Effect of secondary warping on lateral buckling

In the lateral buckling analysis of beams, secondary warping or thickness warping is usually ignored. For angle and tee beams where the contour warping is zero, the secondary warping is shown to have a significant effect on the lateral buckling load. Simply supported tee beams under moment gradient are investigated. Angles and tee sections are shown to be prone to ‘localized’ torsional buckling and a simple formula is presented to calculate this load. The Laplace equation for the warping distribution is solved by a direct application of finite element plate bending elements to obtain more precise values for the secondary warping in tee sections, and this compares well with approximate formulae available in Bleich (1952).