[TowerTalk] Low Cost 20 Foot Mast

[Richard (Rick) Karlquist]

On 10/25/2020 7:53 AM, Grant Saviers wrote:
> Another thing to note is that irrigation tubing comes in several wall 
> thicknesses.

It possibly could, but I haven't had much
luck actually finding thickwall tubing.

> 
> One gotcha I experienced was metal fatigue, since aluminum has no 
> "infinite fatigue life" stress threshold like steel.  My 80m vertical 
> sections harmonically coupled between guys and fractured at the highest 
> stress point. (guys were at couplings)  So guys need to be spaced 
> unevenly to reduce vibration mode coupling.
> 
> Grant KZ1W
> 

I spent years building 90 foot verticals consisting
three thirty foot pipes, of diameter 4", 3", and 2".
The top 2" section would always eventually buckle
for no apparent reason.  It was clearly fatigue.
It turned out after a lot of trial and error that
the vertical needed to be guyed at 30, 60, 75, and
90 feet.  It didn't need to be guyed at 15 or 45 feet.
The 75 foot guys were the critical ones when it came
to the fatigue failure.

Once I figured this out, the vertical always stayed up.

Rick N6RK