Study on Cold-Formed Steel Built-Up Square Sections with Intermediate Flange and Web Stiffeners

This paper describes a series of experiments conducted on cold-formed built-up square sections with intermediate flange and web stiffeners under axial compression with hinged end conditions. The specimens were formed using angle sections with edge, intermediate flange and web stiffeners connected by self- tapping screws. 27 columns were tested by varying the cross section dimensions of the specimen. The column lengths of the specimens varied from 840 mm to 2240 mm. Tensile coupon tests were conducted to find the material properties of the sections. Local buckling, distortional buckling, flexural buckling and interaction of these buckling were observed during the test. The column strengths obtained from the experiments were compared with the design strength calculated using direct strength method (DSM) in the North American Specification for cold-formed steel structures. The reliability of the DSM method was evaluated using reliability analysis. It is shown that, strengths calculated by using direct strength method are reliable and slightly unconservative. Finally, a design recommendation was proposed for DSM to calculate the ultimate strength of cold formed built-up square sections with intermediate flange and web stiffeners.