At 01:21 PM 4/11/2005, Chris Pedder wrote:
>At 18:54 11/04/2005, Jim Lux wrote:
>
> >However, we'll approximate, using Rohn's moment calculation of 37,770 ft
> >pounds. At the top of the 64 ft tower, this is about 590 pounds. So,
> >assuming the wind comes from the direction of the guy, the guy is going to
> >have to resist the 590 pounds.. assuming no deflection (so the angles
> >remain the same) requiring a tension of 590/sin(30) = 1180 pounds. That's
> >an increased downforce of about 1400 pounds, for a total of 2440
> >pounds. Yes, it won't be quite that much, because the downwind guys will
> >relax a bit, etc.
>
>Excuse me, the tower is rated for 120lb (sic) headload and you want to
>apply 590 lb, albeit opposing the 120lb on the antenna? Do you think this
>is a sensible strategy?
I'm not applying the 590 lb... that's the tower applying the load on the
guy from the wind. On that tower, the wind load on the tower (excluding
the antenna) is about 1050 pounds, spread out over the 60 odd feet.. a LOT
more than the little 120 pound load from the antenna. Rohn's calculations
show anywhere from 9 to 5 square feet per segment of the tower as you go up.
One could make a simplifying assumption that the tower can be considered as
a rigid beam supported between two supports, so half the wind load appears
at the bottom and half appears at the top guy (i.e. about 525 pounds on
each).. Then you'd add the load from the antenna (120 lbs) at the top.. If
you do this (which would be typical for a standard uniform section guyed
tower like Rohn 25/45/55) then the load at the guy is actually higher than
I used (525+120 = 645 lbs) with only 525 shear load at the base.
This would be the load if the guy were perfectly slack before the wind came
up, by the way. You've also got to add in the preload on the guy in any
real calculation.
Well.. since you ask, no I don't think it's sensible, but then, the purpose
of the exercise is to show that there isn't necessarily ANY sensible
configuration that's trivial to analyze.
>Chris
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