big rigging forces

[frashdog]

Looking for a way to calculate dynamic forces excerted on a rigging system. I want to be able to be within our system's working load limits with the dynamic forces.

Example: How much force is excerted on a rigging system (block/rope/anchor)with a log falling 8 feet that weighs 500lbs? Locked off versus letting it run a bit to slow it down a bit. I've seen the rigging software that does this...is their an easier way to do it on the job?

We've got a big pine to remove. Lowering all of it is required. I know how to determine log weight and static loads. Just want to be sure we're safe, right!

 

[BostonBull]

Get the Arbormaster rigging software from Sherrill. It has ALL the info you need!

 

[moray]

There are a lot of variables. You can simplify a bit by noting the important variables are how far the load falls, and how far it took you to stop it. For example, say your 500# load falls 8 feet. At this point you start to catch it. If it falls 4 more feet before it has stopped AND the force you applied to stop it was completely uniform, then you can solve the problem. Keep in mind you have to apply 500# just to support the load--anything beyond that will slow it down. You need to apply 3 times the load to stop it in half the distance it already fell. 4 times the load would stop it in 1/3 the distance, and so on.

But the force you apply will not be uniform, meaning the maximum force may be much larger than the simple calculations above. I would imagine the actual maximum might easily be 3 or 4 times the calculated best case. For your example, stopping 500# in 4 feet might mean anywhere from 1500# to 6000#.

Obviously, let it run as far as you can.

 

[rbtree]

First off, no competent rigger would ever let a load fall that far onto a locked off system. But if it were done, the forces would be large. Depending on the energy absorption characteristics of the rope, the forces could be as high a 9000 pounds on the anchor sling and block, and 4500 on the rope...or close. These figures would probably be for full static line, semi static like climb lines or rigging lines would be a little lower.

But, one must keep in mind how far the center of mass of the load falls. An 8 foot log's center of mass would fall 8 feet plus the amount of line between the block and where it's tied to the tree, which would be at least 12-16 inches. So, a 16 foot 1000 pound log, even if let run, could easily generate 6000 pounds of force on the sling and block, meaning the sling would need to rated at least 30,000 pounds. And, if snubbed off, 32000 pounds.....Scary!!!

 

[clearance]

What really bothers me about this thread, is what bothers me about most threads regarding this topic has nothing to do with the rigging system. What bothers me, is-what force is the tree rated for? You can have whatever rigging gear you want, you can even use 11/4" mainline with 20" blocks held to the tree with a 11/2" strap, thats great. What about when the tree snaps off under you, what then?

 

[rbtree]

Yup, clearance, I'm sure it could happen. I do dislike wood lowering, for sure. But, if the tree is of fairly known health, the force applied by a properly run load would be way below what the tree could withstand, given that the force is applied mostly downward. This is helped by using a 70-90 degree open face if deems necessary to keep the load in close.

If there's doubt about the tree's integrity, one should think twice about rigging forces that would be generated by lowering anything substantial.

 

[diltree]

Yup, clearance, I'm sure it could happen. I do dislike wood lowering, for sure. But, if the tree is of fairly known health, the force applied by a properly run load would be way below what the tree could withstand, given that the force is applied mostly downward. This is helped by using a 70-90 degree open face if deems necessary to keep the load in close.

If there's doubt about the tree's integrity, one should think twice about rigging forces that would be generated by lowering anything substantial.

Well Said....we do allot of natural crotch rigging, double and sometimes triple crotching creating a redundancy. Before rigging The condition of the leader used for rigging must be considered but even more important a risk assessment of entire tree itself is always the first thing to examine before any rigging takes place.....When you have a good idea about what the tree can handle, then start thinking about lines, slings and blocks and their capacity's for your rigging system.

 

[frashdog]

What really bothers me about this thread, is what bothers me about most threads regarding this topic has nothing to do with the rigging system. What bothers me, is-what force is the tree rated for? You can have whatever rigging gear you want, you can even use 11/4" mainline with 20" blocks held to the tree with a 11/2" strap, thats great. What about when the tree snaps off under you, what then?

You're funny!

Right on, so the tree is 70-80 foot white pine near 40" dbh, full sun growth with lots of thick branches, a christmass tree if you will. The main gets thick quick going down, tis a stout tree. The Kicker is the 10-15 degree lean over the garage that the base of the tree is inches away from. The tree was hit by lightening hard, at the end of last summer. Home owners want it down.

