[SML] Question about Safe Working Loads

[Stephen Rees]

Ford,
Do you have a wire-rope or polyester sling manufacturer in your area? They
will charge a fee but could probably meet your needs. Here in WNY, I've
used Hanes Supply in BUF before. A similar company in your neck of the
woods could likely do the same.
Steve Rees

On Fri, Apr 24, 2015 at 9:10 AM, Ford Sellers via Stagecraft <
stagecraft at theatrical.net> wrote:

> Thanks Alex!
>
> Next question... is anyone interested in (and capable of) doing
> destructive load testing on our Rig Bar?
> The Lab we have been using can only go as high as 2000kg.
> We think we need to go to between 4000, and 6000kg.
>
> It could be really fun.... I'll bring the beer.
>
> -Ford
>
> -----Original Message-----
> From: Stagecraft [mailto:stagecraft-bounces at theatrical.net] On Behalf Of
> Alex French via Stagecraft
> Sent: Thursday, April 23, 2015 8:29 PM
> To: Stagecraft Mailing List
> Subject: Re: [SML] Question about Safe Working Loads
>
> 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
>
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