Bending response of cover-plated CFS built-up sections: Testing, numerical parametric analysis and design

Abstract

This study investigates the bending response of cover-plated cold-formed steel (CPCFS) built-up sections comprising of plain channel members under pure bending achieved through four-point loading, both experimentally and numerically. Channels were appropriately spaced back-to-back and screw-fastened at the flanges using cover-plates on the tension and compression sides. This novel design for the CPCFS built-up section combines the benefits of box-profile (closed sections) and I-profile (open sections), including high strength-to-weight ratio, simplified fabrication, and enhanced torsional rigidity. Eight CPCFS built-up sections with different cross-sectional aspect ratios were tested for bending about the major axis under simply supported end conditions. Flexural strengths, failure modes, and moment-curvature plots were discussed. Subsequently, a finite element model was developed in ABAQUS and validated against the test response obtained. Afterwards, an extensive parametric analysis was conducted to assess the variational effect of aspect ratios, cross-sectional slenderness, and plate slenderness on the ultimate moment capacity of the CPCFS built-up beams. Finally, the adequacy of the codified Continuous Strength Method (CSM) and Direct Strength Method (DSM) for CPCFS built-up beams was evaluated. Generally, it was observed that the flexural strengths predicted by the codified CSM and DSM for CPCFS built-up beams were unconservative and conservative, respectively. Suitable modifications were proposed to both DSM and CSM to accurately predict the flexural strength of CPCFS built-up beams, which were eventually verified through a reliability analysis.