Seismic performance of special concentric steel braced frames

Abstract

Special concentric braced frames are provided in buildings located in severe seismic zones to resist earthquake loads. The seismic performance of these frames is mainly depend on the capacity of bracing in tension. However, the detailed studies are not available to find the optimal tensile capacity of such bracing to give the acceptable performance under severe earthquake. This paper presents the seismic performance of regular 6, 9, 12 and 15 storey special concentric X-braced frames in which tension bracings are designed for the lateral load of 100%, 70% and 60% of base shear. Demand to Capacity Ratio (DCR) is varied in beam and columns (0.4–0.7) and bracing (0.6–0.9) under design lateral loads. Pushover curves are developed to determine the strength and ductility of the frame for all the DCRs considered in the study. Column DCR of 0.4 and 0.5 is proven to be more effective with bracing DCR of 0.8 and 0.9 in terms of strength and ductility. It is also found that the displacement demand for the frames designed for 60% of the total base shear under maximum considered earthquake is within acceptable limit.