Great Reading - Rigging

Bart_

Active Member
Location
GTA
Guy Meilleur had his fingers in this. At least as a reference. It's British arborist research about rigging forces. 2008, pretty recent and with references going back to the 60's


=========If you're impatient skip straight to chapter 8 Rigging Forces=======

upon some reading found confirmation of 70% hollow trunk ok, thought a west coast guy was pulling my leg

edit - more confirmation info -
When dismantling slender trees with structurally weak stems and/or water-saturated root systems, or trees prone to root failure, the generation of strong oscillations should be avoided (e.g. by retaining lateral branches along the stem when cutting the top, see 2.8), and loads from rigging operations should be minimised (see Chapter 8).


edit - call me plagiarizer, but this is good stuff well written, passing it on:
3. Reduce loads generated in rigging operations (see Chapter 8) by:
  • cutting shorter sections, thus reducing their weight and distance of fall.
  • using appropriate arborist techniques (e.g. the fish-pole technique, cf Donzelli,
    S. Lilly 2001).
  • positioning the friction device at the best position (with regards to stem inclination and cutting direction).
  • adding more rope to the rigging system, by including another arborist block at the base of the tree being dismantled, and shifting the friction device to an adjacent tree (Palmer, K., pers. comm. 2003).
  • retaining lower branches while taking the top out, in order to damp stem oscillations.

edit - the discussion of how a hinge fails progressively is strangely also related to rigging. I forget where, a discussion lead to an engineer/treecutter's video explaining the failure of a hinge and he said the compressive side is damaged first and then fails early when called on to act in tension when holding a side lean. Any who, more excerpt:

The compressive strength of marginal fibres is decisive for load-bearing capacity in these models. On the scale of wood fibres, excessive compression causes permanent deformation that is referred to as primary failure. The ultimate load-bearing capacity may actually be greater than the compressive strength, but the tree would be damaged long before fracture. Green wood is reported to be about twice as strong in tension as in compression (Bodig et al 1982, Niemz 1993). Therefore, failure will occur on the compression side first, by the buckling of fibres (Vincent 1990). Even though the structure will not fail completely when the fibres kink, the tree may not withstand future loads, even if they are significantly lower (primary failure, cf Chapter 2). The compressive strength of fibres parallel to the grain should, therefore, be used as a threshold for strength (cf Wessolly, Erb 1998).


edit - If your tipped in at less than 2" you know you're in the spindlies and you better have a multi-point SRT basal going:
5.5.1 Required diameters of anchor points for climbing
Lilly (2005) proposes a diameter of 4 inches (approximately 10 cm) for a branch to be safe to use as an anchor point in tree climbing. Other sources (e.g. Hagen, Schwarze 1991) state that required diameters are species-dependent. In a report on ‘Safe Work Practice in Arborist Fall Protection’ (for the Canadian Ministry of Training, Colleges and Universities), practising arborists recommended a minimum diameter of 5 cm for branches used as climbing anchor points, and advised keeping the rope against the main stem while climbing, in order to minimise the effect of leverage (Anonymous 2005).


edit - damping branches:
Shock loads, such as those generated by arresting a climber’s fall, or the accidental locking of a friction device during rigging operations, might have a different effect on a woody structure than static loads. The damping properties of limbs that restrict the effect of a dynamic load were studied by Hoag et al (1971), who determined the effect of moisture and leaves on the logarithmic decrement of wind-induced oscillation of branches. It may be justified to argue, therefore, that moisture and leaves will contribute to an increased ability to damp dynamic loads from rigging operations, and add to a branch's bearing capacity in such a scenario.

edit - Spidey, this section is calling your name:

