Interaction between critical torsional flexural and lip buckling in channel sections

The energy method is first used to find the critical stress for anti-symmet ric lip buckling, for any given half-wave length, including the preferred h alf-wave length. The energy method is then applied to describe the critical buckling interaction between the torsional-flexural and anti-symmetric lip modes, and its effect in reducing the critical buckling stress. The result s obtained by the energy solutions are validated by those obtained by finit e element eigenvalue analyses. This paper gives closed form equations which enable the interactive critical stress to be calculated for a member of gi ven geometry. Reductions of up to 24% in the smaller of the individual buck ling stresses have been found for the examples studied. A further paper wil l describe how the interactive critical stress can be incorporated in a des ign method for finding the resistance of the member. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.