[mailto:email@example.com] On Behalf Of Steve Maki
Sent: Freitag, 7. November 2008 04:32
Subject: Re: [TowerTalk] Guying a self-supporter
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
TowerTalk mailing list
My freestanding tapered tower will be up-rated on top load when guyed.
Before it buckles the guy wires will probably break.
The tower is built with massiv steel rods, no tubing anywhere.
So it just depends on the structure of a tower.
An aluminum tower which almost collapse by the weight of a climber will for
sure collapse under the load the guy wires produce.
TowerTalk mailing list