A modified moment resisting connection for ductile steel frames (Numerical and experimental investigation)

The seismic behavior of steel moment resisting building systems are directly affected by the local behavior of beam to column connections. In welded connections, severe stress concentrations at the connection edge coupled with imperfections of the weld roots, may contribute to significant reduction of the seismic performance. In this study, a reduced plate section connection is proposed to shift the stress concentration from the connection face. With this aim, the authors propose drilled holes at cover plates to create an intentional weak point. Applying this method, the stress concentration at the weld roots is significantly diminished and the failure mechanism is altered from premature weld fracture to ductile plate yielding around the holes. This technique eliminates unfavorable local beam failures present in some similar methods and also forces the cover plate to behave as the replaceable fuse of the connection system. As it is revealed from the finite element and experimental investigations, the strength and ductility capacity of the considered connection type is significantly improved and the behavior of the connection seems to be far less dependant of the weld root quality. This might improve the structural reliability of the connection due to the guided failure mechanism.