en Optimal design Optimal design پژوهشي Research <span style="font-size:12pt"><span style="line-height:normal"><span style="unicode-bidi:embed"><span new="" roman="" style="font-family:" times=""><span style="font-size:11.5pt">This study addresses the critical necessity for optimized structural design under fire conditions, where conventional methods often prove inadequate. The research focuses on the optimal design of two three and nine story steel moment-resisting frames, without fireproofing protection. The optimization objectives were to minimize the structural weight while satisfying constraints under critical fire scenarios. The key design constraints included inter-story drift and the demand-to-capacity ratio of structural members. The study employed the Enhanced Vibrating Particles System (EVPS) and the Accelerated Water Evaporation Optimization (AWEO) algorithms. A significant aspect of the investigation involved analyzing various severe fire scenarios to identify which parts of the structures are most vulnerable during a fire event. The results demonstrate the effectiveness of the proposed optimization framework in achieving a lightweight yet resilient structural design that meets regulations under extreme thermal loading.</span></span></span></span></span> Optimization design, Fire scenario, Structural weight, Unprotected steel moment frame 469 484 http://ijoce.iust.ac.ir/browse.php?a_code=A-10-6463-35&slc_lang=en&sid=1 A. Asaad Samani 180031947532846002859 180031947532846002859 No Department of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran S. R. Hoseini Vaez 180031947532846002860 180031947532846002860 Yes Department of Civil Engineering, Faculty of Engineering, University of Qom, Qom, Iran P. Hosseini hoseinivaez@qom.ac.ir 180031947532846002861 180031947532846002861 No Faculty of Engineering, Mahallat Institute of Higher Education, Mahallat, Iran