Experimental Evaluation of Cyclically Loaded Reduced Beam Section Moment Connections

Abstract

This paper describes an experimental study on radius cut reduced beam section (RBS) moment connections for use in seismic resistant steel moment frames. The effects of panel zone strength, composite behavior with a concrete slab, and the beam web-to-column flange connection were specifically addressed in these tests. In total, eight double-sided specimens were designed, fabricated, and tested in this study, providing data for sixteen individual RBS connections. Each specimen was subjected to a standard quasi-static cyclic load pattern. Overall, the specimens performed well with seven of the eight achieving total (elastic plus plastic) story drift ratios of at least 0.04 radians in magnitude before experiencing 20% strength degradation. The other test was stopped due to out-of-plane instability after being loaded to 0.03 radians of total story drift. Comparison of the response of specimens with strong panel zones, balanced panel zones, and weak panel zones relative to beam strength led to the conclusion that weak panel zones allow for the most stable hysteretic response at large drift levels. Inclusion of a composite slab in these tests appeared to stabilize the beams against lateral torsional buckling with no consistently detectable increase in the strains in the bottom beam flange. Welding the beam web to the column flange seemed to decrease the likelihood of weld fracture in these specimens.