Turnbuckle and Shackle Safety Factors for permanent use

[ILoaThePats]

What safety factors and strength reduction factors (applied to the ultimate strength) do you use for shackles and turnbuckles that will be permanently installed in a structure?

 

[ameyerrenke]

I believe they come rated for service loads. I have one sitting on my desk that I believe could take 4x what its rated for.

 

[ILoaThePats]

Thanks ameyerrenke. My understanding is that a shackle/turnbuckles rating is the Working Load Limit, or what should safely be applied for rigging applications where load and direction of load application can be highly variable. Because of the variability they have a high safety factor on the Minimum Ultimate Load. A 1" Crosby G2130 shackle for instance has a Working Load Limit of 8.5Tons, based on a FS=6.0 on the Minimum Ultimate Load (which is 6.0*8.5Tons*2 = 102kips). In a structure, the load is less variable than rigging so a lower FS is appropriate. I was thinking an ASD F.S=2.0 is reasonable (for an allowable load of 102kip/2 = 51kips on the 1" G2130) but I'm looking for opinions or references.

 

[WillisV]

See second page of this:

http://www.modernsteel.com/Uploads/Issues/October_2013/102013_interchange.pdf

Basically the Steel Manual made the judgement of using a safety factor of three for permanent structures instead of five for this type of equipment but in the end it is up to engineering judgement.

 

[JStephen]

Very interesting point. I was just looking at the Crosby catalog, and say, for shackles, they just tabulate the working load, and that is what is stamped on the shackle itself. As opposed to, tabulating an ultimate load and then recommending a safety factor.

Anyway, you kind of hang yourself out to dry if you design for larger loads. You can draw all the chalkboard diagrams you want, but when you hand a jury a shackle stamped with "6,000 lbs" and start explaining why it's okay to load it to 10,000 lbs, it's a hard argument to make. Among other issues, you make it where you're the one guaranteeing the adequacy of that shackle for that load rather than the manufacturer.

A slightly-related issue that has come up in the past: When a lifting product specifically says, "Do not use this to lift people", can you use it to lift people? Engineering principles say "Sure", but it doesn't give you the warm fuzzy feelings doing it, either.

 

[ILoaThePats]

Thanks for the reference WillisV. In our office we typically use a factor of safety of 2, and I've seen some people approach 1.0. If it went to a jury, that's what expert witnesses are for. I see your point though.