Plasticity model for predicting punching shear strengths of reinforced concrete slabs

In this paper, the upper-bound theory of plasticity is employed to predict the punching shear failure loads of reinforced concrete slabs without shear reinforcement and without in-plane restraint. A parabolic Mohr failure criterion is adopted for the concrete to ensure that the important variation in angle of friction of the concrete with stress state is represented, with the material assumed to be rigid-perfectly plastic. The problem is treated as three-dimensional axisymmetric. Using this approach, the generatrix of the failure surface is shown to be a curve. A simplified expression, obtained by, approximating this generatrix to a line, is also derived for the punching strength. The sensitivities of the predicted failure loads to variations in the tension and compression effectiveness factors used for the concrete are investigated. It is found that the predictions correlate well with a range of experimental data for low-, normal-, and high-strength concretes, and for both small-scale and large-scale slabs.