For Class 1 and Class 2 cross sections, along with the conditions mentioned in Cl: 6.2.9.1 of EC3, the Dutch National Annex includes another clause specific to Class 1 and Class 2 round hollow sections.

The bending and axial force interaction for Class 1 and Class 2 round hollow sections may be checked using both of the following formulas:

where

$M_{\mathrm{Ed}}$	=	the design bending moment
$M_{c,\mathrm{Rd}}$	=	the moment capacity calculated per Eqn. 6.13 of EN1993-1-1.
$N_{\mathrm{Ed}}$	=	the design axial force
$N_{c,\mathrm{Rd}}$	=	the compression capacity calculated per Eqn. 6.10 of EN1993-1-1.