The influence of mass irregularity is examined for an eight-storey concentrically braced steel frame with different setback configurations. Three height locations of mass discontinuity and two ratios of seismic weight were considered. A regular structure was also studied for comparison. Both the equivalent static load method and the response spectrum analysis method were used in design. Mass irregularity was found to have limited impact on collapse prevention when static analysis was used. For irregular structures exhibiting lower performance than the regular frame, the response was improved by adopting dynamic analysis but not to the level achieved with the regular structure.
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