Experimental Investigation of Instability-Free Welded Moment Connections With Simplified Weld Details

In capacity designed steel moment resisting frames, inelastic deformations are mostly concentrated in the steel beams and the column fixed ends of the first story. This design concept limits the participation of the column web’s panel zone in the energy dissipation. Experimental evidence from the early 1970s on beam-to-column connections with highly inelastic panel zone design philosophy demonstrated a stable connection hysteretic response. However, the 1994 Northridge earthquake highlighted extensive fractures on connections. These fractures were mostly attributed to: (a) the inadequate toughness requirements of the weld metals, (b) the presence of the weld backing bar after the execution of the complete joint penetration (CJP) welds at the beam flange-to-column face connection, and (c) the increased fracture potential associated with increased panel zone inelastic deformations. Current prequalified connections for seismic applications feature toughness-rated weld metals, rigorous treatment at the beam-to-column face welds as well as limited inelastic panel zone deformations. Motivated by the stringent weld toughness requirements of today’s welded moment connections, this study investigates the response of welded moment connections designed with highly inelastic panel zones and simplified weld details. Contrary to the current design paradigm, the proposed connection features a customised weld backing bar that remains in place after the execution of the CJP welds. The proposed concept was validated with full-scale beam-to-column connection tests that demonstrated a superior cyclic performance up until lateral drift demands of 10% rad. The test results indicated limited damage in the beams until lateral drift demands exceeding 6% rad.