Structural performance of cold-formed steel built-up section beams under non-uniform bending

The experimental investigation and numerical analyses are presented in this paper on cold-formed steel built-up open and closed section beams under either uniform or non-uniform minor axis bending. To the best knowledge of the authors, this is the first study devoted to exploring the effect of non-uniform bending on the behaviour of cold-formed steel built-up section flexural members. In the experimental investigation, the built-up section specimens were assembled by fastening two individual channels as press-braked from G500 and G550 steel sheets. Four-point bending tests of eighteen specimens with varying moment distributions were conducted to examine the flexural performance of the built-up section members experiencing uniform bending and moment gradients. In the numerical simulation, the finite element models were established for the built-up section flexural members and calibrated against the experimental results in terms of moment-deflection response, failure mode and moment capacity. Based on the validated finite element models, additional 300 numerical data of the built-up section beams under uniform and non-uniform minor axis bending were generated through a parametric study. Subsequently, the comparison of moment capacities obtained from the 18 tests and 300 numerical predictions with nominal strengths was carried out to evaluate the appropriateness of the current direct strength method as prescribed in the North American Specification for the built-up section flexural members. Aimed to achieve more suitable strength predictions, the modified design rules were recommended in this study and proven to be generally reliable as well as accurate for the design of cold-formed steel built-up section beams.