Load And Resistance Factor Design For Building Column

Plastic analysis of prismatic compression members in buildings is permitted if (F_y)^½(l/r) does not exceed 800 and F_uless than equal to 65 ksi (448 MPa). For axially loaded members with b/t less than equal to (lambda)_r , the maximum load P _u , ksi (MPa= 6.894 X ksi), may be computed from

P_u = 0.85A_gF_cr

Where A_g=gross cross-sectional area of the member
F _cr =0.658 ^lambda F_y for lambda <= 2.25

=0.877 F_y/lambda for lambda  > 2.25

lambda =(Kl/r)²(F_y/286,220)

The AISC specification for LRFD presents formulas for designing members with slender elements.