On 7/7/2011 12:03 PM, Mark Ketchell wrote:
What you describe is just with dirt bases. I don't know the actual
conditions, but a dirt base and high humidity does not necessarily mean
a failure. I've seen the same things with tower bases (sections) set
in concrete. IOW "In general" it sounds like a poor installation.
Whether set in dirt using a proper dirt base
http://www.rogerhalstead.com/ham_files/Dirt_Base.htm or concrete those
legs must be able to drain and not just at the base either. I've seen
tower legs swelled and split 3 feet above ground. In one instance the
split was about 30 feet above ground in an Aluminum tower. Why?
Spider webs, which emphasizes the need to check that tower legs are
clean WHEN they are installed. Still that is no guarantee they won't
build webs in there after it goes up.
Another issue? A package of hardware still in the leg! Another? The
base was set *IN* concrete. IOW the legs did not extend on into an
aggregate under the concrete so they could drain.
There are areas where bases can not drain even with the crushed rock
or pea stone for the legs to drain in as the soil around it is
impervious, eventually the area under the base fills with water and
we're back to the same problem. In these cases it's "J-bolts" in the
concrete and a pier pin base for guyed towers, or the big block of
concrete for self supporters.
Although my 45 G is constructed with a section set in concrete and lots
of pea stone under the base to drain, I've become a firm believer in
using the pier pin base for anything other than small, lightly loaded
towers.
Some years back A friend had a tower go down in a severe winter storm.
The tower was bent right over the roof of the 2 1/2 story house. The
guys were quite typical of what you see in *most* ham towers with a
tri-bander and 2-meter antenna on top. IOW the typical, soft, guy wire
commonly sold at a number of outlet stores. (Inadequate). I've seen two
men pull one of these guy lines in two which really brought home the
poor strength of this material. Yet in the early days while new to ham
radio I used the same 3/16 guy wire on 3 40 foot towers (with dirt
bases) that were holding KLM monobanders for 20 and 15 with 42 foot
booms and and a 7L Wilson 10 meter monobander that had a 38 or 39 foot
boom. Never had a problem.
At any rate he had a hinged base set in concrete and I'd guess the tower
had been up some where between 10 and 20 years. It was bracketed to the
eves with a through bolt well into the roof. An inspection before going
up showed one of the tower legs to have separated just above the
concrete which made the others suspect so I beat the snot out of them.
They were secure, BUT these were the two legs that formed the hinge.
I had two men holding the tower against the house "just-in-case" and
went up to inspect the bracket. It "looked" good (but bent) so I
proceeded to saw off the part of the tower that was bent over the roof
and hanging to the ground (snow) on the other side. Ohhhh yah! The snow
was 3 feet deep and more in drifts. Yes, I was sawing on the part
*above* the bracket<:-)) The tower came apart cleanly at the cut with
the top portion sliding down the roof and off the other side. Every
thing seemed fine.
I turned around to talk to the guys on the ground when I had a "strange
sensation" and instinctively reached behind me to grab the long eye bolt
sticking out of the roof. "It was a long reach" I had missed a
fracture in the clamp holding the tower to the eye bolt so I was
standing on 30 feet of tower only held in place by two legs which just
happened to be a hinge and the tower had started to swing out away from
the roof.
If it hadn't been for my very good sense of balance it would have gone
down with me on it. I don't think 3 to 5 feet of snow would have
provided much cushion from 30 feet. "Tuck and roll" is not an option
when you are strapped to the tower going down.
There are quite a few ways a tower installation can fail and most of
them go back to the way it was installed with the majority of those
being poor drainage of the base.
I used this link earlier, but this is how I build a dirt base and a
bracket.
http://www.rogerhalstead.com/ham_files/Dirt_Base.htm
ROHN used to sell dirt bases, but I think poor installation technique
was probably the reason you don't see them listed in the catalog any more.
73
Roger (K8RI)
> Several years ago, I went to assist with a tower removal. It was
> only about 40 feet, with nothing but an old 2 meter vertical on it, but
> owner was now too old to remove it himself. Owner said it was "well
> bracketed and surely safe". It actually WAS bracketed to the 2nd story
> eave, and to the wall about head high. There were no guys.
>
> The problem was, it had a dirt base and with the naturally high
> humidity here in Louisiana, moisture had been condensing inside the tower
> legs for years and could not drain out. Upon inspection before climbing, we
> quickly noticed that the tower legs from the part bracketed to the house
> stopped about 2 inches above ground. Yep, there was about a 3 inch gap
> between the tower and the ground, with nothing but the house brackets
> holding the thing up. We cautiously lowered the tower until it touched
> ground and slowly let it lay over. I swore that I'd never recommend or
> participate in an installation using only a dirt base.
>
> There's a reason why Rohn (and other manufacturers) base plates
> have weep holes, and why they recommend the layer of rock in the bottom of
> the hole when you use a starter section. I strongly agree with the LXC
> prime directive - do what the manufacturer recommends, and also W3LPL's
> suggestion of minimum yearly inspection of all your tower and associated
> hardware. Be safe, guys, the life you save might be your own!
>
> 73,
> Mark, K5ER
>
> Louisiana Contest Club
> N5LCC.com
>
>
>> On 7/6/2011 1:22 PM, Eddy Swynar wrote:
>>> Hi Again Roger,
>>>
>> ... I've gone back to using "dirt bases"
>> for small, guyed towers with relatively small antenna systems which work
>> well in our soil. The success of dirt bases and how much tower they
>> will handle is highly dependent on soil conditions as well as the
>> "Freeze/Thaw" cycle
>>
>> 73
>>
>> Roger (K8RI)
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