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Re: Damping percentage

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Benjamin,
 
        Check out ASME-STS-1-2000 for steel stacks.  This has a chapter on damping which might be useful to you.
 
        The stacks that I have designed are smaller in diameter, and taller.  For the most part they are designed to resist wind loading and are intended to remain in the elastic range.  They also have less attachments.  I usually use 0.5% to 1.0 % for welded steel stacks and up to 1.5% for reinforced concrete stacks.  I suspect that local buckling stresses of thin walled cylinders (which yours certainly is) will govern your design and that yielding can never be reached.  I would suggest that you check that out.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Tuesday, September 30, 2008 12:21 PM
Subject: Damping percentage

Hi

I need to check a drying tower consisting its main body in a cylindrical tube of 6-m diameter and 36-m height. It's been considered that the tube will probably be 3/8-in steel plate. At the top of the tube there are several trusses all around the tube, in order to support cyclones and fans. In addition to these there are three levels of maintenance platforms supported in the tube and upper trusses with its corresponding live loads. I've been wondering if I should keep considering a percent damping of 5% in order to perform dynamic analysis.
Am I right in being worried or i am missing something?.

Assuming that I'm right by considering a different percent damping, the next question is... which one?... how can I estimate a reasonable percent?.

It could be extremely difficult to implement any kind of field test, so that i think I will have to refer to book references. Thanks in advance.

Benjamin Arcos
Ingenieria Rioboo
Mexico City

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Atentamente,
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Ing. Benjamín Arcos Reyes.
Visita: http://www.senderodelpeje.blogspot.com/