>
> I'm not an engineer but the analysis is relatively straightforward. It's
> easy to 'simplify' the structure and see what is actually happening in
high
> winds. (As a mathematician I'm more interested in proving the existence of
> solutions rather than actually finding them!)
I am an Engineer (but not a structures guy), and the devil is in the details
of that "simplification". Sure, reduced to a simple non-slender column with
canteliever loads, the analysis is trivial, and, as you say, leg failure is
unlikely. However, you don't have a simple non-slender rigid member. You
have a very slender hollow column, made of many component members, where the
load distribution among the legs and cross braces is not obvious by
inspection. I suspect (but have no evidence) that most towers do not fail
from compression of the base of one leg, but rather, from some sort of
buckling type failures. Even for fairly simple columns (i.e. a uniform tube
of material) the analysis for buckling is non-trivial.
>
> For the experts to suggest that guying a self-supporting fixed tower will
> result in leg failure under compression (assuming sensible guying) is
> untenable.
The experts don't suggest this. The experts suggest that "you don't know
it's safe", and speculate that failure due to increased compression loads
from the guys (perhaps causing a leg failure) might be something to
consider. It's all those mights and perhapses that get in the way.
It's one thing for someone to go out and try something, and accept the
consequences if it doesn't work if planned. That's part of tinkering, or
field day, if nothing else. As a reasonably responsible person, if one
experiments with some sort of structure, one should make sure that if it
does fail, it doesn't hurt anything. Say you're building a tree house for
your kids. You're not going to go out and hire an architect and structural
engineer. You would build it with common sense, and maybe proof test it by
getting a bunch of adults to climb up in it and see if it starts to fail.
Ultimately, if it fails with your kids in it, you have to live with it.
On the other hand, if you were asked to build a tree house for the local
preschool, you'd probably take a somewhat different approach. Injuring your
own kids is bad enough, injuring someone else's is much worse.
It's like climbing a crankup that's cranked up. Sure, it's dangerous. But
maybe it's a manageable risk. Maybe it's not blowing 80 mi/hr. Maybe you
trust that piece of 2" steel pipe you put in there to block it from falling.
They are decisions you make at the time.
And that's what comes out of discussions like this on TT. You'll get a lot
of "things to think about" and ultimately, you make your own decision on
your own stuff. At least you (potentially) know more after the discussion
than before.
If you are uncomfortable with the advice, then you need to go further, and
get your questions answered another way, typically by paying someone for the
information. In exchange for that payment, the advisor accepts some of the
responsibility (and they pay their insurance company to further accept some
of the risk).
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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