Progressive Collapse Analysis of Intermediate Moment-Resisting Steel Frame under Fire-Induced Column Failure

Abstract

This paper evaluated the progressive collapse robustness of steel intermediate moment-resisting frames (MRFs) under different fire-induced column failure scenarios. For this purpose, 3-, 7-, and 12-story intermediate MRFs were modeled numerically and analyzed under different gravity and fire loads. The effects of the seismic design requirements, number of stories, gravity load ratio (utilization ratio), and redundancy and position of the heated column were discussed. Because the investigations included models with different number of stories and different seismic to gravity load ratios, the results can be applied for a wide range of IMFs. The results show that none of the studied frames in the high seismic zone with a low gravity loads ratio experienced progressive collapse under any of the considered fire scenarios. However, by increasing the ratio of gravity loads in frames, the vulnerability to progressive collapse was increased. This suggests that in areas with a lower risk of environmental lateral loads, where MRFs generally are designed for gravity loads and smaller lateral forces, the progressive collapse robustness of MRFs under fire-induced column failure should be given serious consideration. In addition, the results show that the possibility of progressive collapse under the fire-induced column failure scenarios in the first story of low-rise frames is more than that in the first story of high-rise frames, and generally low-rise frames are more vulnerable to progressive collapse than high-rise frames. Furthermore, the possibility of progressive collapse under fire scenarios in the upper stories is more than that in the lower stories, especially for the top story. In this study, a new combined failure mechanism for global collapse of MRFs was identified.