Effect of Steel Moment-Frame Connections on Robustness of Steel Frames Against Progressive Collapse

The effect on connection performance of the potentially large catenary forces that can develop during progressive collapse has not yet been adequately studied in the literature. While undergoing large deformation, the load-resistance mechanism shifts from the traditional flexural mechanism to a catenary mechanism, and the tensile axial force becomes the prevailing factor in structural response. Therefore, also seismically designed beam-to-column connections may not resist progressive collapse since they are subjected to moment, shear, tension, and high ductility demand. This paper investigates the effects of steel moment-frame connections on the progressive collapse resistance of steel moment-resisting frames. To this aim, different seismically designed special moment frame connections (namely, Welded Unreinforced Flange-Bolted Web (WUF-B), welded flange plate (WFP), Welded Top and Bottom Haunch (WTBH), bolted flange plate (BFP), Reduced Beam Section (RBS) connections) are investigated. Their nonlinear behavior under combined axial force and bending moment is evaluated using a refined FEM model. The progressive collapse performance of a reference building is evaluated using both nonlinear static and dynamic analyses. The effect of the connection performance on the progressive collapse behavior and, particularly, on the capacity to fully develop the catenary effect, is finally investigated.