[TowerTalk] US Tower: Broken cable, resolution?

[Al Williams]

I would like to read a mini-tutorial on tower strength and wind loading from
some of our tower experts.
1.  Is it true that the wind speed at say 100' is greater than at 50'?
always?
2. For a free-standing tower, is the failure mode most likely at the very
bottom of tower?,
3. Tri-ex in FirstCalls nice website states that the designer should add up
wind surface area of all of the installations on the tower and that a tower
should be selected that exceeds the total. But they go on to state that for
stacked antenna installations, the tower should be derated.

 Intuitively, it seems to me that lower beams of the stack would not cause
as much stress on the tower as the higher beams and that the towers rating
could be actually be increased.  Or more correctly, the
square footage of the lower installations could be derated. To illustrate my
point, surely a 70' tower rated at 10' sq ft   would withstand a much
greater wind speed if the beam were placed at say the extreme 2' from
ground.

Although these questions refer to free-standing towers, I would like to also
read a tutorial on guyed towers.  I suspect that many other towertalk
readers  would enjoy, appreciate,  and benefit from our
towertalk talkers writings as I have not seen this kind of material in my 20
or so antenna books!

73 k7puc

-----Original Message-----
From: Dick Green <dick.green@valley.net>
To: Tower <towertalk@contesting.com>
Date: Saturday, April 01, 2000 9:12 AM
Subject: Re: [TowerTalk] US Tower: Broken cable, resolution?


>
>I've had an MA-770MDP with a TH-7 at the top for two and a half years, and
>here's my $0.02 on the crank-down subject:
>
>1. Buy the motor drive and remote control. Hand cranking is hard and
>time-consuming. Eventually, you will neglect to do it and will be sorry
when
>that unexpected windstorm comes up.
>
>2. Use the tower at full extension only when needed. I use it that way only
>for contests and chasing rare DX.
>
>3. Leave the tower 20 feet under full extension for all other operating.
The
>70 foot tower is *much* more stable and resistant to wind when lowered to
50
>feet, and a tribander will perform perfectly well at that height for most
>operating needs. I have no doubt that the tower can handle 70 MPH or higher
>winds when lowered to 50 feet. I leave the tower at 50 feet  whenever I'm
>home. Since I work at home, it's at 50 feet almost all the time.
>
>4. Crank the tower down all the way whenever leaving the house overnight.
>
>5. Install a windspeed gauge with a built-in speed alarm and a NOAA weather
>radio with a built-in alert alarm. Do not leave the tower fully extended
>when winds exceed 25MPH. Do not leave the tower at 50 feet when winds
exceed
>35 MPH. Actually, I crank it all the way down when winds get up to about 30
>MPH.
>
>73, Dick WC1M
>
>
>
>--
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>
>


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