Our heartfelt sympathy goes out to the September 11 murder victims, and to any of you who have lost relatives, colleagues, or other friends. We send our thanks, too, to the many caring strangers from around the world who have been sending their good wishes to us in and around New York.
New York, N.Y., September 17, 2001 -- Watching in amazement and horror as the World Trade Center disaster unfolded, many of us had to ask, "How could these majestic buildings be brought down so suddenly?"Part of the answer may lie in the buildings' unusual construction, which is very different from the steel frame construction of most high-rise buildings. As SNYCH's John Tauranac explains in his Essential New York, (Holt, Rinehart and Winston, 1979) the "solid, monolithic look" of the 110-story towers actually concealed a "technological breakthrough" in construction:
"If you had witnessed the construction of the towers, you would not have seen the traditional, twentieth-century steel frame. Instead you would have seen the cores of the buildings rising first (they now house elevator shafts but then housed derricks)."Just one step behind the cores came the walls, erected in prefabricated panels, the columns and spandrels welded together in modules two windows wide by two or three high.
"Once the walls and cores had climbed a few stories, they were linked by prefabricated 13-by-60-foot sections of floor framing. Each section consisted of the plenum between floors and ceilings (the conduits were added later),as well as lengthwise steel trusses for bracing. Crossbeams traverse the towers at every other floor.
"The result of this innovative building system is a variation on a load-bearing wall, with unobstructed 60-foot spaces from the elevator banks to the outside walls."
Each of the towers, in other words, was held up by its reinforced concrete core and the world's strongest curtain walls. Without the usual steel skeleton, the open floors allowed unprecedented space and flexibility. Between them, the two 1,350-foot-high towers provided 7.9 million square feet of rentable floor space, roughly the equivalent of fifty city blocks.After the attacks, the fierce heat of burning jet fuel, plus direct damage from the planes' impact, would have weakened the support for the upper floors to the point of failure. The reinforced concrete core helped keep the buildings standing for more than an hour after the impact, undoubtedly saving thousands of lives. Once the upper section fell, however, the impact produced the rapid, top-down progressive collapse we all witnessed.
Despite the devastating climax, it seems hard to fault the builders for their choice of structural system. No buildings the size of the WTC could withstand the heat from such an inferno; the amazing thing was that they survived the initial impact and then remained standing for as long as they did -- and indeed, a traditionally framed structure might have fallen in an even more catastrophic, sideways fashion, spreading devastation even further through the area.
When the buildings were conceived nearly forty years ago, John F. Kennedy was in the White House and the Beatles, the Apollo Program, and Woodstock -- among other things -- still lay in the future. Who among us, then, ever expected to see the kind of savage hatred that was unleashed on our city last week? As one of the building's engineers said in a recent interview, "This was designed in a period when that kind of terrorist activity was not anticipated by civilized designers."
To many, the World Trade Center stood as a symbol of New York's and America's commercial and financial power. But when it was built, the architect, Minoru Yamasaki, also hoped it would be, as he put it --
"a living representation of man's belief in humanity, his need for individual dignity, his belief in the cooperation of men, and through this cooperation his ability to find greatness."Though the buildings are gone, the ideals they stood for can -- and must -- live on.
Return to Society for New York City History Home Page