Well, OK, here was my response to Bill, also off-line. To maintain
continuity, it's at the bottom.
Steve K8LX
Bill wrote:
> The following was Steve's question to me and my response which was snet off
> the reflector.
>
> Steve said:"Bill,
>
> Are you an engineer? If so, can you devise a case, using a reasonable
> tower and guy system, which contradicts my (and others) "theory"? I've
> put this to a few engineers, and they haven't come up with one. I'd be
> the first to shut up about it if an example could be shown...
>
> Thanks,
>
> Steve K8LX"
>
> My response:
>
> "Steve
>
> Yes I am an engineer but I am not a structural engineer. But I do know
> enough not to make assumptions about the consequences of guying a
> self-supporting structure without knowing more about the effect the guying
> has on the buckling mode. Just saying that you had talked to an engineer
> does not mean anything to me if the engineer is not trained structural
> engineer and I seriously doubt a structural engineer would have passed off
> your scenario so lightly. Such a statement is simply not proof that the
> guying can be done safely.
>
> For example I do know that the buckling mode will depend on the section
> modulus, yield strength, induced compressive stress (when combined with the
> shear stress and bending stress to produce the principle stress) and the
> location of the guys with respect to the length of the guyed sections. Too
> much stress with too little section modulus and yield strength over an
> improper length will induce buckling, which is not the same as the simple
> question of the stress at the base and is much more difficult to analyze.
>
> I addition to being an engineer, I was the chief lawyer for CF&I Steel
> Corporation earlier in my career and later the VP and general Counsel of
> SAAB's onshore aviation operation. I also taught Aviation Law as a
> professor of Flight Technology. I am very familiar with he issues
> considered by companies that produce towers since CF&I was one of them. The
> liability to a company for "failure to warn" is one way litigants claim
> liability against manufacturers. For that reason the warnings have to be
> carefully analyzed and specific. I was, perhaps, better prepared than most
> lawyers to do that as a design engineer (I helped design parts of the Boeing
> 747) so to suggest that the legal position of companies is just something
> the lawyers cook up is pure nonsense.
>
> So it is really up to you to prove that the guying can be done safely and I
> don't think you have even come close. You apparently have no expertise and
> have not given any credible evidence that anyone with approprite expertise
> has made a considered evaluation of the subject and renedred a professional
> opinion. Without that the willingness to accept your short-cutted theories
> is foolhardy.
Well Bill, I'll defer to your expertise, but in all the years this has
been discussed, I've not heard of a single case which disproves the
admittedly seat of the pants theory.
Here's my thought experiment:
Take two towers, one guyed and one self supporter, same height, each
designed for approximately the same loading at the top.
Just for the sake of discussion, so that we have some kind of image in
mind, lets say the towers are 200' tall, and the top face width of the
self supporter is equal to the face width of the guyed tower, and the
guyed tower has 4 equally spaced guy levels.
Now start modifying the guyed tower by tapering it, spreading the base,
increasing the size of legs and diagonals, gradually making it resemble
the self supporter, all the while keeping the guys in place at their
original heights and tensions.
Do any alarm bells start ringing that some failure mode or unsafe
condition is likely while these mods are taking place? To me it seems
reasonable that when the guyed tower reaches the configuration of the
self supporter, it will be stronger than it was before, and therefore
stronger than the unguyed self supporter.
I'm sorry if you're cringing at this moment at my stupidity, but I'm
seriously trying to find out if this is all wet.
While not an engineer, I am in the commercial tower installation
business and see the structural calculations every day. The engineers
I've asked are in the business. Of course like any good engineer they
would never sign off on blanket statements, but OTOH, they couldn't come
up with a good illustration, a concrete example, of why it shouldn't be
done.
Thanks for your indulgence.
Steve K8LX
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