Cohesive-bridging zone model of FRP–concrete interface debonding

External bonding of FRP plates or sheets has emerged as a popular method for strengthening reinforced concrete structures. Debonding along the FPR–concrete interface can lead to premature failure of the structures. In this study, a combined cohesive/bridging zone model is presented to simulate the debonding procedure between the FRP and concrete interface. In this model, the crack processing zone of the interface is modeled by a cohesive zone model and the particle interlocking zone of the interface is modeled by a bridging zone model. Two different linearly softening bond stress–slip laws are used to describe these two different zones. Closed-form solutions of interfacial stress, FRP stress and ultimate load are obtained for a typical single-lap specimen and verified with experimental results. The pulling force applied to the FRP plate is found to be proportional to the square root of the energy release rate at the debonding tip for this model. Such a relationship is then extended to any general shapes of bond stress–slip law through J-integral method. A new approach to experimentally determine the bond stress–slip law is also proposed.