Per section 13.3.1, the factored axial compressive resistance, C_r , of doubly symmetric sections conforming to the requirements of clause 11 for class 1, 2, or 3 sections shall be taken as:

C_r = ϕAf_y(1+λ²ⁿ)^-1/n

where

n	=	1.34 for hot-rolled, fabricated structural sections, and hollow structural sections manufactured according to SANS 657-1
λ	=	$=\frac{kl}{r}\sqrt{\frac{f}{{\pi }^{2}E}}=\sqrt{\frac{f}{f_e}}$

Doubly symmetric sections which may be governed by torsional-flexural buckling shall also meet the requirements of 13.3.2.

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