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Since the collapse of the World Trade Center towers on 9/11/01, many of the structural engineers associated with the Salvadori Center have been helping to assess damage and planning for the return of the World Trade Center neighborhood to safety and livability.

One of the people involved is Dr. Charles Thornton, President of the Center's Board of Directors, who is also the Chairman of The Thornton - Tomasetti Group, Inc. This is the structural engineering firm that worked on what are currently the world's tallest buildings, the Petronas Towers in Kuala Lumpur, Malaysia. In a recent article in The New York Times about the World Trade Center collapse, Dr. Thornton said that even though engineers could design a fortress skyscraper, no one would pay to build it, and it would not be an appealing structure. Newer materials and techniques, not available when the World Trade Center was built, however, could have given people more time to get out. For example, while most stairways in high-rises are in the concrete cores of the building, the cores of the Petronas Towers are also pressurized to keep the smoke and fire out of the stairwells.

February 2002 edition of Why Buildings Fall Down.

Dr. Thornton also said that tall buildings are less likely to topple than midsized buildings because these 50-story-plus structures have more redundancy built into them. But the Times article points out that tall buildings can be more tempting targets for attack.

Matthys Levy, a Salvadori Center board member who also works on the rescue and recovery efforts co-authored Why Buildings Fall Down, and other works with our founder Mario Salvadori. He is a Principal at Weidlinger Associates, a consulting firm that specializes in "blast mitigation," the design of federal and commercial buildings to withstand terrorist attacks. Based on his experiences as a structural engineer and on the situation at the World Trade Center site, he has written a new chapter of Why Buildings Fall Down for its next edition to be released in February 2002.

Ron Check, another Weidlinger engineer, also happens to be married to our Executive Director, Lorraine Whitman. Mr. Check volunteered to help out too. So did Nat Oppenheimer, a Salvadori board member and structural engineer, who taught as a volunteer with Dr. Salvadori in his last years. Mr. Oppenheimer is a Principal at Robert Silman Associates.

Below they discuss their experiences.

Salvadori Center: Why did you volunteer to help after the WTC collapse?

Ron Check: I was born and have lived in NYC all my life, so my roots run deep. I felt a strong need to contribute to the rescue and recovery effort. I was fortunate to be part of the Weidlinger Associates team of structural engineers involved in site safety evaluation at ground zero, assisting The Thornton Tomasetti Group which is the lead engineering firm.

Nat Oppenheimer: Like everyone else, I was looking for a way to pitch in. As a native New Yorker, I also felt a need to see the damage first-hand, so that I could really understand what had happened.

Ron Check on duty at the World Trade Center site.

SC: What were you asked to do there?

RC: Several things. I was involved in the efforts to provide supports (grillage) for the large cranes - some with capacity of 800 tons - being brought onto the site to remove the debris.

I reviewed the damage to the American Express building, WFC 3, checking the slab cracks and examining the steel tiebacks. The southeast corner of the building had been impacted by parts of the WTC towers. It looked as though a giant javelin (actually a large section of column) had pierced the façade of the building.

Lights were needed in the various subbasements in the northwest corner of WTC 6, in the garage. I was asked to evaluate the conditions there and determined that it was safe for electricians to work to the 5th subbasement. (The 6th and 7th subterranean levels were flooded.)

NO: I was part of a large team of volunteer engineers from firms all around the city. We were asked to provide assistance to the contractors. We have surveyed damaged buildings for stability and designed temporary shoring to support them, and also assessed the stability of the piles of debris. Because there is so much heavy equipment sitting on hollow sidewalks, we designed steel "bridge platforms" for the equipment to sit on.

SC: Did you feel that you were in danger, or that other workers could be endangering themselves?

RC: No. Everyone was very conscious of the delicateness of various operations. This led to a very conservative approach in all decision making and actions taken.

NO: We were assigned to work with of the four primary contractors on the site, and I never felt in danger under the contractor we worked with. There is no doubt that the site is a frenzy of activity (with the heavy equipment engaged in a lot of the activity), but the contractors were conscientious in their work.

World Trade Center under construction.

SC: How long do you think it will take before the area is habitable again?

RC: That's very hard to know. There are far too many factors involved in the clean-up to give a clear answer to that question.

NO: It's impossible to say. It depends on what you mean by habitable. Already much of the surrounding area is open and each day the site boundaries are moving in towards the center. It will take months, or a year, to clear the debris out of the plaza area and stabilize the "bathtub" that surrounds the site and prevents the Hudson River from flowing into the underground, or sub-grade, plaza area. Once that is done, it will take a few years before whatever is going to be built is built.

SC: What would have made the WTC safer?

RC: Due to the extreme heat generated by as much as 25,000 gallons of jet fuel (which burns at a temperature as high as 2000ºF), no realistically conventional design could have withstood this event.

NO: To be honest, I think it was a pretty safe structure. I know that doesn't comfort the families of the victims or people who work in tall buildings, but these buildings withstood an inconceivable impact and then stayed up long enough to get a large number of people to safety. Also, because they fell relatively straight down numerous other lives in the surrounding area were saved. A structure designed to withstand the most extreme load condition would be too expensive, too enclosed and too dull in appearance to ever be built. Clearly, lower buildings are not as likely a target, but would collapse just the same as big buildings.

We'd like to know what you think. Have you already begun discussing these issues in the classroom? How did you go about it? If not, do you expect to? How? You can email your responses to these questions and the article to thecenter@salvadori.org.