Shear behaviour of RC beams strengthened with NSM and EB CFRP strips

Abstract

The purpose of this study is to investigate the shear strengthening effectiveness of beams reinforced with near-surface-mounted (NSM) carbon-fibre-reinforced plastic (CFRP) strips and externally bonded reinforcing (EBR) CFRP strips. To accomplish this objective, a total of nine concrete beams were tested. From this study, it is found that the shear stiffness and strength of the beams reinforced by combined NSM and EBR strips were significantly improved compared to the control beam. Failure of the beam reinforced with NSM and EBR strips was initiated by shear cracks, propagated diagonally to the adjacent epoxy grooves without crossing the epoxy, and finally a sudden diagonal crack occurred connecting the point of application of load and the flexural crack. At failure, it was observed that the NSM strips appeared to be well bonded to the concrete. The tensile strains measured in the CFRP strip at the ultimate stage for the beam series strengthened with EBR strips were within the range 700–1200 με, with an average value of 1000 με. For the beam strengthened with combined NSM and EBR CFRP strips, however, the tensile strains in the NSM CFRP strips were found to be in the range 3500–4500 με and strains with EBR strips were measured at around 3000 με. This result shows that the NSM and EBR strips form a good combination to resist applied load and the combined reinforcement of NSM and EBR strips can redistribute the total stress to which the concrete beam is subjected on to the EBR and NSM strips.