I would agree that vandalism is a good reason to safety wire
turnbuckles, but safety is also a good reason. I go with the
engineering data rather than "my tower didn't fall down" arguments.
The following chart re A325 structural bolt torque specs is a bit
instructive:
https://www.easycalculation.com/other/astm-a325-bolt-torque.php
What I note is the 2x difference between plain and galvanized bolt
torque specs. That means galvanized bolt friction is 1/2 of plain bolt
to achieve the same tension. Plus, these tensions, which help keep the
bolt from turning are way beyond what similar sized turnbuckles in tower
service will experience, since the guy wire will fail at much lower
load. Lower tensions and cycling loads are big contributors to
fasteners loosening.
It is also well known that 60 deg threads are not self locking, hence
the big business for all sorts of thread locking means - loctite,
nylocs, lockwashers, Nordlocks, wire locks, etc. Plus, HDG fasteners
have very loose thread clearance tolerances to accommodate the vagaries
of galvanizing. Want to fly in an airplane without wire locked nuts
holding the engine together?
A higher tensile strength rating bought with oversize turnbuckles vs guy
wire is what I do, but I then don't assume that the failure rate of my
turnbuckles is zero. Mine weren't xrayed or proof tested although I
bought Crosby rather than Chinese. Probably good insurance, but still
not a zero failure rate. There are probably a half dozen failure modes
in a turnbuckle and all are in serial so the failure rates are additive.
Shackle ratings are 20% of break strength, one of the largest safety
factors for rigging. I safety wired every pin on my sailboats and all
standing rigging turnbuckles too, a standard yard practice.
For a few dollars, safety wires seem to me to be a good value insurance,
but YMMV for risk taking.
Grant KZ1W
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