I believe I have one way of measuring the stress in the guy wires. I would
like to have some comments whether I'm right or not.
Consider the guy wire as a string in a guitar. The vibration in a guitar
string follows a relatively simple formula that you can check at Wikipedia.
I made some thinking (which may be dangerous) and calculations and found
that the stress in a guy wire can be measured by observing the speed a wave
runs up and down the wire. If you hit the wire (with e.g. your hand) you
will notice that a wave is going up that wire and returns after a short time.
By measure this time and know how heavy the wire is, you can calculate how
much force the guy wire is tensed.
The stress (in Lb) = wire weight (in Lb/foot) multiplied by (the length of
the wire) squared divided by (the return time of the pulse wave) squared
and the whole thing divided by eight(8). The formula looks like this in a
spread sheet : "=1/8*A1/A2*(A3/A4)^2" there A1/A2 is the wire weight per
length unit, A3 is the guy wire length and A4 is the time it takes for the
to return after you "hit" the wire. The formula is off by ~1/2 % as you
should divide by 8.03806 instead of 8 to be more precise. Be aware that a 1%
error in the time measurement results in ~2% error in the result.
I measured ~.75 s on my 100 feet 5/16" steel guy wires (56.6 lb/250 feet)
which indicates 500 lb. Reasonable?
The time might be too short to measure for short guy wires or for Phillys
wire. I leave the method to measure the time for these applications to
somebody else to figure out.
Hans - N2JFS
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