Influence of masonry infills on seismic response of RC frames under low frequency cyclic load

This paper presents an investigation on the seismic behavior of four reinforced concrete (RC) frames. The study is focused on the effect of the Aerated Lightweight Concrete (ALC) blocks infills on the seismic performance of the RC frames and the interaction between infills and surrounding frames. Four RC frames include a control specimen, frame with full-filled infills, frame with large window openings, and frame with eccentric door openings. Based on the low frequency cyclic loading experiments, hysteretic dissipation ability, stiffness degradation, characteristic displacement and load, failure pattern, flexural moments of columns, effective slab width, required ratio of column-to-beam strength, and column shear force are experimentally investigated and analyzed. Tests results indicate that the strength, the initial stiffness and the area of the hysteretic loop at the same load step were influenced significantly by infills when compared with the frame without masonry infills. This effect was reduced due to the large openings in the frame with infills. The column and beam mixed hinges failure was observed in the frame without infills while shear failure appeared at column ends in frames with infills. The testing results also show that inflection points were shifted to columns top because of the infills. Column shear forces were increased significantly due to the diagonal strut effect. Recommendations on useful effective slab width, the required ratio of column-to-beam strength and the equivalent strut width are made to take masonry infills into consideration in design.