Tests and design of built-up section columns

Built-up sections are increasing in popularity as structural elements in the cold-formed steel (CFS) industry. They are composed of two or more component sections connected by discrete fasteners, most commonly screws or bolts, typically spaced evenly along the length. Conventionally, two singly symmetric sections are connected to form a doubly symmetric cross-section. However, this study focuses on sections formed by three or more lipped channel C-sections, which are being used more frequently in recent years. The paper details an experimental investigation of the strength and behaviour of screw-fastened built-up columns with variable lengths. The cross-section configurations include singly-symmetric columns composed of three channel sections (3C), for which the failure mode was either local, distortional and/or flexural-torsional modes, and doubly-symmetric columns formed by four sections (4C) which failed in local and/or flexural buckling modes.