en Optimal design Optimal design پژوهشي Research <span style="font-size:11.5pt"><span style="font-family:&quot;Times New Roman&quot;,serif">This study investigates the optimal design of steel frames with chevron bracing systems and semi-rigid connections using a performance-based design framework and metaheuristic optimization algorithms. Optimization effectively balances design performance and cost in structural engineering. The three algorithms employed were selected based on their proven application to similar optimization problems, enabling identification of the most suitable approach for the present case. Chevron bracing offers architectural benefits and enhances lateral stiffness and strength. However, unbalanced vertical forces from tension and compression braces under seismic loading require nonlinear analysis for reliable capacity estimation. To address this, pushover analyses with multiple lateral load patterns are performed to capture responses consistent with performance-based design principles. Connection behavior plays a decisive role in the global performance of steel frames. Conventional assumptions of rigid or pinned connections oversimplify reality and produce inaccurate predictions. In this study, semi-rigid connections are modeled with greater fidelity by incorporating column panel zones (CPZs) and gusset plate stiffness at bracing joints. CPZs significantly influence energy dissipation and deformation, while gusset plates may contribute up to 40% of connection rotational stiffness. Neglecting these effects can underestimate interstory drift and misrepresent hinge mechanisms. Results show that accounting for initial connection stiffness improves both accuracy and cost efficiency. For 10- and 15-story frames, structural cost were reduced by about 7%, underscoring the value of realistic connection modeling in optimal design.</span></span> Braced steel frame, chevron bracing system, performance-based design, metaheuristic algorithms, semi-rigid connections 63 91 http://ijoce.iust.ac.ir/browse.php?a_code=A-10-6463-46&slc_lang=en&sid=1 K. Farzad keyvan.farzad@iau.ac.ir 180031947532846002895 180031947532846002895 Yes Department of Civil Engineering, Ur.C., Islamic Azad University, Urmia, Iran M. Javanmard Barbin 180031947532846002896 180031947532846002896 No Department of Civil Engineering, Ur.C., Islamic Azad University, Urmia, Iran