>>What are the pros and cons of using a pier point bottom instead of
>>burying a 5'
>>tower section in concrete? Thanks, Pete
>
Sure, Pete.
I have 100 feet of Rohn 45 that stands on a pier pin.
I chose that option because:
1. it was a recommended installation in the Rohn catalogue, which I trust
thoroughly.
2. I thought (probably correctly in my case) that inaccuracies in my
positioning of guy anchors and in the installation of the buried section
(both vertical and rotational directions) would cause unbalanced forces on
the installed tower.
3. The ability of the tower to rotate under tension of the guys would
automatically balance initially unbalanced forces. You could actually see
this happening when we erected the tower. The whole thing shifted into
alignment when we tightened the first guys. I had a surveying engineer
check the alignment of the tower after it was up, with a transit. It was
out of line by only 3/4" at the top when we finished, less than the
diameter of a tower leg.
4. Any accident that occurred during the pouring of the concrete around a
buried base section (like the base section shifting unexpectedly) would be
permanent and potentially disastrous. I know that this can be guarded
against with proper technique, but I am not a professional at this, and I
was worried about my own abilities). (Remember, once you whip up a batch
of concrete, you only have a half hour to figure out what to do with it.)
5. I saw the problem from #4 actually happen in a tower installation just a
few months before I installed mine. It resulted in a twisted, unbalanced
tower that scared me to climb. It was fresh in my mind when I planned my
own installation.
5. Raising the tower with temporary guys was not really a big deal. We
bolted three sections together on the ground, added the base and hauled it
to the vertical (like we sometimes do at field day). Then six of us lifted
it and set it on the pier pin. Slick as a whistle. My bottom set of
permanent guys is at 28 feet, so we could attach them in advance. The
first time I or anyone set foot on my tower, it was 30 feet tall guyed with
1/4" galvanized cable attached to permanent anchors (themselves set in
concrete). In that sense, there were never any temporary guys at all.
I don't mean here to criticize those (the majority, I think) who bury their
base sections. That's undoubtedly a fine way to go. I just wanted to
describe my choice. The tower has been up now since 1990, and I am happy
as a clam with it.
Gl es 73, Bill
Bill Long NY3M
wlong@wmdc.edu
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