Bolt Direct Tensioning 1

[GalileoG]

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!

 

[GalileoG]

What are some direct tensioning procedures?

 

[rb1957]

"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.

 

[civilperson]

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.