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Re: Friction factor for plastic flat bottom tank

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Bill Cain, S.E. wrote:

> snip

> One anchorage system I've seen for cross-linked polyethylene tanks
> (Poly-Cal tanks out of Stockton, CA) is a series of angle posts with cables
> encircling the tank. The system does not directly connect to the tank.  It
> acts sort of like a net to catch the tank when it moves.  Although I'm
> uncomfortable with this design for a high seismic area, I can't suggest
> anything better since plastic is hard to fasten to.
> Bill Cain, SE
> Oakland, CA
> At 05:35 PM 6/2/98 -0400, Lew Midlam wrote:
> >I think there's a provision in the code that prohibits using friction to
> resist lateral loads, but I couldn't find it in a quick flip thru the pages.
> >
> >Lew Midlam, PE
> >==============================

The Poly-Cal system (cable with vertical posts) is designed to restrain the
empty tank with design wind pressures as the weight is insufficient to keep it
stationary. The secondary effect would be to help resist lateral EQ forces.

For smaller tanks frictional forces may be appropriate. The tank analysis for
sloshing and restraint, as I understand it, is pretty complex and is probably
best verified with full scale testing.

Barry H. Welliver