The difference between logging and Suburban Tree Work

[Daniel]

On a tapered hinge resisting side lean - if you made the whole hinge 30% thicker than standard 10%dia thickness then the hinge would be initially 30% stronger (1st power of thickness). If you then cut it to taper 13%dia
(10% + 30% of 10%dia) down to standard you get less than 30% strength increase, without running the math on the geometry I'd estimate +20% strength increase.

e.g. numbers 10% thick hinge on 24" dbh = 2.4" thick, +30% = 3.12" thick

Step1 moments of inertia - simple
Step 2 - calculate normal forces, moments and shear forces - bit harder
Step 3 - calculate and combine stresses into max localized values i.e. compare to yield strength - hard
Step1to3 - do this parametrically with dbh, log length density weight lean angle to learn something e.g. factor of safety
this is all independent of the topic of hinge failure mechanism except as applies to yield strength


So far an interesting side note is that shear stress is max midway as opposed the moment generated normal stress which is max at the edges. Shear is quadratic distribution not linear too.

do you have any science at all to support the idea that a making the hinge 30% thincker would only give it 30% additional strength? data.. measurements from fracturing tree hinges????

and that;s not what I AM talking about.. a fat tapered hinge would leave 20-30% hinge thickness on the tension side.. that's 2-3X thickness where it counts...

 

[evo]

Playing devils advocate here. I could see Bart’s math working for a square 4x4. But the surface area of a 30% thick hinge has to be much greater than 30%. This is an assumption that each sqaure inch of hinge is equal. On a circle there would be more units squared per % of hinge thickness up to the equator of the circle.

Yet this was discussed long ago that green sapwood has more strength in bending than heartwood. So the effects of the thicker hinge would be reduced as the standard face depth/hinge/back cut area has a very different proportion.

This is partly how tapered hinges work, they add more tension against the natural lean to get the tree to swing. The % of the relationship of thickness varies wildly with other variables.
Some of these are
crown balance vs trunk weight
Added forces such as taglines
Head lean along with side lean
Prevailing wind direction (internal tension
wood/compression wood)
Live/dead/decay/declining
And probably the most important SPECIES and TIME OF YEAR

 

[evo]

Also I think a more interesting study would be: in order to initiate movement what amount of heart wood have to be overcome as doesn’t have the same elastic qualities? Ditto with sapwood.
In my experience cutting stove pipe Doug firs with a lean, is it takes much less cutting before movement is initiated. Frequently the challenge is to cut enough wood fast enough to get it in the lay. Yet that sapwood is much stronger due to reaction wood.

 

[Matias]

Playing devils advocate here. I could see Bart’s math working for a square 4x4. But the surface area of a 30% thick hinge has to be much greater than 30%. This is an assumption that each sqaure inch of hinge is equal. On a circle there would be more units squared per % of hinge thickness up to the equator of the circle.

Yet this was discussed long ago that green sapwood has more strength in bending than heartwood. So the effects of the thicker hinge would be reduced as the standard face depth/hinge/back cut area has a very different proportion.

This is partly how tapered hinges work, they add more tension against the natural lean to get the tree to swing. The % of the relationship of thickness varies wildly with other variables.
Some of these are
crown balance vs trunk weight
Added forces such as taglines
Head lean along with side lean
Prevailing wind direction (internal tension
wood/compression wood)
Live/dead/decay/declining
And probably the most important SPECIES and TIME OF YEAR

I have not gotten deep into that last subject, but have heard a little. I would love to hear any thoughts you'd care to share on the subject. I assume that a dried out tree in late summer is gonna behave differently than the same tree plump and hydrated after a good storm season?

 

[evo]

I have not gotten deep into that last subject, but have heard a little. I would love to hear any thoughts you'd care to share on the subject. I assume that a dried out tree in late summer is gonna behave differently than the same tree plump and hydrated after a good storm season?

