Punching shear behavior and corrosion resistance of composite slab-column connections reinforced by BFRP and steel rebar

Abstract

The collapse of Champlain Towers South, Miami in 2021 indicated that flat slab structures in coastal regions show high risk of building collapse due to rebar corrosion. However, to date, few studies have been carried out to prevent these tragic events from happening again. Hybrid steel bars and basalt fiber reinforced polymer (BFRP) bars provide a possible solution due to their excellent corrosion resistance. Thus, in this study, an experimental study of eight large-scale composite slab-column connections is conducted to investigate the advantages of partially replacing steel bars with equal-stiffness BFRP bars to resist corrosion. Two normal reinforced concrete (RC) slab-column connections were first tested as reference specimens, together with two corroded counterparts having a target corrosion degree of 20%. Then, two composite connections with hybrid rebars were tested to investigate the advantage of replacing half of the steel bars with BFRP bars based on the equal-stiffness rule. Finally, two composite connections were reinforced by hybrid rebar and the steel rebar was corroded with a target corrosion degree of 20% to investigate the effectiveness of hybrid reinforcement to compensate for the decrease in punching shear resistance due to corrosion. The test results demonstrated that the punching shear resistance of the RC slab-column connections with tensile reinforcement ratios of 0.52% and 0.91% decreased by 19.7% to 24.3% when the real corrosion degree reached 12.8% and 18.9%, respectively. Replacement of steel rebar with BFRP bar following equal-stiffness rule resulted in slightly greater load resistance but lower ductility energy dissipation capacity. The punching shear resistance of the corroded composite slab-column connections with hybrid bars was greater than that of the corroded conventional RC slab-column connections by 18.9% to 21.5%. To consider the rebar corrosion effects in design, the accuracy of the equations from prevalent design codes was evaluated.