View of the World Trade Center's construction from across the Hudson River

The building of the World Trade Center was conceived as an urban renewal project, spearheaded by David Rockefeller, to help revitalize Lower Manhattan. The project was developed by the Port Authority of New York and New Jersey, which hired architect Minoru Yamasaki who came up with the specific idea for twin towers. After extensive negotiations, the New Jersey and New York State governments, which oversee the Port Authority, agreed to support the World Trade Center project at the Radio Row site on the lower-west side of Manhattan. To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad (renamed as PATH), which brought commuters from New Jersey to the Lower Manhattan site. Image File history File links World_trade_center_new_york_city_construction_flickr. ... Image File history File links World_trade_center_new_york_city_construction_flickr. ... The Hudson River, called Muh-he-kun-ne-tuk in Mahican, is a river that runs through the eastern portion of New York State and, along its southern terminus, demarcates the border between the states of New York and New Jersey. ... This article is about the former World Trade Center (Twin Towers) in New York City. ... 1999 photograph looking northeast on Chicagos now demolished Cabrini-Green housing project, one of many urban renewal efforts. ... David Rockefeller, Sr. ... Woolworth Building, looking south along Broadway Lower Manhattan, from the Brooklyn Bridge, 2005 Rigid airship the USS Akron over Lower Manhattan Lower Manhattan is the southernmost part of the island of Manhattan, the main island and center of business and government of the City of New York. ... Tolls collected at the Holland Tunnel and other crossings help fund the Port Authority. ... Minoru Yamasaki (December 1, 1912 – February 6, 1986) was an American architect best known for his design of the World Trade Center. ... Official language(s) English de facto Capital Trenton Largest city Newark Area  Ranked 47th  - Total 8,729 sq mi (22,608 km²)  - Width 70 miles (110 km)  - Length 150 miles (240 km)  - % water 14. ... NY redirects here. ... Radio Row was a warehouse district in lower Manhattan, New York City. ... Manhattan is a borough of New York City, New York, USA, coterminous with New York County. ... Hoboken- and Newark-bound platform at Exchange Place station in Jersey City. ...

The towers were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. This was accomplished using numerous closely-spaced perimeter columns to provide much of the strength to the structure, along with gravity load shared with the core columns. The elevator system, which made use of sky lobbies and a system of express and local elevators, allowed substantial floor space to be freed up for use as office space by making the structural core smaller. The design and construction of the World Trade Center twin towers involved many other innovative techniques, such as the slurry wall for digging the foundation, and wind tunnel experiments. Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969. Extensive use of prefabricated components helped to speed up the construction process. The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972. Four other low-level buildings were constructed as part of the World Trade Center in the 1970s, and a seventh building was constructed in the mid-1980s. It has been suggested that this article or section be merged with Elevator surfing. ... The former World Trade Centers twin towers used sky lobbies, located on the 44th and 78th floors of each tower. ... Slurrywall excavator A slurry wall is a type of wall used to build tunnels, open cuts and foundations in areas of soft earth close to open water or with a high ground water table. ... A foundation is a structure that transmits loads from a building or road to the underlying ground. ... NASA wind tunnel with the model of a plane A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects. ... 7 World Trade Center is the name of two buildings in New York City: the first opened in 1987 and was destroyed on September 11, 2001; its replacement, the first World Trade Center address to be rebuilt, was finished in 2006. ...

Planning

In 1942, Austin J. Tobin became the Executive Director of the Port Authority, beginning a 30-year career during which he oversaw the planning and development of the World Trade Center.^[1] The concept of establishing a "world trade center" was conceived during the post-World War II period, when the United States thrived economically and international trade was increasing. In 1946, the New York State Legislature passed a bill that called for a "world trade center" to be established.^[2] The World Trade Corporation was founded, and a board was appointed by New York Governor Thomas E. Dewey to develop plans for the project.^[2] Architect John Eberson and his son Drew devised a plan that included 21 buildings over a ten-block area, at an estimated cost of $150 million.^[3] In 1949, the World Trade Corporation was dissolved by the New York State Legislature, and plans for a "world trade center" were put on hold.^[4] Austin J. Tobin (1903 - February 8, 1978), born in Brooklyn, served as the executive director of the Port of New York Authority, the precursor to the Port Authority of New York and New Jersey, from 1942 until 1972. ... Tolls collected at the Holland Tunnel and other crossings help fund the Port Authority. ... World Trade Center (in general) - World Trade Centers (or World Trade Centres), usually abbreviated WTC, arose in the United States and Japan in the 1970s, spearheaded by New York Citys World Trade Center. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... The New York Legislature is the U.S. state of New Yorks legislative branch, seated at the states capital, Albany. ... Thomas Dewey - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... John Eberson (1875 - 1964) was a Romanian born American architect best known for his movie palace designs. ...

