I took another look at my Rohn Catalog and I now see where they do list the rod
angle. Funny, I never noticed that before . . . Still, they don't tell you how
they caluculated it . . .
I learn something new every day . . . even after 48 years of ham radio.
Michael Rauh wrote:
> Jerry, Stan, Dave, Tom,
> I agree with Jerry and Stan - the angle is probably not critical. Rohn
> presents the angle to 0.1 degree in their guyed tower drawings. This seems
> impossibly precise to me - there is probably way more sag or bow in the guy
> anchor than that.
> I also suspect that Dave is correct when he suggests taking the vector sum
> of the loads on the guys when the tower is at its rated wind load to find
> the guy rod angle.
> In thinking about this problem I realized I don't know how to calculate the
> individual loads on each guy wire. I use a rigid body model for the tower
> that will give the total load on the guys, but won't tell me how the guys
> share the load, at least as far as I can see. To figure out the load on
> each individual guy, I think I will need to consider how the tower deflects
> under load.
> Consider a tower with two sets of guys and an antenna on top. I could start
> by assuming the tower is fixed at the top and the base. I calculate the
> wind load and how the tower will deflect under that load. Draw a curve,
> deflection vs. load. Then assume the lower guy is attached at mid-point,
> draw a curve of elongation vs. load. The load on the second guy is where
> the curves meet. The reminder of the load on the tower, including the
> antenna load, is absorbed by the top guy.
> But wait! The top guy elongates under load too, relieving the load on the
> bottom guy. So I will have to set up a system of simultaneous equations in
> order to get the loads on each guy. I will need equations for the
> elongation of the top guy, the bottom guy, the deflection (bowing) and the
> pivoting of the tower. If the tower has a pivot base that is all I need,
> but if the base is cast in concrete I might need an equation to account for
> the force needed to tilt the tower as the guys elongate.
> Does that sound right? Do you know of any references where this kind of
> problem has been worked out? I know Kurt Andress has found guy loads using
> a finite element program. I need to understand the principles involved
> before I resort to a program!
> I think it would be very cool to know how to find the loads on the
> individual guy wires in a tower system.
> Best Regards,
> Mike Rauh, NV7X
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