We did do a climb inspection.

So, where do I find what trees are rated, at diameters.

 

[clearance]

You're funny!

Right on, so the tree is 70-80 foot white pine near 40" dbh, The tree was hit by lightening hard, at the end of last summer.

A pine tree, hit by lightening. Listen up Frashdog, a man who was a climber and an author, an expert on trees was killed when he was lowering on a lightening struck pine tree. True story, sad story, not funny at all.

 

[ddhlakebound]

A pine tree, hit by lightening. Listen up Frashdog, a man who was a climber and an author, an expert on trees was killed when he was lowering on a lightening struck pine tree. True story, sad story, not funny at all.

Well said clearance. Short and to the point.

Here's a link to what clearance was refering to.

http://www.arboristsite.com/showthread.php?t=24808&highlight=donzelli

From the description, it sounds like a bucket truck or crane will be needed to take it out safely.

 

[rbtree]

Well said clearance. Short and to the point.

Here's a link to what clearance was refering to.

http://www.arboristsite.com/showthread.php?t=24808&highlight=donzelli

From the description, it sounds like a bucket truck or crane will be needed to take it out safely.

Donzelli was a knowledgable person, but tree work was never his profession, just research into rigging methods and forces. His main mistakes were: Rigging off a lightning struck tree....dicey at best, imo. However,he had green groundies, and they ran the rigging line sideways and took wraps around a tree some distance away. Therefore, when they snubbed the piece (and they probably failed to let it run, extreme side load was applied to the anchor, and the tree broke below Pete. He hit the ground, then the tree section landed on him.

Frashdog's tree sounds pretty burly, relatively short for its girth. But Id still look for a way to free drop sections. If there's even a 4x4 square area opposite the lean, that's all I'd need to drop rounds. Or less, if the area is padded with some or all of the branches. Plywood can be used to protect fences, and walls.

I have 32 years of tree work under my belt, and do know that I am capable of doing any tree anywhere, with technical rigging skills as good as most top arborists. Many like to lower wood...not me...If I can find a way to drop it, that is always the first plan.

 

[Ekka]

Foam her up boys.

 

[frashdog]

A pine tree, hit by lightening. Listen up Frashdog, a man who was a climber and an author, an expert on trees was killed when he was lowering on a lightening struck pine tree. True story, sad story, not funny at all.

I do apreciate your concern. Well aware of the incident you are referring to. Wasn't there more to blame in that event than just the lighning hit to the tree? Yea, that's not funny is it? So empart me some useful knowledge about lightning hits so you don't sound like my mom, "Oh you got a motorcycle, you know motorcycles are dangerous some one died on one the other day and he was riding for 30 years"

Like I said we did a pre climb due to the concern of the lightning hit mostly. The lightning tore down the bark and jumped into the garage. So from what we saw the hit did not split any wood nor did it ground through the roots. Kinda the common scenario we see with lightning hits around here. No sign of the hit affecting the health of this tree, yet. We definitly are not money hungry cowboys, we are ready to back down the first sign we get that does not allow us to act safe.

So flame away if you must

 

[frashdog]

Donzelli was a knowledgable person, but tree work was never his profession, just research into rigging methods and forces. His main mistakes were: Rigging off a lightning struck tree....dicey at best, imo. However,he had green groundies, and they ran the rigging line sideways and took wraps around a tree some distance away. Therefore, when they snubbed the piece (and they probably failed to let it run, extreme side load was applied to the anchor, and the tree broke below Pete. He hit the ground, then the tree section landed on him.

Frashdog's tree sounds pretty burly, relatively short for its girth. But Id still look for a way to free drop sections. If there's even a 4x4 square area opposite the lean, that's all I'd need to drop rounds. Or less, if the area is padded with some or all of the branches. Plywood can be used to protect fences, and walls.

I have 32 years of tree work under my belt, and do know that I am capable of doing any tree anywhere, with technical rigging skills as good as most top arborists. Many like to lower wood...not me...If I can find a way to drop it, that is always the first plan.

right on. We got plywood coming and they are having us blow chips near the base so I think we may be able to land some sizable chunks in the chip piles to keep them where they land. We have 2 different winches if needed to pull chunks over the lean, too boot there is another big pine close enough set up another system to be reduce the forces on the primary and help us land the wood a bit away.