Seismic Performance of Drilled Flange Beam to Column Connections for Ductile Steel Frames

Extensive damages in welded unreinforced flange connections (WUF) in the Northridge 1994 earthquake led to the development of reduced beam section (RBS) moment connections to prevent premature brittle failure modes in welded connections. This paper investigates the seismic performance of recently developed drilled flange (DF) moment resisting connections as a simple and efficient alternative to RBS connections in seismic regions. DF connections are established by a series of holes made by drilling on the top and the bottom flanges of the beam (along the main axis) to create an intentional weak point, which can prevent stress concentrations at the connection edges. In this study, a series of analytical studies based on previous experimental researches were carried out to evaluate cyclic behaviour of DF,WUF and RBS beam to column connections. Different drilled flange hole configurations and panel zone shear strength ratios were used to obtain an optimum design and prevent premature failure modes in complete joint penetration groove welds. Results show optimum configuration of drilled flange holes in DF connections reduce the rapture index and equivalent plastic strains of critical points on welded joints and comparing with WUF and RBS connections provide an appropriate seismic performance. The diameter of holes increase by distance from column face for the optimum configuration of DF connections.