Experimental evaluation of the masonry infilled reinforced concrete frame under reverse cyclic loading

Abstract. The design of structures that resisting the earthquake induced forces has become increasingly important, especially as masonry infilled reinforced concrete (RC) frames are crucial in resisting seismic forces. This study focuses on the performance of RC frames infilled with masonry walls under extreme seismic loading conditions, which can cause severe damage to support columns, potentially leading to partial or complete building failure. The research investigates how the seismic loading affects the structural behaviour of RC frames infilled with AAC block masonry walls and how performance parameters such as frequency, storey drift, relative stiffness, component strength, energy dissipation and local construction methods influence the overall seismic performance. To simulate earthquake conditions, cyclic loading test was performed on eight half-scale, single-story, single-bay RC frames, designed in compliance with IS 456:2000, IS 1893:2016 and IS 13920:2016 standards. These frames, with 1.5 m x 1.5 m masonry infills, were subjected to displacement-controlled cyclic loading following a standardized protocol. The study aimed to evaluate the stiffness degradation and energy dissipation of RC frames in cyclic load test. The experimental results, demonstrated through hysteretic curves, stiffness degradation trends and energy dissipation, revealed that RC infilled frames show significant potential for use in earthquake-prone regions. Key findings include energy dissipation differences of 17-18% between the first and second halves of the energy loop and a 70-75% reduction in stiffness as displacement increased by 60% at a constant frequency. The frames initially exhibited high stiffness, with slower degradation rates observed under cyclic loading. The research concludes that the seismic performance of masonry-infilled RC frames can be significantly improved by understanding stiffness degradation, load distribution mechanisms and the composite interaction between the infill and the RC frame. These findings are essential for creating more robust designs, reducing the risk of collapse and enhancing safety in earthquake-prone areas.