Column axial load effects on the performance of skewed SMF RBS connections

Abstract

The selection of an appropriate seismic steel system (braced frame, moment frame, shear wall, etc.) is often influenced by architectural considerations. Moment frame configurations offer the most architectural flexibility, but are somewhat limited by a lack of guidance in the AISC seismic provisions regarding the use of non-orthogonal (skewed) beam-column connections. A recent study investigating laterally skewed moment frame connections indicates adequate seismic performance; however, it was observed that skewed connections increase the potential for column twist and column flange yielding. It is unclear how larger column axial loads present in medium-to-high-rise structures will affect the performance of skewed special moment frame connections.This study investigates the effects of column axial loads on skewed special moment frame connections containing reduced beam sections (RBSs). Detailed finite element analyses are used for all investigations, and several beam-column connection configurations are considered, representing: 3 beam-column geometries (shallow, medium and deep columns); 4 levels of skew at the beam-to-column connection; and 4 levels of applied column axial load. Results indicate that for axial loads less than 50% of the column axial capacity, there is little effect on connection rotation capacity. Beam-skew angle is the main contributor to resulting column twist. With the exception of the deep column geometries that experienced local flange buckling at 50% ΦPn axial load, increased column axial loads have little effect on resulting column flange yielding in skewed RBS moment connections.