Collapse resistance analysis of steel frame structures with varying spans using component models

Abstract

This study aims to expand the current research on the progressive collapse resistance of steel frame structures with welded-flange bolted-web connections (WBCs) by investigating both symmetric and asymmetric structures with varying spans. It focuses on developing and validating a component model for WBCs using relevant experimental data. The collapse resistance of full-scale substructures and steel frame structures with varying spans is comprehensively analyzed and evaluated. The main findings are as follows: A simplified two-bar spring model is proposed for WBCs, representing their resistance, internal force, and large deformation responses. Symmetric substructures exhibit higher bearing capacity and deformation due to the effective collaboration between the two-span beams, whereas the substructure’s resistance progressively decreases as the span length increases. Asymmetric substructures exhibit initial local damage in the beam with higher linear stiffness, resulting in asymmetric trends for internal forces of the two-span beams. The beam with higher linear stiffness plays a dominant role in controlling the anti-collapse performance of asymmetric substructures. A proposed formula for accurately and reliably calculating the ultimate rotation of WBCs was put forward. The critical loads of steel frame structures decrease as the linear stiffness ratios of the two-span beams decrease. Accurate fitted formulas are provided for estimating the critical load of steel frame structures with varying spans, offering insights into their capacity to resist progressive collapse when the middle column is removed. Under critical load conditions, steel frame structures primarily resist external loads through bending and vierendeel mechanisms, with minimal contribution from the catenary mechanism.