Saturday, September 11, 2010

August 27th, 2010

Warsaw Poland - A Self Erecting Tower Crane collapsed when it's outrigger beam folded in. The story comes from and no details of any injuries were available.

The basics of Outriggers on Self-Erectors are that the beams are folded in during transport. Obviously you can't drive around with a 4.5 meter x 4.5 meter square. You might catch a few cars and power lines if you do. The beams are folded out and pinned in place as a part of the crane erection process. I've never noted a pin on a self erector "walking up" during operation, but let me lay out a potential cause. The pins are meant to be kept in place with a keeper. It's not as if the pressure of the pin being driven in or gravity is guaranteed to to hold it in place. The action of the crane swinging will cause small movements in this joint. With at least two layer of steel working back and forth, the rolling of the pin in the hole can cause the pin to move upwards. Normally I see this in Tie-In pins on larger tower cranes. The strut to collar pins often try to walk up and I've even seen them attempting to shear off the keeper. So if the pin is not keepered in place properly, this accident could happen with in a few days at the fastest or over a much longer period. Pin "walk", as I call it, is common and should be watched for. Double check your keepers when you assemble cranes!