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One World Trade Center officially opens in New York City, on the site of the Twin Towers


One World Trade Center officially opens in Manhattan on November 3, 2014. The new tower, along with the rest of the World Trade Center complex, replaced the Twin Towers and surrounding complex, which were destroyed by terrorist attacks on September 11, 2001.

As the city and the nation reeled from the attacks, which set into motion the series of U.S-led military operations dubbed the War on Terror, it was decided that the Twin Towers should be replaced by new office buildings, parks, a museum, and a memorial to those who died. In 2002, after cleanup and recovery efforts had concluded, the Lower Manhattan Development Corporation announced a competition to find the chief architect of the new structure. Daniel Libeskind, a Polish-American architect then in charge of a studio in Berlin, won and became the site’s master planner. In reality, however, a number of people and entities, including then-Governor George Pataki, leaseholder Larry Silverstein, and the Port Authority of New York and New Jersey, wrestled over what would happen to the space commonly referred to as “Ground Zero.”

The initial plans for the site were steeped in post-9/11 patriotic sentiment. Libeskind designed an asymmetrical tower that evoked the Statue of Liberty and stood at the same height as the original World Trade Center, topped with a spire rising to 1,776 feet. Pataki dubbed it the “Freedom Tower,” a name which became commonplace but had largely faded from use by the time One World Trade Center opened.

In 2004, Silverstein’s preferred architect, David Childs, officially took over, with Libeskind staying on as the planner of the site. Childs’ “final” design, a symmetrical and more traditional tower that tapers into an octagon at its midway point and then back into a rectangular prism, was unveiled in 2005. The New York Police Department requested further alterations, most notably a windowless, solid concrete base. Meant to protect against truck bombs and other potential attacks, the base has was criticized as “a grotesque attempt to hide [the building’s] underlying paranoia” by New York Times architecture critic Nicolai Ourousoff.

Though its cornerstone was laid in 2004, construction on One World Trade did not begin until the summer of 2006. The slow pace of construction—the tower “topped off” in August 2012 and the spire was not installed until May 2013—was a frequent source of consternation for the building’s developers and the city. At the same time, it allowed space for the tower to become more than a reminder of what had been lost. As architecture critic Kurt Andersen put it, “The fact that it’s taken more than a decade to finish, I think —the gradualism—makes that sense of emblematic rebirth more acute and irresistible.”

Prior to the opening, media conglomerate Condé Nast announced that it would move its New York headquarters from Times Square to One World Trade Center, occupying floors 20 through 44. Its location and the legacy of the original World Trade Center made the tower a natural choice for many financial institutions, but the building’s developers made an effort to bring in a diverse group of tenants, including media and tech companies. Known for its floor-to-ceiling, 360 degree views of Manhattan, Long Island, New Jersey and New York Harbor, One World Trade is now one of the most notable features of the Manhattan skyline, a tribute to the buildings that preceded it but a 21st century New York phenomenon in its own right.

READ MORE: How Ground Zero Got Rebuilt


World Trade Center (2001–present)

The World Trade Center is a mostly completed complex of buildings in Lower Manhattan, New York City, U.S., replacing the original seven buildings on the same site that were destroyed in the September 11 attacks. The site is being rebuilt with up to six new skyscrapers, four of which have been completed a memorial and museum to those killed in the attacks the elevated Liberty Park adjacent to the site, containing the St. Nicholas Greek Orthodox Church and Vehicular Security Center and a transportation hub. [note 1] The 104-story One World Trade Center, the tallest building in the Western Hemisphere, is the lead building for the new complex.

