# D5.D.8.8 Clause 6.3.1.4 - Slenderness for torsional and torsional-flexural buckling

Equations 6.52 and 6.53 of PN EN 1993-1-1:2005 are to be used to calculate the non-dimensional slenderness λT,  to be used for torsional and torsional-flexural buckling checks. PN EN 1993-1-1:2005 does not provide equations to calculate the elastic critical loads Ncr,TF and Ncr,T (refer 6.3.14 of PN EN 1993-1-1:2005).

The NCCI document "SN001a-EN-EU: Critical axial load for torsional and flexural torsional buckling modes" provides methods to calculate the Ncr,TF and Ncr,T factors and therefore these methods are used to evaluate the elastic critical loads for the Polish 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。