Delamination failure in concrete beams retrofitted with a bonded plate

Concrete beams are often retrofitted with bonded steel or composite plates. The failure of the retrofitted member is usually due to delamination of the plate from the beam. Delamination can occur either at the end of the reinforcing plate or at the location of a crack in the concrete beam. This paper will focus on the analysis of delamination initiated at the mouth of a flexural crack. When loading is applied, the flexural crack tends to open and hence induces high interfacial shear stress that may result in delamination. The relation between interfacial shear stress and applied moment is affected by many material and geometric parameters. In this study, the bridging stress in the bonded plate and the maximum interfacial shear stress tau (max) are first related to the crack mouth opening. A fracture mechanics based analysis is then carried out to obtain the crack mouth opening and tau (max) for a given applied moment. Through a systematic parametric analysis, the effect of various parameters on tau (max) is deduced. A combination of parameters that will increase tau (max), and hence increase the likelihood of delamination, can hence be identified and avoided in design.