The
construction of the World Trade CenterThe World Trade Center was a complex in Lower Manhattan in New York City whose seven buildings were destroyed in 2001 in the September 11 terrorist attacks...
was conceived as an
urban renewalUrban renewal is a program of land redevelopment in areas of moderate to high density urban land use. Its modern incarnation began in the late 19th century in developed nations and experienced an intense phase in the late 1940s – under the rubric of reconstruction...
project, spearheaded by
David RockefellerDavid Rockefeller Sr. is an American banker, statesman, globalist, and the current patriarch of the Rockefeller family. He is the youngest and only surviving child of John D. Rockefeller Jr. and the only surviving grandchild of billionaire oil tycoon John D. Rockefeller, founder of Standard Oil. ...
, to help revitalize
Lower ManhattanLower 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...
. The project was developed by the
Port Authority of New York and New JerseyThe Port Authority of New York and New Jersey is a bi-state port district, established in 1921 through an interstate compact, that runs most of the regional transportation infrastructure, including the bridges, tunnels, airports, and seaports, within the New York–New Jersey Port District...
, which hired architect
Minoru Yamasakiwas an American architect of Japanese descent, best known for his design of the twin towers of the World Trade Center buildings 1 and 2. Yamasaki was one of the most prominent architects of the 20th century and his firm, Yamasaki & Associates, continues to do business...
who came up with the specific idea for twin towers. After extensive negotiations, the
New JerseyNew Jersey is a state in the Mid-Atlantic region of the United States. It is bordered on the north by New York, and to the east by the Hudson River, Upper New York Bay, the Kill Van Kull, Newark Bay, the Arthur Kill, Raritan Bay, Sandy Hook Bay, Westchester County, New York City, Long Island, and...
and
New York StateNew York is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous. The state is bordered by New Jersey and Pennsylvania to the south, and Connecticut, Massachusetts and Vermont to the east...
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
ManhattanManhattan is one of the five boroughs of New York City, located primarily on Manhattan Island at the mouth of the Hudson River.New York County, which has the same boundaries as the Borough of Manhattan , is the most densely populated county in the United States, with a 2008 population of 1,634,795...
. To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad (renamed as
PATHThe Port Authority Trans-Hudson is a rapid transit railroad linking Manhattan, New York with New Jersey, and providing service to Jersey City, Hoboken, Harrison, and Newark. It is operated by the Port Authority of New York and New Jersey...
), which brought commuters from New Jersey to the Lower Manhattan site.
The towers were designed as
framed tube structuresIn structural engineering, the tube is the name given to the systems where in order to resist lateral loads a building is designed to act like a three-dimensional hollow tube, hence the name, cantilevered perpendicular to the ground. The system was introduced by Fazlur Rahman Khan while at...
, 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
elevatorAn elevator or lift is a vertical transport vehicle that efficiently moves people or goods between floors of a building...
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 wallA slurry wall is technique used to build reinforced-concrete walls in areas of soft earth close to open water or with a high ground water table. This technique is typically used to build diaphragm walls surrounding tunnels and open cuts, and to lay foundations.A trench is excavated to create a...
for digging the
foundationA foundation is a structure that transfers loads to the earth. Foundations are generally broken into two categories: shallow foundations and deep foundations.-Shallow foundation:...
, and
wind tunnelA wind tunnel is a research tool used in aerodynamic research. It is used to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
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
seventh7 World Trade Center is a building in New York City located across from the World Trade Center site in Lower Manhattan. The name "7 World Trade Center" has referred to two buildings: the original structure, completed in 1987, and the current structure...
building was constructed in the mid-1980s.
Planning
In 1942,
Austin J. TobinAustin Joseph Tobin , 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...
became the Executive Director of the
Port AuthorityThe Port Authority of New York and New Jersey is a bi-state port district, established in 1921 through an interstate compact, that runs most of the regional transportation infrastructure, including the bridges, tunnels, airports, and seaports, within the New York–New Jersey Port District...
, beginning a 30-year career during which he oversaw the planning and development of the World Trade Center. The concept of establishing a "world trade center" was conceived during the post-
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
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. The World Trade Corporation was founded, and a board was appointed by New York Governor Thomas E. Dewey to develop plans for the project. Architect
John EbersonJohn Eberson was a Romanian born American architect best known for his movie palace designs in the atmospheric theatre fashion....
and his son Drew devised a plan that included 21 buildings over a ten-block area, at an estimated cost of $150 million. 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.
Original plans
During the post-war period, economic growth was concentrated in
Midtown ManhattanMidtown Manhattan, or simply Midtown, is an area of Manhattan, New York City home to world-famous commercial zones such as Rockefeller Center, Broadway, and Times Square...
, in part stimulated by the
Rockefeller CenterRockefeller Center is a complex of 19 commercial buildings covering between 48th and 51st streets in New York City. Built by the Rockefeller family, it is located in the center of Midtown Manhattan, spanning the area between Fifth Avenue and Seventh Avenue. It was declared a National Historic...
, which was developed in the 1930s. Meanwhile, Lower Manhattan was left out of the
economic boomThe term boom and bust refers to a great buildup in the price of a particular commodity or, alternately, the localized rise in an economy, often based upon the value of a single commodity, followed by a downturn as the commodity price falls due to a change in economic circumstances or the collapse...
. One exception was the construction of
One Chase Manhattan PlazaOne Chase Manhattan Plaza is a banking skyscraper located in the downtown Manhattan Financial District of New York City, between Pine, Liberty, Nassau, and William Streets. Construction on the building was completed in 1964...
in the
Financial DistrictThe 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 city's major financial institutions, including the New York Stock Exchange and the Federal Reserve Bank of New York...
by
David RockefellerDavid Rockefeller Sr. is an American banker, statesman, globalist, and the current patriarch of the Rockefeller family. He is the youngest and only surviving child of John D. Rockefeller Jr. and the only surviving grandchild of billionaire oil tycoon John D. Rockefeller, founder of Standard Oil. ...
