Failure Analysis: 1940 Tacoma Narrow Bridge
An important element of an engineer’s job is to have the ability to respond to a need by building or creating a device or structure to carry out a given purpose. It is important for this device to be able to perform its purpose without failure as it will be dealing with people life and therefor the highest amount of safety is needed. Though, everything must eventually fail, in some way e.g. a failure in maintenance or a structure failure. This is why a failure analysis is important to an engineer’s job.
A failure analysis is the process of collecting data and analyzing it to determine the cause of failure and then applying this ...view middle of the document...
In the 1880s the Northern Pacific railway proposed an idea of a bridge that will span the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula to provide a route for railway traffic. It was not until June of 1938 where the PWA approved a $6 million dollar for the project that the idea was the implemented.
In November 1938, construction of the first Tacoma Narrows Bridge began. After the bridge’s floor system was completed, engineers and other noticed that the bridge had a vertical oscillation. They knew something was wrong with the design. Workers than gave the nickname “Galloping Gertie” to the bridge for this vertical oscillation. The oscillation observed alerted engineers to find a way to mitigate the problem and some solution were implemented during construction.
On the 1st of July 1940, the bridge was open and hence making it the third longest suspension bridge in the world at that time, in terms of span length. Even though its construction was completed and solution for the vertical oscillation of the bridge was implemented the bridge still had a noticeable vertical oscillation. It was not until four month later on November 7th, 1940, that the bridge began to oscillate in a torsional mode due to the 64km/h wind present at that time. At 11:00 am the bridge began to fail and collapsed. The Tacoma Narrows Bridge failure, probably stand as one of the greatest civil engineering failure to date.
The 1940 collapse of the Tacoma Narrows Bridge is classified under civil engineering failure.
During the construction of the bridge, vertical oscillation of the bridge caused engineers to find and proposals ways to mitigate this problem. Several of these strategies were implemented during its construction phase to help reduce the vertical oscillation of the bridge but none of these strategies actually succeeded in its purpose.
After the opening of the bridge the Washington Toll bridge Authority hired a professor named Fredrick Burt Farquhason, an engineer at the University of Washington, to conduct a wind tunnel test of a scaled model of the bridge and recommend solutions in order to reduce the oscillation of the bridge. Five days before the collapsed of the bridge Fredrick proposed two solutions to the problem. They are:
• To drill holes in the lateral girder along the deck to reduce the lift forces. This would’ve been proven affective as it allowed airflow to circulate through them reducing the lift forces present.
• To attach fairings or deflector vanes alongside the deck, attached to the girder. This would have given it a more aerodynamic shape to the transverse section of the deck.
The first option that Fredrick proposed was not favored due to the irreversible nature of the plan and the second option was chosen but was never implemented due to the fact that the bridge collapsed 5 days after the proposal was made.
There are two main factors that resulted in the collapse...