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The Structural Engineer's Standard of Care

Added08/15/2006

Updated02/04/2016

Author(s) Joshua B. Kardon
Contributor(s) Joshua B. Kardon
Notes Presented at the OEC International Conference on Ethics in Engineering and Computer Science, March 1999
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Year 1999
Publisher National Academy of Engineering, Online Ethics Center
Language English

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Tacoma Narrows Bridge Collapse

Author: Joshua B. Kardon, S.E. 
University of California, Berkeley

This case is an excerpt from "The Structural Engineer's Standard of Care."

In 1940, wind-induced oscillations destroyed the brand new Tacoma Narrows suspension bridge. One hundred years earlier, the dangerous dynamic effects of the wind were known, and suspension bridge design of that era included measures to counter those effects. The engineer for the Tacoma Narrows Bridge superstructure, described as "among the highest authorities in suspension bridge design" (Condron, 1938), was not thought by many at the time to be negligent. This was in spite of the fact that normal competence of suspension bridge designers of almost a century earlier included avoidance of this kind of failure.

Diane Vaughan (1996) wrote about the Challenger explosion. She describes the actions of the engineers and managers of the Space Shuttle program as succumbing to the "normalization of deviance," the gradual acceptance of sequential minor errors and failures, accumulating and culminating in a major catastrophe. The Tacoma Narrows failure may have been an example of this phenomenon. Suspension bridges were being designed and built with ever longer and more slender spans. Construction workers, and the operators and users of the bridges, noticed the tendency of the new bridges to oscillate in the wind. To some extent, the bridge designers accepted that response as reasonable and acceptable performance in light of the tradeoff for lightness, economy and aesthetics. The Tacoma Narrows Bridge was the most slender suspension bridge built up to that time, and its oscillations, so pronounced that the bridge was nicknamed "Galloping Gertie,"ultimately caused its collapse.

The advancement of the state of the art is not always forward. The designer of the Tacoma Narrows Bridge was not considered negligent in his failure to accommodate dynamic wind effects, despite almost a century of bridge design experience pointing to that as a critical design condition. Suspension bridge design and analysis methods, the materials used in bridge construction, and the longer and more slender profiles of the modern bridges, were thought to be sufficiently different from those of the 19th century, that the designer of the Tacoma Narrows Bridge was not held to the standard of care of the earlier era.

 

Cite this page: "Tacoma Narrows Bridge Collapse" Online Ethics Center for Engineering 11/1/2010 OEC Accessed: Wednesday, July 10, 2019 <www.onlineethics.org/Resources/standard_of_care/TacomaNarrows.aspx>