On Apr 17, 2006, at 10:56 AM, ROBERT CARROLL wrote:
> I have a question more or less related to this thread. I have a
> MonstIR
> which is about to go up on 70' of Rohn 55. The system has been
> designed by
> a couple of real pros and I have had a PE look over the design.
> Although I
> am on two acres, the lot is not level and I could not put the tower
> in the
> best location because it turned out a septic field is in the way.
> So I am
> left in a situation where the guys are going to be elevated and
> attached to
> posts, 2/3 of which are in cement per the PE's guidance. They are
> equally
> spaced in azimuth angle and all meet the Rohn minimum distance from
> the base
> of the tower guidance.
>
> I am by no means a structural engineer, but--and I see traces of
> the idea in
> the "small lot" thread--had assumed the guys should also be
> anchored the
> same distance out from the tower. That sounds pretty from a symmetry
> standpoint, but it is just not possible in my case. The PE and the
> tower
> guru say there are fairly frequent commercial installations where
> the same
> problem exists--and in fact where one guy has to be almost
> horizontal due to
> tilted earth. They say the important thing is maintaining the minimum
> attachment distance from the base and the 120 degree spacing. They
> also say
> the guys, though of different lengths of Phillystran, should be set
> to the
> same static tension.
>
> It is too late to change any of this, and I trust the two experts,
> but I
> would appreciate some educational feedback on the subject of guys of
> different lengths.
>
> By the way there will be an upper and lower set of guys, and it is
> unlikely
> the stainless posts will ever bend the way the ones did in the pix
> on the
> reflector this AM. I noticed that installation didn't comply with
> the 2/3
> in the ground requirement of my PE.
> Bob W2WG
I am a physicist not a P.E., but this sounds incorrect to me. I
believe you need to end up with zero net horizontal force at the
attachment point on the tower of each set of guys (i.e., guy tension
X sine of angle between guy and vertical is equal), not equal static
tension. If you have something other than 120 degree spacing it gets
a bit more complicated, but you still want to have zero net
horizontal force component on the tower.
Bob, N7XY
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