Progressive collapse assessment of gravity-load designed European RC buildings under multi-column loss scenarios

Natural and man-made disasters often produce the collapse of multiple structural members at the ground floor of buildings, which may trigger a progressive collapse of the structure. Nonetheless, only a few experimental tests and numerical studies have been carried out to assess the effects of multiple column loss. In this paper, the progressive collapse capacity of gravity-load designed, reinforced concrete (RC) buildings complying with Eurocode 2 is numerically investigated, considering both simultaneous and sequential removal of ground-floor columns. The study focuses on a benchmark RC frame used in previous investigations on singlecolumn loss scenarios, using nonlinear fibre-based capacity modelling and incremental dynamic analysis. Progressive collapse capacity was evaluated at multiple structural scales, in terms of axial strains, beam drifts and gravity load resisted by the structure after column loss. Analysis results allowed the quantification of both load and drift capacities under varying relative location and deactivation times of removed columns, as well as the control point. A comparison with numerical/experimental data highlighted that the sudden loss of two consecutive columns can drastically reduce the load capacity, resulting in a progressive collapse of the RC framed structure. A sequential loss of columns induced either positive or negative variations in load capacity, depending on the ratio between removal times, whereas drift capacity significantly reduced in almost all cases.