I haven't read all the posts on this but did read N3RR's which included the
original inquiry. I am by no means an expert but often do like you're doing
and ask around when I have something that needs to be done.
I agree, by all means, if you can get experienced people to do it, that's by
far the best!
If I'm reading him right, N3RR is saying not to lower it in one lift with a
crane. Ironically, that is how N3RR's very tower, a "heavy duty" AB-105,
was taken down from K6XE's QTH in Maryland. I acquired it, had it taken
down by United States Tower Service (Norm Jeweler, AKA Norm's Rotator
Service), a couple guys with a smallish crane (could reach about 100' as I
recall), and I later sold it to N3RR. They laid it over in one "pick," no
problem. Once it was laid horizontal I got to work on it with an impact
wrench and knocked it down to sections, loaded them on my pickup truck, and
hauled it all home. When N3RR got it I guess he knocked it all the way down
to pieces and had everything regalvanized, did a first class job, and
reinstalled it at his place. It's about the same height as the one you're
talking about. Yours is probably the "regular" AB-105 since that seems to
be a lot more common than the "heavy duty" version. The regular one would
be somewhat less strong and less rigid but also less heavy, both of these
being factors on how readily it can be picked up and laid over without
damaging it. I don't know which would be best able to handle the procedure.
In a similar takedown of three 200' towers at WKIK (AM broadcast, went dark,
wanted towers taken away), I hired a crane -- with Van Brown of East Coast
Antenna Service to supervise. They were "Dura-20," made in Indiana, 20'
sections, all welded, 20" face, pretty nice tower. The crane got in
position, a rigger climbed and attached the crane cable above the center of
gravity (how it's normally done, not at the very top, for some reason --
maybe because not as tall a crane is needed), the guys were removed with the
crane applying up pressure to keep the tower upright and lift it off the
pier pin and insulator. The first tower laid over pretty well...the crane
lifted it off the concrete base, which was elevated a few feet, set it off
onto the grass, then gently and slowly started lowering it over. The tower
bottom being on the ground stabilized that end and it laid over pretty
nicely, though I did notice some bouncing/flexing of the 80' or so that was
above the crane's attachment point. The bouncing/flexing became interesting
in hindsight when the second tower didn't work out quite as well. I guess
the crane operator wasn't quite as gentle with it, went a little faster
since the first one had gone well. While over at about a 45 degree angle,
it buckled just above the crane attachment point, causing the top of the
tower to hit the ground which caused a secondary buckle from the ground
impact. Of course no one was near, there were no objects near, etc. so it
was just the tower that was damaged, those sections that buckled. As I
recall, the third one went okay. Maybe the crane operator went back to
being a little more gentle on that one. But, these were 200' towers; yours
is just 135'...they should be able to attach plenty high enough on the tower
to avoid buckling.
Norm also took down a 100' AB-105 for me at W0YVA in Virginia, lifted it
with his crane and laid it over no problem. I think he was attached pretty
high up near the top.
Lessons: The unsupported tower above the crane attachment point may not be
designed to support a lot of weight and sections above it when suspended
horizontal. Attaching higher may eliminate most of this problem. The crane
operator should be very gentle in laying it over to avoid losing a section
or two if it buckles. That is, avoid it buckling by going slower and
gentler.
Having it taken down section by section may be the most sure way to avoid
any such damage but doing it quicker (crane in one pick) may be the most
cost effective, if you're willing to run the risk of losing a bit of it if
things don't go like they're supposed to.
Many tower takedowns are done by the pros by cutting the guys and letting
them fall over, a controlled fall -- like building demolition or timber
harvesting. In these cases the concern is not so much in salvaging 100% of
the tower or even any of the tower; it's avoiding the sometimes very high
cost of tower removal -- very high in (expert) work crews and crane time if
they're taken down piece by piece. Nevertheless, in these controlled fall
demolitions much of the tower is often undamaged, depending on how durable
the tower was and what kind of ground it fell on. One big takedown was on
marshland and virtually all of the tower survived being "felled." I would
guess taking it all down section by section would have cost well over
$100,000. I don't know what it cost to have it done the quick way.
By all means, be careful, be prudent, hire pros if you can.
Rich Boyd, KE3Q
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