Tacoma Narrows bridge construction started in November 23 1938 until July 1 1940. It cost approximately $ 6,400,000. Its physical properties were 5000 feet in total length, span length of 2800 feet, width of 39 feet, which constituted the two lanes of traffic and eight feet of side girders. L.S Moisseiff, a leader by profession, designed the bridge.
During its construction, it experienced huge vertical oscillations and shortly after it was opened, it was nicknamed ‘Galloping Gertie’ by Tacoma residents because of how it oscillated when it was windy. This made it a tourist attraction site.
On 7th November, 1940, at a time estimated to be 11.00 am stronger winds with almost a speed of 42mph blew causing large vertical oscillations making the connection cable slip and failing of the bridge progressively. The slipping was caused by the greater amplitude produced by the oscillations. The oscillations dampened the torsional oscillations, and they eventually became severe. This was followed by breaking of vertical hangers followed by the collapse of the entire bridge. The towers were damaged beyond repair.
The main reason for the failure of the bridge were solid plate girders had been used for decking replacing the common trusses and two steps in basic parameters had been changed. The technology was not advanced to be able to tackle the situation at hand.
The collapse of the bridge initiated intensive research on behavior in aerodynamics (Vortex shedding, torsional flutter and buffeting). Use of stiff plate girders in bridge construction also ended, and the stiffening trussels use continued. Wind tunnels test were also advocated in bridge construction should be carried before construction of any bridge.
Works cited
http://mceer.buffalo.edu/education/bridge_speaker_series/2009- 2010/presentations/P1%20Lessons%20learned%20from%20Bridge%20Failures_FINAL.pdf
http://aapt.org/Store/upload/tacoma_narrows2.pdf
