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Thread: Crane drop

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    Heck, I'm in New England - we're used to suspended orange colored things dropping at this time of year.

    Why do you think we call it "Fall"?

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    NOT a crane fail . . . more like a rigging fail.

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    Quote Originally Posted by motion guru View Post
    NOT a crane fail . . . more like a rigging fail.
    I agree. That crane was clearly tired of life, and decided to slip free from the surly bonds of slings (and chains), and fly with the angels.

    The crane got what it wanted...

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    Taint a crane,but an excavator.....anyhoo,thats pretty typical of what happens when millenials do anything.....guy watching wanders over to have a look.....like it happens every day ......likely does.

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    And they only had TWO PAYMENTS LEFT !

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    The rigging is flailing around as the dumb ass walks closer to it!

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    its China what the hell...Phil

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    Quote Originally Posted by motion guru View Post
    NOT a crane fail . . . more like a rigging fail.
    ok, now we look to see how it is rigging failure. I see the spreader had slings to doosan to far apart; something catastrophically failed when the doosan hits about 30 degrees and I can not tell what. For those of us that lift stuff all the time it is important to find root cause. for those that lift occasionally it is especially important to understand how to rig.

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    i helped my buddy lift one out of the mud a couple of weeks ago, it had lifting eye on it.


    Sent from my iPad using Tapatalk

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    Got it out!!


    Sent from my iPad using Tapatalk

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    Hard to say, I would definately call it a rigging failure though. The rear straps were too short, and possibly placed wrong. I would have wanted them more vertical. And the whole center of balance felt way too far towards the bucket arm, once it started tipping it was over.

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    "i helped my buddy lift one out of the mud a couple of weeks ago, it had lifting eye on it."

    when rescue crane applied lift---was operator in cab?

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    Headsup!!!

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    Quote Originally Posted by JHOLLAND1 View Post
    "i helped my buddy lift one out of the mud a couple of weeks ago, it had lifting eye on it."

    when rescue crane applied lift---was operator in cab?
    Water got into the computer, fouling things up. It would run on low power mode only.
    The crane was maxed out for the counterweights we had with us. The operator got in the cab and moved the boom up and down to help break the suction. After it broke loose it was no problem.
    I don’t remember the numbers, but it weighed a lot more than the internet said it did, way more than the mud included.

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    I know this sounds unrelated - but same principles apply . . .

    I have designed a number of positioning systems that use multiple cables to accurately position a payload. It could be a 400ft x 100ft barge loaded with rail cars in a slip using coordinated winches, or it could be a gyro-balanced camera hanging by 4 cables from a boom. Their are several rules you want to observe to prevent instability.

    First rule is that you should never have all your cables aligned along vectors that converge at a point in space - this creates a situation where rotation can easily occur about that virtual point . . . and if you have to create a virtual point of rotation - make damn sure it is above the CG or the load can flip.

    Second rule is that you should have the CG of the load as close to centrally located relative to the pick points as possible and preferably well below the pick points.

    Last - the CG should be as low as possible relative to the pick points and as previously mentioned - below any virtual points of rotation (like the hook where all cables from the spreader meet).

    This excavator was picked with the cables attached at the spreader bar at points further apart than the attachment points on the excavator. This creates a virtual point of rotation below the excavator at which point a full rotation of the payload is possible without much change in the tension on any of the cables. The correct way to have done this is to attach the cables on the spreader bar at points dimensionally closer together than the attach points on the excavator - this moves the virtual point of rotation above the spreader bar and the CG of the payload is well below that point of rotation - so risk of instability is eliminated.

    Also the boom and bucket were uncurled - making the CG very near the forward pick points - this was a disaster waiting to happen.

    I wish I could say I learned this all by studying and understanding theory - but when you have a 400 foot long barge going unstable in a slip swinging closer and closer to a rail drawbridge . . . I have applied this lesson over and over again whether rigging heavy equipment or swooping in for a close up of a Superbowl coin toss . . . you can make cable supported payloads rock solid with the right rigging.

    This rigging failure resulting in the loss of the excavator (and hopefully no loss of life) had everything wrong about how it was rigged.

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    Easy to tell what happened. The excavator was rigged below the center of gravity. This is done all the time, but you have to take extra care when rigged like this. When you are rigged below the center of gravity, if it ever starts leaning it will just keep going, because the more it leans, the more weight is transferred to the low side. You can’t stop it once it starts, unless you can let it down.

    What happened here is it started to tilt, once the center of gravity got outside the low side sling, it flipped. After it flipped it put all the weight on one set of slings. This likely overloaded them and they snapped. The the other set of sling got shock loaded, and they also snapped.

    The rigging itself could very well have been properly rated. The way it was rigged was the problem.

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    It appears they used nylon slings to do steel's job.

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    Appears they put fabric slings through the trackframes ,between the rollers ,and hooked to chain sling hooks either side .....front sling can be seen shredded with the fibres loose......As mentioned ,they shoulda taken the bucket off, at least....Too much trouble.

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    Steel or synthetic, I don’t know if it would have mattered. There may have been some abrasion, but the rigging was likely put into an overload situation that was the major cause of the fail. When the excavator rotated, it put the entire load onto 2 slings, which probably weren’t rated for the total load. The first 2 slings failed, then the last 2 were shock loaded also.

    There probably was some abrasion as the excavator rotated, but by that time they had already lost the load.


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