Post punching behaviour of reinforced concrete slab-column connections

Reinforced concrete flat slabs are extensively used in buildings and parking garages. At the ultimate limit state, their design is usually governed by punching shear. In the case where no punching shear reinforcement is provided, failure develops in a brittle manner. Furthermore, punching shear failure of one column may propagate to adjacent columns, eventually leading to the total collapse of the structure. Punching shear failure occurs with almost no warning signs, because deflections are small and cracks at top side of the slab are usually not visible. Over the past decades, several collapses due to punching shear failures have occurred, resulting in human casualties and large damages. Some solutions can be adopted to enhance the post punching behavior of flat slabs and to avoid progressive collapse. This paper presents some results of an extensive experimental campaign performed at the Ecole Polytechnique Fédérale de Lausanne. The post punching behavior of 24 tested slabs, with various flexural reinforcement layouts are introduced and compared. The performance and robustness of the various solutions is investigated to obtain physical explanations of the load-carrying mechanisms.