Friday, October 8, 2010

August 11th, 2009

Nanchong, China I found a second crane Nanchong that collapsed in August of 2009. Link No notes were available on the number of injured involved.
The crane was clearly recently installed and being climbed to it's working height. You can see the climber, the tower hanging from it, and the additional towers on the ground. It's not a common practice to use a small crane to erect a tower crane then climb it later. In the US, most of the cranes are erected to the needed working height and climbing is a less common practice except when the height of the crane will be beyond the maximum free standing height.
Two things stand out to me in this picture. first and foremost, the tower doesn't appear to be plumb. Is that an illusion? I hope. Was the soil not adequate? Was it built out of plumb, I don't know but the appearance is that the mast failed on the side that it's leaning to. That could all be a coincidence.
The other thing that stands out points back to my last post, also about Nanchong and Climbing accident. The hydraulic ram is visible and partially extended. It's on the opposite side of the apparent structural failure. So if the ram is pushing up, the rollers at the bottom of the climber are not tight, and the climber and super structure are allowed to lean too far out of plumb, then you have loading beyond the engineers intention and the point loading (fulcrum) on the side of the tower at the bottom rollers exceeds the design strength and you have a failure just like this one. Add in the potential of the crane being out of plumb to begin with and it's a recipe for failure.


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