SIA- the tree pulling test/theory

[Tony Croft aka hamadryad]

please do come back to this discussion Mr tree

[treemeup]

I've done one tree bend test, the consultant had the micrometer at the base of the tree and if it was going to fail anywhere it would have been after the first fork, we did mention this but he didn't seem too interested

[High Scale]

My friend is contracted in for test pulls on trees, he broke a perfectly good Oak tree once.

[mrtree]

Good to see that people are already pulling out examples of why SIA and SIM are no good. They also show a complete lack of understanding of the test.

 

I've done one tree bend test, the consultant had the micrometer at the base of the tree and if it was going to fail anywhere it would have been after the first fork, we did mention this but he didn't seem too interested

 

So in this case why was a pull test done if there was no fear of the stem breaking? Who hired the consultant? For what test? If the consultant was hired to do the pull test and that is what he did, his job was done. The question of what is the most vulnerable part of the tree (the most likely to fail) was likely not made by the consultant.

 

You also say you have done one bend test. Are you trained or did you just install the cable in the tree?

 

 

"My friend is contracted in for test pulls on trees, he broke a perfectly good Oak tree once."

 

Well something is not right here. How do you pull apart a perfectly good tree? Surely there were defects not in the tree and that is why the tree was subjected to a pull test. Further the person doing the test should not be applying forces that would break an oak.

[treemeup]

Good to see that people are already pulling out examples of why SIA and SIM are no good. They also show a complete lack of understanding of the test. I was just portraying my experience of this technique, I was not saying the test itself was no good, just it's application on this occasion

 

 

 

So in this case why was a pull test done if there was no fear of the stem breaking? Who hired the consultant? For what test? If the consultant was hired to do the pull test and that is what he did, his job was done. The question of what is the most vulnerable part of the tree (the most likely to fail) was likely not made by the consultant. there was fear of the stem failing but above the first fork, he was hired by someone who didn't want the tree felled, not anyone (to my knowledge) with any knowledge of tree care, just an appreciation of trees. and yes the client most probably chose to test the tree at the base (not having an understanding of tree care), not at the weak point of the stem.....and yes the consultant got his money

 

You also say you have done one bend test. Are you trained or did you just install the cable in the tree? I installed the cable and did the winching, but i did make a point of knowing what i was doing and why,as far as the theory went I was fine when it came to the application it was done with one result in mind IMO(and the tree officers). not wanting to go into too much detail on a public forum on the specifics of the job I'll leave it there. I will say however I would now have no worries hiring the equipment and performing the test and doing the calculations myself (I studied hydrography at uni, mapping satellite trajectories and the like )

 

 

"My friend is contracted in for test pulls on trees, he broke a perfectly good Oak tree once."

 

Well something is not right here. How do you pull apart a perfectly good tree? Surely there were defects not in the tree and that is why the tree was subjected to a pull test. Further the person doing the test should not be applying forces that would break an oak.

 

I can see that there is a good case for using this technique (I would use it in certain circumstances) but like all things they must be applied correctly!

[mrtree]

Absolutely, apply correctly.

 

The tree pulling should only be applied in specific situations and after a "normal" tree risk assessment is done.

 

Tree pulling has two applications:

1) to determine toppling or root plate stability

2) to determine the breaking stength of a single stem.

 

It is not much (or no) use in multi stem trees, trees with forks, determining branch failure likelihood etc.

[Tony Croft aka hamadryad]

Absolutely, apply correctly.

 

The tree pulling should only be applied in specific situations and after a "normal" tree risk assessment is done.

 

Tree pulling has two applications:

1) to determine toppling or root plate stability

2) to determine the breaking stength of a single stem.

 

It is not much (or no) use in multi stem trees, trees with forks, determining branch failure likelihood etc.

 

so lets just clarify exactly HOW the breaking strength is calculated, for me the whole thing appears like a sieve

[Tony Croft aka hamadryad]

I have found this rather succinct description of the method, almost immidietley it strikes me that with the crown analysis crown structure and form is not accounted for, this can and does play a massive role in determining the sail area. A trees profile changes a great deal under wind loads, (I speak from personal experience having stood in the forest during a hurricane!)an organic and dynamic being. SIM SIA seem rather rigid in thier approach and it has very limited use as far as i can see thus far.

 

Wind is rarely a constant, and resonence within the tree is the major player in determining the failure, loads that build within the tree, fibres at tension and torsional twisting can be increasingly loaded at a wind load that is even but gusting. the elasticity of a tree can be tested yes but the direction, and complications of resonence and paterns of loading of the wind cannot be calculated.

 

http://www.treeworks.co.uk/downloads/2%20-%20JK_Static%20Integrated%20031203.pdf

[Tony Croft aka hamadryad]

Tree Pulling - Seminar 1 Review

http://www.treeworks.co.uk/downloads/1%20-%20DL%20tree%20Statics%20Final%20Version%20031203.pdf

TreeQinetic - Static Tree Pulling - Sorbus International Limited

http://www2.tree-consult.org/images/pdf/eng/brudi_trees_and_statics.pdf

http://www.treebuzz.com/forum/images/upload/220048-UFIRiskAssessmentBrochure.pdf

http://www.treeworld.info/attachments/f29/16036d1278192608-how-hollow-pull-test-stability-tests-guide-tree-stability-analysis.pdf

The safety assessment of hollow trees has always fascinated

arborists, and the criteria to be employed have led in Europe to

severe public discussions in the professional scene.

Based on Mattheck & Breloer (1995), many tree-consultants state

that the necessary thickness of the residual wall should not be below

a t/R ratio of 0,3 to prevent shell-buckling, cross-sectional flattening

and hose pipe-kinking.

Wessolly & Erb (1998) on the other hand publish the opposite theory

by which often much lower thickness is calculated and accepted.

Their methods are based on the bending theory of the hollow beam.

A complete study was made on a 17,1m high eucalyptus tree

(Eucalyptus camaldulensis) in Spain. In accordance with the above

mentioned theory, which is also employed by Wessolly, the

necessary trunk diameter and residual wall thickness where

calculated for different tree-heights.

The results are contrasted throughout the present publication with

criteria regarding torsion, shear, stress peaks, cross-sectional

flattening and shell-buckling.

The above and the study of scientific literature suggest that the truth

lies somewhat in the middle instead of in both extremes.

[treemeup]

so lets just clarify exactly HOW the breaking strength is calculated, for me the whole thing appears like a sieve

 

I think this is done in a lab, method:breaking sticks and measuring their bend ratio. think these values are logged and averaged for different species