End cover separation in RC beams strengthened in flexure with bonded FRP reinforcement: simplified finite element approach

The flexural performance of RC beams can be improved using externally bonded (EB) or near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. One of the commonly observed failure modes of such FRP-strengthened RC beams is the end cover separation failure mode which involves the detachment of the bonded FRP reinforcement together with the cover concrete along the level of the longitudinal steel reinforcement. This paper presents a simplified 2-D (plane stress) nonlinear finite element (FE) approach for end cover separation failure in RC beams strengthened in flexure with either EB or NSM FRP reinforcement. In this simplified FE approach, only the part of the RC beam between the two cracks near the critical end of the FRP reinforcement is considered. This approach leads to the determination of the FRP debonding strain at the cracked section in the strengthened region adjacent to the crack at the end of the FRP reinforcement, which can then be used to determine the moment acting on this cracked section at debonding failure through conventional section analysis. The validity of the proposed simplified FE approach is demonstrated through comparisons with results from the full 2-D (plane stress) nonlinear FE approach and laboratory tests.