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Re: Torque vs. Tension in Bolts

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Some items of note:

In 1995 we did a residential Foundation Anchorage Program with the SEAOSC 
Structural Methods Subcommittee.  Included in the program was testing of 
adhesive anchors into existing foundations with 2x wood plates.  Using 
standard cut washers in wood applications does not work well.  The City of 
Los Angeles is now requiring 2" (?) square plate washers for most if not all 
wood applications.  When an anchor begins to resist shear load, it 
immediately starts to bend thereby going into tension.  Cut washers dig into 
the plate very quickly.

Additionally, most expansion anchors lose about 50% of their torque in about 
24 hours due to relaxation.  Any wood shrinkage would compound this. It is 
important to fully torque the expansion anchors to make sure they are 
properly set.   Most adhesive anchors and mechanical undercut anchors are 
much stiffer than friction anchors, especially at loads near ultimate 
capacity.  From a cost standpoint, adhesive anchors can also be equal or 
lower in cost to the contractor, especially as the diameter and length 
increases.

Howard Silverman, PE
Covert Operations, Inc.
Anchoring and Injection Systems
www.covertoperations.com
(800) 827-7229