Response of multi-bay, multi-storey masonry-infilled reinforced concrete frames under lateral loading

• Investigated the performance of a multi-storey, multi bay infilled RC frame under lateral load via simplified 3D micromodelling approach • Adverse effect on column of ground story is accurately captured • The influence of different infill strength is examined • Proposed a contact length in order to assess the shear force of columns on ground and first storey. This article presents a comprehensive parametric investigation of infilled reinforced concrete (RC) frames using a simplified micro-modelling (SMM) technique. Numerical analyses were performed by systematically varying the RC frame configuration, masonry compressive strength, infill distribution and number of storeys. Nine 1/3 scale, representative structural configurations, corresponding to prototype infilled RC frames, were examined, ranging from one-storey, single-bay frames to a multi-storey, multi-bay and their structural responses were evaluated and compared. A comparative assessment of inter-storey drift ratios between one-bay and three-bay frames, for both one and six-storey arrangements, across different masonry strengths, revealed pronounced differences in deformation demands and failure mechanisms. Additionally, empirical correlations were derived to estimate the lateral resistance of multi-bay infilled RC frames based on the corresponding resistance obtained from single-bay systems. The numerical results indicated that masonry strength influences the lateral strength, stiffness and overall behaviour of masonry-infilled RC frames. Furthermore, strong infill demonstrated an adverse effect, including damage concentration at the ground storey and brittle shear failure in the RC columns of masonry-infilled RC frames. Based on the numerical results, minimum shear strength criteria for columns in infilled RC frames are proposed to ensure control of the ultimate failure mechanism. Finally, the study provides practical recommendations for the seismic assessment and design of masonry-infilled RC frames, particularly regarding masonry strength selection, column shear design and appropriate modelling strategies.