Structural behaviour of cold-formed steel built-up stiffened box sections under bending, axial compression and web crippling

Abstract

The use of cold-formed steel (CFS) built-up sections in engineering practice is widely gaining popularity due to their ability to provide sustainable solutions and optimised section design opportunities. The aim of this research is to investigate the structural performance of novel CFS built-up stiffened box sections under bending, axial compression and web crippling. In total, 38 experimental tests were conducted, covering bending tests, axial compression tests, and web crippling tests. The material properties of test specimens were obtained from tensile coupon tests. Nonlinear finite element (FE) models were also developed and validated against the experimental test results, which showed good agreement. The validated FE models were then used to conduct a parametric study involving a total of 1700 FE models to investigate the effects of key parameters on the resistance of such CFS built-up stiffened box sections. Because these new sections are very different from those for which current design guidelines in the standards comprising AISI S100 (2016), AS/NZS 4600 (2018) and EN 1993-1-3 (2006) have been developed, the comparison shows that the design strengths predicted by these standards are not a good predictor of the actual performance for all three loading cases. Based on the experimental and numerical results, modified design equations in the form of the Direct Strength Method were proposed for calculating the resistance of CFS built-up stiffened box sections. A reliability analysis was conducted to evaluate the feasibility of the proposed design equations. The results indicated that the proposed design equations can closely predict the resistance of CFS built-up stiffened box sections under bending, axial compression and web crippling.