> From: Jeff Singer <wa2syn@li.net>
> Subject: Tower rating question
> I just lost my Aluma 60'motorized crank-up in the recent windstorms
> here on
> Long Island.
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> 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.
More Stuff Deleted
I think I might understand the engineer's reluctance.
According to my copy of the EIA-222 Rev E, Long Island is an 80 or
85 MPH wind district, depends on the county, and you are only asking
for 50 and 70 MPH data. Also I think Long Island can get some icing
conditions, but I am not familiar with the area. All of these (and
the fact that your last tower blew down) indicate that you probably
need to look at a some higher rated (stronger) towers.
My experience with companies selling towers (other than the
manufacturer) is that they make claims that are somewhat optimistic.
In one case a friend was going to put up a crankup based on the
advertised claims. He is a cautious individual and asked to get
copies of the enginering certification calculations. He had to pay
about $20 for them and when they came, they had about half the wind
load that was in the advertisers literature.
Your best bet is to go to the manufacturer of the tower and ask what
the rated wind load according to EIA-222 Rev E. This is the current
standard. They are working on Rev F but I have not seen an official
copy of it yet.
Unfortunately, EIA-222 doesn't address extendable towers, so some
judgement is in order. IE. Does the tower have to take full wind load in
the Extended Position? There are other questions that have to be
asked depending on the location. And all of this has to play past the
local building officials.
You might want to check with your local ARRL section and ask to
contact the the local Volunteer Consulting Engineer to give you some
guidance, so you can ask the right questions of the manufacturer and
provide the right answers to the building officials.
de n0yvy
Steven H. Sawyers PE
ARRL Volunteer Consulting Enginner Midwest Section
disclaimer: I don't sell towers, I just engineer installations and I
have no financial interest in any tower manufacturer.
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