I have engineered towers and the respective foundations many times over the
years for people.
Some have been dead-man anchors into the ground, some have been on steel posts
above ground.
Some have been free-standing towers, setting on three piers.
My 116' Rohn 25g tower/antenna has a "torque bar" assembly at midpoint and a
"star-guy" assembly at tower apex.
It is an extremely stable structure due to its engineering.
The 8" diameter steel guy posts are elevated off the ground, with back-guy
supports. Each post is minimum 7' buried with 3' diameter hole which was
belled out at the bottom. The rock layer starts ~30" below grade at my
property. The post was studded with rebar along with the hole prior the
concrete pour. Each post concrete riser is minimum 6" above grade to prevent
water migration.
The structure has been standing >17 years, with no guy post movement.
The same structure was standing in Midland, Texas for 12 years, taken down and
re-assembled.
The posts are elevated so the guy cables will clear the roof line.
Thanks N 73,
James Hunt
ki5dq
--------------------------------------------
On Fri, 7/17/15, Grant Saviers <grants2@pacbell.net> wrote:
Subject: Re: [TowerTalk] [Bulk] Re: Guy Posts Math
To: towertalk@contesting.com
Date: Friday, July 17, 2015, 10:24 AM
As others point out the sustained typical pretension of 600# per guy tends to
pull over the post over time. For 100' tower and three guy
levels a ballpark horizontal force is about 1000# at the top of the 7' post.
Then consider a storm that may raise the force by 5x or so.
A big factor in a proper design is the soil and how it resists these forces.
The "post" choices are a back guy to a deadman chunk of concrete, a large
concrete pad to resist the overturning moment and sliding forces, or a deep
enough hole with enough concrete weight and surface area to resist the
moment. Depending on the soil properties one (or two combined) will likely be
best for cost and ease of
construction. So there is no simple "formula" and that is why many homebrew
designs are leaning over.
This is a design where professional help is really needed. The strength of
the post is the easy part.
For my new 140' R65 tower the PE designed 7' post was in the ground 8' with
several yards of concrete. To avoid the mower conflict, I decided to mulch
around a standard Rohn anchor buried base as a simpler, cheaper and easier to
implement design. (also PE
approved).
Grant KZ1W
On 7/17/2015 6:12 AM, Marsh Stewart wrote:
> Fred,
>
> Depending on your soil, under recommended guy tension your guy post might
> start to "lean in" after a while.
>
> I had 60' of guyed Rohn 45G in service for about 23 years. The guy posts
> where 8" ID 1/4" wall steel pipe. Each guy post was 10' long - 6 feet up and
> > 4' in the ground in 2' X 2' X 4' of concrete. Each guy post was also
> filled with concrete. After some time the guy posts began to lean a bit in
> at the top. The guy posts did not bend. If I were going to do it all again,
> I'd make the "face" of the guy post bases to the tower much wider than 2'.
>
> 73,
> Marsh, KA5M
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Fred
> Keen
> Sent: Thursday, July 16, 2015 11:37 PM
> To: john@kk9a.com; TowerTalk@contesting.com
> Subject: Re: [TowerTalk] guy posts math
>
> Well John my cab tractor is about 7'4". I'm in the process of putting up a >
> 70' rohn 45g and have set 8 x 21 beams (8" deep x 21#s per foot) 12' long,
> 4' down into 3' x 3' x 4' concrete bases to allow me 8' of clearance.
>
> (The bases of the beams have three 3/4" x 30" long rebar welded on both
> sides of the sunken beam inside arebar cage.)
>
> My engineering reference scoffed at using pipe as the wide flange beam is so
> much stronger.
>
> Fred KC5YN
>
> Sent from Yahoo Mail on Android
>
> From:"john@kk9a.com" <john@kk9a.com>
> Date:Thu, Jul 16, 2015 at 7:07 PM
> Subject:Re: [TowerTalk] guy posts math
>
> Why does he want them this high? To do it correctly the post and concrete
> need to be professionally engineered.
According to mechanical engineer K5IU, elevated anchors require many yards of
concrete per anchor and a lot of steel. They are
expensive! I used 4' high anchors made from I-Beams at my P40A QTH when I
needed them to clear the house roof. I use Rohn buried
> anchors at my home station and the guys wires are only low close the anchor.
> I do not see this as an issue. I can easily cut the lawn around the anchors
> and cables with my John Deere zero turn 72" mower and the anchors are not in
> an area where anyone normally walks.
>
> John KK9A
>
>
> To: "towertalk@contesting.com" <towertalk@contesting.com>
> Subject: [TowerTalk] guy posts math
> From: Lee George AK4QA <ak4qa@msn.com>
> Date: Thu, 16 Jul 2015 15:34:01 +0000
>
>
> 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,Lee AK4QA
>
>
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