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Q&A - John W. Fisher: A New Perspective on Design

Building a Bridge from the Lab to the Real World

John W. Fisher, one of the world’s preeminent bridge engineers, is a pioneering expert on fatigue and its effects on welded and bolted connections in steel structures. In a career spanning six decades, he has investigated many noted structural failures, including the collapse of the World Trade Center and the I-35W bridge in Minneapolis. The recipient of numerous honors, including election to the National Academy of Engineering, Fisher has been praised for improving health, safety and the economy while advancing the art of bridge engineering and design codes. Fisher is the founder of Lehigh’s world-renowned ATLSS (Advanced Technology for Large Structural Systems) Center.

Q: What are the main qualities necessary to be a good researcher?

A: Ambition, creativity, patience and dedication to what you enjoy doing. And the desire to work with young people.

Q: After serving in the 4th U.S. Army Engineer Combat Battalion, you earned a B.S. from Washington University in St. Louis in 1956 and an M.S. from Lehigh in 1958. What led you then to your lifelong interest in steel bridges?

A: I worked three years as an assistant bridge research engineer with the AASHO (now the American Association of State Highway and Transportation Officials) Road Test. We studied bridges and pavements and conducted a lot of statistically designed experiments whose results are still a primary source of data for the highway design codes in our country and much of the world.

As assistant bridge engineer, I observed bridges and the impact of truck loads on bridges. That’s where I got exposed to the concept of experiment design and to the fact that cracks could develop at welded details. When I returned to Lehigh as a Ph.D. student in 1961, I was the only person among faculty and students who had worked with computers, so I was asked to teach the first course in computers.

Q: How did your research career take shape at Lehigh?

A: Initially I worked on high strength bolted connections for my Ph.D. studies. In 1967, I started my first major project, the effect of weldments on the fatigue strength of steel bridges, funded by the National Cooperative Highway Research Program (NCHRP). The project had five or six phases, and it lasted into the mid-1980s.

At that time, there were many assumptions about what factors were critical to the ability of structures to resist fatigue (repeated stresses). Also, many bridge engineers thought contemporary designs would prevent fatigue cracking in bridges. But those design codes then were largely based on tests done on small specimens.

We conducted statistically designed experiments and found there was only one critical stress condition — the stress cycle. I was the first to propose this and I was opposed by a lot of bridge engineers. But our findings resulted in the adoption, in the U.S. and much of the rest of the world, of comprehensive specifications for designing steel structures, particularly bridges, for fatigue resistance.

Q: What else did you learn from the NCHRP project?

A: When we initiated the project, it was generally assumed that 2 million cycles was the fatigue limit, that if a structural detail withstood that many cycles, it would not fail at, say, 5 or 10 million cycles. But we tested specimens until they failed and discovered that the fatigue limit was different for different details. In some cases the limit was 20 million cycles, not 2 million.

This changed the whole perspective on fatigue design. It also explained why, in the 1970s, we began seeing the first signs of fatigue cracking in bridges that had been designed and built after World War II for the interstate highway system. It turned out these designs were based on erroneous assumptions.

You have to be careful where your knowledge is and how you extrapolate. I think that’s one of the crucial things with any researcher.

Q: You were the founding director of Lehigh’s ATLSS Center when it was established as an NSF Engineering Research Center in 1986. What was the impetus for its creation?

A: We wanted the capability to test full-size elements and specimens so we could assess size effects on building systems subjected to earthquakes and bridges subjected to loads from trucks and trains.

Also, I’m an avid supporter of the interdisciplinary approach. ATLSS provided the opportunity to put several minds to work on the same problem from different perspectives. This is a good experience for students. It gives them new tools to understand problems.

Q: You were part of a team of ATLSS researchers that investigated the damage to steel buildings caused by the 1994 Northridge-Los Angeles Earthquake. What was your conclusion?

A: Because of the dynamic loads of the earthquake, a large number of relatively new buildings developed fractures at welded joints at beam-to-column connections. Many of these structures were rendered unusable even though you could not see the fracture at first because the building had not collapsed or was not tilting.

In retrospect, our knowledge base was limited. The assumptions underlying structural designs relied, again, on tests conducted on small specimens rather than full-scale joints. That earthquake generated a huge amount of studies on scale effects, material effects, welding and the quality of welds. None of these had been adequately studied. We’re still trying today to develop structural systems that are better able to resist dynamic loads.

Q: You served on the national commission that investigated the collapse of the World Trade Center after the Sept. 11, 2001, terrorist attacks. What did you conclude?

A: Both buildings were subjected to a massive impact, which they were able to resist. But the impacts disabled the fire-suppressant systems, and fires destroyed enough depth in the structures to create the instability that caused them to collapse. Never before in the history of the world had large structures been subjected to so many fires at the same time, all of them simultaneously set because of the impact of the fuel tanks.

Q: You’ve campaigned for more research to prevent structural failures and the resulting repair and litigation costs. Have your warnings been heeded?

A: Unfortunately, our society is content to respond to disasters. There are insufficient studies to ensure long-term serviceability and proper quality control. This doesn’t get the attention it should. I have not seen this change much. I’m not sure it ever will.

Q: You have received almost every award in your field. Which have been the most notable?

A: The Fritz Medal is among the top (the award is given by five international engineering professional societies; winners have included Thomas Edison and Alexander Graham Bell). Being the first academic to be named Engineering News Record magazine’s Construction Man of the Year. Also the Outstanding Projects and Leaders (OPAL) Award from the American Society of Civil Engineers for lifetime achievement in education.

Q: What is your teaching philosophy?

A: I try to give students freedom in the way they approach a problem. I often take them into the field so they can see what’s happening and why. My students and I learn a lot working together. I can attribute part of my success to the fact that I have had good students.

Q: How do we educate the next generation of engineers? What are we not doing that we should be?

A: I see too much reliance on models and computers. To understand the basic behavior of structures, you have to get your hands dirty. We need to promote hands-on experience and experimental work or there will be many more failures.

We also have to convince the country of the need for talented engineers. Engineering is the application of science to solve problems. More people would enjoy engineering if they understood this.

Good researchers, says John Fisher, extrapolate only from a reliable base of knowledge.