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The Combined Bending and Axial force Check is executed according to EN 1993-1-1 art. 6.2.9.
In case the elastic verification has been activated within the Steel Setup, for any cross-section class the elastic verification using the yield criterion according to art. 6.2.1(5) is verified instead.
As specified in the code, the type of the check depends on the classification.
Class 1 & 2 cross-sections are by default verified by art. 6.2.9.1
This article gives formulas for the following cross-section types:
For these sections the moment resistance is reduced due to the presence of an axial force.
In case of an extreme axial force which would lead to a negative reduction the formulas from this article cannot be applied. In this case the plastic linear summation according to art. 6.2.1(7) is applied.
For any other class 1 or 2 cross-sections which do not have a reduced moment resistance defined within this article also the plastic linear summation according to art. 6.2.1(7) is applied.
For Circular Hollow Sections (FC 3) the reduced moment resistance due to axial force is calculated according to the formula given in the 2009 correction sheet Ref.[11].
In addition, the resultant shear force and resultant moment is determined. The resultant shear force is used to calculate the reduction for shear according to "Bending, Shear (and Axial force)".
The unity check is then executed as follows:
Class 3 cross-sections are by default verified by art. 6.2.9.2.
For shear, reference is made to "Bending, Shear (and Axial force)". The reduction factor ρ to be used in formula (6.42) is taken as the maximum of ρy and ρz see Ref.[38].
Class 4 cross-sections are by default verified by art. 6.2.9.3 formula (6.44).
Formula (6.44) consists of 3 terms which are summed up by using their absolute values in order to be always on the safe side.