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Flagpoles & Billboards

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Regarding Steve Uthoff's interesting question:
<<I've heard that the flagpole supports are tapered partly 
because it damps out any potential resonance (variable moment of inertia = 
variable natural period) under wind loading.>>

I really don't know the answer, but thinking about it, wouldn't a variable
moment of inertia subject it to MORE resonant frequencies (theoretically one
at every invcremental shift in Moment of Inertia up the pole?)  Whereas a
stiffer pole would have one main mode and then all the other modes, too of
course.  But as long as the main mode was well away from the wind
frequencies, you'd be ok.  Also, you'd have a tougher time doing a dynamic
analysis of a tapered pole.  Just thinking out loud.  One reference you can
check is ANSI/TIA-222-F-1996, (Global Eng. Document, 1-800 854-7179, or
http://global.ihs.com.  I'm not affiliated with them at all, but it's where
someone sent me and they have it.) This is not exactly what you need because
it doesn't seem to address resonance and it deals with antennae not
billboards, but G.E.D. may have other relevant materials in their extensive
catalog.  In addition, ANSI 222-f references AASHTO "Standard Specification
for Structural Supports for Highway Signs, etc." 1985/88, you might check
that out also. G.E.D has this for $41, let me know if it's worth it!

Brian Veit, P.E.