cycles to failure equation

CutHighnLetFly

CutHighnLetFly

Been here a while
Location
Cape Cod, MA
i know im starting threads left and right but there was a thread going about tree removals and big rigging, i think some of you might have seen it...

isnt there an equation that shows a rough estimate of cycles to failure of a rigging line? Something about the ropes breaking strength in relation to the amount of force put on the line and number of times that force is applied?


personally i love this website, i always have questions and someone always has an answer, even if its not what i was hoping i would hear. Hope no one minds me abusing this site for answers all the time!
 
Norm, I remember you posting this before and thanks for putting it up again.

Most of you guys know that in tree work, we use (or should use) a 10:1 ratio for climbing and for rigging work. What some of you may not know is that the cordage industry still goes by the 5:1 ratio which is what is used in commercial rigging applications, where the loads are known and the lifts are static.

Because we are guessing at loads and doing an awful lot of dynamic rigging in tree work, we need a larger margin of safety. Years ago, Don Blair and some others came up with the 10:1 safety factor and the tree care industry has stayed with this ever since.

Now, when you look at Norm’s Excel spreadsheet, you can see how much we can increase our cycles to failure if we use the 10:1 ratio, instead of the 5:1 ratio that the commercial construction industry uses.

I also remember Don telling me that a great safety practice is to “rig wood for manila rope sized pieces, but use polyester double braid rope instead and you’ll never have to worry about cycles to failure”. Some of you younger guys might not grasp the meaning of this, but Norm and others know what I mean.
 
[ QUOTE ]
Nice Norm! Do you have any other info about who tested for and produced this chart?

[/ QUOTE ]

I've had it for a loonnng time. I'm sure it's from one of the big 3 USA rope manufacturers, but don't remember which one.
 
[ QUOTE ]
[ QUOTE ]
Nice Norm! Do you have any other info about who tested for and produced this chart?

[/ QUOTE ]

I've had it for a loonnng time. I'm sure it's from one of the big 3 USA rope manufacturers, but don't remember which one.

[/ QUOTE ]

Yes, thanks Norm. I found this chart in Arborist Equipment by Don Blair. The manufacturer is Samson.

Joe
 
Aslo important to take into account what type of rigging is used. Natural crotch,pulley,shackle,biner?
 
I think if your worrying about cycles, your taking too big of wood, or using too small of ropes.
The ropes we use are meant to have such high safety factors that we shouldnt really be concerning ourselves with cycles. If we are, thats a clue that the wood is too big, or the rope is too old.
I understand the whole comcept of cycles to failure, Im not a moron, but I work in the real world, with multiple crews I cannot keep track of all the cycles the ropes have run, guys move from truck to truck, ropes move as well, I aint sending around a notebook with the ropes, so the only logical solution to this is too work with very high safety factors already factored in.
If your not working in these factors your just tempting fate.
 
Ageed!

This is just a note, not an attack. But without a credible reference, a chart like Norm posted doesnt really carry any weight. While I personally count Norms endorsement as credibility enough I wish that there was some more 'official' documentation for this kind of data.
 
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Nice Norm! Do you have any other info about who tested for and produced this chart?

[/ QUOTE ]

I've had it for a loonnng time. I'm sure it's from one of the big 3 USA rope manufacturers, but don't remember which one.

[/ QUOTE ]

Yes, thanks Norm. I found this chart in Arborist Equipment by Don Blair. The manufacturer is Samson.

Joe

[/ QUOTE ]
 
You must log in or register to reply here.

New threads New posts

Back
Top Bottom