EN-1993-1-1 gives a provision to check the interaction between bending and compression in which two equations are given (Eqn. 6.61 and Eqn. 6.62). These equations consist of multiplicative factors that are related to buckling of the member. While the Dutch National Annex does not say anything about this clause, other than the means of calculation of k_yy, k_yz, k_zy and k_zz, it has different conditions to calculate other buckling factors and parameters, which have been mentioned in other sections of this implementation.

STAAD.Pro uses the method in Annex B.