SIMPLE FORMULAE FOR DISTORTIONAL BUCKLING LOADS OF COLD-FORMED LIPPED CHANNELS SUBJECTED TO MAJOR AXIS BENDING

This paper presents a set of simple formulae for the elastic distortional buckling load of cold-formed lipped channels subjected to major axis bending. These formulae are derived on the basis of an existing theoretical solution in conjunction with numerical results obtained using the Generalized Beam Theory (GBT). Firstly, numerical results for the distortional buckling loads of forty five sections from GBT analyses are presented and interpreted, leading to an approximate expression for the buckling half-wavelength. The rotational restraint, provided by the web to the flange during buckling deformation, is then examined to arrive at an accurate approximate expression. An approximate expression for the modification factor accounting for the effect of the shear and distortional deformation of the flange section is next developed to improve the accuracy of theoretical predictions of distortional buckling loads. Based on these approximate expressions, a simplified equation is finally presented to predict the elastic distortional buckling load of cold-formed lipped channels subjected to major axis bending. The accuracy is shown through comparisons with results from GBT analyses. The proposed formula is easy to apply, and may be directly used in practical design and incorporated into future design codes or guidelines.