You misunderstood the PE. The guys cannot be
at the same tension, because they are different lengths.
Here is why. If the HORIZONTAL tension at a guy point
is not the same with all the guys, the guy point will
move until they are. This is physics 101.
If the horizontal tension in two guys are the same, and
they are at different angles, then the vertical and
longitudinal tensions are different by the cosine rule
that K6LL quoted. i.e. you CANNOT balance the tensions
in the guy wires.
73,
Tom - N1MM
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of ROBERT CARROLL
Sent: Monday, April 17, 2006 1:56 PM
To: 'David Hachadorian'; 'Towertalk Reflector'
Subject: Re: [TowerTalk] Guying on a small lot
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
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of David Hachadorian
Sent: Monday, April 17, 2006 12:47 PM
To: Towertalk Reflector
Subject: Re: [TowerTalk] Guying on a small lot
----- Original Message -----
From: "Jon M. Knodel" <jknodel@msn.com>
To: <towertalk@contesting.com>
Sent: Monday, April 17, 2006 8:38 AM
Subject: [TowerTalk] Guying on a small lot
>I don't know if this question has been brought up on the
>reflector or not, but here it is:
>
> I have a small lot (73' x 122') and want to install a 60'
> Rohn 25G. Because of how the house is set and other
> structures, I am having problems placing the tower where I
> can get the specified 80% guy length (48'). I am pretty
> close to getting it but come up just short on two of the
> legs. On the third one I can get 48' without any trouble.
> On the other two, I am about 4' short (73% instead of
> 80%).
------------------------------
The 48' guy will make an angle (a) with the ground of 51.3
degrees. The 44' guys will be 53.7 degrees. Tension in each
guy wire due to horizontal forces (Fh) on the tower (such as
wind, and the other guy wires) is Fh/cos(a), and there is
only a 6% difference in the cosines of 51.3 and 53.7.
Tension (including pretension) in the two short guys will be
only 6% higher than the other one. I wouldn't worry about
it.
Dave Hachadorian, K6LL
Yuma, AZ
.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|