Tacoma Narrows Part 2: Failure of a Design

By Kim Smiley

The mechanics behind the failure of the Tacoma Narrows Bridge were discussed in a previous blog entry.  There were many design issues with the bridge and the civil engineering community has done an excellent job of studying and incorporating lessons learned from the failure. But a question that may be more pertinent across all engineering disciplines is, “Why did the design process fail?”

How did a bridge get built that would fail in a little over four months?  A root cause analysis of the bridge shows that factors that shaped the doomed bridge design are present in almost every engineering project.  There is as much to learn from the failed process that led to the design as there is from the failed design.

The primary factor that led to the bridge design was cost reduction.  The first design proposed for the Tacoma Narrows Bridge was a conventional suspension bridge that was estimated to cost $11 million.  Funding was an issue for the bridge from the beginning, and the design that was finally approved for the bridge was an elegant bridge with a narrow roadbed and short girders.  In additional to being more aesthetically pleasing, the estimated price tag of $8 million dollars was nicer to look at as well. Another contributing factor is the engineer behind the second design, a very well-known civil engineer Leon Moisseiff.  His credentials were impeccable, and he had previously consulted on the famed Golden Gate Bridge, the Bronx-Whitestone Bridge and others.  Additionally, he helped developed some of the methods used throughout the world to calculate forces in suspension bridges.

In a tale that is probably repeating somewhere right now, a cheaper, flashier design was recommended by a well respected engineer.  Nobody wanted to listen to the voices of dissension among the less well-know engineers (and there were engineers who spoke out against the new bridge design saying it was unsafe).  The project then dramatically fails.

As engineers, there is a lot we can learn from studying how past projects have balanced cost and safety.   There are stories where remarkable profits and success have been achieved by finding a cheaper way to do something.  But sometimes, as in the case of the Tacoma Narrows Bridge, the cheap way costs more in the end.

Learn more about the failure of the Tacoma Narrows Bridge.