As I mentioned before, I calculated the NW guy post with close to a 10'
elevation with a total weight (post, rerod, and concrete, weighs roughly
17,000 pounds. This is for a 100' 45G, guyed at 3 levels. That is about
what I put under my LM470. I have faith in my figures "for me" and only
give them here for comparison and to show the increased requirements in
strength, materials, time and cost when using elevated guys. Those
figures are not a recommendation. BTW, I did have them checked but that
is only for my soil. I may back guy that NW anchor with a lot of
tension with large turnbuckles to try and slowly bring it back to vertical.
Large pipe of structural steel filled with rerod and concrete is
normally strong enough depending on size, length, alloy and wall thickness.
In many areas you need to get a PE to calculate the forces and structure
of the anchors along with a soil analysis. In this thread alone, many
types of soil have been mentioned. In many cases installations
endure(survive) "in spite of the installation", not because of it.
The main concern is the "OVERTURNING MOMENT" at ground level and that
goes up fast with every foot of height. As I showed in my calculations,
a regular guy anchor only has to withstand a fraction of the stress of
an elevated guy. There are two forces. One is the combined force of all
guys to that anchor point. to the ground level anchor consisting of the
tension on the guy with some weight contribution and the second is the
horizontal component at ground level.
Had I known my climbing would soon end, I'd have purchased a LARGE crank
up instead of the 100' 45G. After climbing the 45G, the thought of
anything smaller scares me. It is only the construction of the sections
that makes those sections strong. The unsupported leg of a 25G is easy
to bend and a 45G is not terribly so.
I use elevated guy anchors, because the guys to the NE anchor have to
clear trucks in the driveway. The NW one gives access to the back yard,
while the S anchor has to clear a shed. The NE and S anchors set in
solid clay and have not moved in many years. The big and heavy one to
the NW, should have been back guyed.
One caveat, don't use over size guys. Stick to the manufacturers
recommendations. The extra weight along with the tension can add a
large vertical load to the tower, with out antennas, rotator and coax.
73
Roger (K8RI)
On 7/16/2015 3:41 PM, Bill via TowerTalk wrote:
Suggest you contact an engineer. Wood is a far different material than
whatever you are using. Variables include: diameter of the pipe, thickness
of the wall, whether the interior is filled with concrete and rebar.
Anything you might come up on your own is an educated guess at best . I'm not
a
big fan of guessing on a 100 ft tower.
Some guys use a steel girder as the post.
Bill K4XS/KH7XS
In a message dated 7/16/2015 7:24:58 P.M. Coordinated Universal Time,
ak4qa@msn.com writes:
Does anyone have a the formula for guy posts?
I have a friend that wants tall guy posts (7 feet) for a 100 foot tower so
he can walk under them. I need to show him the stress that is involved in
that as opposed to 2 feet out of the ground.
I've always used the wooden pole rule of thumb; for every foot up you need
3 feet down.
Also, if you have the calculation for the back guy (i.e. earth screws)
well my friends, that would be gravy on my biscuit!
All the best and
73,LeeAK4QA
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73
Roger (K8RI)
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