Progressive collapse of all-steel buckling restrained braced frames

Abstract

A non-linear static pushdown analysis was used to evaluate the progressive collapse potential of all-steel Buckling Restrained Braced (BRB) frames. The frames were modelled using alternate path method in SAP2000®. In framed structures, adequate lateral resistance can be provided with steel braces. But, in seismic areas, these tend to buckle and exhibit reduced strength, stiffness, and resistance under periodic loading. All-steel BRBs are excellent in dissipating energy due to their high stiffness and ductility with reduced cross-sectional area. In this paper, a comparative study was performed to evaluate the improvement in energy dissipation of frames with ordinary concentric steel bracing and all-steel BRB. Firstly, frames with two different types of all-steel BRB obtained from literature were compared. Secondly, the effectiveness of all-steel buckling restrained braced frames under three bracing patterns, namely, double X, inverted V and hexa-bracing patterns were investigated. The progressive collapse potential was estimated from the variation of vertical deflection with the percentage of load. The ductility and support rotations were then determined from the estimated progressive collapse potential. These were then used as acceptance criteria for investigating progressive collapse as per General Service Administration (GSA) specifications.