At 08:35 AM 1/14/2007, jcowens1@comcast.net wrote:
>I disagree with those who say that the old specs are no good today.
>The science of loads and mechanics has not changed over the past 50
>years or more and Tri-Ex did a good job providing these specs in
>drawings on their towers.
Yes..the actual engineering hasn't changed much and the analysis
method would be valid. However an engineering analysis intended for
submission to a regulatory authority would need to be based on things
like material properties of the proposed structure at the time it's
being erected, not what they were when it was new.
I'd find it hard to believe that it would be less expensive to do the
testing and inspection of a used tower than to just buy a new
one. You'd need to do things like run a borescope down the tubes to
evaluate corrosion, do an external inspection for cracks, etc. Or,
possibly, you could set up some sort of proof test (load the
structure on a jig to 2 or 3 times the design load and see if it
deforms more than expected).
All of this would be exceedingly expensive, if you're asking a PE to
sign their name to it and be liable for the results.
>The drawings and engineering info that I have from US Towers for my
>HDX572 MDPL doesn't compare with what I had from Tri-Ex on that
>tower. I had no problem getting either tower permitted where I live.
>The Tri-Ex tower was strong enough that when the bent over (4 ft)
>section was cut off, the remainder of the tower is still useable. It
>is a very well built tower, and better than most guyed towers you
>can buy today. A local ham has bought that tower and intends to fix
>it and re-erect it. He will end up with a good tower that will last
>his lifetime if he doesn't experience a freak accident like I did.
Sure, but he's probably going to have a bit of a chore with his local
regulators, if they want engineering analysis.
OTOH, if he's just going to plant the tower, put antennas on it, and
doesn't require permits or need to prove to someone that it's "safe",
etc., then he'll probably have a long and happy use of the tower.
It's sort of like buying a used car without a warranty. Most of the
time it works out ok, but you never know for sure, do you? These
days, cities want guarantees.
Jim, W6RMK
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