  • 1 WTC: April 27, 2006 [1]
  • 2 WTC: 2008
  • 3 WTC: 2010
  • 4 WTC: January 2008
  • 5 WTC: 2011
  • 7 WTC: May 7, 2002 [2]
  • 1 WTC: November 3, 2014 [3][4]
  • 3 WTC: June 11, 2018 [5]
  • 4 WTC: November 13, 2013 [6]
  • 7 WTC: May 23, 2006 [7]
  • 1 WTC: November 3, 2014
  • 2 WTC: (est.)
  • 3 WTC: June 11, 2018
  • 4 WTC: November 13, 2013
  • 7 WTC: May 23, 2006
  • Transportation Hub: March 3, 2016 [14]
  • 1 WTC: 1,368 ft (417.0 m) [9][8]
  • 3 WTC: 1,079 ft (329 m) [10]
  • 4 WTC: 978 ft (298 m) [11]
  • 7 WTC: 741 ft (226 m) [12]
  • 1 WTC: 104 floors [9]
  • 3 WTC: 80 floors [13]
  • 4 WTC: 78 floors [11]
  • 7 WTC: 52 floors [12]
  • 1 WTC: 3,501,274 sq ft (325,279 m 2 ) [8][9]
  • 3 WTC: 2,232,984 sq ft (207,451 m 2 ) [10]
  • 4 WTC: 2,500,000 sq ft (232,258 m 2 ) [11]
  • 7 WTC: 1,681,118 sq ft (156,181 m 2 ) [12]

The buildings are among many created by the World Trade Centers Association. The original World Trade Center comprised the Twin Towers, which opened in 1973 and were the tallest buildings in the world at the time of their completion. They were destroyed on the morning of September 11, 2001, when al-Qaeda-affiliated hijackers flew two Boeing 767 jets into the complex in a coordinated act of terrorism. The attacks on the World Trade Center killed 2,753 people. The resulting collapse of the World Trade Center caused structural failure in the surrounding buildings as well. The process of cleaning up and recovery at the World Trade Center site took eight months, after which rebuilding of the site commenced.

After years of delay and controversy, reconstruction at the World Trade Center site started. The new complex includes One World Trade Center, 3 World Trade Center, 4 World Trade Center, 7 World Trade Center, and one other high-rise office building being planned at 2 World Trade Center. The new World Trade Center complex also includes a museum and memorial, and a transportation hub building that is similar in size to Grand Central Terminal. 7 World Trade Center opened on May 23, 2006, making it the first of five skyscrapers to have been completed in the World Trade Center complex. 4 World Trade Center, the first building completed as part of the site's master plan, opened on November 12, 2013. The National September 11 Memorial opened on September 11, 2011, while the Museum opened on May 21, 2014. One World Trade Center was opened on November 3, 2014. The World Trade Center Transportation Hub opened to the public on March 4, 2016, and 3 World Trade Center opened on June 11, 2018. 2 World Trade Center's full construction was placed on hold in 2009, with a new design announced in 2015.


After Sept. 11, Twin Towers Onscreen Are a Tribute and a Painful Reminder

Some movie and TV executives excised the towers from pre-9/11 works. Others let them stand. Either way, for many viewers, the melancholy endures.

It can happen abruptly, while flipping through reruns of “Friends” or rewatching a movie like “Armageddon” or “Working Girl”: a sight of the twin towers, dominating the New York skyline like steel sentinel s .

“I used to get so startled when I first saw them in repeats and old shows,” said Sally Regenhard , a skyscraper-safety advocate whose 28-year-old son, Christian, a New York probationary firefighter, died when the towers fell 18 years ago.

Although she still views the towers as “instruments of death,” she added, “I do get less startled now.”

Since the Sept. 11, 2001, attacks on the World Trade Center, filmmakers, television producers, Hollywood executives and even the curators at the National September 11 Memorial & Museum have pondered how best to deal with material showcasing the towers in opening montages (“The Sopranos,” “Sex and the City”) in scenes of computer-generated conflagration (“Armageddon,” “Independence Day”) or as a setting for romance (“Kissing Jessica Stein”) or affectionate satire (“The Simpsons”).

Of course, it’s not just the family members of those lost who are dismayed by images of the towers, which until that day had been a symbol of New York and its financial might. For just about anyone old enough to remember the attacks, these scenes are likely to evoke sorrow, even today.

