FRP Anchors for External Reinforcement of Concrete Structural Elements

415 Pages·2016·24.92 MB·English

by  Marco Rossini

0
POLITECNICO DI MILANO

School of Civil, Environmental and Land Management Engineering

Master of Science in Civil Engineering, Structures

FRP Anchors for External Reinforcement of
Concrete Structural Elements

Advisor: Prof. Carlo POGGI
Co-Advisor: Prof. Antonio NANNI

Master’s Thesis by:
Marco ROSSINI
817293

Academic Year 2015 – 2016
1
2
1 ABSTRACT ...................................................................................... 15
2 INTRODUZIONE ............................................................................ 17
3 COMPOSITES MATERIALS: AN OVERVIEW ....................... 19
3.1 Historical Background ...................................................................................... 19
3.1.1.1 Classical Building Applications ................................................................................................. 19
3.1.1.2 Lighter and Stronger: The War Industry .................................................................................. 20
3.1.1.3 A Durable Solution for Civil Engineering .................................................................................. 20
3.2 Fiber Reinforced Polymers: Material Overview ............................................. 22
3.2.1 The Fibers ....................................................................................................................................22
3.2.1.1 Glass Fibers (GFRP) .................................................................................................................. 22
3.2.1.2 Aramid Fibers (AFRP) ............................................................................................................... 23
3.2.1.3 Carbon Fibers (CFRP) ................................................................................................................ 24
3.2.2 The Resins ....................................................................................................................................25
3.2.2.1 Thermosetting polymers .......................................................................................................... 25
3.2.2.2 Thermoplastic polymers ........................................................................................................... 27
3.2.3 The Industry, Chemistry and Production Process ...................................................................28
3.2.3.1 Carbon Fibers ........................................................................................................................... 28
3.2.3.2 Epoxy Resin .............................................................................................................................. 29
3.3 FRP Laminates for Rehabilitation Purposes................................................... 31
3.3.1 Mechanical Behavior ...................................................................................................................32
3.3.2 Elastic Response ..........................................................................................................................34
3.3.3 Failure Criteria ............................................................................................................................37
3.3.3.1 Maximum Strength Criterion ................................................................................................... 37
3.3.3.2 Tsai-Hill Failure Criterion.......................................................................................................... 39
3.3.3.3 Tsai-Wu Failure Criterion ......................................................................................................... 40
3.3.3.4 Summing Up ............................................................................................................................ 42
3.3.4 Lamina Orientation .....................................................................................................................42
3
3.3.4.1 Hooke’s Law for an Angle Lamina............................................................................................ 43
3.3.4.2 Failure Criteria for an Angle Lamina ........................................................................................ 44
3.3.5 Mechanical Characterization .....................................................................................................44
3.3.5.1 Micromechanics ....................................................................................................................... 44
3.3.5.2 Direct Testing ........................................................................................................................... 45
3.3.6 Structural Applications and Design Criteria Overview ...........................................................46
3.3.6.1 Design Philosophy & Regulations ............................................................................................ 47
3.3.6.2 Flexural Strengthening ............................................................................................................. 49
3.3.6.3 Shear and Torsion Strengthening ............................................................................................ 50
3.3.6.4 Columns Confinement .............................................................................................................. 51
3.3.6.5 Other Applications ................................................................................................................... 51
3.4 The Debonding Problem ................................................................................... 52
3.4.1 Debonding Failure Modes in Flexural Applications .................................................................53
3.4.1.1 End Debonding ......................................................................................................................... 55
3.4.1.2 Debonding by Flexural Cracks – Intermediate Debonding ....................................................... 56
3.4.1.3 Debonding by Shear Cracks ..................................................................................................... 56
3.4.1.4 Debonding by Irregularities and Roughness of the Concrete Surface ...................................... 57
3.4.2 Bond Mechanism & Development Length ................................................................................57
3.4.2.1 Bond-Slip Law, Specific Fracture Energy, Bond Strength ......................................................... 58
3.4.2.2 Maximum Shear Force, Optimal Development Length ............................................................ 60
3.4.2.3 Bond Length Design ................................................................................................................. 63
3.4.3 Debonding Modeling in Flexural Applications .........................................................................66
3.4.3.1 End Debonding ......................................................................................................................... 66
3.4.3.2 Intermediate Debonding .......................................................................................................... 68
3.5 Anchoring Systems for FRP Laminates........................................................... 70
3.5.1 Categorization Based on the Resisted Force .............................................................................70
