Dynamic sensitive failure mode in the progressive collapse of RC structures subjected to column removal scenarios

A series of structural collapse failures over the last decades have triggered an increasing research interest to identify ways to prevent progressive collapse when structures are subjected to local damage due to foreseen or unforeseen actions. Strong nonlinearities, dynamic effects, and system behavior should be taken into account in progressive collapse analyses. In order to avoid time-consuming nonlinear dynamic analyses, approaches using a dynamic increase factor or the energy-based method to the static pushdown curve are widely adopted. However, in this article it is shown that reinforce concrete (RC) structures may be evaluated as safe according to a static analysis but essentially unsafe when considering a dynamic analysis due to the dynamic snap-through behavior. This phenomenon results in a dynamic sensitive failure mode (DSFM) that should be identified in relation to progressive collapse analyses. Comparing with the static situation, the dynamic instability may result in a much more brittle failure mode in the dynamic situation due to the dynamic effects. Hence, the structure becomes sensitive to the dynamic effects and this may further lead to danger of brittle failure, which should be prevented in practice. An efficient method is proposed to approximately determine the load-displacement region where the DSFM occurs. This region is designated as the DSFM window. A two-linear-spring system, a RC beam-column substructure, and a RC frame structure are employed to illustrate the DSFM and verify the proposed method. The results demonstrate that the proposed approach can effectively determine the DSFM window for RC structures subjected to column removal scenarios.