>Hi all...
> I just lost my Aluma 60'motorized crank-up in the recent windstorms
>here on
>Long Island. Fortunately, I am covered by my homeowners insurance.
Hi Jeff,
You are indeed fortunate. If I were your insurance adjuster, you wouldn't
be covered because I am willing to bet the tower specs were exceeded
somewhere. I have listened to a LOT of tower horror stories and the worst
ones involve crankups and right after that, towers made of aluminum. An
aluminum crankup would be my worst nightmare and now it is probably yours, too.
>Naturally, I am looking to replace the whole thing (antennas gone too),
>and am considering a Tri-ex LM470E motorized crank-up, which should be
>better able to hold the antennas than the aluminum job, or so I think. And
>that leads to my question.
The good news is that you are thinking steel instead of aluminum. The bad
news is you are still thinking crankup.
> The advertising material from Tri-ex states the tower will handle 30sf
>at 50mph, 15sf at 70mph. I called the engineer, and he says that the
>50mph rating is NOT a rating, just a comparison for my "information," and
>that the 70mph rating is what he stands behind. Although quite a friendly
>and knowledgeable soul, I can't actually get him to commit to anything.
Is that rating cranked up or cranked down? Don't assume anything. A good
reason why he won't stand behind the more aggessive ratings is simply
because he does not have confidence in his tower. He should know its true
capability better than anyone. Listen to him and get it in writing. He is
vague and evasive because he is responsible for what he tells you and he
feels like he is going out on a limb (which he is).
> Does anyone here have any experience with this tower? I am planning to
>put up another KLM KT34-XA, and try a KLM 40M-4 (4el 40) instead of my
>destroyed 40-2CD. Total windload is 21sf, total antenna wt is 156 lbs.
Like a lot of single tower installations, you are planning to stack two
beams. When you get the written commitment from the tower manufacturer,
make sure he understands that one of the antennas will be significantly
ABOVE the top of the tower on a mast. This will affect his answer. I
believe most tower square footage ratings assume the entire wind load is
within a foot or two of the top of the tower.
> The popular US Tower HDX572 is also rated 30sf at 50mph, but NOT rated
>at 70mph, and just a bit too expensive. I wonder how they compare.
Again, you are asking someone to give you an opinion of a potentially very
dangerous situation. Smart qualified engineers will either charge you an
arm and leg for that opinion or won't give it to you. They have to build up
their legal defense funds some way because if they hand out opinions on this
subject, they will certainly be hauled into court eventually. You may as
well round file the opinions you get from other than smart qualified engineers.
>Any insight here would be most appreciated. Perhaps you could tell me
>of some other successful similar installations that would give me some
>perspective. My contest station is off
>the air, waiting for the insurance check to arrive,and I'm anxious to make
>final decisions so that I can begin to get back on track.
>
>Thanks & 73 de JEFF WA2SYN
>
>wa2syn@li.net
I have several important questions I would love to have you answer about
your Alumina tower that failed so I can build my knowledge base about tower
failures:
1. Was this a guyed tower?
2. Was it cranked up at the time?
3. Did the wind loading of the antennas exceed the rating of the tower?
4. Did the design of the installation take into account that part of the
antenna load was well above the top of the tower?
5. Were there any signs of metal fatigue that could have indicated the
tower was weakened well before actual failure?
6. Where and how did it actually fail? Fold over at the base? Crumple
into a heap? Guy system failure?
7. Was it iced at the time?
8. How strong would you estimate the winds were?
These are tough questions, but answering them will fill in a lot of gaps in
our knowledge about what not to do when it is our turn. The answers to
these may be somewhat embarassing to you so I can't blame you if you just
ignore this message.
I DO have one STRONG piece of advice, though I doubt you will like it:
Abandon the idea of using a crankup and consider using well guyed Rohn 55.
It probably won't cost any more than the crankup you are considering. Since
I am not a smart qualified engineer, be sure to have my suggestion double
checked by someone who is.
I really hate to hear it when someone loses their antennas. I guess no one
was hurt. Good luck, Jeff, and be careful.
Stan W7NI@teleport.com
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