Punching of edge columns with and without shear reinforcement: an experimental investigation

Most research efforts in the past related to the punching resistance of reinforced concrete slabs have concentrated on the response of internal slab-column connections, where significant advances in the state-of-the-art have been performed. Other than internal connections, edge slab-column connections are also very common cases in flat slabs, with a strength usually governed by punching shear conditions as well. Their response is more complex than those of internal slab-column connections, due to the potential moment transfer from the slab to the column and to the uneven shear and moment fields. However, scanty experimental evidence is available due to the difficulty of testing such system under realistic conditions. As a consequence, knowledge on the phenomena governing failure is still limited and predictions of the strength are in most cases performed by adapting punching shear models for internal slab-column connections. In this paper, the main results of an experimental programme on edge slab-column connections is presented, comprising specimens both with and without shear reinforcement. A novel test setup was developed to effectively introduce the effect of continuity in the direction perpendicular to the free edge of the slab. Moreover, refined measurements were performed by using Digital Image Correlation on the concrete surfaces and Fibre-Optic Measurements in selected flexural reinforcement bars and shear reinforcement, allowing for direct measurements of displacements and strains in the critical regions. Based on the experimental observations, a discussion is held on the mechanics governing punching failures of edge slab-column connections.