The originalTwo World Trade Center (also known as theSouth Tower,Tower 2,Building Two, or2 WTC) was one of the Twin Towers in the originalWorld Trade Center Complex inNew York City. The Tower was completed and opened in 1973 at a height of 1,362 feet (415 m) to the roof, distinguishable from its twin, theNorth Tower (1 World Trade Center), by the absence of a television antenna. On the 107th floor of this building was a popular tourist attraction, "Top of the World Trade Center Observatories," and on the roof was an outdoorobservation deck accessible to the public and a disusedhelipad at the center.[3] The address of this building was2 World Trade Center, with the WTC complex having its ownZIP code of10048.
The South Tower was destroyed along with the North Tower in theSeptember 11 attacks. At 9:03 a.m,[b] seventeen minutes after its twin was hit, the South Tower was struck byUnited Airlines Flight 175. Although it was the second of the two skyscrapers to be hit by a hijacked airliner, it was the first tocollapse, at 9:59 a.m.,[c] after burning for 56 minutes. Of the 2,977 victims killed in the attacks, around 1,000 were in the South Tower or on the ground.
In 1961, thePort Authority of New York and New Jersey agreed to build theWorld Trade Center on the site of theHudson Terminal inLower Manhattan, New York City.[10] OnSeptember 20, 1962, the Port Authority announced the selection ofMinoru Yamasaki as lead architect andEmery Roth & Sons as associate architects.[11] Yamasaki devised the plan to incorporate twin towers. His original plan called for the towers to be 80 stories tall,[12] but to meet the Port Authority's requirement for 10,000,000 square feet (930,000 m2) of office space, the buildings would each have to be 110 stories tall.[13] Yamasaki's design for the World Trade Center, unveiled to the public onJanuary 18, 1964, called for a square plan approximately 207 feet (63 m) in dimension on each side.[12][14]
In March 1965, the Port Authority began acquiring property at the World Trade Center site.[15] Demolition work began onMarch 21, 1966,[16] and groundbreaking for the construction of the World Trade Center took place onAugust 5, 1966.[17] In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers.[18] Construction on the South Tower was under way byJanuary 1969.[19] Thetopping out ceremony for 2 WTC (the South Tower) occurred onJuly 19, 1971.[19] The South Tower began accepting tenants inJanuary 1972,[20] and a ribbon cutting ceremony took place onApril 4, 1973.[21]
On February 26, 1993, aRyder truck filled with 1,500 pounds (680 kg) of explosives (planted byRamzi Yousef) detonated in the North Tower's underground garage.[23] 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.[24] Six people were killed and 1,042 others were injured in the attacks.[25][26]
In February 2001, the Port Authority leased the entire World Trade Center complex toVornado Realty Trust.[27] However, Vornado insisted on last minute changes to the deal,[28] and the next-highest bidder,Silverstein Properties, signed a lease for the complex onJuly 24, 2001.[29]
A 360° panoramic view of New York City and surrounding areas from the Top of the World observation deck, circa August 2001. North is near center and the North Tower is left.