7.1 STRENGTH LOSS DUE TO KNOTS
The mechanical properties of ropes are usually tested under standardised conditions, using testing procedures specified in industrial norms (e.g. EN 2307, CI 1801). These standards refer to an undisturbed, straight, section of new rope only. However, where a knot is concerned, bending of the fibres, and the effects of friction, cause a strength loss that varies with the type of rope and knot in question.
Publications on the strength of knots used in arboriculture are somewhat rare. Commonly used instruction books usually only refer to the fact that knots weaken the strength of rope (if they mention it at all), but do not specify strength loss for particular knots (e.g. Lilly 2005; Schütte 2007).
Specialised knot books refer to this issue from a general perspective:
“Knots weaken rope. The sharper the curve, the tighter the nip (the binding, frictional pressure within the knot that keeps it from slipping), the greater the chance that the rope will break. If it does, it separates immediately outside the knot.” (Budworth 1985)

edit - I'll stick to nylon slings:
High performance fibres are reported to lose a large amount of their strength when knotted. Pilkerton et al (2001) state that Amsteel ropes, when knotted, failed at loads 80 to 90% lower than their rated strength. Similarly, ropes made from Dyneema (a trade name of Beal Ropes applied to a high strength cord known as Spectra in North America, cf Moyer, 2000) lost almost 80% of their tensile strength when knotted with a Bowline, in tests carried out by the manufacturer (Gleistein Ropes 2004). Since knots are required in most rigging operations, these ropes must be used with care and should preferably be attached via a spliced eye (a method of attachment which would require the use of karabiners, and which, as such, is not recommended where dynamic loading is involved).

edit - well, whaddayouknow, you gotta keep it lubed:

“Tests conducted in a study by Smith (1988) indicate that treatment with concentrated fabric softener reduced the strength of a new rope. Frank (1989) showed that certain ropes treated with dilute softener (per manufacturer’s recommendations) were stronger than the same rope without softening, after ageing and washing. Frank reported that the likely mechanism at work explaining these results is that the fibre lubricants contained in new rope are lost with age, allowing the fibres to cut one another. Fabric softener replaces some of the lubricants. Excess softening leaves the rope effectively wet, with the corresponding loss in strength.
“With this mechanism in mind, a further argument for treatment with fabric softener would be its effect on spring rate. Since a rope’s spring rate is determined by both nylon material properties and fibre weave, it is likely that fabric softener will help prevent stiffening, due to loss of internal lubrication. In dynamic situations, the underlying physics shows that preserving the spring rate is as important as preserving its strength, toward the goal of avoiding rope breakage” (Storage et al 1990).

edit - have mercy on your rope, let it run:

Eventually, shock loading will speed up the decline of a rope’s strength more than loads generated by lifting and winching operations, which avoid the abrupt changes in tension that are typical for dynamic shock loads (Lilly, 2005). In operations that involve fall arrest, failure under shock loading may occur after relatively few load cycles. In a test carried out at Teufelberger, Austria, a 14 mm kernmantel rope (48 kN tensile strength) failed after 14 impact load cycles that generated forces of less than 40% of its rated strength (design factor 2.5). As shown in Figure 7.20, some ropes would have been able to sustain more than 100 load cycles when lifting at the same load level.

edit - these guys wrote rigging force software based On Donelli's model of snubbing a log into a rope with known elasticity and assuming the rope takes all the hit, no run:

Educational software developed by Brudi & Partner TreeConsult, in cooperation with ArborMaster Training Inc, USA, allows arborists to input parameters that are determinable and adjustable in a specific rigging scenario. Rigging 1.0 (see Figure 8.3) can then show the effects on the peak force in a worst-case scenario that result from making changes to the following four parameters:
  • log weight
  • rope length
  • rope types of various stiffness
  • distance of fall
Comparisons of peak forces calculated by Rigging 1.0 with loads measured in drop tests in a realistic rigging scenario, have shown that the load is overrated by a factor ranging from 2 to 3, when using the simple equation above. The same is true for comparisons of drop tests carried out by Donzelli et al (1998) when similar deviations were noted. Such considerable deviations can hardly be accounted for by the factors that are neglected in this simple energy transfer model (some of which are listed in the previous paragraph). Obviously, the mechanical model used by both Peter Donzelli and Rigging 1.0 does not sufficiently match the real kinematical process in rigging operations.

1000 character limit - now you got to read it for yourself...

