Rated Capacity vs WLL

[precast78]

It is always confusing every time I review lifting capacity of a sling. So we got a quote from this company. We wanted to buy a 4 leg bridle (see the link for the type 400). Here is their technical info on the product :

http://www.hanessupply.com/webcatalog/Documents/Wire_Rope_Sling_Technical_Info.pdf

.

According to that sheet it is giving me the Rated Capacity. Isn't rated capacity pretty much the breaking strength in the lab?

On the quote though, they put exactly the same numbers as that page except they say it is WLL. It also says it has 5:1 Safety of Factor.


When I designed it I multiply my load by 5 and figured out I needed an 8 Ton cable (60 degree angle) breaking strength. It looks like the 14 ton (60 degree) capacity they listed on the technical info is for the combine (4 legs) capacity. What do you think? Do you think this number really has 5:1 factor of safety?

 

[AELLC]

Rated capacity is safe load allowed. When the rated capacity is exceeded, that is starting to eat into the FS, so for example, a rated capacity of 5 tons means that 25 tons will break the cable if the FS was 5.

 

[dhengr]

Precast78:
There is some variation from code to code or std. to std., but the thought process is the following: you start with the manufacturer’s breaking strength for the particular wire rope and divide by 5 to get to the working strength for that wire rope. This factor of safety is fairly high because this type of equipment tends to be reused, abused, neglected and not inspected as regularly as we would like. Furthermore, many users assume the FoS is there to be used by them, so what’s a 15-20% overload, they think. Then, sling capacity can be further reduced by the efficiency adjustments of the various fittings and connectors used in making up the sling. Finally, it should be obvious to you that the total sling assembly capacity (WLL?) will decrease as the sling legs assume an angle away from a perfectly vertical lift (straight lift). Because the governing design criteria is the strength of the sling assembly itself.

I believe that most sling assembly companies will proof test an assembly to 1.5 times the working strength of the assembly. This testing level is something you should spec. in your order for the slings. Ask your sling supplier to define the various acronyms such as WLL, IPS and EIPS; and ask them to explain their load tables, etc., so that you can use them properly. There should be no embarrassment in doing that. Ask them what fitting efficiency adjustments they have used in setting you the allowable capacities.

 

[BAretired]

I didn't know what WLL meant, so I checked with another supplier. It means "Working Load Limit". See attached.

http://www.katradis.com/products.php?category=wire&page=slings_wll

BA

 

[chicopee]

"WLL" means working lifting load

 

[chicopee]

Go on line and download the Crosby catalog as there is a definition section.

 

[BAretired]

As is often the case, acronyms can have more than one meaning. They should be avoided where possible.

BA

 

[precast78]

Thanks guys. I guess this website confused me.

http://www.rigginglifting.com/information/2007-12-27/2007122741.html

According to this page that rated capacity is the breaking strength. Anyway, I am designing a lifting device and wanted to make sure the cables have enough FOS. It sounds like the capacity listed has 5 FOS already so I need to redo my calc. I guess what I wanted was the breaking strength, not WLL.

 

[dhengr]

Precast78:
I believe IPS = Improved Plow Steel and EIPS = Extra Improved Plow Steel. Again, ask your sling supplier, they’re selling the slings and should be willing to dig up this info. for you. You must read btwn. the lines a bit; the sales guy will regurgitate some b.s. which he thinks he’s heard, so ask for someone from the engineering dept. Then, ask the same question three slightly different ways so you are sure you get the same answer each time, and understand how to apply it. Also, I really think we need a whole bunch more undefined acronyms, each with at least 37 different potential meanings, so we all sound very knowledgeable when using them, but can be assured that most people won’t have any idea what the hell we are talking about, because we are to damn lazy to define the acronyms, at least on first usage. The OP’er. wants some free advice, and then expects those willing/helpful members to waste their own time looking up the potential meanings of acronyms, which he’s too damn lazy to define. Why should we waste our time, when the OP’er. won’t spend his to present a meaningful question?

When you are looking for internet info. on a subject, you should at least look for material which is not written in pigeon-English. And, the link you have provided leaves a lot to be desired, in my mind. While I don’t think your link is out-n-out wrong, it might be misleading or misunderstood, so you really have to read btwn. the lines. Again, ask your supplier, have him put it in writing in his quote to you, or in a letter. Breaking strength should be pretty clear to all of us; either for the particular wire rope or for the full sling assembly. While rated strength, rated cap’y., and assembly cap’y. could have a hundred meanings. Rated cap’y. to me means some engineering judgement has been applied to the cap’y., not just its physical min. breaking strength. There will be a FoS, and some fittings or rope bending reductions applied. Then your original OP attachment would show these further cap’y. reductions due to hardware, fittings, attachment means and wire rope bending, etc., as well as geometrical variations such as wire rope angle from vert.

 

[structSU10]

A note on the FOS being 5 - It is supposed to also account for dynamic load effects. No matter how "slow" or controlled a pick is, there is always going to be a fairly large initial acceleration. If the picker has an off day, and there is a bit of a jerking action to the load, your DLF can be 2 or so depending on severity, so the higher FOS is used as an easier way to account for this.

 

[PersonalProfile]

Depends on your criteria etc, though in AU:

WLL (although in other standards, we use MRC - Maximum Rated Capacity) = "usable rating".
Breaking force = "literally breaking force".
Min SF = 5:1 (plus various other physical / geometric derating factors etc, as required).

Also, for other than two leg slings, we still only recognise two legs of the slings (as if the load is rigid, load sharing is unlikely to be achieved), viz:

http://www.nobles.com.au/Products/Lifting-Slings/Wire-Rope-Lifting-Slings/Wire-Rope-Slings

Regards,
Lyle

 

[chicopee]

You should use the WLL instead of the breaking strength because the breaking strength is only a statistical value, so you not really sure where you stand in the safety of things. The factor of safety of 5 does away with a lot of uncertainties with the construction of the wire rope.