This paper examines the effects of torsional post-buckling on the strengths of tee section steel columns which fail in local, torsional or flexural modes. Flexural-torsional buckling is not considered, but the post-buckling movement of the effective centroid and the ensuing bending effects are.
It is shown that the elastic torsional buckling loads of tee section columns are greater than or equal to their local buckling loads, while their torsional and local post-buckling behaviours are very similar. Design codes which require separate account to be taken of torsional and local buckling duplicate their allowances for these effects and ignore the torsional post-buckling strength.
It is found that the effective section method used in most codes to allow for local buckling and post-buckling is probably conservative, and that allowances for the movement of the centroid are over-conservative.
It is suggested that close design approximations for the strengths of tee section columns can be obtained by ignoring the effects of movement of the centroid and torsional buckling, and instead using the lower of the axial compression section resistance determined for the effective section and the member resistance calculated by ignoring local buckling.
Author: N.S. Trahair, University of Sydney Research Report R936.