Original plans

Architect's model for the proposed World Trade Center on the East River

During the post-war period, economic growth was concentrated in Midtown Manhattan, in part stimulated by the Rockefeller Center, which was developed in the 1930s. Meanwhile, Lower Manhattan was left out of the economic boom. One exception was the construction of One Chase Manhattan Plaza in the Financial District, by David Rockefeller, who led urban renewal efforts in Lower Manhattan.^[5] In 1958, Rockefeller established the Downtown-Lower Manhattan Association (DLMA), which commissioned Skidmore, Owings and Merrill to draw up plans for revitalizing Lower Manhattan. The plans, made public in 1960, called for a World Trade Center to be built on a 13 acre (5.25 ha) site along the East River, from Old Slip to Fulton Street and between Water Street and South Street.^[6][7] The complex would include a 900 foot (275 m) long exhibition hall, and a 50-70 story building, with some of its upper floors used as a hotel.^[8] Other amenities would include a theater, shops, and restaurants.^[9] The plan also called for a new securities exchange building, which the Downtown-Lower Manhattan Association hoped would house the New York Stock Exchange.^[7] Image File history File links Size of this preview: 800 × 588 pixelsFull resolution (1024 × 752 pixel, file size: 685 KB, MIME type: image/png) This image is a faithful digitalization of a unique historic Image, and the copyright for it is most likely held by the person who took the... Image File history File links Size of this preview: 800 × 588 pixelsFull resolution (1024 × 752 pixel, file size: 685 KB, MIME type: image/png) This image is a faithful digitalization of a unique historic Image, and the copyright for it is most likely held by the person who took the... View of Midtown from Empire State Building. ... Lower Plaza at Rockefeller Center. ... In economics, the term boom and bust refers to the movement of an economy through economic cycles due to changes in aggregate demand. ... One Chase Manhattan Plaza, New York City One Chase Manhattan Plaza is a banking skyscraper located in the downtown Manhattan Financial District of New York City. ... A view up Broad Street in the Financial District in Manhattan Federal Hall The Financial District of New York City is a neighborhood on the southernmost section of the borough of Manhattan which comprises the offices and headquarters of many of the citys major financial institutions, including the New... David Rockefeller, Sr. ... 1999 photograph looking northeast on Chicagos now demolished Cabrini-Green housing project, one of many urban renewal efforts. ... Shaklee Terraces, San Francisco, designed in 1982 with a flush aluminum and glass facade and rounded corners. ... Woolworth Building, looking south along Broadway Lower Manhattan, from the Brooklyn Bridge, 2005 Rigid airship the USS Akron over Lower Manhattan Lower Manhattan is the southernmost part of the island of Manhattan, the main island and center of business and government of the City of New York. ... An acre is the name of a unit of area in a number of different systems, including Imperial units and United States customary units. ... A hectare (symbol ha) is a unit of area, equal to 10 000 square metres, commonly used for measuring land area. ... New York City waterways: 1. ... Fulton Street is a busy street located in Lower Manhattan. ... South Street in Manhattan is noted for its seaport, also called the South Street Seaport. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... The metre or meter is a measure of length. ... Exhibition Hall of the Makaryev Fair. ... For security (collateral), the legal right given to a creditor by a borrower, see security interest A security is a fungible, negotiable interest representing financial value. ... The New York Stock Exchange (NYSE), nicknamed the Big Board, is a New York City-based stock exchange. ...

David Rockefeller suggested that the Port Authority would be a logical choice for taking on the project.^[7] Rockefeller argued that the Trade Center would provide great benefits in facilitating and increasing volume of international commerce coming through the Port of New York.^[9] Given the importance of New York City in global commerce, Port Authority director Austin J. Tobin remarked that the proposed project should be the World Trade Center, and not just a "world trade center".^[10] After a year-long review of the proposal, the Port Authority formally backed the project on March 11, 1961.^[11] New York, New York and NYC redirect here. ... March 11 is the 70th day of the year in the Gregorian calendar (71st in leap years). ... 1961 (MCMLXI) was a common year starting on Sunday (the link is to a full 1961 calendar). ...

Agreement

Location of World Trade Center and originally proposed site

The States of New York and New Jersey also needed to approve the project, given their control and oversight role of the Port Authority. Objections to the plan came from New Jersey Governor Robert B. Meyner, who resented that New York would be getting this $335 million project.^[5] Meanwhile, ridership on New Jersey's Hudson and Manhattan Railroad (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958, after new automobile tunnels and bridges opened across the Hudson River.^[12] Towards the end of 1961, negotiations with outgoing New Jersey Governor Meyner regarding the World Trade Center project reached a stalemate. In December 1961, Tobin met with newly elected New Jersey Governor Richard J. Hughes, and made a proposal to shift the World Trade Center project to a west side site where the Hudson Terminal was located.^[13] In acquiring the Hudson & Manhattan Railroad, the Port Authority would also acquire the Hudson Terminal and other buildings which were deemed obsolete.^[13] On January 22, 1962, the two states reached an agreement to allow the Port Authority to take over the railroad and to build the World Trade Center on Manhattan's lower west side.^[14] The shift in location for the World Trade Center to a site more convenient to New Jersey, together with Port Authority acquisition of the H&M Railroad, brought New Jersey to agreement in support of the World Trade Center project. Image File history File links Size of this preview: 731 × 599 pixelsFull resolution (1200 × 984 pixel, file size: 733 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Size of this preview: 731 × 599 pixelsFull resolution (1200 × 984 pixel, file size: 733 KB, MIME type: image/png) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Official language(s) English de facto Capital Trenton Largest city Newark Area  Ranked 47th  - Total 8,729 sq mi (22,608 km²)  - Width 70 miles (110 km)  - Length 150 miles (240 km)  - % water 14. ... Robert Baumle Meyner (July 3, 1908 - May 27, 1990) of Phillipsburg, New Jersey was the Democratic Governor of New Jersey from 1954 to 1962. ... NY redirects here. ... A drawing of the northern of the two underground junctions on the New Jersey side. ... The Hudson River, called Muh-he-kun-ne-tuk in Mahican, is a river that runs through the eastern portion of New York State and, along its southern terminus, demarcates the border between the states of New York and New Jersey. ... Richard Joseph Hughes (August 10, 1909–December 7, 1992) was the Democratic Governor of the U.S. state of New Jersey from 1962 to 1970. ... Other service New York City Subway Other information Opened 1909 / 1971 / 2003 Services The World Trade Center PATH station originally opened on July 19, 1909 as the Hudson Terminal. ... January 22 is the 22nd day of the year in the Gregorian calendar. ... Year 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar) of the Gregorian calendar. ...

