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Re: Torque vs. Tension in Bolts

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Bolts installed through wood do not maintain the initial tension because of
gradual compressing of the wood fibers and change in moisture content.

The most convenient to use mechanical anchors are those that can be drilled
thru the plate using the plate as a template.  However, this kind is very
sensitive to hole diameter.  If the hole size is over sized, usually because
the bit wobbles, the anchor does not hold.

I have the best results with the self-drilling expansion anchors.  Torque
and hole size are not critical.  The disadvantage is that the holes most be
marked, the plate moved, the holes drilled, then the plate repositioned.

Paul J. Martin, PE, SE
ADM Design Services
Decatur, IL
-----Original Message-----
From: Peder and/or Cathy Golberg <golberg(--nospam--at)>
To: seaint(--nospam--at) <seaint(--nospam--at)>
Date: Wednesday, July 14, 1999 12:32 AM
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