Local buckling of S700 high strength cold-formed steel built-up I-sections subjected to combined compression and minor-axis bending

This paper presents an experimental and numerical study into the cross-section behaviour and strength of S700 high strength cold-formed steel built-up I-section stub columns under combined compression and bending. An experimental programme, including tensile coupon tests, measurements of initial local geometric imperfections and ten minor-axis eccentric compression tests, is first presented. A numerical modelling study, in which finite element models were developed, validated against the eccentric compression test results and used to conduct parametric studies, is then described. The experimental and numerical results were used to assess the applicability of existing European and North American codified design interaction curves to S700 high strength cold-formed steel built-up I-section stub columns under combined loading. The evaluation results revealed that (i) the codified effective width expressions yielded conservative end points for the design interaction curves (i.e. the cross-section resistances under pure compression and pure bending) and thus overly conservative ultimate load predictions, while (ii) the direct strength method resulted in more accurate ultimate load predictions, but still with conservative bending end points. Finally, a modified design expression was assessed and shown to provide improved predictions of ultimate loads over the design codes for S700 high strength cold-formed steel built-up I-section stub columns under combined compression and bending.