Numerical investigation and design of cold-formed steel built-up section beam-column members under moment gradients

This paper presents the numerical investigation and design of cold-formed steel (CFS) built-up section beam-column members experiencing non-uniform minor axis bending. Detailed considerations of material nonlinearity and initial imperfections were involved in developing finite element models of the thin-walled built-up section members undergoing eccentric compression. The finite element models calibrated against the existing experimental results were then employed for a parametric study. Numerical predictions of 279 built-up section beam-columns over a broad spectrum of cross-sectional geometries and moment distributions along the member length were obtained in this investigation. For the built-up open and closed section members included in the numerical analyses, non-uniformly distributed moments resulted in the strength enhancements by average of 39% and 37%, respectively. Furthermore, based on the 279 numerical predictions obtained in this investigation and 91 data collected from the literature, the nominal strengths predicted by the design rules codified in the current standards and proposed in the previous studies were examined for the CFS built-up section beam-column members with end moment ratios ranging from −1.0 to 1.0. Underpinned by the assessment results, design recommendations and modified design rules were provided for the CFS built-up open and closed section members undergoing synchronous axial load and non-uniform minor axis moment, respectively.