Tuesday, December 14, 2010

December 9th, 2009

Liaoning, China In the process of being climbed, a tower crane counter jib lost support at the top pendant connection. It immediately fell crashing into the climber killing at least one and injuring two others. The dead man and the two other workers had to be rescued by the fire department. The accident is similar to another accident that I reported on just last week. Notice the pendants hanging straight down on next to the red arrows and the tower on the jib still on the where the yellow arrow is.

It's important to note the accidents on the counter jibs because you don't generally see them failing as often as the jib of the crane. I don't think of them taking the same level of stress, but clearly the can fail just the same. On this particular one, I'm not sure if it's a weld failure at the Tower Top of if it was a pin failure as if possibly it didn't have the keeper, or a proper keeper retaining the pin. I think of some of the older 390 and 550 Liebherrs that had pendants that had to be removed in order to be shipped on a truck. They had a single pin that was a pain to install due to lining up two pendants at once, but worse was trying to drive it out later. It could tie up an assist crane for 20 minutes on the seemingly simplest of project that just never seemed to work out well.

Look over the structure of the tower top, the keeper installation, the pin itself, and pendants including the welds. The vibrations sometimes induced by a bouncing climber on a pin that doesn't have the right keeper in place could cause that pin to walk all of the way out just like this accident's potential cause.

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