Performance-based optimisation of long-span steel frames with multi-tier Y-bracing

This study presents a performance-driven optimisation framework for long-span steel frames equipped with multi-tiered Y-shaped bracing systems. An enhanced genetic algorithm is integrated with non-linear time-history analysis in the OpenSees software program to identify optimal bracing configurations, including tier numbers, relative heights and brace connection angles. The objective function minimises total structural weight while satisfying performance-based seismic constraints such as inter-storey drift limits, ductility demands and brace stability requirements. The numerical modelling incorporates non-linear material behaviour, brace buckling effects and validated connection mechanics to ensure realistic seismic response prediction. A case study of a 120 × 54 m steel frame located in a highly seismic zone demonstrates the effectiveness of the proposed methodology, achieving weight reductions of 12–21% while maintaining compliant seismic performance. The results highlight the potential of advanced evolutionary optimisation for improving the efficiency of long-span braced steel structures under seismic loading.