Cyclic Testing of Steel Moment Connections Rehabilitated with RBS or Welded Haunch

Abstract

The effectiveness of using the reduced beam section (RBS) and welded haunch for seismic rehabilitation of pre-Northridge steel moment connections was investigated through cyclic testing of six full-scale specimens—three of them incorporated lightweight concrete slabs. Test results showed that, unless the low-toughness E70T-4 groove weld was replaced by notch-tough weld metal, introducing RBS to the beam bottom flange alone could not prevent brittle fracture in the groove weld of the top flange. The presence of a concrete slab or removing steel backing only improved the cyclic performance slightly. Although two RBS specimens with weld replacement performed well, a new type of ductile fracture along the “k” line of the beam was observed. With E70T-4 groove welds in place, however, the welded haunch specimens performed better than the RBS specimens. No brittle fracture occurred when the slab was present. The composite slab only increased the beam positive flexural strength by about 10%.