Evaluation of Sloped RBS Moment Connections

Abstract

AISC 358 provides steel connections that are prequalified for use in special and intermediate moment frames (SMF and IMF). Implicit in this standard is that the beam and column are orthogonal to each other in the elevation of the frame. To evaluate the effects of a sloped connection considering an angle of deviation from orthogonal of 28°, two reduced beam section (RBS) moment connections with W36×231 beam and W36×302 column were cyclically tested. Although both specimens met the acceptance criteria of AISC 341, brittle fracture of top flange weld soon followed, a failure mode not typical of an RBS connection. Finite-element analysis demonstrated that the strain demand was not symmetric between two flanges. The strain demand at the heel location was higher than that at the opposite flange and increased with the angle of the slope. The AISC 341 welding requirement for steel backing removal, back-gouging, and fillet reinforcing should be linked to the heel and toe locations, not the top and bottom flanges, for a sloped connection. A preferred RBS configuration where the center of the RBS is perpendicular to the longitudinal axis of the beam, not parallel to the column as was used in the test specimens, was proposed.