My worst overload was 120' of Rohn 45 with a two element 40 10' above the
top of the tower, and 5 element Hygain Long John 20 meter on top of the
tower, then a A3S at 85' and then a side swing arm mounted 5 element 15 10'
over a 5 element 20 (all "Long Johns") from 65 to 75'. To me that was a lot.
The Rohn was guyed only twice at 60' and 110' (should have had at least
three sets of guys but to swing the swing arm and the 15/20 monobanders,
could not have the third set of guys). Stayed up years and years. That
installation came down when a tornado passed directly over my house and my
towers and the tower I am discussing buckled in the center above the bottom
guy because three 80-90' pine trees (along with another 70 or so pine trees)
were laid over and all three trees directly hit one of the guys pulling out
the opposing guy wire from the wire clamps and pulling the top half of the
tower over until it folded to the ground.
If it had not been for the trees, I think that the Rohn would have survived
and I would have some elements or booms to deal with....
73
Gary W5FI
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Stan Stockton
Sent: Thursday, February 18, 2010 2:37 PM
To: TowerTalk@contesting.com
Subject: [TowerTalk] wind load
I am curious how many guys have first hand knowledge of an amateur radio
tower (properly guyed) coming down as a result of overloading and how
many instances there really might be as compared to the number of
towers that
are severely overloaded?
I had a tower buckle one time because a tree fell on the top set of guy
wires, but honestly have had seen a lot of towers WAY overloaded,
beyond
what I would ever do, and in 40 years cannot remember ever knowing
anyone who had a tower failure with ham antennas installed.
In most cases the tower specs include a huge amount of safety factor
along with specs that include multiple, large coax cables from top to
bottom.
Everyone has a comfort level which needs to be satisfied.
73...Stan, K5GO
> ----- Original Message -----
> From: "Charles Coldwell" <coldwell@gmail.com>
> To: "Tower Talk" <towertalk@contesting.com>
> Sent: Thursday, February 18, 2010 1:37 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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>> http://lists.contesting.com/mailman/listinfo/towertalk
>
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