Leslie E. Robertson, a brilliant conceptualist who designed the structural systems of the original World Trade Center in New York City, has died. The Distinguished Member was 92.

Robertson, P.E., S.E., Dist.M.ASCE, NAE, died one day before his 93rd birthday. He was world-renowned as an innovator for structures small to supertall. When he was director of the New York City office of the Seattle structural firm Skilling Helle Christiansen Robertson, he designed his first high-rise – the two record-tall Twin Towers of the WTC in lower Manhattan. After their completion in 1973, they stood as the tallest buildings in the world.

Robertson's association as structural engineer for the towers lasted until 2001, when they were destroyed by terrorists on 9/11.

The late John Skilling, the SHCR principal in charge of the WTC project, "considered Les a genius," says Jon Magnusson, current senior principal and former chairman and CEO of Magnusson Klemencic Associates, a successor firm to the Skilling organization.

For the WTC Robertson took the opportunity to engage in pioneering research with the development of the first boundary layer wind tunnel and the first experiments on human sensitivity to the sway of buildings. He conceived and later helped patent the viscoelastic damper with engineers from 3M Co. He also developed a technique for calculating stack pressure in high rises and the concept of the shaft wall partition.

Leaving SHCR in 1982, Robertson founded Leslie E. Robertson Associates, where he spent much of his career. Until his death he was with See Robertson Structural Engineers, which he cofounded with his wife, SawTeen See, herself a structural engineer. Other feats throughout his career included the Shanghai World Financial Center and work on bridges, museums, and theatres. He helped install large-scale works by the American sculptor Richard Serra.

Robertson felt all the grief at the collapse of the World Trade Center that anyone did who worked on it, though he realized the responsibility wasn’t with the structural core. "My sense … that I could have done better continues to haunt me," he wrote in The Structure of Design. Being an anti-war activist, he regretted the involvement of the United States in Iraq that arose in the aftermath of the attacks.

One day in the early 1980s, he was presented with a stick-figure model of the Bank of China Tower, in Hong Kong. The tapering figure had been made by the son of the tower’s architect, I.M. Pei, who instead of involving anyone in his office, went straight to his friend Robertson. "I had an inkling it would make sense from a structural point of view. Les's immediate reaction was that it did. I saw the building as a series of triangles. He saw them as structure, as a superframe. That was his conception."

After considering himself a "terrible student," Robertson dropped out of high school at age 16 to join the Navy, not too long before the German surrender in 1945, he said in an Engineering News-Record profile.

Robertson was honored by ASCE with the OPAL Award for design in 2003, and was a Life Member. He received numerous other accolades and awards over his lifetime, and was selected to NAE in 1975. ENR named him its man of the year in 1989. One of his extracurricular activities was as chairman of the Council on Tall Buildings & Urban Habitat, from 1985 to 1990.

“Les Robertson was an omnipresent force at almost all CTBUH conferences and other activities for almost 50 years,” said Antony Wood, the group’s CEO. “To say he will be missed is, quite literally, a towering understatement.”