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

[Patrick Greenlee]

It is not that tough to calculate.  The tension in your guys can be 
treated a a vector and resolved into two orthogonal components. An 
illustrative example:

Suppose the height of the connection of a guy to the tower is 4 units 
and the distance from the tower to the guy anchor in the ground is 3 
units. Then as you may recall from school, the guy length is the 
hypotenuse of a right triangle and is 5 units long. Forces are 
distributed in proportion to this triangle.  For simplicity lets say the 
guy tension is 5 units.  Then the down force on the tower due to this 
guy is 4 units.

  Another approach is to work with sines and cosines.  For an example 
lets assume you have your guys at a 45 degree angle to the ground, i.e. 
the ground anchor is as far from the tower as the guy to tower 
connection point is above grade. As you may recall at 45 degrees the 
sine and cosine are both 0.707, equal to each other but any angle could 
be used and te force be calculated.  Anyway, in this example the added 
down force on the tower due to this one guy is equal to 0.707 times the 
tension in the guy. In practical installations the side forces generated 
by the guys cancel each other and the net result is a down force of all 
the guy's down forces added to the weights of tower and other equipment.

Patrick   NJ5G

On 5/31/2015 7:48 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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