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RE: Double Nuts on Anchor Rods

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I have seen double nuts indicated for the retention of embedded anchor ends and anchor plates in ASCE Petrochemical Energy Committee "Design of Anchor Bolts in Petrochemical Facilities". And leveling nuts are indicated in AISC Design Guide 1 Column Base Plates although I prefer other methods of leveling.

Barrett in "Fastener Design Manual" advises against using jam nuts for the purpose of locking a nut.

Generally if cyclic loads are an issue, I prefer to use an anchor rod that I will have tensioned using a hydraulic tensioner. This requires the shaft to be unbonded. STS 1 for stacks requires that bolts be re-tensioned after 30 days of service. This is a good idea for anything that is subject to cyclic loads. It gives time for any creep or inadvertent bonding to release, and the anchor rod may loose tension.

I don't have much of a problem with using double nuts on the embedded anchored end, but I prefer not to use them as a means of locking the nut above the base plate. A properly designed and tensioned anchor rod will not loosen if the rod has a pretension force greater than the service tension load.

The reason that you see them in the applications that you cite is that the anchor rods are not tensioned uniformly, predictably or properly and the rods will become stressed unequally. As the loads are cycled, some anchor rods stretch to the point where other anchor rods contribute to load resistance. When the loads cycle, the stretched anchor rods will become loose.

Regards,
Harold Sprague





From: "Ken Peoples" <kspeoples(--nospam--at)lvta.net>
Reply-To: <seaint(--nospam--at)seaint.org>
To: "Seaint" <seaint(--nospam--at)seaint.org>
Subject: Double Nuts on Anchor Rods
Date: Thu, 12 Jan 2006 10:35:13 -0500

When we are doing structural steel detailing, we sometimes see double nuts on anchor rods - especially for industrial work. I am curious if any of you know of any particular recommendations from AISC (or any other authority) regarding using double nuts for anchor rods. I often see them where there are vibrations (screens), cranes, towers or stacks.

Best regards,


Kenneth S. Peoples, P. E.

LVTA
Lehigh Valley Technical Associates, Inc.
1584 Weaversville Road
Northampton, PA 18067

Phone: 610-262-6345
Fax: 610-262-8188

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