3.5.2 Categorization Based on Debonding Type ................................................................................71
3.5.3 Categorization Based on Strengthening Application................................................................71
3.5.3.1 Anchoring Solution for Flexural Strengthening ........................................................................ 71
3.5.3.2 Anchoring Solutions for Shear Strengthening .......................................................................... 72
3.5.3.3 Anchoring Solutions for Column Confinement & Joint Strengthening ..................................... 73
4
3.5.3.4 Other Applications ................................................................................................................... 73
3.5.4 Categorization Based on Mechanical Function.........................................................................74
3.5.4.1 Type I – Bond Improvement: Pull-Out Critical .......................................................................... 74
3.5.4.2 Type II – Bond Improvement: Shear Critical ............................................................................. 74
3.5.4.3 Type III – Equilibrium Critical ................................................................................................... 75
3.5.4.4 Type IV – Ductility Critical ........................................................................................................ 76
3.5.5 Categorization Based on Construction Typology .....................................................................77
3.5.5.1 Transverse Wrapping ............................................................................................................... 77
3.5.5.2 Anchor Spikes ........................................................................................................................... 78
3.5.5.3 Metallic Anchors ...................................................................................................................... 81
3.5.5.4 Concrete Embedment .............................................................................................................. 83
3.5.5.5 Surface Preparation ................................................................................................................. 84
3.5.6 Anchor Testing ............................................................................................................................86
3.5.6.1 Pull-Out Test ............................................................................................................................ 87
3.5.6.2 Direct Shear Test ...................................................................................................................... 88
3.5.6.3 Bending Tests ........................................................................................................................... 90
3.5.7 Research Direction ......................................................................................................................90
3.5.7.1 The Need for a Unified Approach ............................................................................................. 90
3.5.7.2 Available Guidelines ................................................................................................................. 91
4 ANCHORING SPIKES: STATE OF THE ART REVIEW ........ 93
4.1 Manufacturing & Installation........................................................................... 93
4.1.1.1 Fiber Rolls / Fiber Bundles ........................................................................................................ 93
4.1.1.2 Pre-Cured / Wet Dowel ............................................................................................................ 93
4.1.1.3 One-Step / Two-Step Fan-Sheet Impregnation ........................................................................ 94
4.1.1.4 Sheet Drilling / Undrilled Application ....................................................................................... 94
4.1.1.5 Wet / Dry Applications ............................................................................................................. 94
4.2 Characterization ................................................................................................ 96
4.2.1 Fundamental Parameters ...........................................................................................................96
4.2.1.1 Material Properties .................................................................................................................. 96
4.2.1.2 Dowel Geometry ...................................................................................................................... 97
5
4.2.1.3 Fan Geometry .......................................................................................................................... 98
4.2.1.4 Global Geometry .................................................................................................................... 101
4.2.1.5 Position .................................................................................................................................. 103
4.2.1.6 Configuration ......................................................................................................................... 103
4.2.1.7 Quality ................................................................................................................................... 104
4.2.1.8 Surrounding ........................................................................................................................... 104
4.2.2 Pull-out Characterization .........................................................................................................104
4.2.2.1 Collapse Mechanisms ............................................................................................................ 104
4.2.2.2 Ozbakkaloglu & Saatcioglu (2009) ......................................................................................... 105
4.2.2.3 Kim & Smith (2010) ................................................................................................................ 107
4.2.3 Shear Characterization .............................................................................................................110
4.2.3.1 Collapse Mechanism .............................................................................................................. 110
4.2.3.2 Kobayashi & Al. (2001) .......................................................................................................... 112
4.2.3.3 Eshwar & Al. (2008) ............................................................................................................... 114
4.2.3.4 Orton & Al. (2008) .................................................................................................................. 115
4.2.3.5 Zhang & Smith (2013) ............................................................................................................ 116
4.2.3.6 Brena & McGuirk (2013) ........................................................................................................ 120
4.2.3.7 Berneschi (2015) .................................................................................................................... 122
4.2.3.8 Sun & Al. (2016) ..................................................................................................................... 123
