Friday, June 6, 2008

December 13th 2006

Seattle A Kroll luffing tower crane that had just been climbed the day before and was found to be spinning rapidly in the morning due to the jib being caught in the winds. There were a few problems here. Rigging was left on the hook and had swung into the glass on the adjacent building. Virtually every manual says to strip the hook. Second, the placement of the crane was too close to the neighboring building so the crane was not able to be boomed down far enough act as a weather cock. As a result the wind caught the jib, started the crane in motion, and there was nothing to stop it.

In the video and other videos you'll hear people state that it has to spin in the wind. It has to be able to move with the direction of the wind. I don't see a tornado over head and this is not what spinning with the wind means. The tower is being worked excessively hard while the crane is spinning that fast. The crane itself cannot swing that fast so the moment load kps are growing beyond intended loads. The grease in the motors and Rotec are low rpm. So you start spinning at 5 times the rated speed and heat will generate. If a motor or bearing were to seize due to over use like this, that crane would dismount like a gymnast on a pommel horse.

A cure is to let the swing brakes drag a bit to prevent this from happening again. If the crane can vane before 40 mph it's better than letting it tear itself apart. This is just like anyone who's tit is about to be in a ringer... nope, everything is just fine here. this happens all of the time, you've just never seen it. Shenanigans!

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