One thing more to consider. It seems to me that perhaps sometime
about 5-10 years ago the national requirements changed. Most
municipalities adopted the new standards. This caused tower
manufacturers either de-rate their towers, or redesigned them to be
stronger to meet the new requirements. As an example, Heights Towers
chose to redesign its' towers to meet the new requirements. As a
result, towers that were manufactured some years ago and rated for X
wind load, would NOT be rated for the same windload by todays
standards. If someone wants more information on this, I believe this
was discussed here some months ago and someone posted the specific
national standard that changed.
If what I remember is true, and adding what's been written here on
this reflector, the following guidelines seem prudent:
A) Using a catalog to evaluate a used tower may be problematic unless
you know for sure that the catalog data is both; a) from the exact
same manufacturer date, and b) the same model and manufacturer, as the
tower being erected.
B) Using new catalog data to evaluate an older tower could be very
dangerous as the new catalog would quite possibly be describing a
currently manufactured, STRONGER tower.
C) It is very risky to mix data regarding freestanding and guyed
towers to develop a site solution. The towers are designed very
differently, and loads/ratings do not compute equally, or in other
words, are not interchangeable.
D) Manufacturers rating data/loads are developed using specific
installation parameters. Changing those parameters could adversely
affect the specifications. Most tower manufacturers will only stand by
their calculations if the site is built according to the manufacturers
EXACT specification.
E) While manufacturers have a safety factor, it is DANGEROUS to guess
at that value and/or develop a site plan that in any way negates or
utilizes the safety margin.
F) Sites that use "house brackets" should be subject to special
scrutiny as little is published about how to calculate the
appropriate loads and dissipate the loads over a large enough space.
G) Any site, on which the tower/antenna height is such that if it
failed and fell would mean that the tower/antenna would fall upon a
neighbors property, should be built to the highest, most conservative
standards to insure that property/personal injury does NOT occur to a
neighbors property. Think of it this way, no building or other
structure would be allowed to be built in such a way as to jeopardize
anothers property or personal being. A tower is a structure, and one
that if failed, can cause considerable damage or personal injury to
others!
It seems to me that we have a MORAL obligation to live up to the image
that we aren't cowboys -- that we ARE knowledgeable, technically
astute persons who put safety first, and therefore should do
everything in our power to "DO THE JOB RIGHT". No compromises, no
integrity lapses, regardless of cost or difficulty. If an individual
can't do that -- then he/she shouldn't put the tower up!
73 from.......
Bob Otto
N8NGA@one.net
Cincinnati, Ohio
**********************************************
DXCC 10M ** DX is !! ** WAS 10M
There is a very fine line between
"HOBBY" and "MENTAL ILLNESS"
**********************************************
When trouble arises and things look really bad,
there is always one individual who perceives a
solution and is willing to take command.
VERY OFTEN THAT PERSON IS CRAZY!
**********************************************
Tuesday, January 16, 2001, 5:39:39 PM, you wrote:
GDE> Actually, all the back and forth on this caused me to go back and look at
MY
GDE> copy of the Rohn Ham Tower Catalog which shows a number of different
GDE> scenarios:
GDE> 1.) 110 MPH Basic wind speed ratings for everything from 40 to 170 ft.
GDE> of 45G. (60 ft. will support 9.6 sf of antenna...guyed at 25 ft.
GDE> with
GDE> 3/16 EHS tensioned to 400# and 55 ft. with 1/4 EHS tensioned to
660#
GDE> The same tower height, with a single 3/16 EHS 400# set of guys will
GDE> support 16.7 sf at 70 MPH).
GDE> 2.) 70, 80 and 90 MPH ratings for everything from 40 to 100 ft. of
GDE> bracketed 45G
GDE> (60 ft. will support 33.3 sf at 70 MPH, 24.7 sf at 80 MPH and
GDE> 17.0 sf
GDE> at 90 MPH...bracketed at 23 and 46 ft. levels).
GDE> What it does NOT show is any ratings for bracketed towers in excess of 90
GDE> MPH
GDE> wind speed ratings. My guess is they don't recommend it. That's not to
say
GDE> that
GDE> it "can't" be done...just that if you want to be sure that it is done
GDE> safely, you'll get
GDE> someone who is qualified to 'run the numbers' to check the installation.
GDE> ARRL
GDE> has a Volunteer Engineer program, similar to the Volunteer Counsel program
GDE> for
GDE> legal issues, and I'd wager you could find someone to take a look at your
GDE> proposed
GDE> installation for a LOT less than $1800/hr.
GDE> 73/Be Safe, Gerald W5BA
GDE> w5ba@compuserve.com
GDE> <snip>
>> It seems that the tower specs provided by the manufacturers are not
GDE> adequate
>> for many areas of the country. Why they choose not to give us the specs
GDE> we
>> need, I will not venture to guess, but they are the only ones that can do
GDE> it
>> properly.
GDE> <snip>
GDE> --
GDE> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
GDE> Submissions: towertalk@contesting.com
GDE> Administrative requests: towertalk-REQUEST@contesting.com
GDE> Problems: owner-towertalk@contesting.com
===8<===========End of original message text===========
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