Initial damage and residual behavior of RC beam-slab structures following sudden column removal-numerical study

High fidelity solid-element-based numerical models built in LS-DYNA are employed to study the progressive collapse resistance of reinforced concrete (RC) beam-slab substructures with an emphasis on the effect of initial damage caused by dynamic response from sudden removal of a column. In particular, the numerical models consider the bond-slip behavior between concrete and reinforcement in the joint regions, and incorporate element erosion in order to predict the failure modes such as reinforcement fracturing, concrete cracking and crushing. The finite element modeling is validated by experimental results in terms of both dynamic behavior following sudden column removal and residual behavior under quasi-static loading. After the validation, para-metric studies are performed to investigate the influence of the equivalent gravity load and shock-induced initial acceleration. The study clearly shows that the dynamic response due to sudden column removal can induce great reduction in the progressive collapse resistance of substructures through the initial damages. The compressive arch action (CAA) and compressive membrane action (CMA) are more easily damaged by the dynamic response following sudden removal of a column, constituting less reliable load resisting mechanisms against the pro-gressive collapse compared to the tensile catenary action (TCA) and tensile membrane action (TMA). Structures with larger applied load would suffer more from the dynamic response. Moreover, the initial upward acceleration in the event of blast or explosion is extremely unfavorable to the development of CAA and CMA by introducing transient upward movement before the downward deflection under gravity load. A comparison of the dynamic load amplification factors (DLAFs) is also made between the cases with and without significant initial damage due to dynamic response. It is concluded that ignoring the initial damage of structures can underestimate DLAF and further overestimate structural resistance, resulting in the structural design for mitigating progressive collapse in the events of explosion and impact on the unsafe side.