There was some recent discussion on towertalk about using cranes to
install towers. I am confused by what I read. On the one hand,
various people mentioned that you can't just assemble 90 feet of
Rohn 25 on the ground and casually lift it up into place because
it will bend in the middle, etc. On the other hand, I seem to remember
some postings saying that cranes could be used for tower erection,
but without specifics.
My only experience with this is that once I helped someone increase
their 60 ft Rohn 25 with a triband Quad to 80 ft with the help of
a crane. This was done by attaching the crane to the tower at the
40 ft level and lifting it up 10 feet, installing a new section
at the bottom, and lifting up another 10 ft and installing an
additional new section at the bottom. The tower was then lowered
back onto the base. I was one of the guy rope holders whose job
was to keep the tower upright. I gather this was the trick, since
trying to assemble the whole tower on the ground and lift it up would
bend the tower according to Towertalk discussions. I don't remember
how the crane grabbed the tower so as to not bend the cross members or break
the welds.
Would it be practical to build a new tower from scratch be
assembling the top few sections on the ground and then lifting
that assembly up and inserting additional sections underneath.
How do you determine how many sections can be assembled on the
ground? How high of a tower can be built this way (apparently
at least 80 ft)? How much crane time is needed?
Any other ideas? (I hate climbing :-)
Rick Karlquist N6RK
rick@area.com
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