[TowerTalk] Guyed self-supporters (was "Concrete suggestions")

[Steve Maki]

N4ZR wrote:

>At 11:47 PM 4/16/03 -0400, K3BU at aol.com wrote:
>
>>So you are saying that self supporting towers have "weaker legs" than guyed
>>towers? Look around!
>>Again, with guys, legs in the self supporting tower share the vertical load.
>>Yes there is some additional vertical component from the guy, but that is way
>>below what would break the legs.

>I don't think it's possible to make such a blanket statement.  The only 
>right answer would be "it depends."  The only thing you know for sure is 
>that guying a self-supporting tower is putting forces on it that it is not 
>designed for.  There may be plenty of margin, or there may not.

In my very simplified mental model, I'm picturing a 45º upwind
guy attached at the top of the tower, a perfectly rigid 100'
tower with a 10' face width base, and 1000 lbs of wind force
all concentrated at the guy attachment point.

With the 45º guy, we should have 1000 lbs of downward component
from the wind, right? Add to that the downward component of the
pre-tension (of 3 guys), say 1500 lbs, and we have 2500 lbs of
compression, spread equally over 3 legs - 833 lbs per leg.

Now, remove the guy. We now have tension from the wind in the
upwind leg(s), and compression from the wind in the downwind
leg(s), right? Now we have a 10'/100' lever arm, or about
10,000 lbs of compression from the wind in the downwind leg(s).

Where am I going wrong in this admittedly oversimplified model?

--
Steve K8LX