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RE: High Mast Light Pole Anchor Bolts

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Rich,
By building code, wind and seismic are generally not considered to induce fatigue.  That is not the case for petrochemical facilities and stacks because they are prone to vortex shedding.   You need to start with the installation recommendations by the manufacturer and determine if those recommendations appear logical. 
 
If grout was the original design assumption then the grout should be repaired.  ANY structure subject to fatigue should have the anchor rods tensioned to a force greater than the required service load.  Consider that the anchor rods are threaded.  Consider notch effect on fatigue.  If you preload the anchor rod, you take fatigue out of the picture.  It also is a test of the existing integrity of the anchor rod.  The anchor rod preload should exceed the applied service load and the base plate will be "clamped" to the supporting concrete.  This is similar to what is required for any high strength bolt (A325 or A490) subjected to tension or fatigue. 
 
This would be a good opportunity to bring out an NDT guy to test for any cracking with ultrasound and inspect the integrity of the welds.  This is a bit scary.  Especially when you throw in all of the possible problems with corrosion and the adequacy of the original design.  Which may be suspect. 

Regards, Harold Sprague


 

From: seaint04(--nospam--at)lewisengineering.com
To: seaint(--nospam--at)seaint.org
Subject: High Mast Light Pole Anchor Bolts
Date: Mon, 4 May 2009 17:21:42 -0500

I’ve been asked to inspect several school high mast light poles due to a rash of failures.  Here is a link to an article about the failures:

http://www.statesman.com/search/content/news/stories/local/04/12/0412lightpoles.html

 

It seems the failures have been linked to one manufacturer, Whitco Co LLP poles.

 

While doing an inspection last week I ran across a problem not associated with the pole failure in question.  At one of the high mat lights all but one of the anchor bolts was loose on one high mast light pole.  I could wiggle the washers around.  I couldn’t wiggle the bolt, but I could wiggle the washer.  The bolts are 1.25” diameter.  In addition, the grout pad below the base plate was broken into pieces.  The grout pad was very thin, perhaps 0.25” thick.  The base plate is probably about 26” in diameter.

 

I need to recommend a repair for this condition.  What I’m wondering is what would be wrong with the following procedure:

1.       Tighten the nuts up on the base plate.

2.       Pressure inject grout below the base plate.

 

I have thought of the following concerns:

1.       Should the bolts be snug tight or pre-tensioned.  I do not know anything about the original design.  The bolts are galvanized.

2.       What if the bolts have loosened at the base?  Is it possible to do some testing to determine if the bolts are still bonded to the concrete or if they have deformed somehow at the embedded base of the bolts and don’t have adequate anchorage?

3.       Can I pressure inject such a small gap on such a large base plate and be assured the grout has adequately filled below the base plate.  The base plate is 2” thick.

4.       Should the pole be lifted up first before grouting below the base plate, or just fill in the thin gap as exists below the plate.  If I required lifting the pole first and installing a new grout pad then I could get a thicker grout pad below the base plate.  Obviously lifting the pole requires bringing cranes out to lift the pole.

 

I’m guessing some of you that have experience with large highway mast poles can give me some insight on this issue.  I would appreciate any help you could give.

 

Thanks in advance.

 

Rich

 



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