4.3 Strengthening Applications ............................................................................. 125
4.3.1 Flexural Strengthening .............................................................................................................125
4.3.1.1 Lam & Teng (2001) ................................................................................................................ 125
4.3.1.2 Piyong & al (2003) ................................................................................................................. 126
4.3.1.3 Eshwar & al (2005) ................................................................................................................ 126
4.3.1.4 Smith & al (2011) ................................................................................................................... 127
4.3.1.5 Smith & al (2013) ................................................................................................................... 130
4.3.1.6 Nardone & al (2011) .............................................................................................................. 133
4.3.2 Shear Strengthening ..................................................................................................................133
4.3.3 Column & Joint Strengthening ................................................................................................133
5 EXPERIMENTAL PROGRAM................................................... 135
6
5.1 Material Characterization .............................................................................. 135
5.1.1 Concrete .....................................................................................................................................135
5.1.1.1 Compressive Strength – ASTM C39 ........................................................................................ 135
5.1.1.2 Derived Properties – ACI 318 ................................................................................................. 137
5.1.1.3 Derived Properties – EC2 ........................................................................................................ 137
5.1.1.4 Design Properties ................................................................................................................... 139
5.1.2 Steel .............................................................................................................................................140
5.1.2.1 Tensile Strength – ASTM A370 ............................................................................................... 140
5.1.2.2 Design Properties ................................................................................................................... 141
5.1.3 CFRP Sheet ................................................................................................................................144
5.1.3.1 Dry Fibers ............................................................................................................................... 144
5.1.3.2 Epoxy...................................................................................................................................... 144
5.1.3.3 Impregnated Sheet ................................................................................................................ 145
5.1.3.4 Bond Strength ........................................................................................................................ 146
5.1.3.5 Design Properties ................................................................................................................... 147
5.1.4 CFRP Anchor Spikes ................................................................................................................148
5.1.4.1 Dry Fiber & Epoxy................................................................................................................... 148
5.1.4.2 Pull-Out Characterization ...................................................................................................... 148
5.1.4.3 Shear Characterization .......................................................................................................... 150
5.1.4.4 Design Properties ................................................................................................................... 152
5.2 Specimens Preparation .................................................................................... 156
5.2.1 Concrete Specimens...................................................................................................................156
5.2.1.1 Rebars Instrumentation ......................................................................................................... 156
5.2.1.2 Molds Set-Up ......................................................................................................................... 157
5.2.1.3 Casting ................................................................................................................................... 157
5.2.1.4 Demolding .............................................................................................................................. 157
5.2.1.5 Sandblasting .......................................................................................................................... 159
5.2.2 FRP Application ........................................................................................................................160
5.2.2.1 Sheet Application ................................................................................................................... 160
5.2.2.2 Drilling & Hole Preparation .................................................................................................... 162
5.2.2.3 Anchors Installation ............................................................................................................... 163
5.2.2.4 Strain Gages Application........................................................................................................ 166
7
5.3 Experimental Matrix ....................................................................................... 167
5.3.1 Unreinforced Sample.................................................................................................................167
5.3.1.1 Materials ................................................................................................................................ 167
5.3.1.2 Geometry ............................................................................................................................... 168
5.3.2 Anchored Series .........................................................................................................................169
5.3.2.1 Control Sample....................................................................................................................... 169
5.3.2.2 Matching Series ..................................................................................................................... 170
5.3.2.3 Position Series ........................................................................................................................ 171
5.3.2.4 Number of Anchor Series ....................................................................................................... 172
5.3.2.5 Sandwich Effectiveness Series ................................................................................................ 173
5.3.3 Experimental Set-Up .................................................................................................................174
