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!."
73
Bill
W7VP
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