[SML] Question about Safe Working Loads

[Alex French]

On Wed, Apr 22, 2015 at 6:16 PM, Bill Conner via Stagecraft
<stagecraft at theatrical.net> wrote:
> varies based on component.  WIre rope is 8:1; fibre rope 10:1, a
> number of hardware components 5:1 or the manufacturer's WWL.  It
> really depends on what this is and what kind of wear in normal use, as
> well as other factors.

To put it a little more philosophically- any standards or conventions
come down, either through data or assumptions, to variability.

Structural design standards use much lower safety factors (and the
correct term is "safety factor" in that context, "design factor" is
not a common term in structural engineering), because an I-Beam is a
big hunk of steel that doesn't vary a lot- in general nothing's going
to happen to your I-Beam that unexpectedly weakens it without being
obvious.

A shackle has a lot more ways it can get over-stressed or damaged, but
it's still a good sized hunk of steel.  So 5:1.

Wire-rope can be much more easily damaged (8:1), but fiber (10:1) rope
can be damaged even more easily, and without it being obvious.  All
sorts of hardware and rope used in technical rescue is likely to be
considered using even higher safety factors, in part because the
environment and use conditions has huge variability.

So you might get a little guidance from thinking about your hardware
in that light.  Is there the possibility for variability in
manufacturing that wouldn't be obvious? Is there a possibility of
damage that wouldn't be obvious or could be ignored?

Alex French