Some aspects of dynamic punching shear of RC flat slabs

Flat slabs are commonly used in residential construction and considered a simple, fast and efficient construction method for multi-story residential buildings, which are characterized by moderate spans and relatively low live design loads. The flat slab-column joint is known as a weak connection where the flat slab loads are transferred to the column and punching shear failure may develop as a result. Standards and codes instruct for the design rules and details to prevent punching shear and ensure safe transfer of the static loads. However, when dynamic loads are acting on the slab and/or the inertia of the upper slab is involved in a failure scenario, considerably higher dynamic loads are acting on the flat slab connection and may activate a dynamic punching shear failure. When flat slab-column connections failure occur in a certain flat slab, the slab may fall down with increasing velocity and impact the slab underneath. This scenario is in the focus of the present study, as its outcome determines whether the slab underneath arrests the falling slab or whether its connections will fail, thus leading to progressive collapse. This paper aims at presenting a study on the dynamic impact of slabs and investigate the modes of damage and failure depending on major parameters of the slabs. Existing design codes refer only to static punching shear resistance of slabs with and without shear reinforcement. The present study illuminates the dynamic aspects of the response and should be of much interest and importance.