I am playing with some ideas for a self supporting, rotating tower of 20-25-30
meter height for an imagined future contest station setup. The bottom bearing
could be a slewing ring gear like this
http://www.nbcgroup.co.uk/SlewingRings.aspx?PageID=61 or a smaller "light" type
(Those bearings are normally used for construction site cranes and are readily
available). The 56cm light series with external gear ring can with load profile
#2 take between 30-40 kNm (3-4 metric tonnes on a one metre arm). The station
setup would have three of those self supporting rotating towers set up in a
triangle. The benefit would be no guy wires, possible to stack several antennas
on towers without hitting guy wires, possible to place towers close to property
limits, possible to setup with crane in one operation etc.I know the towers
should ideally be higher, but the above design criteria are considered for this
time.
I need some advice on calculating the loads on the bottom bearing. How do I
calculate the expected moment on the bottom bearings?
Next question: what is the force upwards on the upwind leg and the forces
downwards on the downwind legs of the tower from this moment ?
Would a method like this be suitable?:
==============================
Find the effective cross sectional area of the whole tower in question
Multiply that with the maximum wind speed squared
Then we have the side load on the whole tower.
Divide the length from the base to the top of the tower in half
Multiply that half distance with the side load calculated above
Then we have the moment acting on the bottom of the tower (?)
Additionally: how do we calculate the stress on each of the legs of the tower
to determine if the tower will withstand a given maximum wind speed without
breaking?
73
LB3HC
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