[TowerTalk] Antenna wind load vs tower specs.

[Grant Saviers]

My largest tower is 142' of Rohn 65G double Phillystran 25k# guys at 62' 
and 122', 20' section above the top guys.  It's partially in 100' trees 
and I wanted the tower to have a chance to win a tree fall on a guy 
experience.  The 20' top section w/o guys was to accommodate two ring 
rotators.

At the top is 15' of 3" mast to a 2L JK 80m beam ~300#, prop pitch 
rotator.  I made a UV resistant UHMW 4" thick radial bearing, mounted it 
on a  waterjet cut 1/4" steel HDG top plate with a 316 stainless steel 
thrust ring bearing on the UHMW.
then 3L full size 40m, 48' boom, ~300# at 140' on K0XG ring
and 5L 20m 48' boom, ~200# at 124' on K0XG ring

All PE engineered (he designs and builds towers worldwide)  The 
commercial tower erector and antenna installer was complimentary of the 
tower's stability.  Maybe some 65 mph wind so far in 4 years. One large 
ice storm but  accumulated to 1.5" only on lower beams. Lot's of sag but 
all survived.

One calibration is to check the load capacity of an unguyed tower of the 
same height as the amount above the guys.  For 65G 110mph 3 second 
exposure B that is 95 sq ft at 20'.  Really only my 80m and 40m are in 
that calculation since the 20m is essentially at the base, so I'm way 
below 95 sq ft.  I'm as comfortable as one should be with a big tower 
and lots of aluminum.  It is serviced and checked annually top to bottom.

Grant KZ1W
Redmond, WA


On 4/29/2018 14:06 PM, Ed Sawyer wrote:
> I have seen these depictions of the guy wires so low on the tower however I
> have never built or seen one done that way.  Typically the top guys are
> somewhere on the last section.  Personally - I like the guys at the 5 ft
> below the top point.  That gives the most strength vs access to the top
> balance.
>
>   
>
> I have to think that the top guys being 15 ft below the top of a tower that
> is using 10 ft sections and only 80 ft  tall is seriously reducing the load
> capability.
>
>   
>
> Curious as to opinions in this area.
>
>   
>
> Ed  N1UR
>
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