Composite construction is a generic term to describe any building construction involving multiple dissimilar materials. Composite construction is often used in building aircraft , watercraft , and building construction . There are several reasons to use composite materials including increased strength, aesthetics , and environmental sustainability .
169-536: The World Trade Center in Lower Manhattan , New York City, was destroyed on September 11, 2001, as a result of al-Qaeda 's terror attacks . Two commercial airliners hijacked by terrorists were deliberately flown into the Twin Towers of the complex, resulting in a total progressive collapse that killed almost 3,000 people. It was the deadliest and costliest building collapse in history. The North Tower (WTC 1)
338-807: A 1970 account was supposed to accommodate 130,000 people. On a typical weekday, an estimated 50,000 people worked in the complex and another 140,000 passed through as visitors. The World Trade Center was so large that it had its own zip code: 10048 . The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower. The Twin Towers became known worldwide, appearing in numerous movies and television shows as well as on postcards and other merchandise. It became
507-451: A 362 foot (110 m) telecommunications antenna or mast that was built on the roof in 1979 (which was upgraded in 1999 to accommodate DTV broadcasts). With this addition, the highest point of the North Tower reached 1,730 feet (530 m). Chicago's Willis Tower , then called Sears Tower, which was finished in May 1973 , reached 1,450 feet (440 m) at the rooftop. When completed in 1973,
676-755: A New York icon, in the same league as the Empire State Building, the Chrysler Building, and the Statue of Liberty . The World Trade Center was compared to Rockefeller Center , which David Rockefeller's brother Nelson Rockefeller had developed in midtown Manhattan. One World Trade Center and Two World Trade Center, commonly referred to as the Twin Towers , were designed by architect Minoru Yamasaki as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. They were
845-488: A business writer, it also was the origin of the electronic component distribution business. The idea of establishing a World Trade Center in New York City was first proposed in 1943. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project, but the plans were put on hold in 1949. During the late 1940s and 1950s, economic growth in New York City
1014-520: A collapse mechanism on September 21, 2001. They later contributed to an MIT collection of papers on the WTC collapses edited by Eduardo Kausel called The Towers Lost and Beyond . Immediately following the collapses, there was some confusion about who had the authority to carry out an official investigation. While there are clear procedures for the investigation of aircraft accidents, no agency had been appointed in advance to investigate building collapses. A team
1183-529: A dozen adjacent and nearby structures were damaged or destroyed by debris from the plane impacts or the collapses. Four of the five remaining World Trade Center structures were immediately crushed or damaged beyond repair as the towers fell, while 7 World Trade Center remained standing for another six hours until fires ignited by raining debris from the North Tower brought it down at 5:21 that afternoon. The hijackings, crashes, fires and subsequent collapses killed an initial total of 2,760 people . Toxic powder from
1352-423: A fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors with shear connections to the concrete slab for composite action . The trusses had a span of 60 ft (18 m) in the long-span areas and 35 ft (11 m) in the short-span area. The trusses connected to the perimeter at alternate columns, and were therefore on 6.8 ft (2.1 m) centers. The top chords of
1521-401: A half. As Flight 175 struck the South Tower, the shockwave shattered glass on the east face of the North Tower adjacent to the fireball, which aggravated the fires already burning in the North Tower and released plumes of smoke from the newly opened windows. It is unknown whether Flight 11's impact did the same to windows on the South Tower. In any case, the major debris from Flight 11 flew past
1690-505: A height of 1,377 ft (420 m). On a clear day, visitors could see up to 50 miles (80 km). 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. Windows on the World, the restaurant on the North Tower's 106th and 107th floors, opened in April 1976 . It
1859-485: A replacement for traditional cement. The traditional cement used as stucco rapidly deteriorates. The deterioration causes the material to easily crack due to thermo-processes becoming permeable to water and no longer structurally sound. The United States Environmental Protection Agency in conjunction with Materials and Electrochemical Research Corporation tested a cement-polymer composite material consisting of crumb rubber made from recycled rubber tires and cement . It
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#17330849066882028-406: A single unit from a structural point of view. When this occurs, it is called composite action . One common example involves steel beams supporting concrete floor slabs. If the beam is not connected firmly to the slab, then the slab transfers all of its weight to the beam and the slab contributes nothing to the load carrying capability of the beam. However, if the slab is connected positively to
2197-411: A square plan approximately 208 feet (63 m) in dimension on each side. The buildings were designed with narrow office windows 18 inches (46 cm) wide, which reflected Yamasaki's fear of heights as well as his desire to make building occupants feel secure. His design included building facades clad in aluminum-alloy. The World Trade Center was one of the most striking American implementations of
2366-410: A strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces, each consisting of three columns, three stories tall, connected by spandrel plates. The spandrel plates were welded to the columns to create
2535-542: A surprise to some in the engineering community. The structural engineers working on the World Trade Center considered the possibility that aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in fog had crashed into the 79th floor of the Empire State Building . A year later, a C-45F Expeditor crashed into the 40 Wall Street building. Once again, fog was believed to have been
2704-409: A utility shaft that ran vertically between floors. Areas at the furthest extent of the fire were extinguished almost immediately; the original fire was put out in a few hours. Most of the damage was concentrated on the 11th floor, fueled by cabinets filled with paper, alcohol-based fluid for office machines, and other office equipment. Fireproofing protected the steel and there was no structural damage to
2873-406: Is composite decking . This material is typically made from wood–plastic composite or fiberglass reinforced plastic (FRP). Such materials do not warp, crack, or split and are as versatile as traditional pressure treated wood. Composite decking is made through several different processes, and there are a multitude of sizes, shapes, and strengths available. Depending on the type of composite selected
3042-486: Is a simple form of composite construction sometimes used in North American light frame construction . This occurs when a steel plate is sandwiched between two wood joists and bolted together. A flitch beam can typically support heavier loads over a longer span than an all-wood beam of the same cross section . The traditional decking material is pressure-treated wood. The current material many contractors choose to use
3211-520: Is closer to the site's eastern border. It was on this shoreline, close to the intersection of Greenwich and the former Dey Street , that Dutch explorer Adriaen Block 's ship, Tyger , burned to the waterline in November 1613, stranding him and his crew and forcing them to overwinter on the island. They built the first European settlement in Manhattan . The remains of the ship were buried under landfill when
3380-463: Is going to come down very shortly"; this proved correct less than a minute later, when the North Tower collapsed at 10:28 a.m., one hour and 42 minutes after being struck. Because all escape routes from within, above, and immediately below the impact zone were severed when Flight 11 crashed, no one above the 91st floor survived. The collapsing towers generated enormous clouds of dust and debris, which enveloped lower Manhattan; light dust reached as far as
3549-505: The 1993 World Trade Center Bombing Memorial fountain. The plaza was pervaded by Muzak background music that came from installed loudspeakers. For many years, the Plaza was often beset by brisk winds at ground level owing to the Venturi effect between the two towers. Some gusts were so strong that pedestrians' travel had to be aided by ropes. In 1997 Tony May opened an Italian restaurant in
