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RE: Steel Water Tank Foundation

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Rich,
I assume that you are talking about the seismic design of this tank.
For some background on this you can go to the seaint site, click on papers and download an article we presented to the 1999 SEAOC convention titled "Dynamic Analysis and Design of Large Steel Liquid Reservoirs".  Since then,  ASCE 7-05 has developed  the procedure for dynamic analysis incorporating the effects of a rigid foundation that Veletsos, Haroun, and Malhotra, among others had been doing research on for the last couple of decades.  Now, there is the 2005 Addendum 4 of API 650 Appendix E and AWWA D100-05 which have completely switched over and deleted the empirical solution method used before, that had been developed by Wozinak and Mitchell in their 1978 paper.  That methodology combined the theoretical basis from  Housner and Jacobson,  with empirical data from tank failures such as what occurred in the Alaska earthquake of 1964. 
One of the main objects of that effort was to encourage the design of tanks that would have a diameter at least twice as large as their height which is what you have described.  When that condition exists, even in most of zone 4, no anchorage is required and the ring wall is used to provide a level base for construction and to confine the engineered soil base.  The steel ring outside of the tank is also for containment.  This is actually the best design, if anchorage is not required, because it permits some deformation at the base without rupture which dissipates seismic energy and can then be corrected by re-leveling the tank.  All of this assumes that the tank bottom and shell plates are properly designed in accordance with  API 650 or AWWA D100.
STRUCTURE Magazine will have an issue with the theme of non-building structures in 2007 and we expect to have an article on this subject; that will be in March.
Richard Hess
-----Original Message-----
From: Rich Lewis [mailto:seaint04(--nospam--at)lewisengineering.com]
Sent: Thursday, September 28, 2006 8:05 AM
To: seaint(--nospam--at)seaint.org
Subject: Steel Water Tank Foundation

I was asked to research a foundation design for a large steel water tank.  The tank is about 50 feet diameter and 24 feet tall.  It looks like a typical oil field tank.  Are there publications that give foundation design recommendations for large diameter tanks?  What is the best source of design criteria?

 

The owner has stated that typically they put down sand and gravel and sit the tank directly on that.  Then they build a steel ring around the tank, beyond the tank perimeter,  to contain the soil underneath.  Is this a common procedure?  I would have expected a concrete ring footing below the tank.

 

If a concrete ring footing is used, does it only carry gravity load, or is it subject to tension forces from horizontal forces from the soil as well?

 

Thanks for any insight you can give.

 

Rich