Performance-based optimum seismic design of self-centering steel moment frames with SMA-based connections

Shape memory alloys (SMAs) have found several applications in earthquake-resilient structures. However, because of high material costs, their implementation on industry projects is still limited. Developing design approaches that minimize the use of expensive SMAs is critical to facilitating their widespread adoption in real structures. This paper proposes a performance-based seismic design optimization procedure for self-centering steel moment-resisting frames (SC-MRFs) with SMA-bolted endplate connections. The topology optimization uses a metaheuristic algorithm to minimize the frame's total cost, including the initial construction and expected repair costs. The design variables are the steel beam and column sections, SMA connection properties, and the topology of the SMA connections. Different constraints are considered, such as the constructability of the chosen steel sections, member strengths, performance-based design, Park-Ang damage index, and strong-column weak-beam requirements. Furthermore, the seismic safety of optimal designs is assessed by calculating adjusted collapse margin ratios according to FEMA-P695. An illustrative optimization study using three- and nine-story SC-MRFs is presented. The optimal SC-MRFs are then assessed in terms of cost and seismic performance. The results confirm the effectiveness of the proposed optimum design, which minimizes the use of SMAs while ensuring improved seismic performance. The case studies show that the optimal placement of SMA connections can reduce the total cost by up to 71% and 61% for the three- and nine-story SC-MRFs, respectively, compared to nonoptimal frames. Moreover, the optimal SC-MRFs exhibit more uniform drift distributions, lower residual story drifts by up to 96%, and increase collapse capacity by up to 102%.