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“It almost seems like it’s the biggest issue in American etiquette,” said the director Sam Raimi , who in 2002 confronted an unusual challenge: how to release a long-awaited blockbuster, “Spider-Man,” that featured an elaborate scene in which the hero foils the helicopter escape of bank robbers by trapping them in an enormous web stretching from the north tower to the south tower.

For Mr. Raimi and his associates, leaving in that scene was “unfathomable.”

“We didn’t think it was our right, in the middle of the summer after this terrible massacre, to show a scene of such heartbreak for so many,” he said. Mr. Raimi added that he was thinking about victims’ children going to see the movie for fun or as an escape. “I didn’t want to pull them back into the heart of that tragedy,” he said.

Mr. Raimi was not alone in excising the towers from film or video in the immediate aftermath of their collapse. Both “The Sopranos” and “Sex in the City” deleted them from their opening credits, starting in 2002. The directors of “Kissing Jessica Stein” and “People I Know,” whose films were on the verge of premiering when the attacks took place, delayed their releases so they could reshoot scenes that depicted the towers as indomitable landmarks.

The producers of “The Simpsons” also halted the rebroadcast of a 1997 episode featuring a tiny Homer racing across the wide Trade Center plaza (he was trying to make it to a restroom on the top floor of the north tower) as the skyscrapers loom above him.

But as time passes, even the worst wounds begin to heal. As glimpses of the pre-2001 towers began to conjure wistfulness and nostalgia more than horror and trauma, the “Simpsons” episode was put back into syndication. And this year, the original hand-drawn cel depicting Homer’s mad dash to relieve himself was welcomed by the 9/11 museum’s curator, Alexandra Drakakis, as a “hilarious and tender” donation.

“I know my heart hurts when I see them in old images,” said the director Bart Freundlich , who did not delete several shots of the towers from his 2001 film, “World Traveler,” starring Julianne Moore and Billy Crudup . “They don’t just represent something tragic but something marvelous about the city as well.”

Join Times theater reporter Michael Paulson in conversation with Lin-Manuel Miranda, catch a performance from Shakespeare in the Park and more as we explore signs of hope in a changed city. For a year, the “Offstage” series has followed theater through a shutdown. Now we’re looking at its rebound.

Thinking back nearly two decades, filmmakers like Jennifer Westfeldt , who was a writer and co-star of “Kissing Jessica Stein,” have not exactly second-guessed their editing decisions but looked back on them with the bittersweet benefit of time and distance.

Ms. Westfeldt debuted her movie at the Toronto International Film Festival on Sept. 10, 2001, just hours before the attacks. She recalled the joy she felt after her film, replete with gauzy, golden-hour shots of the towers, was applauded. A New Yorker, she awoke the next day to news of the attacks and spent the next 48 hours camped in front of a TV, crying and contacting loved ones.

Her movie had a second screening on Sept. 12, she said, and “the people who went basically reported back that there were audible gasps and sobs at those images.”

“It was just gut-wrenching,” she added. “All these images that were meant to be beautiful and romantic were now harrowing and triggering in the midst of a rom-com that was intended to make you laugh, not traumatize you.”

Ms. Westfeldt said she and her colleagues debated intensely about whether to leave in the Trade Center scenes and risk “inflicting more pain on people,” or remove them and possibly “erase or misrepresent history.” In the end, they chose to reshoot the scenes. She asks herself now whether the original scenes might have stood the test of time as the despair of losing the towers ebbed.

Michael Nozik , producer of the 2002 movie “People I Know,” starring Al Pacino, felt the same way. “We wanted to make sure we were not seen as exploitative and insensitive at a time when there was so much grief,” he said of the reshoot. Now, he said, “It’s nice to look at all the beautiful images of the Trade Center because it’s more like honoring them than the horror of recalling that event.”

Some directors, though, do not support altering a pre-9/11 picture based on post-9/11 sensibilities. Among them is Michael Bay , the maker of “Armageddon,” a 1998 summer disaster flick that shows one of the towers ablaze after a meteor strike.

“You can’t change history,” Mr. Bay said. “Art is art — it’s a form of expression.”

