The progressive collapse of the World Trade Center showed the devastating consequences of pancake-type collapses, triggering significant research on failed-floor impacts for different forms of construction. In current high-rise construction, concrete flat slabs supported on columns are used widely, and, in this case, the fall of the slab could be prevented depending on the detailing and the horizontal propagation of the collapse from one support to adjacent supports. The activation and interaction of different phenomena during horizontal propagation governed by the slab-column response was investigated in this study for cases of flat slabs with and without integrity reinforcement. This paper focuses on slabs without punching reinforcement which are more critical. A slab system analytical model is presented based on a column removal scenario considering the dynamic response of the column-slab connections before and after punching including membrane effects. The model was verified using finite-element models with solid elements at the connections. The results highlighted the key role of integrity reinforcement in preventing slabs from falling by means of activating tensile membrane action concentrated around the columns. (C) 2021 American Society of Civil Engineers.
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