Visitors on the viewing platform on the South Tower's roof, looking north towardMidtown Manhattan in 1984
Although most of the space in the World Trade Center complex was off-limits to the public, the South Tower featured a public glass-enclosed observation deck on the 107th floor calledTop of the World and an open-air deck with the height of 110 stories.[30][31][32] The observation deck opened in December 1975 and operated from 9:30 a.m. to 11:30 p.m. (June to August) and from 9:30 a.m. – 9:30 p.m. (September to May).[33][34] After paying an entrance fee in the second floor, visitors were required to pass through security checks added after the1993 World Trade Center bombing.[35] They were then sent to the 107th-floor indoor observatory at a height of 1,310 feet (400 m) by a dedicated express elevator, which could be only accessed by entering the core.[31] The exterior columns were narrowed to allow 28 inches of window width between them. In 1995, the Port Authority leased operation of the observatory to Ogden Entertainment, which decided to renovate it.[36] On April 30, 1997, the Top of the World tour reopened after renovations were finished.[37] Dellmont Leisure Design, aLa Crescenta firm led by formerDisney Imagineer David Schweninger, carried out the renovations.[38] Attractions added to the observation deck included 24 video monitors, which provided descriptions of 44 points of interest in six languages; a theater showing a film of a simulated helicopter tour around the city called "Manhattan Magic";[39][31][40] a model of Manhattan with 750 buildings; aKodak photo booth and two gift shops.[39] The 107th-floor also featured asubway-themed food court that featuredSbarro Street Station andNathan's Famous Hot Dogs with a dining area that simulatedCentral Park.[41][42]
Weather permitting, visitors could ride two short escalators up from the 107th-floor viewing area to an outdoor platform at a height of 1,377 ft (420 m).[43][31][44] On a clear day, visitors could see up to 50 miles (80 km).[41] An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing. This left the view unobstructed, unlike the observation deck of the Empire State Building.[42]
At 9:03 a.m. EDT onSeptember 11, 2001, five terrorists crashedUnited Airlines Flight 175 into the southern face of the South Tower.[45][46] Three buildings in the World Trade Center complex, including 2 WTC,collapsed due to fire-induced structural failure.[47] The light construction and hollow nature of the structures allowed the jet fuel to penetrate far inside the towers, igniting many large fires simultaneously over a wide area of the impacted floors. The fuel from the planes burned at most for a few minutes, but the contents of the buildings burned over the next hour to hour and a half.[48]
The fires might not have been as centrally positioned, nor as intense, had traditionally heavy high-rise construction been standing in the way of the aircraft. Debris and fuel would likely have remained mostly outside the buildings or concentrated in more peripheral areas away from the building cores, which would then not have become unique failure points. In this scenario, the towers might have stood far longer, perhaps indefinitely.[49][50] The fires were hot enough to weaken the columns and cause floors to sag, pulling perimeter columns inward and reducing their ability to support the mass of the building above.[51] The South Tower collapsed at 9:59 a.m. after burning for 56 minutes in the fire caused by the impact of United Airlines Flight 175 and the explosion of its fuel.[47]
Minoru Yamasaki was the lead architect for the tower, andEmery Roth & Sons were the associate architects.[11] During the World Trade Center's construction, the structural engineers ended up following draft versions of New York City's 1968building codes, which incorporated "advanced techniques" inbuilding design.[52] The Twin Towers used a tube-frame design, which required 40 percent less structural steel than conventional building designs.[53] The structures were inspired by the architectural ethic ofLe Corbusier and was the seminal expression of Yamasaki's gothic modernist tendencies.[54] Yamasaki was also inspired byIslamic architecture, elements of which he incorporated in the buildings' design, having previously designed Saudi Arabia'sDhahran International Airport with theSaudi Binladin Group.[55][56]
When completed in 1973, the South Tower became the second tallest building in the world at 1,362 feet (415 m), behind the North Tower. Its rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high.[57] Each tower stood over 1,350 feet (410 m) high, and occupied about 1 acre (4,000 m2) of the total 16 acres (65,000 m2) of the site's land.[58]
