The 8th edition Manual of Steel Construction in Part 4: Connections (page 3 of chapter 4), states the following,
Ft = 0.33 Fu.
Ft = allowable tensile stress in threaded fastener
Fu = specified minimum tensile strength of the fastener
There is no other explanation for this equation given in the book.
What happens past Ft? I know that the material yields at roughly 75% x Fu = Fy, and totally fails at Fu, but could someone please explain the physical meaning of Ft. Is it a fatigue limit? Does the book assume the bolt could yield past this point?