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Re: Torque vs. Tension in Bolts

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> From: Peder and/or Cathy Golberg <golberg(--nospam--at)e-z.net>
> Subject: Torque vs. Tension in Bolts
> 
> Can someone tell me a rule-of-thumb formula or another method to convert
> the torque value placed on a bolt to the tension value.  I had a formula
> that a mechanical engineer gave about 10 years ago that I have now
> aparently misplaced and it is something I don't recall ever seeing in a
> text book.  I do read, however, in the AISC Connections book that any
> published method of conversion is not acurate.
> 
> My situation is for the use of expansion anchor bolts in concrete to
> connect a wood plate (sill or ledger).  The wood will crush before the
> required torque is achieved without a plate washer.  I want to determine
> just how big these plate washers need to be but need to convert torque
> value to do this.
> 
> Do others call out plate washer sizes in details, use more expensive epoxy
> anchors, or is this something that gets ingnored and the anchors are not
> always installed properly?
> Thanks in advance.
> 
> Peder Golberg, PE
> Portland, Oregon

	Maybe I am missing something,  why convert to torque?  What you need to
know is the the tension state of the bolt, correct?  If you are
measuring torque, then you are basically measuring the rust on the
bolt.  If you need an accurate (although relatively expensive) method,
use dimples washers.  By compressing the dimples on the washer, it
indicates the tensile state of the bolt.  As far as torque being a bad
way to measure, AISC is correct.  I have read studies that were
performed in a lab (ideal conditions) were actual tensions values based
upon measured torque varies by as much as 100% of the desired tension. A
second method is "turn of the nut".  Have the construction crew "firmly"
seat the nut then turn a prescribed number of turns.  I believe this
method is in the AISC connections manual as well. If you can't find
"turn of the nut" in the AISC manual, let me know and I will see if I
can send you additional information.

Jake Watson, E.I.T.
Salt Lake City, UT