Distortional buckling of channel beam-columns

Cold-formed lipped channel sections have been widely used in light gauge steel construction. Among the several possible buckling modes, the distortional buckling mode involving rotational deformation of the flange-lip combination about the flange-web junction is often the strength-governing mode. While many studies have been carried out on this buckling mode, the method of Lau and Hancock (J. Struct. Eng. ASCE 113 (1987) 1063), which models the phenomenon as the flexural-torsional buckling of the flange-lip combination with elastic restraints from the web appears to be the most effective in producing a relatively simple closed-form solution for design use. This article extends the Lau and Hancock method, which was developed for axially loaded columns to beam-columns subjected to combined axial compression and biaxial bending. Particular attention is paid to the case of axial compression in combination with uniaxial bending in the plane of symmetry. Numerical results from the present closed-form solution are compared with those from the finite strip method, showing a close agreement between the two. The numerical results also lead to a number of useful observations on the distortional buckling behavior of these beam-columns, which should be useful in the future development of a simplified solution for direct design use.