There are several recent research efforts to provide guidelines for the design and assessment of structures susceptible to progressive collapse. Robustness is defined as the ability of a structure to withstand events like fire, explosions, impact or the consequences of human error, without being damaged to an extent disproportionate to the original cause, i.e. without progressive collapse. Modern building codes treat robustness with two different strategies: 1) increasing continuity and enhancing the load distribution ability after a member loss; and 2) increasing the specific local resistance of the key elements to accommodate accidents. This paper studies the effect of seismic design level and building height on the robustness of steel frame buildings prone to progressive collapse. Three steel moment resisting frame buildings with heights of 5, 10, 15-story (representing low, medium, and high rise buildings) were designed for three seismic zones (representing low, medium, and high seismicity) using the International Building Code (IBC). The buildings had a rectangular plan of 3x6 bays with 5.0m spans. To assess the progressive collapse potential of the buildings, Alternate Path Method (APM) recommended by the U.S. General Service Administration (GSA) and the Department of Defense (DoD) guidelines is adopted. Nonlinear dynamic analysis of the 3-D frame models is conducted for 6 different ground floor column removal scenarios, and the progressive collapse resistance of the buildings is investigated using chord rotations, and consequent internal forces of the members. The results show different quantitative levels of progressive collapse resistance for buildings with different heights and seismic zones.
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