Wind Collapse Capacity of a Three-Story Building with Ductile Steel Moment Frames Compared to Nonductile Frames

Although the traditional approach in building engineering is to keep the main wind force resisting system elastic, doing so can inhibit capacity-based seismic design, and it is not always the most cost-effective approach. The purpose of this study is to determine the wind collapse capacity of a three-story building with ductile steel moment frames compared to nonductile moment frames for a range of design wind speeds. To incorporate the potential for inelasticity, the ductile steel moment frames are designed using reduced main wind force resisting system loads. The nonductile moment frames, which are not specifically detailed to be ductile, are designed using unreduced loads. Nonlinear pushover analysis of finite element models is used to determine static system overstrength and collapse mechanisms based on an open country terrain. Nonlinear incremental dynamic analysis is used to determine collapse safety. The results show that both ductile and nonductile steel moment frames have adequate wind collapse capacity, but the ductile moment frames have 42% higher system overstrength, on average, compared to nonductile steel moment frames for the same design loads, and greater collapse margin ratios compared to nonductile steel moment frames. The findings suggest that limited inelasticity in a ductile steel moment frame system may be acceptable if the frame meets drift requirements.