[TowerTalk] Why preload guy lines?

[Steve Maki]

Tom Rauch wrote:

>> When any wire or cable is tightened, it becomes more
>> rod-like. At that point it doesn't really make any
>> difference what the material is - it still exhibits
 >> the same property - and deflection, which is what
>> you're measuring. If cables are the same size, they'll
>> read the same.
 >>
>> I've even measured Phillystran with one (it'll only
>> measure the HPTG4000 - it's the only one that'll fit
 >> into the mouth of the gauge).

>> You'll nootice that the Loos is about a foot long.
>> It's just measuring the deflection in whatever it's
 >> attached to. I think there are just some simple physics
 >> involved to measure the tension.  The Loos gauge was
 >> designed for sailboat rigging but measuring other cables
 >> is no problem.

> I've been thinking about this and I don't see how any
> tension gauge that  requires scale compensation for wire
> diameter could be immune to effects of wire stiffness.
> 
> When I look at it, it appears to me the Loos tenisoon gauge
> actually measures bending of a tiny area of wire between the
> two nubs at one end with the long area just serving as a
> "reference point" for the bending between the two fixed nubs
> that are at one end.
> 
> Or do I have that wrong?
> 
> 73 Tom

Right, it's a measure of the force required to bend a wire
under a particular tension.

So there are two components of the 'resistance': that caused
by the tension, and that caused by the wire stiffness.

The wire stiffness remains constant. At low tensions, it
dominates. As the tension increases, becomes a smaller and
smaller percentage of the total. The question is what
percentage of the total at common (10%) pre-tensions?

I don't own the Loos gauge, but gather that:

1) The supplied chart or table does not give alternate
calibrations for different guy material.

2) The chart is calibrated for flexible cable (wire rope).

The larger gages I own have alternate calibrations, but
only for the overlapping guy size range (1/2" to 3/4")
where EHS is available in both 1x7 and 1x19 configurations.

I would think it might be useful for someone to actually
calibrate the Loos for 3/16" EHS at 400 lbs, and 1/4" EHS
at 600 lbs, and take away any doubt. I may pick one up
from Champion and do it. I should have one of these in my
kit anyway.

73,
Steve K8LX