'Dadio throws a big top'. A reply to unjust criticisms

[defenderjack]

i climb trees and i cut trees , and if for one minute i thought knowing all about mechanical cleavages or what ever else you went on about would help, i would probably be doing another job earning much better money !

[slack ma girdle]

At the risk of going against the flow, i think that pete has put forward a good arguement. He might not be have all the facts right, but i for one struggle with maths and therefore defer to the person with the expertise in the subject.

Pete ignore the heathens above, when they can come up with a better argument............

[Xerxses]

Valid point Bannister!

[MattyF]

It all worked I am peronally happy it did.. Don't think you watched any of the other vids especially the one that went wrong... I'm not up for spiking up a stem 10 - 5 ft putting in a small gob and felling a tree... I may be an idiot for disputing your calculations but there's too Many factors to consider on releasing a stem of 8+ ton of presure when your attached to it and your calculations don't measure those and can't... years of working with timber have tought me that.

[scotspine1]

This is a belated response to the closed thread ‘Dadio throws a big top’ posted 05-09-11. I‘ve considered the posted criticisms of the techniques used in the movie from an engineering perspective, using structural mechanics as a guide. Seems to me that several of the hurried criticisms don’t stand up to much scrutiny at all. Whereas, if one takes the time to absorb the content of the movie and all information the maker clearly provided, the mechanics can be analysed using basic structural mechanics and a basic knowledge of rigging

The geometry of the stem and the cuts (the hinge and the step) are all clearly there at the end of the movie and the text. Looking at the images, I have estimated the position of the hinge and I’ve also estimated the distance between the hinge and the pull line anchor point as maybe 6m (20’) from the fact that the stem above the cut is stated as 40’

I’ve estimated the offset (step cut) will provide a theoretical resistance of about 2kN (cleavage resistance) before the hinge starts to load. That’s the ‘safety valve’ preventing a barber’s chair (that’s my assumption anyway). This was a major issue for some Arbtalkers

The moment of resistance of the hinge wood can be calculated given the information in the movie. Admittedly, some engineering knowledge is a grasp of maths is required here. A basic cantilever calculation can then be applied to find the approximate load required to make the hinge yield. That’s the maximum force that could develop in the pull line because above that, the hinge will fail. Do the calcs as I have and you will find the hinge provides a moment of resistance (to rupture in bending ) of not more than 30kNm. So, with a lever arm of 6 m it will take a force of 5kN to break the hinge. That’s the theoretical max possible force in the pull line and I’ve probably conservatively estimated the moment of the hinge wood (I’ve used 80 N/mm 2 as the modulus of rupture which is probably high). That’s well within the permissible stress for the line. Dadio also gives information about the pull line ‘True Blue’ and clearly knows something of its properties. Its manufacturer states a breaking strength of about 32.3kN (I’ve assumed it was 12mm)

There has been a statement that this line could have been dangerous if it had snapped: well if it were steel then maybe. But it’s not; look at the rope manufacturer’s published data on its elastic properties. There might have been a danger to the cameraman from the block catapulting towards him but is it not possible that the cameraman was out of range?

Dadio discusses the size of the notch and the vectors evolved as the stem is pulled. No calculations needed really; you can see his assumptions were broadly correct: the stem landed where he engineered it to land!

So what have I learned from this exercise?

1. Absorb all of the information available before proceeding to criticise. I know its a hazard of instantaneous communication, but ignorance is still no excuse

2. Just because a technique is unfamiliar does not necessarily make it unsound

3. Conversely, those who may believe that because they have ‘always done it like this’ they are necessarily always correct, should perhaps reflect on the principal at 2 above

4. Having raised my head above the parapet I should now expect to receive incoming fire!

 

Pete,

 

Thanks for the post.

 

I realise you've spent a bit of time and effort on this issue, but with respect your analysis comes across like someone with little or no understanding of the risks and hazards involved in large tree removal. How much experience do you have of working on large trees?

