That was common for skyscrapers at the time, and the Port Authority of New York and New Jersey, which owned the buildings, was exempt from the city’s fire safety codes. Two months after the release of the blockbuster movie The Towering Inferno, a three-alarm blaze in the North Tower in 1975 raised concerns that the Twin Towers had no sprinklers. Number of sprinklers in the towers: 3,700 Some 11,000 of these shock absorbers were installed in each tower, diminishing the sway to about 12 inches side to side on windy days, according to the 9/11 Memorial & Museum. So the chief engineers developed viscoelastic dampers as part of the towers’ structural design. With this study, one of the first of its kind for a skyscraper, engineers tested how the towers’ innovative tubular structural design, lighter than the traditional masonry construction, would handle strong winds.īut they also realized that in the winds coming off the harbor, the towers could sway as much as 10 feet, making office space potentially tough to rent. winds, the equivalent of a category 1-force hurricane. Windspeed the towers could sustain: 80 m.p.h.Įngineers concluded in wind tunnel tests in 1964 that the towers could sustain a thrashing of 80-m.p.h. On 9/11, the tower’s elevator shafts became an efficient conduit for airplane fuel-and deadly fire. That innovation lessened the amount of space the elevators took, leaving more rentable floor space. The Twin Towers had 198 elevators operating inside 15 miles of elevator shafts, and when they were installed, their motors were the largest in the world. The towers’ innovative elevator design mimicked the New York City subway, with express and local conveyances. Twin Towers' elevator speed: 1,600 feet per minute Views of the World Trade Center still under construction along the Manhattan skyline, taken from New Jersey shore. The 1.2 million cubic yards of soil dug up to build the “bathtub” were used to add 23 acres to Lower Manhattan-about a quarter of the area of a planned community of parks, apartment buildings, stores and restaurants nearby called Battery Park City that lines the Hudson River. Extra land created by building the WTC: 23 acres If they hadn’t, engineers fear the Hudson River would have flooded the city’s subway system and drowned thousands of commuters. On 9/11, the crashing debris damaged the walls, but they mostly held up. It didn’t keep water in, but rather kept water from the Hudson River out-and away from the Trade Center complex. Using a technique developed by Italian builders in the 1940s, the towers’ builders used slurry, a mud-type material lighter than soil, to dig a 70-foot-deep trench and keep the surrounding soil from collapsing as they poured in concrete to form three-foot-thick walls, like a waterproof “bathtub.”īut it worked like a bathtub in reverse. So engineers dug a huge rectangular hole seven stories down into the soft soil to reach bedrock. To build such tall towers on landfill that had piled up onto Lower Manhattan for centuries, the towers needed exceedingly strong foundations. With 10 million square feet of office space-more than Houston, Detroit or downtown Los Angeles had at the time, according to The New York Times-the World Trade Center came to be dubbed “a city within a city.” Depth of the Twin Towers’ foundation: 70 feet The Twin Towers’ innovative design, which placed structural load on the outside columns rather than inside pillars, facilitated the owners’ desire for a maximum amount of rentable space. Rentable floor space: about one acre per floor These facts and figures offer some perspective on the engineering and architectural feats that made the Twin Towers possible. Calling the project “the architecture of power,” Ada Louise Huxtable, an architecture critic for The New York Times offered a prescient warning when the towers were going up in 1966: “The trade-center towers could be the start of a new skyscraper age or the biggest tombstones in the world,” she wrote. The Trade Center complex was so big, it had its own zip code.īut some of the same impressive architectural elements may have also helped worsen the tragedy on the fateful morning of September 11, 2001. From the South Tower observation deck on a clear day, visitors could see 45 miles. They contained 15 miles of elevator shafts and nearly 44,000 windows-which took 20 days to wash. The towers' eye-popping statistics amply illustrate that ambition: They rose a quarter-mile in the sky. Even before they became iconic features of the New York City skyline, they reflected America’s soaring ambition, innovation and technological prowess. When the World Trade Center’s Twin Towers opened to the public in 1973, they were the tallest buildings in the world.
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