On 11/27/2013 3:28 AM, Matt wrote:
A raising fixture similar to the commercial ones is very easy to build.
Whether the tower will easily adapt to one is something else, but with a
little ingenuity should work.
73
Roger (K8RI)
This may or may not be of use to you but thought I would offer an
alternative. I have 4 cranks-ups and 2 don't have raising fixtures. For
each of these without fixtures I elongated the foundation excavation and
dropped a 20 ft stick of schedule 40 pipe centered at the appropriate
location prior to placing concrete. I welded cap plates and reinforced
mountings for a 2-ton chain hoist at the top of each of these the pipes.
Suggest to do the stress and flexure analysis on the lifting loads for the
tower before sizing the pipe. I ended up with 6" pipe on one installation
and 8" on the other (a larger HD tower). On the advice of my structural
engineering friend, I fabricated the rebar cages with additional "U" straps
wrapped around the pipe on a 2" larger radius tied back deep into the center
of the concrete with angle turnouts on the ends. - and doubled up on the
spacing through the bottom (and top for good measure) few feet of the
foundation. This is to strengthen the foundation for the side loads (ie
avoid blowing out the side of the foundation at the bottom corner) that are
imparted when the pipe is under bending stress.
To raise or lower the tower I just hang the chain hoist on the pipe, connect
to the tower and she comes right up - very sturdy.
Good luck on your tower project.
73
Matt
KM5VI
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