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Re: seaint Digest for 23 Mar 2012

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I concur with Harold.

structures generally experience forces from seismic due to their own inertia. The Earth moves and inertia tries to hold the structure in place.

We routinely model earthquake forces on structures as if the structure was trying to resist an external force, (like wind or hydraulic pressure) but this is only a convenient simplification.

So, if the tank is buried and the earth moves, unless the tank is very large, (which I would suggest is several hundreds of feet), the compressive wave's effect on the "upstream" side of the tank is transferred radially to the soil on the "downstream" of the.

Much of our concerns in structures are involved with anchoring the structure against sliding and against overturning. With a buried tank, we will see sloshing, but if the tank was completely full with a non-compressible liquid, we would not even see this.

Does anyone know of a buried tank that was damaged in an earthquake? If so, I suspect the tank was not damaged by the seismic forces, but by uneven displacement or the backfill.

Anyone? / eric

On 3/24/2012 12:00 AM, admin wrote:
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                        seaint Digest for 23 Mar 2012

Topics covered in this issue include:

    1: RE: Underground Tanks
              by Harold Sprague<spraguehope(--nospam--at)hotmail.com>
    2: Re: Underground Tanks
              by "h.d.richardson"<h.d.richardson(--nospam--at)telus.net>



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From: Harold Sprague<spraguehope(--nospam--at)hotmail.com>
To:<seaint(--nospam--at)seaint.org>
Subject: RE: Underground Tanks

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Tim=2C
This is a poorly defined area of study.  I would suggest that you start wit=
h the Foundation Engineering Handbook by Winterkorn and Fang=2C Chapter 23.=
   That will give you some of the basics.  Then I would suggest that you loo=
k at 2009 NEHRP Recommended Seismic Provisions=2C page 354=2C "Seismic Late=
ral Earth Pressures".   But this will still not address your particular con=
dition (which is generally ignored by the industry).  Another good resource=
  is from the DOE "Seismic Design and Evaluation Guidelines for The Departme=
nt of Energy High-Level Waste Storage Tanks and Appurtenances".  One of the=
  authors is Dr. Anestis Veletsos.  He is at Rice and well respected in the =
tank industry. =20
=20
The best approach would be to require an analysis by an independent consult=
ant such as:
=20
Tank Industry Consultants
7740 West New York Street
Indianapolis=2C IN 46214
Voice: 317-271-3100=20
=20
I contend that seismic on buried tanks is generally ignored because the con=
tention for seismic is that the entire soil mass moves in unison and does n=
ot impose an unbalanced load on the walls of the tank until the tank gets v=
ery large.  And "very large" is not defined.  You will still get impulsive =
and convective fluid forces=2C but they will not come close to the passive =
soil pressures. =20
=20
Regards=2C Harold Sprague
=20


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