R25 is 41.1 #/section so your nude tower weighs in at 500# or so with
bolts etc.
A single 3/16" guy at max load of 2000lbs (50% of break strength) and a
45 deg angle to the tower could put a perpendicular force of 1414# on a
leg, at a Z brace. In a smooth lift that force would never happen even
with the 120' of tower horizontal.
You can be sure that W8JI "ran the numbers" before his removal. The
sling around (and threaded through so it won't slip) the tower at 2/3
height insures it will stay vertical at the initial lift. I'd rig with
two slings as chokers to the pair of legs opposite the lift cable and
then crossed over on the third leg to the hook so the tower won't rotate
in the slings. Your crane operator will likely have a good suggestion
about how to rig.
Once you clear the base, then laying down the tower is where there is
risk on the two legs that are first on the ground and start taking the
load. Those short stubs would be easy to bend. Done right you never
have the tower in a full horizontal position with a point lifting load
at the 2/3 of height. Some short blocking e.g. 6x6 could be used at the
bottom Z brace as the place to take the load, that would be better and
placed along the length would allow easier removal of the bolts. This
takes some coordinated moving of the crane tip and hoist line to not
have the base slide around while lowering, but it's done all the time.
Don't lay the low end down on a saw horse, they are too unstable. You
will need tag lines if there is a breeze.
/For my new tower, using a crane for the erection, I had to lift Rohn 65
20' sections from saw super strong saw horses because the ring rotators
were already installed. I hoisted the low end in a sling from a fork
lift and maneuvered it forward as the crane operator did the lift. A
section with two rings weighed about 1300#. You could use a mid size
tractor or fork lift in your situation to hold the bottom end off the
ground with slings while the crane lowers the entire tower. Then you
could load it on to cheap saw horses for ease of disassembly.
I'm assuming you are hiring a pro crane company, this is not a job for
amateurs, sign hangers, etc..
Grant KZ1W
On 3/9/2016 17:12 PM, Steve wrote:
I am planning on taking a 120 ft 25g tower down with a crane ,any suggestions ?
can i take the whole tower down and lay it over or will it buckle ? any thought
s or tips welcome Thanks
Steve Flory W9KOP
sflory@mindspring.com
"I like climbing towers because people look up to me"
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