Nonlinear seismic responses and lateral force transfer mechanisms of RC frames with different infill configurations

Due to the architectural efficiency of masonry-infilled reinforced concrete frames, the frames are highly common structural forms for buildings. However, the infills can significantly modify the structural behaviour of these frames, which can be detrimental to the seismic performance of buildings. This study investigates the seismic response and failure mechanisms of infilled RC-frame structures with five different infill configurations: (1) full infills, (2) 2/3-storey-height infills, (3) a soft first storey, (4) infills with window openings and (5) infills with door openings. The nonlinear response history behaviour of the masonry-infilled RC frames under four realistic earthquakes, namely, the 1979 El Centro, 1987 Superstition Hills, 1995 Kobe and 1999 Chi-Chi earthquakes, were simulated using discrete-finite element analysis with damage-based constitutive relations. The analysis indicated that the degrees of continuity and regularity of the infill panels crucially affect the seismic performance of structures. As long as out-of-plane collapse of infills does not occur, full-height and continuous-infill panels can enhance the overall stability and energy dissipation of frame structures. By contrast, discontinuous infills can inflict serious damage localised at the points of discontinuity in the frame members. Furthermore, the analysis revealed that the design concept of “strong column-weak beam” may not be always applicable to infilled frames.