BRUNO THÜRLIMANN 1923–2008

BY JOHN E. BREEN

BRUNO THÜRLIMANN, professor emeritus of structural engineering at the Swiss Federal Institute of Technology in Zurich and a visionary, pioneering expert on engineering applications of plasticity theory in both steel and concrete structures, died on July 29, 2008, at the age of 85. Bruno Thürlimann was elected a member of NAE in 1978 “for accomplishments in theory, research, design and construction of steel, reinforced concrete, and prestressed concrete structures.”

In November 1850, when President Zachary Taylor signed a Convention of Friendship, Commerce and Extradition between the United States and Switzerland, he said it was his hope that “the two freest peoples on earth will treat each other reciprocally on a footing of equality.” A century later, Bruno Thürlimann, who was born a Swiss citizen and became a naturalized American citizen in 1957, was the embodiment of a bridge between the two nations for transferring technical ideas between the two worlds and improving structural engineering in both. A warm, compassionate, open-minded teacher and researcher, he brought scientific ideas and rigorous mathematical theories from Europe to underpin the highly empirical base of North American structural design. And he brought nonlinear and plastic approaches for structural design back to Switzerland. Throughout his career, he was a truly international presence, a highly respected lecturer, and a consultant worldwide.

He was born on February 6, 1923, to a family with a tradition in medicine in Gossau, St. Gallen, Switzerland. In 1935, he entered the Jesuit boarding school Stella Matutina (Morning Star) in Feldkirch, Austria, where two elder brothers, his father, and his grandfather had been educated. The Jesuit ratio studiorum, which emphasized intellectual, literary, philosophical, social, and scientific training and included sports, such as swimming, hiking, and skiing, was designed to teach skills, foster democratic leadership, and create esprit de corps. This course of study had a formative influence on Bruno as a future leader. Unfortunately, after the Anschluss of 1938, the Nazi persecution of the Jesuits resulted in the closing of the school. Thürlimann transferred to the College St. Michael in Fribourg where he obtained his Swiss Matura.

Thürlimann chose to study civil engineering at the famous Swiss Federal Institute of Technology at Zurich (ETHZ), but his studies were repeatedly interrupted by military service to defend Switzerland’s neutrality during World War II. After receiving his engineering diploma in 1946, he was an assistant at ETHZ for two years. He then continued his studies at Lehigh University in Pennsylvania where he did graduate work on cylindrical shell roofs with Professor Bruce Johnson and received his Ph.D. in 1951.

In 1951–1952, Bruno was a research associate in William Prager’s Division of Applied Mathematics at Brown University, the same years Prager and his colleagues published the theorems that provided the theoretical basis for the limit design of beams and frames. When Bruno returned to Lehigh as a Research Professor in 1953, he played a key role in the revolutionary development of radically new methods of designing with structural steel based on nonlinear material and geometric models. The limit-design approaches required greatly improved knowledge of local and lateral stability of severely plasticized portions of steel beams and columns. Bruno developed design techniques for steel elements in compression and welded steel-plate girders that are still essential to all modern steel design codes. In recognition of his work, the American Society of Civil Engineers awarded him the Norman Medal in 1963 for a paper on inelastic instability of steel structures and the Mosseiff Award in 1964 for a paper on the bending strength of welded-plate girders—both key elements in the new design technologies for steel structures.

In 1960, Bruno dramatically switched gears when he returned to ETHZ as chair of structural concrete, a position he held until he became Professor Emeritus in 1990. Applying his intimate knowledge of plasticity to steel structures, he conceived a systematic application of plasticity for reinforced and prestressed concrete, materials that are much more limited by strain than steel. Entrenched senior faculty, enamored with the beauty and consistency of elastic theory, considered his plasticity theory and its implications a sacrilege. Staying well within the limits of politeness and respect, Bruno summoned his powers of logic, rigor, and inventiveness in extending plasticity to encompass all combinations of axial load, flexure, shear, and torsion in both reinforced concrete and prestressed concrete; eventually, he convinced students, practitioners, and regulatory authorities. His theories were rigorously based and were confirmed by carefully conceived large-scale experimental research.