Controversy

Even once the agreement between the states of New Jersey, New York, and the Port Authority was finalized, the World Trade Center plan faced continued controversy. The site for the World Trade Center was the location of Radio Row, which was home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents.^[5] The World Trade Center plans involved evicting these business owners, some of whom fiercely protested the forced relocation.^[5] In June 1962, a group representing approximately 325 shops and 1,000 other affected small businesses filed an injunction, challenging the Port Authority's power of eminent domain.^[15] The dispute with local business owners worked its way through the court system, up to the New York State Court of Appeals, which in April 1963 upheld the Port Authority's right of eminent domain, saying that the project had a "public purpose".^[16][17] On November 12, 1963, the United States Supreme Court refused to accept the case.^[18][19] Under the state law, the Port Authority was required to assist business owners in relocating, though many business owners regarded what the Port Authority offered as inadequate.^[18][20] Questions continued while the World Trade Center was constructed, as to whether the Port Authority really ought to take on the project, described by some as a "mistaken social priority".^[21] Radio Row was a warehouse district in lower Manhattan, New York City. ... Look up Injunction in Wiktionary, the free dictionary. ... Eminent domain (U.S.), compulsory purchase (United Kingdom, New Zealand, Ireland), resumption/compulsory acquisition (Australia) or expropriation (Canada, South Africa) in common law legal systems is the inherent power of the state to seize a citizens private property, expropriate private property, or rights in private property, without the owner... The Court of Appeals is New Yorks highest appellate court, created in 1847, replacing the Court for the Trial of Impeachments and the Correction of Errors. ... is the 316th day of the year (317th in leap years) in the Gregorian calendar. ... Year 1963 (MCMLXIII) was a common year starting on Tuesday (link will display full calendar) of the Gregorian calendar. ... Federal courts Supreme Court Chief Justice Associate Justices Elections Presidential elections Midterm elections Political Parties Democratic Republican Third parties State & Local government Governors Legislatures (List) State Courts Counties, Cities, and Towns Other countries Politics Portal      The Supreme Court of the United States (SCOTUS) is the highest judicial body in the...

Private real estate developers and members of the Real Estate Board of New York also expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.^[5][22] An especially vocal critic was Lawrence A. Wien, owner of the Empire State Building, which would lose its title of tallest building in the world.^[5][23] Wien organized a group of builders into a group called the "Committee for a Reasonable World Trade Center" which demanded the project be scaled down.^[24] Real estate is a legal term that encompasses land along with anything permanently affixed to the land, such as buildings. ... The Empire State Building in New York The Empire State Building is a 102-story Art Deco skyscraper in New York, NY. Its name is derived from the nickname for the state of New York. ... While determining the worlds tallest structure has generally been straightforward, the definition of the worlds tallest building or the worlds tallest tower is less clear. ...

In January 1964, the Port Authority inked a deal with the State of New York to locate government offices at the World Trade Center.^[25] The Port Authority began signing up some commercial tenants in the Spring and Summer of 1964, including several banks.^[26] In 1965, the Port Authority signed up the United States Customs Service as a tenant.^[27] The United States Customs Service (now part of U.S. Customs and Border Protection or CBP) was the portion of the US Federal Government dedicated to keeping illegal products outside of US borders. ...

A final obstacle for the Port Authority was getting approval from New York City Mayor John Lindsay and the New York City Council. They raised concerns about the limited extent that the Port Authority involved the city in the negotiations and deliberations. Negotiations between The City of New York and the Port Authority were centered on tax issues. A final agreement was made on August 3, 1966, that the Port Authority would make annual payments to the city in lieu of taxes, for the portion of the World Trade Center leased to private tenants.^[28] In subsequent years, the payments would rise as the overall real estate tax rate increased.^[29] This article does not cite any references or sources. ... New York City Hall The New York City Council is the lawmaking body of the City of New York. ... is the 215th day of the year (216th in leap years) in the Gregorian calendar. ... 1966 (MCMLXVI) was a common year starting on Saturday (the link is to a full 1966 calendar). ... Property tax, millage tax is an ad valorem tax that an owner of real estate or other property pays on the value of the property being taxed. ...

Design

On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect, and Emery Roth & Sons as associate architects.^[30] Originally, Yamasaki came back to the Port Authority with the concept of twin towers, but with each building only 80 stories tall. Yamasaki remarked that the "obvious alternative, a group of several large buildings, would have looked like a housing project".^[31] is the 262nd day of the year (263rd in leap years) in the Gregorian calendar. ... Year 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar) of the Gregorian calendar. ... Minoru Yamasaki (December 1, 1912 – February 6, 1986) was an American architect best known for his design of the World Trade Center. ... Emery Roth (1871 – August 20, 1948) was an American architect who built many of the definitive New York City hotels and apartment buildings of the 1920s and 30s, incorporating Beaux-Arts and Art Deco details. ...

A typical floor layout and elevator arrangement of the WTC towers

To meet the Port Authority's requirement to build 10 million square feet (930,000 m²) of office space, the buildings would each need to be 110 stories tall. A major limiting factor in building heights were elevators. The taller the building, the more elevators are needed to service the building, requiring more space-consuming elevator banks.^[32] Yamasaki and the engineers decided to use a new system with sky lobbies, which are floors where people can switch from a large-capacity express elevator, which goes only to the sky lobbies, to a local elevator that goes to each floor in a section. The local elevators were stacked on top of each other, 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, while also increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of required elevator shafts.^[33] The World Trade Center towers were the second supertall buildings to use sky lobbies, after the John Hancock Center in Chicago.^[34] This system was inspired by the New York City Subway system, whose lines include local stations where local trains stop and express stations where all trains stop.^[35] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A square foot is by definition the area enclosed by a square with sides each 1 foot long. ... It has been suggested that this article or section be merged with Elevator surfing. ... Unbuilt supertall skyscraper, The Illinois Supertall is a term that refers to a skyscraper exceeding 1000 feet or 300 meters. ... Several buildings bear this name, all built by John Hancock Insurance and named after John Hancock. ... Nickname: Motto: Urbs In Horto (Latin: City in a Garden), I Will Location in the Chicago metro area and Illinois Coordinates: , Country United States State Illinois County Cook & DuPage Settled 1770s Incorporated March 4, 1837 Government  - Mayor Richard M. Daley (D) Area  - City  234. ... The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority, an affiliate of the Metropolitan Transportation Authority as MTA New York City Transit. ...