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#17330849066883718-642: The Borough of Manhattan Community College 's Fiterman Hall building, located adjacent at 30 West Broadway, to the extent that the building was not salvageable. In August 2007, Fiterman Hall was scheduled for dismantling. A revised plan called for demolition in 2009 and completion of the new Fiterman Hall in 2012, at a cost of $ 325 million. The building was finally demolished in November 2009 and construction of its replacement began on December 1, 2009. The adjacent Verizon Building , an Art Deco building constructed in 1926, had extensive damage to its east facade from
3887-477: The Empire State Building , 2.93 mi (4.72 km) away. The debris cloud from the North Tower collapse was also larger and more widespread than that of the South Tower, because the collapse of the North also kicked up dust from the South Tower. As the North Tower collapsed, heavy debris hit 7 World Trade Center, causing damage to the south face of the building and starting fires that continued to burn throughout
4056-540: The Federal Bureau of Investigation (FBI), and one member of the United States Secret Service (USSS). The total death toll for civilian and non-civilians is estimated to be 2,606 persons. The destruction of the Twin Towers has been called "the most infamous paradigm" of progressive collapse . Each collapse began with the local failure of the vertical load-bearing components of the floors that were hit by
4225-473: The National Institute of Standards and Technology (NIST) obtained a three-page white paper that stated the buildings would survive an aircraft-impact of a Boeing 707 or DC 8 flying at 600 mph (970 km/h). In 1993, John Skilling , lead structural engineer for the WTC, said in an interview conducted after the 1993 World Trade Center bombing : "Our analysis indicated the biggest problem would be
4394-452: The National Institute of Standards and Technology (NIST) published the results of its investigation into the collapse . It found nothing substandard in the towers' design, noting that the severity of the attacks was beyond anything experienced by buildings in the past. The NIST determined the fires to be the main cause of the collapses, finding that sagging floors pulled inward on the perimeter columns, causing them to bow and then buckle. Once
4563-697: The New York City Police Department (NYPD), 37 members of the Port Authority Police Department (PAPD), five members of the New York State Office of Tax Enforcement (OTE), three officers of the New York State Office of Court Administration (OCA), one fire marshal of the New York City Fire Department (FDNY) who had sworn law enforcement powers (and was also among the 343 FDNY members killed), one member of
4732-487: The University of California at Berkeley , explained that the high temperatures in the fires weakened the steel beams and columns, causing them to become "soft and mushy", and eventually they were unable to support the structure above. Astaneh-Asl also suggested that the fireproofing became dislodged during the initial aircraft impacts. He also explained that, once the initial structural failure occurred, progressive collapse of
4901-457: The Verizon Building , and 3 World Financial Center had impact damage from the towers' collapse, as did 90 West Street. One Liberty Plaza survived structurally intact but sustained surface damage including shattered windows. 30 West Broadway was damaged by the collapse of 7 World Trade Center. The Deutsche Bank Building, which was covered in a large black "shroud" after September 11 to cover
5070-407: The framed-tube structural system used in the twin towers. The Port Authority's Engineering Department served as foundation engineers , Joseph R. Loring & Associates as electrical engineers , and Jaros, Baum & Bolles (JB&B) as mechanical engineers . Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli , director of
5239-458: The shoreline was extended beginning in 1797 and was discovered during excavation work in 1916. The remains of a second eighteenth-century ship were discovered in 2010 during excavation work at the site. The ship, believed to be a Hudson River sloop , was found just south of where the Twin Towers stood, about 20 feet (6.1 m) below the surface. Later, the area became New York City's Radio Row , which existed from 1921 to 1966. The neighborhood
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5408-469: The "North Tower", was, at 1,368 ft (417 m), six feet taller than Two World Trade Center (WTC 2), the "South Tower", which was 1,362 ft (415 m) tall. Numerous closely spaced perimeter columns provided much of the structural strength, along with gravity load shared with the steel box columns of the core. Above the tenth floor, there were 59 perimeter columns along each face of the building spaced 3 ft 4 in (1.02 m) on center. While
5577-477: The 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building. Only 1 WTC (North Tower) actually had a spire antenna fitted, which was added in May 1979. The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported
5746-441: The 10th and 13th floors, a sign that the building was unstable and might cave to one side or "collapse". During the afternoon, firefighters also heard creaking sounds coming from the building and issued uncertain reports about damage in the basement. Around 3:30 pm FDNY Chief Daniel A. Nigro decided to halt rescue operations, surface removal, and searches along the surface of the debris near 7 World Trade Center and evacuate
5915-432: The 1960s by Bangladeshi-American structural engineer Fazlur Rahman Khan , was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. Each of the World Trade Center towers had 236 high-strength, load-bearing perimeter steel columns which acted as Vierendeel trusses . The perimeter columns were spaced closely together to form
6084-587: The 1960s. In its final report on the collapses, the NIST stated that it could find no documentation examining the impact of a high-speed jet or of a large-scale fire fueled by aviation fuel. Until the mid-1970s, the use of asbestos for fireproofing was widespread in the construction industry. But in April 1970, the New York City Department of Air Resources ordered contractors building the World Trade Center to stop
6253-400: The 707, the fuel load was not considered in the design. I don't know how it could have been considered." He also said that the main difference between the design studies and the event that caused the towers to collapse was the velocity of the impact, which greatly increased the absorbed energy, and was never considered during the construction process. During its investigation into the collapse,
6422-452: The 90-something floor" had collapsed. The New York City Police Department aviation unit also relayed information about the deteriorating condition of the buildings to police commanders. At 9:51 a.m., seven minutes before the collapse, the NYPD aviation unit reported that large pieces of debris were hanging or falling from the South Tower. The implied threat of an imminent collapse was sufficient for
6591-537: The 91st floor and left the stranded workers in an insufferable inferno from which jumping was their only means of escape; Flight 175 struck the South Tower through the southeast corner of the skyscraper's southern facade and left the northwesternmost stairwell undamaged from top to bottom. The intact stairway meant people in the South Tower were not completely trapped, which may have influenced their decision to jump. The fireballs resulting from each impact were likely very similar, but appeared vastly different in size despite
6760-568: The Greatest Bar on Earth and Cellar in the Sky (reopened after Labor Day ) replaced the original restaurant offshoots. In 1999, Cellar in the Sky was changed into an American steakhouse and renamed as Wild Blue. In 2000 (its last full year of operation), Windows on the World reported revenues of $ 37 million, making it the highest-grossing restaurant in the United States. The Skydive Restaurant, which
6929-646: The Hudson River. In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes , the Port Authority offered to take over the H&;M Railroad. They also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH . With
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7098-469: The NYPD to order its officers to evacuate, although none of the helicopter pilots specifically predicted that either tower would fall. During the emergency response, there was little communication between the NYPD and the FDNY , and overwhelmed 9-1-1 dispatchers did not pass along information to FDNY commanders at the scene. At 9:59 a.m., the South Tower collapsed, 56 minutes after Flight 175 crashed into it. Before
