Performance-Driven Optimization of Long-Span Steel Frames with Multi-Tiered Y-Bracing Using an Extended Genetic Algorithm

Y-shaped multi-tiered bracing systems are widely used in steel frames located in seismic zones due to their high ductility, stable energy dissipation, and architectural adaptability. However, limited research has addressed their optimal configuration in long-span structures. This study fills that gap by developing a genetic algorithm (GA)-based optimization framework using MATLAB and OpenSees to minimize structural weight while ensuring seismic performance. The optimization targets include the number of bracing tiers, their heights, and connection angles. A case study of a 120 × 54 m, 20 m-high steel frame located in a high seismic zone was analyzed through nonlinear time history analysis based on American seismic codes. Results show a structural weight reduction of 12%–21%, with optimal brace angles ranging from 37° to 52°. The proposed method improves both structural efficiency and architectural integration, providing a practical solution for the seismic design of long-span steel frames with Y-shaped multi-tiered bracing.