Original architectural and engineering model

Yamasaki's design for the World Trade Center was unveiled to the public on January 18, 1964, with an eight-foot model.^[31] The towers had a square plan, approximately 207 feet (63 m) in dimension on each side.^[36] The buildings were designed with narrow office windows, only 18 inches (45 cm) wide, which reflected on Yamasaki's fear of heights and desire to make building occupants feel secure.^[37] Yamasaki's design called for the building facades to be sheathed in aluminum-alloy.^[38] In all, the World Trade Center complex contained six buildings within the 16 acre (6.5 ha) superblock. Image File history File linksMetadata Size of this preview: 450 × 600 pixelsFull resolution (1704 × 2272 pixel, file size: 953 KB, MIME type: image/jpeg) Original architectural/engineering model of the World Trade Center, on exhibit at the Skyscraper Museum in New York City. ... Image File history File linksMetadata Size of this preview: 450 × 600 pixelsFull resolution (1704 × 2272 pixel, file size: 953 KB, MIME type: image/jpeg) Original architectural/engineering model of the World Trade Center, on exhibit at the Skyscraper Museum in New York City. ... is the 18th day of the year in the Gregorian calendar. ... 1964 (MCMLXIV) was a leap year starting on Wednesday (the link is to a full 1964 calendar). ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... A person with acrophobia would fear such a height Acrophobia (from Greek , meaning summit) is an extreme or irrational fear of heights. ... City Blocks are a part of the fictional universe recounted in the Judge Dredd series that appears in the UK comic book 2000 AD. // Overview Also known as starscrapers or stratoscrapers (compare skyscraper), they are the most common form of mass-housing in Mega-City One, averaging a population of...

The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups.^[39][38] Lewis Mumford, author of The City in History and other works on urban planning, criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets".^[40] Television broadcasters raised concerns that the World Trade Center twin towers would cause interference in television reception for viewers in the New York City area.^[41] In response to these concerns, the Port Authority offered to provide new television transmission facilities at the World Trade Center.^[42] The Linnaean Society of the American Museum of Natural History also opposed the Trade Center project, citing hazards the buildings would impose on migrating birds.^[43] The American Institute of Architects (AIA) is a professional organization for architects in the United States. ... Lewis Mumford (October 19, 1895 – January 26, 1990) was an American historian of technology and science. ... The City in History: Its Origins, Its Transformations, and Its Prospects is a 1961 work by American theorist of society and technology Lewis Mumford. ... Urban planning is concerned with the ordering and design of settlements, from the smallest towns to the worlds largest cities. ... The New York metropolitan area is the most populous in the United States and the fourth most populous in the world (after Tokyo, Seoul, and Mexico City). ... The Linnean Society of London is the worlds premier society for the study and dissemination about taxonomy. ... This article does not cite any references or sources. ... Flock of Barnacle Geese during autumn migration Bird migration refers to the regular seasonal journeys of varying distances undertaken by many species of birds. ...

The structural engineering firm Skilling, Helle, Christiansen, Robertson worked to implement Yamasaki's design, developing the tube-frame structural system used in the buildings. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and the Port Authority's Chief Engineer, Rino M. Monti, oversaw the project.^[44] Leslie E. Robertson (1928-) was the chief engineer in charge of design of the now destroyed World Trade Center in New York. ... Bostons Big Dig presented geotechnical challenges in an urban environment. ... Electrical Engineers design power systems… … and complex electronic circuits. ... Mechanical engineering is an engineering discipline that involves the application of principles of physics for analysis, design, manufacturing, and maintenance of mechanical systems. ... The Tishman Realty & Construction is a construction management and real estate development company. ... A general contractor is an organization or individual that contracts with another organization or individual (the owner) for the construction of a building, road or other facility. ...

Structural design

As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York, including building codes. Nonetheless, the Port Authority required architects and structural engineers to follow the New York City building codes. At the time when the World Trade Center was planned, new building codes were being devised to replace the 1938 version that was in place. The structural engineers ended up following draft versions of the new 1968 building codes which incorporated "advanced techniques" in building design.^[45] A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. ... Building design is the design of architectural exterior/interior spaces, engineered elements and shelter design. ...

The World Trade Center towers included many structural engineering innovations in skyscraper design and construction, which allowed the buildings to reach new heights and become the tallest in the world. Traditionally, skyscrapers used a skeleton of columns distributed throughout the interior to support building loads, with interior columns disrupting the floor space. The tube-frame concept was a major innovation, allowing open floor plans and more space to rent. The buildings used high-strength, load-bearing perimeter steel columns called Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure. There were 59 perimeter columns, narrowly spaced on each side of the buildings. These were designed to provide support for virtually all lateral loads (such as wind loads) and to share the gravity loads with the core columns.^[46] Structural analysis of major portions of the World Trade Center were computed on an IBM 1620.^[47] Taipei 101, the worlds tallest building as of 2004. ... Skyscrapers are tall, internally supported structures where the majority of load bearing structure, outside of that providing structural support for dead load is specifically designed to provide for large free spaces between supporting elements while still providing for the structural support and the building utilities required for the densely populated... Taipei 101, the worlds tallest building, is located in Taipei City, (Republic of China). ... This article does not cite any references or sources. ... Deconstructing a Roman pillar. ... The steel cable of a colliery winding tower. ... In architecture and structural engineering, a truss is a structure comprising one or more triangular units which are constructed with straight slender members whose ends are connected at joints. ... The IBM 1620 was announced by IBM on October 21, 1959 and marketed as an inexpensive scientific computer. It was withdrawn on November 19, 1970. ...

Typical WTC architectural floor plan

The perimeter structure was constructed with extensive use of prefabricated modular pieces, which consisted of three columns, three stories tall, connected together by spandrel plates. The perimeter columns had a square cross section, 14 inches (36 cm) on a side, and were constructed of welded steel plate.^[48] The thickness of the plates and grade of structural steel varied over the height of the tower, ranging from 36,000 to 100,000 pounds per square inch^[49] (260 to 670 MPa). The strength of the steel and thickness of the steel plates decreased with height because they were required to support lesser amounts of building mass on higher floors.^[48] The tube-frame design required 40 percent less structural steel than conventional building designs.^[50] From floor #7 to the ground level and down to the foundation, the columns were spaced 10 feet (3 m) apart.^[51] All columns were founded on bedrock, which unlike that in Midtown Manhattan, where the bedrock is shallow, is at 65–85 feet (20–26 m) below the surface.^[52] Image File history File links Size of this preview: 609 × 599 pixelsFull resolution (1017 × 1001 pixel, file size: 304 KB, MIME type: image/png) Typical WTC tower architectural floor plan Source: NIST NCSTAR1-1 - http://wtc. ... Image File history File links Size of this preview: 609 × 599 pixelsFull resolution (1017 × 1001 pixel, file size: 304 KB, MIME type: image/png) Typical WTC tower architectural floor plan Source: NIST NCSTAR1-1 - http://wtc. ... Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and strength. ... Bedrock is the native consolidated rock underlying the Earths surface. ...

