Shear Behavior of RC Beams Strengthened with Side-Bonded BFRP Grids

This study examined the shear behavior of reinforced concrete (RC) beams that were strengthened with externally bonded composite reinforced mortar (CRM) layers consisting of basalt fiber-reinforced polymer (BFRP) grids and polymer cement mortar (PCM). The variable parameters included the shear span ratios (1.6, 2.0, and 2.4), strengthening materials (BFRP grids and BFRP sheets), bonding materials (PCM and epoxy resin), and angles between the longitudinal bars of the BFRP grid and the beam axis (0 degrees and 45 degrees). A total of 10 RC beams were cast and tested in the four-point flexural experiments. Three beams served as control specimens, four beams were strengthened with the 0 degrees BFRP grids (one beam and three beams using epoxy resin and PCM as bonding materials, respectively), and one beam was strengthened with the 45 degrees BFRP grids using PCM as the bonding material. The remaining two beams were strengthened with the BFRP sheets and PCM, respectively. The experimental results demonstrated that the BFRP grids effectively improved the ultimate load of the strengthened beams, and the contribution of the BFRP grids to the ultimate load was not sensitive to the shear span ratio. The RC beam strengthened with the 45 degrees BFRP grids displayed an improved ability to restrict the development of diagonal cracks and restrain the degradation of the flexural stiffness compared to the beam strengthened with the 0 degrees BFRP grids. Moreover, owing to the reliable interface performance between the BFRP grids and the concrete substrate, all of the BFRP grid-strengthened beams failed in shear, while the BFRP sheet-strengthened beam experienced local debonding with insufficient ductility. In conclusion, the BFRP grid was considered an effective strengthening material for RC members.