> Roger (K8RI) on TT K8RI-on-TowerTalk at tm.net
> Thu Feb 11 08:02:17 EST 2016 wrote:
> Contrary to popular belief, a real 25G is not a strong tower by itself.
> Stretchy guys scare me!... It takes very little movement at 30 feet
> to break a tower at the base set in concrete.
Which is PRECISELY why I would never recommend setting the base of a guyed
tower of any height in concrete, but use a pier pin and base plate. The only
occasion on which I would bury a tower base would be in conjunction with a
house bracket (IMO another poor choice) or to make it self-supporting;
according to Rohn, the maximum self-supporting height of 25G is 30 to 40 ft,
depending on the maximum wind load and assuming no ice.
For a guyed tower, there is no advantage whatever to setting the tower base in
concrete. First of all, you still have to temporarily guy the first section in
order to plumb it and maintain it in position until the concrete sets, and
there is no way to correct a plumbing error after the concrete sets, if you
inadvertently get the measurements wrong. Why not just use a pier pin/base
plate, temporarily but securely guy the tower section, go on up with
additional sections till you install the first set of permanent guys, and then
continue from there? Plus, you avoid losing height by burying part of the tower
below grade, and the base plate sitting on top of the concrete pier greatly
reduces the likelihood of water accumulating inside the tower legs to
eventually rust out the structure or worse still, in cold climates, fracture
the tower legs from freezing.
Don k4kyv
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