In a message dated 12/24/99 13:27:29, you wrote:
>Is the tower 25G or 45G? I don't think I'd do it for 25G - the legs
>don't have the leg capacity to take 67% more guy tension preload. This is my
>'non-engineer' perspective.
I'm not sure that's quite right Steve. For a 190' 25G tower my 1992 Rohn
catalog shows six guys per leg. If the bottom section of a 190 foot tower
can support six guy lines plus the additional weight of an extra 90 feet of
tower weight it's hard to see why 5 guys on 100 feet would be a problem.
What additional guywires gains us in additional capacity/safety would be nice
to know. I've considered guying my (planned) 100 footer in four places and
using 1/4" EHS instead of the suggested 3/16". My logic is that the
additional guywire will help the tower resist twisting and the thicker
guywire is less elastic which whould help control bending. The added cost is
a fraction of a 100' tower project so it seems a good idea. None of this
will stop a hurricane wind, but's it is a bit of over engineering which seems
helpful.
I'd be interested on additional input to this whole line of thought.
Particularly from people that could model some hypothetical towers and show
why different things are good or bad. A good example (well for me...) would
be to compare a 100' 25G tower built to Rohn specs vs the same height tower
guyed at the top with four equally spaced guy wires of 1/4" EHS. I'd also be
interested in the difference between the suggested 80% anchor to tower
distance compared to 85 or 90%. Logic suggests that an additional guywire
per leg (4 vs 3), heavier wire and additional tower-anchor spacing would all
be good ideas.
In anycase it's a real shame that the "data" we all have to work with is
either the not always applicable Rohn Catalog specs or anecdotal evidence
from other projects. We have easy access to great tools like NEC for
modelling antennas and horrible tools for figuring out how to hold them up in
the air!
Cheers,
Mark
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