Simulating concrete cover separation in RC beams strengthened with near-surface mounted reinforcements

The near surface mounted (NSM) technique for strengthening reinforced concrete (RC) beams normally utilizes fibre reinforced polymer (FRP) bars or strips placed within grooves made on the soffit of the beams. For RC beams strengthened with NSM the failure mode would normally be the premature debonding failure by separation of concrete cover. A few methods have been proposed to predict the failure loads. The application of these methods however were found to be limited by the empirical formulations that were used, which severely affects their accuracy when applied to situations outside of the testing regime that formed the empirical formulations. To address this issue, in this paper the moment-rotation technique and the global energy balance technique were combined to predict the failure load. The proposed method is more versatile as it requires significantly less empirical formulations when simulating NSM strengthened RC beams as the mechanics of the beam such as crack formation, crack widening and tension stiffening are simulated directly. The proposed method was validated against published experimental results. Comparison between simulated and experimental load-deflection curves shows that the method is able to give good accuracy.