When the World Trade Center Twin Towers opened to the public in 1973, they were the tallest buildings in the world. Even before they became iconic features of the New York skyline, they reflected America’s ambition, innovation, and technological prowess.
The breathtaking statistics of the towers amply illustrate this ambition: they soared a quarter of a mile into the sky. They contained 15 miles of elevator shafts and nearly 44,000 windows, which took 20 days to wash. From the South Tower Observation Deck on a clear day, visitors could see 45 miles. The Trade Center complex was so big it had its own zip code.
But some of the same awe-inspiring architectural elements may also have contributed to the fateful morning tragedy of September 11, 2001. Calling the project “the architecture of power,” Ada Louise Huxtable, architecture critic for The New York Times offered a premonitory warning when building the towers in 1966: “Shopping center towers could be the start of a new era of skyscrapers or the tallest tombstones in the world,” she wrote.
These facts and figures offer some perspective on the technical and architectural feats that made the Twin Towers possible.
READ MORE: The construction of the World Trade Center: 8 surprising facts
Construction time: 14 years (from formal proposal to completion)
David Rockefeller, grandson of the first American billionaire, had the idea of building a World Trade Center in the port district of Lower Manhattan in the 1950s. In 1960, leaders of cities, states and businesses gathered. are joined to us.
The New York and New Jersey Port Authority presented a formal proposal to the governors of both states in 1961, then hired an architect and cleared 14 blocks of the city’s historic grid. They innovated in 1966.
Two or three stories came up every week. The towers used 200,000 tons of steel and, according to the 9/11 Memorial & Museum, enough concrete to build a sidewalk between New York and Washington, DC.
The ambitious project overcame community opposition, design and construction setbacks, attempted sabotage by New York real estate rivals, and major engineering challenges to open in April 1973 when it was still under construction. The towers were completed in 1975.
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Number of architectural design projects: 105
After creating over 100 design ideas with various combinations of buildings, architect Minoru Yamasaki’s team settled on a seven-building complex with a centerpiece of two identical 110-story towers. The design of the towers featured a distinctive steel cage exterior made up of 59 precise, narrowly spaced thin steel columns on either side.
An architect’s model of the World Trade Center project, c. 1965.
Underwood Archives / Getty Images
Construction cost: over $ 1 billion
According to The New York Times, the cost of building the towers has soared to over $ 1 billion (over $ 5,000 billion today), well beyond its original budget of $ 280 million. Project managers faced cost overruns when performing safety, wind and fire tests. And engineers have adopted or created innovative construction techniques and new technologies to make towers lighter and taller.
Rental area: approximately one acre per floor
The innovative twin tower design, which placed a structural load on the exterior columns rather than the interior columns, facilitated homeowners’ desire for maximum rental space. With 10 million square feet of office space, more than Houston, Detroit or downtown Los Angeles had back then, according to The New York Times– the World Trade Center has been dubbed “a city within a city”.
Twin Towers foundation depth: 70 feet
To build towers this tall on landfills that had piled up in Lower Manhattan for centuries, the towers needed extremely strong foundations. So the engineers dug a huge rectangular seven-story hole in the loose soil to reach the bedrock.
Using a technique developed by Italian builders in the 1940s, the tower builders used slurry, a mud-like material lighter than soil, to dig a trench 70 feet deep and keep the surrounding soil from s ‘collapse when they poured concrete to form walls three feet thick, like a tight “tub”.
But it worked like an upside down tub. It did not hold water inside, but rather kept water from the Hudson River out and away from the Trade Center complex. On September 11, the crashing debris damaged the walls, but most of all they held up. If they hadn’t, engineers fear the Hudson River might have flooded the city’s subway system and drowned thousands of commuters.
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Additional land created by the construction of the WTC: 23 acres
The 1.2 million cubic meters of earth dug to build the “tub” was used to add 23 acres in Lower Manhattan, or about a quarter of the area of a planned community of parks, apartment buildings, of shops and restaurants nearby called Battery Park City which borders the Hudson River.
Views of the World Trade Center still under construction along the Manhattan skyline, taken from the Jersey Shore.
Bettmann / Contributor via Getty Images
Twin towers elevator speed: 1,600 feet per minute
The Twin Towers had 198 elevators operating within 15 miles of elevator shafts, and when they were installed, their motors were the largest in the world. The innovative design of the tower elevators mimicked the New York subway, with express and local transportation. This innovation reduced the space occupied by elevators, leaving more commendable floor space. On September 11, the tower elevator shafts became an efficient conduit for aircraft fuel and a fatal fire.
READ MORE: How the World Trade Center design cost lives on September 11
Wind speed the towers could withstand: 80 mph
Engineers concluded in wind tunnel tests in 1964 that the towers could withstand winds of 80 mph, the equivalent of a Category 1 hurricane. With this study, one of the first of its kind for a skyscraper , engineers tested how the towers’ innovative tubular structural design, which is lighter than traditional masonry construction, would withstand strong winds.
But they also realized that in winds from the port, the towers could sway up to 10 feet, making office space potentially difficult to rent.
The chief engineers therefore developed viscoelastic dampers as part of the structural design of the towers. According to the 9/11 Memorial & Museum, some 11,000 of these shock absorbers were installed in each tower, decreasing the sway to about 12 inches from side to side in windy weather.
Number of sprinklers in the towers: 3,700
Two months after the release of the hit film Imposing Hell, a three-alarm fire in the North Tower in 1975 raised concerns that the Twin Towers did not have sprinklers.
It was common for skyscrapers at the time, and the New York and New Jersey Port Authority, which owned the buildings, was exempt from the city’s fire safety codes. But in the face of pressure from state lawmakers and Center employees, Port Authority officials spent $ 45 million to install some 3,700 sprinklers in the two buildings during the 1980s.
But the sprinklers failed when they were needed most. On September 11, the attacking planes broke the water intake system on impact, so they did not function.
READ MORE: 9/11 Lost and Found: Items Left Behind
Height of the tightrope walker between the towers: 1350 feet
On the morning of August 7, 1974, French acrobat Philippe Petit walked over 130 feet between the Twin Towers on a wireframe about a quarter of a mile in the air. Thousands of commuters looked up, gasping in amazement.
Bursting with confidence in his 45-minute show, the tightrope walker lay down on the wire, knelt on one knee, spoke to the seagulls and teased the police who were waiting to arrest him. Using his 50-pound, 26-foot-long balancing pole, he traversed the tallest buildings in the world eight times before coming to a stop when it started to rain.
Originally criticized as a “white elephant,” the new towers struggled to attract tenants in the early years. Petit’s show, followed by a paratrooper jumping from the North Tower and a toy maker scaling the South Tower wall, began to turn the tide, making the towers more human and accessible to New Yorkers and to tourists.
READ MORE: When a French daredevil walked the tightrope between the Twin Towers
Shaking force when falling towers: similar to 2.1 and 2.3 earthquakes
On September 11, 2001, seismologists at 13 stations in five states, including the most distant in Lisbon, New Hampshire, 266 miles away, found that the collapse of the South Tower at 9:59 a.m. caused a tremor. comparable to that of a small earthquake recording 2.1 on the Richter scale. The measurements of the north tower collapsed half an hour later: 2.5 on the Richter scale.
