Engineers change approach to skyscraper design after Sept. 11 terrorist attacks

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Posted 8:45AM on Thursday, May 2, 2002

NEW YORK - The Sept. 11 terrorist attacks have changed the process of designing skyscrapers by requiring anticipation of the unknown, says a structural engineer with the firm that built the World Trade Center. Engineers, who are used to working with hard data, now must imagine scenarios without facts and figures, said William Faschan, of Leslie E. Roberston Associates, the firm that built the World Trade Center. "When it comes to earthquakes and wind, there's a whole history in building for that," Faschan said. "When it comes to what's a terrorist going to do, who are they, there are just so many unknowns out there." Faschan spoke to a group of structural engineers in New York on Wednesday, shortly after the Federal Emergency Management Agency and the American Society of Civil Engineers released a new report on the trade center collapse. The study determined that the twin towers could have survived the impact of the hijacked 767s. They fell victim to the intense blaze that caused their steel columns to soften and buckle. "This is not the end of the story -- there will now be a new set of research conducted by the National Institute of Standards and Technology that's just beginning," Faschan said. On Capitol Hill Wednesday, NIST Director Arden Bement said he will focus immediately on how to better protect buildings from intense fires like the one that brought down the twin towers. The agency will use the findings to recommend changes to building and fire codes. "It's critical that we understand better the relationship between fire and structural collapse," Bement told the House Science Committee. Of particular interest to investigators is 7 World Trade Center, which is believed to have sustained little structural damage. It was the first fireproofed steel structure to collapse due to fire alone. The two-year, $16 million investigation by NIST is also expected to study ways to "harden" exit stairways to make them less susceptible to impact and to space them out so one blow might not render them all impassable. Such designs might have allowed occupants on the floors above where the planes hit to have escaped. ------ On the Net: House committee: http://www.house.gov/science FEMA: http://www.fema.gov