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RE: Drilled pier cracks

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Once I had a case where cracks were appearing in new piers for heavy-duty
wood-handling equipment in a paper mill. It got peoples' attention when a
huge chunk of concrete spalled off the top of the pier; this ol' chunk
probably weighed 120 lbs.

Long story short, it was apparent that the grouting sleeves for the anchor
bolts were full of water, not grout. The contractor hadn't grouted properly.
Water freezes even in Mississippi if the temperature gets below 32° F.
Freezing water expands (anyone with an ice cube tray knows this but I had a
difficult time convincing my Southern colleagues that this was the likely
cause of the problem). Contractor had to drill through the sides of the
piers into the grout sleeves to fix this, but it was still far far cheaper
than rebuilding the piers (and with special urethane shock pads) as had been
talked about.

This is likely not the problem in the case of this antenna tower. But
sometimes it pays to look at unlikely modes of failure.


   Tom Barsh, P.E.
   Codeware Inc
   www.codeware.com

 

> -----Original Message-----
> From: nmoore [mailto:nmoore(--nospam--at)mail.innercite.com] 
> Sent: Tuesday, June 21, 2005 3:18 PM
> To: seaint(--nospam--at)seaint.org; seaint(--nospam--at)seaint.org
> Subject: Re: Drilled pier cracks
> 
> Rich:
> 
> It looks the bolts are failing.  We've done many towers and 
> poles and have never used hooked anchor bolts.  The original 
> calculations should provide you with the forces that the 
> bolts are suppose to resist.  I always count on the surface 
> of the embedded nut to resist pull out, using the cone 
> section to transfer the anchor bolt loads over to the 
> perimeter rebar circle.
> 
> First thing, which has already been suggested, is to provide 
> some temporary guys and THEN do the fix, which will probably 
> be redesigning the top of the pier and providing the repair 
> procedures.  Depending on where you are, there are tower 
> companies that can do this kind of work - such as temporarily 
> supporting portions of the tower; concrete demo and replacement, etc.
> 
> If you are on the West Coast, Towers Structures, Inc. in 
> Minden, Nevada, can do this.  
> 
> 
> Neil Moore, S.E.
> neil moore and associates
> 
> distressed structures investigations
> 
> 
> ---------- Original Message ----------------------------------
> From: "Rich Lewis" <seaint02(--nospam--at)lewisengineering.com>
> Reply-To: <seaint(--nospam--at)seaint.org>
> Date:  Tue, 21 Jun 2005 14:18:14 -0500
> 
> >I was sent some pictures of a concrete drilled pier for a 
> cell phone tower.
> >The top of one of 3 piers is cracked.  The cracks radiate 
> from the anchor
> >bolt group.  There is a somewhat circular crack that 
> surrounds the bolts and
> >then about 8-12 cracks radiate out to the edge.  It appears 
> the anchor bolts
> >have been pulled up slightly.  I am told the top surface is 
> out of level on
> >this particular pier, with the crown in the middle.
> >
> > 
> >
> >I have a copy of some of the original calculations of the 
> pier.  There are
> >10-1" dia. Bolts per leg, 78" long.  The note says it is to 
> have a 180
> >degree bend.  I have never seen an anchor bolt with a 180 
> degree bend.  Is
> >this common for this type of application?
> >
> > 
> >
> >In order to repair this I think I need to establish the 
> extent of cracking
> >and integrity of the pier.  Is there a reasonable way to 
> establish this?  Is
> >there an ultrasonic type test that can be run?  What kind of 
> results would
> >it tell me?  The pier is 6 ft. in diameter and 41 ft. deep.
> >
> > 
> >
> >Anyone ever run into a repair like this before?  Any 
> suggestions on a fix?
> >If I could establish that the pier was sound down a certain 
> depth form the
> >top I could request demolishing the bad section and 
> repouring concrete if it
> >wasn't too deep.  Another solution would be to drill 2 piers 
> adjacent to
> >this one and tie the existing leg into the new piers.  I 
> would assume that
> >taking the tower down is not an option right now.
> >>
> >Thanks for any suggestions.
> >>
> >Rich
> > 
> 
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