“Movies are shot, edited and finished for the world to see,” he continued. “They don’t get re-edited because history changes. If we go there, that means every movie must change. Every book, every short story, every painting of New York in the past 30 years. It would never end.”

Other film and TV makers say it comes down to timing — to asking yourself whether you’ve violated the rule of “too soon.”

The British director Paul Greengrass grappled with that question when he decided, in 2006, to make “United 93,” about the Sept. 11 plane that crashed in Pennsylvania after its passengers revolted against their hijackers. As the first commercial post-9/11 feature, it was assailed as distasteful before its release. But when it came out, it was critically acclaimed and saluted by the passengers’ loved ones for its verisimilitude and poignant “let’s roll” ending.

“When I see the towers now, I get a feeling of sadness and loss,” Mr. Greengrass said. But, “in a funny way,” he added, “I also see them as a beacon of what was and what can be.”

Jan Seidler Ramirez, the chief curator at the memorial museum, said her institution would not shy away from exhibiting both serious and silly images of the towers. Visitors, she said, can watch a nine-minute film that pays homage to the Trade Center’s role in “The Wiz,” “Home Alone 2” and various Superman movies, thrillers and crime dramas.

“I see it as a positive sign of civic healing for the towers to be reintroduced into the background of films and elsewhere,” Ms. Ramirez said, “or seen in postcards and comic books of that era.” She even has the campy “King Kong” 1976 movie poster on display, in which the towers serve as the title character’s last bastion against mankind’s helicopters and flamethrowers.

“For the kids who never saw them,” she added, “they now have a reference for how tall they were and the way they owned the skyline.”

Mary Fetchet, whose 24-year-old-son, Brad, died in the attacks, said, “Many people have understandably fond memories of the towers and the old skyline.”

“There has been healing,” said Ms. Fetchet, who helped found Voices of September 11th, an advocacy group for survivors. But she cautioned that “for a lot of people in our community, the images of the towers remain a very difficult and unpredictable trigger.”


New York's twin towers – the ɿiling cabinets' that became icons of America: a history of cities in 50 buildings, day 40

In the depths of the emotional underworld at Ground Zero, an eerie place of crushed fire engines on plinths and dramatically lit scorched steel columns, is a fascinating site of architectural archaeology.

Marching in a mute line around the exhibition halls of the 9/11 Memorial Museum stand the original foundation pads of New York’s iconic “twin towers”, their rusted steel plates still bolted firmly into the Manhattan bedrock. Across the hall, a grid of massive steel bolts emerges from the 20-metre-high slurry wall, the vast concrete barrier that was cast to keep out the waters of the Hudson River and which held firm when the towers collapsed on 11 September 2001, stopping the subway tunnels beneath from flooding.

Along with a few charred columns which loom like devil’s forks above the entrance to the museum, this is all that exists of the original World Trade Center. But perhaps even more so in their absence, the twin towers remain one of the most powerful symbols of New York City.

The towers’ windows were so narrow partly because Minoru Yamasaki was afraid of heights. Photograph: Chris Kasson/AP

Where the ungainly obelisk of SOM’s One World Trade Center now stands, surrounded by a motley collection of stubby slabs, once rose the two sleekest symbols of America’s unbridled capitalist ambition and technical prowess the identical twin kings of global finance, dressed in matching silver pinstripe suits.

Designed by Japanese-American architect Minoru Yamasaki, they were the tallest towers in the world when they were completed in 1974, standing as glistening beacons of structural innovation. They employed a radical framed tube structure to carry the load in their facades – thereby doing away with the need for columns inside, freeing up the interior for more office space (and requiring as little as half the material needed for conventional steel-framed construction).

The elevator system was revolutionary, too. Buildings so tall didn’t usually make much economic sense, given the amount of space that had to be given over to lift shafts at the lower floors, the taller you went. So the engineers devised a plan to divide each building into thirds, with elevator “sky lobbies” where people would transfer to local lifts to reach their required floors. The system saved 70% of the space that would have been used in a traditional lift shaft.

