Here's where I'm unclear. Let's say, in addition to the 10
lb load at
the top, you put a 10 lb load in the middle of the tripod.
What do you see on the scales?>>
Steve,
Getting our arms around a complex issue like this may be
difficult without a drawing or experiment.
I think the important point is the guyline converts what
would be large amounts of tension on some legs and
compression on others to MUCH less compression and greatly
reduces if not eliminates leg tension.
Think of a self-support as a guyed tower with guylines
folded in so far they are integrated into the vertical
members of the tower. Now imagine you move the guys outwards
to anchor points some distance from the base when guys are
added.
The only possible danger might be allowing some area near
the middle of the tower to kick out from direct wind force
and forces transmitted down through the structure from the
top, BUT the forces transmitted down through the tower would
be less with guylines than without them.
The only exception I can think of would be if you really
seriously overbuild the guylines to the point that the
static tension increases the load to make some lower area of
the tower try to kick out. The solution there would be to
reduce tension or add another set of lines.
I think the only problem is not knowing where to attach the
guys or what size they should be for optimum rating. I don't
think there will be very many cases where the wind load
rating will decrease.
Imagine tramming a large antenna up on a slender mast. How
many people on this reflector would devote a week and 394 kB
of text to warning people that back-staying the mast will
make it more prone to fail as the antenna is trammed up,
because it was never designed to have a backstay? There we
have a very slender flexible column, and don't think twice
about countering the side force caused by the tram line
tension. Naturally any fool could bend the mast or decrease
the load survival by using excessive back-guy tension....but
we all pretty much know (I hope) the back stay is a good
safety idea.
If I had a self-support tower near a power line, I'd back
guy or safety guy it with a loose but stout line if it was
self supporting. The real worry is always common sense and
using funky materials, that's why the general population
should stay away from power lines. We tend to use rope and
wire and flimsy antennas, and tend to NOT take precautions.
73 Tom
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