Torsional and flexural torsional buckling — A study on laterally restrained I-sections

Torsional and torsional–flexural buckling of columns under axial compression–as defined in the Eurocode 3-1-1(2005)–may practically occur in axially compressed I-sections, which are laterally restrained so that weak axis flexural buckling is prevented and buckling is initiated by torsional deformation about the axis of lateral restraint. The present study is focussed on the development and representation of specific buckling curves for this type of buckling mode. This is based on numerical simulations taking into account material nonlinearities as well as geometric imperfections and residual stresses. The study not only illustrates the typical buckling curves for torsional buckling, but also the transition from torsional buckling to main axis flexural buckling when the column length increases. It also shows that the use of weak-axis buckling coefficients for torsional buckling–as given in the rules of Eurocode 3-1-1–may lead to rather conservative results in many cases.