Pat Barthelow wrote:
>
> I am musing over a sketch of a guyed tower, plan view, and wonder
> how the positioning of guy anchor points changes with sloped ground. Does
> one try to
> keep constant angle by all guys to the tower, by changing the anchor
> radius, or do you keep a constant distance to the anchor point, with the
> resulting different vertical angles? Also, if the ground rises a
> significant amount on one side, then for a 2 level guy system, the top
> guy, and the middle guy, assuming they would converge to a single point
> anchor, on level ground, intesect the real world sloping
> ground at two points that have significant spacing between them. In this
> instance,
> with sloped ground, do you anchor the top and middle guys at 2 locations?
> If the angles of different guys at, say, the center guy point on the
> tower, are different, and the guys are tensioned equally, there will be
> different horizontal and vertical force components attributable to each
> guy.....How do you deal with sloped ground when guying?
>
> 73, DX, de
> Pat, AA6EG/N6IJ;
> aa6eg@hh.tmx.com
> 599 DX Drive, Marina CA 93933
> "The Contest Station from the Government"
>
> --
> FAQ on WWW: http://www.contesting.com/towertalkfaq.html
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
Hi Pat,
Due to the challenges of my property here on a hilltop in rocky
Connecticut, I have had to deal with this issue for both of my towers
(Rohn 45).
The ground level varies as much as 10' vertically between the anchors of
my towers and the angles between the anchors vary from 112 - 128 degrees
from each other. This was due to the presence/absence of immovable rock
ledge and other obstacles. Needless to say the lengths of the guy wires
also vary. On my short tower (100'), (for the same height guying point
on the tower) the long guy is 20' longer than the others due to the
necessity of putting it out farther and a 7' drop vertically. Not a big
deal.
On the big tower (130') the differences are much larger. The long guy
at the 40' level is about 70' longer than the others, and the anchor
point is about 10' lower vertically than the others. This was necessary
for a variety of reasons.
Although the angle of the guys is different for each leg due to
different guy lengths and vertical heights, there is no problem with
proper tension or support. In fact, for our purposes (supporting a
tower and a few antennas) the only relevance is whether or not the
anchors are placed far enough away from the tower (min. 70% of the tower
height) so as to allow enough room under the guy wires for rotation of
the lower antennas if you want them to rotate.
If you put the anchors out at least 70% of the tower height you will be
fine. 80% is even better if that is possible.
I know that Rohn doesn't like 7-10' differences in the "height" of the
anchors from each other, but that is a liability issue. In the real
world, do what you have to do and don't worry about it!
If you are concerned about the possible differences in heights and
lenths of the guys, then I suggest that you make everything really heavy
duty. On both of my towers I decided to use the BIG GA345501 7' steel
anchors with the equalizer plate, 1/4" EHS, steel rebar cages in each
anchor hole, and about 2 cubic yards of concrete for each. I also used
"Ice Clips" on each guy wire preform (that was pointing up) as added
protection, and on the big tower I used Guy Brackets AND torque bars.
ALL the guys for each leg should come to the SAME anchor point.
When using widely variant guys, put the LONGEST guy on first and tension
that one first. The reason is that there is a lot more sag in the
longer guy and it will take significantly MORE turns of the turnbuckle
to change the tension a given amount than it will take for a shorter guy
wire.
If you do the shorter guys first you will discover (through experience)
why you made a mistake in NOT doing the longer guy first. Suffice it to
say that is a REAL PITA to have to redo the guys when you realize that
you can't adequately tension everything AND get the tower straight
UNLESS you start again WITH THE LONGER GUY FIRST! Don't make that
mistake.
Hope this helps and good luck with your project!
73
Bob KQ2M
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|