[TowerTalk] guy posts math

[Roger (K8RI) on TT]

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 at 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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