Amirkabir University of Technology AUT Journal of Civil Engineering 2588-2899 10 3 2026 07 01 Progressive Collapse Assessment of Steel Moment Frames with the RBS Connections by Considering Different Seismicity and Ductility Levels 227 242 6077 10.22060/ajce.2026.24128.5919 EN Behzad Rezaie Department of Civil Engineering, Amirkabir university of technology, Tehran, Iran Payam Tehrani Department of Civil Engineering, Amirkabir university of technology, Tehran, Iran 0000-0001-5171-4239 Behrouz Behnam Department of Civil Engineering, Amirkabir university of technology, Tehran, Iran 0000-0002-8348-4711 Journal Article 2025 05 05 Extreme events such as earthquakes can damage vertical load-bearing elements, particularly columns, potentially triggering progressive collapse in building systems. This vulnerability is more pronounced in steel moment-resisting frames due to their relatively limited redundancy. Although previous studies have investigated the progressive collapse behavior of moment frames under different seismicity and ductility levels, the influence of key seismic design parameters—such as reduced beam section (RBS) connections, ductility level, and the strong column–weak beam (SC–WB) principle—remains insufficiently understood, with conflicting findings reported in the literature. This study aims to systematically evaluate the role of these seismic design parameters in the progressive collapse response of steel moment frames. To this end, 5-, 10-, and 15-story buildings were designed for low, medium, and high seismicity levels, considering both intermediate and special moment frames with RBS connections. A total of 340 column removal scenarios were analyzed using nonlinear dynamic analysis in OpenSees, employing a lumped plasticity modeling approach. Structural performance was assessed in terms of damage percentage index (DPI), ductility demand, and vertical nodal displacement. The results indicate that ductility demands in all cases remained within code-prescribed performance limits, suggesting that RBS connections provide adequate robustness against progressive collapse under column removal scenarios. However, neglecting the SC–WB principle significantly increases ductility demand and vertical displacement, by up to 1.83 and 1.56 times, respectively, in critical cases. Furthermore, the ductility level of the lateral-resisting system strongly influences structural response, particularly in medium seismicity conditions, where weaker member sizes lead to reduced robustness and amplified deformation demands. https://ajce.aut.ac.ir/article_6077_58182b82110146887c02dbd78719e3d5.pdf