Tom,
If you want to try some unorthodox methods you might try to "drill down" a
couple (or 4) screw anchors and attach your 3'x3' concrete plate to them, or
better, attach some "H" or "I" steel beams to them and then attach your tower
there. I have been playing with the idea of using screw anchors to build the
base for a self-supporting tower. You can easily reach frost-free ground and
the possible pull force of a screw anchor is well known. (I don't remember what
screw anchor I used, 6" or 8", but they are good for 14,000#.
I always felt a little uneasy with attaching a tower to a building. I don't
know how much force you can put on a building and would be very afraid of the
tower ripping the point-of-contact off the house. I know it's done and I can
just assume it's OK. You have to calculate how much, worst case, force you can
expect and then see if your house is strong enough for that, keeping in mind
that this force is varying and will cause fatigue.
Supporting a 40' tower at 16' with only 7 sqf of wind load doesn't sound that
bad but I don't know the wind situation in your case. My tower should be able
to survive 135 mhp and I hope it never gets tested to that amount.
Hans - N2JFS
-----Original Message-----
From: Tom Hellem <tom.hellem@gmail.com>
To: Hans Hammarquist <hanslg@aol.com>
Sent: Sat, Jan 30, 2016 1:21 pm
Subject: Re: [TowerTalk] Fwd: Rohn 45 Base Section
Thanks, Hans. Yes there are drain holes.
I was hoping to avoid the need for guying by using the house
bracket as I mentioned. My property is not big enough for
a proper set of guys. Do you think the house bracket will handle it?
Or to put another way, is the tower stout enough to handle 7 sq. ft. of antenna
with 24 feet of tower projecting above the highest point of support?
The house bracket will be designed in such a way as to mitigate the
twisting forces, at least for the bottom 16' of tower between the house bracket
and the concrete base.
73 and thanks again for your response.
Tom
K0SN
On Sat, Jan 30, 2016 at 9:45 AM, Hans Hammarquist via TowerTalk
<towertalk@contesting.com> wrote:
Tom,
My first question is:" Is there drain holes where the tower legs attach to the
plate?" If not, drill some, either on the side of the legs. You don't what
water to accumulate and freeze there.
I can only assume you are going to use guy wires with the tower as I doubt a 3'
x 3' plate will be big enough to support a self supporting tower.
The size of the foot is all depending on what is underneath. You might have a
problem with the soil freezing under the concrete plate with unwanted results
such as a cracked plat, a plate that is lifted in one corner and therefore is
twisting your tower.
I have seen example there a plate, similar to the one you have, is just
standing on the ground and stayed that way for a long time with no problem. You
have to add torque wires to take up the turning force from your antenna in such
a case.
I sure several towertalk members will add advice.
Regards and best 73 de,
Hans - N2JFS
-----Original Message-----
From: Tom Hellem <tom.hellem@gmail.com>
To: TowerTalk <TowerTalk@contesting.com>
Sent: Fri, Jan 29, 2016 12:38 pm
Subject: [TowerTalk] Rohn 45 Base Section
I acquired several sections of Rohn 45 lately and the one
that was used as a base section looks like a regular straight
section with a heavy galvanized plate welded to the bottom
of it. The plate steel is easily 1" thick, and the entire assembly
must have been sent to the galvanizer as all the welds are galvanized
as well as the plate. The edges of the plate project beyond the faces of the
tower about 7" on all 3 sides.
My question is, if I pour a concrete pad say 3' x 3' x 16" deep and embed 3
1" anchor bolts in it for bolting the base down to it, will it be equal
or close to equal in strength as a tower section embedded in the same
concrete?
My plan is to erect 40 feet and place a Force 12 C-3 atop it ( I think 7
SQ Ft or so)
and attach it to the gable end of my roof with a house bracket at the 16'
level.
The roof structure will be beefed up substantially to accommodate the
bracket.
I know the Rohn book probably won't allow it, but what does the collective
wisdom
say about my chances of it staying in the air? I live in Missoula, MT.
73
Tom
K0SN
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