Influence of Beam-to-Column Connection Behavior on the Progressive Collapse Resistance of Steel Frames Considering Catenary Action

This study investigates the influence of beam-to-column connection behavior on the progressive collapse resistance of steel moment-resisting frames (MRFs), considering catenary action. When a column is removed due to accidental or extreme events, the load-carrying mechanism transitions from flexural to tensile catenary action. This transformation subjects connections to significant axial tension in addition to bending moments, potentially reducing their rotational capacity. Despite extensive research on seismic connection performance, the combined effects of bending and axial tension remain insufficiently explored. To address this gap, two commonly used connection typologies, the Welded Flange Plate (WFP) and the Reduced Beam Section (RBS), were investigated through detailed finite element modeling to capture their nonlinear response under increasing axial forces. The connection models were integrated into global building analyses to evaluate the progressive collapse response following column removal scenarios. Nonlinear static and dynamic analyses were conducted on a three-story steel MRF designed according to Eurocodes. Results demonstrate that catenary action significantly alters the force-deformation behavior of beam-to-column connections, leading to reductions in plastic bending and rotational capacities. The conventional design assumptions (such as rigid and full-strength connections) and the use of a standard dynamic amplification factor were found to lead to inaccurate predictions of structural response. The findings highlight the necessity of explicitly modeling connection nonlinearities and suggest that refined dynamic amplification factors and detailing strategies are required to ensure the robustness of steel frames subjected to column loss.