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RE: Circular Tanks

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Melissa

     Stan Scholls comment on the physical characteristic of sludge are correct. 
Sludge can vary from 65 to 75 #/ft.^3. The angle of repose can vary from 15 to 
more then 35 degrees. The amount of solids in the sludge will determine the 
weight and angle of repose. The amount of solids is dependent on the type of 
dewatering done.
     Be careful in treating the sludge as a liquid. Housner's equations can 
give unconservative results when tanks are actually filled with a solid. I 
would also check the case of the sludge acting as an added mass using either a 
response spectra or UBC type analysis. The concrete mix and curing are also 
important is preventing unwanted cracking. Minimum steel per ACI 350 is a good 
place to start. Additionally keep the total amount of cement and flyash low. 
Don't increase cement to improve pumpability and keep the same  water cement 
ratio. The first 7 days of cure are very important in reducing cracks.

Acie Chance

-----Original Message-----
From:	Melissa Toth [SMTP:mtoth(--nospam--at)theschneidercorp.com]
Sent:	Tuesday, July 11, 2000 8:31 AM
To:	seaint(--nospam--at)seaint.org
Subject:	Circular Tanks

Hello Everyone!

I am a structural E.I. working on designing a circular concrete tank for sludge 
storage for a wast water treatment plant.  I have very little experience in 
this, and have searched your archives for help.  I need some guidance on doing 
the seismic design for this tank.  I have the general design mostly complete, 
but need to make sure that everything is adequate for the seismic forces.  It 
is not an elevated structure, but one that only sits far enough into grade to 
get below the frost line.  Any help would be greatly appreciated.  Thank you

--Melissa J. Toth, E.I.


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