Slab thickness-shear reinforcement interaction on shear strength of interior slab-column connections

The effects of slab thickness and punching shear reinforcement ratio on the individual contributions of concrete and reinforcement on punching shear strength of interior slab-column connections are theoretically investigated. Numerical results of verified models are utilized to evaluate the effect of slab thickness, and the amount and detailing of punching shear reinforcement on punching shear capacity. Further, design code provisions are discussed in light of the obtained results. Extensive nonlinear FE models were developed and analyzed via ABAQUS software. Results of the developed FE models were first examined against Cairo University lab's 16 half-scale specimen tests. It is demonstrated that the developed FE model predicts the punching shear behavior of interior slab-column connections with practically adequate accuracy. Next, 65 full-scale FE models of slab-column connections were analyzed to study how slab thickness and punching shear reinforcement ratio affect concrete and reinforcement punching shear strength contributions. The analyzed cases included single, hat, multi, and closed stirrup. Results showed that slab thickness and the amount and detailing of shear reinforcement have important effects on the punching shear capacity of slab-column connections. The effectiveness of punching shear reinforcement is significantly influenced by both slab thickness and shear reinforcement ratio. Thicker slabs increase reinforcement strains with the same shear reinforcement. Besides, for thin slabs (ts = 160 mm), the concrete contribution decreases with the increase in shear reinforcement after cracking. Finally, the comparison between the FE results and the design codes (ACI, ECP, and EC2) showed that the ACI and ECP codes underestimate the punching strength of cracked concrete. To address this underestimation, a new formula was proposed and validated.