Experimental investigation of cold-formed steel built-up closed section columns with web stiffeners

This paper presents an experimental investigation conducted on cold-formed steel built-up closed section columns with web stiffeners. To fabricate a built-up closed section, the single open sections were formed by brake press operation with high strength steel plate of thickness of 0.48 and 1.0 mm, then two identical sections were connected together face-to-face by self-tapping screws. After the measurements of material properties and the initial geometric imperfections were made, the built-up closed section specimens with inward or outward stiffeners at the web were tested between fixed-end boundary conditions with various column lengths ranging from 300 to 3200 mm. The tested specimens were failed by local buckling and interaction between local and flexural buckling. The ultimate strengths of the specimens were used to compare with the column strengths predicted using direct strength method, which is adopted in the North American Specification and Australian/New Zealand Standard for cold-formed steel structures. In addition, a reliability analysis was performed for this design method to access its reliability with cold-formed steel built-up closed section compression members. The results show that the direct strength method is applicable for the design calculation of cold-formed steel built-up closed section compression members with web stiffeners.