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Re: A new angle on "Sliding"

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Ben,

        I personally don't think you need to anchor this tank to the foundation;
I think anchor bolts would cause more problems in foundation design than they
would prevent.  If wind uplift is considered a problem leave a minimum one or
two feet (62.4 to 124.8 p.s.f.) of water in the tank except for emergency use
such as fire fighting.  If sliding is a problem consider setting the tank
slightly below grade to mobilize some soil shear force.

        Not being a tank or seismic "expert" there are two I would spend more
effort on than anchor bolts: stresses in the tank itself due to ovaling effects
from sloshing; and tank deformations due to the tank sitting in the trough or on
the crest of a vertical "soil wave" resulting from an earthquake.

        Good luck.

Regards,

H. Daryl Richardson

"Yousefi, Ben" wrote:

> 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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