t/R = 0.3 | 70% hollow or 30% solid?

[Mick Dempsey]

[Dan Maynard]

34 minutes ago, jfc said:

Sycamore. Was decay by dryad's saddle.

Stem failure, looking at it as an engineer I'd actually say not that likely since there is a reasonable wall thickness and enough support from the inside to stop it buckling.

 

Decay proceeding down into major roots would seem to be the biggest concern to me, then whole thing falls over.

[jfc]

27 minutes ago, Dan Maynard said:

Stem failure, looking at it as an engineer I'd actually say not that likely since there is a reasonable wall thickness and enough support from the inside to stop it buckling.

 

Decay proceeding down into major roots would seem to be the biggest concern to me, then whole thing falls over.

That section was about 3m up the stem. Lower down the decay changed to hollowing, not sure how the roots were. Although gotta go back and grind the stump in a few weeks.

 

[daltontrees]

16 hours ago, Dan Maynard said:

Stem failure, looking at it as an engineer I'd actually say not that likely since there is a reasonable wall thickness and enough support from the inside to stop it buckling.

 

Decay proceeding down into major roots would seem to be the biggest concern to me, then whole thing falls over.

Yes decayed and hollow are different things where stem buckling is a possibility. Decayed material  will prevent it as long as it's not too soft. If tis is Dryads Saddle it hasn't got to the mushy stage yet.

Can't say whether it should have been removed, since the crown is gone and there is no information on Targets. Dacayed roots would definitely be a bigger worry than stem failure.

[dangb93]

17 hours ago, Dan Maynard said:

since there is a reasonable wall thickness

Assuming the wood strength of that reasonable wall thickness is still sufficient   

[jfc]

6 hours ago, daltontrees said:

Yes decayed and hollow are different things where stem buckling is a possibility. Decayed material  will prevent it as long as it's not too soft. If tis is Dryads Saddle it hasn't got to the mushy stage yet.

Can't say whether it should have been removed, since the crown is gone and there is no information on Targets. Dacayed roots would definitely be a bigger worry than stem failure.

The decayed area was mushyish, you could push a thumb into it if pushed really hard.

Loads of targets. Crown had died back a lot in last 2yrs. 

There was a big cavity at the base, no support from downward growing roots from the bole.

It looks to.me to be only 1/6 of the radius unaffected by decay. In a couple of areas it was only 25mm unaffected.

[jfc]

23 hours ago, Mick Dempsey said:

Is that a Horse Chestnut? 
Isn’t species important in these decisions?

I didn't make the decisions on whether the tree was to stay or go. The picus guy made recommendations. 

I'm no expert, but feel that sycamore, beech, horse chestnut have little resistance to decay fungi. Trees with heartwood are more resistant I think. But happy to be corrected.

[Acer ventura]

On 05/12/2023 at 21:18, Paul Cleaver said:

Tree surveyors shoud not use Matthecks equation literally, just a guide 

 

 

 

 

 

Hi Paul

 

Mattheck's t/R = 0.3 is a terrible 'guide', though.

 

t/r = 0.3 is a point on a spectrum of hollowness, that's only considering some of one part of the 'Form' in a tree's Safety Factor (which is what we're trying to figure out).

 

 

t/R = 0.3 would be too much hollowness for a particular species of tree (Material properties). With particular crown dimensions and location (Load). And a particular stem diameter and geometry (Form).

 

Improve the Material properties, and t/R = 0.3 would be fine.

 

Or, lower the height or location (Load), and t/R = 0.3 would be fine.

 

Or, increase the section modulus by widening the diameter, and t/R = 0.3 would be fine.

 

Your critical t/R could be any ratio. It's just one part of the 'Form' in the tree Safety Factor puzzle.
 

Edited December 11, 2023 by Acer ventura

[Acer ventura]

We've carried out a substantial overhaul and update of our t/R ratio guide.

It's called, Why t/R ratios don't work

 

You can download it with additional explanatory commentary here.

https://validtreerisk.help/Why-tR-Ratios-Do-Not-Work

 

 

[dangb93]

Can the T/R ratio even be applied to anything else than a circular stem? What if the stem is irregular in cross section? I think Mattheck says to use the thinnest residual wall thickness, but where do you measure the radius in an irregular stem - the shortest radius, the largest radius, or somewhere between? But then I suppose the term "radius" is only to do with perfect circles, and many trees are not circles. (Don't worry, I am not a blind user of the T/R ratio)....