The Twin Towers' facades were made of high-strength, load-bearing perimeter steel columns which acted asVierendeel trusses.[59][60] Although the columns themselves were lightweight, they were spaced closely together, forming a strong, rigid wall structure.[61][62] There were 59 perimeter columns, narrowly spaced, on each side of the building.[63][60] In all, the perimeter walls measured 210 feet (64 m) long on each side, and the corners werebeveled.[64][62] The perimeter structure was constructed of prefabricated modular pieces connected byspandrel plates.[62] From the 7th floor to the ground level, and down to the foundation, the columns were spaced 10 feet (3.0 m) apart to accommodate doorways.[65][60] All columns were placed onbedrock 65–85 feet (20–26 m) below the surface.[66]
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.[67] The South Tower's structural core was oriented with the long axis north to south.[68] The core columns supported about half the towers' weight.[68] All elevators were located in the core. Each building had three stairwells, also in the core, except on themechanical floors.[63] The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses, which connected to the perimeter columns.[69]
Hattrusses (or "outrigger truss") located from the 107th floor to the top of the North and South towers were designed to support a tall communicationantenna on top of each building.[69] The South Tower never had an antenna fitted.[70] 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.[71] In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner crashing into the building.[72] TheNational Institute of Standards and Technology (NIST) found a three-pagewhite paper that mentioned another aircraft impact analysis, involving impact of a jet at 600 mph (970 km/h), was indeed considered, but NIST could not locate the documentary evidence of the aircraft impact analysis.[73]
Sprayed-fire resistant materials (SFRMs),gypsum wallboard, andvermiculite were used to provide fireproofing to the interiors.[63] More fireproofing was added after a fire in February 1975,[74] but after the1993 bombing, inspections found fireproofing to be deficient.[75] The 1968 New York City building codes did not requiresprinklers for high-rise buildings, except for underground spaces,[76] but the entire complex was retrofitted by 2001.[77]
Note: Floor numbers in red are part ofUnited Airlines Flight 175's impact area during the September 11 attacks, with floors above this zone marked indark gray.
^The collapsebegan at 9:58:59 a.m.; ergo it would not have been fully destroyed until 9:59.
^The exact time is disputed. The 9/11 Commission report says 9:03:11,[4][5] NIST reports 9:02:59,[6] some other sources report 9:03:02.[7]
^NIST and the 9/11 Commission both state that the collapse began at 9:58:59 a.m.,[8]: 80 [9]: 322 which is rounded to 9:59[8]: 84 [9]: 322 for simplicity. If the Commission's claim that the South Tower was struck at 9:03:11 is to be believed, then it collapsed after 55 minutes and 48 seconds, not 56 minutes.
^Building and Fire Research Laboratory (September 2005).Visual Evidence, Damage Estimates, and Timeline Analysis(PDF).National Institute of Standards and Technology (Report). United States Department of Commerce. p. 27.Archived(PDF) from the original on September 11, 2021. RetrievedAugust 24, 2021.
^"World Trade Center Facts and Figures".911memorial.org. RetrievedJanuary 3, 2022.From the opening day of the South Tower Observation Deck in December 1975 through close of business on the night of September 10, 2001, more than 46.3 million visitors experienced the views from the tower's summit.
^"Ticket Information". Top of The World Trade Center.Archived from the original on April 5, 2001. RetrievedDecember 20, 2021.
^American Iron and Steel Institute (1964). "The World Trade Center – New York City".Contemporary Steel Design.1 (4). American Iron and Steel Institute.
^William Baker; Johnathan Barnett; Christopher Marrion; Ronald Hamburger; James Milke; Harold Nelson (September 1, 2002). "Chapter 2. WTC 1 and WTC 2".World Trade Center Building Performance Study.FEMA. p. 33.... the loads initially carried by the damaged exterior columns were transferred by Vierendeel truss action to the remaining exterior columns immediately adjacent to the impact area.
^Sadek, Fahim.Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers(NCSTAR 1–2 appendix A). NIST 2005. pp. 305–307.
Evans, David D.; Richard D. Peacock, Erica D. Kuligowski; W. Stuart Dols; William L. Grosshandler (September 2005).Active Fire Protection Systems (NCSTAR 1–4) (Report). National Institute of Standards and Technology.
Sivaraj Shyam-Sunder; Richard G. Gann; William L. Grosshandler; Hai S. Lew; Richard W. Bukowski; Fahim Sadek; Frank W. Gayle; John L. Gross; Therese P. McAllister; Jason D. Averill; James R. Lawson; Harold E. Nelson; Stephen A. Cauffman (September 2005).Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Tower (NIST NCSTAR 1)(PDF) (Report). Federal Building and Fire Safety Investigation of the World Trade Center Disaster. National Institute of Standards and Technology (NIST).
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