Friday, September 18, 2015

How weather can turn a crane into a deadly weapon

A crane collapsed at the Grand Mosque in Mecca, Saudi Arabia, on September 11, 2015, killing 110 and injuring 400 of the visitors inside. It was a stormy, blustery day, but cranes are for lifting big things off the ground and engineered to be very, very stable. So how could one flip so disastrously?

"Their physics are pretty simple," says Henry Petroski, an engineer who studies structural failure at Duke University. "Whatever you’re lifting is a significant force, and that has to be balanced by the crane’s geometry." The crane that fell on the Grand Mosque was a crawler crane, with four basic geometrical parts: superstructure, boom, mast,
and cables.

Wind is a crane’s greatest foe, and even a perfectly set-up structure is susceptible. This is because the boom acts like a giant lever that the wind can push upon. On the evening of the collapse, Mecca’s
airport weather station showed sustained winds around 25 mph.

"If you think about it, the higher up you have the boom, the less wind it will take to push the crane over," says Terry McGettigan, a 43-year veteran crane operator and proprietor of the crane safety site Towercranesupport.com.

For more of the Wired story: www.wired.com


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