
1.2.2.7 Thermal Coeffcient of Expansion ...................................... 18
1.2.2.8 Lightweight Concrete ......................................................... 18
1.2.3 Steel ....................................................................................................19
1.2.3.1 Reinforcing Steel ................................................................ 19
1.2.3.2 Prestessing Steel .................................................................20
1.2.4 FRP .....................................................................................................24
1.2.5 AASHTO Stress Limits for Concrete Segmental Bridges .................25
1.2.5.1 Stress Limits for Concrete ..................................................25
1.2.5.2 Prestressing Steel ................................................................26
1.3 Basic Concept of Segmental Construction ......................................................27
1.4 Typical Segments .............................................................................................27
1.4.1 Typical Sections .................................................................................27
1.4.2 Preliminary Dimensions ....................................................................28
1.4.2.1 General................................................................................28
1.4.2.2 Girder Height h ...................................................................29
1.4.2.3 Flange Thickness t .............................................................30
t
1.4.2.4 Web Thickness t ................................................................ 31
w
1.4.2.5 Web Spacing b ................................................................... 31
t
1.4.2.6 Length of Top Flange Cantilever b .................................... 31
c
1.4.3 Ducts ................................................................................................... 31
1.4.3.1 General................................................................................ 31
1.4.3.2 Duct Sizes ........................................................................... 32
1.4.3.3 Locations of Tendons in the Ducts ..................................... 32
1.4.3.4 Duct Spacing ....................................................................... 33
1.4.3.5 Duct Radius and Tangent Length ....................................... 33
1.4.3.6 Bonded and Unbounded Tendons .......................................33
1.4.4 Joints between Segments ....................................................................34
1.4.4.1 Match-Cast Joint .................................................................34
1.4.4.2 Cast-in-Place Closure Joint .................................................34
vii
viii Contents
1.5 Typical Construction Methods ........................................................................ 35
1.5.1 Introduction ........................................................................................ 35
1.5.2 Span-By-Span Construction Method ................................................. 35
1.5.3 Balanced Cantilever Segmental Construction Method ......................36
1.5.3.1 Precast Segments ................................................................36
1.5.3.2 Cast-in-Place Segments ......................................................37
1.5.4 Progressive Placement Construction ..................................................38
1.5.5 Incrementally Launched Construction ...............................................38
1.5.6 Spliced Precast Girder Construction ..................................................39
1.6 Economic Span Ranges ...................................................................................40
1.7 Post-Tensioning Systems and Operation .......................................................... 41
1.7.1 Introduction ........................................................................................ 41
1.7.2 Stressing Equipment ........................................................................... 41
1.7.3 Anchorages .........................................................................................44
1.8 Post-Tensioning Steel and Anchorage Protection ............................................45
1.9 General Design Procedures and Bridge Aesthetics .........................................50
1.9.1 General Design Procedures ................................................................50
1.9.2 Segmental Bridge Aesthetics.............................................................. 51
1.9.2.1 Harmony with Surroundings .............................................. 51
1.9.2.2 Proportion ...........................................................................51
1.9.2.3 Simplicity of Details ...........................................................53
1.9.2.4 Artistic Shaping ..................................................................53
References .................................................................................................................. 57
Chapter 2 Loads on Bridges and General Design Methods ........................................................ 61
2.1 Introduction ..................................................................................................... 61
2.2 Types of Loads on Concrete Segmental Bridges ............................................. 61
2.2.1 General Description ........................................................................... 61
2.2.2 Dead Loads......................................................................................... 62
2.2.3 Live Loads ..........................................................................................62
2.2.3.1 Vehicle Live Load ...............................................................62
2.2.3.2 Pedestrian Live Load ..........................................................65
