DISTORTIONAL BUCKLING LOADS OF COLD-FORMED LIPPED CHANNELS

Distortional buckling is an important buckling mode governing the stability design of cold-formed steel channels. This paper presents a set of simple formulae for the elastic distortional buckling loads of cold-formed lipped channels subjected to eccentric compression or pure bending. These formulae are derived from an existing theoretical solution on the basis of parametric studies and with the assistance of finite strip buckling analyses. Firstly, results from parametric studies on the distortional buckling loads for the two extreme load cases of axial compression and pure bending are presented and interpreted, leading to approximate expressions for the buckling half-wavelength, in which a modification factor is included to account for the effect of the shear and distortional deformation of the flange section. The rotational restraint, provided by the web to the flange during buckling deformation, is then examined, and an enhanced approximate expression considering the rotational restraint is proposed. Based on these approximate expressions, two simplified formulae are finally presented to predict the elastic distortional buckling loads of cold-formed lipped channels subjected to eccentric compression and pure bending respectively. These formulae are shown to be accurate through comparisons with results from finite strip buckling analyses. They are easy to apply, and may be directly used in practical design and incorporated into future design codes and guidelines.