Punching failure and analytical model for rectangular flat slabs with equal flexural capacities in orthogonal directions

Despite the practical use of rectangular flat slabs with equal flexural capacities in orthogonal directions, their punching behavior has not been addressed. In this paper, the mechanical behavior of such slabs under varying tensile reinforcement ratios and plan dimensions has been investigated, using nonlinear finite element analysis in ABAQUS. Initially, the numerical model of the interior slab-column connection under static vertical loads was developed and thoroughly verified using 20 symmetrical and 9 asymmetrical specimens, covering wide variations in various parameters. Subsequently, parametric studies were conducted on rectangular slabs with equal flexural capacities in both directions, utilizing 54 simulations. The results indicated that the slab aspect ratio strongly affected the load-rotation curves, tensile reinforcement stress, cracking patterns, and shear forces in both directions, as well as their symmetry, despite being designed with equal flexural capacities in orthogonal directions. A novel approach, derived from the critical shear crack theory (CSCT), was developed for this slab type and then compared with existing models. It is noted that the ACI code cannot accurately predict the punching capacity. Although the EN1992–1-1 (2023), MC2010, and CSCT models accurately predict punching capacity, especially when the MC2010 and CSCT models account for two directional rotations, they lack in predicting deformation capacity. However, the proposed model offers accurate predictions for punching and deformation capacities. Its innovations include refining the load-rotation equation, validating the CSCT failure criterion, and quantifying the non-uniform shear force between orthogonal directions.