[TowerTalk] Guy Posts Math

[J. Hunt]

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 at pacbell.net> wrote:

 Subject: Re: [TowerTalk] [Bulk] Re:  Guy Posts Math
 To: towertalk at 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 at contesting.com] On Behalf Of Fred Keen
 > Sent: Thursday, July 16, 2015 11:37 PM
 > To: john at kk9a.com; TowerTalk at 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 at kk9a.com" <john at 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 at contesting.com" <towertalk at contesting.com>
 > Subject:    [TowerTalk] guy posts math
 > From:    Lee George AK4QA <ak4qa at 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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