[TowerTalk] Aluminum vs Steel Masts

[Kurt Andress]

HA!

The anecdotal evidence, so far is overwhelming!

Everyone should run out there and replace their high quality steel masts
with a new 6061-T6 aluminum tube. Taking the old one down will be a real
bear, but you'll feel much better putting the new, light flex monster up
there. Right?

Not even close!

Let's review a few fundamentals.

6063-T6 extruded or drawn aluminum tube can be found anywhere with a
yield strength of 35 Ksi (that's 35,000 psi). If one shops and demands
cert's it can be found with a yield strength of 40 Ksi.
Aluminum has a modulus of elasticity of 10 Msi (that's millions of psi).

Dogmeat 1010 HREW (Hot Rolled Electrically Welded) steel tubing has a
yield strength of 35 Ksi. It has a modulus of elasticity of 29-30 Msi.
There are a host of other steel alloys and manufacturing processes that
provide from 35 - 118 Ksi yield strengths and all are also in the 29-30
Msi rating for elastic modulus.

So, if we shall analyse anecdotally, we can surmise that the fellow who
had his mast fail under supposed lower winds and loading than the fellow
with the aluminum mast must have used one of the dirtbag steel alloys,
like A120, A53, A 106, (pipe stuff) or 1010 CREW.
They all have lower yield strengths than 6061-T6. In this is your case,
please, go out and replace your dirtbag mast with an aluminum one!

But, since you're willing to go to the effort, please consider this.
A really good steel mast will be 3 times stronger and will bend 1/3 as
much as the same size aluminum one under the same load. Why not replace
it with the stronger, stiffer one? That way, you can work DX instead of
moon bounce when the wind blows!

For anyone to suggest that aluminum masts are as good or better than
than steel ones first requires a definition of as good or better, and
what one is going to compare!

Why is mast stiffness important? Keeping this on the purely anecdotal
platform it started upon, does anyone seriously think that their
tower/antenna system is best when the antennas are flailing about on a
flexible noodle?

An aluminum mast can be designed not to break under the proper load
case, it will need to have a moment of inertia that is 3 times larger to
be as stiff, it needs to be much larger and/or thicker to be as strong
as the high quality steel masts.

73, Kurt


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