Fcr for flexural-torsional buckling

[hardyworld]

I am checking th capacity of an existing compression member. The example in my LRFD 1st Edition Manual of Steel Construction shows that:

Fcr = Fy * e^(-.419*lam^2) when: lam <= 1.5

In my case, lam >1.5

What is the Equation for Fcr in this case?

I'm am used to using Fcr = Fy * Q * .686^(Q*lam^2) and Fcr = Fy * .877/(lam^2) equations as needed. But I do not know the complementary equation for the one shown above.

Thanks for the help.

 

[Teguci]

KL/r should not exceed 200. This limiting factor is for your own good. Anything that exceeds the 200 value is too slender and should be upsized or braced. It won't be worth much anyhow.

 

[Teguci]

Current equations:

Fe = (PI^2 x E) /[(KL/r)^2] Similar to Lambda

Fcr = [0.658^(Q x Fy/Fe)] x Fy ; for Fe > 0.44 Q x Fy

Fcr = 0.877 Fe ; for Fe < 0.44 Q x Fy