Numerical study on interaction between steel stirrups and shear-strengthening NSM FRP strips in RC beams

RC beams shear-strengthened with externally bonded or near-surface mounted (NSM) FRP reinforcement usually fail by the debonding of FRP in a brittle manner. When the FRP reinforcement debonds, the internal steel stirrups may have not reached their yield strength, so the contribution of the latter to the shear resistance of the beam is compromised to some extent. This phenomenon is referred to as the adverse shear interaction between the steel stirrups and the bonded FRP shear reinforcement. This paper examines such shear interaction in RC beams shear strengthened with NSM FRP strips using a simple computational model. Numerical results obtained from this model show that in such beams, most of the steel stirrups reach their yield strength, so the interaction does not have a significant adverse effect on the shear resistance of the beam. This may be seen as yet another advantage of the NSM FRP strengthening method.