Just to remind you that when you start to calculate how the tower behave at
various wind speeds you have to consider the surface of the rest of the tower.
Yes, the force from the antenna is varying propositional to the square of the
wind speed but the forces on the rest of the tower is varying the same way. You
need that data too. The tower might be overloaded at 100 mph even without any
additional antennas.
Hans - N2JFS
-----Original Message-----
From: Charles Coldwell <coldwell@gmail.com>
To: Tower Talk <towertalk@contesting.com>
Sent: Thu, Feb 18, 2010 2:37 pm
Subject: Re: [TowerTalk] wind load
On Thu, Feb 18, 2010 at 1:34 PM, Stan Stockton <stan@aqity.com> wrote:
>
> I could be wrong about this but have always thought (from an old Rohn book)
> that 70 MPH equated to 30 pounds per SF of antenna.
OK, so in my example if the maximum wind load at 70 MPH is 15 sq ft,
and we have 30 pounds per square foot, that works out to 450 pounds of
force. That sounds reasonable.
If we believe the force grows as the wind speed squared, and that a 70
MPH wind puts 30 pounds per square foot of force on the tower (and
that a 0 MPH wind puts 0 pounds), then the constant of proportionality
is 30/4900. So that means the general formula would be
F = 3/490 * W * W * A
where F is the force in pounds, W is the wind speed in MPH, and A is
the antenna effective cross-sectional area in square feet.
What's the title/author of the Rohn book?
--
Charles M. Coldwell, W1CMC
"Turn on, log in, tune out"
Winchester, Massachusetts, New England (FN42kk)
GPG ID: 852E052F
GPG FPR: 77E5 2B51 4907 F08A 7E92 DE80 AFA9 9A8F 852E 052F
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