The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.^[53] The modular pieces were typically 52 inches (1.3 m) deep, and extended for two full floors and half of two more floors.^[48] 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, and served to transmit shear stress between columns, thus allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically, so the column splices between adjacent modules were not at the same floor.^[48] Shear stress is a stress state where the stress is parallel or tangential to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ...

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.^[48] The columns tapered with height, and consisted of welded box-sections at lower floors and rolled wide-flange sections at upper floors. The core in 1 WTC was oriented with the long axis east to west, while that of 2 WTC was oriented north to south. All of the elevators were located in the core. Each building had three stairwells that were also located in the core, except on the mechanical floors where they were located outside of the structural core.^[54] A mechanical floor, mechanical penthouse, or mechanical level is a floor of a high-rise building that is dedicated to mechanical and electronics equipment. ...

Schematic of composite floor truss system

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, provided lateral stability to the exterior walls, and distributed 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 the floors. The trusses had a span of 60 feet (18.2 m) in the long-span areas and 35 feet (11 m) in the short span area.^[48] The trusses connected to the perimeter at alternate columns, and were therefore 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, which helped reduce the amount of sway felt by building occupants. The trusses supported a 4 inch thick (10 cm) lightweight concrete floor slab, with shear connections for composite action.^[48] Image File history File links Size of this preview: 800 × 415 pixelsFull resolution (934 × 485 pixel, file size: 172 KB, MIME type: image/png) Schematic of composite floor truss system in the World Trade Center Source: Figure 1. ... Image File history File links Size of this preview: 800 × 415 pixelsFull resolution (934 × 485 pixel, file size: 172 KB, MIME type: image/png) Schematic of composite floor truss system in the World Trade Center Source: Figure 1. ... This article does not cite any references or sources. ... Concrete being poured, raked and vibrated into place in residential construction in Toronto, Ontario, Canada. ... Viscoelasticity, also known as anelasticity, describes materials that exhibit both viscous and elastic characteristics when undergoing plastic deformation. ...

Hat trusses (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communications antenna on top of each building.^[48] Only 1 WTC (north tower) actually had an antenna fitted, which was added in 1978.^[55] The truss system consisted of six trusses along the long axis of core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower. In architecture and structural engineering, a truss is a structure comprising one or more triangular units which are constructed with straight slender members whose ends are connected at joints. ... A Yagi-Uda beam antenna Short Wave Curtain Antenna (Moosbrunn, Austria) A building rooftop supporting numerous dish and sectored mobile telecommunications antennas (Doncaster, Victoria, Australia) An antenna or aerial is a transducer designed to transmit or receive radio waves which are a class of electromagnetic waves. ...

Wind effects

The tube frame 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 have thick, heavy masonry for fireproofing of steel structural elements.^[56] During the design process, wind tunnel tests were done at Colorado State University and at the National Physical Laboratory in the U.K. to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.^[57] Experiments were also done to evaluate how much sway occupants could tolerate. Subjects were recruited for "free eye exams", while the real purpose of the experiment was to subject them to simulated building sway and find out how much they could comfortably tolerate.^[58] Many subjects did not respond well, experiencing dizziness and other ill effects. The chief engineer Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. 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.^[59] The Empire State Building in New York The Empire State Building is a 102-story Art Deco skyscraper in New York, NY. Its name is derived from the nickname for the state of New York. ... Masonry in action; a Mason at work. ... Fireproofing, a passive fire protection measure, subject to bounding, refers to the act of making materials or structures more resistant to fire, or to those materials themselves. ... NASA wind tunnel with the model of a plane A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects. ... Colorado State University is a public land grant institution of higher learning located in Fort Collins, Colorado in the United States. ... The National Physical Laboratory (NPL) is the national measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington in the London Borough of Richmond upon Thames. ... Motto  2(French) God and my right Anthem God Save the Queen 3 United Kingdom() – on the European continent() – in the European Union() Capital London Largest conurbation (population) Greater London Urban Area Official languages English (de facto)4 Government  -  Monarch Queen Elizabeth II  -  Prime Minister Gordon Brown Formation  -  Acts of... // Pre-syncope is a sensation of feeling faint. ... Leslie E. Robertson (1928-) was the chief engineer in charge of design of the now destroyed World Trade Center in New York. ... Damping is any effect, either deliberately engendered or inherent to a system, that tends to reduce the amplitude of oscillations of an oscillatory system. ...

Fire protection

Sprayed-fire resistant materials (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams.^[60] Gypsum wallboard in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns.^[60] Vermiculite plaster was used on the interior-side and SFRMs on the other three sides of the perimeter columns for fire protection.^[60] The 1968 New York City building codes were more lenient in some aspects of fire protection, such as allowing three exit stairwells in the World Trade Center towers, instead of six as required under older building codes.^[61] Fireproofing, a passive fire protection measure, subject to bounding, refers to the act of making materials or structures more resistant to fire, or to those materials themselves. ... Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. // Heating gypsum to between 100°C and 150°C (302°F) partially dehydrates the mineral by driving off exactly 75% of the water contained in its chemical structure. ... Drywall, the ubiquitous interior building material. ... Vermiculite is a natural, non toxic mineral that expands with the application of heat. ...

The 1968 New York City building codes did not require sprinklers for high-rise buildings, except for underground spaces. In accordance with building codes, sprinklers were originally installed only in the underground parking structures of the World Trade Center.^[62] Following a major fire in February 1975, the Port Authority decided to start installing sprinklers throughout the buildings. By 1993, nearly all of Tower 2 [South Tower] and 85% of Tower 1 had sprinklers installed,^[63] and the entire complex was retrofitted by 2001.^[64] Fire sprinklers are an active fire protection measure subject to stringent bounding. ... High-rise is a 1975 novel by J. G. Ballard. ...

