Close Call: Rigging Point Failure

[breffni]

yeah no doubt about it !as the ground crew where out the way and it broke out over the dz as I hoped if it did .. still surprised me it lasted as long as it did ! That's being under pressure though , this was the second tree of the day.. I was told the first only needed a branch off to get it to commit with the winch ..more like a good third ! Not a day I will forget any way [ATTACH]220828[/ATTACH]

Showing off your fancy bar! Big shot!

 

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[TIMON]

Timon, hit the 3 dots top right of the screen then select 'Web View'.

Vid then plays on YouTube.

 

 

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Thanks Mark! [emoji106][emoji106]

 

 

Timon.

[Loler UK]

wow, it was less the angles creating double loading (looks like 1.4) but the MOMENT you created (lever) due to the resulting direction of force on the stem that failed. Timber is much stronger in compression, 2nd to that 100kg on a 1m lever creates 980.665Nm of torque (lets just say 100Nm of torque) that same 100kg log/ force is on a 7m lever, that's 7x the moment (torque, lever whatever you choose to call it)

 

the angle of a redirect does effect the anchor force but in trees our primary consideration should be the resultant DIRECTION of force. We did a demo a few years ago where we had a modular tree made of broom handles slotted into angled steel tubes and showed how some typical arb redirect placements in fact weakened an anchor point (often bending it in the opposite direction to that it would have been but increasing the "lever effect" or moment. see page 22 of the VTO lit posted above.

 

had your point on the failed section been 5 or so meters lower BOTH anchors would have been stronger despite the theoretical increase if you only consider the deflection angle

Edited May 27, 2017 by Loler UK
typo

[stihlmadasever]

Hi mugs , I think another reason it failed and bear in mind your main rigging point didn't is because you had the second pulley in so effectively doubling the load on that anchor point , I did some thing similar and caught it on film my reasoning for doing it was I just needed to clear one side of the tree to fell it and there was no decent rigging point high enough on that side of the tree so I set up a double kind of rigging point on smaller stuff with the idea it would share the load and would be high enough to get the back top out with the intention of moving it down to a more suitable diameter for the timber which stupidly I didn't as I had another tree to get down and it was Saturday so it was a rushed job...like you I'm assuming at the time with the idea in my head it would share the load but I think what it actually does it double it like with an SRT base anchor and it ripped the lot out .. tbh I was kind of expecting it hence the one handed saw use so I could grab my hitch quick and bail out !

I've been too embarrassed to post in the forum before this mess but like you said if others can learn by it ..

 

Thanks for sharing that matty and i get what your saying,although i think in a multi anchor riggin scenario the weight cannot be equally shared as the first anchor will always be subjected to a higher impact force than the second.

Ive had instances where ive pushed the limits of my equipment and by luck or whatever ive gotten away with it.

Its difficult to give any difinitive answers where riggin is involved as its usually specific to that situation ie the forces involved,the type of tree being cut and a whole host of variables.

Experience and a bit of luck will save most of us from what happened to you that day.

Squeaky bum mate

[Mark J]

Have a squish at this re: angles of dangles. https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://vtio.org.au/wp-content/uploads/2010/07/Working-the-Angles-i.pdf&ved=0ahUKEwjGxrXyrpDUAhXDIpoKHbT6BfQQFgiGATAX&usg=AFQjCNFFw4ffYIVLTLYhzIOcHk3i4YFOJQ&sig2=ext3svTPY0EQqU1IQHpIdg

 

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[MattyF]

Thanks for sharing that matty and i get what your saying,although i think in a multi anchor riggin scenario the weight cannot be equally shared as the first anchor will always be subjected to a higher impact force than the second.

 

 

That's what you would think right ?

The link that was put earlier in the thread I've stole some photos from and the link explains better but the stem on the right going to the bollard is taking most of the force, look how it stands upright in the last picture whilst the limb with the section being lowered has barely moved. So it not sharing the force maybe the weight but it looks like it doubles the load on the anchor ?

Edited May 27, 2017 by MattyF

[MattyF]

wow, it was less the angles creating double loading (looks like 1.4) but the MOMENT you created (lever) due to the resulting direction of force on the stem that failed. Timber is much stronger in compression, 2nd to that 100kg on a 1m lever creates 980.665Nm of torque (lets just say 100Nm of torque) that same 100kg log/ force is on a 7m lever, that's 7x the moment (torque, lever whatever you choose to call it)

 

the angle of a redirect does effect the anchor force but in trees our primary consideration should be the resultant DIRECTION of force. We did a demo a few years ago where we had a modular tree made of broom handles slotted into angled steel tubes and showed how some typical arb redirect placements in fact weakened an anchor point (often bending it in the opposite direction to that it would have been but increasing the "lever effect" or moment. see page 22 of the VTO lit posted above.

 

had your point on the failed section been 5 or so meters lower BOTH anchors would have been stronger despite the theoretical increase if you only consider the deflection angle

 

Sounds an interesting course are there any more soon?

[MattyF]

Just seen a load more pics and vids on instagram of rigging ring and pulley action ... it clearly shows two pulleys together with the pulley that goes to the bollard moving massively towards the lowering pulley , this looks like it's it's created a two to 1 advantage on the main weight bearing point and the more I think about it looks increasingly dangerous and a wonder more folk are not getting seriously hurt considering the current tree rigging trends..

[stihlmadasever]

Just seen a load more pics and vids on instagram of rigging ring and pulley action ... it clearly shows two pulleys together with the pulley that goes to the bollard moving massively towards the lowering pulley , this looks like it's it's created a two to 1 advantage on the main weight bearing point and the more I think about it looks increasingly dangerous and a wonder more folk are not getting seriously hurt considering the current tree rigging trends..

 

Any chance of a wee link to a relevant vid matty.

Very interested to see those

[Marc]

Just seen a load more pics and vids on instagram of rigging ring and pulley action ... it clearly shows two pulleys together with the pulley that goes to the bollard moving massively towards the lowering pulley , this looks like it's it's created a two to 1 advantage on the main weight bearing point and the more I think about it looks increasingly dangerous and a wonder more folk are not getting seriously hurt considering the current tree rigging trends..

 

I would have to agree, the most recent failure I'd seen was similar to both the video you posted and and the thread video, the rigging started well but as the angles increased so did the lever effect until failure. Nothing serious happened the climber was experienced and had good work position still it was avoidable another large contributing factor to that incident was the ropeman not allowing any run.

 

One of the best riggers I have worked with is also one of the most basic this has shaped the way I approach rigging as adding complexity can introduce in expected forces unless you have a very good understanding of all that is going on.

 

Mike (loleruk) is a very smart guy and I respect his approach and understanding of the dynamics involved, sometimes though we just need a simple language to understand how to achieve safe rigging, i have been lucky to work with some talented individuals who cannot articulate the force involved yet instinctively know how to rig safely.