Former skyscraper in Manhattan, New York
The original One World Trade Center (also known as the North Tower, Tower 1, Building One, or 1 WTC) was one of the Twin Towers of the original World Trade Center complex in New York City. It was completed in 1972, stood at a height of , and was the tallest building in the world until 1973, when surpassed by the Sears Tower in Chicago.
It was distinguishable from its twin, the original 2 World Trade Center, also known as the South Tower, by the telecommunications antenna on its roof. Including the antenna, the building stood at a total height of . Other things that made the North Tower distinguishable from its twin was a canopy connected to the North Tower's west facade on street level as well as two pedestrian walkways that extended from the west and south promenades of Three and Six World Trade Center to the North Tower's north and south facades on plaza level, all of which the South Tower lacked. The building's address was 1 World Trade Center, and the WTC complex had its own ZIP code (10048) due to its large size.
The original World Trade Center was destroyed in the terrorist attacks of September 11, 2001. Struck by American Airlines Flight 11 at 8:46 a.m., the North Tower was the first of the Twin Towers to be hit by a hijacked aircraft, and the second to collapse, at 10:28 a.m. The North Tower stood for 102 minutes after the aircraft impact. Of the 2,977 victims killed in the attacks, around 1,700 were in the North Tower or on the ground.
The North Tower was succeeded by the present-day One World Trade Center tower, which was opened in November 2014 as the lead building of the redeveloped World Trade Center site. At the National September 11 Memorial &amp; Museum, the northern pool marks the spot where the North Tower once stood.
History.
Development.
In 1961, the Port Authority of New York and New Jersey agreed to build the World Trade Center on the site of the Hudson Terminal in Lower Manhattan, New York City. On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth &amp; Sons as associate architects. Yamasaki devised the plan to incorporate twin towers. His original plan called for the towers to be 80 stories tall, but to meet the Port Authority's requirement for of office space, the buildings would each have to be 110 stories tall. Yamasaki's design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately in dimension on each side.
In March 1965, the Port Authority began acquiring property at the World Trade Center site. Demolition work began on March 21, 1966, and groundbreaking for the construction of the World Trade Center took place on August 5, 1966. In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers. Construction work began on the North Tower in August 1968. The topping out ceremony for 1 WTC (the North Tower) took place on December 23, 1970. The first tenants moved into the North Tower on December 15, 1970, while it was still under construction, and a ribbon cutting ceremony took place on April 4, 1973.
Operation.
On February 13, 1975, a three-alarm fire broke out on the North Tower's 11th floor, spreading to the 9th and 14th floors. At that time, the World Trade Center had no fire sprinkler systems. A disgruntled custodian was discovered to have deliberately started the fire and was criminally charged. Following the fire, in 1981, the Port Authority announced a $45 million plan to install sprinklers throughout the World Trade Center.
The first terrorist attack on the World Trade Center occurred on February 26, 1993, at 12:17 p.m. A Ryder truck filled with of explosives (planted by Ramzi Yousef) detonated in the North Tower's underground garage. According to a presiding judge, the conspirators' chief aim at the time of the attack was to destabilize the North Tower and send it crashing into the South Tower, toppling both skyscrapers. Six people were killed and 1,042 others were injured in the attacks. Following the bombing, floors that were blown out needed to be repaired to restore structural support.
In February 2001, the Port Authority leased the entire World Trade Center complex to Vornado Realty Trust. However, Vornado insisted on last minute changes to the deal, and the next-highest bidder, Silverstein Properties, signed a lease for the complex on July 24, 2001.
Destruction.
At 8:46 a.m. (EDT) on September 11, 2001, five hijackers affiliated with al-Qaeda crashed American Airlines Flight 11 into the northern facade of the North Tower between the 93rd and 99th floors. Seventeen minutes later, at 9:03 a.m. (EDT), a second group of five terrorists crashed the hijacked United Airlines Flight 175 into the southern facade of the South Tower, striking between the 77th and 85th floors.
By 9:59 a.m. (EDT), the South Tower collapsed after burning for approximately 56 minutes. After burning for 102 minutes, the North Tower collapsed due to structural failure at 10:28 a.m. (EDT). When the North Tower collapsed, debris fell on the nearby 7 World Trade Center, damaging it and starting fires. The fires burned for hours, compromising the building's structural integrity. Seven World Trade Center collapsed at 5:21 p.m. (EDT).
Together with a simultaneous attack on the Pentagon in Arlington, Virginia, and a passenger revolt that resulted in a plane crash in Shanksville, Pennsylvania, the attacks resulted in the deaths of 2,996 people (2,507 civilians, 343 firefighters, 72 law enforcement officers, 55 military personnel, and the 19 hijackers). More than 90% of the workers and visitors who died in the towers had been at or above the points of impact. In the North Tower, 1,355 people at or above the point of impact were trapped, and died of smoke inhalation, fell, jumped from the tower to escape the smoke and flames, or were killed when the building eventually collapsed. One stairwell in the South Tower, Stairwell A, somehow avoided complete destruction, unlike the rest of the building. When Flight 11 hit, all three staircases in the North Tower's impact zone were destroyed, making it impossible for anyone above the 91st floor to escape. 107 people below the point of impact also died.
