Tightening bolts to 90% yield stress. 2

[wannadie]

When tightening a bolt, I have read that I should tighten to provide preload of the order to 90% of the yield stress in the fastener.

I understand the importance of preload, but find the 90% extremely high with little safety factor due to the unpredictable nature of coefficient of friction and tightening controls.

What do other people do? Are there any other standards besides VDI 2230 which is really far to complex for my needs.

 

[teb1]

"If an external load that tends to separate the members is applied, some of the compression on the plates will be relieved. (I agree) In turn, some of the tension on the bolt will be relieved. (I disagree!) "

Please elaborate on this, RJCJR9.

Thanks.

 

[imagitec]

teb1,

You're correct. I know what I meant, but it wasn't what I wrote. I was thinking of the "tension" only as the reaction to the initial compression of the members, i.e., the preload. Applying an external load to the members relieved some of their compression, thus reducing the "tension". But the net force will still go up because of the applied load, just not the full amount. That is a mucky, imprecise way to think about, and an even worse way to explain it. Thanks for setting me straight.

Rob Campbell, PE
Finite Monkeys -

http://www.livejournal.com/users/robcampbell