Effects of Panel Zone Strength and Beam Web Connection Method on Seismic Performance of Reduced Beam Section Steel Moment Connections

This paper presents test results on eight reduced beam section (RBS) steel moment connections. The testing program addressed web connection type (bolted versus welded) and panel zone (PZ) strength as the key variables. Specimens with medium PZ strength were designed to promote energy dissipation from both PZ and RBS regions such that expensive doubler plates were not needed. Both strong and medium PZ specimens with a welded web connection were able to provide satisfactory connection rotation capacity for special moment-resisting frames. However, specimens with a bolted web connection performed poorly due to premature brittle fracture of the beam flange at the weld access hole. A plausible explanation for the higher incidence of base metal fracture in bolted web specimens was presented based on the measured strain data. Test results from this study and by others showed that panel zones could easily develop a plastic rotation of 0.01 rad without causing distress to the beam flange groove welds. At this deformation level, the amount of beam distortion (i.e., buckling) was about one half that developed in strong PZ specimens. A criterion for a balanced PZ strength that improves the plastic rotation capacity while reducing the amount of beam buckling is proposed.