Mark Chisholm 2000 referenced pg 224 ....
.
 
Last edited:

Jehinten

Well-Known Member
Location
Evansville
Guy Meilleur had his fingers in this. At least as a reference. It's British arborist research about rigging forces. 2008, pretty recent and with references going back to the 60's


upon some reading found confirmation of 70% hollow trunk ok, thought a west coast guy was pulling my leg
Haven't had a chance to read that yet, but at Arborfest 2 years ago an instructor said that as long as the hollow is centered in the trunk you can lose 80% of diameter before you lose 20% of the strength.
 
A ~45 ft tall spruce I took down in this summer's festivities - leaning way towards the house. No rigging, just careful cutting on the top and took small pieces on the way down. If I recall, this hollow section was about the first 10 feet of the tree from the ground. Tree top was still green though. I tightly wound the bottom trunk section with ~100' of bull rope up to nearly 8 feet (maybe more for the thought that I had done something to help stay upright) but it was actually amazing how strong the thing still was. Center of the hollow section was filled with really nice loamy material - HO kept this for their flower beds.
The learning - soda straws can be pretty strong I guess.
Wish people wouldn't left them get to this stage though, before taking them down
 

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dsptech

Well-Known Member
Location
North East
I'll tell you a little story about this one...

I knew the tree was in bad shape but canopy had healthy wide growth.
I knew it was hollow but it was supporting it's top and survived through many severe wind storms we've had this season.

It was a risky job to take on for a solo climber and many guys had passed on the job over several years.
The elderly woman who lived alone that this tree belonged to was desperate.
The surrounding properties in this suburban neighborhood were as risk and they let her know it.
I was doing a job on a street behind her and she put her grandson in his stroller and walked about a half mile around to find me.
I was up in a tree while she desperately tried to get my attention.
I had my ear muffs on and saw running and I didn't notice her till I re-positioned and remove my muffs.
I looked over and she was waving at me with both arms while the stroller with her grandson in it was rolling away down the driveway.
I yelled out to her an she went scrambling after him as fast as she could to grab him.
At that point the home owner came out and gave her one of my cards.

Later on I found out from him that she gave another tree guy $1200 deposit to cut down the tree.
Needless to say, the tree was still standing a few years later.
I met with her and I felt bad so I decided to take it on.
She told me every morning that she was praying for me and then would leave for the day as fast as she could.
She couldn't bare to watch.

When I got the tree height down enough to drop it I cut my notch around 4 1/2' up from the ground hoping to hit some good holding wood.
Used a 42" bar so I wouldn't have to dicker around with it.
When the notch fell out I realized how bad it really was.
It became apparently worse as I cut the stump down in sections.
The tree was around 45" DBH but flared out to around 6' at it's widest point.
Each layer I cut down I saw the with of the hollow get wider and wider.
Once I had it down to stump grinder height I realized what wee little bit of that trunk was actually holding that tree up.

IMG_20200715_112535.jpg

I knew then that it had to be because of that little old woman's desperate prayers that kept that tree from falling.
She said she could finally sleep at night without fear of that tree falling after many years of worry.
Her neighbors were thrilled as well as they all stopped by to thank me.

She told me later that it wasn't her that found me but that it was God who sent me to her.
It felt really good to have helped her.
 

Reach

Well-Known Member
Location
Atglen, PA
I'll tell you a little story about this one...

I knew the tree was in bad shape but canopy had healthy wide growth.
I knew it was hollow but it was supporting it's top and survived through many severe wind storms we've had this season.

It was a risky job to take on for a solo climber and many guys had passed on the job over several years.
The elderly woman who lived alone that this tree belonged to was desperate.
The surrounding properties in this suburban neighborhood were as risk and they let her know it.
I was doing a job on a street behind her and she put her grandson in his stroller and walked about a half mile around to find me.
I was up in a tree while she desperately tried to get my attention.
I had my ear muffs on and saw running and I didn't notice her till I re-positioned and remove my muffs.
I looked over and she was waving at me with both arms while the stroller with her grandson in it was rolling away down the driveway.
I yelled out to her an she went scrambling after him as fast as she could to grab him.
At that point the home owner came out and gave her one of my cards.

