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At the time of their completion, the 110-story-tall Twin Towers, including the original 1 World Trade Center (the North Tower) at 1,368 feet (417 m), and 2 World Trade Center (the South Tower) at 1,362 feet (415.1 m), were the tallest buildings in the world; they were also the tallest twin skyscrapers in the world until 1996, when the Petronas ...
- 1 WTC: 1,728 feet (526.7 m)
- 99 (North Tower); 95 (South Tower)
- Overview
- 1. A little-known Japanese-American architect was chosen to design the World Trade Center.
- 2. The Empire State Building’s owner helped mount opposition to the World Trade Center project.
- 3. To build a deep foundation that wouldn't be flooded by the nearby Hudson River, engineers used an innovative ‘slurry trench’ method.
- 4. The twin towers’ design provided stability from the outside in—without a forest of interior support columns.
- 5. Though made of super-strong steel, the towers were designed to sway in high winds.
- 6. To hoist hundreds of thousands of pounds of steel to dizzying heights, builders imported 'kangaroo' cranes.
- 7. The innovative elevator design drew inspiration from New York City's subway system.
- 8. Using its exemption from local building codes, the Port Authority halved the number of stairwells in the towers.
- HISTORY Vault: 9/11 Documentaries
To build the twin towers, architects and engineers employed innovative—and sometimes unproven—techniques and technology.
In early 1962, when the Port Authority of New York and New Jersey officially authorized a plan to build the World Trade Center in Lower Manhattan, it came just months after President John F. Kennedy announced the U.S. goal of sending astronauts to the moon. The vision for the seven-building complex—which would cost an estimated $470 million (more than $4 billion in today’s dollars) and include the two tallest buildings in the world—embodied that same brand of American optimism and ambition.
Born into a poor family of Japanese immigrants in Seattle, Washington, Minoru Yamasaki put himself through college working in fish canneries in Alaska. He started his career in New York, working for the firm that built the Empire State Building, and rose to helm his own firm in Detroit. By 1962, when Yamasaki applied to design the World Trade Center, he had completed work on a single high-rise building: Detroit’s Michigan Consolidated Gas tower, which had just 30 stories.
The Port Authority chose Yamasaki based on his proposal to design a vast trade center that still had the intimate, human-focused qualities of his other designs. Tasked with building the world’s tallest building, Yamasaki settled on a design of two towers and five other buildings that would together comprise some 15 million square feet of office space.
Perhaps motivated by self-interest as well as concern, a group of leading New York City real estate developers (unsuccessfully) challenged the Port Authority to scale down its proposal for the World Trade Center beginning in 1964. Led by Lawrence Wien, an owner of the Empire State Building, the Committee for a Reasonable World Trade Center joined a...
Constructing what was then the tallest building in the world posed one of the most challenging foundation projects ever faced on the island of Manhattan. The chosen site for the project was built on landfill that had gradually extended the west side of Lower Manhattan into the Hudson some 700 feet over the centuries. Building the foundation of the twin towers required digging 70 feet to the bedrock and excavating more than 1 million cubic yards of dirt.
To avoid flooding the site, workers dug a 3,500-foot-long, three-foot-wide trench around the perimeter of the site (comprised of more than 150 22-foot-long sections) and filled it with a slurry made from water and bentonite, an absorbent type of clay. Because the slurry was denser than the dirt that surrounded it, it prevented the dirt from filling the trench. Steel cages some seven stories high and weighing 25 tons each were then lowered inside the trench panels and concrete poured around it, forcing the lighter slurry up and out. The completed foundation was commonly known as “the bathtub”—though it was a tub that kept water out, and not in.
Traditional skyscrapers owed their stability to a system of large vertical columns running through each floor at intervals of 15-30 feet, with the exterior walls providing little support on their own. But in order to open up the vast swaths of office space called for in the planned twin towers, engineers put the bulk of the buildings’ strength outs...
The builders of the World Trade Center put extensive research into the effect of wind on the towers, commissioning one of the earliest wind tunnel studies for a skyscraper and performing perceptual tests disguised as eye exams on unsuspecting subjects to figure how much the building could sway in high winds without people noticing. To ultimately mi...
New York City, circa 1970: view from the Hudson River of the first tower of the World Trade Center under construction, with 'kangaroo' cranes.
In all, workers used some 200,000 tons of steel to construct the twin towers of the World Trade Center. But getting that steel to the top of the building during construction posed a thorny challenge, since the towers’ planned height topped even the world’s tallest cranes at the time. So engineers turned to an Australian-designed, self-contained crane nicknamed the “kangaroo crane” that used heavy-duty hydraulics to “jump” upward as many as three floors at a time as the towers rose.
With 110 stories in each tower, engineers faced the challenge of designing an elevator system that wouldn’t eat up a gigantic share of the available space inside the building. Their solution mimicked the city’s express and local subway system: They split the building into three zones, each served by an express elevator. People would get off at one ...
In addition to the elevators, the decision to place the building’s staircases in the center of each tower was also designed to maximize open office space. At the time the World Trade Center was built, city building codes required six staircases for buildings of the towers’ height. But as an interstate agency, the Port Authority was exempt from such...
Explore this collection of extraordinary documentary films about one of the most challenging days in U.S. history.
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- Sarah Pruitt
- 2 min
Dec 3, 2009 · The attacks on the towers on 9/11 destroyed lives and radically altered the skyline of New York City, destroying the twin columns of glass and steel that over the years had come to embody the...
Due to the ingenuity of architects and engineers who developed new construction methods to build the 110-story towers, the Twin Towers climbed above lower Manhattan’s existing skyline and loomed over New York City.
By 1964, when the intended scale of the scheme had been made public with plans for twin 110-story towers, private real estate developers and members of the Real Estate Board of New York also expressed concerns about the World Trade Center's much-"subsidized" office space going on the open market, competing with the many vacancies in the private ...
- 1 WTC: 1,728 feet (526.7 m)
- 1 and 2 WTC: 99 each
Feb 26, 1993 · Due to the ingenuity of architects and engineers who developed new construction methods to build the 110-story towers, the Twin Towers climbed above lower Manhattan’s existing skyline and loomed over New York City.
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Sep 11, 2011 · The Twin Towers were the centerpieces of the World Trade Center complex. At 110 stories each, 1 WTC (North Tower) and 2 WTC (South Tower) provided nearly 10 million square feet of office space for about 35,000 people and 430 companies.
