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Re: Stack Strakes

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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,

H. Daryl Richardson

----- Original Message ----- From: "Ray Minor" <ray.minor(--nospam--at)hapco.com>
To: <seaint-seaosc(--nospam--at)mail-list.com>
Sent: Tuesday, February 05, 2013 7:22 AM
Subject: RE: [SEAINT-SEAOSC] Stack Strakes

Daryl,

In our lab tests of an aluminum lighting pole mounted on a rigid frame with nothing attached to the pole but a rigid mass at the top, we got a damping ratio of 0.0018. This same pole with one of our impact dampers gave us a damping ratio of 0.0088. Some dampening would be provided by the electrical wiring, bolted joints, light fixtures and the soil around the foundation of lighting pole in the field, so the laboratory damping ratios are probably considerable lower than for an installed pole.

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: Monday, February 04, 2013 4:58 PM
To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Stack Strakes

Ray,

Truncated 823 characters in the previous message to save energy.

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