# D5.D.6.4 Clause 6.3.2.3(1) – LTB for rolled sections or equivalent welded section

The FR-NA provides equations to evaluate the λ_{LT,0} and α_{LT} factors given in clause 6.3.2.3

For rolled doubly symmetric sections use:

${\overline{\lambda}}_{LT,0}=0.2+0.1\frac{b}{h}$

${\alpha}_{LT}=0.4-0.2\frac{b}{h}{\overline{\lambda}}_{LT}^{2}\ge 0$

Note: Since EN 1993-1-1:2005 limits the value of λ

_{LT,0}to 0.4, STAAD.Pro limits λ_{LT,0}to a maximum value of 0.4.For welded doubly symmetric sections use:

${\overline{\lambda}}_{LT,0}=0.3\frac{b}{h}$

${\alpha}_{LT}=0.5-0.25\frac{b}{h}{\overline{\lambda}}_{LT}^{2}\ge 0$

For other sections:

λ_{LT,0} = 0.2

α_{LT} = 0.76

And for all sections, β = 1.0

These equations and factors are then applied to equation 6.57 of NF EN 1993-1-1 to evaluate the Lateral Torsional Buckling reduction factor χ_{LT}.