[TowerTalk] Guying a self-supporting tower

[Bob Kellow, W5LT]

If you want to guy a self supporting tower it needs to be done very
carefully (read: professional analysis).
But then, isn't the title an oxy-moron? If it is self supporting, why does
it need to be guyed? If it is designed according to industry standards for
the applicable wind zone and antenna loads, it should not fall down (at
least it is no more likely than any other type of tower).
But to the subject at hand: most others have touched on the real issues: the
tower is being applied in a manner for which it was not designed, at least
in most cases; and the stresses applied are distributed differently than the
designer assumed. 
The original proposal mentioned a single set of guys at the top,
"pre-tensioned at normal values" what ever that is. With only one set of
guys, the tower becomes one long, unsupported slender column and is subject
to over-all buckling, not the local buckling that was considered by the
designer. This was mentioned in one message. 
On the subject of "guy tension", consider that the tension must be such that
all the wind loads are transferred to tension in the guys and compression on
the tower. These must be quite high, because you do not want the tower to
move under load. If it does, the leeward guy will go slack, with
unpredictable results when the wind gust stops. Also, the top sections of a
typical slender SS tower are not designed for very high compressive loads
(like the lower sections are) and would be more prone to fail under the
loads required by a single set of guys. Unknown resonances are also likely
to be created which would have unknown effects. Please note that slender SS
towers are allowed to move under load, they shed load that way and
efficiently transfer loads to the base. 

My 3 cents,

Bob, W5LT