Thursday, April 23, 2009

April 23rd, 2009

Admore Park, Singapore Potain Luffing tower crane has suffered a structural failure at 30 stories. The accident happened at 11:20 pm due to high winds. Luffers are partifularlly suceptable to failures in the winds. Depending on the length of boom, the boom angle needed to allow for proper weather vaning at night is critical. If the winds start and hit the boom dead on and surge it would be possible to blow it over backwards. If the swing braes were not opened or dragging too hard then the same thing could happen, the boom gets blown over backwards. About eight years ago there was a story locally of high winds coming up during a dismantle of a old Pecco 280. The counterjibs were solid diamond plate 6 plus feet wide sitting in I beams. To dismantle the counterjib you hoist up the counterjib to maybe 15 degrees from the horizontal. Winds started coming in hard and fast and hitting 70 mph while they were elevated. The counterjib started lifting off of the mobile cranes rigging and changing from loose to tight to loose. The mobile crane was now ending up over capacity at times and so the decision was made to put the jib back together and in a horizontal condition rather than taking the chance to collapse the mobile crane too. The point, winds can be fierce and they must be respected. Wind loads grow exponentially on structures so mind the boom angles and if you are on a luffer with the brakes dragging, remember this accident they go through the blog. It's all too common.  

No comments: