Behaviour and design of cold-formed steel C-sections with cover plates under bending

This paper presents an experimental, analytical and numerical investigation on the correlation between non-dimensional slenderness and pure bending strength of stiffened cold-formed steel as a construction material. Cover plates with three different thicknesses (1.6, 2 and 4 mm) were incorporated to evaluate the slenderness effects on flexural performance of C-sections installed at top flanges only as it would be the predicted location for local and distortional buckling. The lateral supports were provided to prevent lateral torsional buckling in the experiment investigation. Application of the Direct Strength Method led to an extensive parametric study to investigate the moment capacity and buckling modes of specimens with different cover plate thicknesses. A nonlinear finite element model was developed and verified against the test results in terms of failure buckling modes. Moreover, a newly recommended non-dimensional slenderness of DSM in order to address the plastic strength for stocky sections was proposed in this paper. The results explicitly showed that the cover plate reduced the non-dimensional slenderness which resulted in improved buckling capacity. Also, it was concluded that the design strengths predicted by the current DSM in accordance with the American specification guideline, AISI, was conservative for sturdy sections as these sections can develop plastic moment.