[TowerTalk] Guy Cable

[W2RU - Bud Hippisley]

The recent discussions about whether wire "rope" is suitable for guying 
towers seem to me to have mostly missed  the primary issue, which I 
believe is this:

In many guyed tower configurations, a major component of stress on 
certain tower sections during periods of high winds is a *bending* 
stress (in contrast to, say, a purely compressive force).  This bending 
stress originates in the *elongation* of the guy wires under increased 
tension from the wind loading on the tower and antennas.  Flexibility of 
the guying material is of little import here -- only its tendency to 
stretch under the applied loads.  If you are trying to obtain maximum 
utilization of a guyed tower (i.e., "more stacked beams!!!"), relative 
elongation for a given length and a given wind loading is the 
specification you should be concerned with.

K7NV has some good modeling studies on his web site; it's been a while 
since I've gone through them, and as I recall his thrust was primarily 
to analyze the relative impact on tower loading from low beams versus 
high beams, but the message is clear -- low stretch guy wires allow you 
to do much more with a given tower.

Bud, W2RU