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RE: Double Nuts on Anchor Rods

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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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