You never know what you'll find when dismantling a tower...
I was recently involved in dismantling the antennas of a silent key. One
was a Mosley trap tribander on 50 feet of Rohn 25G, bracketed to the house
near the roof peak, at about 22 feet. No guy wires. Under-engineered to
start with.
Checking things over before climbing, we noticed right away that the 25G
just disappeared into the ground. Figuring that someone must have put a
couple of inches of dirt over the concrete base, I began poking around with
a shovel...then digging a little...then digging a lot. Where's the base?
The ground was quite sandy, and before we knew it we had 50 feet of 25G and
a tribander hanging from a single house bracket with nothing under it! The
tower went about 20 inches into the ground -- and stopped. No concrete, no
nothing, just the ends of less than 2 feet of 25G below the surface, in
poor soil. Thank heaven it was a calm day.
A neighbor who lived in the shadow of this accident waiting to happen, told
us this setup had been there, without mishap, for at least 15 years. He
said people had climbed the tower several times.
We dug down below the tower legs enough to be able to compact the soil a
bit (we had reached a ayer of clay) and wedge bricks in under the legs,
then reburied the legs before any climbing. The first climb was to attach
guy ropes. (We had planned to do that anyway because we weren't comfortable
about 28 feet of tower above the house bracket with a tribander sitting on
it.) We also tied off the tower legs at the point where they entered the
ground to a couple of convenient fenceposts, as an extra measure to help
prevent the bottom from kicking out.
The rest of the operation was uneventful, and the tower was, amazingly,
rock solid the whole time. Even so, once the tribander was off we decided
not to risk any more climbing. We removed the house bracket using a
ladder, and lowered the whole tower using the guy ropes, with two people
standing on the bottom of the exposed 25G to keep it steady.
I wonder how many other 50-foot towers are holding up antennas without
benefit of concrete?
Paul Elliott N3GPU
Westminster, Maryland USA
*************************************************************
The N3GPU Web Pages http://www.flash.net/~pelliott
*************************************************************
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|