Theoretical analysis of stress distributions in FRP side-bonded to RC beams for shear strengthening

Extensive research has been conducted on the strengthening of reinforced concrete (RC) beams with externally bonded fibre reinforced polymer (FRP) composites in the last decade. The FRP composites are usually installed following one of three common schemes: complete wrapping, U jacketing, and side bonding (bonding on their sides only). Experimental studies have shown that most side-bonded beams fail due to debonding of the FRP from the concrete. A key factor influencing the contribution of the FRP to the shear capacity of the beam is the stress (or strain) distribution in the FRP at the ultimate limit state. This paper presents a theoretical study of the stress distribution in the FRP along the critical shear crack at debonding failure of side-bonded beams for several assumed crack width variations, using a rigorous FRP-to-concrete bond-slip model. Numerical results show that Chen and Teng's (2001a, 2003a) simple assumption for the stress distribution in the FRP results in satisfactory predictions for the effective FRP stress in most cases. However, it can become unconservative for beams lightly reinforced in flexure but this is less relevant in practice because flexure rather than shear is the intended control failure mode.