[TowerTalk] Why preload guy lines?

[K7LXC@aol.com]

In a message dated 8/4/2005 11:33:11 PM Pacific Daylight Time, 
towertalk-request at contesting.com writes:

>  This question has been bugging me for a while. I've been trying to figure 
out
why tower guys are preloaded. I haven't worked out why that is an advantage
over simply tightening them enough to take up the slack. I run the math on
wind loading and such and the preload always seems to increase the stress on
the tower. There must be something I am overlooking.

    You need to take a look at the big picture. A tower is a structure 
designed within certain industry and engineering standards. All of the proper 
components and specifications are necessary for the tower's reliability. 

    As far as 'preload', I don't know if there's an engineering definition 
but from my point of view the preload could be *any* value - and not necessarily 
the proper one. 

    Guy wires are tensioned to 10% of the ultimate breaking strength of the 
cable; i.e. 400 pounds for 3/16" EHS which has an UBS of 3900 pounds @ 70 
degrees F. Guy wires at less than this value will be too loose and in a wind can be 
slammed/hammered due to the slack in the guys produced by excessive tower 
movement. Guy wires with a tension higher than the prescribed value will exert 
more compressive force on the legs of the tower (the leg strength of the tower 
is the limiting factor of tower capacity) and use up most of all of the 
compressive load before there's even an antenna on it. 

    Even if you didn't know the reason why, you should be following the LXC 
Prime Directive to "DO what the manufacturer says". 

    The easiest and cheapest way to have the proper tension is to use a Loos 
Guy Wire Tensioner. They're pretty accurate too. One for 3/16" and 1/4" - the 
most common ham sizes - is available from www.championradio.com for $79.00. 

Cheers,
Steve     K7LXC
Champion Radio Products
TOWER TECH -
Professional tower services for commercial and amateur
Cell: 206-890-4188