None of these innovations, however, turned out to be of much use when the buildings first opened – given that, at the time, there was precious little demand for such office space in Lower Manhattan at all. The Port Authority of New York and New Jersey – which developed the buildings at the behest of Chase Manhattan Bank’s chairman David Rockefeller – filled much of the north tower with its own offices, while the State of New York ended up occupying 50 floors of the south tower to stop the embarrassment of it standing empty.

Nor was the project received with much warmth by contemporary critics. Lewis Mumford compared the towers to a gigantic pair of filing cabinets, while others said they looked like the boxes that the Empire State Building and the Chrysler Building came in. Broadcasters raised concerns that the towers would interfere with television reception, while the bird lobby even protested that the buildings posed a grave hazard to migrating fowl.

The downtown Manhattan skyline, shown here from Liberty State Park in 1998, was utterly dominated by the twin towers. Photograph: Joseph Sohm/Visions of America/Corbis

The architectural community had hesitations about Yamasaki, too, many seeing his soft-edged modernism as too mannered and prissy. “He has developed a curiously unsettled style,” wrote New York Times critic Ada Louise Huxtable, “which involves decorative traceries of exotic extraction applied over structure or worked into it. His choice of delicate detail on massive construction as a means of reconciling modern structural scale to the human scale of the viewer is often more disturbing than reassuring”.

Huxtable took particular offence to the way his soaring metal columns branched into two to form gothic arches at the base of the towers: “Here we have the world’s daintiest architecture for the world’s biggest buildings,” she concluded.

Those who worked inside the towers didn’t really take to them either, with many complaining about the narrow windows. Often attributed to the need for all those denselypacked structural tubes of steel, their narrow width was also partly down to the fact that Yamasaki himself was afraid of heights, so didn’t like expansive panoramic windows at such altitude. He preferred the psychological sense of security provided by windows that were narrower than his own shoulder span, so he reduced their width even further than the structure demanded. Frustrating for the occupant, perhaps, but from the street, such narrow spacing of these great columns gave the towers the striking appearance of seamless blocks of solid metal.

Dedication ceremonies attract a standing-room-only crowd to the World Trade Center. Photograph: NY Daily News via Getty Images

The objections of New Yorkers to the imposition of these gleaming twin totems were not just aesthetic. Having first been commissioned in 1962, by the time the complex opened, the tide had long since turned against the top-down approach of razing existing streets to build towers perched atop barren podiums.

The 16-acre site where the World Trade Center was built had been a densely packed area of existing industries, small businesses and more than 100 residents known as Radio Row, of the kind that urban activist Jane Jacobs fought so passionately to save. Radio Row was bought up under eminent domain, residents were evicted, and the 14 irregular street blocks swept away to make way for Yamasaki’s abstract superblock. There, retail was hidden away in the depths of the podium, so as not to interfere with the clean white tabletop above – which became a plaza so windswept that it sometimes necessitated the use of ropes to cross it safely.

In his book, The Pentagon of Power, published in 1970, Mumford raged that the project stood as an “example of the purposeless giantism and technological exhibitionism that are now eviscerating the living tissue of every great city”. Indeed, by the time it was completed, the whole endeavour seemed decidedly rearguard. With the rise of the Landmarks Preservation Commission, Radio Row might well have qualified as one of New York’s historic districts, along with Greenwich Village, Soho and Brooklyn Heights. It is telling that, less than a decade later, Battery Park City (a development built on reclaimed land, using rubble from the World Trade Center excavations) made much of the fact that it would have “traditional” blocks and street frontages, like the rest of the city.

Since the entire complex was destroyed by the events of 9/11, the hated podium may have gone – but what has taken its place can scarcely be said to offer a much better example of urban design. The two waterfall voids, marking the footprints of the towers, may provide a spectacularly powerful memorial, but they are surrounded by the clumsy debris of security sheds, ventilation shafts and a gargantuan concrete bunker for screening vehicles.

Along with the 60-metre-high concrete base of what was once called the “Freedom Tower”, Yamasaki’s minimalist hymn has been replaced by a compromised landscape, representative less of freedom than political compromise and paranoia.


