Stiffener Effects on Torsional Buckling of Columns

Torsional stability of centrally loaded columns, having doubly symmetric sections, often is critical. The torsional stability can be improved by locally placed plates connecting the different flanges of the column partially preventing the section to warp and thus, improving the contribution of warping to the stability resistance. The warping restraint stiffness is used in the determination of the transitional conditions at the stiffeners. These together with the boundary conditions and the linear, homogeneous differential equations formulates the eigenvalue problem. The eigenvalue problem is solved in two ways: (1) One locally placed stiffener and; (2) two locally placed stiffeners arranged symmetric with respect to the column mid span. The solutions are shown in graphs which may be used as design charts. From these graphs it can be seen that the optimal position of the stiffener is about 1/5 or 1/6 of the span for one or two stiffeners. The maximum obtainable increase of the buckling load depends of the proportion of the warping resistance to the torsional resistance. These are presented in graphs.