To be honest, I'm not sure what the question is either :-) Folks seem to
be equating self support towers with crankups, and who knows what else...
Just to clarify the question in my OWN addled brain - I'd like to see an
example of a normal tapered self support tower that has to be de-rated
after a reasonable guy system is added.
> Steve First I did not claim to be an expert. Quite the contrary. I
> am only one who has doubts on the basis of my experiences.
> At one time many years ago I had a free standing Universal tower made
> from aluminum. It was not tapered in the manner you are suggeting.
> Your analysis may well be correct for a tapered tower although I
> still have concerns about the buckling modes. In the case of the
> Universal tower I would have substantial fears about its
> susceptibility to buckling depending on the spacing of the guys
> particularly considering the lower modulus of elasticity and yield
> strength of of aluminum.
> The buckling mode is one where the deflection of the tower between
> the guys becomes excessive when the stresses of the resulting bending
> moments associated with the deflection are combined with the
> compressive stress of the weight of the tower and whatever it is
> supporting, the induced stress of the the guy loads, the torsional
> load of the twisting moments (which even if reduced by the guys
> through torsion brackets marginally increases the guy loads), the
> stress from the bending moments of the mast and antennas induced into
> the top of the tower and the bending moments from the wind load on
> the tower sections becomes so excessive that the principal
> compressive stress (Mohrs Circle) exceeds the compressive yield
> strength and casues the tower to buckle, usually between the guys.
> In most commercial cases I would expect that the structural engineers
> have looked carefully at the peak stresses that are induced by all of
> therse loads and designed the distance between the guys to lim it the
> column based horizontal deflection and thus the exposure to buckling.
> But that is not what I understood the quesion to be here. I
> understood it to be that any freestanding tower could be guyed and
> thereby make it less prone to failure. That is were I disagree. In
> the case of my Universal aluminum tower I would be very hesitant to
> do such a thing without having a design structural engineer clear it.
> If my understanding was wrong then as Rosanna Rosannadana said,
> "Never mind!."
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