Experimental study on progressive collapse behavior of frame structures triggered by impact column removal

Abstract

In the research field investigating the progressive collapse of building structures, event-dependent collapse processes have gained increasing attention in analytical and numerical studies. Different events could cause varying effects on progressive collapse resistance. The alternate load path could be related to events that could also lead to variations in load actions. However, experimental studies on reinforced concrete (RC) frame structures triggering structural column removal by the low-velocity impact have not been reported. Therefore, this paper performed an initial experimental study employing impact loading as the extreme event to investigate subsequent progressive collapse behavior of structures. Tests were conducted on six RC substructures consisting of a two-span beam and a structural column. Gravity loads were applied to the top of substructures, and a pendulum impact setup was utilized to remove RC columns by low-velocity impact. When the column underwent lateral failures, the downward force exerted by longitudinal steel bars of the column, before they fractured, pulled the two-span beam beyond the compressive arch action (CAA) stage, leading to a collapse process entirely different from their event-independent counterparts. The parametric study based on experimental results indicated that low-elevation impact and increase of column longitudinal bars detrimentally affected the performance of two-span beams resisting progressive collapse, while the increase in concrete strength partially improved the residual bearing capacity after impact column removal (ICR). Based on a dynamic model, a simplified calculation method is proposed for quantifying the downward force.