Experimental assessment of column rectangularity in flat‐slab slab–column connections

Abstract This paper presents an experimental investigation of the punching shear behavior of seven 3.00 m × 3.00 m × 0.20 m flat slabs without shear reinforcement, supported by internal rectangular columns. The column side lengths were varied to obtain aspect ratios, c max / c min , from 1.67 to 4.00, while the flexural reinforcement and overall slab geometry were kept constant. The tests were designed to prevent flexural failure and to isolate the influence of column rectangularity on punching resistance. The results show that increasing the column aspect ratio enhances the punching capacity, with strength gains of up to 27% in the tested configurations. All specimens failed by punching, and the crack patterns and failure surfaces became progressively more directional as the column rectangularity increased. The experimental results were compared with the predictions of NBR 6118:2023, EN 1992‐1‐1:2023, ACI 318:2025, and MC 2020:2024. All four design codes provided safe predictions for the tested slabs, with ACI 318:2025 being the most conservative on average and NBR 6118:2023 the least conservative. Overall, the code formulations captured the main trend of increasing punching resistance with column rectangularity, although their accuracy depended on the column geometry and the effective depth.