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March 9th, 2011 MARTY SMITH | Dr. Know
 

Dr. Know: Cranes & Earthquakes

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Like most downtown construction sites, the one near my office is dominated by a very tall, very slender crane. In an earthquake, these things seem like they’d keel right over. Should I duck? —Son of Arlee

Come on, you should know this drill by now. It’s the sturdy, solid-looking things that kill you in an earthquake: brick buildings, cathedrals, Roman aqueducts. Flimsy, wobbly things, engineers assure us, are the ones that survive an earthquake without a scratch. (Apparently, the absolute safest place to be in an earthquake would be under a boulder balanced on a drinking straw. You first.)

The cranes you’re talking about are called tower cranes, and in fairness to their designers, it’s not like they just throw them up there and get the fattest guy on the crew to hold the bottom steady. The base of the crane is fixed in a concrete pad, which is in turn usually anchored to bedrock. As for the tower itself, the mystic power of wobblitude takes care of that.

“During normal operations, a 260-foot-tall tower crane can move up to three feet off of centerline in any direction,” says Gaytor Rasmussen, a Washington crane inspector and former operator who actually has a blog called Tower Crane Accidents. (God, I love the Internet.) “As an earthquake hits, it isn’t likely to move the crane further.” 

In other words, the thing is already swaying so sickeningly—even in the best of times—that not even the Big One can make it any more terrifying. 

Granted, there was a major earthquake-related crane accident in Taipei in 2002. But if it’s any consolation, the roughly 250 large crane collapses that have happened since then all took place on stable ground—they were caused by good, old-fashioned human error and negligence. I’ll bet you feel better already.

 
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