Study of seismic behavior of Drilled Flange (DF) connection with slot hole

Extensive damages in welded unreinforced flange (WUF) connections in 1994 Northridge earthquakes has led to the idea of using reduced beam section (RBS) connections and Drilled Flange (DF) connection to prevent brittle failure modes in welded joints. In this paper, the seismic behavior of DF moment resisting connection with slot holes as an easy-to-construct method for DF connection in seismic regions was investigated. DF connection is made by drilling at top and bottom beam flange along beam main axis to establish intentional weak point to reduce stress concentration at beam to column flange welded connection. In this investigation, Finite Element models which were validated with previous experiments were utilized to consider the effect of slot holes compared to circular holes on rupture potential of beam to column welded connection. The utilized FE models of DF connection with various geometric properties and different panel zone strength ratios were developed to investigate the optimum slot hole configuration and reduce the rupture potential at CJP groove weld. The results showed that the optimum drilled slot holes is able to shift the plastic strain at beam to column welded connection having the ratio of slot hole length to hole diameter (L/D) by up to 2. Using the latter holes configuration, the plastic strain at beam to column weld connection and around the holes decreases up to 28 and 70% respectively compared to corresponding values of DF connection with circular holes.