Remember the WA Bridge That Collapsed 5 Months After Being Built?
Have you heard the story about the shortest-standing bridge in Washington State history? It literally collapsed within 5 months' time.
Plans for the Bridge Started Back in 1889
The Kitsap Peninsula was mostly isolated in the early history of Washington State. There was a proposal created by the railroad company Northern Pacific in 1889 to construct a bridge connecting the peninsula to the rest of the state. Nothing happened with the project until the mid-1920s when authorities started gathering funds, consulting with engineers, and campaigning for the project.
Two Competing Designs for the Bridge
There were two different designs for the bridge. One from a state engineer working for the State Highway Department was a more standard design and cost $11 million. The other was designed by Leon Moisseiff, the engineer responsible for designing the Golden Gate Bridge. Moisseiff's design was much cheaper, slimmer, and took advantage of a new theory for static wind pressure to make it more streamlined. The Moisseiff design won out being the cheaper design and the new bridge planning began.
The Bridge Opened in July 1940
Construction of the new bridge to connect the Kitsap Peninsula to Washington started in September of 1928 at a total cost of $8 million. The bridge was completed in July 1940 with only two lanes because planners expected light traffic. At the time it was the 3rd longest suspension bridge in the world. The design only had 8-foot girders to help keep the bridge stable in the wind. That narrow design miscalculation is what led to tragedy less than 5 months later.
The Tacoma Narrows Bridge Collapses
If you hadn't guessed yet, the bridge was called the Tacoma Narrows Bridge. Less than 5 months after opening, the Bridge started swinging on a windy day on November 7, 1940. The designer's theory about static wind pressure was proven wrong when only 40-mile-per-hour winds caused the bridge to twist and swing violently.
40 Mile Per Hour Winds Cause the Collapse
The bridge started violently shaking and twisting, with the swings getting stronger with each wobble. Eventually, the bridge gave out and half of it collapsed into the Pudget Sound below. According to the classic video footage, a dog was the only reported casualty of the collapse. That dog was left inside a stalled car and both fell into the water when the bridge gave out. You can watch all the dramatic footage in the YouTube video below.
The Tacoma Narrows Bridge is Now an Example
After the Tacoma Narrows Bridge collapsed, textbooks about engineering use it as an example of simple forced mechanical resonance. The lessons learned from this tragedy influenced long-span bridge designs going forward. Think about that fact the next time you walk or drive across a narrow suspension bridge safely. And remember that sometimes, you get what you pay for.