7267-475: The North Tower had been struck almost directly midway into the structure, the three main stairways (A, B, and C) in the tower core were all damaged or blocked by debris preventing escape to lower floors. In the South Tower, the impact was east of center to the central section of the tower and close to the southeast corner, resulting in stairway A in the northwest portion of the central core being intact and only partially blocked, and 18 civilians managed to escape from
7436-515: The North Tower was not going to last much longer and recommended that emergency vehicles be pulled away from the complex. At 10:20 a.m., the NYPD aviation unit reported that "the top of the tower might be leaning", and a minute later confirmed that the North Tower was buckling on the southwest corner and leaning to the south, prompting an officer to begin urging all NYPD personnel in the building's vicinity to retreat at least three blocks in every direction. The aviation unit declared at 10:27 "the roof
7605-475: The North Tower within Tobin Plaza for musicians and performers. These series of concerts and events were called "CenterStage at the World Trade Center". At the center of the plaza stood the monumental sculpture The Sphere by German artist Fritz Koenig . The world's largest bronze sculpture of modern times was surrounded by a fountain. The site had other sculptures such as Ideogram , Cloud Fortress , and
7774-425: The North Tower. Flight 175's much higher impact speed inflicted structural damage even more catastrophic than Flight 11's, which was compounded by the plane slicing through the southeastern corner rather than the center, unbalancing the South Tower on one side. The uneven weight distribution was significantly aggravated by Flight 175 crashing much lower down, between Floors 77 and 85, resulting in more pressure on both
7943-447: The Port Authority leased operation of the observatory to Ogden Entertainment, which decided to renovate it. On April 30, 1997, the Top of the World tour reopened after renovations were finished. 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
8112-512: The Port Authority's approved plans to privatize the World Trade Center in the late 1990s, they sought to lease it to a private entity in 2001. Bids for the lease came from Vornado Realty Trust ; a joint bid between Brookfield Properties Corporation and Boston Properties ; and a joint bid by Silverstein Properties and the Westfield Group . Privatizing the World Trade Center would add it to
8281-409: The Port Authority's chief engineer, John M. Kyle Jr., involved digging a trench, and as excavation proceeded, filling the space with a slurry consisting of a mixture of bentonite and water, which plugged holes and kept groundwater out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the slurry out. It took fourteen months for the slurry wall to be completed. It
8450-550: The September 11 attacks, mentions of the complex in various media were altered or deleted , and several dozen "memorial films" were created. The World Trade Center experienced several major crime and terrorist incidents, including a fire on February 13 , 1975; a bombing on February 26 , 1993; and a bank robbery on January 14 , 1998, all of which led to the terrorist attacks on September 11, 2001, when al-Qaeda -affiliated hijackers flew two Boeing 767 jets, one into each of
8619-423: The South Tower became the second tallest building in the world at 1,362 feet (415 m). Its rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high. Each tower stood over 1,350 feet (410 m) high, and occupied about 1 acre (4,000 m ) of the total 16 acres (65,000 m ) of the site's land. During a press conference in 1973, Yamasaki
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#17330849066888788-427: The South Tower collapsed, 18 people escaped from the impact zone and the floors above, including Stanley Praimnath , who had seen the plane coming at him. They made it out via Stairwell A, the only stairway left intact after the crash. There may have been other previously trapped occupants who were descending from the impact zone when the tower collapsed. Numerous police hotline operators who received calls from people in
8957-432: The South Tower fell, NYPD helicopters relayed information about the deteriorating conditions of the North Tower, while FDNY commanders issued orders for firefighters in the North Tower to evacuate. Poor radio reception meant firefighters inside the North Tower did not hear the evacuation order from their supervisors on the scene, and most were unaware that the other tower had collapsed. An NYPD officer said at 10:06 a.m. that
9126-448: The South Tower were not well informed of the situation as it rapidly unfolded. Many operators told callers not to descend on their own, even though it is now believed that Stairwell A was probably passable at and above the point of impact. The South Tower's collapse shattered windows and damaged other exterior elements along the North Tower's southern and eastern facades, although this was insufficient to cause its subsequent collapse. After
9295-445: The South Tower, while the more significant pieces of wreckage from Flight 175 similarly missed the already burning North Tower. In both instances, some of these parts landed on other nearby buildings, resulting in further destruction. The fires in each building had different attributes, as was evident in the responses and behavior of people trapped in each. Countless windows in the North Tower were smashed by occupants seeking relief from
9464-678: The Twin Towers' replacement, the new One World Trade Center , which opened in 2014. When they opened in 1973, the Twin Towers were the tallest buildings in the world. At the time of the attacks, only the Petronas Towers in Kuala Lumpur , Malaysia , and the Willis Tower (known then as the Sears Tower) in Chicago were taller. Built with a novel "framed tube" design that maximized interior space,
9633-408: The Twin Towers, seventeen minutes apart; between 16,400 and 18,000 people were in the Twin Towers when they were struck. The fires from the impacts were intensified by the planes' burning jet fuel, which, along with the initial damage to the buildings' structural columns, ultimately caused both towers to collapse . The attacks killed 2,606 people in and around the towers, as well as all 157 on board
9802-560: The Twin Towers, the plan for the World Trade Center complex included four other low-rise buildings, which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s, to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16-acre (65,000 m ) superblock . The World Trade Center complex housed more than 430 companies that were engaged in various commercial activities. The complex hosted 13,400,000 square feet (1,240,000 m ) of office space, which according to
9971-401: The World Trade Center towers could be subjected to and structural response to those forces. Experiments also were done to evaluate how much sway occupants could comfortably tolerate; however, many subjects experienced dizziness and other ill effects. One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of
10140-564: The World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority's Chief Engineer, oversaw the project. As an interstate agency, the Port Authority was not subject to the local laws and regulations of the City of New York, including building codes . Nonetheless, the World Trade Center's structural engineers ended up following draft versions of New York City's new 1968 building codes. The framed-tube design, introduced in
10309-447: The afternoon on the 11th and 12th floors of 7 World Trade Center, the flames visible on the east side of the building. During the afternoon, fire was also seen on floors 6–10, 13–14, 19–22, and 29–30. In particular, the fires on floors 7 through 9 and 11 through 13 continued to burn out of control during the afternoon. At approximately 2:00 pm, firefighters noticed a bulge in the southwest corner of 7 World Trade Center between
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#173308490668810478-429: The afternoon. Structural damage occurred to the southwest corner between Floors 7 and 17 and on the south facade between Floor 44 and the roof; other possible structural damage includes a large vertical gash near the center of the south facade between Floors 24 and 41. The building was equipped with a sprinkler system , but had many single-point vulnerabilities for failure: the sprinkler system required manual initiation of
10647-528: The aircraft impact. NIST concluded that the aircraft impact sheared off a significant portion of the fireproofing, contributing to the buildings' collapse. In WTC 1 , the impact stripped the insulation off most core columns (43 of 47) on more than one floor, as well as floor trusses over a space of 60,000 sq ft (5,600 m). In WTC 2 the impact knocked off insulation from 39 of the 47 columns on multiple floors, and also from floor trusses spanning an area of 80,000 sq ft (7,400 m). After
