Effects of Masonry Infill Wall on the Performance of RC Frames to Resist Progressive Collapse

Masonry-infilled (MI) panels, which serve as partitions in buildings, are normally considered as architectural elements. Their weights are considered in progressive collapse analysis, but the resistance of the walls is normally ignored in design guidelines. Simple structural analysis predicts that the infill walls, which are commonly equivalent to compressive struts, increase not only the lateral load resistance but also the vertical load resistance of the reinforced concrete (RC) frames. Because extra vertical resistance might reduce the risk of failure, it is necessary to quantify the effects of MI walls on the load resisting capacity of RC frames to mitigate progressive collapse. However, few studies, especially experimental studies, have been carried out on this topic. Thus, six multistory by multibay RC subframes were designed and tested, subjected to push-down loading regimes. The six subframes were categorized into two groups: (1) bare frames without MI walls and (2) infilled frames with MI walls. The failure modes, load-displacement curves, deformation shapes, and strains of the specimens are measured and compared. The effects of the MI wall on the load resisting capacity, initial stiffness, and load resisting mechanisms of RC frames to resist progressive collapse were also evaluated and discussed. The experimental and analytical results indicated that ignoring the effects of MI walls in progressive collapse design may result in substantial inaccuracy in predicting the stiffness, strength, and failure modes of infilled frames to resist progressive collapse. Infill walls with low height/span ratio may fail in splitting of the equivalent compressive struts prior to crushing.