# WLL versus ultimate breaking strength of rope



## Plasmech (Nov 4, 2009)

Looking at a 5/8" polyester bull rope that has a nominal 3,000 lb WLL (work load limit) and a 15,000 breaking strength. Does this *really* mean that I must absolutely not exceed 3,000 lbs on say a come-along pull and that if I do, the rope *should* be retired? Or is this not realistically true? I'd imagine guys put much more than 3,000 lbs on 5/8" ropes on a daily basis without retiring them. Thanks for any help!


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## lego1970 (Nov 4, 2009)

I'm not really sure. I always thought the WLL was about 10% of the breaking strength of the rope. Knots reduce the breaking strength in half or something like that and a free fall of only 10 feet muliplys the weight on the rope something like 5 to 10 times, so I think that's why the WLL is so much lower then the actual breaking strength. On a climbing line I don't ever work it hard. Occasionaly I rope something out with the tail end of my rope but it's never more then the weight of a person. I don't know what to tell you on a rigging line, but I would think as long as you didn't shock load it and the areas where you had the knots doesn't look or feel like it's damaged, then it's probably ok. Where a knot has been, the outside strands on a bend take all the workload and the inside is relaxed. So when you take the knots out, really pay attention to those areas. Good luck and I'm sure someone else with more knowledge will chime in.


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## Job Corps Tree (Nov 4, 2009)

*will versus ultimait breaking strength of rope*

Our Certified tree Worker class here at ACRTinc.Job Corps we teach that WILL is the safe working load (safe working load limit) for a Rope is 1/10 of the new Ropes Tensile strength( Maximum Breaking Strength for new Rope) ever time you put a pull on a rope you will weaken it the more hard pulls the sooner the rope will fail. everthing we do or use is with a 1/10 safety margin


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## TheTreeSpyder (Nov 4, 2009)

Different folks and systems place the ratio of WLL : Tensile at different points. 

For example dragging wouldn't have such a high margin as overhead lifting etc. Also, you might only be able to load a line at 90% tensile 25x, but 1000's of times at 50% etc. Mostly these are static loading conditions considered. Then we have environmental 'degrading' of use or non-use (sun, air, gas/oil, feline urine etc.); then there is grit that can get into lines and be worked back and forth on loading stretches to tear up lines/cut threads inside. So, different people, environments and industries might place different ratios on lines..and some manufacturers themselves might be more conservative to leave more 'headroom' to their quoted nos.

But, yet another factor to consider; would be the needed dynamics/ elasticity of a line under dynamic loading conditions. This usually is taken from line first in it's life span. Also, there are different ranges of recover -ability of the elastic hysterics. Part of the elongation might be unrecoverable, some might take minutes or hours to recover, and some is immediately recoverable. So, what worx 1x, mighty not another, for these (t)reasons; or even matching lines bought at same time, used seemingly same. 1 line might have more of the elasticity 'beaten' out of it permanently or even just temporarily. So, on a dynamic loading; 1 line might break, or even just not buffer the loading the same (so takes more loading on all connected points like tighten knots more, more likely to overpower support etc.).

Also, if elastic dampening is needed, tensile and length (besides construction and materials) must be considered. Because the longer the loaded line part, the more elasticity that can be granted. But, also a higher tensile line of the same construction and manufacture will give less dampening/buffering/elasticity to the same dynamic loading. Now, that means; that a lower tensile line will have a lower WWL to the static part of the loading, but will have more elastic dampening "WWL" to the dynamic part of the loading! So the tension wouldn't be as great in a dynamic loaded line of less tensile under same conditions. this also applies to pulley giving 2:1 support; each leg of support is less dynamic to same impact (so more bounce in SRT than DdRT). And you only count the length of line in a leg of support to calc elasticity; so the 'extra' line doesn't help in a 2:1 vs. 1:1 support.


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## squad143 (Nov 5, 2009)

As posted in another Thread.

Article on tree rigging concepts:

http://www.treemettlenexus.com/article4.html

Gives a good understanding of relationship between Breaking Strength(BS), Safety Factor(SF), Working Load Limit (WLL) and Cycles to Failure(CTF).


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## alonfn4 (Dec 5, 2012)

I called samson ropes today to get some info there tenex and stable braid ropes have a 5:1 working load limit or 20% of the rated MBS
they say never to exceed the WLL, but we do overload them all of the time with static loads like the come-along... I have a dedicated line for that we don't rig off of it any more.

always better to just used a bigger rope when you can


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## Plasmech (Dec 5, 2012)

Holy old threads, Batman.


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