Resonating with You

A couple of my “Devil Wind” readers have asked me about the resonator and how it worked.  I’m not an engineer, but I put in a call to Gus’ buddy Keith McKay, CEO of Pueblo Technologies in Cambridge, Massachusetts, and he was happy to talk about the science of resonation and earthquake safety.

Sammy:  Thanks, Keith, for helping us out with resonator science.

Keith:  Sure.  Happy to help.  I know it sounds like science fiction, but base isolation and seismic control systems have been around for a long time.  Your very own City Hall building in Los Angeles has been retrofitted with such a system.

Sammy:  Didn’t know that.  What does the system do?

Keith:  It keeps buildings from falling down in case of an earthquake.

Sammy:  That’s a real good thing.  How does it do that?   We get some strong quakes in LA.

Keith:  Well, did you ever see that video of the Tacoma Narrows Bridge?

Sammy:  The one that fell in the 1940’s?  They called it Galloping Gertie?

Keith:  Yes, you can see a video of the bridge online.  (http://www.youtube.com/watch?v=j-zczJXSxnw )  The winds made the bridge buckle and sway like a wave.  Suspension bridges hang, they’re suspended.  Usually, you can’t tell they’re flexible, and that they move.

Sammy:  Works for me.  I like to drive on solid ground.

Keith:  In most cases, wind doesn’t move bridges much.  But with Tacoma Narrows, wind moved the bridge a lot.   The wind often  synchronized with the bridge’s natural swaying, making the swaying stronger and stronger.  The wave built up more and more, and eventually became so big that the bridge collapsed.

Sammy:  Wow.  That is one impressive video.  Was anyone killed—I hope not…

Keith:  No people, thank heavens.  The owner of the car couldn’t get his dog, and…

Sammy:  Oh, that’s sad…    But buildings aren’t bridges.  They’re built on solid ground.

Keith:  Yes, but they actually  sway, not only with earthquakes but with wind, too.  If you’ve ever been on a top floor of the Sears Tower in Chicago—it rocks, literally.  That flexibility actually makes the building less likely to fall.

Sammy:  Good to know.  So a flexible building can ride out an earthquake?

Keith:  Sometimes.  But if it’s a real strong earthquake, the forces might overcome the building’s ability to stay up—that’s where base isolation and control systems can help.

Sammy:  How so?

Keith:  Well, imagine earthquake or wind forces rocking a building.  Now what if you place a giant pillow between the building and the ground—the pillow would cushion and dampen the forces and make the building sway less.

Sammy:  Sure…

Keith:  Then, you add a computer control system that measures the earthquake forces and actually adjusts the pillow to counter the forces.  simply put, the earthquake pushes 3 feet one way, the control system adjusts the base, the pillow, to push back 3 feet.

Sammy:  Um…

Keith:  Here, stack 5 blocks on a plate.  Pick up the right rim of the plate and the blocks fall to the left.

Sammy:  Yes.

Keith:  Now, try it again.  This time, when you pick up the plate from the right side, take your left hand and push on the blocks towards the right—pushing back.

Sammy:  I can keep the blocks up.  I see.  But in “Devil Wind”, the buildings fell down.

Keith:  Well, there’re a lot more blocks making up a multi-story building, of course.  But the principle is the same.  Measure the quake with the control system and instruct the system to act like your left hand and oppose the quake forces.  If, however, you break into the system and cause it to work in the same direction as the quake forces, the building will fall down even faster.

Sammy:  Scary.  But in “Devil Wind”, we didn’t have an earthquake.

Keith:  No, but you had Devil Winds.  And explosions.  They’d make buildings sway like the Tacoma Narrows bridge, then, the bad guys could sneak into the control system,  and, rather than counter the swaying, synch up the system to magnify the swaying.  The building reaches a point where the resonating wave is so strong, it overcomes the ability of the building to flex.  Like the Tacoma Narrows bridge, it falls down.

Sammy:  Awful.   I’m so glad ‘the bad guys’ haven’t dared try this again.  I hope people are protecting their control systems so they can’t be manipulated.

Keith:  Don’t worry, they are.  That’s a big part of the work our company does.  Firewalls, encryption, IT security.

Sammy:  That’s reassuring.  Thanks, Keith, for taking the time to enlighten us today.  Stay warm in New England!

Keith:  Spring’s finally here—we will.  Wishing you and all of California a quiet seismic year.

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