Punching shear tests in flat slabs supported on re-entrant corner columns

Abstract

The punching strength and deformation capacity of slab-column connections is governing for design at ultimate limit state of flat slabs. This phenomenon has been investigated since decades with experimental programmes in an effort to derive empirical or mechanical design approaches. Such efforts, due to the complexity of the phenomena, have mostly been addressed to axisymmetric inner slab-column connections, which correspond to the simplest academic case and are not directly covering a large variety of practical situations. Although some tests are also available for other configurations, such as edge or corner connections, no experimental evidence is found on relevant cases for practice such as re-entrant corner columns. The lack of experimental data in this latter case raises questions on the design of such connections, as extrapolating results from other cases is not a simple task due to the complexity of the phenomena implied (such as redistributions in the shear field and moment transfer between slab and column). In order to advance the knowledge on the response of re-entrant connections and to provide a sound design approach for them, this paper presents the results of an investigation specifically addressed at this case. To that aim, seven specimens were tested under different conditions, varying the load eccentricity, flexural reinforcement and shear reinforcement arrangement at the edges. The tests were instrumented with refined measurements, allowing to understand in a detailed manner the response of the slabs during testing in the shear-critical region. The experimental results are later compared to current design codes, leading to a number of conclusions with practical relevance. Finally, on the basis of the knowledge acquired from the tests, a mechanical approach is proposed based on the Critical Shear Crack Theory to assess the punching response. This approach is shown to lead to accurate and reliable predictions of the punching strength, improving those of current design codes.