10816-443: The airplanes failed. Aside from the structural damage, the impacts had removed fireproofing from a large part of the impact zone allowing the structural steel to heat rapidly. As a result, the core columns were weakened and began to shorten due to creep. The hat truss resisted this by shifting loads to the perimeter columns. Meanwhile, web diagonals of the 60 foot trusses supporting the long-span tenant floor area began to buckle, causing
10985-467: The architectural ethic of Le Corbusier and was the seminal expression of Yamasaki's gothic modernist tendencies. He was also inspired by Islamic architecture , elements of which he incorporated in the building's design, having previously designed Saudi Arabia's Dhahran International Airport with the Saudi Binladin Group . A major limiting factor in building height is the issue of elevators;
11154-423: The area due to concerns for the safety of personnel. At 5:20:33 pm EDT on September 11, 2001, 7 World Trade Center started to collapse, with the crumble of the east mechanical penthouse, while at 5:21:10 pm EDT the entire building collapsed completely. There were no casualties associated with the collapse. When 7 World Trade Center collapsed, debris caused substantial damage and contamination to
11323-619: The area for the World Trade Center by March 1965, and demolition of Radio Row began in March 1966. It was completely demolished by the end of the year. Approval was also needed from New York City Mayor John Lindsay and the New York City Council . Disagreements with the city centered on tax issues, and the New York City Planning Commission wanted the Port Authority to increase its payments in lieu of taxes (PILOT) to
11492-440: The attacks, some from smoke inhalation. Sheikh Omar Abdel Rahman and four other individuals were later convicted for their involvement in the bombing, while Yousef and Eyad Ismoil were convicted for carrying out the bombing. 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. Following
11661-605: The bathtub began in late 1967. Construction work began on the North Tower in August 1968 , and construction on the South Tower was under way by January 1969 . The original Hudson Tubes , which carried PATH trains into Hudson Terminal, remained in service during the construction process until 1971, when a new station opened. The topping out ceremony of 1 WTC (North Tower) took place on December 23 , 1970, while 2 WTC's ceremony (South Tower) occurred on July 19 , 1971. Extensive use of prefabricated components helped to speed up
11830-400: The beam with studs, then a portion of the slab can be assumed to act compositely with the beam. In effect, this composite creates a larger and stronger beam than would be provided by the steel beam alone. The structural engineer may calculate a transformed section as one step in analyzing the load carry capability of the composite beam. In 19th-century shipbuilding, composite construction was
11999-409: The bombing, floors that were blown out needed to be repaired to restore the structural support they provided to columns. The slurry wall was in peril following the bombing and the loss of the floor slabs that provided lateral support against pressure from Hudson River water on the other side. The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex,
12168-436: The building's damage, was deconstructed because of water, mold, and other severe damage caused by the neighboring towers' collapse. In addition to this, many works of art were destroyed in the collapse . In the immediate aftermath of the attacks, numerous structural engineers and experts spoke to the media, describing what they thought caused the towers to collapse. Abolhassan Astaneh-Asl , a structural engineering professor at
12337-544: The buildings would each have to be 110 stories tall. The Port Authority publicly presented a model for the complex on January 18, 1964. The original plans called for two towers rising 1,350 feet (410 m), as well as several six-story buildings surrounding a central plaza (later the Austin J. Tobin Plaza ). These buildings were to include office space, restaurants, a hotel, exhibition space, stores, and an information center about world trade. The agency released its final model of
12506-527: The center marking where the Twin Towers stood. One World Trade Center , the tallest building in the Western Hemisphere at 1,776 feet (541 m) and the lead building for the new complex, completed construction in May 2013 and opened in November 2014. The western portion of the World Trade Center site was originally under the Hudson River . The shoreline was in the vicinity of Greenwich Street , which
12675-424: The center, causing more symmetrical impact damage to the North Tower's core and leaving more of its structural support intact. The fires also took more than an hour to spread to the south side of the building, where there was fireproofing damage. Traveling at 440 miles per hour, Flight 11 crashed through Floors 93 and 99, leaving only 10 floors' worth of structural weight pressing down on the damaged, burning section of
12844-427: The city called "Manhattan Magic"; a model of Manhattan with 750 buildings; a Kodak photo booth and two gift shops. The 107th-floor also featured a subway -themed food court that featured Sbarro Street Station and Nathan's Famous Hot Dogs with a dining area that simulated Central Park . Weather permitting, visitors could ride two short escalators up from the 107th-floor viewing area to an outdoor platform at
13013-511: The city government. On August 3 , 1966, an agreement was reached whereby the Port Authority would make annual PILOTs for the portion of the World Trade Center leased to private tenants. In subsequent years, the payments would rise as the real estate tax rate increased. In May 1967, the New York City Planning Commission approved several changes to the street grid that would allow the Port Authority to begin acquiring land for
13182-402: The city's tax rolls and provide funds for other Port Authority projects. On February 15 , 2001, the Port Authority announced that Vornado Realty Trust had won the World Trade Center lease, paying $ 3.25 billion for the 99-year lease. Vornado outbid Silverstein by $ 600 million though Silverstein upped his offer to $ 3.22 billion. However, Vornado insisted on last minute changes to
13351-589: The collapse of 7 World Trade Center, though it was successfully restored at a cost of US$ 1.4 billion. Many of the surrounding buildings were also either damaged or destroyed as the towers fell. 5 World Trade Center endured a large fire and a partial collapse of its steel structure and was torn down. Other buildings destroyed include 3 World Trade Center , 4 World Trade Center , 6 World Trade Center , and St. Nicholas Greek Orthodox Church . The World Financial Center buildings, 90 West Street , and 130 Cedar Street suffered fires. The Deutsche Bank Building ,
13520-768: The collapses, Leslie E. Robertson said: "To the best of our knowledge, little was known about the effects of a fire from such an aircraft, and no designs were prepared for that circumstance. Indeed, at that time, no fireproofing systems were available to control the effects of such fires." During the September 11 attacks , four teams of al-Qaeda terrorists hijacked four different jetliners. Two of these jetliners, American Airlines Flight 11 and United Airlines Flight 175 , both Boeing 767s , were hijacked after takeoff from Boston's Logan International Airport . In its final moments, American Airlines Flight 11 flew south over Manhattan and crashed at roughly 440 mph (710 km/h) into
13689-598: The collapses. Only a fraction of a percent of the buildings remained for analysis after the cleanup was completed: some 236 individual pieces of steel, although 95% of structural beams and plates and 50% of the reinforcement bars were recovered. World Trade Center (1973%E2%80%932001) The original World Trade Center ( WTC ) was a complex of seven buildings in the Financial District of Lower Manhattan in New York City . Built primarily between 1966 and 1975, it
13858-510: The completion of the Sears Tower in 1973. They were not surpassed until the construction of the Burj Khalifa , which opened in 2010. The towers were also the world's tallest twin towers until 1996, when the Petronas Towers opened. Each tower had a total mass of around 500,000 tons. The original World Trade Center had a five-acre (two-hectare) plaza around which all of the buildings in
14027-407: The complex in March 1966. Despite public criticism over the height of the 110-story twin towers, Yamasaki & Associates and Emery Roth & Sons made only relatively minor changes to the plans, which were released in May 1966. The revised plans called for the twin towers and four additional low-rise structures to surround the central plaza. Yamasaki's design for the World Trade Center called for
