Answer:
The elastic torsional buckling force for torsional buckling Ncr,T is calculated as follows:
${\mathrm N}_{\mathrm{cr},\mathrm T}\;=\frac1{{\mathrm i}_{\mathrm M}^2}\;\cdot\;\left(\frac{\mathrm\pi^2\;\cdot\;\mathrm E\;\cdot\;{\mathrm I}_{\mathrm w}}{{\mathrm L}_{\mathrm T}^2}\;+\;\mathrm G\;\cdot\;{\mathrm I}_{\mathrm t}\right)$
${\mathrm i}_{\mathrm M}\;=\;\sqrt{{\mathrm i}_{\mathrm u}^2\;+\;{\mathrm i}_{\mathrm v}^2\;+\;{\mathrm u}_{\mathrm M}^2\;+\;{\mathrm v}_{\mathrm M}^2}$
where
| E | is the modulus of elasticity, |
| G | is the shear modulus, |
| Iw | is the warping resistance, |
| It | is the torsion moment of inertia, |
| iu, iv | are the principal radii of gyration, |
| um, vm | are the coordinates of the shear center in the principal axis system, |
| LT | is the torsional buckling length. |
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