Effect of concrete masonry infill walls on progressive collapse performance of reinforced concrete infilled frames

In practice, infilled frame is a common structure but the contribution of infill walls is typically ignored in previous research on progressive collapse. To this end, numerical models based on solid-element are employed to investigate the behavior of reinforced concrete (RC) frames with concrete masonry infill walls under a middle column removal scenario (CRS). The numerical models of bare and infilled frames are initially validated through previous experimental results. Then the numerical models are used to illustrate the effects of infill walls on the load transfer mechanisms of the frames under a CRS and the interaction between infill walls and frame members. Thereafter, the size effect of the frame models is discussed and the numerical models are further extended to study the effects of pertinent geometric parameters on the progressive collapse behavior, including the height of partial-height infill walls, the opening position and area of wall panels as well as the number of stories. The results indicate that the load transfer mechanism of a two-story infilled frame in a middle CRS is the frame action provided by frame members and the truss mechanism provided by the interaction of infill walls and surrounding frame members, in which the latter remarkably enhances the initial structural stiffness and peak resistance. For the multi-story infilled frame with opening in which the geometric and mechanical properties are identical in each story, the load transfer mechanism is basically independent of the number of stories, whereas for the frame with full-height infill walls, the composite effect of multi-story walls is evident, increasing the peak structural resistance. Therefore, if each full-height infill wall is simplified into equivalent strut models in structural analysis, the results are underpredicted but on the safe side.