Cohesive zone model of FRP-concrete interface debonding under mixed-mode loading

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, the FRP-concrete interface debonding under general mixed-mode loading is analyzed using a cohesive zone model. A novel nonlinear bond-slip model is used to simulate the shear stress-separation law of the FRP-concrete interface; while the normal stress-separation law of the interface is approximated by a linear elastic model. Closed-form solutions of interfacial stresses, FRP stress are obtained for a typical single-lap specimen for the whole debonding process and verified with experimental results. This model provides a unified description of debonding initiation and progression of the FRP-concrete interface. The mode mixity of the debonding is also retrieved naturally in this model. Parametric studies are conducted to provide a better understanding of the mode-dependent debonding process of the FRP-concrete interface. The present model can be used to analyze mixed-mode debonding of the FRP-concrete interface efficiently and effectively.