bolt direct tensioning
 

bolt direct tensioning
hi all,
when it is specified that a bolt is to be direct tensioned to 70% of capacity, would it mean that i can obtain that direct tension force by multiplying the bolt area by its ultimate strength and then by 0.70, or are there additional factors that i have to take in consideration? a prompt response would be appreciated!
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what are some direct tensioning procedures?
"direct tensioning procedures" sounds like preload (via torque wrench).
there are "standard" tables for preload in "typical" (shear)applications, depending on the size. a rule of thumb is t = p*d/5 (t=torque, p-=preload, d = diameter).
the high value of preload you've quoted (70% fty) is usually applicable to bolts with tension loads applied; in order that the joint doesn't gap inservice.
use the bolt area at the threads. only use high strength bolts, a325 & a490. tension indicators are very reliable, either the washers with bumps or paint and the break off bolt.