Conference paper

Punching shear strength and behaviour of compact reinforced concrete footings

concrete footings with and without transverse reinforcement. Even though that punching shear failures have already been deeply investigated, there is still scanty experimental information on full-scale reinforced concrete footings failing in punching shear. The results of an experimental programme addressed to this issue (punching of reinforced concrete footings with and without shear reinforced) are presented in this paper. A total number of 5 square specimens were tested with a nominal thickness of 550 mm, where the influence of the side length of the footings, the column size (and thus shear slenderness) and the presence of top and transverse reinforcement were investigated. The experimental results show that punching strength increases with the increase of the column size and with the decrease of the size of the footing. It also results as experimental evidence that a significant flexural-shear interaction might occur for high shear loads, leading to much lower flexural strengths than those calculated according to yield-line theory. Limit analysis might be a consistent tool to investigate the failure of concrete struts provided that cracking is properly accounted for, particularly with reference to the effective concrete compressive strength as a function of the state of deformations. In this sense, the kinematical theorem of limit analysis is used to investigate on the governing failure mechanisms and to calculate failure loads. The theoretical results show that an important flexural-shear interaction occurs, leading to a smooth transition between the flexural and punching shear failures. The experimental results are analysed based on theoretical considerations resulting from the application of limit analysis. It is shown that a consistent agreement can be found between such theoretical approach and the experimental evidences.

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