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Re: Sloshing Damping

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You can also find the formulas in AWWA Standards D-100 (Steel Tanks) and D-110 (wire wrapped prestressed Concrete tanks as well as the standard for bolted steel tanks which I think is D-103.  The basic theory treats tanks as a 2 degree of freedom system with an "impulsive" mode which captures the effect of water moving with the shell, the shell and the foundation  and a "convective" mode which considers the sloshing of the fluid (water for the AWWA materials). The formaulas are quite similar to the last version of API 650 I looked at. The 1/2% damping accounts for the fact that there is little to produce damping when you expect the tank to behave in an essentially elastic manner.  So the forces are larger than you would get with 5% damping. For normal buildings, the 5% damping is a surrogate for allowing damage and plastic deformation to occur.
Bill Cain, S.E.
Berkeley CA  
In a message dated 11/22/2006 1:31:51 A.M. Pacific Standard Time, masroor(--nospam--at) writes:
There is nothing secretive about this. The formulae and graphs are documented in API codes. The forces are much reduced for large shallow tanks. 
----- Original Message -----
Sent: Wednesday, November 22, 2006 4:29 AM
Subject: RE: Sloshing Damping

I did several tank seismic calculations in the past using some complicated formulas developed by the petroleum industry to take sloshing into account.  In most cases it reduced the overall lateral force, but in some increased it from that of the 5% damped levels.  I don't know if any of these formulas are available for use beyond the petroleum industry however.  They were kind of secretive about them.

William.Sherman(--nospam--at) wrote:
It doesn't reduce your seismic shear.  Normally acceleration response spectra is based on 5% damping for buildings.  For sloshing water, the damping is reduced to 0.5%, which in turn increases the spectral response. The response at 0.5% damping is 1.50 times that at 5% damping.
Bill Sherman

From: Rich Lewis [mailto:seaint04(--nospam--at)]
Sent: Tuesday, November 21, 2006 3:07 PM
To: seaint(--nospam--at)
Subject: Sloshing Damping

ASCE 7 allows for 0.5% damping for sloshing of material in a storage tank.  How do I use this number to reduce the seismic shear?

Mark Pemberton, S.E.

Pemberton Engineering
502 Mace Blvd., Suite 2B
Davis, CA 95616

Ph:  (530) 792-0511
Fax: (530) 792-7109
Bill Cain, S.E.
Berkeley CA