Influence of moment redistribution and compressive membrane action on punching strength of flat slabs

• Numerical model compares the behavior of isolated specimens and actual flat slabs.
• Moment redistribution and membrane action stiffen the response of continuous slabs.
• Comparisons to unusual tests from the literature validate the numerical model.
• The physical approach of CSCT allows predicting the punching capacities.
• Actual slabs may show higher capacities than predicted by existing design methods.

The punching shear strength of interior column connections of flat slabs has traditionally been investigated with isolated test specimens subjected exclusively to hogging bending moments. However, the behavior of such specimens is different from that of actual flat slabs, as the potentially beneficial phenomena of moment redistribution between hogging and sagging moments and compressive membrane action cannot take place in the conventional experiments. In the present paper, an axisymmetric numerical model is introduced that allows analyzing the role and significance of these effects on the flexural deformations of continuous flat slabs. Combined with the failure criterion of the Critical Shear Crack Theory, this model can be used to predict the punching capacities of such slabs. Comparisons are made to the results of some unconventional punching tests from the literature showing sound agreement between the modeling results and the experimental observations. The results suggest that the punching capacity of continuous slabs with low amounts of flexural reinforcement in the interior column regions may be underestimated in the current codes of practice.