[TowerTalk] How to stiffen a mast

[Jim Lux]

At 12:12 PM 1/31/2005, Rick Karlquist wrote:
>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%.

Or, even a steel tube.. the 4th power making tubes almost as stiff as a 
solid bar works for all materials..  A thin wall steel tube is probably 
stiffer than a solid aluminum bar of the same OD (or weight).



>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?
>
>
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