I love this....it's visiting my in-laws. - Mike
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Bill
Sent: Thursday, November 06, 2008 8:51 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Guying a self-supporter
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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