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Re: Shrinkage of Concrete Floodwall

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Stan,
 
The amount of water lost through say, 1/16" wide cracks at certain spacing at the time of flooding (water 2-3 ft above the top of levee)  can be relatively easily estimated (I've done it recently).  It is likely to be minor, comparable to amount of seepage through the levee and to the amount of rain attributable to the ground outside the wall.  From this perspective, cracking of the wall does not appear to have any significant effect on "hundreds of homes."  
 
Whatever your crack-related solution may be (including doing nothing), cracking of the concrete wall due to thermal expansion does not look like a huge problem for "hundreds of houses."  The 20-ft joint spacing appears as good as anything else - justifiable, for example, by PCA "Rectangular Concrete Tanks" Figure 1-2 (#4@12" each face, they recommend smaller rebars at smaller spacing for thermal/shrinkage). 
 
I would be more concerned about cracking due to settlement and seepage under the wall foundation (with its subsequent undermining and further settlement).  But this is a totally different issue.
 
Have a great weekend,
 
V. Steve Gordin,
Registered Structural & Civil Engineer
Irvine CA
 
P.S. I want to thank Matthew Stuart and you, Stan, for bringing the issue of elections to this list.  Without your input - as bothersome as it originally seemed to be :) - I would have never gone to the ASCE website, read whatever was available there about the two candidates, and voted. Great idea, good job. SG
 
----- Original Message -----
Sent: Saturday, June 27, 2009 14:58
Subject: Re: Shrinkage of Concrete Floodwall

Ralph:
 
The wall is a floodwall.  Hundreds of homes will depend on it every 100 years or so.  The expansion joints will be sealed with expandable/contractable waterstops.  Hopefully, the product chosen will also be vandal-proof.  Thus, at the moment, my concern is the wall itself.
 
Stan 

On Sat, Jun 27, 2009 at 2:26 PM, Ralph Kratz <rhkratzse(--nospam--at)aol.com> wrote:
Stan, just curious, but why are cracks a concern, whereas the potential similar-size gap in an expansion joint isn't?

Ralph Hueston Kratz
www.rhkse.com

Sent from my iPhone 3G


On Jun 26, 2009, at 12:16 PM, Stan Caldwell <stancaldwell(--nospam--at)gmail.com> wrote:

Shrinkage of concrete during curing seems to me to be one of those fuzzy areas of structural engineering practice.  Perhaps some of you can help shave the fuzz.

We have to design a small concrete floodwall on top of an existing levee.  The wall will be about 300 ft. long, 12 in. thick, and 2 to 3 ft. tall.  Joint spacing will be based on shrinkage, and joint width will be based on thermal expansion (101 dF in Dallas today).  Back to the shrinkage problem, this is a flood protection wall so we do not want any cracks.  We are thinking of 20 ft. joint spacing, but are having trouble justifying this choice, or any other, based on available literature.

Any thoughts?

Stan R. Caldwell, P.E.
HALFF Associates, Inc.
Richardson, Texas




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