A suspension bridge across the narrows of Puget Sound, connecting the Kitsap peninsula1 with the mainland of Washington State. The original bridge collapsed on November 7, 1940, just four months after it was opened to traffic.

Nearly everyone who's taken first-year college physics (and some high schoolers in advanced physics classes) has seen the famous footage of this bridge collapsing. It had already demonstrated a tendency to oscillate sinusoidally under the influence of wind gusts, an effect most disconcerting to those who traveled across it.

The wind which actually caused it to collapse, though fairly strong (around 40 mph), was hardly brutal. The collapse was brought about by the fact that the aerodynamics of the bridge structure generated vortices which rotated near or at the resonance frequency of the bridge. The resulting resonant vibration of the already-too-flexible bridge span, a bucking and twisting motion about the long axis, was caught by a movie camera, up to the bridge's spectacular demise.

After a redesign with the aid of improved aerodynamic theory, a second bridge was constructed at that point, which is still in use today.

1The original w/u, drawing from Britannica.com, named this the Olympic peninsula. I stand corrected.

The original Tacoma Narrows Bridge, connecting Tacoma and Gig Harbor, opened to the public on July 1, 1940. A little more than four months later on November 7, a moderate windstorm (40 MPH) caused the 5,939 foot-long bridge to meet a spectacular demise when parts of it crashed into Puget Sound.

When the bridge opened in July, the public immediately gave her the name "Galloping Gertie" due to the way she would "gallop" in relatively light winds. In fact, many drivers saw and felt the wave motion of the bridge as cars in front would disappear momentarily and driving across the bridge had a feeling of a roller coaster ride. Obviously this is extremely bad for a bridge to do and attempts were made to rectify the situation but none worked out. If that wasn't enough, the bridge was designed to catch the wind instead of letting it flow through, thus increasing the rolling motion of the bridge and as was the trend at the time, the bridge was built with maximum lightness, slenderness, and flexiblity.

Finally, on the day of its collapse, the bridge started a corkscrew motion that continued to increase until the bridge's main span had a 600 foot-long chunk break off, turn upside-down and crash into the Narrows (The part of Puget Sound that separated the peninsula and the Washington mainland). At its peak the difference in height between the two sides of the bridge reached 28 feet, and afterwards the other two spans sagged 45 feet along, also causing the main towers to buckle under the increased weight.

Today, most people accept that the bridge's demise was caused by resonance, however some believe it may have been caused by self-excitation. In 1992 the underwater remains of the bridge were put on the National Register of Historical Places to prevent salvagers from taking pieces of it. Also, a new Tacoma Narrows Bridge was built 10 years later, and after 29 months of construction was opened on October 14, 1950.


And now you walk away from this again, the most natural and magical and compelling thing I've ever had the chance to witness or imagine could exist between two people. The bridge screams above me, the sound of the whole Antarctic ice shelf coming apart in one focused moment of car exhaust and coal power plants and CFCs, the cracking of brain and heart and hope. Then comes a fusillade of Mauser rifles and Maxim machine guns as the guy wires begin snapping under the strain of a deck warping like an oscilloscope, and I'm the man leaping, rifle in hand, tin soup bowl helmet on head, to impale himself in the wire. I'm the January shipwreck on the shoals around your island paradise, deckhands leaping into the frigid waves while their captain sits down in his chair, sings some long forgotten song and pours himself a last glass. I'm the bottle that, caught in a furious undertow, shatters under the pressure of the ocean's depths long before it reaches a shoreline where you might stand to welcome the message I carry. I'm the guy who drove his car out onto this bridge in the midst of its death throes and I'm the engineer who missed last week's lecture on resonant frequency.

The wind is wailing through the Narrows as you walk away again, and all the conifers on the slopes above me shrink away like the men of the 7th Infantry fleeing the deadly freeze and blizzard of steel that swept down the mountains at the Chosin Reservoir. My hands frozen by the gales, I'm the North Korean peasant farmer tearing bark from the last of the beautiful trees of his homeland to fill his famine stomach. I'm the hills of grain kept locked in a military storehouse and never given the chance to fill anyone with warmth and life. I'm a bag of all the letters lost to January winds and the miserable powerlessness on the face of all the senders who expected replies. I'm standing in the snow and the waves sigh as they strike the crumbling beach, and I'm sitting in Leonard Coatsworth's car as it is tossed this morning into Puget Sound.

And now you walk away from this again, and the steel deck plates twist and shout, and I brace myself against the screaming cold and pore over alone what we may have lost. And I'm the man looking at you, through the wires or on the bus, knowing that you're the one. And you're the one walking away again.

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