From the issue dated December 7, 2001
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Scholars Work to Rebuild the World Trade Center VirtuallyComputer models could help minimize destruction from earthquakes or terrorist attacksBy JEFFREY R. YOUNG A few days after the terrorist attacks on the World Trade Center,
He has been examining countless pieces of steel taken from Ground Zero as part of an effort to build a detailed computer simulation of the towers' last moments. Once the computer model is finished, Mr. Astaneh-Asl and his colleagues will virtually reenact the disaster in an effort to understand precisely how the planes brought the structures down, and whether skyscrapers can be built to withstand such attacks. His investigation -- supported by a $45,000 grant from the National Science Foundation -- is something like an autopsy of the landmark buildings. And it has already yielded important clues, he says. He and other researchers say that such computer-aided research projects could provide new insights into building design. 'Pancaking Collapse' What looks like a giant bite taken out of one piece of steel, for instance, might have been caused by one of the hijacked planes' engines slamming through the column, a hollow, rectangular, steel tube three feet wide and 18 inches deep. The fact that the piece is still partially intact suggests to Mr. Astaneh-Asl that it remained standing after impact. He says the buildings might have survived the plane crashes if the ensuing jet-fuel fires had not weakened the upper floors and started a "pancaking collapse." To support his theory, he cites the way the steel has been bent at several connection points that once joined the floors to the vertical columns. If the internal supporting columns had collapsed upon impact, he says, the connection points would show cracks, because the damage would have been done while the steel was cold. Instead, he describes the connections as being smoothly warped: "If you remember the Salvador Dalí paintings with the clocks that are kind of melted -- it's kind of like that. That could only happen if you get steel yellow hot or white hot -- perhaps around 2,000 degrees." "The buildings did well under circumstances," he says, arguing that the steel "was holding the load until the floors collapsed." He points out that the World Trade Center's ability to stand for about an hour after the initial impacts probably saved the lives of more than 20,000 people who escaped during that time. Mr. Astaneh-Asl has set up an office in Jersey City, at one of the two recycling facilities that are processing steel beams pulled from the wreckage of the towers. The facility is run by Hugo Neu Schnitzer East, a scrap company that donated the office space and is helping the professor in his work. He spends days at a time away from Berkeley, examining what he calls the "hills of steel." As of late last month, the recycling center had collected about 12,000 beams, according to Bob Kelman, senior vice president of the company. Mr. Astaneh-Asl has devised a classification system to group the various types of damage, and has enlisted the help of workers at the recycling center, training them to spot metal beams that might yield clues. Among the features he asks workers to look for are intense "fire burn" and any unusual bending patterns in the metal. Workers take digital photos of the steel that they process, he says, and save pieces that look unusual. Officials did not originally consider the steel useful to their investigations, and so at first it was consigned to be melted down without examination. In fact, the column with the bite out of it was being cut into pieces when Mr. Astaneh-Asl saw it and asked to save it. "The most important contribution of my career was to go to New York right after the attacks," he says. Like so many people who rushed to the scene, the researcher says he hoped he could do something to help. Visiting the site just after the attacks was "a really horrifying experience," he says. It looked "like a piece of video taken from Hiroshima documentaries." But his initial visit paid off: "It ended up making it possible for future researchers to have the steel saved." The Smithsonian Institution's National Museum of American History recently contacted Mr. Astaneh-Asl about acquiring key pieces of the twin towers for preservation. Only the Beginning Examining physical evidence from the site is only the beginning of his project. Next year, the professor plans to take a sabbatical from Berkeley to focus his attention on using computers to create a "full-fledged, realistic model of the whole World Trade Center -- including other buildings, not just the towers." "Then we'll bring the plane in -- to the computer model -- and hit the building with various scenarios." To create the model, Mr. Astaneh-Asl plans to work with David B. McCallen, director of the Center for Complex Distributed Systems at Lawrence Livermore National Laboratory. They have worked together in the past, most recently on a computer model showing the effects of earthquakes on San Francisco's Bay Bridge. The two researchers plan to use specific