Collapse risk of steel framed buildings with deep columns under tri-directional excitation

Abstract

Deep steel columns are widely used in steel buildings with perimeter moment frames (PMFs). Although their seismic behavior has been well examined at the member level, their influence on frame collapse response requires further exploration, especially their interaction with composite slabs, gravity frames, and ground motion components. To address this shortcoming, the collapse risk assessment of a set of steel buildings with PMFs and deep columns is performed via two modeling approaches: the conventional planar frame and the sophisticated space frame. The models are capable of capturing the instability, fracture, and collapse behavior in frame systems. The simulation results show that each additional ground motion component applied promotes the development of collapse mechanisms and significantly increases collapse probability, and that composite slabs combined with gravity frames greatly improve collapse capacity despite introducing additional local failures. Moreover, limiting slenderness ratios and controlling local buckling of deep columns is essential to prevent frames from vertical progressive collapse (VPC) and ensure sufficient collapse resistance. The available highly ductile limits (HDLs) are accordingly critiqued and revised. Due to the large discrepancies in the collapse risks determined by the two approaches, space frame modeling is suggested to accurately assess the collapse capacity of steel PMFs involving deep columns.