New design curves for lateral–torsional buckling—Proposal based on a consistent derivation

The stability design of beams and columns is generally treated in international design codes by using–for all buckling cases–the same curves used for column buckling. One example is the use of column buckling curves for the design of steel members against lateral–torsional (LT) buckling in Eurocode 3. During the national implementation phase of this code, the design provisions for LT buckling have once again come under scrutiny. The work presented in this paper is to be seen in the context of this scrutiny. In addressing some open questions regarding LT buckling, it proposes a new formulaic description of the buckling resistance that is more accurate than the current expressions and–at the same time–mechanically more consistent with other member design rules. Thereby, a step-wise procedure is adopted that traces the development of the European column buckling curves. The resulting formulation yields very accurate results for all studied sections and all practical ranges of length, and also has the advantage of using a categorization of the sections according to the depth-to-width ratio h/bh/b that is consistent with the one used for the column buckling case, reflecting the higher residual stresses occurring below a ratio of h/b=1.2h/b=1.2. It is believed that the proposed formulation could find acceptance in the design community once it is expanded to include other load cases, methods of section fabrication, cross-sections, etc., and complemented by the appropriate safety elements required by the Eurocode or other international codes.