Architecture.
Minoru Yamasaki was the lead architect for the tower, and Emery Roth &amp; Sons were the associate architects. During the World Trade Center's construction, the structural engineers ended up following draft versions of New York City's 1968 building codes, which incorporated "advanced techniques" in building design. The Twin Towers used a tube-frame design, which required 40 percent less structural steel than conventional building designs. The structures were inspired by the architectural ethic of Le Corbusier and was the seminal expression of Yamasaki's gothic modernist tendencies. Yamasaki was also inspired by Islamic architecture, elements of which he incorporated in the buildings' design, having previously designed Saudi Arabia's Dhahran International Airport with the Saudi Binladin Group. 
When completed, the North Tower stood tall. It featured a telecommunications antenna or mast that was built on the roof in 1979 (upgraded in 1999 to accommodate DTV broadcasts). With this addition, the highest point of the North Tower reached . Each tower stood over high, and occupied about of the total of the site's land.
Facade.
The Twin Towers' facades were made of high-strength, load-bearing perimeter steel columns which acted as Vierendeel trusses. Although the columns themselves were lightweight, they were spaced closely together, forming a strong, rigid wall structure. There were 59 perimeter columns, narrowly spaced, on each side of the building. In all, the perimeter walls measured long on each side, and the corners were beveled. The perimeter structure was constructed of prefabricated modular pieces connected by spandrel plates. From the 7th floor to the ground level, and down to the foundation, the columns were spaced apart to accommodate doorways. All columns were placed on bedrock 65–85 feet (20–26 m) below the surface.
Structural features.
The building's core housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m), and contained 47 steel columns running from the bedrock to the top of the tower. The North Tower's structural core was oriented with the long axis east to west. The core columns supported about half the towers' weight. All elevators were located in the core. Each building had three stairwells, also in the core, except on the mechanical floors. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses, which connected to the perimeter columns.
Hat trusses (or "outrigger truss") located from the 107th floor to the top of the North and South towers were designed to support a tall communication antenna on top of each building. Only the North Tower actually had an antenna fitted, which was added in 1978. The framed-tube design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind. In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner crashing into the building. The National Institute of Standards and Technology (NIST) found a three-page white paper that mentioned another aircraft impact analysis, involving impact of a jet at , was indeed considered, but NIST could not locate the documentary evidence of the aircraft impact analysis.
Sprayed-fire resistant materials (SFRMs), gypsum wallboard, and vermiculite were used to provide fireproofing to the interiors. More fireproofing was added after a fire in February 1975, but after the 1993 bombing, inspections found fireproofing to be deficient. The 1968 New York City building codes did not require sprinklers for high-rise buildings, except for underground spaces, but the entire complex was retrofitted by 2001.
Tenants at the time of the attacks.
The tenant list below was compiled from the original list provided by CoStar Group (a provider of electronic commercial real estate information), quoted by CNN, and was sourced from UnBlinking.com. Cantor Fitzgerald's corporate headquarters were located in 1 World Trade Center.
SOURCES: CoStar Group, CNN, and Unblinking.
Floor unknown: Alliance Global Finance, Associated Charter Marine, Carreden Group, CIF Agency, Dimetol International Trade, Eastern Capital Corporation, Falcon International Freight, First Pacific Rim, GAC Shipping, Garwood Financial, Globe Shipping Company, GSI Cargo Service, Hachijuni Bank, Hanil Securities, Lin Brothers International, Pluto Commodities, Port Newark
92nd floor.
The 92nd floor, though technically the first floor below Flight 11's impact zone, did not have any survivors. Sixty-nine people reported to work that morning, including 67 employees of Carr Futures, a tenant on the 92nd floor. The impact itself spared every single person on Floor 92 and did no damage to the floor directly. However, the force of the crash collapsed walls and inflicted nonstructural damage such as smashed windows, broken ceiling tiles and severed electrical wires, as well as causing knee-deep flooding throughout various rooms on the 92nd floor after the water pipes burst. Multiple calls were recorded from people trapped on the floor, the workers reporting that although the stairs on the 92nd floor had not been destroyed, they were walled off by fallen debris from Flight 11's impact zone immediately above. In addition to the stairs being rendered impassable, the centralized impact into the North Tower's core also interrupted elevator service in the skyscraper from its 50th floor and higher, severing all escape routes for anyone above the 91st floor.
Initially, conditions on the 92nd floor were likely not dissimilar to what they were on the 91st, from which everyone survived and escaped. The situation changed very quickly when flammable aviation fuel spilled down into the 92nd floor, igniting fires that rapidly began consuming its east side; within 12 minutes of the impact, the first known fatalities from the floor occurred over a three-minute period when eight workers were forced to jump from the northern end of the tower's east side to escape a rapidly advancing wall of flames.
Those who remained made their way to an unoccupied area on the west side of the floor that was initially free of smoke and fire. However, images show that the blaze on the tower’s north face eventually spread westward to their safe haven in that section of the floor, making conditions there unsurvivable.
The last phone call from the North Tower came from Thomas McGinnis, a trader on the