Slenderness for Torsional Buckling

Notations

A : Gross cross-sectional area of member

A_eff : Effective area

E : Modulus of Elastisity

f_y : Specified minimum yield stress of the type of steel being used

N_cr : the elastic critical force for the relevant buckling mode

Torsional Buckling Limit State

Buckling occurs when the element rotates around its longitudinal axis. The limit state of torsional buckling is applicable to axially loaded columns with doubly symmetric open sections with very slender cross-sectional elements consisting of 4 corners placed back to back.

for Class 1,2 and 3

for Class 4 cross-section