Modelling of FRP debonding from concrete substrate

For concrete beams retrofitted with bonded fiber reinforced plastic (FRP) composite plate,failure often occurs due to debonding of the plate from the concrete surface. To predict the failure load, a proper model for FRP debonding is required. Experimental results indicate that after debonding starts, there is significant residual shear stress along the interface, which should be considered in the model. In this paper, two approaches are presented for the modeling of FRP debonding. In the strength-based approach, debonding is assumed to start once a critical shear stress is reached at the interface. In the energy-based approach, the initiation (and growth) of the debonded zone is taken to occur once the energy release rate of the system reaches a critical value. Since the interfacial shear stress derived from experimental measurements is often much higher than the shear strength of concrete gone can argue that the strength-based approach is physically not correct. However, comparison between the analytical expressions obtained with the two approaches reveal a very interesting fact. By defining an effective shear strength in terms of the interfacial fracture energy, simple expressions obtained with the strength-based approach can provide very good approximation to the debonding behaviour obtained numerically from a much more complicated energy-based analysis. The strength-based approach can hence be employed to provide a simple engineering model for practical applications.