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RE: A new angle on "Sliding"

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Ben,

I have also typically seen very large tanks like this with positive
anchorage around the base, however, AWWA D100 & D103 do allow unanchored
tanks.

AWWA D100, Section 13.3.3.7.5:  "Ground-supported tanks full of product
have not been found to slide off their foundation.  When a sliding check
is required by purchaser, a coefficient of friction equal to tan 30 deg.
can be assumed."

AWWA D103, Section 12.2.2:   "Flat-bottom tanks may be anchored or
unanchored to resist earthquakes."  There are some footnotes and
additional checks that a designer is to follow through with.

I know there are pluses and minuses with both systems, but it appears
that these standards at least allow for both.  If you would like
additional info and data, I'd suggest you give Steve Meier of "Tank
Industry Consultants" a call or send him a note.  He's at
meier(--nospam--at)tankindustry.com or (317) 271-3100.

Good luck,
Dave K. Adams, S.E.
Lane Engineers, Inc.
979 N. Blackstone St.
Tulare, CA 93274
PH:  (559) 688-5263
FAX: (559) 688-8893
E-mail:  davea(--nospam--at)laneengineers.com





-----Original Message-----
From: Yousefi, Ben [mailto:Ben.Yousefi(--nospam--at)ci.sj.ca.us]
Sent: Thursday, November 14, 2002 3:37 PM
To: seaint(--nospam--at)seaint.org
Subject: A new angle on "Sliding"


We are currently reviewing a steel water tank that is approximately 300
feet
in diameter and approximately 40 feet high. The designer is proposing to
not
have any anchorage from the tank to the perimeter ring foundation that
the
tank wall is resting on. His point is that, there is sufficient friction
between the tank wall and the foundation to resist the seismic forces
from
the tank itself and any sloshing forces from the water!

I have not in, my entire professional life, seen a case where a
structure of
this magnitude would not use any positive anchorage from the
superstructure
to the foundation. There is some code language in the UBC, such as
sections
1605.2.3 and 1809.3, that deal with anchorage of walls and buildings.
And to
me it is clear that what is being referred to in those sections is
positive
anchorage. However, the designer is insisting that using friction is an
acceptable method of resisting seismic forces in tank design. Any input
from
those experienced with this type structure is appreciated.

Ben Yousefi, SE
San Jose, CA

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