QUANTITATIVE EVALUATION OF EFFECT OF VARIOUS SPAN-TO-DEPTH RATIOS ON THE COLLAPSE PERFORMANCE OF PLANAR STEEL FRAMES

After the removal of a column caused by the unexpected extreme loading of the building structure, the remaining structure mainly relies on the double-span beams connected with the failed column to mitigate the progressive collapse, therefore, the span-to-depth ratios of the double-span beams has significant effects on the internal force redistribution among each story and the development of the anti-collapse mechanisms of the multi-story planar frames. To investigate the effect of span-to-depth ratios on the progressive collapse performance of steel frames, the collapse analysis of three-story steel frame models with various beam depths and beam spans was numerically studied. Firstly, the correctness of the numerical modeling method was verified by the collapse test results of a two-story sub-frame. Then, the refined modeling methods were applied to the analysis of progressive collapse performance of steel frames with various span-to-depth ratios. The load response, load distribution, deformation characteristic and load-resisting mechanisms of models are investigated in detail. The results showed that the resistances provided by flexural mechanism and catenary mechanism are mainly determined by span-to depth ratios and beam span, respectively. Through the principle of energy conservation, the different resistant contribution coefficients of each story are quantitatively obtained, and corresponding empirical formulas were proposed, which can be used as a reference for resistance evaluation before the design of structural anti-collapse.