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Re: Anchor Bolts in Fatigue

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        The force in the anchor bolt is equal to the GREATER of the pretension OR the applied bolt load.  If the pretension is 125% of the fatigue loading it should never change, hence, zero stress range, hence zero fatigue (unless I'm misunderstanding your description of the problem).
        The best "bond breaker" is a sleeve.  You can buy commercial products, "Wilson Sleeves", that are very good; or you can make your own sleeves with a suitably sized pipe and a washer (larger than the pipe, if desired, so that it can act as an anchor plate) at the bottom end.  Sleeves have the added advantage of allowing you to make some adjustment for misaligned anchor bolts by bending the bolt.  I've usually seen sleeves filled with grout after the installation; but that would be going against your requirement for a "bond breaker".  I guess you could fill them with grease, asphalt, or some other non corrosive substance to keep water out.
        I'll leave the corrosion part of your question to others to answer.
H. Daryl Richardson
----- Original Message -----
From: Deke Black
Sent: Tuesday, August 28, 2007 12:57 PM
Subject: Anchor Bolts in Fatigue

I have a few questions about specifying anchor bolts that will be subjected to fatigue loads.  Hopefully somebody has some experience and can help me.


My first question, I was going to specify A449 threaded rod because I know A449?s properties are similar to A325, or Grade 8 bolts, which are commonly used for fatigue (and have limiting stresses based on the number of cycles).  Is anyone aware of limiting stresses for fatigue loads of either F1554 Gr.105 or A354 Gr. BD?


Secondly, there is going to be a pretension in the bolt (I believe 125% of the fatigue loading).  The manufacturer of the equipment is calling for there not to be a bond between the anchor bolt and the concrete in the top 7? of embedment (from the underside of the base plate down).  It was my understanding that you should not have the bond for the full length of the anchor bolt, and to develop the pretension in the head (or bearing plate) at the bottom of the anchor bolt.  It seems that you would have a problem keeping the pretension over time if the lower portion of the bolt bonds to the concrete.  Also, what is the best way to keep the concrete and the shaft of the anchor bolt from bonding?  I?ve read to grease the bolt, but I?ve also heard not to.  I also heard of using a bond breaker (the same as used for forms) and of putting on electrical tape around the bolt.  Are any of those the ?best? method, or are there any that are better?


Last, I need a method of corrosion protection.  I don?t want to hot dip galvanize because the bolts are high-strength and are subject to fatigue.  Would the best method be a paint that contains zinc ? and if so, can anyone point me in the right direction for the specification of such a paint?


Thanks for your help!


Deke Black