Numerical study on collapse-resistant performance of multi-story composite frames under a column removal scenario

Abstract In practice, when building structures are subjected to local damage caused by extreme loads, all stories above the failure column consequently deform and play a major role in the internal force redistribution and rebalancing for resisting the external load. However, because of the high cost and laboratory space constraints, most existing experimental tests on progressive collapse are primarily focused on single-story sub-assemblages. In a previous experimental work, to investigate the collapse performance of a multi-story composite frame, a 1/3 scale three-story composite sub-frame with top and seat with double web angle (TSDWA) connections was tested quasi-statically. However, whereas many factors have a significant influence on the progressive collapse performance, the corresponding experimental data proved too limited to allow their analysis. Consequently, to address these limitations and explore the effects of key parameters on the progressive collapse behavior of multi-story composite frames, a series of progressive collapse simulations were conducted in this study and the corresponding critical parameters identified. First, a finite element model of the three-story composite sub-frame was established and validated with the prior experimental results. Then, the effects of composite slabs and lateral restraints on the collapse performance were investigated using a refined model. Subsequently, the effect of model size was determined and parametric analyses were carried out to investigate the effects of key parameters on the progressive collapse performance, including number of stories, span-to-depth ratio, and column-removal position. Finally, the TSDWA connections were reinforced by adding stiffeners on both sides of the top and seat angles, which effectively improved the collapse resistance of the multi-story composite frame under different collapse conditions.