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RE: Steel Water Storage Tank- Foundation Settlement Criteria

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Following the Northridge earthquake I investigated a much larger tank with
about 3 inches of settlement in one quadrant of the footing. There was a gap
between the floor plate and the footing ring.  The tank was drained to
relieve the stress on the shell to bottom plate weld and a Grout dam was
added to the perimeter and low pressure grout injected into the void behind
the dam, care taken not to lift the tank.  It was obviously unacceptable to
have the shell supporting the floor plate.  I know this is not the answer to
your question yet it is how I handled a similar the problem.   I did some
analysis to identify the additional bending stress the shell could take and
I felt comfortable with the solution.

Dan Novak
ASL Consulting Engineers 

-----Original Message-----
From: Lakhani, Sid [mailto:slakhani(--nospam--at)ebmud.com]
Sent: Wednesday, August 18, 1999 6:48 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: Steel Water Sorage Tank- Foundation Settlement Criteria 


I am concerned about the safety of a steel tank.  The tank foundation (
concrete footing ring) has settled approximately one inch along the
diameter.  
Tank data:
Diameter= 45 ft
Heght=30 ft
Flat Bottom w/ 1/4 inch steel plate.
Tank designed per AWWA D100-96
One inch settlement is between two points on the footing diameter.
My questions are:
Is there any design criteria/guideline for steel tank settlement ?
What precautionary measures should be taken ?
Does any body has experience in eleviating similar situation ?
Thanks!   Sid Lakhani