[Tony Croft aka hamadryad]

This is a belated response to the closed thread ‘Dadio throws a big top’ posted 05-09-11. I‘ve considered the posted criticisms of the techniques used in the movie from an engineering perspective, using structural mechanics as a guide. Seems to me that several of the hurried criticisms don’t stand up to much scrutiny at all. Whereas, if one takes the time to absorb the content of the movie and all information the maker clearly provided, the mechanics can be analysed using basic structural mechanics and a basic knowledge of rigging

The geometry of the stem and the cuts (the hinge and the step) are all clearly there at the end of the movie and the text. Looking at the images, I have estimated the position of the hinge and I’ve also estimated the distance between the hinge and the pull line anchor point as maybe 6m (20’) from the fact that the stem above the cut is stated as 40’

I’ve estimated the offset (step cut) will provide a theoretical resistance of about 2kN (cleavage resistance) before the hinge starts to load. That’s the ‘safety valve’ preventing a barber’s chair (that’s my assumption anyway). This was a major issue for some Arbtalkers

The moment of resistance of the hinge wood can be calculated given the information in the movie. Admittedly, some engineering knowledge is a grasp of maths is required here. A basic cantilever calculation can then be applied to find the approximate load required to make the hinge yield. That’s the maximum force that could develop in the pull line because above that, the hinge will fail. Do the calcs as I have and you will find the hinge provides a moment of resistance (to rupture in bending ) of not more than 30kNm. So, with a lever arm of 6 m it will take a force of 5kN to break the hinge. That’s the theoretical max possible force in the pull line and I’ve probably conservatively estimated the moment of the hinge wood (I’ve used 80 N/mm 2 as the modulus of rupture which is probably high). That’s well within the permissible stress for the line. Dadio also gives information about the pull line ‘True Blue’ and clearly knows something of its properties. Its manufacturer states a breaking strength of about 32.3kN (I’ve assumed it was 12mm)

There has been a statement that this line could have been dangerous if it had snapped: well if it were steel then maybe. But it’s not; look at the rope manufacturer’s published data on its elastic properties. There might have been a danger to the cameraman from the block catapulting towards him but is it not possible that the cameraman was out of range?

Dadio discusses the size of the notch and the vectors evolved as the stem is pulled. No calculations needed really; you can see his assumptions were broadly correct: the stem landed where he engineered it to land!

So what have I learned from this exercise?

1. Absorb all of the information available before proceeding to criticise. I know its a hazard of instantaneous communication, but ignorance is still no excuse

2. Just because a technique is unfamiliar does not necessarily make it unsound

3. Conversely, those who may believe that because they have ‘always done it like this’ they are necessarily always correct, should perhaps reflect on the principal at 2 above

4. Having raised my head above the parapet I should now expect to receive incoming fire!

 

 

an extrordinary post! followed by some very ordinary ones!

Edited September 23, 2011 by Tony Croft aka hamadryad

[Mike Hill]

Pete,

 

Thanks for the post.

 

I realise you've spent a bit of time and effort on this issue, but with respect your analysis comes across like someone with little or no understanding of the risks and hazards involved in large tree removal. How much experience do you have of working on large trees?

 

That is a very good question.

 

When working with Timber,Tension is best avoided or managed in a way that reduces the likelyhood of injury.Creating Tension and then being close to where the Energy is releasted is doubly dangerous.

 

The calculations you showed us are depend on there being constants.Constant load on the Rope and Constant intergrity within the Hinge,should either of the above two be compromised then the likely hood of an accident or damage increases exponentially.

[Andy Collins]

 

an extrordinary post! followed by some very ordinary ones!

 

I'll have you know that "cleavage resistance" s far from ordinary

[Neil Frost]

If anyone has any examples of gravity resistant cleavage, please post.

[skyhuck]

All these sums don't change the fact that it would have been quicker and easier to have done the job differently.

 

Plus Daniel did not do the math and IMO got lucky.

 

As for the comment about a snapping ropes not being dangerous, that is simple not true, today I snapped a throw line (about 4mm) while pulling a bull rope up a tree, the end hit me below the eye and was pretty painful, my groundie said the make left looked like I had been punched in the face. I dread to think what damage a 1/2" rope with a breaking strain of 3tonne would do if it snapped and hit you.