Rigging Failure - Hong Kong 16

[azcats]

Dropped a large excavator down a shaft.

Couple videos towards the end.

[URL unfurl="true"]https://vertikal.net/en/news/story/36364/crane-drops-load[/url]

 

[waross]

The first mistake was using a fore and aft spreader.
The second mistake was inappropriate sling angles from the lift points to the spreader.
The third mistake was not securely fastening the sliding anchor points on the spreader to which the lower slings were connected.
Watch the spreader carefully.
You see it tip because of inappropriate angles.
The problem was not with anything to do with the excavator.
The problem was bad rigging on several counts.
I have done a little rigging.
I have watched the video closely several times.
By contrast.
Courtesy IRstuff

Here, the center of gravity is between the slings. If the CG is off center, the load will tip slightly until the CG is directly beneath the center of lift (at the spreader).
The slings and the spacing between them form a triangle that encloses the CG.
If the CG is off center the load may not be level but it will be stable.

In contrast, the failed rigging, when it started to shift, moved the CG closer to the front slings, putting more weight on them.
This put more weight on the front of the spreader and tipped it more.
The CG was already close to the front slings.
As more weight came on the front slings, they exerted more force on the spreader, tipping it more.
That raised the rear further.
As the spreader continued to tip, the rear rose higher and higher, putting the CG closer and closer to the front slings.
Then the CG passed the front slings and the action speeded up dramatically.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Denial]

I think you have nailed it, DVD.

 

[bimr]

At the 21 second mark, the left front rigging breaks with a noise that alerts the workers to back away. Then the left front rigging continues to stretch allowing the machine to pivot.

 

[dik]

Thanks DVD... didn't know that about rigging...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[Alistair_Heaton]

I suspect the spreader was set too wide so the lift points were out side the area of the excavator. This will lead to the straps not griping the sides of the machine via friction and the whole lot having the stability of a hammock.

 

[bimr]

Diagrams that illustrate waross's comments:

 

[waross]

There was more here than is shown in the rigging diagrams.
The diagrams show simple spreaders. The top slings are connected directly above the lower slings.
In this lift, the spreader was oversized.
The top slings connected to the ends of the spreader while the lifting slings were attached inboard of the ends.
The lower slings were not vertical but were spread outwards.
This is not to contradict the rigging comments above.
This is to suggest that the way that this was rigged made a bad situation worse.
Help me out here: It looks as if one of the attachments to the spreader slides towards the end of the spreader and stops abruptly just as things start breaking.
Does anyone else see this or am I mistaken?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

The front slings were vertical it appeared to me and the rear at an angle away from the unit.

I suspect the spreader was for lifting concrete buckets/skips and had the ability that you could drop one side to pour.

 

[bimr]

The first rigging diagram is actually from the manufacturer of the excavator. As you pointed out, the key mistake made that led to the failure was using the fore and aft spreader.

 

[LionelHutz]

I see nothing that would indicate the attachment points on the spread could move or did more. I also see nothing indicating a sling on the front corner broke before it started to roll over. The spreader doesn't look like it would be a "dumping" spreader either.

The slings were passing through the tracks just above the bottom track, between the roller wheels just like the diagram bimr posted says to do. But, the spreader was wrong. As the excavator rolls forwards, the rear sling gets pulled backwards enough it slips/jumps between the back roller wheel and the track and stops against the rear wheel (drive wheel?). The front sling also started to pull backwards against the roller wheel to the rear of where it was positioned. The slings did hold that weight after shifting for a second or two but they likely got up against an edge and either got cut or tore from the load being spread uneven across their surfaces.

 

[waross]

Thanks Lionel. I hadn't noticed the slings moving on the machine.
I did notice the small dust cloud around the bottom of the rear of the machine, probably from the sling shifting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LittleInch]

It just wasn't rigged level from the moment we saw it.

So we don't know if the arm started moving or how it was when it was lifted off the ground.

Right from the start the arm looks like it is too far and the bucket too far from the excavator.

once it starts to move the process is nearly inevitable.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TiCl4]

Did anyone notice the guy in the green shirt in the video in the OP link at 0:32-0:36? He stands casually by while torn rigging whips by and appears to slingshot back with an ENTIRE cinder-block at high speed. It missed him by perhaps 15-20 feet.

 

[SuperSalad]

Did anyone notice the guy in the green shirt in the video in the OP link at 0:32-0:36? He stands casually by while torn rigging whips by and appears to slingshot back with an ENTIRE cinder-block at high speed. It missed him by perhaps 15-20 feet.

That's the person I was referencing in my 16 Oct 20 17:13 post. That person is either oblivious, fearless, or much more perceptive than I could've been in that situation to gauge where it would be safe to stand.

Andrew H.

http://www.MotoTribology.com

 

[Sparweb]

Yes, many of us noticed and commented on him.

It's his job: He's the cameraman.
He knows this is going to happen, and his job is to be ready for the accident:
Record it all with his phone, and share it with his friends.
You just gotta have nerves of steel to do a job like that seriously.

http://www.sparweb.ca