Tacoma Narrows

Following entry is a record in the “Catalogue of Catastrophe” – a list of failed and troubled projects from around the world.

Washington State – USA
Project name : Tacoma Narrows
Project type : Suspension bridge
Date : 1940 (filed under historical failures)
Cost :
 $6.4M in 1940 – $105M adjusted to 2012 costs

Synopsis :
If you are putting together a list of failed projects from the history books it would be hard to ignore the Tacoma Narrows bridge. At the time of its opening in summer 1940 it was the world’s third longest suspension bridge. Within four months of that date it was a twisted pile of wreckage at the bottom of the gorge. Film of the failure shows how strong winds caused the bridge to start to oscillate and twist. When wind speeds hit the right speed (42 Mph) the oscillation was magnified due to resonant frequency effects and after 1 hour of incredibly violent twisting the central span of the bridge collapsed.

Tacoma Narrows - opening day

Tacoma Narrows – opening day – 1940
source wIki commons

During construction flaws in the design had already started to appear. Crews building the bridge were aware that when the wind came up the bridge had a tendency to move. A certain amount of motion is expected in a bridge, but the issue was strong enough that workers nicknamed the bridge “Galloping Gertie”. In response to the concerns Engineers came up with a number of solutions that were retrofitted to the design as the project progressed. Those solutions were found to be ineffective and so the Engineers continued looking for a permanent solution after the bridge was open to the public.

Clearly the Engineers were not fully aware of the dangers they were exposing the public to. Although they knew the design was prone to motion it was not until the wind hit the right speed that the magnitude of the problem became apparent. Fortunately when the collapse did occur there was no lose of human life (although a pet dog was killed). The story does however have a positive side. Lessons were learned and mankind’s understanding of how structures respond to wind forces was greatly advanced. The film of the Tacoma failure is now a standard part of many Engineering courses and serves as a warning to future Engineers illustrating the responsibility they have to the public.

Classic film of the bridge collapsing

Contributing factors as reported in the press:
Lack of technical knowledge available at the time (failure to appreciate how the oscillations experienced during construction could magnify in stronger winds).

Reference links :

  1. Tacoma Narrows – Wikipedia page
  2. Video of the collapse