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• Numerical models for CFS built-up columns with spacers were developed. • Detailed nonlinear response of CFS built-up columns was investigated. • Predictions as per current Australian/European CFS standards were inconsistent. • Improved design equations were proposed for better/reliable strength predictions. This paper deals with the numerical investigation aimed to study the axial capacity and the nonlinear deformation response of pin ended cold-formed steel (CFS) built-up columns under monotonic axial loading, applied concentrically. The built-up sections were constructed by adequately spaced channel sections in a back-to-back configuration, connected through webs by means of connecting elements (CFS channels) called spacers. Self-driving screws were used as fasteners to assemble together the lipped channels and spacers. Finite element (FE) models were established and verified against the previously published built-up columns with similar configuration. An extensive parametric study was conducted by varying the key parameters like plate slenderness of the lipped channels, unbraced chord slenderness, and global slenderness in order to investigate their variation on the ultimate compression resistance of these built-up columns. The effective width method was used to determine the design strengths for these built-up columns using the AS/NZ Specifications and European Specification on cold-formed steel structures, which were later compared with the results obtained from the numerical parametric study. This study indicated that the provisions that are given in the current AS/NZS and European Specification in predicting the strengths of the built-up column with spacers had shortcomings. Therefore, new design equations for the reliable design strength predictions of the CFS built-up column composed of lipped channels with spacers were proposed. The incorporation of spacers curtailed the local buckling half-wave length, which improved the buckling resistance, predominantly in the columns failing by local buckling. [ABSTRACT FROM AUTHOR]

The present paper reports the numerical parametric study on the structural behaviour of battened cold-formed steel built-up box columns composed of four lipped angles. The validated numerical model with the experimental results reported by the author in the comparison paper was employed to carry out parametric studies to produce numerical data over a wider range of global column slenderness by varying the sectional compactness of the lipped angle section, batten spacing, and global column slenderness. The numerically derived results were employed to check the accuracy of the current design rules. The results of the assessment revealed the limitation of the current design rules in the prediction of the capacity of the CFS built-up battened box columns, which was mainly associated with the influence of unbraced chord slenderness and interconnector stiffness on the buckling behaviour. Therefore, improved design procedure was proposed in the framework of AS/NZS specifications (AS/NZ 4600:2018) and European standards (EN1993-1-3:2006) for the safe, less scattered and reliable design strength predictions of battened CFS built-up columns composed of four lipped angles. • The CFS built-up battened column composed of four lipped angles were investigated. • Lower unbraced chord slenderness can improve the axial strength by up-to 28%. • Also, it is more dominant in intermediate columns with lower sectional compactness. • AS/NZ-4600's upper limit for the relative unbraced chord slenderness is recommended. • Reliable design equations are proposed for CFS battened columns. [ABSTRACT FROM AUTHOR]