Friday, June 6, 2008

January 16th 2007

Starting the year off right, Liverpool has a tower crane collapse over backwards in winds reported at 35mph. Looking at the picture you can see where the tower bent, so the only question is was the tower poorly built and or damaged, or did the tower strike something solid like the form work?

Most of us know that you cannot touch the boom of a crane to the load. So why is it ok for a tower to hit anything? The answer is it is not ok, but once a month I'm telling someone to clear formwork back from a crane.
There was a freak wind that took tension off of the boom as it was boomed up with a load on. while the boom was loose the boom rope dislodged from the sheave even though the guides were in place. The operator began to boom down but since the rope was not in the sheave, the rope was only loosening on the drum and the boom was not moving. When the boom finally moved it shock loaded the crane. Did the extra movement with dynamic loading cause the tower failure at a weld or by touching the form work?
It's highly unusual that the rope would dislodge. Was the pin back as far as it safely could be? It met safety standards with only 4 mm of clearance. but if the pin location was as close to the straight plane as possible, can the rope really jump the sheave and tighten enough to flatten out? It's a very odd situation and unfortunate.

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