Wednesday, December 29, 2010

November 26th, 2007

Xi'an China. A Tower Crane suffered a structural failure injuring one worker. The crane broke from it's base and leaned into the scaffolding next to the building. The stop must have been very soft due to the scaffolding bending which may have been critical in keeping the crane as vertical as it was.

Clearly you can see the base of the crane from the screenshots. It would appear that the base was fabricated, set in place for the concrete pour, and the tower was added later. You can see clearly where the red arrow is (photo below) pointing where the welds broke. It's certainly possible that the welds were simply poor quality and that's why they failed. but let me complicate this in order to help prevent this from happening in the future.

You'll notice that the legs are welded to the lower frame. Since you don't only have to hold the crane down, you have to be concerned about the torsional moments induced. The twisting forces. If you've ran a crane before, you know that it's substantial. The welding should include bevels with multiple passes. I would have added gusseting running at least off of the two sides. This will aid in absorbing that torsional force, but it will help reduce any flex in the structure vertically as well due to compression or tension in the over turning. It also adds more weld and who can complain about more glue? The other thing that I would do if it's feasible, is plan to bury this base in concrete to aid in stabilizing it. This would hold that base as stable as is possible and limit any potential cracking due to those movements over the life of the crane, or length of time on that job site.

I couldn't get the video to play on any other source than on the website. YouTube and blogger both reject it. The video loads horribly but the link is here in case you want to see the story or watch the new coverage of the accident.


No comments: