Steve- this will probably be the only time I will loudly dissagree with
you, and this is only in a couple of points. I am not professionally
involved, like Kurt, and can afford any Flack
In regard to the golden rule- concerning following the manufacturers spec-
this is ONLY TRUE if the manufacturer has been honest with us. The fact is-
placement on the tower MUST make a difference in the loading. Take the
ridiculous extreme, where the load (antenna) is at the base- it is very
obvious that the wind load is a minimum, and not because the wind is less.
It is also obvious that the bending moments have to change as the load is
moved up the tower.
The manufacture rmay , for various reasons, claim there is no difference in
the allowed load, but he has other motives in his claim. One- he gets paid
for special case analysis- two- he tries to mantain a very safe margin, to
avoid legal liability- and three- he simply cannot afford the manpower to
analyse all cases. Even the several manufacturers Engineers will (and
have, here on this forum) have different opinions about the critical
loading. In their defense, They do not usually claim the the loads are the
ones the tower will withstand- they only say they are the "allowed" loads,
meaning they will back them up. Lawyers are trained to quibble, and these
specs are written , mostly, by lawyers.
you will be safe, as an installer, if you follow the specs, but, being
realistic, you KNOW the manufacturers claim is false to fact. Kurt is
probably right in avoiding the controversy of dissagreement, but, as any
good Engineer is designed in his heart to feel, he cannot let engineering
falsehood go by without saying SOMETHING.
The fact is, the placement on the tower DOES make a difference in the
loading. The proper consideration of the difference is not an easy job, and
does require information the manufacturer is not about to release, as well
as considerable engineering know-how. Please note using a PE is ONLY a
requirement if legal problems are involved. Many engineers are even more
capable than the average PE of doing the needed calculations. PE's
concentrate on specs and legality, others frequently concentrate on the
loads and strengths.
We used to hire one PE to keep to sign off on the work that was done by
real experts. The government required that a PE sign off, even though
everyone knew the work was of a nature that was not within the realm of
knowledge of most PEs.
Bill- W4BSG
At 09:43 AM 12/27/1998 EST, you wrote:
> It is. The whole idea of TowerTalk was to present a forum where
>questions (and everyone's got them) could get answered and topics
discussed. I
>think that it's been successful in its mission. And the most important basic
>discussion is PROPER ENGINEERING.
>
> Kurt, you're one of only a handful of TowerTalkians whose technical
>expertise I trust on a consistent basis. Heck, I don't even trust 99% of hams
>to be able to tie a decent knot properly. TowerTalk is endeavoring to provide
>parameters and advice that anyone can follow safely. Anyone wanting to
>consider "out of the box" scenarios is always told to "get a PE involved" for
>obvious reasons. And ALL of these discussions are appropriate.
>
> But I will always draw the line at exceeding or 're-engineering' a
>manufacturer's specs without proper engineering involvement. I
-
Bill Aycock --- Persimmon Hill
Woodville, Alabama, US 35776
(in the N.E. corner of the State)
W4BSG -- Grid EM64vr
baycock@HiWAAY.net
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|