Bananas and Tree-Biomechanics. Frank Rinn

Bananas and Tree-Biomechanics Frank Rinn (pdf-version for download: send email to info@rinntech.com)

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 2 / 43 1. I am not an Arborist! 2. I do not know a lot of tree species, many fungi, how to prune a tree,... (So, please do not ask questions about all these aspects. ) 3. After having worked as a carpenter on our family business, I studied physics and developed resistance drilling (1986) and other methods for tree ring analysis (dendro-climatology), then sonic tomography,... 4. Tree/timber inspection was a side-effect of these scientific studies.

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 3 / 43 Trees are living on earth since Millions of years. Thus, obviously, in the average, they seem to be stable enough! But: Did trees had enough time to adapt to urban settings? (Root cutting, soil compaction, stem damages,...) => Can we trust trees as natural structures in urban settings?

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 4 / 43... probably not every plant...

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 5 / 43... trees are more trustworthy?...

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 6 / 43 Sorry, not always!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 7 / 43 =>?? C H A N G E??! as tree experts we mainly have to look for changes " in structural strength (due to decay, aging,...) " of site conditions (wind load, soil,...)! when we want to assess the tree s condition and to evaluate eventually increased risk. =>! The new ISA Tree Risk Assessment Qualification will help looking for relevant changes of load or structural strength!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 8 / 43 The German situation (since 1990): extreme positions! VTA (t/r>1/3, H/D>50, L/D>40) SIA t/r>1/10! Tree to be felled if visual inspection can not ensure safety (because technical inspection too expensive and dangerous ).! Every (road-side) tree has to be drilled regularly (written proof) (because roots could be decayed).! Drilling kills trees : coring&resistance recording=fungi-autobahn! Only sonic tomography and / or pull-test accepted!! Exclusively this device, this method,, accepted.! 1. drilling => 2. sonic tomography => 3. pulling

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 9 / 43 One of the basic questions to answer by bio-mechanics: How hollow is a tree to be allowed? (and still save)

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 10 / 43 This kind of discussion, going on since 1990, is senseless, because...

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 11 / 43 Would you leave such trees standing?

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 13 / 43 there are many old and even very high trees that are hollow since decades but still standing => The rule t/r>1/3 seems to be not correct somehow, even not for these forest stand trees. They are standing up since decades, although heavily decayed and hollow.

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 14 / 43 Would you have cut this tree down?

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 17 / 43 => The rule t/r > 1/3 is valid for many trees, especially for young forest stand trees, having circular stems and central decay, because of tangential tension stresses dominate the failure modes.

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 18 / 43 Coconut palms mostly have 1/3 of the radius as strong wood. => t/r ~ 1/3 seems to be a natural design for specific structures. Is this valid for urban trees?

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 20 / 43 At stem base, often included bark leads to segmented cross sections

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 22 / 43 Urban trees that have to be inspected technically are mostly 1. old 2. not circular 3. may have included bark 4. decay is mostly not concentric => the 1/3 rule is correct but not valid for these trees! But, relative strength loss of a cross section can be calculated based on the geometrical distribution of intact and decayed parts. And the weakest bending direction can be determined.

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 24 / 43 Why are these old hollow trees still standing (safe)? > because load carrying capacity (W) of a cross-section is proportional to Material Strength * Diameter³ load carrying capacity ~ (Material Strength) * Diameter³ => height / wind load of old trees do not grow but diameter does! => a small increase in D leads to a big increase in W! => D+1% => W+~3%, doubling after 25years!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 25 / 43 In terms of strength loss, location of decay is more important than size!

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 27 / 43 ==>! Structural strength loss (= loss in load carrying capacity) " is not proportional to loss of cross sectional area by defects " may be both - much lower - much higher " than loss of cross sectional area! But, this approach only takes into account bending loads and leads to crazy results if it comes to real thin shell walls:

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 28 / 43 Free online ( SIA ) calculation of required shell wall thickness of trees: major inputs: tree species tree height site (city, flat-land) typical crown shape

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 29 / 43 Due to this SIA-calculation, a shell wall of 2cm (<1inch) would be sufficient for a 20m (~60ft) tree (BHD = 1m ~ 3ft)!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 30 / 43 Where do mature urban fail? Mostly not at 50" height by trunk failure! (happens in forests) Typical distribution in urban settings: ~ 80% ~ 15% ~ 5% crown / limb / branch uprooting stem-breakage

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 31 / 43 => Shell wall thickness is an appropriate measure in forest stands with centrally rotten cylindrical trees but not for the typical mature urban tree! => Stem assessment is more important in terms of indicating what is going on in root and/or crown/limbs/forks! => Relative strength loss depends more on location than on size of decay! => t/r > 1/3 = a rule of thumb in rare cases, not more! => t/r ~ 1/10 = only valid for glass/concrete, not for trees! => the really dangerous zone starts between 1/3 and 1/10 depending on age, decay location, load and stand!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 32 / 43 => Bananas help understanding Tree Biomechanics tree safety strength ~ function of material, shape and size,... load ~ function of weight, size, and (mainly) wind

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 33 / 43! Most trees initially fail by (shear) cracks caused by dynamic / torsional loading.! Urban trees to be inspected are mostly old or very old, not circular, decayed and/or hollow! => Thresholds from young forest trees (t/r>1/3) and engineering (t/r>1/10) both can not be applied.! => No simple rule of thumb for evaluating tree stability!! => Every tree needs an individual approach!! => We have to study mature trees loaded to failure for finding non-destructive measures for tree safety!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 34 / 43 The German Association of Certified Arborists Fachverband geprüfter Baumpfleger started 2009 loading trees to failure after having inspected them with all available equipment.

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 40 / 43 => one of the major results from comparing methods: strength loss can be obtained on different ways!

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2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 42 / 43 => sonic tomography delivers similar values for bending strength loss of stem crosssections as pull-test!

2012 FRANK RINN BANANAS AND TREE-BIOMECHANICS 43 / 43 =>! There is a need for a " basic understanding => banana bio-mechanics! and a " guideline (ISA qualification on tree risk assessment TRAQ) Thank you for your attention! (pdf-version for download: send email to info@rinntech.com)