# D5.D.3.5 Clause 6.3 – Buckling resistance of members

The D-NA introduces a new clause 6.3.0, which in turns requires the checks as per clauses 12.1.2.2, 12.13.2 and 12.1.4.2 of NEN 6771 to be applied.

## Clause 12.1.2.2 (NEN 6771)

This clause in NEN 6771 determines the relative torsional slenderness and is given as:

${\lambda}_{\theta ,rel}=\sqrt{\frac{{N}_{c;u;d}}{{F}_{E;\theta}}}$

Where:

N_{c;u;d} = A·f_{y;d}

- A = area of section
- f
_{y;d}= the yield stress - F
_{E;θ}is the Euler-torsion formula

This value of slenderness is to be used to calculate the modification factors used in section 6.3 of EC-3.

## Clause 12.1.3.2 (NEN 6771)

This clause works out the relative torsional-flexural buckling slenderness for compression members. The relative torsional-flexural buckling slenderness is given as:

${\lambda}_{tk,rel}=\sqrt{\frac{{N}_{c;u;d}}{{F}_{E;tk}}}$

Where

N_{c;u;d} = A·f_{y;d}

- A = area of section
- f
_{y;d}= yield stress - F
_{E;tk}is the Euler torsional buckling strength