Experimental investigation of distortional-lateral torsional buckling interaction of single channels restrained by angle cleats

Framing systems composed of cold-formed steel lipped purlins as transversal members and connected to the main frame of cold-formed steel lipped channels as longitudinal members at its top flange, are widely used in steel construction. Restraints to restrict lateral-torsional and distortional buckling interaction, in the unbraced lengths are always required, which result in the cost of materials. The effects of bolting or welding the top flange of the longitudinal channels at the connecting area can always destabilize and cause premature failure of the member itself, followed by the collapse of the entire frame. For this reason, a cleat angle connection that prevents these effects is introduced to connect both members through their webs. The main aim of this experimental study is to investigate distortional-lateral torsional buckling interaction between two cleat-purlin connections when left unbraced. In this investigation, three different cross-sections of 300 × 75 × 20 × 3.0 mm, 300 × 65 × 20 × 3.0 mm, and 300 × 50 × 20 × 3.0 mm are employed. The span lengths of the test specimens are chosen from the signature curve obtained for each cross-section using the Constrained and Unconstrained Finite Strip Method (CUFSM). Coupon tests are carried out to determine the material properties of the lipped channel sections and four point loading is used for all the test specimens. The results from the experimental tests are compared to Direct Strength Method (DSM) (AISI S100-12).