Effects of masonry infill walls with openings on seismic behaviour of long-span GLD RC frames

Five long-span reinforced concrete (RC) frame specimens with various configurations of masonry infill walls were tested under lateral quasi-static cyclic loading. The specimens were half-scale models of gravity-load-designed (GLD) RC frames of typical school buildings, and comprised one bare frame and four frames with either a full infill, partial-height infill, central-opening infill or side-opening infill. All the specimens were heavily instrumented with strain and displacement sensors to gain in-depth information on the interaction effects between the frame and infill walls. The test results showed that the interaction mechanism varies greatly from case to case. For example, the fully infilled wall behaved like two inclined compression-only struts but with characteristics quite different from those of conventional diagonal struts. The infill wall with a side opening behaved just like one strut, actively engaging only when the wall was pushed by the frame, and thus creating an unsymmetrical cyclic force–deformation behaviour of the infill frame.