[TowerTalk] pipe anchors

Sat Oct 29 15:36:15 PDT 2011

I use steel I beams in concrete for my 100 foot 45G. It has been up more
than 10 years. It has a KT36XA, F12 80M rotatable dipole and 2 el
40M yagi about 17 feet above the top of the tower (total of about 15
sq ft). The I beams stick out of concrete blocks about 6 feet. The concrete
blocks are 3.5x3.5x4 feet in primarily clay. The tower has been through 60 
mph
winds several times and a tornado and the I beams have not budged.  Guy
connections are at the top of the I beam.

I was just looking at putting up another tower and more I beams. Three I 
beams
9 feet long with tabs drilled and welded at the top for guy connections were 
about $550
(W8x21). You really need an engineer to calculate what size of  I beam (or 
pipe) you
would need. The W8x21 is probably overkill for a 40 foot lightly loaded 
tower for most
places.

73, Larry  W6NWS
----- Original Message ----- 
From: "K8RI on TT" <k8ri-on-towertalk at tm.net>
To: <towertalk at contesting.com>
Sent: Saturday, October 29, 2011 2:44 PM
Subject: Re: [TowerTalk] pipe anchors

> On 10/29/2011 12:09 PM, Richard wrote:
>> I live on a small city lot and am in the process of installing a 40 ft
>> Rohn 25G tower in my back yard with a pier pin base. I'd really like to
>> avoid using screw in anchors
>
> Screw in anchors are notoriously unreliable.  Yes, I know there are
> those who have used them for years, but they are highly dependent on
> soil conditions and the quality of the anchor.  They are best avoided.
>
>>in such close quarters and would prefer to
>> use an elevated guy anchor like pipe set in cement. I originally thought
>> that 11 ft would be great to clear my roof line but have been told that
>> would require a pipe larger than what I can obtain around here. Revising
>> my plans a 4 ft high pipe in the corners of the back yard would still be
>> better than going to ground level. Can anyone give me an approximate
>> idea as to what size pipe and what size base might be needed?
>
> Elevated guys usually fall in the "not recommended" class as well. That
> said, I use them on a heavily loaded, 100' 45G but they are filled,
> large, braced, and set in 17,000# of concrete. I had to go that route to
> clear the house and driveway. Hence the overkill on the anchors.  Still
> after 10 years, the NW guy which is in the least stable soil (sand and
> clay mix) has moved about 8" to 10" out of plum, meaning that great big
> block of concrete is rotating in the ground.
>
>>
>> My tower is 40 ft, I would have at most 12 lbs of wind load on it, my
>
> These are my thoughts and not a recommendations: <:-))
>
> Fortunately a lightly loaded, 40' 25G does not take a lot of guying.
> What you can get away with 95% of the time and what's recommended are
> two different things. Just remember that when you do not use the
> recommended guying you are playing the odds.  Actually all installations
> play the odds. It's just that with the recommended installation the odds
> are strongly in your favor for all but very unusual conditions. IE ice
> storms and abnormally high winds for your area.
>
> Recently we had some unusually strong winds from the NE which is an
> unusual direction for us.  A friend found himself out hanging onto the
> NE guys at 2:30 AM in the rain after the tree they were anchored to,
> broke off. When there was a lull in the storm he moved his little 4WD
> SUV out in the yard and hooked the guys to the bumper hitch.
>
> When I took down my old 90 footer (lightly loaded) I gave him the
> elevated guy anchors which were 4" pipe which like your location were
> set in heavy clay. However although his tower is only about 50 feet (I
> think) it is heavily loaded. He set one of those anchors in his sandy
> yard and it was immediately shifting.  We settled on welding reinforced
> "ears" made of 1/4" steel plate, to each side of the pipe giving it a
> wide foot print. 1/4" steel plate made it a lot heavier too.   Now the
> pipe (guy anchor) appears to be at least several feet wide and extends
> well down into the ground and is no longer moving.
>
> The pipe is also going to be poured full of concrete to make it more
> rigid and to keep out water which around here would freeze and break the
> pipe.  With 4" pipe it wouldn't hurt to insert a 1/2" rerod down the
> center before pouring the concrete into it. That would also add more
> rigidity to the anchor. Remember that regular schedule 40 pipe is very
> easy to bend.  I prefer schedule 80, or structural steel tube but that
> does not come with galvanizing.  Use a "closed" eye bolt and install it
> "before" filling the pipe with concrete.
>
> With elevated guys remember the attach point above ground acts like a
> lever so if you are running 400# tension 4' above the ground you have
> 1,600 ft lb of leverage at ground level.  That is enough to bend smaller
> pipe or cause said pipe to shift position in the ground and it doesn't
> take a lot of wind to increase that force significantly.
>
> "I would guess" that 4" pipe set at least 5 or 6' deep and extending
> high enough to give you a 4' elevated anchor, set in 400 or 500# of
> qukrete(TM) would suffice for your system as described. Please note, I
> said *guess*.
>
> 73
>
> Roger (K8RI)
>
>> soil is a pretty heavy clay with no sand and no rock at least down to 4
>> ft., our wind zone is said to be 70 MPH. Any input would be greatly
>> appreciated.
>
>
>>
>> 73
>>
>> Richard / N5YPJ
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