Influence of opening location and reinforcement detailing on the punching capacity of flat slabs

Punching shear failure in reinforced concrete flat slabs is a critical structural concern due to its brittle nature, which can trigger progressive collapse of a building. This phenomenon becomes even more complex when openings near the column are required for the passage of building services, as they interrupt the stress flow and reduce the critical perimeter of the slab-column connection. This study presents an experimental and numerical investigation into the influence of opening location and reinforcement detailing on the punching shear capacity of flat slabs. Building on the experimental results of a reference slab (LR) from Liberati et al. (2019), a new slab with an opening (LF1Q) was tested to complement the dataset. These combined experimental data were used to calibrate a finite element model in ABAQUS, employing the Concrete Damaged Plasticity (CDP) model. Subsequently, a parametric analysis was performed to evaluate the sensitivity of the system to opening location (0d, 1d, 2d, and 3d) and three distinct reinforcement configurations (R1, R2, and R3). The results indicate that the proximity of the opening to the column face is the most significant factor in capacity degradation, with ultimate load increases of up to 76% observed when moving the opening from 0d to 3d. Regarding reinforcement, the R3 configuration, which concentrates longitudinal and transverse bars around the opening, proved to be the most effective, especially for more distant openings, achieving a 96% increase in load capacity compared to the unreinforced adjacent configuration. A comparative analysis of design codes revealed a general trend of overestimating the strength of slabs with openings near the column, with the new generation of Eurocode 2 providing the most accurate predictions relative to the numerical data. From a practical design perspective, these findings indicate that structural engineers should ideally position openings at least 2d away from the column face and adopt optimized reinforcement detailing, such as the R3 configuration, to safely mitigate stress discontinuities and the non-conservative strength predictions of current codes.