For a guyed tower not much of a base is needed, only enough square feet
to be below the soil bearing limit at max wind load and then enough to
not slide from the force created when the tower bends. When I think
about a pier base which induces no bending moment in base section, the
only lateral force is the sine(angle of tilt) x total vertical load.
Angle of tilt is a very small number of degrees so there isn't much
horizontal force. For a buried base, there are overturning forces in
the base which are beyond my pay grade to calculate.
I think the Rohn larger & deeper base footings are designed to insure
the freestanding tower is stable with the construction loads before the
first guys are attached. Or work is stopped due to the approaching
thunderstorm. At 35' on R25 before the first guys are attached is an
informative experience.
My PE engineered base for 140' of Rohn 65 is 4x4x2' and the soil
pressure is less than me standing on one foot. We installed temporary
guys after 30' of tower was up as first guys were at 60'.
Grant KZ1W
On 1/5/2016 11:49 AM, AA6DX - Mark wrote:
'Sez guyed ...Mark AA6DX
-----Original Message-----
From: john@kk9a.com
Sent: Tuesday, January 05, 2016 11:07 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Buried section base...and lightning protection.
1/6 of a yard of concrete for a freestanding tower?
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Buried section base...and lightning protection.
From: Ken <wa8jxm@gmail.com>
Date: Tue, 5 Jan 2016 12:42:18 -0500
I am totally amazed at how concrete has weakened over the years.
For a 50' guyed tower, all I used was 30" square and 8" deep.
Ken WA8JXM
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