Construction

In March 1965, the Port Authority began acquiring property at the World Trade Center site.^[65] The Ajax Wrecking and Lumber Corporation was hired for the demolition work, which began on March 21, 1966 to clear the site for construction of the World Trade Center.^[66] Demolition of the Old Myer Building, Perth, Western Australia. ... March 21 is the 80th day of the year (81st in leap years) in the Gregorian calendar. ... 1966 (MCMLXVI) was a common year starting on Saturday (the link is to a full 1966 calendar). ...

Groundbreaking was on August 5, 1966, marking the beginning of construction of the World Trade Center's foundations.^[67] The site of the World Trade Center was located on landfill, with the bedrock located 65 feet (20 m) below.^[68] In order to construct the World Trade Center, it was necessary to build the "bathtub", with the slurry wall along the West Street side of the site, to keep water from the Hudson River out. This method was used in place of conventional dewatering methods because lowering the groundwater table would cause large settlements of nearby buildings not built on deep foundations.^[69] The slurry method involves digging a trench, and as excavation proceeds, filling the space with a "slurry" mixture, composed of bentonite which plugs holes and keeps water out. When the trench was dug out, a steel cage was inserted, with concrete poured in, forcing the "slurry" out. The "slurry" method was devised by Port Authority chief engineer John M. Kyle, Jr. Towards the end of 1966, work began on building the slurry wall, led by Montreal-based Icanda, a subsidiary of an Italian engineering firm, Impresa Costruzioni Opere Specializzate (I.C.O.S.).^[70] It took fourteen months for the slurry wall to be completed, which was necessary before excavation of material from the interior of the site could begin.^[70] The original Hudson Tubes, which carried PATH trains into Hudson Terminal, remained in service as elevated tunnels until 1971 when a new PATH station was built.^[71] Groundbreaking is a traditional ceremony in many cultures that celebrates the first day of construction for a building or other project. ... August 5 is the 217th day of the year in the Gregorian calendar (218th in leap years), with 148 days remaining. ... 1966 (MCMLXVI) was a common year starting on Saturday (the link is to a full 1966 calendar). ... Albury landfill, Surrey, England A landfill, also known as a dump, is a site for the disposal of waste materials by burial and is the oldest form of waste treatment. ... Slurrywall excavator A slurry wall is a type of wall used to build tunnels, open cuts and foundations in areas of soft earth close to open water or with a high ground water table. ... The last elevated portion of the West Side Highway by Trump Place apartment complex The West Side Highway (officially the Joe DiMaggio Highway, formerly the Miller Highway) is a mostly-surface section of New York State Route 9A (NY 9A) that runs from West 72nd Street along the Hudson River... The Hudson River, called Muh-he-kun-ne-tuk in Mahican, is a river that runs through the eastern portion of New York State and, along its southern terminus, demarcates the border between the states of New York and New Jersey. ... Cross section showing the water table varying with surface topography as well as a perched water table The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. ... Timber frame building showing considerable, but tolerable settlement Settlement in construction refers to the distortion or disruption of parts of a building due to either; unequal compression of its foundations, shrinkage such as that which occurs in timber framed buildings as the frame adjusts its moisture content, or by undue... A deep foundation installation for a bridge in Napa, California. ... This article needs additional references or sources to facilitate its verification. ... The term archaeological excavation has a double meaning. ... Bentonite - USGS Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite, (Na,Ca)0. ... Nickname: Motto: Concordia Salus (in unity, prosperity) Coordinates: , Country Canada Province Quebec Founded 1642 Established 1832 Government  - Mayor Gérald Tremblay Area [1][2][3]  - City 365. ... Downtown Hudson Tubes carry PATH Trains under the Hudson River to and from the World Trade Center station. ... Late-night and weekend service: The World Trade Center PATH station, originally opened on July 19, 1909 as the Hudson Terminal. ...

World Trade Center in 1973

Construction work began on the North Tower in August 1968 with construction beginning on the South Tower by January 1969.^[72] In January 1967, $74 million in contracts were awarded to the Pacific Car and Foundry Company, Laclede Steel Company, Granite City Steel Company, and Karl Koch Erecting Company to supply steel for the project.^[73] The Port Authority chose to use many different steel suppliers, bidding on smaller portions of steel, rather than buy larger amounts from a single source such as Bethlehem Steel or U.S. Steel as a cost-saving measure.^[74] Karl Koch was also hired to do all the work of erecting the steel, and a contract for work on the aluminum facade was awarded to the Aluminum Company of America.^[73] Tishman Realty & Construction was hired in February 1967 to oversee construction of the project.^[75] Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... This article or section does not cite any references or sources. ... PACCAR, Inc. ... It has been suggested that this article or section be merged into Alton Steel. ... The United States Steel Corporation (NYSE: X) is an integrated steel producer with major production operations in the United States and Central Europe. ... Karl Koch Steel Consulting is a steel construction firm, based in Oyster Bay, New York. ... The steel cable of a colliery winding tower. ... Bethlehem Steel Corporations flagship manufacturing facility in Bethlehem, Pennsylvania, in the United States. ... The United States Steel Corporation (NYSE: X) is an integrated steel producer with major production operations in the United States and Central Europe. ... This article or section does not cite its references or sources. ... The Tishman Realty & Construction is a construction management and real estate development company. ...

