Nonlinear fracture mechanics of flexural–shear crack induced debonding of FRP strengthened concrete beams

External bonding of FRP plates or sheets has emerged as a popular method for strengthening reinforced concrete structures. Debonding along the FRP–concrete interface can lead to premature failure of the structures. In this study, the FRP– concrete interface debonding induced by a flexural–shear crack is analyzed using a nonlinear fracture mechanics approach. A bilinear bond-slip model is used to simulate the shear traction-separation law of the FRP–concrete interface; while the normal traction-separation law of the interface is approximated by a triangular model. Closed-form solutions of interfacial stresses, the axial force of the FRP plate are obtained for the whole debonding process and verified with numerical analysis using finite element analysis. The peeling effect induced by the flexural–shear crack is accounted for and its effect on the interface debonding is examined in detail in this study. Parametric studies are conducted to provide a better understanding of the mode-dependent debonding process induced by the flexural–shear crack. The present model provides a unified description of the debonding initiation and propagation, which can be used to analyze mixed-mode debonding of the FRP–concrete interface efficiently and effectively.