S700 high-strength cold-formed steel built-up I-section stub columns: Testing, numerical modelling and design

This paper presents experiments and numerical simulations on S700 high-strength cold-formed steel (CFS) built-up I-section stub columns to investigate their cross-sectional behaviour and resistances. Each built-up I-section comprised two identical press-braked channel sections assembled back-to-back using G12–24TPI screws. The experimental programme was firstly conducted, including tensile coupon tests, measurements of initial local geometric imperfections and compression tests on twelve stub columns. Local buckling was identified for all the specimens upon testing, but with no failure found in the screws or the adjacent material. The numerical programme was then performed, where stub column finite element models were established and validated against the experimental results and parametric studies were conducted to generate further numerical data. The generated results were used to assess the applicability of the current European and American design guidelines for CFS structures to S700 high-strength CFS built-up I-section stub columns. Both the effective width and direct strength methods were considered and each was shown generally to yield consistent and accurate resistance predictions, though with some scope for improvement. Modified design provisions based on the Direct Strength Method were thus proposed for S700 high-strength CFS built-up I-section stub columns and shown to result in improved design accuracy.