# D5.D.10.7 Clause 6.3.1.4 - Slenderness for torsional and torsional-flexural buckling

Equations 6.52 and 6.53 of NBN-EN 1993-1-1:2018 are to be used to calculate the non-dimensional slenderness parameter, λT,  to be used for torsional and torsional-flexural buckling checks. The NBN-EN 1993-1-1:2018 does not provide equations to calculate the elastic critical loads Ncr,T,F and Ncr,T (refer 6.3.14 of SS EN 1993-1-1:2005). Therefore, the NCCI document "SN001a-EN-EU: Critical axial load for torsional and flexural torsional buckling modes" provides methods to calculate the Ncr,T,F and Ncr,T factors and hence will to be included in this implementation of the Belgian NA.

ねじれ座屈に対する限界軸荷重は以下のように算出されます。

where
 $i o 2$ = $i y 2 + i z 2 + y o 2 + z o 2$ iyおよびiz = それぞれ、Y-Y（弱軸）とZ-Z（強軸）についての断面二次半径

$N c r , T F = i o 2 2 ( i y 2 + i z 2 ) [ N c r , y + N c r , T − ( N c r , y + N c r , T ) 2 − 4 N c r , y N c r , T i y 2 + i z 2 i o 2 ]$

これらの式の詳細については、NCCIドキュメントSN001a-EN-EUを参照してください。

The program will only consider channel sections and Tee- sections while working out the critical torsional and Flexural Torsional buckling loads as per Cl 6.3.1.4.