Cyclic stability criteria for steel moment connections with reduced beam section

A statistical study was performed to evaluate the cyclic instability of steel moment connections with reduced beam sections (RBS). Based on test results of 55 full-scale specimens, regression analyses were performed to evaluate the relationships between response quantities (plastic rotation capacity and strength degradation rate) and slenderness parameters for buckling. Regressions analyses performed on a linear and a nonlinear model showed that the response quantities are highly dependent on the slenderness ratio of web local buckling, not lateral-torsional buckling. Relationships between the response quantities and the slenderness ratios for both web and flange local buckling modes were developed. For a target plastic rotation capacity, the limiting width-thickness ratio of web local buckling for seismic design is presented. An investigation of the concrete slab effect showed that it would increase both the strength and plastic rotation capacity of the RBS beams under positive bending. Under negative bending, however, the slab only enhanced the plastic rotation capacity slightly, implying that the slab cannot be counted on to brace the beam bottom flange.