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Fibre buckling or constriction - Opinions Please


Gary Prentice
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All quite confusing...

 

Mattheck & Breloer in "the Body Language of Trees" (p103) plot the strength loss relative to t/R ratio according to some mysterious and undisclosed formula whch they claim is based on a hollow flexible beam. No mention of shell buckling. If you have a formula for it please put me out of my misery.

 

The curve begins to look like what if you plot Wagener as remaining strength on the basis of d/D = 1 - t/R which I think is correct (proof available if you really want it, it stretches to 3 post-it notes, can you tell my stationery is running low?), but the celebrated sudden steepness of the curve cited by M&B around t/R 0.35 simply isn't there in the Wagener cubed function. Another hour of my life wasted this morning.

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I'm not sure which formulas I actually have, not that I'd physically be able to calculate them anyway. I'll post some stuff up when I get home.

 

I really need to reread what I've already written to refresh my memory, but the shell buckling part is around the same page or section you mention.

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Yes. oh yes.

Writing an assignment currently on strength loss formulas, a critical analysis. I've looked at Wagener, Smiley and Friedrich, Bartrams revised and Wessolly's SIM/SIA.

Wagener and the others use bending theory compared to Matthecks shell/plate buckling/kinking and shearing hypothesis. I was reading a NASA article at the weekend about shell buckling - for some unremembered reason, which was quite interesting, about building the lunar module. :confused1:

"It does seem hard to get any decent stuff about solid stems. There's plenty to be had about homogeneous rods, but I can't apply it to trees because they are very very definitely not homogeneous or isotropic."

 

And therein lies the rub. As Karl Niklas put it recently, this science is so fraught with generalisations, assumptions, and simplifications that any conclusions from it are extremely limited. "...we must always challenge what we are told." ;) And yet we sally forth into that yawning chasm. Why?

 

The tree we see is vertical.

Specified works can make it more likely to stay vertical.

That's about all this arborist can defendably communicate.

But it's enough for most assignments. :001_smile:

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The tree we see is vertical.

Specified works can make it more likely to stay vertical.

That's about all this arborist can defendably communicate.

But it's enough for most assignments. :001_smile:

 

You obviously haven't met my tutor:lol:

 

Sometimes I start to think we may as well consult the tarot cards as to make an accurate assessment.

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Jules, the buckling formulae is page 39, The body Language of Trees. But the function

σ - f(t/R) for the specific loading and tube geometry has still to be specified

 

FAILURE MODES FOR TREES AND RELATED CRITERIA C. Mattheck, K. Bethge, R. Kappel, P. Mueller, I. Tesari International Conference ‘Wind Effects on Trees’ September 16-18, 2003, University of Karlsruhe, Germany Provide some more mechanical formulas too

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Yes. oh yes.

Writing an assignment currently on strength loss formulas, a critical analysis. I've looked at Wagener, Smiley and Friedrich, Bartrams revised and Wessolly's SIM/SIA.

Wagener and the others use bending theory compared to Matthecks shell/plate buckling/kinking and shearing hypothesis. I was reading a NASA article at the weekend about shell buckling - for some unremembered reason, which was quite interesting, about building the lunar module. :confused1:

"It does seem hard to get any decent stuff about solid stems. There's plenty to be had about homogeneous rods, but I can't apply it to trees because they are very very definitely not homogeneous or isotropic."

 

And therein lies the rub. As Karl Niklas put it recently, biomechanical science is so fraught with generalisations, assumptions, and simplifications that any conclusions from it are extremely limited. And yet we sally forth into that yawning chasm. Why?

 

The tree we see is vertical.

Specified works can make it more likely to stay vertical.

That's about all this arborist can defendably communicate.

But it's enough for most assignments. :001_smile:

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I'm getting a sense of deja vu, Guy.

 

Going on with my assignment, the minuses are, so far, far outweighing the positive attributes of t/R. The benefits of simple maths simply don't balance against everything else.Maybe we've all become conditioned to oversimplify such a complex conglomerate of factors.

 

P.S When did K Niklas say that?

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"I'm getting a sense of deja vu, Guy.

Sorry bout that. :blushing:

 

"Going on with my assignment, the minuses are, so far, far outweighing the positive attributes of t/R. The benefits of simple maths simply don't balance against everything else.Maybe we've all become conditioned to oversimplify such a complex conglomerate of factors.

 

Eggs Ackley. Our 'soft' science suffers from 'data envy'. Researchers want to seem more credible, so instead of observing trees more closely over time, they borrow formulas from 'hard' sciences, like engineering, physics, math...

 

"P.S When did K Niklas say that?"

 

Last August at ISA Intl, and again last month at the EuroArbConf in Italy.

 

I'm sorry if your tutor requires that you swallow all this simplified pseudoscience, then spit the appropriate quantity and quality back out. I agree; the state of the biomechanical arts is rather sorry. :thumbdown: I tend to agree with Tony and Albert E. on this.

Edited by treeseer
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