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Cb : The lateral-torsional buckling modification factor
E : Modulus of elasticity of steel = 29,000 ksi (200 000 MPa)
Fcr : Lateral-torsional buckling stress for the section as determined by analysis, ksi (MPa
Fy : Specified minimum yield stress of the type of steel being used, ksi
Its : Effective radius of inertia
J : Torsional constant
ho : Distance between the flange centroids, in. (mm)
Lb : Length between points that are either braced against lateral displacement of the compression flange or braced against twist of the cross section, in. (mm)
Lp : The limiting laterally unbraced length for the limit state of yielding, in. (mm)
Lr: The limiting unbraced length for the limit state of inelastic lateral-torsional buckling, in. (mm),
Mn : The nominal flexural strength
Mp : Plastic bending moment
ry : Radius of gyration about y-axis
Sx : Elastic section modulus taken about the x-axis, in.3 (mm3)
Zx = Plastic section modulus about the x-axis, in.3 (mm3)
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The nominal flexural strength, Mn, should be the lower value obtained according to the limit states of yielding (plastic moment) and lateral-torsional buckling.
Yielding Limit State