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ASEE PRISM
  American Society for Engineering Education
American Society for Engineering EducationOCTOBER 2006Volume 16 | Number 2 PRISM HOMETABLE OF CONTENTSBACK ISSUES
FEATURES
Trouble on the Horizon - BY THOMAS K. GROSE
Get SMART - BY THOMAS K. GROSE
Tulane's Next Move - BY JEFFREY SELINGO

DEPARTMENTS
COMMENTS
CONTRIBUTORS
BRIEFINGS
REFRACTIONS: ENGINEERING AND HISTORY - BY HENRY PETROSKI
CLASSIFIEDS
LAST WORD: The College Payoff - BY ANTHONY P. CARNEVALE

TEACHING TOOLBOX
Let Go of My Legos - Those little bricks are a wonderful way to teach engineering to youngsters. BY ALICE DANIEL
BOOK REVIEW: An Inconvenient Truth - BY ROBIN TATU
TEACHING: The Plague of Self-Plagiarism - BY PHILLIP WANKAT AND FRANK OREOVICZ
ON CAMPUS: The Write Solution- BY LYNNE SHALLCROSS










 
REFRACTIONS: Engineering and the City - BY HENRY PETROSKI Henry Petroski  

This site of this year’s annual conference provided a showcase for the marvels of engineering.

Engineers design the future; historians analyze the past. These oversimplifications may highlight some fundamental differences between the practice of engineering and history, but when taken as indicative of divergent and exclusionary objectives, they can lead to both inferior engineering and inferior history.

In their enthusiasm for advancing the state-of-the-art by pushing the limits of cutting-edge  technology, some engineers do not look back at the history of their field.In their enthusiasm for advancing the state-of-the-art by pushing the limits of cutting-edge technology, some engineers do not look back at the history of their field. They do not see it as relevant. Even if they do have an armchair interest in the history of what they are currently engaged in, they tend to compartmentalize that interest or see it as an avocation they will pursue in their retirement.

This was the situation among suspension-bridge engineers, especially in the 1920s and ’30s. In a remarkable technological leap, Othmar Ammann designed the George Washington Bridge to have a main span almost double that of the previous record holder. The daringness of this, plus the shallowness of the long deck of the bridge provided a paradigm for subsequent suspension bridge designers to follow. Bridges with less and less stiff decks resulted, culminating in the Tacoma Narrows Bridge that twisted itself apart in a moderate wind.

While the undisputed leaders in the field of bridge design were following Ammann’s lead, they were also disregarding the history of suspension bridges. Although they knew about the wind susceptibility of wooden-decked bridges of a century earlier, they considered it irrelevant to the design of modern steel structures.

Yet in 1840, no less an engineer than John Roebling had distilled from his study of historic failures of suspension bridges what was necessary to do in order to design a bridge that could stand up to the wind. He explicitly stated that the deck of a successful suspension bridge must be heavy, have a stiffening truss and have supplementary cables to check unwanted motion.

Roebling incorporated these necessary features into the Brooklyn Bridge, but in subsequent decades, they were systematically eliminated from the bridges of Ammann and his contemporaries. First, the cable stays were done away with as redundant, leaving those on the Brooklyn Bridge to be a somewhat quaint but distinguishing feature. Next, the stiffening truss was abandoned in the name of aesthetics. And, finally, weight itself was shed in optimally designed bridges with very narrow roadways.

In the immediate wake of the Tacoma Narrows collapse, all the lessons of history were recalled. There was a failure analysis of the Tacoma tragedy, which reached conclusions not that much different from what Roebling had concluded a century earlier. After an understandable hiatus, suspension bridges began to be built once again, but their wind-resisting features were more influenced by historical rather than modern examples.

Historians have been analogously guilty of ignoring engineering. They generally have not paid as much attention to developments in technology as they have to those in politics. Yet the Brooklyn Bridge played a significant role in the consolidation of separate political and geographical entities into the New York City that we know today.

Historians of technology have been calling for some time for more recognition of the effects of technical developments on the course of human events. In the absence of textbooks giving what they consider a balanced view of history, some sympathetic historians proposed to team up to write such a book, and they did so with support of the Alfred P. Sloan Foundation. To the best of my knowledge, their effort has achieved only modest recognition, but this should not keep engineers from incorporating relevant history into their own textbooks.

Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. This essay is based in part on his Distinguished Lecture at the ASEE annual conference held in Chicago in June. Some of the ideas in this essay and the lecture are elaborated upon in his latest book, “Success Through Failure: The Paradox of Design.”

 

 


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American Society for Engineering Education