# D14.C.6.4 Torsional or Torsional-Flexural Buckling

Per section 13.3.2, the factored compressive resistance, Cr , of asymmetric, singly symmetric, and cruciform or other bisymmetric sections not covered under 13.3.1 shall be computed using the expressions given in 13.3.1 with a value of n = 1.34 and the value of fe taken as lesser of Fex and Feyz for single symmetric section, with the y axis taken as the axis of symmetry.

$f e y z = f e y + f e z 2 Ω [ 1 − 1 − 4 f e y f e z Ω ( f e y + f e z ) 2 ]$
where
 fey = $π 2 E ( K y L y r y ) 2$ fez = $( π 2 E C w K Z 2 L Z 2 + G J ) 1 A r ¯ 0 2$ Ω = $1 − ( x 0 2 + y 0 2 r ¯ 0 2 )$ x0 ,y0 = = the principal coordinates of the shear center with respect to the centroid of the cross-section. $r ¯ 0 2$ = $= x 0 2 + y 0 2 + r x 2 + r y 2$

For asymmetric sections, fe is the smallest root of:

$( f e − f e x ) ( f e − f e y ) ( f e − f e z ) − f e 2 ( f e − f e y ) ( x 0 r ¯ 0 ) 2 − f e 2 ( f e − f e x ) ( y 0 r ¯ 0 ) 2 = 0$
where
 fex = $π 2 E ( K x L x r x ) 2$

The parameters KY, LY, KZ, and LZ are applicable for this.