2.2.4 Dynamic Loading due to Moving Vehicles .......................................65
2.2.4.1 Dynamic Loading Analysis ................................................65
2.2.4.2 Dynamic Loading Allowance: IM ......................................68
2.2.4.3 Centrifugal Forces: CE .......................................................68
2.2.4.4 Braking Force: BR ..............................................................69
2.2.4.5 Vehicular Collision Force: CT ............................................70
2.2.5 Wind Loads ........................................................................................ 70
2.2.5.1 Introduction ........................................................................ 70
2.2.5.2 Wind Pressure on Structures: WS ...................................... 71
2.2.5.3 Wind Pressure Applied to Vehicles: WL ............................ 72
2.2.6 Earthquake Loads .............................................................................. 72
2.2.6.1 Introduction ........................................................................ 72
2.2.6.2 Earthquake Loads Determined by AASHTO
LRFD Specifcations .......................................................... 76
2.2.7 Water Loads (WA) ..............................................................................83
2.2.8 Vessel Collision Loads (CV) ..............................................................84
2.2.9 Ice Loads (IC).....................................................................................84
2.2.10 Temperature Loads .............................................................................84
Contents ix
2.2.10.1 Uniform Temperature .........................................................84
2.2.10.2 Temperature Gradient .........................................................85
2.2.11 Miscellaneous Loads ..........................................................................85
2.2.12 Construction Loads ............................................................................86
2.3 General Design Methods .................................................................................87
2.3.1 Introduction ........................................................................................87
2.3.2 Basic Theory of the LRFD Method ...................................................88
2.3.2.1 Mathematical Models of Load and
Resistance Variations ..........................................................88
2.3.2.2 Probability of Failure and Safety Index .............................. 91
2.3.2.3 Determining Load and Resistance Factors .........................92
2.3.3 General Provisions of the AASHTO LRFD Method .........................94
2.3.3.1 General Design Equation ....................................................94
2.3.3.2 Design Limit States ............................................................96
2.3.3.3 Load Combinations and Load Factors for Design ..............97
2.3.3.4 Load Combinations and Load Factors for
Segmental Bridge Construction ........................................100
2.3.3.5 Resistance Factors ............................................................ 101
References ................................................................................................................ 103
Chapter 3 Fundamentals of Segmental Bridge Analysis and Design .......................................105
3.1 Basic Concepts of Prestressed Concrete Structures ......................................105
3.1.1 General Behaviors of Prestressed Concrete Structures .................... 105
3.1.2 Bending Analysis for Prestressed Girders ....................................... 109
3.1.2.1 C-Line Method ................................................................. 109
3.1.2.2 Equivalent Load Method .................................................. 111
3.1.3 Basic Design Concepts ..................................................................... 114
3.1.3.1 Estimation of Concrete and Tendon Areas ....................... 114
3.1.3.2 Determination of Post-Tensioning Force and
Effciency Ratio of Cross Section ..................................... 116
3.1.3.3 Determination of Tendon Placement Limiting Zone ........ 116
3.2 Losses of Prestressing ................................................................................... 118
3.2.1 Instantaneous Losses ........................................................................ 119
3.2.1.1 Losses Due to Elastic Shortening of Concrete
in Post-Tensioning Members ............................................. 119
3.2.1.2 Losses Due to Duct Friction ............................................. 121
3.2.1.3 Losses Due to Anchor Set ................................................125
3.2.1.4 Elongation of Tendons ...................................................... 127
3.2.2 Time Dependent Losses ...................................................................128
3.2.2.1 Time Dependent Losses for Segmental Bridges ...............128
3.2.2.2 Estimations of Time Dependent Losses for
Preliminary Design of Segmental Bridges .......................128
3.3 Bending and Torsion of I-Girder ................................................................... 130
3.3.1 Introduction ...................................................................................... 130
3.3.2 Bending ............................................................................................ 130
3.3.3 Torsion ..............................................................................................132
3.4 Bending and Torsion of Box Girders ............................................................. 137
3.4.1 Introduction ...................................................................................... 137
3.4.2 Bending ............................................................................................ 138
3.4.2.1 Shear Stress ....................................................................... 138
