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Tacoma, Washington

Tacoma Narrows Bridge

This famous bridge twisted itself into oblivion, but not for the reason you might think. 

The original Tacoma Narrows Bridge opened on July 1, 1940, and collapsed into Puget Sound on November 7, 1940. The suspension bridge spanned the Tacoma Narrows strait between Tacoma and the Kitsap Peninsula in Washington State.

The Narrows Bridge was poorly designed, and high winds caused it to roll and eventually collapse. The bridge has been used as a cautionary tale to engineering students since its collapse and is still found in physics textbooks today as an example of periodic frequency and forced resonance.

The common explanation for the bridge collapse, that the bridge’s resonant frequency matched the frequency of the wind and set the bridge on an ever increasing oscillation, is now known to be false. The real culprit is a phenomenon known as aeroelastic flutter, and though the idea of a feedback loop between the air and the movement of the bridge is correct, it had little to do with the natural frequency of the bridge. Of course, for the people on the bridge that day, this was neither here nor there. In the words of one survivor:

“Just as I drove past the towers, the bridge began to sway violently from side to side. Before I realized it, the tilt became so violent that I lost control of the car […] The car itself began to slide from side to side of the roadway. On hands and knees most of the time, I crawled 500 yards or more to the towers […] Safely back at the toll plaza, I saw the bridge in its final collapse and saw my car plunge into the Narrows.”

Luckily the only death from the bridge collapse was that of a dog too scared to be rescued from its owner’s vehicle.

The bridge was deemed a loss, and because of steel shortages during WWII, the steel in the cables was sold. It took the state of Washington about ten years to rebuild the Narrows Bridge, and it was designed so a disaster such as the one in 1940 would not happen again. The newly rebuilt bridge was opened on October 14, 1950 and was longer and wider than the original.

At the time of the 1940 disaster the Narrows Bridge was the third longest suspension bridge in the world.

Today the remains of the original Narrows Bridge are in much the same place they fell. The wreckage has created an artificial reef and is on the National Register of Historic Places.