Finite element analysis of punching shear behaviour of concrete slabs supported on rectangular columns

Design provisions for punching shear of reinforced concrete flat slabs supported on rectangular columns vary greatly and are typically based on empirical results. Due to the large cost and time required to conduct experimental tests the empirical database for slabs supported on rectangular columns is small. Properly calibrated, nonlinear finite element models (FEM) provide an efficient way to expand experimental databases, conduct parametric studies and verify design provisions. In this paper, the results from a parametric study of the impact of column rectangularity (aspect ratio) on the punching shear behaviour of interior slab-column connections without shear reinforcement under static concentric vertical loading are provided. The study was conducted using a three-dimensional nonlinear FEM based on the concrete damaged plasticity model available in ABAQUS. The FEM, summarized herein, was calibrated using seven experimental specimens of slabs supported on square and rectangular columns from literature. The parameters studied were the column aspect ratio, and the ratio of the minimum column dimension to the effective slab depth. These parameters were selected based on a review of literature and design provisions. The impact of column rectangularity on the predicted load-deflection response, slab crack patterns and shear stress distribution in the slab along the column perimeter are analyzed. The results for the 77 slab-column connections simulated in the parametric study demonstrate that the impact of column rectangularity is not dependent on the column aspect ratio alone, and becomes more severe as the ratio of the minimum column dimension to the effective slab depth increases.