14196-404: The complex, including the Twin Towers, were centered. World Trade Center officials had wanted the plaza to be a "contemplative space" or a Zen garden . In 1982, the plaza was renamed after Port Authority's late chairman, Austin J. Tobin, who authorized the construction of the original World Trade Center. During the summer, the Port Authority installed a portable stage, typically backed up against
14365-401: The complex. On September 20 , 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth & 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 10,000,000 square feet (930,000 m ) of office space,
14534-461: The construction of the World Trade Center took place on August 5 , 1966. The site of the World Trade Center was located on filled land with the bedrock located 65 feet (20 m) below. To construct the World Trade Center, it was necessary to build a " bathtub " with a slurry wall around the West Street side of the site, to keep water from the Hudson River out. The slurry method selected by
14703-513: The construction process, and the first tenants moved into the North Tower on December 15, 1970 , while it was still under construction, while the South Tower began accepting tenants in January 1972 . The complex had 111 tenants with a combined 1,800 employees by late 1971. When the Twin Towers were completed, the total costs to the Port Authority had reached $ 900 million. The ribbon-cutting ceremony took place on April 4 , 1973. In addition to
14872-471: The contributing factor in the collision. Leslie Robertson , one of the chief engineers working on the design of the World Trade Center, said that he considered the scenario of the impact of a Boeing 707 , which might be lost in the fog and flying at relatively low speeds while seeking to land at either JFK or Newark Airports . In an interview with the BBC two months after the towers collapsed, Robertson said: "with
15041-462: The course. Windows on the World was forced to close following the 1993 World Trade Center bombing as the explosion damaged receiving areas, storage and parking spots used by the restaurant complex. On May 12, 1994, the Joseph Baum & Michael Whiteman Company won the contract to run the restaurants after Windows's former operator, Inhilco , gave up its lease. After its reopening on June 26, 1996,
15210-443: The deal, including a shorter 39-year lease, which the Port Authority considered nonnegotiable. Vornado later withdrew and Silverstein's bid for the lease to the World Trade Center was accepted on April 26 , 2001, and closed on July 24 , 2001. On September 11, 2001 , Islamist terrorists hijacked two commercial airliners and crashed them into the Twin Towers. One group led by Mohamed Atta crashed American Airlines Flight 11 into
15379-667: The decking materials can be used for a number of other construction projects including fences and sheds. In a composite steel deck, the dissimilar materials in question are steel and concrete. A composite steel deck combines the tensile strength of steel with the compressive strength of concrete to improve design efficiency and reduce the material necessary to cover a given area. Additionally, composite steel decks supported by composite steel joists can span greater distances between supporting elements and have reduced live load deflection in comparison to previous construction methods. Cement-polymer composites are being developed and tested as
15548-501: The design to stack local elevators within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently. This increased the amount of usable space on each floor from 62 to 75 percent by reducing the number of elevator shafts. Altogether, the World Trade Center had 95 express and local elevators. The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing
15717-427: The destroyed high-rises was dispersed throughout the city and gave rise to numerous long-term health effects that continue to plague many who were in the towers' vicinity, with at least three additional deaths reported. The 110-story towers are the tallest freestanding structures ever to be destroyed , and the death toll from the attack on the North Tower represents the deadliest terrorist act in world history. In 2005,
15886-501: The electrical fire pumps, rather than being a fully automatic system; the floor-level controls had a single connection to the sprinkler water riser; and the sprinkler system required some power for the fire pump to deliver water. Also, water pressure was low, with little or no water to feed sprinklers. Some firefighters entered 7 World Trade Center to search the building. They attempted to extinguish small pockets of fire, but low water pressure hindered their efforts. Fires burned into
16055-626: The entire structure was inevitable. César Pelli , who designed the Petronas Towers in Malaysia and the World Financial Center in New York, remarked, "no building is prepared for this kind of stress." On September 13, 2001, Zdeněk P. Bažant , professor of civil engineering and materials science at Northwestern University , circulated a draft paper with results of a simple analysis of the World Trade Center collapse. Bažant suggested that heat from
16224-403: The fact that all the fuel would dump into the building. There would be a horrendous fire. A lot of people would be killed. The building structure would still be there." In its report, NIST stated that the technical ability to perform a rigorous simulation of aircraft impact and ensuing fires is a recent development, and that the technical capability for such analysis would have been quite limited in
16393-523: The fire and was criminally charged. The first terrorist attack on the World Trade Center occurred on February 26, 1993, at 12:17 p.m. A Ryder truck filled with 1,500 pounds (680 kg) of explosives (planted by Ramzi Yousef ) detonated in the North Tower's underground garage. The blast opened a 100 ft (30 m) hole through five sublevels, with the greatest damage occurring on levels B1 and B2 and significant structural damage on level B3. Six people were killed and 1,042 others were injured in
16562-514: The fires was a key factor, causing steel columns in both the core and the perimeter to weaken and experience deformation before losing their carrying capacity and buckling. Once more than half of the columns on a particular floor buckled, the overhead structure could no longer be supported and complete collapse of the structures occurred. Bažant later published an expanded version of this analysis. Other analyses were conducted by MIT civil engineers Oral Buyukozturk and Franz-Josef Ulm , who also described
16731-492: The first intact floor beneath impact. The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load were applied gradually, but of only 6 additional floors if the load were applied suddenly — as was the case. Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC tower (12 floors in WTC 1 and 29 floors in WTC 2),
16900-428: The floor plate of the lower section, mediated by a growing layer of rubble consisting mainly of concrete from the floor slabs. The energy from each impact was "reintroduced into the structure in [the] subsequent impact, ... concentrate[d] in the load-bearing elements directly affected by the impact." This overloaded the floor connections of the story immediately beneath the advancing destruction, causing them to detach from
17069-408: The floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings. From there collapse proceeded through two phases. During the crush-down phase, the upper block destroyed the structure below in a progressive series of floor failures roughly one story at a time. Each failure began with the impact of the upper block on
17238-419: The floors to sag by more than 2 feet. This pulled in the perimeter walls, which buckled. The floors above the impact zone now fell freely onto the undamaged structure below. The North Tower lasted around 46 minutes longer than its twin, having been struck 17 minutes before the South Tower was attacked and standing another half-hour after the South Tower collapsed. This was because Flight 11 struck more or less in
17407-497: The floors. The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants. Hat trusses (or "outrigger trusses") located from
17576-457: The governors of both New York and New Jersey . New Jersey Governor Robert B. Meyner objected to New York getting a $ 335 million project. Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate. At the time, ridership on New Jersey's H&M Railroad had declined substantially—from a high of 113 million riders in 1927, to 26 million in 1958—after new automobile tunnels and bridges had opened across
17745-431: The ground floor lobby, more than 90 floors below the impact. Flight 175's impact into the South Tower's south face was offset to the east rather than being centralized like Flight 11, leaving the sides of the tower as the only real direction in which the fuel could travel, producing a visibly larger fireball on the outside. Almost all the deaths in the Twin Towers occurred in the zones above the points of aircraft impact. As
