Expert: Failure leads to successful design

Henry Petroski, Aleksandar S. Vesic Professor of Civil Engineering and Professor of History at Duke University: “Imagine that the ‘Titanic’ had not hit an iceberg. Imagine that the ‘Titanic’ had successfully reached New York. It would have been hailed as a tremendous success. What would have been the consequences of that?”

2:48 p.m., May 10, 2006--Henry Petroski, Aleksandar S. Vesic Professor of Civil Engineering and Professor of History at Duke University, shared his views on successful bridge design at UD's first annual Arnold D. Kerr Lecture in Engineering Mechanics and Design.

Petroski said learning through failures and understanding exactly what went wrong is the way to achieve successful design. Using the Titanic as an example, Petroski said ship design would have not been improved had the Titanic stayed afloat.

“Imagine that the Titanic had not hit an iceberg,” he said. “Imagine that the Titanic had successfully reached New York. It would have been hailed as a tremendous success. What would have been the consequences of that?”

Petroski said the sinking of the Titanic forced engineers to redesign ships to be safer.

Petroski used slides of suspension bridges from the 1850s to the 1940s to illustrate the significance of learning from failure.

In 1826, the Menai Strait Suspension Bridge in northwest Wales was built with a high clearance to allow ships to pass underneath it.

Petroski said wind would move the bridge and make it unsafe to travel. This danger, as well as the need to carry railway trains, Petroski said, stimulated change in the way engineers had to approach bridge design.

“If you were going to build bridges to carry railway trains you had to think of it in a new context, “ he said.

Petroski said two models of suspension bridges emerged in the late 19th Century that are still evident today. British engineer Robert Stephenson created the Britannia Tubular Bridge, a 500-foot-long tube that could support trains as well as allow ships to pass underneath it. American engineer John A. Roebling build the Niagara Gorge Suspension Bridge, which was hailed as a great success.

Petroski said the ability of Roebling's bridge to withstand wind and storms indicated successful design.

Petroski: “This is one of the problems with studying successful models. You don’t know their weaknesses.”

A variety of suspension bridge designs followed Roebling's around the country. Petroski said the infamous collapse in 1940 of the Tacoma Narrows Bridge in Seattle, however, was an example of how engineers needed to focus more on bridge failures in order to strengthen bridge design.

“This is one of the problems with studying successful models,” he said. “You don't know their weaknesses.”

Petroski said bridges today have trusses, weight, girders and stays that help stabilize bridges in high winds. However, he said he is concerned with the designs of modern cable-stay bridges because engineers have yet to figure out how to stabilize the cables in the wind.

“I have great concern that if cable-stay bridges continue to be built, we may see another Tacoma Narrows Bridge,” he said.

Author of more than 12 books, Petroski is a fellow of the American Society of Civil Engineers and a member of the American Academy of Arts and Sciences and the National Academy of Engineering.

Sponsored by the Department of Civil and Environmental Engineering, the lecture series was established in honor of Arnold D. Kerr, Professor Emeritus of Civil Engineering.

Article by Julia Parmley AS' 07
Photos by Kathy F. Atkinson

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