[TowerTalk] Weight of tower on the main bearing of a rotating tower?

[Joe Subich, W4TV]

 > Any idea how much weight the bearing will actually have to take?

As a starting point, about 78% of the pretension of the top guy wires
(assuming 80% guying - or 80 foot radius for a 100 foot tower) will
be converted to downward force on the tower.  For your 6700# guys
that's 6700 * 0.10 * 0.78 * 3 ... about 1560# for the top set of guys.
Add a second set of guys at 2/3 height and around 65% of the pretension
becomes downward force ... 1300#.  For a third set at 1/3 height, about
40% of the pretension is downward force ... 800#.

That means 3700# give or take for the static load of the guy wires.
*HOWEVER* that's the minimum is calm winds and no ice load.

How much would 1/2" or 3/4" of radial ice covering the entire surface
weight?  If you had winds that loaded the guy wires to 50% of their
breaking strength, the downward force imparted by the guy wires would
be five times as great as the no wind condition.

It's those dynamic forces that you need to design for <G>.


73,

    ... Joe, W4TV


On 2015-05-31 8:48 AM, Richard Thorne wrote:
> I'm finishing up the rebuild/refurbish of the parts for a 55g rotating
> tower.
>
> I was pondering and I'm curious.  How much weight will the main bearing
> have to take? It's one thing to add up all of the components on the
> tower but then there's the downward force of the guy wires.
>
> I did some quick math and I'll probably have less than 2500 pounds of
> tower, rotating rings, antennas, coax assembles etc.  I'll be using 1/4"
> guy material which is rated at 6700 lbs and requires 10% tension.  The
> rotating base will be at ground level.
>
> Any idea how much weight the bearing will actually have to take?
>
> Thanks
>
> Rich - N5ZC
>
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