4 to one bend ratio

[oceans]

If you're referring to the doubling of the load at the change of direction point, it's the deflection angle more than just the number of rigging points that matters. You can still have load-multiplication (more than L) at any part of a multi-point rigging. So, while there's some load sharing, in the illustration below the four rigging points are "sharing" a total of almost 4 times the actual load (3800 lbs).

View attachment 30094

There is still at least one important factor left out of that equation. That being the energy absorbing capability of the rigging line itself. Another would be more difficult to quantify, but that being how the groundman manipulates the rope through the friction device.

I would also consider that the rigging points are distributing the load. While the angle of deflection can create load multiplication, the bisect of that angle of deflection also exhibits the direction the force is applied. I believe that is what the drawing is attempting to impart. This may be why you put the word 'sharing' in quotes. To my mind, sharing sounds more linear, where I think this is more about vectors. The direction of force is most critical to us, since one of our goals is to put the tree into compression when applying forces to it.

You are correct that each rigging point is now applying a load to the tree from its own location, but when these forces are in compression, the potential/theoretical 2:1 becomes less important.

 

[RescueMan]

There is still at least one important factor left out of that equation. That being the energy absorbing capability of the rigging line itself. Another would be more difficult to quantify, but that being how the groundman manipulates the rope through the friction device.

My annotated diagram is of static loads, as it's nearly impossible to accurately determine dynamic loads without real-time measurements. But the energy-absorbing qualities of both the rope and the groundman's technique can reduce ONLY the dynamic multiplier effects on the rigging points - the static loads are the minimum loads those points experience at all times.

I would also consider that the rigging points are distributing the load. While the angle of deflection can create load multiplication, the bisect of that angle of deflection also exhibits the direction the force is applied. I believe that is what the drawing is attempting to impart... The direction of force is most critical to us, since one of our goals is to put the tree into compression when applying forces to it.

Yes, I addressed in another thread the benefits of vectoring the load, not so much in compression along the long axis of the stems (which a single top block on the main stem would do better than multiple blocks), but from secondary stems towards the primary stem to prevent shearing of the secondary stems.

Mark Chisholm discussed this in the article I took this graphic from: Engineering a Tree Removal (which is archived on this site).

 

[oceans]

My annotated diagram is of static loads...the static loads are the minimum loads those points experience at all times.

That would be true, if the groundman did not allow the load to run. The load would first be dynamic, until it hung motionless in the air, at which point it would become static. The static load baseline is important, but it may not be the minimum load applied in an actual rigging scenario...that being if the groundman allowed the load to run. How free the load runs, and until what point is what would create that minimum load applied.

 

[RescueMan]

How free the load runs, and until what point is what would create that minimum load applied.

You're right. If the load was never significantly slowed down before it hit the ground, the dynamic loads would be less than the static loads. But any rigging system has to account for less than ideal circumstances and for maximum possible loads.

 

[oceans]

You're right. If the load was never significantly slowed down before it hit the ground, the dynamic loads would be less than the static loads. But any rigging system has to account for less than ideal circumstances and for maximum possible loads.

Yes, I agree whole heartedly, thus vectors are king. The spare change beyond creating ideal vectors when accounting for the worst becomes the tools applied and the skill in operation of them.

This becomes the sticking point for many (myself included). Since the world is not perfect, nor are any of its inhabitants, we may run into trouble if we rely on skill alone. It is important for us to properly envision what is about to happen before our eyes, and how it looks "on paper". With that knowledge, we can work most effectively, while allowing enough room for error. I don't think I'm wrong to think that many rely on some amount of skill alone, but I am humbled by trees, and I doubt luck is an endless river I can drink from.

I know this is why I personally am so drawn to tree work. I can apply knowledge, skills, and creativity in one place, and work to find a happy balance of these aspects. I enjoy discussions following a day of working with all three than a day of working with one aspect alone.

 

[RescueMan]

I am humbled by trees, and I doubt luck is an endless river I can drink from.

And you're a poet to boot!

 

[oceans]

And you're a poet to boot!

Striving for warrior poet, but poet will do for now.

 

[baumeister]

Very nice conversation oceans and rescue man. I am going to use that in some training work with my guys. I really appreciate your input. This is turning out to be a very beneficial thread for me thanks again.