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RE: Circular Concrete Tanks without Prestressing

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It is my understanding that it has been found over time that there are more
problems with leakage in tanks with numerous expansion joints versus tanks
adequately reinforced with construction joints only.  Even though the
continuous concrete still cracks, with adequate reinforcement the cracks are
small and tend not to leak.  Expansion joints control concrete cracking
better but tend to fail themselves more often.  I also feel that a
continuous tank should perform better under seismic conditions than a tank
with expansion joints.  

On the subject of failed expansion joints, I am currently working on repairs
at a rectangular concrete basin at which the waterstops in the existing
1/2-inch expansion joints have failed and are leaking.  Does anyone have a
good solution on how to repair failed waterstops in expansion joints without
demolishing the concrete and replacing the PVC waterstop and where treatment
equipment must travel across the joint surface? 

> -----Original Message-----
> From: David Hall [mailto:Dahl(--nospam--at)]
> Sent: Tuesday, January 25, 2000 5:12 PM
> To: seaint(--nospam--at)
> Subject: Circular Concrete Tanks without Prestressing
> Our firm has designed a circular concrete tank to be 
> constructed in northern Washington.  The design was done 
> under the above listed publication.  However, this design was 
> done from what I am now told a 1960's version of this 
> publication.  I have a copy of the 1993 version.
> Anyway, the base slab was detailed as being placed in 
> segments (8 total) opposite of each other within the tank 
> with expansion joints separating these pours and an 18 " wide 
> by 12" reinforced continuous footing below this joint to 
> prevent differential sentiment which would cause leaks.  This 
> is the recommended method prescribed in the 1960's version.
> The 1993 version as eliminated this method and recommends 
> using ACI 350R with consideration given for the "z" factor to 
> reduce cracking.
> Can anyone tell me why the 1960's method was removed from the 
> code.  I am providing the final QM review and the engineer 
> who designed the tank insists his design is the way to go.
> Also, that tank is above grade and seismic considerations 
> were accounted for.  Plans are going out to bid shortly.
> Thank you for your assistance.
> David A. Hall, S.E., P.E.