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RE: Damping percentage

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The SEAOC Blue Book commentary has a history and discussion of the R factor.
Paul Feather PE, SE

From: Gordon Goodell [mailto:GordonGoodell(--nospam--at)]
Sent: Tuesday, September 30, 2008 1:39 PM
To: seaint(--nospam--at)
Subject: RE: Damping percentage



I?m interested in the history of ?R? (as part of a master?s thesis).  Do you have any references you could point me to?  The K stuff was before my time, but I?m slowly tracking it down.




Gordon Goodell


From: Tom.Hunt(--nospam--at) [mailto:Tom.Hunt(--nospam--at)]
Sent: Tuesday, September 30, 2008 2:05 PM
To: seaint(--nospam--at)
Subject: Re: Damping percentage



Considering all the other inaccuracies, gross assumptions, fudge factors, etc. that comprise your overall seismic evaluation, changing the percent damping is probably an unnecessary refinement.  Consider for the moment that our famous seismic "R" factor has no scientific basis and has been tweaked and expanded from the original 6 "K" factors from the 1970s and 1980s (i.e. R became 1/K).  Also consider that damping depends on numerous factors such a material characteristics, geometric configuration, and stress levels which makes it somewhat nonlinear.

That said, you will find various suggested percent damping ratios for non-building structures in some of the nuclear related texts and documents which might show a percent damping as low as two or three for a structure such as yours.  Some of our nuclear engineers might be able to find you a more direct text reference.

Thomas Hunt

"Ing. Benjamín Arcos Reyes" <barcosr(--nospam--at)>
09/30/2008 11:21 AM
Please respond to seaint





Damping percentage



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

< \_

Ing. Benjamín Arcos Reyes.

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