Investigation of the effect of openings of interior reinforced concrete flat slabs

Installation of building utilities often requires the creation of openings near existing slab-column connections. These openings reduce the concrete area that sustains the shear stresses, thus, the developed shear stresses are increased and contribute to the risk of punching shear failure. In this paper, nonlinear finite element analysis (FEA) using a previously calibrated coupled plasticity-damage model for concrete is performed for interior slabs with square openings. An interior reinforced concrete flat slab without shear reinforcement, which was tested under gravity loading, is considered as the reference slab. The effect of the location and the size of the opening on the punching shear resistance are examined. Punching shear predictions according to ACI 318-14, Eurocode 2-2004, and fib Model Code 2010 are compared to the FEA results. Finally, probabilistic analyses using the Monte Carlo simulation are considered, and fragility analysis is performed to estimate the probability of the punching shear resistance related to the size and distance of the opening.