Effects of FRP-concrete interface bond properties on the performance of RIC beams strengthened in flexure with externally bonded FRP sheets

Fiber reinforced polymer (FRP) sheets have been increasingly used as externally bonded reinforcements in the rehabilitation of concrete structures. The efficacy of the FRP bonding technology highly depends on the bond integrity between the FRP sheets and the concrete. The bond performance may directly influence the cracking of the concrete, whereas the presence of concrete cracks would impair the bond between the FRP sheets and the concrete. This paper aims to clarify the effect of interface bond properties on the performance of FRP-strengthened reinforced concrete (RC) beams in terms of concrete cracking, interface stress transfer, and failure mechanisms using nonlinear fracture mechanics based finite element analyses. To represent the typical crack patterns and capture the local interaction between FRP debonding and concrete cracking, a specially designed structural model with uniformly distributed cracking is used within the frame of the discrete crack approach. A detailed parametric study is performed to investigate the effects of interface bond properties in terms of stiffness, strength, fracture energy (or toughness), and bond curve shape. It is concluded that bond fracture energy (or toughness) is the main parameter influencing the structural strength and ductility. This study may serve as a valuable reference for optimization of the FRP-concrete bond interface in practical applications.