[TowerTalk] How to stiffen a mast

[Rick Karlquist]

Stiffness (not strength) is proportional to the quantity:

OD^4 - ID^4.

In your current case, this is 2.5^4 - 1.5^4 = 39 - 5 = 34

The best you could possibly do with an aluminum insert is to emulate
a solid rod, in which case the stiffness would be higher by
a factor of 39/34 which is a 15% increase in stiffness.  I
believe steel is about 3 times stiffer than aluminum, so
a solid steel rod would get you a factor of 49/34 or 44%.

Rick N6RK

Barkey, Patrick M. said:
> I've been using 24 foot, half inch wall, 2.5 inch OD aluminum masts
> on all of my towers for quite a few years, with no failures or real
> problems.  During the recent ice storm, however, a couple of them
> flexed a little more than I'd like to see (they've since sprung back).
>
> Now that I have the opportunity to think this over, I am wondering
> if it would be of any value to try to add a little more stiffness to
> the existing mast by driving something into the hollow center.
> I've got a 1.5 inch ID hole to work with - perhaps some pipe or
> solid rod could be driven into it?