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Re: Circular Concrete Tanks without Prestressing

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David, I have designed many such tanks is South Louisiana in accordance with
ACI 350. I have never experienced a problem with differential settlement. I
have never used the continuous footing under the joints.

Depending upon the depth of the tank, the foundation may very well be
compensated. That is, the weight of the soil you are taking out is nearly
equal to the weight of concrete and liquid you are adding back. Since the
"net" soil bearing is low, I would not expect much settlement let alone
differential settlement. Our problem here is uplift not bearing. We have to
take the water table to be at ground surface.

Randy Russ, P.E.
Russ Engineering Group, Inc.
Baton Rouge, La.
rruss(--nospam--at)eatel.net

-----Original Message-----
From: David Hall <Dahl(--nospam--at)deainc.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Tuesday, January 25, 2000 6:33 PM
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.
>
>
>