Experimental and numerical investigation on cold-formed steel built-up section pin-ended columns

The thorough test programme and numerical simulation were conducted to examine the buckling behaviour and loading capacity of cold-formed steel (CFS) built-up section members subjected to axial compression. In the test programme, the folded-flange channels of steel grades G500 and G550 were designed to assemble the novel built-up section compressive members. Two types of built-up sectional profiles were formed by composing channels with self-tapping screws. A total of twenty-two built-up section specimens with member lengths varied from 300 to 1500 mm were compressively loaded under pin-ended supports. The initial geometric imperfection measurements, test rig arrangement, loading procedure and test results were fully reported. In the numerical simulation, the extensive parametric study incorporating 224 CFS built-up section columns was performed to further generate numerical data covering a broad range of sectional configurations and geometric parameters. After that, the comparisons of loading capacities obtained from experiments and numerical simulation with nominal compressive strengths calculated on the basis of direct strength method (DSM) as stipulated in the Australian/New Zealand Standard and the North American Specification were conducted to assess the applicability of the current design rules for CFS built-up section members under compression. The results manifest that the codified DSM equations are generally conservative and fairly scattered to predict the resistances of the newly designed built-up section columns. The modifications of codified DSM equations are thus proposed in this study for the CFS built-up open and closed section compressive members. It is found that the modified DSM formulae reliably provide overall precise and less scattered strength predictions.