This paper proposes an improved method for determining the gravity resistance of a moment resisting beam-column assembly following an interior column loss. The proposed method accounts for the connection's damage evolution and for the catenary mechanism developed by the assembly as it deflects downward. Through a full-scale laboratory test and finite element simulations, the complete responses of moment resisting beam-column assemblies including the connection's damage evolution are investigated under different beam span-to-depth ratios. The welded unreinforced flange-bolted web (WUF-BW) connection method is used for its robustness in developing the catenary action. It is found that, under the same span-to-depth ratio, beam-column assemblies exhibit similar normalized load-rotation relationships, even with different beam depths. The assembly with a larger span-to-depth ratio is able to develop the gravity resistance earlier, and provides a higher ultimate resistance by developing a more effective catenary mechanism. On the other hand, the assembly with a smaller span-to-depth ratio exhibits a more ductile response. A simplified curve model of the gravity resistance development of a moment beam-column assembly with damage evolution has been proposed for a convenient assessment of the progressive collapse resistance following a central column loss.