17914-480: The hellish conditions inside. While some windows were broken in the South Tower, it was relatively uncommon by comparison. Victims were only occasionally spotted inside open windows, and no crowds were present outside of the tower, as in the Impending Death photograph of the North Tower burning. Numerous people fell or jumped to their deaths from the burning towers. Three were spotted from an east-facing window on
18083-423: The impact traveled down at least one elevator shaft and exploded on the 78th floor of the North Tower, as well as in the main lobby. The towers' light construction and hollowness allowed the jet fuel to penetrate far inside them, igniting many large fires simultaneously over a wide area of the impacted floors. The fuel burned for at most a few minutes, but the buildings' contents burned over the next hour or hour and
18252-565: The impacted floors and the floors above that. Fewer than 200 of the civilian fatalities occurred in the floors below the impact points but all 147 civilian passengers and crew on the two aircraft as well as all 10 terrorists perished, along with at least 18 people on the ground and in adjacent structures. All told, emergency personnel killed as a result of the collapse included 342 members of the New York City Fire Department (FDNY), 71 law enforcement officers including 23 members of
18421-619: The lease to Silverstein Properties in July 2001 . During its existence, the World Trade Center symbolized globalization and the economic prosperity of the U.S. Although its design was initially criticized by New Yorkers and architectural critics, the Twin Towers became an icon of New York City. It had a major role in popular culture , and according to one estimate was depicted in 472 films. The Twin Towers were also used in Philippe Petit 's tightrope-walking performance on August 7, 1974. Following
18590-469: The long axis of core and four along the short axis. This system allowed optimized load redistribution of floor diaphragms between the perimeter and core, with improved performance between the different materials of flexible steel and rigid concrete allowing the moment frames to transfer sway into compression on the core, which also mostly supported the transmission tower. These trusses were installed in each building to support future transmission towers, but only
18759-400: The main buildings of the World Trade Center. Construction of the North Tower at One World Trade Center began in 1966 with the South Tower at Two World Trade Center. When completed in 1972, 1 World Trade Center became the tallest building in the world for two years, surpassing the Empire State Building after its 40-year reign. The North Tower stood 1,368 feet (417 m) tall and featured
18928-404: The mid-1860s. Early experiments with the system started with a patent issued in 1839, under which the steamer Assam was built. Other patents followed, with differing methods of electrically insulating the iron frames and fastenings from the copper sheathing. Surviving examples are HMS Gannet (1878) , a steam and sail-powered warship, and the clipper Cutty Sark . A flitch beam
19097-429: The modular pieces off-site at the fabrication shop. Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically so that the column splices between adjacent modules were not on
19266-413: The morning of August 7, 1974, Philippe Petit performed a high-wire walk between the North and South Towers of the World Trade Center. For his unauthorized feat 1,312 feet (400 m) above the ground, he rigged a 440-pound (200 kg) cable and used a custom-made 30-foot-long (9.1 m), 55-pound (25 kg) balancing pole. He performed for 45 minutes, making eight passes along the wire. Though Petit
19435-494: The new location and the Port Authority's acquisition of the H&M Railroad, New Jersey agreed to support the World Trade Center project. As part of the deal, the Port Authority renamed the H&M "Port Authority Trans-Hudson", or PATH for short. To compensate Radio Row business owners for their displacement, the Port Authority gave each business $ 3,000 without regard to how long the business had been there or how prosperous it was. The Port Authority began purchasing properties in
19604-475: The north of the superblock. Beneath the World Trade Center complex was an underground shopping mall . It had connections to various mass transit facilities, including the New York City Subway system and the Port Authority's PATH trains. One of the world's largest gold depositories was located underneath the World Trade Center, owned by a group of commercial banks. The 1993 bombing detonated close to
19773-408: The north tower was ultimately fitted with one. Though fire studies and even an analysis of the impacts of low-speed jet aircraft impacts had been undertaken before the towers' completion, the full scope of those studies no longer exists. Nevertheless, since fire had never before caused a skyscraper to collapse and aircraft impacts had been considered in their design, their destruction initially came as
19942-512: The northern facade of the North Tower (WTC 1) at 8:46 a.m., hitting the 93rd through 99th floors. Seventeen minutes later, United Airlines Flight 175 flew northeast, over New York Harbor , and crashed into the southern facade of the South Tower (WTC 2) at 9:03 a.m., striking between the 77th through 85th floors at 540 mph (870 km/h). The impacts failed the exterior columns in
20111-535: The northern facade of the North Tower at 8:46:40 a.m.; the aircraft struck between the 93rd and 99th floors. Seventeen minutes later, at 9:03:11 a.m., a second group led by Marwan al-Shehhi crashed the similarly hijacked United Airlines Flight 175 into the southern facade of the South Tower, striking it between the 77th and 85th floors. Composite construction In structural engineering , composite construction exists when two different materials are bound together so strongly that they act together as
20280-414: The outer walls of the collapsed North Tower struck the ground 11 seconds after the collapse started, and parts of the South Tower after 9 seconds. The lower portions of both buildings' cores (60 stories of WTC 1 and 40 stories of WTC 2) remained standing for up to 25 seconds after the start of the initial collapse before they too collapsed. In both towers, the section of the building that had been damaged by
20449-410: The outside, pushed by the increasing pile of rubble. Consequently, the walls peeled off and separated from the buildings by a large distance – about 500 ft (150 m) in some cases – hitting neighboring buildings and starting fires that would later lead to the collapse of Building 7. Some connections broke as the bolts snapped, leaving many panels randomly scattered. The first fragments of
20618-421: The perimeter and core columns. The perimeter columns peeled away and the cores were left without lateral support. This continued until the upper block reached the ground and the crush-up phase began. Here, it was the columns that buckled one story at a time, now starting from the bottom. As each story failed, the remaining block fell through the height of the story, onto the next one, which it also crushed, until
20787-413: The perimeter wall columns and core columns than in the North Tower and causing them to snap more quickly. The difference in the impacts was such that a senior FDNY chief reportedly expressed strong disbelief that the North Tower would collapse even after witnessing the collapse of the South Tower, because the North had not been struck at a corner. When the columns failed, the entire building above fell onto
20956-493: The planes and progressed to encompass the whole of the structure. Structural components were severed, releasing gravitational energy that transferred loads downwards by way of serially propagating impact forces. Excepting the top floors of the building, which would not have released sufficient gravitational energy to bring about a total collapse, the collapses could have begun with the failure of any story. The towers collapsed symmetrically and more or less straight down, though there
21125-413: The planes carrying similar amounts of combustibles. This is because a substantial portion of the jet fuel was channelled into the North Tower instead of being sprayed out into the open. Flight 11 crashed almost midway into the North Tower's central core, causing the ignited jet fuel to shoot through elevator shafts down as far as the basement and concourse levels, with a flash fire exploding from elevators in
21294-431: The plaza next to 4 World Trade Center called "Gemelli". The following year, he opened another restaurant in an adjacent place called "Pasta Break". On June 9, 1999, the outdoor plaza reopened after undergoing $ 12 million in renovations. This involved replacing marble pavers with over 40,000 gray and pink granite stones, as well as adding benches, planters, food kiosks, and outdoor dining areas. Although most of
