English prof here, Hank. I have no idea what an "overturning moment"
is and I'm not sure about the "plan dimensions."
There are 2 sets of manuals for the HG52SS - one says 30"X30"X42"
deep, the other 42"X42"X5.5 feet deep. That is all I have to work with
here and my assumption is their enginering is for "average" soil,
including possible sandy soil. I have rock - completely rock. Antenna
will never be more than a single monobander at a time and I am
essentially a quad guy, so a 2el on a 10-12 foot boom (multi-banded)
is what is going up here. Tower is 52 feet tall fully extended and
will be lowered when serious storms threaten. Mast out the top will be
about 4-6 feet, for a total height of 56'-58' to the quad boom (or
about 70-75 feet to the top wire). Should be more than sufficient from
here with us 1800 feet up on the side of a hill.
I am considering small rebar-sized holes deeper into the rock and
epoxying them in and then tying them to the standard base for this
tower with the overlapping top of the concrete pour out at least a
foot on all sides, so the concrete from the side, looks like this
(with the ground under the top "wings" virtually all rock):
----------------------------------
------- ------
- -
- -
----------------------
Michael Goins, k5wmg
Professor, Writing
University of Texas at San Antonio
On Fri, Feb 12, 2010 at 10:17 AM, Hank Lonberg <kr7x1@verizon.net> wrote:
> Mike:
>
> An engineer wouldn't break your bank, but I digress.
>
> You don't say what the plan dimensions are of your 3.5' deep
> hole are so it is hard to tell you anything but you could have
> drilled and grouted some reinforcing bars vertical in a grid
> pattern into the rock and utilized them as, rock nails, for a
> lack of better term. This would have allowed you to build the
> foundation shallower, but since you didn't ask earlier on here
> I couldn't have given you the idea. I would be hard pressed to
> give you exact pattern dimensions as I don't know what your
> over-turning moment is.
>
> Regards
> Lonberg Design Group, Ltd.
> Hank Lonberg, P.E.,S.E. / KR7X
> President
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Michael
> Goins
> Sent: Friday, February 12, 2010 6:54 AM
> To: towertalk
> Subject: [TowerTalk] tower installation HG52SS
>
> Guys, I'm needing some help here.
>
> I am installing a HG52SS about 16 miles north of San Antonio
> in an
> area that is nearly all solid rock and I have two sets of
> factory
> specs on installation instructions from HyGain. One says (and
> I'm
> going from memory here, but I'm pretty sure I am correct)
> 30X30X42"
> for the hole and the other says 42"X42"X5.5 feet for the hole.
> The
> issue is that under an inch or so of soil here it is virtually
> all
> solid rock. We are now down about 3 1/2 feet into solid rock
> on all
> four sides, and it has required a large jackhammer and many
> hours to
> get there. Assuming the base hole is to be designed for both
> compressive and lateral movement, there is no way it is going
> anywhere, either way.
>
> This location is where I plan to live the remainder of my
> life, so I
> want it right. The tower will have a 2 el quad on it, and
> likely
> nothing every bigger than a 3 or maybe 4 el monobander as I
> have never
> owned a commercial antenna and have always built my own. With
> it being
> a crank-up, one antenna at a time (especially the 2 el quad)
> is
> sufficient for me.
>
> My question is: Is this sufficient, considering the ground
> materials?
> I am highly considering the hole as is, wth a pad one to two
> feet tall
> around it above ground and tied into the factory rebar base
> (which I
> will have to cut down and slightly re-do in order to make it
> fit the
> current hole). With a sufficiently tied-in top pad, the tower
> cannot
> move in any direction as the above ground part would try to
> push down
> onto the rock around it, which it cannot do (as the rock 1"
> and less
> underground is solid).
>
> An engineer is out of the questions as I am an average guy,
> teaching
> college for what often feels like minimum wage. I am also at
> least 16
> miles form the nearest possible engineer which would add to
> the cost
> factor.
>
> Again, this is an amateur tower installation. The load will
> never be a
> lot as the tower is not rated for a lot of load. It cranks up
> and
> down, and I monitor the weather here, so it would be lowered
> when
> conditions suggested that it would be prudent.
>
> I could sure use some opinions.
>
> Michael Goins, k5wmg
> Pipe Creek, Texas
> Fast cars, slow boats, big dogs, and summers off to write
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