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For the limit state of inelastic lateral-torsional buckling and doubly symmetric I-shaped members

L_{r} = 1, 95 \cdot r_{t s} \cdot \frac{E}{0, 7 F_{y}} \cdot \sqrt{\frac{J \cdot C}{S_{x} h_{o}} + \sqrt{{(\frac{J c}{S_{x} h_{o}})}^{2} + 6, 76 {(\frac{0, 7 F_{y}}{E})}^{2}}}

E	Modulus of elasticity
F_y	Yield strength
J	Torsional constant
S_x	Elastic section modulus taken about the x-axis
h_o	Distance between the flange centroids

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