21463-528: The plaza. 6 World Trade Center , at the northwest corner, housed the United States Customs Service . 5 World Trade Center was located at the northeast corner above the PATH station, and 4 World Trade Center , located at the southeast corner, housed the U.S. Commodities Exchange . In 1987, construction was completed on a 47-floor office building, 7 World Trade Center , located to
21632-478: The point of aircraft impact and the floors above that. The exact numbers of who perished and where in some cases is not precisely known; however the National Institute of Standards and Technology report indicated that a total of 1,402 civilians perished at or above the impact point in the North Tower with hundreds estimated to have been killed at the moment of impact. In the South Tower, 614 civilians perished at
21801-460: The regions hit by the fuselage, engines, and fuel-filled wing section (34 columns in the North Tower and 26 in the South Tower). Damage also extended to the tips of the wings and tailfin. In addition, several core columns were either severed or heavily damaged, especially in the path of the fuselage. About one third of the fuel was consumed in the initial impact and resulting fireball. Some fuel from
21970-429: The remains of the other buildings were demolished. On May 30, 2002, the last piece of WTC steel was ceremonially removed. A new World Trade Center complex is being built with six new skyscrapers and several other buildings, many of which are complete. A memorial and museum to those killed in the attacks, a new rapid transit hub , and an elevated park have opened. The memorial features two square reflecting pools in
22139-408: The restaurant two out of four stars, signifying a "very good" quality. In his 2009 book Appetite , William Grimes wrote that, "At Windows, New York was the main course". In 2014, Ryan Sutton of Eater.com compared the now-destroyed restaurant's cuisine to that of its replacement, One World Observatory . He said, "Windows helped usher in a new era of captive audience dining in that the restaurant
22308-405: The roof finally hit the ground. The process accelerated throughout, and by the end each story was being crushed in less than a tenth of a second. As the fires continued to burn, occupants trapped in the upper floors of the South Tower provided information about conditions to 9-1-1 dispatchers. At 9:37 a.m., an occupant on the 105th floor of the South Tower reported that floors beneath him "in
22477-400: The same floor. Below the 7th floor to the foundation, there were fewer, wider-spaced perimeter columns to accommodate doorways. The core of the towers 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
22646-404: The second floor, visitors were required to pass through security checks added after the 1993 World Trade Center bombing . 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. The exterior columns were narrowed to allow 28 inches of window width between them. In 1995,
22815-447: The south side of the 79th floor, while the 100–200 people who fell or jumped from the four faces of the North Tower had no other means of escape from the insufferable heat, smoke and fire consuming its top 18 stories. Such differences imply that conditions did not deteriorate as rapidly, or become as inhospitable, in the South Tower as in the North. The damage to the North Tower by Flight 11's centered impact severed all escape routes above
22984-500: 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 called Top of the World and an open-air deck with the height of 110 stories. 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). After paying an entrance fee in
23153-542: The spraying of asbestos as an insulating material and vermiculite plaster was used instead. After the 1993 bombing , inspections found fireproofing to be deficient. Before the collapses, the towers' owner, the Port Authority of New York and New Jersey , was in the process of adding fireproofing, but had completed only 18 floors in WTC 1, including all the floors affected by the aircraft impact and fires, and 13 floors in WTC 2, although none were directly affected by
23322-524: The sways. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level. In March 1965, the Port Authority began acquiring property at the World Trade Center site. Demolition work began on March 21 , 1966, to clear thirteen square blocks of low rise buildings in Radio Row for its construction. Groundbreaking for
23491-434: The taller the building, the more elevators are needed to service it, requiring more space-consuming elevator banks. Yamasaki and the engineers decided to use a new system with two " sky lobbies "—floors where people could switch from a large-capacity express elevator to a local elevator that goes to each floor in a section. This system, inspired by the local-express train operation used in New York City's subway system, allowed
23660-438: The tower. In addition to fire damage on the 9th through the 14th floors, the water used to extinguish the fire damaged a few of the floors below. At that time, the World Trade Center had no fire sprinkler systems . On March 12, 1981, the Port Authority announced a $ 45 million plan to install sprinklers throughout the World Trade Center. A disgruntled custodian, 19 year old Oswald Adorno, was discovered to have deliberately started
23829-454: The tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads , providing lateral stability to the exterior walls and distributing wind loads among the exterior walls. The floors consisted of 4-inch (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported
23998-741: The towers had a high strength-to-weight ratio requiring 40 percent less steel than more traditional steel-framed skyscrapers. In addition, atop WTC 1 stood a 362 ft (110 m) telecommunications antenna erected in 1978, bringing that tower's total height to 1,730 ft (530 m), though as a nonstructural addition, the antenna was not officially counted. The towers were designed as framed tube structures, which provided tenants with open floor plans uninterrupted by columns or walls. The buildings were square and 207 ft (63 m) on each side but had chamfered 6 ft 11 in (2.11 m) corners, making each building's exterior roughly 210 ft (64 m) wide. One World Trade Center (WTC 1),
24167-479: The towers were square, the interior cores were rectangular and supported by 47 columns that ran the full height of each tower. All the elevators and stairwells were in the core, leaving a large column-free space between it and the perimeter that was bridged by prefabricated floor trusses. As the core was rectangular, this created a long and short span distance to the perimeter columns. The floors consisted of 4 in-thick (10 cm) lightweight concrete slabs laid on
24336-477: The transmission tower. 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 compared to traditional structures, such as the Empire State Building that has thick, heavy masonry for fireproofing of steel structural elements. During the design process, wind tunnel tests were done to establish design wind pressures that
24505-421: The trusses were bolted to seats welded to the spandrels on the perimeter side and a channel welded to interior box columns on the core side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers, which helped reduce the amount of sway felt by building occupants. The towers also had a "hat truss" or "outrigger truss" between the 107th and 110th floors, consisting of six trusses along
24674-499: The two aircraft. Falling debris from the towers, combined with fires in several surrounding buildings that were initiated by falling debris, led to the partial or complete collapse of all the WTC complex's buildings, including 7 World Trade Center , and caused catastrophic damage to 10 other large structures in the surrounding area. The cleanup and recovery process at the World Trade Center site took eight months, during which
24843-464: The upper section of the building began to move downward, a total progressive collapse was unavoidable. The cleanup of the World Trade Center site involved round-the-clock operations and cost hundreds of millions of dollars. Some of the surrounding structures that had not been hit by the planes still sustained significant damage, requiring them to be torn down. Demolition of the surrounding damaged buildings continued even as new construction proceeded on
25012-410: The use of an iron hull framework which was covered in timber planking to provide the water-tight skin of the hull. If properly insulated fastenings were used on the timber, the underwater hull could be covered with copper sheathing without the problem of galvanic corrosion . Copper sheathing prevented fouling and teredo worm , but could not be used on iron hulls. The iron framework of composite ships
