Optimum drilled flange moment resisting connections for seismic regions

Extensive damage in welded unreinforced flange (WUF) connections in previous earthquakes has led to the idea of using reduced beam section (RBS) connections to prevent brittle failure modes in welded joints. Using a similar concept, drilled flange (DF) moment resisting connections are established by a series of holes drilling on the top and the bottom flanges of the beam to create an intentional weak area to shift nonlinear deformations. DF connections are very easy-to-construct and they can also prevent the premature local buckling modes in the reduced section of RBS connections. This study aims to improve the performance of DF connections to make them viable alternatives to RBS connections for ductile steel frames in seismic regions. A wide range of experimentally validated non-linear FE models are used to investigate the effects of different design parameters such as drilled flange hole locations, hole configurations, panel zone shear strength ratio and doubler plate thickness. The results indicate that there is an optimum location and configuration for the drilled flange holes, which can reduce by up to 40% the maximum Equivalent Plastic Strain and Rupture Index of DF connections. It is shown that using strong panel zones can also improve the seismic performance of DF connections by reducing stress concentrations at the CJP groove weld lines. The results of this study are used to develop optimum design solutions for DF connections, which should prove useful in practical applications.