Seismic Analysis and Performance of High Strength Composite Special Moment Frames (C-SMFs)

Abstract

Composite special moment frames (C-SMFs) usually consist of concrete-filled steel tube (CFT) columns, wide flange (WF) steel beams, and rigid beam-to-column connections. The current International Building Code (IBC 2015) prevents the use of high strength materials (steel yield stress Fy≥450MPa and concrete compressive strength f'c≥70MPa) for CFT columns in C-SMFs. This is due to the lack of knowledge of the overall seismic behavior of high strength C-SMFs. This paper evaluates the seismic performance of high strength C-SMFs by conducting nonlinear static pushover (NSP) and nonlinear time-history (NTH) analyses using analytical models developed and benchmarked by the authors. The NSP analyses indicate that high strength C-SMFs have good lateral load-deformation behavior, and the effects of local degradation on the lateral response are negligible when the roof drift angle is less than an upper bound limit (approximately 1.5%). The NTH analyses indicate that high strength C-SMFs satisfy the acceptance criteria (including the interstory drift angle) specified in FEMA-350 and ASCE 7-10 for Immediate Occupancy, Life Safety, and Collapse Prevention performance levels when subjected to the frequent occurrence earthquake (FOE), design basis earthquake (DBE), and maximum considered earthquake (MCE), respectively. Higher mode effects dominate the seismic performance of taller (12-story) high strength C-SMFs, but dynamic instability is not an issue when the maximum roof drift angle is less than the plateau drift angle (∆p), which corresponds to the onset of negative stiffness in the lateral load-displacement response from the NSP analyses.