Another thing to note is that irrigation tubing comes in several wall
thicknesses.
As was noted, the thinnest wall will not handle u-bolts. The tube is
swaged into the couplings at the ends. Unless a plug + collar can be
machined to fit, making a new end, best to only use the factory lengths.
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.
The thin wall is easily damaged and dents substantially reduce the
strength for slender column buckling.
Grant KZ1W
On 10/24/2020 20:35, Richard (Rick) Karlquist wrote:
On 10/24/2020 1:59 PM, jimlux wrote:
On 10/24/20 1:06 PM, Tony wrote:
The key on stiffness is diameter - a 4" diameter thin wall tube is
enormously stiffer than a 2" diameter solid bar- because it goes as
the fourth power of radius.
Rick N6RK used 4" (?) aluminum irrigation tubing for verticals. You
might be able to find it used ("Rain for Rent", for instance).
Actually, the stiffness is proportional to the difference
between the OD to the 4th power and the ID to the 4th power.
For a constant wall thickness, this means the the
stiffness is proportional to the mean diameter cubed.
Rain for Rent now only carries aluminum tubing at the Fresno
store, AFAIK. They never carried used tubing that I know of.
Any attachment to the tubing has to be in the form of a
sleeve that wraps around it. A U-clamp will simply collapse
the tubing.
The verticals I have made out of irrigation tubing have mostly
been guyed. But I have made some that were only 30 feet high.
But even those, didn't have anything on top. For EME, you would
need to use a falling derrick to erect it.
I don't know if there is any wiggle room in "I can't anchor
guy wires to the ground", but my experience is that guyed
masts are much easier/cheaper,stronger, etc than self supporting
ones. Most people underestimate the difficulty of the latter.
Rick N6RK
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|