Equivalent section is always used in lateral buckling calculations. In most cases equivalent section is equal to section which is applied to member.

If it is impossible to calculate lateral buckling with member's section (L-shape sections, tapered sections, different sections, etc.) then equivalent section is changed to the section for which it is possible to calculate lateral buckling.

For stability calculations equivalent section is used only if field is combined of members with different sections, or field has tapered section.

In all other cases member's section is used.

If reduction factor for lateral buckling (χ_{LT}) is needed for stability calculations, then it is always calculated with equivalent section.