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EFFECTS OF THE NUMBERS OF STORIES AND SPANS ON THE COLLAPSE-RESISTANCE PERFORMANCE OF MULTI-STORY STEEL FRAME STRUCTURES WITH REDUCED BEAM SECTION CONNECTIONS

The progressive collapse of a building structure under an accidental load involves a relatively complex mechanical behavior. To date, the collapse of single-story beam-column assemblies has been investigated extensively, revealing the resistance development of beams during progressive collapse. However, few studies of the progressive collapse behavior of multi-story frame structures have performed a systematic analysis of the Vierendeel action (VA) at a comprehensive level. It is difficult to convert quantitative analysis results accurately from the component level to the overall structure level to evaluate the collapse resistances of structures. To investigate the effects of the numbers of stories and spans on the collapse resistances of steel frame structures, a refined numerical simulation study of a multi-story frame model with different numbers of stories and spans was performed. First, the correctness of the finite element modeling method was verified by the collapse test results of a single-story and two-story frame. Then, the finite element modeling method was applied to study the collapse resistances of multi-story frame structures with different stories and spans. The load–displacement response, internal force development, deformation characteristics, and resistance mechanisms were analyzed, and the contributions of the flexural and catenary mechanisms of each story were separated quantitatively. The results illustrated that the VA can improve the load-carrying capacity to a certain extent in the small deformation stage, but can also cause the frame structures to undergo progressive collapse from the failure story to the top story. The bearing capacity of the multi-story frame did not have a simple multiple relationship with the number of stories. Increasing the number of spans can improve the collapse resistance in the large deformation stage, which is more obvious when the number of stories is smaller, and this accelerates the upward transmission of the axial tension force among the stories, although this effect is minimal for frames with few stories.