data from Mr. Astneh-Asl's on-site investigation, going so far as to incorporate details from individual steel beams into the computer model. Some of the beams have identification numbers stamped onto them, pinpointing where they were in the buildings. That information might let researchers who are reconstructing the catastrophe to work backward, from the damage done to the beams back to their original location. "It will get down to modeling the individual elements," says Mr. McCallen. The simulation will be designed, he says, to pre-sent the "complete collapse in excruciating detail." While computer models have become commonplace in engineering, Mr. McCallen says it is unusual for engineers to make such a detailed model of an actual collapse. But this model will show researchers how the World Trade Center's building materials reacted to extreme forces. "That makes the simulation more challenging and more difficult," he says. Testing Virtual Buildings The model will also allow researchers to test how various structural changes -- such as increasing the fire-resistant materials built into the floors -- might have helped prolong the survival of the towers and possibly save more lives. "Engineers in an earlier period would have built [physical] models and tested them," says Jeffrey K. Stine, a curator of engineering and environmental history at the American-history museum. "Here you're doing it virtually." Priscilla P. Nelson, director of the Division of Civil and Mechanical Systems at the National Science Foundation, says the World Trade Center simulation "could lead to the generation of new computer models that will really enhance our ability to understand structural response." That could help make new buildings safer in the event of earthquakes or terrorist attacks. Mr. Astaneh-Asl is not the only researcher working on computer models of the destroyed buildings. A team from the American Society of Civil Engineers that is assessing the terrorist damage in New York and at the Pentagon, outside Washington, plans to use computer simulation in its investigation, says W. Gene Corley, the team's leader, who is senior vice president of Construction Technology Laboratories, a materials-testing company in Skokie, Ill. "Definitely, computer modeling will be used by everyone who investigates it," he says. "Our fire people are modeling the fireball, because we want to know how much of the fuel was consumed" in the jet-fuel fire that raged after the second plane hit the World Trade Center. "We also are modeling how the fire developed and spread through the buildings." 'Just One Small Tool' Some engineers, however, question the usefulness of creating a finely detailed computer model of the attack on the twin towers. "The story of what took place there is not going to be revealed by some magic computer analysis," says Barry J. Goodno, a professor of structural engineering at the Georgia Institute of Technology who is a program coordinator for the MidAmerica Earthquake Center. "Computer simulation is just one small tool, but I don't see it as a key component at all." Mr. Goodno, who has been to Ground Zero as part of another team assessing the damage there, says the most important task is old-fashioned, hands-on study of the debris, which provides the raw data without which the computer models would be useless. Even before September 11, Mr. Astaneh-Asl had been working on a new design to help protect buildings from terrorist attacks -- though he says he was thinking of weapons like car bombs or shoulder-launched missiles rather than airplanes. He says his proposed design -- which involves bolting concrete slabs to sheer, steel-plated exterior walls -- might keep the fuel-filled wings of a plane from getting inside a building in the event of a similar attack. Mr. Goodno, however, argues against trying to devise elaborate ways to make buildings terrorist-proof. "We can't afford to make buildings blast-proof or earthquake-proof," he says. He believes that engineers should focus on helping buildings stand long enough to allow occupants to escape. "The most important part of the building," he points out, "is the occupants." Extreme Events Mr. McCallen, of Lawrence Livermore, hopes that a computer model will help to determine whether fortifying skyscrapers against attacks is economically feasible. "Does it make sense," he asks, to plan for extreme events? Or "is it so far out there, and should we just worry about not letting an airliner hit one of these buildings?" One way or another, Mr. Astaneh-Asl predicts, people will continue to build skyscrapers, and continue to improve their designs. "There's no question whether skyscrapers will be there or not," he says. "The human spirit is much, much stronger than these things. For 10,000 years, structural engineer-ing was the place where humans showed their spirit of conquering. And by building these tall buildings, you conquer something more valuable than just making space for living." http://chronicle.com Section: Information Technology Page: A27
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Copyright © 2001 by The Chronicle of Higher Education