25181-403: The vault. Seven weeks after the September 11 attacks, $ 230 million in precious metals was removed from basement vaults of 4 WTC. This included 3,800 100-Troy-ounce 24 carat gold bars and 30,000 1,000-ounce silver bars. On February 13, 1975, a three-alarm fire broke out on the North Tower's 11th floor. It spread to the 9th and 14th floors after igniting telephone cable insulation in
25350-516: The world until 1996, when the Petronas Towers opened. Other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC , 5 WTC , 6 WTC , and 7 WTC . The complex contained 13,400,000 square feet (1,240,000 m ) of office space and, prior to its completion, was projected to accommodate an estimated 130,000 people. The core complex cost about $ 400 million (equivalent to $ 2.31 billion in 2023). The idea
25519-577: The world's first world trade center . They had two choices: the east side of Lower Manhattan , near the South Street Seaport ; or the west side, near the Hudson and Manhattan Railroad (H&M) station, Hudson Terminal . Initial plans, made public in 1961, identified a site along the East River for the World Trade Center. As a bi-state agency, the Port Authority required approval for new projects from
25688-451: Was a warehouse district in what is now Tribeca and the Financial District . Harry Schneck opened City Radio on Cortlandt Street in 1921, and eventually, the area held several blocks of electronics stores, with Cortlandt Street as its central axis. The used radios, war surplus electronics (e.g., AN/ARC-5 radios), junk, and parts were often piled so high they would spill out onto the street, attracting collectors and scroungers. According to
25857-452: Was a 180-seat cafeteria on the 44th floor of 1 WTC conceived for office workers, was also operated by Windows on the World. In its last iteration, Windows on the World received mixed reviews. Ruth Reichl , a New York Times food critic, said in December 1996 that "nobody will ever go to Windows on the World just to eat, but even the fussiest food person can now be content dining at one of New York's favorite tourist destinations". She gave
26026-527: Was a destination in itself, rather than a lazy by-product of the vital institution it resided in." Five smaller buildings stood on the 16-acre (65,000 m ) block. One was the 22-floor hotel, which opened at the southwest corner of the site in 1981 as the Vista Hotel ; in 1995, it became the Marriott World Trade Center (3 WTC). Three low-rise buildings (4 WTC, 5 WTC, and 6 WTC), which were steel-framed office buildings, also stood around
26195-438: Was asked, "Why two 110-story buildings? Why not one 220-story building?" His tongue-in-cheek response was: "I didn't want to lose the human scale." Architectural critic Ada Louise Huxtable criticized the design of the twin towers when they were first announced, saying: "Here we have the world's daintiest architecture for the world's biggest buildings." The twin towers had more floors (at 110) than any other building before
26364-544: Was charged with criminal trespass and disorderly conduct, he was later freed in exchange for performing for children in Central Park . On February 20, 1981, an Aerolíneas Argentinas airliner was guided away by air traffic controllers after radar signals indicated it was on a collision course with the North Tower (1 WTC). The aircraft, which departed from José Joaquín de Olmedo International Airport in Guayaquil , Ecuador, and
26533-520: Was completed under the auspices of the latter. The investigation was criticized by some engineers and lawmakers in the U.S. It had little funding, no authority to demand evidence, and limited access to the WTC site. One major point of contention at the time was that the cleanup of the WTC site was resulting in the destruction of the majority of the buildings' steel components. Indeed, when NIST published its final report, it noted "the scarcity of physical evidence" that it had had at its disposal to investigate
26702-522: Was concentrated in Midtown Manhattan . To help stimulate urban renewal in Lower Manhattan, David Rockefeller suggested that the Port Authority build a World Trade Center there. Plans for the use of eminent domain to remove the shops in Radio Row bounded by Vesey , Church , Liberty , and West Streets began in 1961 when the Port Authority of New York and New Jersey was deciding to build
26871-473: Was dedicated on April 4, 1973, and was destroyed during the September 11 attacks in 2001. 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
27040-515: Was developed by restaurateur Joe Baum at a cost of more than $ 17 million. As well as the main restaurant, two offshoots were located at the top of the North Tower: Hors d'Oeuvrerie (offered a Danish smorgasbord during the day and sushi in the evening) and Cellar in the Sky (a small wine bar ). Windows on the World also had a wine school program run by Kevin Zraly , who published a book on
27209-407: Was heavily damaged. After the bombing, the Port Authority installed photoluminescent pathway markings in the stairwells. The fire alarm system for the entire complex needed to be replaced because critical wiring and signaling in the original system were destroyed. A memorial to the victims of the bombing, a reflecting pool , was installed with the names of those who were killed in the blast. It
27378-484: Was later destroyed following the September 11 attacks. The names of the victims of the 1993 bombing are included in the National September 11 Memorial & Museum . In January 1998, a DeCavalcante crime family member Ralph Guarino gained maintenance access to the World Trade Center. He arranged a three-man crew for a heist that netted over $ 2 million from a Brinks delivery to the North Tower's 11th floor. On
27547-412: Was less bulky and lighter than timber, so allowing more cargo in a hull of the same external shape. The weight saving was particularly significant. The strength and stiffness allowed sailing vessels to be driven hard as the accumulated straining of the hull did not produce the leaks that would develop in the older wooden built ships. Composite hulls were used for the majority of the clippers built from
27716-519: Was necessary before the excavation of material from the interior of the site could begin. The 1,200,000 cubic yards (920,000 m ) of excavated material were used (along with other fill and dredge material) to expand the Manhattan shoreline across West Street to form Battery Park City . The Port Authority awarded $ 74 million in contracts to various steel suppliers in January 1967, and excavation of
27885-808: Was quickly assembled by the Structural Engineers Institute of the American Society of Civil Engineers , led by W. Gene Corley , Senior Vice President of CTLGroup . It also involved the American Institute of Steel Construction , the American Concrete Institute , the National Fire Protection Association , and the Society of Fire Protection Engineers . ASCE ultimately invited FEMA to join the investigation, which
28054-508: Was scheduled to land at nearby JFK Airport , was flying at a much lower altitude than regulations recommended. The 1995 PCA world chess championship was played on the 107th floor of the South Tower. On February 8, 2000, a worker was crushed to death and another was injured by an industrial cooling unit. Slow leasing was a hallmark of the old World Trade Center complex. The Twin Towers suffered high vacancy rates for decades. The complex achieved 95% occupancy only in mid-2001. Following
28223-462: Was some tilting of the tops of the towers and a significant amount of fallout to the sides. As the collapse progressed, dust and debris could be seen shooting out of the windows several floors below the advancing destruction, caused by the sudden rush of air compressed under the descending upper levels. During each collapse, large portions of the perimeter columns and the cores were left without any lateral support, causing them to fall laterally towards
28392-400: Was suggested by David Rockefeller to help stimulate urban renewal in Lower Manhattan, and his brother Nelson , then New York's 49th governor, signed the legislation to build it. The buildings at the complex were designed by Minoru Yamasaki . In 1998, the Port Authority of New York and New Jersey decided to privatize it by leasing the buildings to a private company to manage. It awarded
28561-424: Was the first building to be hit when American Airlines Flight 11 crashed into it at 8:46 a.m., causing it to collapse at 10:28 after burning for one hour and 42 minutes. At 9:03 a.m., the South Tower (WTC 2) was struck by United Airlines Flight 175 ; it collapsed at 9:59 a.m. after burning for 56 minutes. The towers' destruction caused major devastation throughout Lower Manhattan , and more than
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