FRP-Strengthened Metallic Structures Xiao-Ling Zhao (CJ*; CRC Press Taylor & Francis Croup Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Croup, an informa business
Contents Preface Acknowledgm ents Notation Author xm XV xvn XXV 1 Introduction 1 1.1 Applications of FRP in strengthening metallic structures 1 1.2 Improved performance due to FRP strengthening 2 1.3 Current knowledge on FRP strengthening of metallic structures 2 1.4 Layout of the book 11 References 11 2 FRP composites and metals 17 2.1 General 17 2.2 Fibre-reinforced polymer 17 2.2.1 Carbon fibre-reinforced polymers 18 2.2.2 Glass fibre-reinforced polymers 19 2.3 Adhesives 19 2.4 Cast/wrought iron, steel, and aluminium 21 2.4.1 Cast/wrought iron 21 2.4.2 Steel 21 2.4.3 Aluminium 22 2.5 Future work 24 References 25 3 Behaviour of the bond between FRP and metal 29 3.1 General 29 v
vi Contents 3.2 Testing methods 29 3.2.1 Methods of bond test 29 3.2.2 Methods of strain measurement 32 3.3 Failure modes 32 3.3.1 Typical failure modes 32 3.3.2 Key parameters affecting failure modes 34 3.4 Bond-slip model 36 3.4.1 Strain distribution 36 3.4.2 Bond-slip curves 37 3.4.3 Bond-slip model 42 3.4.4 Estimation of bond strength and effective bond length 45 3.4.4.1 Hart-Smith (1973) model and Xia and Teng (2005) model for bond between CFRP plate and steel 45 3.4.4.2 Modified Hart-Smith model (Fawzia et al. 2006) for bond between CFRP sheets and steel 46 3.5 Effect of temperature on bond strength 47 3.5.1 Influence of subzero temperature on bond strength 47 3.5.2 Influence of elevated temperature on bond strength 48 3.5.3 Theoretical analysis of effect of elevated temperature on bond 51 3.6 Effect of cyclic loading on bond strength 54 3.7 Effect of impact loading on bond strength 55 3.7.1 Effect of impact loading on material properties 55 3.7.2 Effect of impact loading on bond strength 56 3.8 Durability of bond between FRP and metal 58 3.9 Future work 61 References 62 4 Flexural strengthening of steel and steel-concrete composite beams with FRP laminates 67 J. G. TENG AND D. FERNANDO 4.1 General 67 4.2 Failure modes 70 4.2.1 General 70 4.2.2 In-plane bending failure 71 4.2.3 Lateral buckling 72
Contents vii 4.2.4 End debonding 73 4.2.5 Intermediate debonding 74 4.2.6 Local buckling of plate elements 74 4.3 Flexural capacity of FRP-plated steel/composite 4.3.1 General 76 4.3.2 FRP-plated steel sections 77 4.3.3 FRP-plated steel-concrete composite sections 76 sections 79 4.3.3.1 Neutral axis in the concrete slab 81 4.3.3.2 Neutral axis in the steel beam 83 4.3.4 Effects of preloading 84 4.3.5 Moment-curvature responses 85 4.4 Lateral buckling 86 4.5 Debonding failures 87 4.5.1 General 87 4.5.2 Interfacial stresses in elastic FRP-plated beams 87 4.5.3 Cohesive zone modelling of debonding failure 90 4.5.4 End debonding 92 4.5.4.1 General 92 4.5.4.2 FE modelling 92 4.5.4.3 Analytical modelling 93 4.5.4.4 Suppression through detailing 94 4.5.5 Intermediate debonding 95 4.5.6 Local buckling 98 4.5.6.1 Design against flange and web buckling 98 4.5.6.2 Additional strengthening 4.6 Other issues 101 against local buckling 100 4.6.1 Strengthening of beams without access to the tension flange surface 101 4.6.2 Rapid strengthening methods 101 4.6.3 Fatigue strengthening 101 4.7 Design recommendation 103 4.7.1 General 103 4.7.2 Critical sections and end anchorage 103 4.7.3 Strength of the maximum moment section 104 4.7.3.1 Moment capacity at in-plane failure 105 4.7.3.2 Moment capacity at lateral buckling failure 105 4.7.3.3 Design against local buckling 105 4.8 Design example 106
viii Contents 4.8.1 Geometric and material properties of the beam 106 4.8.2 ln-plane moment capacity of plated section 106 4.8.3 Suppression of end debonding 111 4.8.4 Design against local buckling 112 4.9 Conclusions and future research needs 113 References 114 5 Strengthening of compression members 121 5.1 General 121 5.2 Methods of strengthening 121 5.3 Structural behaviour 125 5.3.1 Failure modes 125 5.3.2 Load versus displacement curves 129 5.4 Capacity offrp-strengthened steel sections 129 5.4.1 C R?-strengthened CHS sections 129 5.4.1.1 Modified AS 4100 model 129 5.4.1.2 Modified EC3 model 135 5.4.1.3 Design curves 138 5.4.2 GFRF'-strengthened CHS sections 140 5.4.3 CFR?-strengthened SHS sections 141 5.4.3.1 Bambach et al. stub column model 141 5.4.3.2 Shaat and Fam stub column model 143 5.4.4 CFR?-strengthened lipped channel sections 144 5.4.4.1 Modified EC3 stub column model 144 5.4.4.2 Modified AISI-DSM stub column model 145 5.4.5 CFRP-strengthened T-sections 146 5.5 Capacity of CFRP-strengthened steel members 146 5.5.1 CFRP-strengthened SHS columns 146 5.5.1.1 Fibre model and FE analysis 146 5.5.1.2 Shaat and Fam column model 147 5.5.2 CFRP-strengthened lipped channel columns 150 5.5.2.1 Modified EC3 column model 150 5.5.2.2 Modified AISI-DSM column model 152 5.6 Plastic mechanism analysis of CFRP-strengthened SHS under large axial deformation 153 5.6.1 Equivalent yield stress due to CFRP strengthening 154 5.6.2 Plastic mechanism analysis 155