Strong Enough?

The twin towers were built between 1966 and 1973. No building constructed at that time would have been able to withstand the impact of the terrorist attacks in 2001. We can, however, learn from the collapse of the skyscrapers and take steps to construct safer buildings and minimize the number of casualties in future disasters.

When the twin towers were constructed, the builders were granted some exemptions from New York's building codes. The exemptions allowed the builders to use lightweight materials so the skyscrapers could achieve great heights. According to Charles Harris, author of "Engineering Ethics: Concepts and Cases," fewer people would have died on 9/11 if the twin towers had used the type of fireproofing required by older building codes.  

Others say the architectural design actually saved lives. These skyscrapers were designed with redundancies—anticipating that a small plane could accidentally penetrate the skyscraper skin and the building would not fall from that type of accident.

Both buildings withstood the immediate impact of the two large aircraft bound for the West Coast on 9/11. The north tower was hit at 8:46 a.m. ET, between floors 94 and 98—it did not collapse until 10:29 a.m., which gave most people one hour and 43 minutes to evacuate.  Even the south tower was able to stand for a remarkable 56 minutes after being hit at 9:03 a.m. ET. The second jet hit the south tower on lower floors, between floors 78 and 84, which structurally compromised the skyscraper earlier than the north tower. Most of the south tower occupants, however, began evacuating when the north tower was hit.

The towers could not have been designed any better or stronger. Nobody anticipated the deliberate actions of an aircraft filled with thousands of gallons of jet fuel.


World Trade Center Plaza Pop Culture

The twin towers were not the highest skyscrapers in America—the 1973 Willis Tower in Chicago took that honor—but they were taller than the Empire State Building and soon became the focus of stunts and other pop culture phenomenons.

On August 7, 1974, Philippe Petit used a bow and arrow to assemble a steel cable between the two towers and then he walked across the tightrope. Other daredevil stunts included parachuting from the top and scaling the exterior facade from the ground.

In the 1976 remake of the classic film, King Kong (originally released in 1933), the giant ape's New York antics are relocated to Lower Manhattan. Instead of the original Empire State Building feat, Kong climbs from one tower of the Trade Center and leaps to the other before his inevitable fall.

The Sphere, a 25-foot bronze sculpture by German artist Fritz Koenig (1924-2017), commissioned in 1966, stood on the plaza between the twin towers from 1971 until the day the towers fell. (Damaged but basically intact, the 25-ton sculpture was moved to Battery Park as a memorial and symbol of American persistence. In 2017, the sculpture was moved to Liberty Park overlooking the 9/11 Memorial Plaza.)


How was the construction of the World Trade Center unique?

Long before the World Trade Center became synonymous with the most damaging terrorist attack in U.S. history, it was a symbol of engineering brilliance. Upon its completion in 1973, the two towers that rose from the 16-acre (64749.7-square-meter) complex consisting of seven different buildings in lower Manhattan were the tallest structures in the world. But the construction of such mammoth structures had its challenges.

The first major challenge was the building site itself. The location selected for the project, on Manhattan's Lower West Side, had been built upon generations of landfill that had actually grown and compacted on itself so much that it had extended the Lower West Side of Manhattan into the Hudson River. To reach a solid base of bedrock, workers had to dig down 70 feet (21.3 meters). But because of the proximity of the river, a barrier needed to be created that would keep the excavated section of the city from filling with water as fast as the earth was removed.

The answer was something that became known as the slurry trench method. A trench dug deep in the ground was filled with a slurry mixture made from water and an expanding clay known as bentonite. This slurry was denser than the surrounding dirt, so it kept the ditch from caving in. Once filled with the mixture, a steel cage was dropped in that weighed 25 tons and stretched to a height of seven stories. Concrete was then poured into the trench. As the concrete was heavier than the slurry, it forced the clay mixture out and hardened around the cage, making a section of underground wall. Workers then moved on to the next section. When the wall was complete, forming what became known as the "bathtub," the rest of the earth was removed from inside it without danger of flooding the newly opened space.

