Shear strengthening of reinforced concrete deep beams using near-surface mounted hybrid carbon/glass fibre reinforced polymer strips

This study investigated the efficacy of near surface mounted (NSM) hybrid carbon/glass fibre reinforced polymer (FRP) strips for strengthening of shear-deficient reinforced-concrete (RC) rectangular deep beams. A specific focus was the interaction of FRP with steel stirrups, which were arranged in both aligned and unaligned configurations for different FRP and stirrup volume fractions. Five unstrengthened reference beams and seven strengthened beams were tested. The NSM-FRP increased the beam shear strength up to 55.8%, alleviated debonding between concrete and strengthening material, and enhanced the deformational characteristics of the strengthened beams. The FRP/stirrups interaction also affected the contribution of NSM-FRP to the shear strength of the beams. Moreover, this study proposes a model based on the modified compression field theory (MCFT) to determine the shear capacity of the beams. The proposed formulation accounts for the FRP/stirrups interaction, which is not considered in the currently available models for the NSM-FRP strengthened RC beams. The average theoretical to experimental shear capacities ratio was 0.96 with a standard deviation of 3.19%.