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RE: Earthquake loads on water retaining structures

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You absolutely need to consider the mass of the fluid in your seismic
calculations. It accounts for most of the seismic force!

There is also more to it than just figuring out the base shear and
overturning moment associated with the water mass. The distribution of
horizontal wall pressure is no longer triangular when hydrodynamic forces
are added in, and the hydrodynamic component results in decreases in wall
pressure on one side of the tank at the same time it is increasing wall
pressure on the opposite side. And don't forget the vertical component of
seismic force, which effectively increases the specific gravity of the fluid
and also increases the wall pressure. 

You also need to consider seismic effects from the soil pressure if your
tanks are backfilled. Make sure your tanks have enough freeboard to keep the
contents from sloshing out. ACI 350.3R-01 provides guidance on all this. 

-----Original Message-----
From: Wayne E. Beckingham [mailto:wbeckingham(--nospam--at)stroudpence.com]
Sent: Thursday, July 18, 2002 6:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Earthquake loads on water retaining structures


I am designing sedimentation basins for a WTP.  I am unable to figure out if
I have to include the weight of the water in the tanks when calculating the
lateral earthquake forces.


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