srm01,
Are you kidding me???
Blodgett's Formula, circa 1985~ and Allowable Stress Design, AISC Red Book, 8th ed. or Green Book,9th ed.
AISC 13th Ed, 10-90 Table 10-6, LRFD or modified ASD.
Look for the formula for this table 10-6, in the footnotes or in the companion examples volume.
Good...