Another concern unique to the construction of the World Trade Center was the fact that the PATH commuter rail line ran directly through the center of the construction site. Instead of interrupting service, engineers designed a protective cradle for the underground line and as a result, the train ran throughout the entire project, carrying 130,000 passengers a day [source: 911veritas].

How Was The World Trade Center Unique?

There were two main factors that greatly distinguished the two main towers of the World Trade Center from anything that had been built before them: their walls and their elevators.

Prior to the construction of the Twin Towers, skyscrapers were designed to support themselves through large internal columns spaced about 30 feet (9 meters) apart, which interrupted the flow of interior space. For this project however, the engineers came up with a different solution -- the exterior walls themselves would support the bulk of the structure, and they would get a boost from one single column of beams in the center.

This allowed for a much more open plan on every floor of the building, which not only had aesthetic value but had financial worth as well -- the more floor space, the higher the rent the buildings' owners could collect.

Adding to the creation of open floor plans was the design of the elevators. A classic problem in skyscrapers is that as buildings grow taller, the number of residents increases. With more residents, more elevator shafts are needed. But the more elevator shafts there are, the less floor space there is for tenants.

This issue was solved in the construction of the twin towers through the use of express and local elevators. In much the same way the New York City subway system worked, express elevators would take passengers to "sky lobbies" placed on various floors throughout the building where they would then disembark and switch to local elevators to get to their required floor. The use of this system cut the number of required elevator shafts in half, thus preserving valuable floor space.

Not only was the construction of the World Trade Center unique, but the tools used to construct it were as well. To erect the tallest building in the world, "kangaroo cranes" were brought over from Australia. These mighty building machines could raise themselves up through the use of heavy-duty hydraulics, in effect growing with the building itself. The building of the Twin Towers marks the first time such cranes were used in America .

World Trade Center Design and Materials

The design of the Twin Towers is often called a "tube within a tube," referring to the fact that all of the weight of the building was supported by the external walls and an internal column. Previously, the exterior walls of a skyscraper were called curtain walls -- they weren't relied upon for strength, so it wasn't imperative that super-sturdy materials were used for them.

But for towers one and two, the external walls would not only bear the weight of the interior floors, but they would also have to withstand tremendous pressure from the wind. Because the external "tube" of each tower was perforated with openings for windows, the entire web of steel could shift in strong winds, transferring the load from the windward side to the leeward side of the buildings through something known as Vierendeel action [source: FEMA].

For the columns that comprised the walls, a mixture of 12 different types of steel with yield points between 42,000 pound per square inch (psi) and 100,000 psi were used, while the interior columns consisted of a steel known as A36, a designation which meant it had a yield strength of 36,000 psi. The thickness of these columns also varied -- from as thin as 0.25 inch (6.35 millimeters) at the top of the building to as thick as 4 inches (10.16 centimeters) at the base [source: FEMA]. In all, 200,000 tons of super-strong steel (which had just recently become available in 1968) were used to create the two towers [source: Gayle].

Just inside the walls, at approximately 10,000 locations throughout each tower, visco elastic dampers were installed [source: FEMA]. These were basically large shock absorbers that could bend with wind pressure and then return to their original form. Because the towers were designed to sway and adjust in the wind, these dampers helped reduce the impact of this movement on occupants. It was the first time this technology had ever been used in a high-rise [source: FEMA].

The floors that flowed between the supporting walls and interior columns were made from 0.5 inch (1.27 centimeter) thick steel slabs covered in 4 inches (10.2 centimeters) of lightweight concrete.

Overall, 425,000 cubic yards (324935.8 cubic meters) of concrete were poured, 43,600 windows were installed, 12,000 miles (19312.1 kilometers) of electrical cables were laid and 198 miles (318.6 kilometers)of heating ducts were installed [source: Ross] to create the two majestic towers that helped define Manhattan's skyline for 30 years.


