Punching Strengthening of Concrete Slab-column Connections Using Near Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) Bars

This paper investigates experimentally the effect of near surface mounted (NSM) carbon fiber reinforcement polymer (CFRP) bars as externally strengthening on the punching shear behavior of interior slab-column connections. Many researchers used NSM as a novel strengthening technique in various structural elements. However, the strengthening of slab-column connections using NSN is relatively new. Seven Reinforced concrete (RC) square slabs with a concentric column were tested over simply supported four sides. One control specimen was tested without strengthening, four specimens were strengthened using NSM-CFRP bar installed in pre-cut groove surrounded the column at the tension side of the slab, and two specimens were strengthened using externally bonded (EB) CFRP strips which have the same tensile force of the CFRP bars. The arrangement and the location of the strengthened materials were also test variables. The test results showed that using NSM strengthening technique significantly increased the punching shear capacity and ultimate stiffness compared to using EB strengthening technique. Where the increasing in the punching capacity and ultimate stiffness were 18% and 13-18%, respectively. Moreover, the NSM-CFRP bars greatly reduced the cracks in the punching shear zone around the columns. The measured ultimate punching shear capacity for the tested specimens showed very reasonable agreement with the calculated punching loads based on an analytical model for slab-column connections strengthened using FRP that account for its arrangement and location.