I’m unsure if you get to pick up on the differences we have observed up here. Doug fir limbs are a great example, but we have noticed it amongst many other species, ranging from normal to abnormal.
Red alder is one that has a huge seasonal difference mid winter (frozen) and mid summer they tend to hinge poorly and are more prone to barber chair.
Doug’s will pop limbs easily and more unpredictably during droughts. Other times of year they will be more stringy. Both can be used to the advantage of the climber depending on the situation

If I recall Norm Hall spoke a lot about this and had some rad diagrams. But this was part of the old notch depth arguments..

 

[Daniel]

And probably the most important .... TIME OF YEAR

not so much around here until you get well below freezing, which I have very little experience with because I try not to work when it's that cold...

Yet this was discussed long ago that green sapwood has more strength in bending than heartwood.

I disagree with that as a generalization though it is likely true, in some species, though the effect is minimal and dead vs live is another factor. I would like to see some science where the wood fibers are tested. I have heard the wood workers at th tree house insist that they can sapwood bends more eaily or is less brittle or something, but that may not translate to greater holding ability in a hinge. I just don't believe it makes that much of a difference and is universally true.

I AM quite sure that the sapwood has offers more strength against side lean because of the placement of the hinge fibers. The outer most fibers have the most leverage to fight the lean. It's their placement trhat matters, not the difference in qualities of the fibers themsleves.

Does anyone have an idea of how to test wood fibers for hinge stregth in a measureable way trhat could be used as data?

Yet that sapwood is much stronger due to reaction wood.

definitely makes a difference as does height of the hinge fibers on the trunk. I try to use raction wood to make the hinge stronger when possible.

You can also get a wider hinge by going into the trunk flare, which one might think is a good thing, but the squirelly grain in wood fibers in some trunk flares offer little holding ability, so on anything tricky I take the hinge up above the flare.

 

[southsoundtree]

I find flare wood to be very split resistant. I can't say how it bends or shears.

 

[evo]

not so much around here until you get well below freezing, which I have very little experience with because I try not to work when it's that cold...

I disagree with that as a generalization though it is likely true, in some species, though the effect is minimal and dead vs live is another factor. I would like to see some science where the wood fibers are tested. I have heard the wood workers at th tree house insist that they can sapwood bends more eaily or is less brittle or something, but that may not translate to greater holding ability in a hinge. I just don't believe it makes that much of a difference and is universally true.

I AM quite sure that the sapwood has offers more strength against side lean because of the placement of the hinge fibers. The outer most fibers have the most leverage to fight the lean. It's their placement trhat matters, not the difference in qualities of the fibers themsleves.

Does anyone have an idea of how to test wood fibers for hinge stregth in a measureable way trhat could be used as data?


definitely makes a difference as does height of the hinge fibers on the trunk. I try to use raction wood to make the hinge stronger when possible.

You can also get a wider hinge by going into the trunk flare, which one might think is a good thing, but the squirelly grain in wood fibers in some trunk flares offer little holding ability, so on anything tricky I take the hinge up above the flare.

The nature of the beast has the sapwood at the furthest point from the side lean, thus on a tapered hinge this is the zone of the widest point. Or in your words the strongest part of the hinge, and that doesn’t necessarily have to do with wood fiber but location.

Surely timing of year plays a part which may be more noticeable with leaf drop. As leaves alone can make a huge weight difference. Does this make the wood any different? Probably not by itself.
On a naturally leaning tree, and more so with an angiosperm, tension wood IS reaction wood. A phototropic tree behaves differently than a partly uprooted leaning tree.

Check out ‘Anatomy of seed plants, by Esau’ one eye opening thing is all the cell walls and how they are arranged within the cell. Remember trees are essentially fractals and it’s interesting to think about the micro cell structure on a macro level.

 

[evo]

I find flare wood to be very split resistant. I can't say how it bends or shears.

Exactly, the reaction wood at the zone of radical taper.
Sure it is converted to heartwood as normal, yet when there is fiber pull to the roots, it’s easy to see the stringy nature of sapwood vs heartwood.

This brings up another point of defining strength. In this case aren’t we talking about shear vs other forces? Or would mode of failure be more accurate since we are manipulating the wood to initiate a controlled failure, overcoming ‘strength’ in a predictable mode of controlled failure.

 

[davidwyby]

Sapwood - any absorbent material with more water in it is more flexible than with less. Whether stronger or not, I don't know/depends. With too much water, material becomes weak and mushy...especially if "dead". Sapwood will hinge longer but whether or not it will hold tension against side lean...thinking about some conifers you see felled with sizwheels, etc., sometimes the sap wood holds all the way down into the roots - hardwoods not so much. @evo jinx!

Kind of restating what I said about momentum, I will theorize that a large part of the reason that a thick hinge and heavy pull works to overcome side lean is not so much that the thick hinge holds longer or better. Dead wood does not flex or hold far at all into the tree's arc of fall. It's because everything has to be tensioned and preloaded so hard to overcome the hinge that when it lets go, a lot of acceleration, momentum, kinetic energy is instantly achieved and depending on how much of that there is vs. how much the side weight is, the momentum carries the tree to the lay before gravity can overcome it.

 

[davidwyby]

For this type of discussion, I think one needs to specify at least generalities, species, and live or dead. IIRC, Daniel made an example of a dead hardwood. That ain't gonna hinge. It's gonna snap and fly, it's fate is dependent upon external factors - the lean and the rope.

 

[Daniel]

I will theorize that a large part of the reason that a thick hinge and heavy pull works to overcome side lean is not so much that the thick hinge holds longer or better. It's because everything has to be tensioned and preloaded so hard to overcome the hinge that when it lets go, a lot of acceleration, momentum, kinetic energy is instantly achieved

It's not a theory.. it's just common sense.

And exactly what I said.... but there's more to it than that.. we've all seen how fast the rope goes slack when the tree starts to fall... you don't get much time after the start of the fall with any pull line, no matter how heavily loaded. The pull is only good momentarily.. the hinge has to take over fairly soon... and fatter hinges take over better than thin hinges...

The heavily loaded pull line works together with the fat hinge. I repeatedly said this. To see the effect, you need a lot of pull on the line.. though a heavy front lean can also work. And I've seen fat hinges alone on front leaners work so well that it's clear that the holding ability of the fat hinge is NOT just because the pull line has more pre-loading. I know this stuff because I've seen it in action. Nothing is goign to change my mind.. there's nothing you can say or show on paper with some fancy math that's going to over-ride that personal experience.

Dead wood does not flex or hold far at all into the tree's arc of fall.

I do not believe that is universally true. Definitely in some species, but not all. It's probably not just dead that counts.. it's dead and decayed that really makes the kind of difference you're talking about. As even in the poor hinging wood I have seen suprisingly strong holding wood when the hinge is cut fat and given room to flex. The size of the fiber pull is revealing and shows which hinges had a lot of holding strength and which didn't.... and you can hear a holding hinge squeak and moan on video, which when played in slow motion shows clearly how long it held...

 

[Daniel]

I find flare wood to be very split resistant. I can't say how it bends or shears.

Anyone that splits much firewood can see how much harder the trunk flare is to split than the straight grain above the flare. I used to think that quality would offer greater holding ability for the hinge in the flare, but found out a long time ago that it doesn't. Or at least it isn't reliable enough to be worth taking a chance on. I thought that was common knowledge.... if it's not, it should be... that squirelly grain is hard to split, but doesn't make good hinge wood!

 

[Daniel]

Bingo! That's why I did it, and it did what I wanted, but that's not the little pecker. I was hoping Daniel would find it.

The only tree i remember cutting in the woods for a long time is in this video...

PS... i did look at another job in the woods today. . I might use that snipe trick after all