The Tacoma Narrows Bridge was the third largest in the world in 1940. Unfortunately that wouldn’t last too long. On November 7th, 1940 only four months after being open it collapsed due to violent swaying and flexing. Some of the reasons for its collapse were that it was put in an area of Tacoma that was prone to high winds and the engineer used solid girders instead of open trusses to cut costs. Another issue that engineers later learned about was its lack of aerodynamics. With that said we will conduct a risk analysis of key factors from this project.
In this case study the failure of the Tacoma Narrows Bridge was a combination of many factors, including design flaws. It used shallow plate girders to decrease the weight instead of deep open stiffening trusses, which rendered the bridge less stable. Also, the structure, quite simply, was too long for its width. A wider bridge might have survived, but the roadway was too narrow to withstand the other stresses. Aerodynamics and a strange-sounding phenomenon called "self-excitation" also played a role. As the span began to undulate and became more unstable, the instability fed more instability. Therefore, when the span started its twisting motion, it also fed the instability flames, until the structure failed. “Self-excitation” means that one thing leads to another, turning back upon itself until collapse.
I believe that the engineers originally had a good project planned but once the oscillations of the bridge were observed during construction, it prompted them to find ways to reduce the motion of the bridge. I believe this was the point when they began shooting from the hip and were just scrambling to fix it. There were a few unique aspects of the Tacoma Narrows Bridge. For one they used solid girders instead of open trusses. The bridge was also a very narrow bridge which hadn’t been done before for a bridge of that length. It was also constructed in a location that was known for high winds. I don’t...
Cited: Guyer, J. P. (2010). Ethical Issues from the Tacoma Narrows Bridge Collapse. Retrieved January 20, 2013, from Ceden Engineering: http://www.cedengineering.com/upload/Ethical%20Issues%20Tacoma%20Narrows.pdf
Objectives of Risk Mitigation and Planning. (n.d.). Retrieved January 20, 2013, from Department of TRansportation: http://international.fhwa.dot.gov/riskassess/risk_hcm06_05.cfm
What Happened to the Tacoma Narrows Bridge? (n.d.). Retrieved January 2013, from wiseGeek: http://www.wisegeek.com/what-happened-to-the-tacoma-narrows-bridge.htm
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