This type of deflection problem is well known to structural
engineers. The problem may be associated with vortex shedding
and structural resonance. In which case, the pipe may go through
very substantial amplitudes of vibration under relatively low
wind forces.
On the other hand a 25' tall by 2.5" O.D. pipe is very slender
and relatively flexible. It could simply be experiencing
large deflection due to the applied wind loads or in response
to wind gust effect.
Wayne Davison, SE, CE
Jim Jarvis wrote:
> 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@ieee.org
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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