Rigging Point Failure

[TreesRGood]

CreTree: The concept of fatigue is very simple, when a motion is repeated, the object that is doing the work becomes weak. For example, when you run, your leg and other muscles of your body become weak, not always to the point where you can't move them anymore, but there is a noticeable decrease in quality output. This same principle is seen in materials. Fatigue occurs when a material is subject to alternating stresses, over a long period of time. It also depends on how the ground guy responded to the load when it was cut. Did he dynamic load the line? Or did he let it run nice and smooth? These are all contributing factors when failures like this occur. There could be more faults that led up to this than just the limb failing.

But I agree with what you said 100%. Were both correct, I guess it just depends how its said. Thanks for that though, its deff an eye opener.

 

[CreTree]

Very good point Tim. I neglected to consider the spar as a "tool". The trunk is indeed a part of the system and honestly a much more sacrificial part. Too many drops on one point, especially at this time of year, with the load increasing can certainly be associated with Cycles to Failure.
Thanks.

 

[Fairfield]

If this has been put in a chat room already then sorry for the repeat post. I think it is inportant to have an idea of what kind of forces are being applied with change of directions. You said that the angle was 45 or greater. 100 lb will have a about 141lbs of force to the COD. Thats not placeing any kind of shock load as small as it may be. I try not to be a math freak when it comes to rigging but it does help at times.

 

[Tony]

Six easy ways to reduce force in a rigging system:

1. Put more rope in the system
2. Expand rope angle at the rigging point
3. Limit distance of fall
4. Decelerate fall slowly
5. Use a more elastic rope
6. Cut smaller pieces

Any of these could have been used, but I think #6 would have been the best.

Tony

 

[Daniel]

I think #2 is a go to move.. on every large removal.. why wouldn't you use everything to advantage.. there are a lot of factors to consider in any large rigging scenario.. why would you put yourself in a position to have to consider if your overhead rigging anchor point can handle the weight. That's only a consideration in situations of dire need.

I go with everything else first, so #6 comes last!

Tony you might consider adding cutting technique to that list.

I rigged a big old piece of wood off a dead elm years ago.. had the rope through two crotches.. so much weight the two crotches came together.. tough stuff that elm.. even dead elm!

 

[Tony]

Daniel,

I agree cutting technique can certainly help manipulate forces into a rigging system, but usually along with one or more of the other six. However, you still make a valid point.

I too like to alter everything, before piece size, but sometimes it's just simpler, safer and in the case of a sketchy rigging point an excellent, oft ignored option.

Tony