[TowerTalk] How critical is the 120 degree ...

[Grant Saviers]

The steeper the angle (smaller angle to tower) the more tension is 
needed to provide the same horizontal restoring force at the connection 
of the guy to the tower.  The needed horizontal force is determined by 
the total wind load and strength of the tower.

The limiting but informative end points are:

Horizontal guys - 1lb of tension equals 1lb of horizontal force and no 
downforce

Vertical guys - 1lb of tension equals no horizontal force and 1lb of 
downforce

As the angle decreases the amount of tension needs to increase for the 
same horizontal force.  At small angles it approaches infinite. Thus, 
the force on rotating bearings increases with shorter guy baselines.

The amount of downforce is limited by the buckling and compressive 
strength of the tower, a complex calculation for slender towers.  The 
downforce is total static weight tower + everything else plus vertical 
load from all guys all levels at the maximum wind load when upwind guy 
tensions are the maximum.

So for shorter than catalog guy base lengths and loads, better have a PE 
do the calcs.  (beyond my pay grade).

Grant KZ1W



On 7/27/2021 04:56, john at kk9a.com wrote:
> In the U.S., the standard guy anchor distance is 80% of the tower height but
> I have heard in Europe 60% is more common.  Is that correct?
> 
> I have no answers to your questions but if you are using a rotating tower I
> believe that a larger anchor distance makes it easier for the guy bearings
> to turn.
> 
> John KK9A
> 
> 
> Jari Jussila oh2bu wrote:
> 
> Hi ...
> 
> I'm sure these topics have been discussed earlier, but could not find
> any thread ..... Sri ...
> 
> We are at our club erecting two towers. A rotating steel tower being 31
> m high and a aluminium telescope mast 18+18 m = 32 meters.
> 
> B) The steel tower height is 31 m - it's a rotating tower - but the
> upper bearing is at 23 m ( leaving 8 meters for the antennas) and the
> lower bearing at 11 meters.
> 
> Whats the advise of anchor point distance? Some say, that the 60 %
> (distance for  the tower) should be calculating from the total height
> (31 x 0,6 = 18,6 meters).
> Some say, it should be calculating from  the upper bearing (23 m x 0,6 =
> 12.8 m)
> 
> Whats your opinion?
> 
> Jari, OH2BU
> For OH3AC Club Station
> 
> 
> 
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