Nonlinear response of high-strength cold-formed steel built-up members subject to cyclic compression

• The cyclic behavior of G550 high-strength cold-formed steel built-up compression members was studied through both experimental and numerical methods. • Sections with higher member and section slenderness showed more rapid degradation in strength and stiffness after reaching the peak stage. • Higher section slenderness resulted in increased axial ductility in closed built-up sections. • Increased member slenderness led to a reduced energy dissipation capacity. Cold-formed steel (CFS) built-up sections have attracted attention for their enhanced strength and stability over single channels. While previous research has focused on the axial behaviour of CFS built-up sections under monotonic compression, studies on their cyclic performance are limited. Cyclic actions can affect the material properties and potentially cause early failure, making it crucial to understand the cyclic behaviours of CFS built-up sections. This research examined the cyclic responses of G550 high-strength CFS built-up compression members through experimental and numerical investigations. Different built-up sections, such as open-lipped built-up sections (OL series) and closed-unlipped built-up sections (CU series), composed of various section sizes and screw spacings, were studied. These proposed parameters assessed the influence of the member slenderness and section slenderness on the CFS built-up sections with thin-walled profiles. The results demonstrated that the cyclic actions have little influence on the structural performance of the CFS built-up sections at the pre-peak stage. At the post-peak stage, a faster degradation in strength and stiffness was observed for specimens with greater member slenderness and section slenderness. Moreover, the increase in section slenderness leads to higher axial ductility for the CU series but minimal influence on the OL series. Furthermore, a greater member slenderness leads to smaller energy dissipation capacity, especially for the specimens with smaller section slenderness. The OL series is recommended to be designed as a strength-control element that provides structural stability and integrity, such as primary columns. In contrast, the CU series can be used as the sacrificial element to dissipate energy, such as lateral bracing in the framing system, to minimise the risk of catastrophic collapse subject to extreme loadings such as typhoons or earthquakes.