On 9/22/2010 10:40 PM, Dave Hachadorian wrote:
> Go here:
> http://www.rohnnet.com/rohn-25g-tower
As Dave has listed, the ROHN book gives all the information needed to
properly set the guy anchors.
> Download brochure.
>
> Standard anchor designs are all in there for various heights
> and windspeeds.
>
> Raised anchors are another matter, and require either
> professional engineering, or brute force overkill.
And more than a little luck even with a thorough soil analysis.
End up with a much wetter season than normal and clay will flow allowing
the whole works to move.
Other soils also change viscosities and texture which can adversely
affect their ability to hold the anchor, sometimes drastically
.
I use anchors elevated close to 10', but they are 5" heavy wall steel
pipe, poured and rodded with each set in about 17,000# of concrete.
THEY STILL MOVE! Not much to be sure, but with 3 sets of guys, one at
600# and two at 400# tension gives 1400# of tension about 13' above the
center of the concrete. That is 1400X13=18,200# of rotating, or turning
moment on that concrete block. So even though the top of the block sets
about a foot below the surface the over turning moment exceeds the
weight of the anchor by over half a ton. That leaves the block dependent
on the soil for support and resistance to the over turning moment.
Two of those posts ARE MOVING! In nearly 10 years it's only been a
couple inches in 10' so they are likely to outlast me and any hams I
know, including the young ones. But the point is they are moving and
the mass of the concrete plus the resistance of the soil is not rock solid.
If these were typical posts set in a yard or two of concrete they would
have to be replaced in just a few years.
If I had not had to clear a driveway the anchors would not be elevated
and I'd use any chance to anchor them normally.
My recommendation is to never use elevated guys unless absolutely necessary.
I would like to add one other recommendation that has become apparent
over the years as I've seen it done far too often to the point of
expecting it and I can not emphasize it enough. Do not over guy! Do not
use over size guys! Just going up one size in guy line can increase the
load on the tower base beyond safe limits. IOW as they often say on
here...Follow the prime directive! Do what the manual says.
73
Roger (K8RI)
>
> Dave Hachadorian, K6LL
> Yuma, AZ
>
>
> --------------------------------------------------
> From: "Mac English"<km9zkb9mdl@yahoo.com>
> Sent: Wednesday, September 22, 2010 7:25 PM
> To:<towertalk@contesting.com>
> Subject: [TowerTalk] Rohn 25 Guy Anchor
>
>> I have never done an installation of guy anchors by rohn
>> (GAC303). How deep does
>> the hole get dug? I assume at least 4 feet min. Would the
>> hole be a 2x2x4 hole?
>> How do I get the rod at the angle it needs to be while the
>> concrete gets poured?
>> Does the hole get dug beyond the point of where the anchor
>> exits the ground?
>> What size re-bar is needed? Is it number 7? What kind of
>> wire gets used to hold
>> the re-bar together? Do I have to build forms for the
>> concrete re-bar cage?
>>
>>
>> I have only ever done the installation of I-beams as
>> anchors. Those are quick
>> and dirty. I am unable to pull that installation off this
>> time. So this is what
>> I guess I will have to do unless someone could give me
>> some other suggestions. I
>> was thinking maybe some kind of steel posts in the ground
>> 5 feet deep by about
>> 24in wide in concrete. If so what size posts would I need
>> as far as diameter,
>> thickness, length etc.
>>
>> Thank you,
>>
>>
>> Mac
>> KM9Z
>>
>>
>>
>> _______________________________________________
>>
>>
>>
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