Collapse Behavior of Unequal-Span Multistory Composite Frames under the Scenario of Removing an Internal Column

To satisfy the requirements of architectural aesthetic and function demands, unequal-span composite frames are widely employed in practical engineering applications. However, there has been relatively limited investigation on the collapse-resistant performance of such frame structures. To elucidate the collapse behavior of the unequal-span multistory frame structures under the scenario of removing an internal column, two one-third scaled three-story planar frames with unequal (2/3:1) and equal (1:1) spans were subjected to static testing, and the anticollapse performance including the load-bearing capacities, failure modes, development of axial force, and load-transferring mechanisms was determined. The test results revealed that the unequal-span specimens reached their maximum load during the early stage of small deformation, whereas the equal-span specimens achieved their maximum load at the final failure position owing to the collaborate action of equal-span double-span beams. Subsequently, numerical modeling methods were validated using the tests results, and the influence of the axial compression ratios of adjacent columns on the structural collapse resistance was examined. Furthermore, the collapse behavior of unequal-span composite frames was further investigated using full-scale models, with a focus on three types unequal-span cases for double-span beams, and specific resistant contribution coefficients were proposed as an crucial design reference for unequal-span composite frames to mitigate progressive collapse.