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Re: Anchor bolt sleeve - pretensioning

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Mark,

There are several suppliers of dome spring washers that you should be able to "Google".  Below is one example:

http://www.bellevillesprings.com

Thomas Hunt, S.E.
Fluor



Mark Johnson <markajohn(--nospam--at)yahoo.com>
02/02/2009 04:43 PM
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Re: Anchor bolt sleeve - pretensioning





Tom,

Spring washers is an interesting idea.  Please dig up a spec or a URL for something you've used.

thanks,
MJ

--- On Mon, 2/2/09, Tom.Hunt(--nospam--at)fluor.com <Tom.Hunt(--nospam--at)fluor.com> wrote:

From: Tom.Hunt(--nospam--at)fluor.com <Tom.Hunt(--nospam--at)fluor.com>
Subject: Re: Anchor bolt sleeve - pretensioning
To: seaint(--nospam--at)seaint.org
Date: Monday, February 2, 2009, 2:19 PM


Rajendran,


For heavy industrial designs this done quite often.  The problem is that there is a natural "bond" between the anchor rod and concrete of approximately 60 psi.  Anchor bolt sleeves typically only go down about a foot to two feet whereas long anchor bolts for towers and vertical vessels can be 6 to 8 feet long.  Your pretension will be a function of the strain which will be a function of the anchor bolt length.  Until (and if) your pretension breaks the natural bond all the strain is in the top few feet of your anchor bolt.  If you have a significant seismic event the natural bond will break and you will loose all your pretension.  


As a side note, pretension in anchor bolts is not an exact science as you still need to deal with concrete shrinkage, creep, humidity, etc. just as in prestress concrete design.  Then there is the issue of actually determining in the field the pretension load.  When I am forced into such a design I typically call out for Belleville dome spring washers.


As for breaking the bond on the shaft, the old tried and true method is to grease the anchor bolt however in practice they often get more grease on the rebar than the bolt.  I personally like to call out plumbers Teflon tape.


Thomas Hunt, S.E.

Fluor




Padmanabhan Rajendran <prajendran(--nospam--at)ymail.com>
02/02/2009 12:58 PM

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Anchor bolt sleeve - pretensioning







In its section on anchor bolt with sleeves, the ASCE booklet "Wind Loads and Anchor bolt design for petrochemical facilities" recommends breaking the bond (by wrapping a tape) between the bolt and the concrete between the bottom of the sleeve and up to 1" above the bolt head. This is claimed to prevent loss of bolt pretension.

How many of you follow the above specification? I use standard sleeve and do not specify breaking the bond as recommended in ASCE. Are there any recorded cases of foundation failures which resulted from loss of bolt pretension?


Rajendran



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