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Tuesday, April 15, 2014

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Civil engineering lecturer draws on experience with WTC

Charles Thornton will give a seminar on the ongoing work at the World Trade Center at 4 p.m. Thursday, Oct. 4, in 222 Bowen Hall.

When Charles Thornton teaches Princeton engineering students how to build tall buildings, a lot of his wisdom comes from having seen many that fell down.

Thornton, a visiting lecturer who teaches a required senior-level course for undergraduate civil engineering majors, is chairman and managing principal of the Thornton-Tomasetti Group Inc., a 500-person engineering firm that has built some of the biggest buildings and analyzed some of the worst structural failures in the world.

Undergraduates this semester are gaining insight from a grim addition to their syllabus as Thornton relates to them the experience of leading the engineering assessment of the damage that resulted from the Sept. 11 terrorist attacks in New York and Washington.

"This is going to be on the minds of everybody," said Thornton. "It's going to affect how we design tall buildings. It's going to affect the public's perception of tall buildings."

Students in the class work in small groups to solve real-life engineering problems from a 60-story building that Thornton-Tomasetti is currently building. "So we will now be addressing these issues from the trade center in the design of this building," said Thornton.

There are many steps that could be taken to make buildings more resistant to such assaults, he said. One approach might be to encase steel columns in concrete, as was done in the 1950s, instead of using the spray-on fireproofing materials currently in use. "But it's a lot more expensive," he said.

It's important to note, he said, that, despite severe damage, the trade towers survived the impacts of the aircraft as they were supposed to; it was the intense fire that caused the collapse.

Thornton has seen the plusses and minuses of engineering tradeoffs for many years. His firm performed the engineering for the tallest building in the world, the Petronas Towers in Kuala Lumpur, Malaysia, and has built many other buildings and sports and entertainment complexes around the world. One-third of the company's operations, however, are devoted to disaster response and the analysis of failed buildings.

"I personally investigated the collapse of the Hartford Coliseum in 1978," Thornton recalled. "If it had collapsed six hours earlier, 7,000 people would have died."

By the afternoon of Sept. 11, New York City had hired Thornton's firm to lead the engineering effort in Lower Manhattan. The work is proceeding along two main lines. First, engineers from Thornton-Tomasetti and from other New York firms that are working in coordination with the company are assessing the structural integrity of buildings in the surrounding area. Second, engineers are on the site 24 hours a day to consult with the construction companies that are removing debris.

"We are telling them where they can and cannot put cranes, bulldozers, forklifts -- in some cases they are moving around on existing structures, not on streets," Thornton said.

This kind of engineering is very different from the calm, collected analysis that goes into designing a building. "Protecting police, fire and rescue workers is paramount," he said. "So I would say the pressure on any one of these engineers to call it right and not jeopardize any of the rescue workers is probably the biggest burden."

"It's sometimes easy to just be safe and conservative, but if there's a need to get people into a building to see if there are any survivors, then you're on the edge," he continued. "You're basically calling shots and hoping you're right. Even if you have (a building's structural) drawings, you can still make a mistake. That weighs heavily on the psyche of all these people. And they're tired and they are breathing smoke and dust."

As Thornton relates these observations to his class, it can only add to his goal of showing students how engineers work and tackle problems. "It's a great course to give them a feeling for what structural engineers and architects really do," he said.

Contact: Marilyn Marks (609) 258-3601

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