Post-repair seismic assessment of steel MRFs prone to soft-story mechanisms using rocking walls: cost-performance analysis

Abstract Coupling a rocking wall with a moment-resisting frame (MRF) is a viable and practical solution to mitigate the risk of soft-story mechanisms. However, little research has been conducted to investigate the retrofitted MRFs’ post-repair performance and the cost-performance of intervention. This research conducted a numerical parametric study to assess the cost-effectiveness of the retrofitting approach and shed light on the seismic performance of the retrofitted frames. To this end, three steel benchmark MRFs (i.e., three-, six-, and nine-floor height implicitly representing low-, mid- and relatively high-rise buildings, respectively) were selected, and pinned constraints were applied to the end of frames columns to induce the soft-story mechanism. Through coupling a base-rocking wall to the benchmark MRFs, thirteen different retrofitted scenarios were created considering different height and stiffness for the wall. Risk and performance assessment and seismic fragility analysis of the retrofitted scenarios were conducted by performing pushover and incremental dynamic analysis. The cost of retrofitting was estimated for each scenario, and a performance index was introduced to evaluate the efficiency of retrofitting intervention and, after that, to conduct a cost-performance analysis. The results showed that the retrofitting approach considerably decreases residual drift, especially in low-rise buildings. The best performance was achieved in low-rise buildings, and the retrofitting efficiency decreased by increasing the building’s height. Increasing the attached wall’s height has a stronger effect on reducing the retrofitted scenarios’ collapse probability. Besides, increasing the height of the attached wall has a more pronounced effect than stiffness in improving the safety and inter-story drift uniformity of retrofitted scenarios. In terms of performance, for low-rise buildings, employing a less stiff wall leads to a better result, although for mid- and high-rise buildings, scenarios with longer and stiffer wall greatly outperform others. In terms of cost-effectiveness, using a shorter and less stiff wall outperforms other scenarios by a large margin.