A Look at the New One World Trade Center

Despite a decade of planning, the recent appearance of the new World Trade Center tower in the skyline of New York has been startling for many reasons, not the least of which being that the Port Authority of New York and New Jersey, the maker of bridges and tunnels and a few large buildings on historically less controversial sites, has managed to complete its construction (almost). This is a big accomplishment, even if you set aside all of the extraordinary considerations of this particular site and just consider Hudson River politics: imagine trying to get the respective governors of New York and New Jersey to agree on wallpaper, much less the western hemisphere’s largest office building (3 million square feet, to be exact), which is connected to many of the city’s subway lines as well as the Port Authority’s own trans-Hudson railway, commonly known as PATH.

There have been several visions for One World Trade Center, as it is formally known, beginning with Daniel Libeskind’s master plan, in 2003, when it was still referred to as the Freedom Tower, and then a controversial redesign by David Childs of Skidmore, Owings & Merrill—a redesign that for the most part survived yet another redesign, in 2005, after the New York Police Department weighed in and suggested the glass tower be further modified for safety. Since 2008 New Yorkers have seen an erector set–like spectacle when they look to the bottom of Manhattan Island: concrete follows the ascension of steel, at the pace of a floor a week.

But in these past few months, people in New York and nearby are at last getting a glimpse of what will be (by early 2014), and what is taking shape is a kind of classical obelisk, a monumental building. As little as five years ago, One World Trade Center was beginning to seem like a nearly $3.2 billion project to develop millions of square feet of office space that would not rent. (The Wall Street Journal reported in January that the tower and its escalating costs earned the distinction of being the world’s most expensive building.) Suddenly, though, 1 WTC is filling up. (Condé Nast, *AD’*s parent company, is renting 1.2 million square feet.) Thanks in part to the tax breaks offered post­–9/11, lower Manhattan is hot, with new residential buildings, new parks, new restaurants. And it’s not just hot in real-estate terms—it’s also the neighborhood with the highest number of newborns in New York City.

Almost forgotten in the midst of all this is the fact that the building that has emerged is one of the safest, technologically advanced, and environmentally sensitive in the world. “It has a concrete core, with very thick concrete walls,” says Eduardo del Valle, a design consultant for the Port Authority, which took control of the project in 2006. (Del Valle has a personal connection to the building—his first job as an architect was in an office on the 86th floor in the old World Trade Center’s south tower.) The three-foot concrete slabs are designed to withstand high winds and earthquakes there’s also a rocklike anchor, referred to as the building’s “podium,” constructed to withstand other things. “The podium has some hefty blast-resistant walls at the base,” says del Valle. There are state-of-the-art fire-suppression systems, specially protected elevators (70 in total), and a separate, dedicated stairway for fire and safety personnel. “I can tell you that it may not be the tallest building in the world, but it is certainly the safest,” says del Valle.

It will also be one of the world’s greenest. Much of the materials used in its construction come from postindustrial recycled materials, and more than three-quarters of its waste will be recycled. Typically, glass walls are designed with iron in them, for structural stability, but the iron has been reduced here, to increase visibility and to allow as much daylight in as possible, reducing the need for electric illumination. “This glass will be clearer than the old World Trade Center’s,” del Valle says. “Compared to an older skyscraper, you will definitely see a clearer view.” There are also rainwater-collecting tanks that will help cool the tower and irrigate landscaping such innovations will reduce water consumption by about 30 percent beyond what is saved in a typical water-efficient building in New York City.

Visually, the most striking feature of the interior is, without question, the cavernous lobby. Thanks to the boxlike structure of the podium, there is a soaring 60-foot ceiling—think of Radio City Music Hall’s theater, bathed in light.

Childs has stressed the point that the building is to both mark the site of the old towers and be a beacon for the future, like a lighthouse, and, partly as a result, the tower-topping spire will rise 408 feet, to bring the building to the historically symbolic height of 1,776 feet, making it the tallest in not only New York but also the nation. As a beacon, One World Trade Center is already working just fine—it’s visible from over 20 miles away, and people are looking up again. “I get e-mails all the time,” del Valle says, referring to acquaintances who live across the Hudson River in New Jersey. “Just yesterday I got a photo from a friend and it said, ‘Looking good.’”