In a message dated 98-03-12 00:51:27 EST, wmal@taconic.net writes:
<< Rohn suggests in their specs. to scope the guys at 80 percent of the
tower hieght (in this case a 50 footer) and to guy at 23' and 45'. Fine.
Now a utility co. lineman friend believes that putting the guy anchors
out 40' for a 50' tower is crazy. He brings up a valid point that the
more real estate that the guys cover increases the probability of a tree
falling and catching those cables. >
The 80% is ONE scenario. It's a good compromise and the standard one
that Rohn uses. Yes, you can have guys closer or farther away but you should
recalculate the forces (or have a PE do it) if you want to change things
significantly.
Do not take the advice of your lineman friend. He deals with extremely
strong wooden poles that are generally 60 feet or less tall along roads where
they don't have much need or access for guy anchor real estate. They use
bigger wire for guying and screw in anchors. In other words, it's totally
different.
The LXC Prime Directive is "DO what the manufacturer says". Do not
violate that rule.
>The guy installation will consist fo
using a commercial 10mm guy, preforms, and anchor system. He assures me
that there is NO weather situation, short of a tornado, that will budge
this system. I believe him, I have the hardware here in front of me and
it is very heavy. >
Hold on there, Bucko. Rohn specs call for EHS guy cable. There are 7
different grades of wire rope and EHS (Extra High Strength) is the strongest.
Utility companies do not use EHS, they use the other grades. A Utility Grade
is only about 50% as strong as EHS so is NOT suitable for holding your tower
up.
Do you have the Rohn book? If you don't, they're five bucks from TOWER
TECH, Box 572, Woodinville, WA, 98072. Did I mention the LXC Prime Directive?
>But he says that a tree falling across a guy will
surely bring it down in a pile. So he suggests bringing the anchors in
to around 20-25'. This would in fact would put a steeper angle on the
guys allowing them to "shed" a falling object better and lessen the area
for the potential.>
Rohn 25 has a small fraction of the strength of a wooden pole. A tree
falling on a 3/16 inch EHS guywire will pull the tower down if it doesn't snap
the cable first. Bringing the guys in closer won't make that much difference -
the tower and cables aren't that strong to prevent damage. Trees are HEAVY and
they'll take down just about any tower.
Are nearby trees that big of a concern of yours? Can you fall some of
them or at least have an arborist trim a bunch of branches off (thus reducing
it's exposed windload area)? I would suggest following the Rohn spec and build
what you want. If it does fail and fall harmlessly, big deal. That's why
you've got homeowners insurance. Rebuild it and keep going.
> I think that all make good sense BUT....(here's the
64k question) will that increase the downward compression of the tower
too much and cause a problem? Or am I making a mountain from a mole
hill. And do you see the need for using Rohn's GA25GD (tower guy
attachment assembly) for a 50 footer w/ 8sq.ft. windload. Or should I
save these questions for when I get bored with the 50 and decide to put
up a 100'! >>
Yes, build it to Rohn specs. While Rohn would probably recommend using
the Guy Assembly, for your situation I'd say it's optional. The Rohn book has
a drawing of a guy wire terminated around a tower leg so it's not as good as
the Guy Assembly but will work. Change any parameter and using it becomes more
necessary.
73 and GL, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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