[TowerTalk] Mast stiffness

[Jim Jarvis]

When this thread started, I just KNEW someone would 
throw in Viagra.  

At the outset, this was about some 2.5" od, 0.5" wall
24' STEEL masts.  The complaint was, "they flexed more
than I was comfortable with <snip> but they since came
back."   It wasn't clear whether they took a set, and
somehow recovered, or if they simply flexed and returned
to normal when the load was removed.  

I suspect it was merely flexing, because once overstressed
and deformed, I've never seen metal return to its original 
shape.  As a result, I suspect this may be a non-problem.  

If in doubt, get an M.E. to look up the properties of the tube 
in question, then calculate the windload upon it, given the conditions
you think prevailed at the time of observation.  Was the load
anywhere near close to the tube's rating?  (I'd betcha it wasn't)

With respect to using wood to add strength to a tube...I doubt
oak would do much for steel,  but in the case of aluminum, which
has a much higher modulus of elasticity, and lower strength, a 
properly fitting oak dowel WILL significantly increase the strength 
of the tube. Reason?  It keeps the wall from deforming, adds its own 
strength to the structure, and it tends to deflect less than aluminum.
Again, an M.E. would have to run the numbers to see how much
improvement you get...but I'm betting it's substantial.

In closing,  I'd like to see someone LIFT a 2.5" od solid steel
rod, 24' long, let alone get it vertical into a tower.  
Totally Tubular (TT) is the only way to go, dudes.  
(this WAS a west coast question, wasn't it?)

N2EA
jimjarvis at ieee.org