Axial load effects on flush end-plate moment connections

This numerical study focuses on the behavior of flush, end-plate, moment connections subjected to combined bending moment and axial force. Beams within frames are subjected to lateral loads (e.g. earthquake and wind) in the form of axial forces and bending moments. Thus, both must be considered in seismic design. In pitched-roof portal frames, sway frames or frames with incomplete floors, the level of axial forces in such joints may be significant. To partially fulfill this dual requirement, two distinctive flush, end-plate, moment connections were investigated: one to exhibit thick, connection-plate behavior and the other to exhibit thin, connection-plate behavior. The magnitude of the imposed axial force changes the failure mode. When subjected to reversed cyclic loading, distinctive behaviors between the two end-plate connection types were observed. During cyclic loading, in the axial compressive force phase, there was an increase in the ultimate bending moment, yielding bending moment, initial stiffness, and dissipated energy. Reductions occurred in all of these elements during the tensile axial force phase. As expected, the thin end-plate had notably higher ductility than the thick end-plate connection. In both connections, the maximum moment capacity under compressive axial force nearly equaled 30% of the beam’s section yield stress.