Damage Evolution in the Event of Impact-Punching Shear of RC Flat Slabs

This paper investigates the evolution of damage in a reinforced concrete flat slab that is impacted by a flat slab that is falling from above due to failure of its connections with its supporting columns, thus starting a progressive collapse scenario. The momentum transmitted to the impacted slab develops severe damage at the column-slab connection zone of the impacted slab and causes complete failure of the connection within a very short duration. This paper aims at investigating the processes occurring during this short duration from the instant of contact between the impacting slabs until a complete failure of the impacted slab-column connections is reached, thus gaining insight into the evolution of the damage. Understanding these processes will enhance the understanding of the governing mechanisms and contribute to improve the design of these connections and lead to derive physically based engineering models. Using a powerful numerical simulation, a structural model for the present investigation had been established and the entire failure event is analyzed. The damage increase in the concrete within the slab is carefully followed, showing a radial spread of a full-damage zone outward from the column circumference that exceeds several column widths within less than 20 ms, during which a complete failure of the connection occurs. During this time, the rebars in the connection zone undergo plastic deformation and failure, and the reinforcement contribution to the shear resistance of the connection decreases rapidly. The paper investigates the growth of damage with time and examines the rate of processes in the different reinforcement types. It examines the effect of the ductility of the steel rebars and investigates the dependence of concrete damage on the effectiveness of the shear reinforcement. This study provides a deep new insight on the complex short-duration mechanisms involved in this impact event.