Enhancing the pushover procedure for steel setback frames: a comparison of non-adaptive methods and a proposed simplified envelope procedure

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Nonlinear static procedures (NSPs) are essential for preliminary seismic assessment; however, conventional procedures based on the fundamental mode of vibration often show limitations in evaluating vertically irregular structures where higher modes exert a significant influence. This study investigates seven advanced NSPs using 15 two-dimensional (2D) ten-story steel setback frames, comparing target displacements and storey drift profiles against nonlinear time-history analysis (NTHA) results. For the investigated structural configurations, findings reveal that while the extended capacity spectrum method (ECSM) and improved upper bound (IUB) methods provide excellent accuracy, other sophisticated procedures offer no significant gain over conventional methods. Based on the results of this study, a simplified envelope procedure is proposed to improve conventional pushover analysis by combining first-mode and uniform load patterns with an improved upper-bound target displacement. The evaluation demonstrates promising results, although the precision of the proposed procedure diminishes under pronounced higher-mode effects in severe setback frames. The proposed method offers a practical, easy-to-implement alternative for the seismic assessment of mid-rise steel setback frames.