Friday, July 9, 2010

April 26th, 2002

Dusseldorf Germany I'm unsure about the location. The article notes the street name, but never mentions the city. A tower crane on a cross base fell over. fortunately the accident happened during lunch and so no one on the ground was injured. Additionally the operator was only in some mental shock. He did suffer some minor scrapes and bruising. The crane fell towards the up hill side with the counter jib striking the building first which slowed the progress of the fall. This is also part of what saved the life of Warren Yeakey, the tower crane operator in Bellevue Washington USA.

Looking at the overhead picture, it's not clear as to why the cross base failed. Did it have a structural failure? Did the ground give way? The ballast is present and the crane was not working at the time of failure so I'll assume that it wasn't a lack of ballast. One thing that I have experienced on a cross base is the ballast attempting to "walk" on the beams. If the ballast is not secured in place somehow, minor flexing in the horizontal beams can move the weights. you would think that it would be impossible, but it happens. Some of the older cranes don't have methods to lock the weights in place, and these are the ones that we really need to be aware of. Most late model cranes have recesses to prevent this walking of weights. If you had a crane that didn't have this, I'd want to mark the weights on the beams and strap them in place just for that warm and fuzzy feeling and as a best practice.

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