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 th e plate from the beam. Delamination can occur either at the end of the rein forcing plate or at the location of a crack in the concrete beam. This pape r will focus on the analysis of delamination initiated at the mouth of a fl exural crack. When loading is applied, the flexural crack tends to open and hence induces high interfacial shear stress that may result in delaminatio n. The relation between interfacial shear stress and applied moment is affe cted by many material and geometric parameters. In this study, the bridging stress in the bonded plate and the maximum interfacial shear stress tau (m ax) are first related to the crack mouth opening. A fracture mechanics base d analysis is then carried out to obtain the crack mouth opening and tau (m ax) for a given applied moment. Through a systematic parametric analysis, t he effect of various parameters on tau (max) is deduced. A combination of p arameters that will increase tau (max), and hence increase the likelihood o f delamination, can hence be identified and avoided in design.