When I was still an architecture student, a teacher told me, "We learn more from buildings that fall down than from buildings that stand up." What he meant was that construction is as much the result of experience as of theory. Although structural design follows established formulas, the actual performance of a building is complicated by the passage of time, the behavior of users, the natural elements—and unnatural events. All are difficult to simulate. Only selected building components are tested in furnaces for fire resistance, for example, or analyzed on vibrating platforms for earthquake resistance. Similarly, only mock-ups of facades are pressure-sprayed to test their ability to keep out driving rain. Buildings, unlike cars, can't be crash-tested.
The first investigative report of the World Trade Center collapse, by the Federal Emergency Management Agency and the American Society of Civil Engineers, was released last May. Disappointingly, the six-month inquiry was inconclusive. It did not reveal any design deficiencies, or any "specific structural features that would be regarded as substandard," nor did it make any definite recommendations to safeguard tall buildings. Such recommendations will come. The National Institute of Standards and Technology is beginning a two-year, $16 million study of the twin-tower collapse that will address three pressing questions: whether current testing standards and building codes are adequate to resist catastrophic fires; whether building codes sufficiently take into account what engineers call progressive collapse, the chain reaction that leads to extremely rapid collapse (in the case of the World Trade Center towers, about 10 seconds); and how existing buildings can be made less vulnerable to terrorist attack.
