Progressive collapse resistance of framed buildings with partially encased composite beams

Several research contributions stemmed from the increasing interest in progressive collapse-resistant design and assessment of structures, which was driven by extreme events all around the world. Most of studies focused on the robustness of steel and reinforced concrete (RC) structures, highlighting a knowledge gap on the progressive collapse resistance of framed buildings with partially encased (PE) continuous composite beams, which are an attractive solution compared to, for instance, their cast-in-place RC counterparts. This paper presents the main outcomes of a numerical investigation that was aimed at evaluating/exploring the vertical load-carrying capacity of framed buildings with PE beams after column loss. A numerical fibre-based model was developed and successfully validated against experimental data on two full-scale composite beam specimens, indicating a high accuracy level of the models with displacement-based fibre elements. Then, a wide set of framed building structures with PE beams was generated according to Eurocodes, evaluating their progressive collapse resistance through the alternate load path method. Pushdown analysis was carried out to investigate the gravity load capacity under increasing downward displacement at the location of the removed column. Analysis results outline a huge sensitivity of progressive collapse resistance to the beam type (i.e. PE versus RC), beam depth and span length, with minor influence of longitudinal reinforcement in the case of PE beams. The peak load capacity under column loss was characterised at several limit states corresponding to increasing levels of damage, allowing the proposal of multiple regression models for progressive collapse design and assessment.