5.3.3.1 Load Application .................................................................................................................... 174
5.3.3.2 Boundary Conditions .............................................................................................................. 175
5.3.3.3 Deflection Measurement ....................................................................................................... 175
5.3.3.4 Strain Measurement .............................................................................................................. 176
5.3.4 Final Matrix ...............................................................................................................................178
5.3.4.1 Geometry and Configurations ................................................................................................ 178
5.3.4.2 Load Cycles............................................................................................................................. 181
5.4 Design Calculations.......................................................................................... 182
5.4.1 Conventions ................................................................................................................................182
5.4.2 Design Assumptions & Sectional Properties ...........................................................................182
5.4.2.1 Stage I – Uncracked Elastic Section ....................................................................................... 184
5.4.2.2 Stage II – Cracked Elastic Section ........................................................................................... 185
5.4.2.3 Stage III – Cracked Inelastic Section ....................................................................................... 186
5.4.3 Sectional Analysis ......................................................................................................................188
5.4.3.1 Elastic Approach .................................................................................................................... 188
5.4.3.2 Equilibrium Approach ............................................................................................................ 188
5.4.4 Structural Analysis ....................................................................................................................191
5.4.4.1 Equilibrium – Point Load ........................................................................................................ 191
5.4.4.2 Equilibrium – Self-Weight ...................................................................................................... 192
5.4.4.3 Deflection – Euler-Bernoulli Beam Theory ............................................................................. 192
5.4.4.4 Deflection – Timoshenko Beam Theory ................................................................................. 193
8
5.4.4.5 Deflection – Strain-Based Approach ...................................................................................... 193
5.4.4.6 Deflection – Results Discussion .............................................................................................. 195
5.4.5 Equivalent Ultimate Strain Approach .....................................................................................198
5.4.5.1 End Debonding ....................................................................................................................... 198
5.4.5.2 Intermediate Debonding ........................................................................................................ 200
5.4.5.3 Anchors’ Failure ..................................................................................................................... 201
5.4.6 Balanced Section ........................................................................................................................204
5.4.6.1 Internal Reinforcement Balance ............................................................................................ 205
5.4.6.2 External Reinforcement Balance ............................................................................................ 206
5.4.7 Load Phases................................................................................................................................207
5.4.7.1 Cracking ................................................................................................................................. 207
5.4.7.2 Yielding .................................................................................................................................. 208
5.4.7.3 Intermediate Debonding ........................................................................................................ 208
5.4.7.4 Anchors’ Failure ..................................................................................................................... 209
5.4.7.5 Sheet Rupture ........................................................................................................................ 209
5.4.7.6 Concrete Collapse .................................................................................................................. 210
5.4.7.7 Steel Rupture ......................................................................................................................... 210
5.4.7.8 Results .................................................................................................................................... 210
5.4.8 Check on End Debonding .........................................................................................................213
5.4.8.1 Optimal Development Length ................................................................................................ 213
5.4.8.2 Provided Development Length ............................................................................................... 214
5.4.8.3 End Debonding Check ............................................................................................................ 216
5.4.9 Check on Shear Strength ..........................................................................................................218
5.4.9.1 Shear Strength – EC2 ............................................................................................................. 218
5.4.9.2 Shear Strength – ACI318 ........................................................................................................ 219
5.4.9.3 Shear Strength Check ............................................................................................................. 220
5.5 Data Analysis .................................................................................................... 221
5.5.1 Experimental Sectional Properties ...........................................................................................221
5.5.1.1 Neutral Axis Location ............................................................................................................. 221
5.5.1.2 Flexural Stiffness .................................................................................................................... 221
5.5.2 Experimental Equivalent Ultimate Strain ...............................................................................222
5.5.2.1 Backward Sectional Equilibrium ............................................................................................ 222
9