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

[Grant Saviers]

Get out your trig capable calculator and you can get a rough estimate of 
the vertical load from the guys.

A guy generates a horizontal force that provides the force to resist the 
wind and a vertical force which has no benefit, but is the value of 
interest to you.  If G is the guy tension, and A is the angle of the guy 
to the tower, then two formulas resolve the guy tension into the 
horizontal force H and the vertical force V

sin(A) = H/G   and cos(A)= V/G  check: when A=0 then the guy is straight 
up and provides no H and all V since cos(0)=1
Or rearranging, H=G*sin(A)  and V= G*cos(A)

Now some assumptions, which ignore a bunch of reality

1. the wind is blowing directly on one set of guys and they are taking 
all of the wind load.
2. the guy tension is the same in each guy level, an alternative 
assumption is the H force is the same at each level, then calculate G 
etc.  Neither are correct for a number of reasons.
3. the maximum guy tension is the recommended 40% of breaking strength 
(I think a common misconception is 6700# breaking strength guys are good 
for 6700#.  That is true, but they will permanently stretch well before 
6700# load which is obviously a bad thing in a guy system.  So let's 
assume that conservative engineering was done for your design).  Note, 
if larger guys are used for top guys then use the 40% of breaking 
strength for that diameter.

For each guy level calculate the force V and add them up for a rough 
estimate of the wind load on the rotating bearing.

I'm not a PE, but do remember a bit of mechanics from my BS Eng. Caveat 
emptor!  Best you ask a structural engineer for an answer.

Grant KZ1W


On 5/31/2015 5:48 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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