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

The effect on connection performance of the potentially large catenary forc-es 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 ca-tenary 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 com-bined 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, par-ticularly, on the capacity to fully develop the catenary effect, is finally in-vestigated.