Extensive use of prefabricated parts for the perimeter framing and floor truss systems helped speed up the construction process and reduce costs, while providing greater quality control.^[50] Steel components were freighted into a Penn Central yard in Jersey City. From there, they were brought in early morning hours through the Holland Tunnel to the construction site, and lifted into place by a crane.^[76] Larger pieces were brought to the construction site by tugboats.^[77] A special type of crane, suitable for constructing such tall buildings, that used hydraulics to lift components and provided its own power was used in construction of the World Trade Center. The Favco Standard 2700 Crane, manufactured by Favelle Mort Ltd. of New South Wales, Australia was informally called a "kangaroo crane".^[78] This article or section does not cite its references or sources. ... For the Jurassic 5 album, see Quality Control (album) In engineering and manufacturing, quality control and quality engineering are involved in developing systems to ensure products or services are designed and produced to meet or exceed customer requirements. ... The Pennsylvania and New York Central Transportation Company, almost always called Penn Central, was an American railroad company that operated from 1968 until 1976. ... Location of Jersey City within New Jersey. ... Clifford Milburn Holland, 1919 Traveling through the Holland Tunnel, from Manhattan to New Jersey. ... A modern crawler type derrick crane with outriggers. ... The Le Four manoeuvering in Brest harbour A tugboat, or tug, is a boat used to manoeuvre, primarily by towing or pushing other vessels (see shipping) in harbours, over the open sea or through rivers and canals. ... Table of Hydraulics and Hydrostatics, from the 1728 Cyclopaedia. ... Capital Sydney Government Constitutional monarchy Governor Professor Marie Bashir Premier Morris Iemma (ALP) Federal representation  - House seats 50  - Senate seats 12 Gross State Product (2004-05)  - Product ($m)  $305,437 (1st)  - Product per capita  $45,153/person (4th) Population (End of March 2006)  - Population  6,817,100 (1st)  - Density  8. ... Species Macropus rufus Macropus giganteus Macropus fuliginosus Macropus antilopinus A kangaroo is a marsupial from the family Macropodidae. ...

In 1970, tugboat workers went on strike, halting the transport of material to the construction site.^[79] The Port Authority attempted other means of transporting material, including via helicopter. When this method was tried, the helicopter lost its load of steel into the Kill Van Kull.^[80] Some other mishaps occurred during the construction process, including disruption of telephone service in Lower Manhattan when telephone cables were crushed by pile drivers.^[81] On March 16, 1970, a propane gas explosion injured six workers when a truck hit a propane tank.^[82] In all, 60 workers were killed in construction accidents while the World Trade Center was being built.^[83] A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors consisting of two or more rotor blades. ... The Kill Van Kull is a tidal strait approximately 3 miles long and 1000 feet wide separating Staten Island and Bayonne, New Jersey, USA. The name kill comes from an old Dutch word for water channel It connects Newark Bay with Upper New York Bay. ... This article or section includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... A pneumatic crane working as a pile driver. ... March 16 is the 75th day of the year (76th in leap years) in the Gregorian calendar. ... 1970 (MCMLXX) was a common year starting on Thursday. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ...

Construction of 1 World Trade Center (North Tower) was completed on December 23, 1970, with 2 World Trade Center (South Tower) completed on July 19, 1971.^[72] The first tenants moved into the North Tower in December 1970, and into the South Tower in January 1972.^[84] The buildings were dedicated on April 4, 1973; Tobin, who had resigned the year before, was absent from the ceremonies.^[85] December 23 is the 357th day of the year (358th in leap years) in the Gregorian calendar. ... 1970 (MCMLXX) was a common year starting on Thursday. ... is the 200th day of the year (201st in leap years) in the Gregorian calendar. ... Year 1971 (MCMLXXI) was a common year starting on Friday (link will display full calendar) of the 1971 Gregorian calendar. ... is the 94th day of the year (95th in leap years) in the Gregorian calendar. ... Year 1973 (MCMLXXIII) was a common year starting on Monday (link will display full calendar) of the 1973 Gregorian calendar. ...

Building the World Trade Center involved excavating 1.2 million cubic yards (917,000 m³) of material.^[86] Rather than transporting this material at great costs out to sea or to landfills in New Jersey, the fill material was used to expand the Manhattan shoreline across West Street.^[86] Work to demolish the piers began on January 5, 1967, including Pier 7 to Pier 11 which were all constructed around 1910.^[87] The demolition work moved forward, despite conflicts between David Rockefeller, Governor Nelson Rockefeller and Mayor John Lindsay regarding plans for Battery Park City.^[88] Landfill material from the World Trade Center was used to add land, and a cellular cofferdam was constructed to retain the material.^[68] The result was a 700 foot (210 m) extension into the Hudson River, running six blocks or 1,484 feet (450 m).^[86] This land was a "gift" to New York City, allowing more tax-generating developments in Battery Park City.^[89] The cubic yard (symbols yd³, cu. ... The cubic meter (symbol m³) is the SI derived unit of volume. ... Official language(s) English de facto Capital Trenton Largest city Newark Area  Ranked 47th  - Total 8,729 sq mi (22,608 km²)  - Width 70 miles (110 km)  - Length 150 miles (240 km)  - % water 14. ... Manhattan is a borough of New York City, New York, USA, coterminous with New York County. ... For the type of foundation, see Deep foundation. ... January 5 is the 5th day of the year in the Gregorian calendar. ... 1967 (MCMLXVII) was a common year starting on Sunday of the Gregorian calendar (the link is to a full 1967 calendar). ... David Rockefeller, Sr. ... Nelson Aldrich Rockefeller (July 8, 1908 – January 26, 1979) was an American Vice President, governor of New York State, philanthropist and businessman. ... This article does not cite any references or sources. ... The promenade of Battery Park City. ... This article is about the former World Trade Center (Twin Towers) in New York City. ... dam stands for dekametre. ... Tax rates around the world Tax revenue as % of GDP Economic policy Monetary policy Central bank   Money supply Fiscal policy Spending   Deficit   Debt Trade policy Tariff   Trade agreement Finance Financial market Financial market participants Corporate   Personal Public   Banking   Regulation        A tax is a financial charge or other levy imposed on...

The original estimates put forth by the Port Authority had the costs for construction of the World Trade Center at $350 million — an optimistic figure.^[90] In December 1966, the Port Authority announced increased cost estimates, bringing the estimated total to $575 million.^[91] This announcement brought criticism of the project from private real estate developers, The New York Times, and others in New York City.^[92] The critics charged that the Port Authority figure was an unrealistically low estimate, and they estimated the project would end up costing $750 million.^[93] When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.^[94] The project was financed through tax-exempt bonds issued by the Port Authority.^[95] The New York Times is a daily newspaper published in New York City by Arthur Ochs Sulzberger Jr. ... A tax exemption is an exemption to the tax law of a state or nation in which part of the taxes that would normally be collected from an individual or an organization are instead foregone. ... In finance, a bond is a debt security, in which the issuer owes the holders a debt and is obliged to repay the principal and interest (the coupon) at a later date, termed maturity. ...