In later years, he extended the plasticity theory to masonry structures. He lectured widely and, in time, his plasticity approach to structural concrete was accepted as an important element for design codes in Switzerland, Europe, and the Americas, particularly when combined flexure, shear and torsion actions were considered.

Throughout his career, Thürlimann was much in demand as a consultant on major engineering projects. Unlike many “academic” engineers who do not relate well to the “dirty” reality of everyday engineering, he quickly grasped the essence of complex situations, regardless of whether the complexity arose from a technical issue or financial or business considerations. He was called on for important decisions on projects as diverse as the CN Tower in Toronto, the record- setting Gateway Bridge in Brisbane, the overly flexible John Hancock Building in Boston, the Louvre Pyramid, and the forensic investigation and redesign of the Norwegian Contractors Sleipner A Platform, which had caused a $700 million loss when it imploded during construction.

Throughout his career, Bruno opened new worlds for his students and colleagues. He held daily coffee meetings for everyone in his institute and ski excursions and institute swims across the Lake of Zurich to built spirit and continuity among his assistants and former assistants. He taught more than 3,000 undergraduates, had more than 100 assistants, and supervised 41 doctoral students. He attracted excellent students, inspired them, and kept them interconnected.

In addition to being a major force in Swiss building code groups, he chaired major technical committees in both American and European organizations. His crowning organizational achievement was his presidency of the International Association for Bridge and Structural Engineering (IABSE) from 1977 to 1985. Under his leadership, the organization greatly increased the number and improved the quality of its conferences, publications, and committees. Although Bruno was a man of great culture and knowledge, he was always easy to approach, ready for a discussion, and able to put people at ease with a story or joke.

He received wide recognition for his many contributions to structural engineering, including election to membership in NAE, the Swiss Academy of Technical Sciences, and similar Spanish, German, and Serbian Academies. He received honorary degrees from Stuttgart and Glasgow universities, was an Honorary Member of both the American Concrete Institute and the American Society of Civil Engineers, and was awarded the French Prix Albert Caquot Medal and the Danish Ostenfeld Gold Medal. IABSE presented him with the International Award of Merit in Structural Engineering for his lifelong contributions. By the time he retired in 1990, he had developed his institution into one of the leading centers in the world for research on structural concrete, with modern laboratories and an excellent team that continued his work.

That gave him more pleasure, he said, than his closet full of awards and diplomas.

Above all, Bruno Thürlimann was a person of great wisdom, who recognized the importance of sustainability in engineering early on. In a major essay in 1980, based in part on a previous study by one of his former students, he called attention to the total energy requirements for producing a wide range of building materials. Comparing the energy requirements for five-meter span beams of various materials but equal strength, the study had shown as much as a 260 percent difference between the requirements for producing a steel beam and a prestressed concrete beam.

In a challenging essay, “Technology and Man,” in 1979, he called on engineers to let their technical and scientific work be guided by intelligence, reason, and humility. In his characteristic way, he foresaw that, despite how far technology had taken us, “even at the end of the 20th century, we have limited knowledge and are still bound by many errors.” In his lectures, he brilliantly separated pure mathematical derivations from the fudging of factors to fit experimental boundary conditions. He believed that “nature, as well as the human spirit, follows the path of a steady evolution,” and he cautioned that science does not protect against foolishness. He urged his listeners to always inform the public of the state of “our ignorance in making our pronouncements.”

After his retirement, Bruno enjoyed his home life, his supportive wife, Susi, and his family. He maintained informal contact with his vast network of former students, colleagues, and international body of friends from his IABSE days.

On July 29, 2008, Bruno Thürlimann died of sudden heart failure while swimming in the lake of Zurich. He is survived by his wife, Susi, two sons, one daughter, and four grandchildren.