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Concrete In Australia : March 2011
38 Concrete in Australia Vol 37 No 1 FEATURE 3. End shear 1. Concrete crushing 2. FRP rupture 7. Flexural crack debond 8. Flexure-shear crack debond 6. Shear crack debond 4. End cover peeling 5. End interfacial debond Figure 3. Observed failure modes in FRP retrofitted beams. 2.2 Failure modes of concrete beams retrofitted with FRP Concrete beams can be strengthened by bonding FRP on the tension zone. FRP-retrofitted beams can fail in a number of modes as illustrated in Figure 3. e most common modes can be categorised into: classic flexural failure (concrete crushing or FRP rupture), end debond (end cover peeling), and midspan debond (flexural crack debond, flexure-shear crack debond, shear crack debond). Out of these failure modes, end debond is perhaps the most complex and its failure mechanism is still the subject of some debate. ere have been numerous models developed to predict the failure loads of retrofitted beams. Some of these models have been incorporated into design guidelines (ACI 440, fib Bulletin 14, Concrete Society TR55, Standards Australia HB305). ese models have been verified by Pham and Al-Mahaidi (2005). It has been found that the error inherent in the models to predict end debond failure mode is significantly large compared to that of the models to predict flexural failure or midspan debond. Available design guidelines are therefore quite conservative in dealing with end debond. Figure 4. Validation results for (a) ACI 440 formula and (b) Pham and Al-Mahaidi's model to predict end debond. Vexp (kN) Vexp (kN) Vcal (kN) Vpredicted (kN) (a) ACI440.2R (2008) detailing rule. (b) Pham and Al-Mahaidi (2006).