Punching shear behavior of FRP reinforced concrete slabs under different opening configurations and loading conditions

This study investigates the punching shear behavior of reinforced concrete (RC) flat slabs using theoretical and non-linear finite element analysis techniques (NLFEA). The internal slab-column connection was studied under the combined effect of openings and loading eccentricity. No additional reinforcement was introduced after the opening was made to simulate the effect of opening in an existing structure. Thirty-six slabs were simulated (1800 mm × 1800 mm × 120) mm3 for the length, width, and depth, respectively. The investigated parameters were: (i) reinforcement type (basalt FRP, carbon FRP, and steel); (ii) the existence of opening and its location (with or opposite to the eccentricity side); and (iii) eccentricity value (0, 75, 150, and 225 mm). The slabs were supported at 1500 mm in both directions using eight high-strength bolts and were analyzed up to failure under square column loading of 150 mm side. All simulated slabs failed in punching shear. It was concluded that both the opening and loading eccentricity adversely affected the behavior of the slab, where using FRP bars as an internal reinforcement causes the slab's ductility index to be significantly reduced. Moreover, Increasing the loading eccentricity value adversely affects the slab's behavior. It reduces its ultimate capacity, ultimate deflection, cracking deflection, plastic stiffness, and energy absorption. The type of reinforcement affects the general behavior of the flat slabs. Slabs reinforced with steel reinforcement have the highest cracking and ultimate load, followed by slabs with CFRP, and BFRP reinforcements, respectively. Meanwhile, the relationship is inversed for the ultimate deflection. Simulation results were compared to those obtained from different international design codes (ACI 318–19, EC2, MC 2010, ACI 440, CSA/S806–12, and JSCE), and all overestimated the punching shear capacity of the tested slabs with the JSCE and the ACI 318 the JSCE have approximately the same predictions.