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Re: Tank Deadman

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Ernie Natividad wrote:

> I'm designing a concrete deadman for an underground storage tank subjected
to
a buoyant force due to water level rising above an empty tank.  I'm using
two
flat straps restraining the tank and connected to the 12 inch thick concrete
slab below the tank.  In calculating the downward forces resisting the
buoyant
force, how much of the soil above the tank and the deadman can I use?  How
much is the net weight of the soil(soil weight minus buoyant force due to
the
volume of water displaced by the soil, in PCF)?  Can I use the horizontal
projected area of the soil directly above the tank and the concrete slab
deadman up to the soil surface above? <

If you apply the full hydrostatic uplift force to the bottom of the slab,
you
can use the full concrete and soil weight above the horizontal projection of
the slab as a downward force.  Some engineers would also use side friction
at
the perimeter of the failure surface, but this requires more geotechnical
information and many geotechnical engineers recommend against using side
friction for sustained uplift loads.  You also need to apply a safety factor
-
and the safety factor may vary with what you include in the resisting
forces.
(Also, for the hold down strap make sure you consider corrosion resistance.)