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Calculate Lateral-Torsional Buckling Modification Factor Cb:

Calculation:
Designer/Checker:

Input:

AISC F1(3)
For singly symmetric members in single curvature and all doubly symmetric members, calculate Cb, the lateral-torsional buckling modification factor for nonuniform moment diagrams when both ends of the segment are braced.

Absolute value of maximum moment in the unbraced segment (Mmax - kip-ft or kN-m)
Absolute value of moment at quarter point of the unbraced segment (MA - k-ft or kN-m)
Absolute value of moment at centerline of the unbraced segment (MB - k-ft or kN-m)
Absolute value of moment at three-quarter point of the unbraced segment (MC - k-ft or kN-m)

Output:

Lateral-torsional buckling modification factor, Cb = (12.5Mmax)/(2.5Mmax + 3MA + 4MB + 3MC)
For doubly symmetric members with no transverse loading between brace points, Cb reduces to 1.0 for the case of equal end moments of opposite sign (uniform moment), 2.27 for the case of equal end moments of the same sign (reverse curvature bending), and to 1.67 when one end moment equals zero. For cantilevers or overhangs where the free end is unbraced Cb = 1.0.

Lateral-torsional buckling modification factor, Cb =

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