Finite element analysis of end cover separation in RC beams strengthened in flexure with FRP

The use of externally-bonded (EB) or near-surface mounted (NSM) FRP reinforcement in the strengthening of reinforced concrete (RC) beams in flexure has become increasingly popular in recent years. Such beams are likely to fail by end cover separation in which a major crack in the concrete initiates at a cut-off point of the FRP reinforcement and propagates along the level of steel tension bars, leading to the detachment of the FRP reinforcement together with the cover concrete. Due to the complexity of this failure mode, no reliable finite element (FE) approach for its accurate prediction has been published despite many previous experimental and theoretical studies on the problem. This paper presents a novel FE approach for predicting end cover separation failures in RC beams strengthened in flexure with either externally bonded or near-surface mounted FRP reinforcement. In the proposed FE approach, careful consideration is given to the constitutive modelling of concrete and interfaces. Furthermore, the critical debonding plane at the level of steel tension bars is given special attention: the radial stresses exerted by the steel tension bars onto the surrounding concrete are identified to be an important factor for the first time ever and are properly included in the FE approach. The proposed FE approach is shown to provide accurate predictions of test results, including load–deflection curves, failure loads and crack patterns.