SIA- the tree pulling test/theory

[Tony Croft aka hamadryad]

I believe that trees being such complex, compartmentalised structures that can contain many internal pockets of slightly modified or even heavily modified wood that its not realistic to presume all trees of a given species or properties will behave in the same ways.

 

I take further issue with the optimisation of a tree in a given location, no two trees are exposed to the same forces or situations, a tree will form a tension and compressive optimised form to those prevailing conditions, to pull test a tree in a direction is only one truth, and can be very misleading.

 

lets take a tree that has lost a major side root on the compression side and is in effect a triangular fram within the ground. If we attach a rope to the peak and pull it will lift and sit verticaly, attach the rope to the middle of a beam on the triangle and pull and it will do something entirely different.

 

So a true pull test would be carried out one each direction, or it is false reading.

[sean freeman]

My very distant understanding is that the 'gold standard' around which it is possible to base the calculations on was (and is) the Stuttgart table of wood strength, you used to be able to view the table in the documents available on the tree consult website, but that website now appears to have been altered...but google (don't you love it!) still finds this one http://www2.tree-consult.org/images/pdf/eng/brudi_trees_and_statics.pdf

 

Mr Tree has very ably stated what the limitations are, and when you consider the common form of urban tree they are limitations that seriously limit its application for most of the tree related concerns we get to see here; those limitations (correctly but frustratingly) prevented the statics test from being applied to the Laman Street Figs in Newcastle NSW.

[mrtree]

You need to speak to the people that developed the method and practicioners in an attempt to even answer your questions. The answers to many of the questions will take hours of explaination in some cases.

 

This is an engineering based method that has been throughly researched (first papers published in the eary 1980's) and based on engineering principals that are used in the design and analysis of buildings etc. Its methods intergrate three important components, the load, the strength properties of the wood and the architecture of the tree.

 

There has been something like 8000+ pull tests done and the word is that only one or two trees have failed after being declared safe (I wonder what the comparable numbers are for VTA and other methods of tree risk assessment). That is not proof of the validity of the method but it does seem to indicate that even if the method is a sieve it does provide an answer that closely mimics the "truth" of the tree.

[mrtree]

There are lots of limitations to this method but in some cases it does provide some very interesting results that helps the consultant, etc., to make more informed choices about the tree. It is information that must be used in conjunction with other information, it does not give an answer.

 

As we all know we can say a tree is safe but if the owner of the tree does not believe our methods, our abilities, or they "know more than us", arboricultural knowledge will contribute very little to final decision about the tree.

[sean]

I helping the Treeworks guys with a pulling test in Regents park in a couple of weeks so will see what info I can glean.....will be climbing and installing the kit etc...

[mrtree]

If you want to glean information one pull test is not the place. Read the papers at Neville Fay's website to try to get an understanding of what is happening. The method is pretty straight forward but the principal behindc. it are engineering based and this somewhat difficult to approach if you are not an engineer et

[Tony Croft aka hamadryad]

Im am more interested in finding out the complex and "difficult" differences between the two methods that caused such a great divide in the community.

 

one of these I believe to be the very core basis of buckle over shear, and if anyone can shed light on this i would be eternally grateful.

 

I am fascinated in these methods and in forwarding the assessment process and need to understand the whole industry wide approach and history to the various ,methods to be fully conversant on all the methods available to me as a practitioner.

 

Division and conflict within our industry is to be resolved at all costs, in order to avopid conflicts one must seek the common ground between the two.

[mrtree]

Hamadryad, you need to speak to the people who developed the VTA and the tree pulling methods, I very much doubt anybody here has the knowledge to discuss the buckle vs. shear and other issue which are something that may require a lifetime of study.

 

If you want to find out what casued such a divide in the community in the past and what is now causing problems within SIA, why new systems are available and why some people seem to spend every moment destroying the idea of SIA you need to become part of the VTA or SIA groups at the highest levels. I can tell you there is lots of conflicts that date back decades and they often have little to do with science.

[Tony Croft aka hamadryad]

Hamadryad, you need to speak to the people who developed the VTA and the tree pulling methods, I very much doubt anybody here has the knowledge to discuss the buckle vs. shear and other issue which are something that may require a lifetime of study.

 

If you want to find out what casued such a divide in the community in the past and what is now causing problems within SIA, why new systems are available and why some people seem to spend every moment destroying the idea of SIA you need to become part of the VTA or SIA groups at the highest levels. I can tell you there is lots of conflicts that date back decades and they often have little to do with science.

 

It was science that started the divide. I am waiting for the historic papers on the development of SIA, I do not wish to rubbish the method at all, but I do want a DEEP understanding of the issues, i.e buckle over shear and this does not require a lifetimes study, not at all.

 

I might say that its not even up for debate, shear is the obvious, and to think otherwise is what fascinates me and why i need to understand, it does make no sense to me.

 

as for the VTA "group" I consider myself well and truly in it (not in the highest regard though! just in THAT camp), Ive been a veracious reader of clauses work for years and achieved practitioner level under Claus in 2008/9.

[mrtree]

I think it is interesting that only a couple people have anything to say on this thread.

 

It is not surprising as this is a very complex method to understand the intricacies of and as such very few people have ever read beyond the summary of what the test is and what it does.