Buckling capacities of axially loaded, cold-formed, built-up C-channels

Cold-formed, built-up members are common compression elements in cold-formed steel joists, and these built-up members are susceptible to unique buckling behaviors. Built-up member design is addressed in Section C4.5 of the American Iron and Steel Institute 2001 Specification. Over 150 experimental compression tests on closed-section, built-up members formed of intermediately welded c-channels were conducted, and these experimental values were compared to theoretical buckling capacities based on the Section C4.5 modified slenderness ratio. Use of the modified slenderness ratio was exceedingly conservative. Capacities based on the unmodified slenderness ratio and C4.5 fastener and spacing provisions were consistently conservative.