K7LXC@aol.com wrote:
> In a message dated 1/18/01 6:51:47 AM Pacific Standard Time, aa4lr@arrl.net
> writes:
>
> > Just because an exact installation isn't in the catalog doesn't mean it
> > is impossible. If that's so, almost NONE of the uses of Rohn 20, 25,
> > (35), 45, 55 are possible.
>
> Huh? How do you figure that?
>
> > There's only a extremely small percentage of
> > installations that follow the catalog installations EXACTLY. (For one,
> > almost NO ONE has perfectly level ground)
> >
> > I think it is good to exercise extreme caution when you run off the
> > tables in the catalog -- using a PE seems cautious enough.
>
> When "you run off the tables in the catalog" you're doing something the
> manufacturer does not recommend. You will be violating the LXC Prime
> Directive of "DOing what the manufacturer says" and your results are
> virtually guaranteed to fail.
>
> Cheers, Steve K7LXC
Normally, I fully support Steve and his conservative position on tower
installations. What I DON'T believe is that Rohn has "super-engineers" that
are somehow vastly superior to other PE's in the world. If you want to do
something not specifically recommended by Rohn, it may well be an acceptable
idea but it is still a good idea to have it double checked by a PE who has
expertise in structural engineering.
If we are to truly believe that it is always unsafe and dangerous to deviate
from published Rohn advice as it appears in their catalog, how can we deal with
all of the information that appears on Rohn Drawing No. A810214R6? In case you
are not familiar with it, this drawing appears in all of Rohn's latest catalogs
and earlier versions of it appear in earlier catalogs. It is on page HA-80 in
the current Rohn Consumer Catalog.
Here are some specifications taken directly off that page:
ALL FOUNDATIONS:
1. Concrete dimensions -- plus or minus 1"
Think about this for just a second. It means, without a doubt, that if your
foundation hole is more than 1 inch TOO LARGE, it violates the LXC Prime
Directive.
2. Depth of Foundation -- plus 3" or minus 0"
This means if your foundation hole is more than 3" DEEPER than Rohn's
foundation drawing shows, it violates the LXC Prime Directive.
There is more. Read it for yourself. There are also sections dealing with
ANCHOR BOLTS and SELF-SUPPORTING TOWERS.
GUYED TOWERS
15. Anchor Alignment (perpendicular to guy radius) -- 0.1 degree.
Sure, you want the anchors to be set so they are parallel with the pull of the
guy wires, but "within 0.1 degree"? How in heck do you even measure that to
within that tolerance? But it is there, in black and white, in the sacred Rohn
book, and if you deviate from it you violate the "LXC Prime Directive".
16. Anchor Rod Slope -- Plus or minus 1.0 degree
This is an interesting one since none of Rohn's guying charts actually tell us
what the ideal anchor rod slope is. How can you know when you are within 1
degree of it? (and, incidentally, how do you measure it?) Still, there it is,
right in the Rohn book, and you better follow it to the letter or you will
violate the LXC Prime Directive.
There are lots more items like this on that same page. I find it interesting
that nobody has ever seemed interested enough to discuss this. I think we
intuitively recognize that these items just aren't nearly as important to safe
tower construction as the other items we DO discuss. So, apparently, it is OK
to deviate from the Rohn book, in violation of the LXC Prime Directive, if we
do it with common sense. Unfortunately, we don't all HAVE common sense . . .
The "NI Prime Directive" would tell you to use common sense in your tower
construction and if you are not totally comfortable with that, hire a PE.
Don't get me wrong. I basically support Steve's conservative approach to tower
installation. I just don't seem to have the same degree of confidence that he
has in the Rohn engineers. A LOT of the stuff in the Rohn book is there for
legal "CYA" reasons and I think that is what most of the stuff on Drawing No.
A810214R6 is there for.
Stan
w7ni@teleport.com
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