Critical debonding length in FRP flexurally strengthened RC members

Reinforced concrete (RC) beams and slabs bonded with tension face fibre reinforced polymers (FRP) are susceptible to premature failure by intermediate crack (IC) induced debonding, otherwise known as IC debonding, that originates at a flexural crack. Two key parameters needed in the determination of IC debonding are (1) the load required to initiate localised debonding near the base of flexural cracks, and (2) the length of debonded plate required to cause complete loss of load carrying capacity of the FRP-strengthened member. These two parameters are investigated in this paper using a local deformation model previously reported by the authors (Gravina and Smith 2004, Smith and Gravina 2005). A recently published bond-slip relation for the FRP-to-concrete interface (Lu et al. 2005) is used to determine the onset of debonding while the local deformation model is used to investigate the debonded plate length in FRP-strengthened RC cantilever slabs. The results are compared with Chen and Teng's (2001) effective bond length and then recommendations given.