Compressive Membrane Action Effects on Punching Strength of Flat RC Slabs

The design of reinforced concrete flat slabs in practice can be governed at failure by punching shear close to concentrated loads or columns. Punching shear resistance formulations provided by codes are calibrated on the basis of experimental tests on isolated slabs supported on columns in axisymmetric conditions. Nevertheless, the behavior of flat slabs can be different than isolated specimens due to the potentially beneficial contributions of moment redistributions and compressive membrane actions. Accounting for the significance of these effects, nonlinear finite element analyses are performed with the crack model PARC_CL implemented in Abaqus. This paper aims to investigate a series of punching shear tests on slabs with and without shear reinforcement, different reinforcement ratios and loading conditions accounting for the potential contribution to the enhancement of the punching strength due to compressive membrane action (CMA). The numerical results with a multi – layered shell modeling are then post – processed adopting the failure criterion of the Critical Shear Crack Theory (CSCT). The results pointed out the significant outcomes and differences between standard specimens and actual members showing how the current codes of practice may underestimate the punching capacity.