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RE: Stack Strakes

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Daryl,

We have measured natural frequency of installed poles but not to compare it 
 to calculated frequencies.  Our impact damper's performance is not very 
dependent on the frequency.  We do have different dampers for 1st mode and 
2nd mode vibration because of differences in the frequencies and 
amplitudes.

Robert Conners of Perdue University has done some testing of high mast 
(100'+ tall) lighting poles with fiber rope wrapped around it.

Ray

-----Original Message-----
From: seaint-seaosc(--nospam--at)mail-list.com [mailto:seaint-seaosc(--nospam--at)mail-list.com] On 
Behalf Of h.d.richardson(--nospam--at)shaw.ca Sent: Tuesday, February 05, 2013 1:22 PM
To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Stack Strakes

Ray,

        This is information worth knowing!  This provides me with moral 
support me for using damping ratios of 0.005 to 0.01.  The stacks I design 
usually have igniter lines plus aircraft warning lights etc. added to the 
stack.

        But tell me, have you ever measured the actual natural frequency of 
 a pole in the field to determine how much it varies from the calculated 
fixed end natural frequency?  Since I need the natural frequency to 
calculate the gust factor for wind loading by Canadian code procedures my 
procedure has been to assume fixed conditions to get an upper bound for the 
 natural frequency then run a few trials with a range of lower assumed 
natural frequencies.  Computer spreadsheets make this easy.

        Thank you very much for your contribution to date.  I can hardly 
wait to read what more you may be so kind as to write.

Best regards,

Truncated 1085 characters in the previous message to save energy.

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