eff is the elastic critical moment of the gross cross-section, for lateral-torsional buckling about the relevant axis;

is the section modulus of the effective cross-section, if subject only to moment about the relevant axis.

NOTE: Information for the calculation of Mcr is given in annex F of ENV 1993-1-1.

(2) This method should not be used for U-sections and similar sections that have a significant angle between the principal axes of the effective cross-section, compared to those of the gross cross-section.

6.4 Distortional buckling

(1)P Distortional buckling shall be taken into account where it constitutes the critical failure mode.

(2) The effects of distortional buckling should be allowed for in cases such as those indicated in figures 6.4(a), (b) and (c), if the lowest elastic critical stress for a distortional buckling mode, evaluated by examining the various possible deformation modes, is lower than the elastic critical stresses for local and overall buckling, as indicated in figure 6.5.

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