allowable stress of steel bars

[par060]

I have a simple beam made of a 3/4" x 5.5" steel bar. How should I determine Fb?

 

[srm]

The slenderness for the lateral torsional buckling calculation can be calculated from the formula:

Lambda = 2.8 x [(length x depth / thickness ^ 2}] ^ 0.5

Knowing lambda and the material design stress, pb can be read off the relevant table in the code.

In your case the depth is 5.5 and the thickness is 0.75.

 

[ishvaaag]

I suggest you make the check along LRFD Chapter F and appendix to Chapter F that have explicit formulations for the bending of plates in strong axis bending.

If you have access to Mathcad 2000 you have at its Collaboratory site posted worksheets of free download that will make the calculation for you.