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RE: Double Nuts on Anchor Rods

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1. There is no agreement on where the jam nut should be placed (above or below) the structural nut.
2.  It is too unpredictable to be reliable.
3.  It impacts the capacity which nut is tensioned first.

That said, if the nuts are tensioned to snug, and you use to identical nuts, it should not make much of a difference. However if you tension the anchor rod to any significant tension, it would take a spud wrench with a cheater bar to loosen the nut. Tampering should not be an issue, and the jamb nut serves no real purpose.


Regards,
Harold Sprague





From: "Roger Davis" <rdavis(--nospam--at)sdsarch.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Double Nuts on Anchor Rods
Date: Fri, 13 Jan 2006 10:58:40 -0600

Why does Barrett advise against using jamb nuts?

Hydraulic tensioning doesn't seem appropriate for some places where I would
consider jamb nuts.  What about some suspended load where you use rods
rather than using structural sections and shear connections?

Roger C. Davis
Architect


205 N. Dewey St.
Eau Claire, WI 54703
P (715) 832-1605
F (715) 832-7850


-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: Friday, January 13, 2006 10:27 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Double Nuts on Anchor Rods

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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