Contents ix 5.7 Design examples 158 5.7.1 Example 1: CFRF'-strengthened CHS stub column 158 5.7.1.1 Solution using the modified AS 4100 model given in Section 5.4.1.1 158 5.7.1.2 Solution using the modified EC3 model given in Section 5.4.1.2 160 5.7.2 Example 2: CFRF'-strengthened SHS stub column with local buckling 161 5.7.3 Example 3: CFRF-strengthened SHS stub column without local buckling 164 5.7.4 Example 4: CFRP-strengthened SHS slender column 165 5.8 Future work 168 References 170 6 Strengthening of web crippling of beams subject to end bearing forces 175 6.1 General 175 6.2 Cold-formed steel rectangular hollow sections 177 6.2.1 Types of strengthening 177 6.2.2 Failure modes 179 6.2.3 Behaviour 179 6.2.4 Increased capacity 181 6.2.5 Design formulae 183 6.2.5.1 Design formulae for unstrengthened RHS 183 6.2.5.2 Design formulae for CFRPstrengthened RHS (if web buckling governs for unstrengthened RHS) 185 6.2.5.3 Design formulae for CFRPstrengthened RHS (if web yielding governs for unstrengthened RHS) 186 6.3 Aluminium rectangular hollow sections 186 6.3.1 Types of strengthening 186 6.3.2 Failure modes 187 6.3.3 Behaviour 187 6.3.4 Increased capacity 189 6.3.5 Design formulae 189
x Contents 6.3.5.1 Modified AS 4100 formulae for unstrengthened aluminium RHS 189 6.3.5.2 Modified AS 4100 formulae for CFRP-strengthened aluminium RHS 189 6.3.5.3 AS/NZS 1664.1 formula for web bearing capacity of aluminium RHS 191 6.3.5.4 Modified AS/NZS 1664.1 formula for web bearing capacity of CFRPstrengthened aluminium RHS 192 6.4 LiteSteel beams 194 6.4.1 Types of strengthening 194 6.4.2 Failure modes and behaviour 194 6.4.3 Increased capacity 195 6.4.4 Design formulae 197 6.4.4.1 Modified AS 4100 formulae for unstrengthened LiteSteel beams 197 6.4.4.2 Modified AS 4100 formulae for CFR?-strengthened LiteSteel beams 198 6.5 Open sections 199 6.5.1 Types of strengthening 199 6.5.2 Failure modes and increased capacity 199 6.5.3 Design formulae 200 6.5.3.1 Modified Young and Hancock (2001) formulae for CFRPstrengthened channel section 200 6.5.3.2 Modified AS 4100 formulae for CFRP-strengthened I-section 201 6.6 Design examples 202 6.6.1 Example 1 (cold-formed RHS) 202 6.6.1.1 Solution according to AS 4100 given in Section 6.2.5 for unstrengthened RHS 202 6.6.1.2 Solution according to modified AS 4100 given in Section 6.2.5 for CFRP-strengthened RHS 204 6.6.2 Example 2 (aluminium RHS) 205 6.6.2.1 Solution according to modified AS 4100 given in Section 6.3.5 205 6.6.2.2 Solution according to modified AS 1664.1 given in Section 6.3.5 206 6.6.3 Example 3 (LiteSteel beams) 207
Contents xi 6.7 Future work 208 References 208 6.6.3.1 Solution according to modified AS 4100 given in Section 6.4.4 for unstrengtbened LSB 207 6.6.3.2 Solution according to modified AS 4100 given in Section 6.4.4 for CFRP-strengthened LSB 208 7 Enhancement of fatigue performance 211 7.1 General 211 7.2 Methods of strengthening 211 7.3 Improvement in fatigue performance 215 7.4 Fatigue crack propagation 218 7.5 Prediction of fatigue life for CCT (centrecracked tensile) steel plates strengthened by multiple layers of CFRP sheet 220 7.5.1 Boundary element method approach 220 7.5.1.1 Boundary element method 220 7.5.1.2 BEM model of CCT steel plates strengthened by multiple layers of CFRP sheet 222 7.5.1.3 BEM simulation results 227 7.5.2 Fracture mechanics approach 228 7.5.2.1 Fracture mechanics formulae for CCT steel plates 228 7.5.2.2 Average stress in steel plate with CFRP sheet 229 7.5.2.3 Effective stress intensity factor in steel plate with CFRP sheet 231 7.5.2.4 Fatigue life of CCT steel plates strengthened by multiple layers of CFRP sheet 233 7.6 Stress intensity factor for CCT steel plates strengthened by CFRP 234 7.6.1 Existing approaches 234 7.6.2 Stress intensity factor for CCT steel plates without CFRP 236 7.6.3 Influence on stresses in steel plate due to CFRP 236
xii Contents 7.6.4 Influence of crack length and CFRP bond width on SIF 238 7.6.5 SIF for CCT steel plates strengthened by CFRP 241 7.6.6 Influence of key parameters on SIF reduction due to CFRP strengthening 243 7.7 Future work 248 References 248 Index 253