Friday, October 8, 2010

August 31st, 2010

Changchun City, China A tower crane collapsed killing 4 and injuring 1. Link No details are really given and the pictures don't share enough to see the exact cause, but one picture is worth 1000 words.

The tip of the crane in the accident shows that the Load Line is improperly terminated. Normally you would see the wedge and socket running to a swiveled connection that would allow the rope to spin out and prevent the block from ever twisting up and allowing the rope to work as a non-rotating rope. These applications vary, but look at the termination closely. It appears that the rope is simply ran around the tip, turned into an eye, then three wire rope clips have been added. Even the tip of this rope appears to not be secured from fraying. The strength of the rope is compromised to an assumed 75% of capacity with the clamping method since it includes the live end. The bending of a rotation resistant rope around a boxed tube puts it well outside of the D/d ratio allowed further weakening the rope. The prevention of the rotating of the rope will only lead to the twisting of the block and potentially core failure. This may well be the dumbest, or at least equal to the dumbest, thing that I've seen an erector ever do. I can only dream what the actual cause of the failure is. Homemade mild steel nuts on the mast bolts?  


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