is a stem stronger bare or with limbs and top?
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richard t
ArboristSite Operative
Never mind This question just made my QI drop a few points.
StrataTree
ArboristSite Operative
Hmmm, judge it you must...may the FORCE be with you!
its complex dynamics but one answer is yes a tree structure is in fact self designed harmonic dampening device Eg is left alone a tree may endure wind or stress better than if pruned to lessen canopy sail or stems. This is due to the sums of whole being better in distributing energy than the parts.
the study is here but a lot to read
http://www.amjbot.org/content/93/10/1522.full.pdf
[video=youtube;id214DotunI]http://www.youtube.com/watch?v=id214DotunI[/video]
watch trees in high wind one part moves the others but as they do the structure adsorbs the movement or moment coverts and spread the energy over the larger area like dampener in you car suspension. If you prune off all the limbs of a canopy tree it just may weaken its ability to absorb energy as it transferred into a single stem or trunk and has no avenue of dispersal.
the study is here but a lot to read
http://www.amjbot.org/content/93/10/1522.full.pdf
[video=youtube;id214DotunI]http://www.youtube.com/watch?v=id214DotunI[/video]
watch trees in high wind one part moves the others but as they do the structure adsorbs the movement or moment coverts and spread the energy over the larger area like dampener in you car suspension. If you prune off all the limbs of a canopy tree it just may weaken its ability to absorb energy as it transferred into a single stem or trunk and has no avenue of dispersal.
in respect to tree work more so than nature. if theres a separation. for example, I am doing an enormous maple. it has a 6' dia trunk with about 4 30" and 4 20" stems. only one grows straight up, the rest are at about a 45 degree angle. the tree is about 90' tall and 90' wide. so I climb out to the end and start removing the tip, and branches. one every time I take a few hundred lbs off it lifts some. once its bare, I can shake it easily. obviously there is no resistance to my movement other than the rigidity of the stem. but, would it now have to be loaded to the point it was when weighted and then go to its failure point or did it lose strength within the wood grain and/or because it has no resistance to the load?
lets say as is it would take rigging a 2000 lb piece that fell 3' to break it in its natural state.
you remove 1000 lbs of top and limbs. would it now withstand a heavier load, same or less?
lets say as is it would take rigging a 2000 lb piece that fell 3' to break it in its natural state.
you remove 1000 lbs of top and limbs. would it now withstand a heavier load, same or less?
If you leave the top and limbs on the stem holding the rigging block, when you apply the load to the block, the stem will have less horizontal movement and there will be less harmonic motion in the stem. The harmonic motion is easily seen if you are on top of a single stem, say about 50' up, where the stem has been stripped and topped. If you wiggle at the top, you can see the stem vibrate down to the ground. Think about holding a piece of rope and letting it hang. If you wiggle your hand, you can see the harmonic vibration flow down the rope. You can see the same thing in the stem. What the top and branches do is dampen that harmonic vibration.
To answer your question, the fibre strength in the stem is going to remain the same whether the top is in it or not. However, if you remove the top and apply the same loading, the harmonic vibration may cause a failure if there is a weakness(hidden cavity) or poor branch connection in that stem.
I'm afraid it's not very clear, but I hope it's understandable.
without the damping of side limbs the motion or moment is exaggerated, in regards to your strength query I'd say no loss of tensile wood strength but a lot more wobble
[video=youtube;YI-yjMSclpg]https://www.youtube.com/watch?v=YI-yjMSclpg[/video]
[video=youtube;YI-yjMSclpg]https://www.youtube.com/watch?v=YI-yjMSclpg[/video]
