Performance -Based Design Optimization of Steel Braced Frames Equipped with Shape Memory Alloys

A seismic optimization procedure based on nonlinear static analysis is utilized in this paper for topology optimization of shape memory alloy (SMA) braced frames (SMA-BFs) equipped with NiTi or Fe-based SMA braces. In the framework of performance-based seismic design, the seismic topology optimization is performed on ۵- and ۱۰-story SMA-BFs with NiTi or Fe-based SMA braces. A center of mass optimization algorithm is firstly implemented for the topology optimization of SMA-BFs. The cross-sectional area of columns and SMA braces and the length and placement of SMA braces are considered as size and topology design variables. The total relative cost of SMA-BFs is regarded as the objective function while considering constraints related to the construction, strength, and performance-based design in the optimization process. Subsequently, incremental dynamic analysis (IDA) is conducted to assess the seismic capacity of topologically optimal SMA-BFs. The collapse capacity of the optimal frames is evaluated by generating IDA and fragility curves according to the FEMA P۶۹۵ methodology and calculating adjusted collapse margin ratio (ACMR) values. The topologically optimal SMA-BFs with NiTi or Fe-based SMA braces are compared in terms of total relative cost and seismic safety. The results demonstrate the greater effectiveness of Fe-based SMA braces than NiTi braces in reducing the initial cost and improving seismic performance. The cost reduction by using Fe-based SMAs in ۵- and ۱۰-story SMA is up to ۸۹% and ۷۹%, respectively. Moreover, Fe-based SMA-BFs exhibit less peak story and residual story drift ratios and a more uniform distribution of lateral displacement over the height of the frame than NiTi braced frames. In addition, the optimal ۵- and ۱۰-story Fe-based SMA-BFs with the highest ACMR values, respectively, have ۴۶% and ۵۷% higher collapse capacity than optimal frames with NiTi. None of the ۱۰-story optimal NiTi SMA-BFs have acceptable collapse safety, indicating the need for using Fe-based SMAs, which provide larger recoverable strains.

کلیدواژه ها:

Performance-based design ، Topology optimization ، Steel braced frames ، Shape memory alloys