SIA- the tree pulling test/theory

[Tony Croft aka hamadryad]

So, I am interested in a discussion on this method of hazard evaluation, but have not looked into it any more since my first dip of the toes and finding that the whole concept is based on buckles being the initial failure starter as apposed to Clause Matthecks theory on shear before buckle, he is right of course.

 

so can anyone tell me more about this conflict of theories, and more about the method of tree pulling?

[mrtree]

I can certainly talk about pulling but not much about shear vs. buckling.

 

One thing to keep in mind is that that there is a huge issue of egos, hurt feelings and pride in the issue of Mattheck vs. the pulling guys.

[Tony Croft aka hamadryad]

unfortunately i do not know THAT part of the story, and hope to understand all sides of the argument.

 

so lets exclude the buckle shear equation for a moment (surprised you know about pulling theory without this basic knowledge? does this indicate a weakness in the training?)

[skyhuck]

How is it possible to know that the pulling has not weakened/damaged the tree??

[Tony Croft aka hamadryad]

How is it possible to know that the pulling has not weakened/damaged the tree??

 

easy tiger:001_smile: lets find out whats involved first!

[mrtree]

The basic idea is that you pull such that you do not damage or weaken the tree. By measuring tilt of the root plate you never pull beyond a 0.25 degrees. Failure generally occurs between 2.5 and 4 degrees. When tensioning (or compressing) fibres a load of 1 to 2 tonnes (10 o 20 kn) is applied which is below the "specific elastic limit" of wood fibres.

[skyhuck]

easy tiger:001_smile: lets find out whats involved first!

 

Fair enough

 

I'm genuinely interested

[skyhuck]

The basic idea is that you pull such that you do not damage or weaken the tree. By measuring tilt of the root plate you never pull beyond a 0.25 degrees. Failure generally occurs between 2.5 and 4 degrees. When tensioning (or compressing) fibres a load of 1 to 2 tonnes (10 o 20 kn) is applied which is below the "specific elastic limit" of wood fibres.

 

How are defects manifested, during the pulling??

[Tony Croft aka hamadryad]

The basic idea is that you pull such that you do not damage or weaken the tree. By measuring tilt of the root plate you never pull beyond a 0.25 degrees. Failure generally occurs between 2.5 and 4 degrees. When tensioning (or compressing) fibres a load of 1 to 2 tonnes (10 o 20 kn) is applied which is below the "specific elastic limit" of wood fibres.

 

but this cannot apply to all wood fibres? or is that why a load of 1-2 tons is used, allowing a slight degree of genetic differences? or does all wood break at this stated elastic limit?

[mrtree]

I have to go out but there is a variation in wood fibre strength, that is why there are tables for modulis of elasticity by species.

 

 

How are defects manifested during the pull? Well they are not really. The idea is that the trained and knowledgable assessor finds the areas of the tree that needs to be assessed for strength. Thus you will likely pull at the thinnest part of a shell around a hollow, or very near a defect and measure the reaction of the tree. The movements are so small they are measured with a micrometer.