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RE: Sloshing/Seismic forces on immersed bodies

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Gray,
Bodies submerged in a liquid are generally referred to as submerged 
appurtenances to get it in the appropriate lingo.

Option 1:  In the old days, we used to calculate the seismic demand on the 
component without consideration for convective forces and add a seismic 
component that included the dead load of the submerged appurtenance and an 
additional mass equal to the weight of the displaced fluid.  That is still 
a good gut check.

Option 2:  The starting point is the ASCE 7-10, Section 15.7.6.1.4 Internal 
 Elements, but it is more of a general performance provision.  You will 
need to evaluate the seismic demand without the fluid and add it to the 
seismic demand due to the convective forces.  The impulsive fluid foces are 
not added.

You will need to calculate the height of the wave per the ASCE 7 Chapter 15 
 or referenced documents, calculate the velocity of the wave based on the 
size of the tank and period and then calculate the wave forces.  See ASCE 
7-10, Section 5.4 for the hydrodynamic wave height and forces on pier 
components.

You should calculate this at various fluid depths.  When the tank is about 
half full, you will have a hydrodynamic force acting at about midspan which 
 will be the maximum bending stress.  The maximum shear stress will be at 
other fluid depths.

Option 3:  Run a CFD model.  This is the most accurate, but I have to hire 
a smart guy to do it.  I have smart guys that I can recommend if you want 
to go that route.

Other than the API, AWWA, ACI 350.3 references, there is also "Seismic 
Design and Evaluation Guidelines for the Department of Energy High-Level 
Waste Storage Tanks and Appurtenances."  You can get this on line: 
<http://cirrus.mail-list.com/seaint-seaosc/27061159.html>

Regards, Harold Sprague

> Date: Thu, 2 Aug 2012 07:32:11 -0500
> From: ghodge(--nospam--at)hodgestructural.com
> Subject: [SEAINT-SEAOSC] Sloshing/Seismic forces on immersed bodies
> To: seaint-seaosc(--nospam--at)mail-list.com
> 
> I am evaluating the design requirements for equipment and components
> immersed inside ground supported tanks. I am familiar with determining
> convective and impulsive forces on the tank resulting from seismic
> acceleration, but those methods do not seem applicable to determining
> the forces exerted on equipment immersed in the liquids stored in the
> tank. Is anyone familiar with a method for determining the forces
> exerted by sloshing liquids on bodies immersed within a liquid storage
> tanks?
> 
> Thank you, in advance.
> 
> Gray Hodge

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