Later on I found out from him that she gave another tree guy $1200 deposit to cut down the tree.
Needless to say, the tree was still standing a few years later.
I met with her and I felt bad so I decided to take it on.
She told me every morning that she was praying for me and then would leave for the day as fast as she could.
She couldn't bare to watch.

When I got the tree height down enough to drop it I cut my notch around 4 1/2' up from the ground hoping to hit some good holding wood.
Used a 42" bar so I wouldn't have to dicker around with it.
When the notch fell out I realized how bad it really was.
It became apparently worse as I cut the stump down in sections.
The tree was around 45" DBH but flared out to around 6' at it's widest point.
Each layer I cut down I saw the with of the hollow get wider and wider.
Once I had it down to stump grinder height I realized what wee little bit of that trunk was actually holding that tree up.

View attachment 71201

I knew then that it had to be because of that little old woman's desperate prayers that kept that tree from falling.
She said she could finally sleep at night without fear of that tree falling after many years of worry.
Her neighbors were thrilled as well as they all stopped by to thank me.

She told me later that it wasn't her that found me but that it was God who sent me to her.
It felt really good to have helped her.
That’s a great story, truly incredible the way it all worked out! I’m glad you were able to take on that tree, and complete the project with no issues. And I would agree with her, that God’s hand was in this project.
 

Jehinten

Well-Known Member
Location
Evansville
Recent large hollow Sycamore removal. Took a couple of extra precautions while setting up rigging on this one. Guy roped it back to the trunk on the left and fishing pole rigged it to help with the heavy lean and curve of the trunk.
 

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Lupin_IV

Member
Location
St Paul
I'll tell you a little story about this one...

I knew the tree was in bad shape but canopy had healthy wide growth.
I knew it was hollow but it was supporting it's top and survived through many severe wind storms we've had this season.

It was a risky job to take on for a solo climber and many guys had passed on the job over several years.
The elderly woman who lived alone that this tree belonged to was desperate.
The surrounding properties in this suburban neighborhood were as risk and they let her know it.
I was doing a job on a street behind her and she put her grandson in his stroller and walked about a half mile around to find me.
I was up in a tree while she desperately tried to get my attention.
I had my ear muffs on and saw running and I didn't notice her till I re-positioned and remove my muffs.
I looked over and she was waving at me with both arms while the stroller with her grandson in it was rolling away down the driveway.
I yelled out to her an she went scrambling after him as fast as she could to grab him.
At that point the home owner came out and gave her one of my cards.

Later on I found out from him that she gave another tree guy $1200 deposit to cut down the tree.
Needless to say, the tree was still standing a few years later.
I met with her and I felt bad so I decided to take it on.
She told me every morning that she was praying for me and then would leave for the day as fast as she could.
She couldn't bare to watch.

When I got the tree height down enough to drop it I cut my notch around 4 1/2' up from the ground hoping to hit some good holding wood.
Used a 42" bar so I wouldn't have to dicker around with it.
When the notch fell out I realized how bad it really was.
It became apparently worse as I cut the stump down in sections.
The tree was around 45" DBH but flared out to around 6' at it's widest point.
Each layer I cut down I saw the with of the hollow get wider and wider.
Once I had it down to stump grinder height I realized what wee little bit of that trunk was actually holding that tree up.

View attachment 71201

I knew then that it had to be because of that little old woman's desperate prayers that kept that tree from falling.
She said she could finally sleep at night without fear of that tree falling after many years of worry.
Her neighbors were thrilled as well as they all stopped by to thank me.

She told me later that it wasn't her that found me but that it was God who sent me to her.
It felt really good to have helped her.
Awesome story, thanks for the reply. The more comprehensive photo was illuminating, it's amazing what holds these trees up sometimes for many years. It's good to know either where people draw the line or what their methods are if they choose to work on a more structurally questionable tree.
 

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