Infilled steel frame structures are known to perform better as compared to infilled concrete frames under seismic loading. In comparison with masonry infilled reinforced concrete (RC) frame structures, very little research has been done on masonry infilled steel frames structures. Contribution of masonry infill in the positive performance of the infilled structures is widely recognized but no codes provide the clear and detailed guidelines on the design of infilled frame structures especially infilled steel frame structures due to the complex and unpredictable behaviour of masonry during an earthquake event. This study aims to provide a detailed insight into the composite behaviour of steel frame structures with unreinforced masonry infill under seismic loading. Time history analyses have been performed on masonry infilled steel moment resisting frame structures and structural performance has been evaluated in terms of global structural performance parameters of fundamental time period, maximum roof displacement and base shear and local parameters of interstorey drift ratios, structural member forces and infill stresses. The effect of masonry infill on the performance of infilled steel moment resisting frames has been investigated by varying the number of bays, number of storeys, percentage opening in the infill wall, location of the opening, type of openings, number of openings, infill strength, outer frame strength and infill thickness. The results of this research will help to understand the complex behaviour of masonry infilled steel frames for different variations mentioned above.

In general practice, buildings can range from small residential houses to large commercial plazas. Size of the structure may change at base with the type of building and availability of area. Bay analysis has been performed to analyze the effect of variation in number of bays on infilled frames. Four three storey models (Bare and Masonry infilled) with number of bays varying from one to four have been considered in this study. Non-linear static analysis or pushover analysis has been performed in Perform-3D and capacity spectrum method of ATC-40 followed by seismic vulnerability assessment framework proposed by Kyriakides (2007) have been used to derive the vulnerability curves for all models considered in this study. Results of seismic vulnerability assessment have been used to determine the effect of variation of number of bays on the seismic vulnerability of masonry infilled steel and RC frames. Vulnerability curves of bare frames have also been compared with the vulnerability curves of infilled frames for both steel and RC frame structures to determine the percentage decrease in the seismic vulnerability of masonry infilled frames as compared to bare frames.