Other buildings

The World Trade Center complex included four other smaller buildings constructed during the 1970s. 3 World Trade Center was a 22-story building, which was home to the Marriott World Trade Center. It was designed by Skidmore, Owings and Merrill in 1978-79.^[96] 4 World Trade Center, 5 World Trade Center, and 6 World Trade Center were all 8-9 story buildings that were designed by the same team as the Twin Towers, including Minoru Yamasaki, Emery Roth & Sons, and Skilling, Helle, Christiansen, Robertson.^[97] A seventh building (7 World Trade Center) was built in the mid-1980s, just to the north of the main World Trade Center site. The 47-story building was designed by Emery, Roth & Sons, and constructed on top of a Con Edison power substation.^[98] Marriott with Twin Towers, July 2001 The Marriott World Trade Center Hotel was a 22-story[1] steel-framed building with 825 rooms. ... Shaklee Terraces, San Francisco, designed in 1982 with a flush aluminum and glass facade and rounded corners. ... World Trade Center 4 was a 9-story low-rise office building in the southeast corner of the site, in Lower Manhattan, New York City. ... 5 WTC, upper right corner. ... 6 World Trade Center was the U.S. Customs House: a 537,693 square foot (49,953 m²), 7 story low rise building, in Lower Manhattan, New York City. ... 7 World Trade Center is the name of two buildings in New York City: the first opened in 1987 and was destroyed on September 11, 2001; its replacement, the first World Trade Center address to be rebuilt, was finished in 2006. ... Consolidated Edison Company of New York (NYSE: ED) (Con Edison, or Con Ed) is a utility company in New York state, USA. Con Edison is a regulated utility that provides electric service in New York City and most of Westchester County, New York. ... An aerial substation A substation is the part of an electricity transmission and distribution system where voltage is transformed from low to high and vice versa using transformers. ...

Modifications

Over time, numerous structural modifications were made to suit the needs of tenants in the Twin Towers. Modifications were made in accordance with the Port Authority's Tenant Alteration Review Manual and were reviewed by the Port Authority to ensure the changes did not compromise structural integrity of the buildings. Oftentimes, openings were cut in the floors to allow new stairways to be built to connect tenant floors. Some steel beams in the core were reinforced and strengthened to accommodate heavy live loads, such as large amounts of heavy files that tenants had on their floors.^[99]

Repairs to structural elements on the lower levels of 1 WTC [North Tower] were made following the 1993 World Trade Center bombing. The greatest damage occurred on levels B1 and B2, with significant structural damage also on level B3.^[100] Primary structural columns were not damaged, but secondary steel members experienced some damage.^[101] Floors that were blown out needed to be repaired, to restore the structural support they provided to columns.^[102] The slurry wall was in peril following the bombing and loss of the floor slabs which provided lateral support to counteract pressure from Hudson River water on the other side.^[103] The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex, was heavily damaged and replaced with a temporary system for the summer of 1993.^[103] The fire alarm system for both towers needed to be replaced, after critical wiring and signaling in the original system was destroyed in the 1993 bombing. Installation of the new system took years to complete, and replacement of some components was still underway at the time of the September 11, 2001 attacks.^[104] The World Trade Center bombing was the February 26, 1993 attack in the garage of the New York City World Trade Center. ... Refrigeration is the process of removing heat from an enclosed space, or from a substance, and rejecting it elsewhere for the primary purpose of lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. ... Note: in the broadest sense, air conditioning can refer to any form of heating, ventilation, and air-conditioning. ... A Wheelock MT-24-LSM fire alarm horn and strobe. ... A sequential look at United Flight 175 crashing into the south tower of the World Trade Center The September 11, 2001 attacks (often referred to as 9/11—pronounced nine eleven or nine one one) consisted of a series of coordinated terrorist[1] suicide attacks upon the United States, predominantly...

See also

• Collapse of the World Trade Center
• Freedom Tower
• 150 Greenwich Street
• 175 Greenwich Street
• 200 Greenwich Street
• Plans to rebuild the World Trade Center
• Philippe Petit, who wirewalked between the two towers

Ground Zero debris with markup showing building locations. ... For the building in Florida of the same name, see Freedom Tower (Miami). ... A rendering of the new World Trade Center as completed. ... A rendering of the new World Trade Center as completed. ... A rendering of the new World Trade Center as completed. ... Proposal for Rebuilt Twin Towers, from Triroc. ... Petit at WTC, 1974 Philippe Petit (born August 13, 1949) is a French high wire artist who gained fame for his illegal walk between the former Twin Towers in New York City on August 7, 1974. ...

References

The Otis Elevator Company is the worlds largest manufacturer of vertical transportation systems, principally elevators and escalators. ... For the Manfred Mann album, see 2006 (album). ... is the 341st day of the year (342nd in leap years) in the Gregorian calendar. ... The American Society of Civil Engineers (ASCE) was founded in 1852 to represent members of the civil engineering profession worldwide. ... A36 steel is a standard steel alloy which is the most common structural steel used in the United States. ... Yield strength, or the yield point, is defined in engineering and materials science as the stress at which a material begins to plastically deform. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... May 16 is the 136th day of the year (137th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 135th day of the year (136th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 135th day of the year (136th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 135th day of the year (136th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 135th day of the year (136th in leap years) in the Gregorian calendar. ...

External links

• New York: A Documentary Film - The Center of the World - Building the World Trade Center, an 18-minute film, with construction footage, produced by the Port Authority in 1983
• World Trade Center - Skyscraper Museum
• Corus in construction - Systems evolution. Retrieved on 2007-05-14.
• NIST and the World Trade Center
• New York's World Trade Center - A Living Archive - by author, Eric Darton
• The Death of New York's Radio Row, by Syd Steinhard - Downtown Express