, who led
urban renewalUrban renewal is a program of land redevelopment in areas of moderate to high density urban land use. Its modern incarnation began in the late 19th century in developed nations and experienced an intense phase in the late 1940s – under the rubric of reconstruction...
efforts in Lower Manhattan. In 1958, Rockefeller established the Downtown-Lower Manhattan Association (DLMA), which commissioned
Skidmore, Owings and MerrillSkidmore, Owings and Merrill LLP is a Chicago-based architectural and engineering firm that was formed in 1936 by Louis Skidmore and Nathaniel Owings; in 1939 they were joined by John O. Merrill. They opened their first branch in New York City, New York in 1937. SOM is one of the largest...
to draw up plans for revitalizing
Lower ManhattanLower 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...
. The plans, made public in 1960, called for a World Trade Center to be built on a site along the
East RiverThe East River is a tidal strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates Long Island from the island of Manhattan and the Bronx on the North American mainland...
, from Old Slip to
Fulton StreetFulton Street is a busy street located in Lower Manhattan. It is in New York City's Financial District, a few blocks north of Wall Street. It runs from Church Street at the site of the World Trade Center to South Street, terminating in front of the South Street Seaport...
and between Water Street and
South StreetSouth Street in Manhattan is noted for its seaport, also called the South Street Seaport.Sometime in the early 1980s, South Street was refurbished from its abandoned status into a tourist attraction to create an atmosphere similar to places like Baltimore's Inner Harbor.Most of South Street sits...
. The complex would include a 900-foot (275 m) long
exhibition hallA convention center, in American English, is an exhibition hall, or conference center, that is designed to hold a convention. In British English very large venues suitable for major trade shows are known as exhibition centres while the term "convention centre" is sometimes used for intermediate...
, and a 50–70 story building, with some of its upper floors used as a hotel. Other amenities would include a theater, shops, and restaurants. The plan also called for a new
securitiesA security is a fungible, negotiable instrument representing financial value. Securities are broadly categorized into debt securities ; equity securities, e.g., common stocks; and derivative contracts, such as forwards, futures, options and swaps. The company or other entity issuing the security...
exchange building, which the Downtown-Lower Manhattan Association hoped would house the
New York Stock ExchangeThe New York Stock Exchange is a stock exchange located at 11 Wall Street in lower Manhattan, New York City, New York, USA. It is the largest stock exchange in the world by United States dollar value of its listed companies' securities...
.
David Rockefeller suggested that the Port Authority would be a logical choice for taking on the project, and argued that the Trade Center would provide great benefits in facilitating and increasing volume of international commerce coming through the Port of New York. Given the importance of
New York CityNew York is the most populous city in the United States, and the center of the New York metropolitan area, which is among the most populous urban areas in the world. A leading global city, New York exerts a powerful influence over worldwide commerce, finance, culture, fashion and entertainment...
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". After a year-long review of the proposal, the Port Authority formally backed the project on .
Agreement
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 GovernorThe Governor of New Jersey is the chief executive of the U.S. state of New Jersey. The current holder of that office is Jon Corzine, who re-assumed executive powers on May 7, 2007 from acting Gov. Richard Codey, after recuperating from an automobile accident on April 12, 2007...
Robert B. MeynerRobert Baumle Meyner of Phillipsburg, New Jersey was an American Democratic Party politician, who served as the 44th Governor of New Jersey, from 1954 to 1962...
, who resented that New York would be getting this $335 million project. 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 RiverThe Hudson River is a river that flows from north to south through eastern New York. It rises at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains, flows past Albany, and finally forms the border between New York City and New Jersey at its mouth before emptying into...
. Toward 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. HughesRichard Joseph Hughes was an American Democratic Party politician, who served as the 45th Governor of New Jersey, from 1962 to 1970 and as Chief Justice of the New Jersey Supreme Court from 1973-1979...
, and made a proposal to shift the World Trade Center project to a west side site where the Hudson Terminal was located. In acquiring the Hudson & Manhattan Railroad, the Port Authority would also acquire the Hudson Terminal and other buildings which were deemed obsolete. On , 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. 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.
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 RowThe phrase Radio Row is a nickname for an urban street or district specializing in the sale of radio and electronic equipment and parts. Radio Rows arose in many cities with the 1920s rise of broadcasting and declined after mid century.-New York:...
, which was home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents. The World Trade Center plans involved evicting these business owners, some of whom fiercely protested the forced relocation. In June 1962, a group representing approximately 325 shops and 1,000 other affected small businesses filed an
injunctionAn injunction is an equitable remedy in the form of a court order, whereby a party is required to do, or to refrain from doing, certain acts. The party that fails to adhere to the injunction faces civil or criminal penalties and may have to pay damages or accept sanctions for failing to follow the...
, challenging the Port Authority's power of
eminent domainEminent domain , compulsory purchase , resumption/compulsory acquisition or expropriation is the inherent power of the state to seize a citizen's private property, expropriate property, or seize a citizen's rights in property with due monetary compensation, but...
. The dispute with local business owners worked its way through the court system, up to the
New York State Court of AppealsThe New York Court of Appeals is the highest court in the U.S. state of New York. The Court of Appeals consists of seven judges: the Chief Judge and six associate judges which are appointed by the Governor to 14-year terms...
, which in April 1963 upheld the Port Authority's right of eminent domain, saying that the project had a "public purpose." On , the
United States Supreme CourtThe Supreme Court of the United States is the highest judicial body in the United States, and leads the federal judiciary. It consists of the Chief Justice of the United States and eight Associate Justices, who are nominated by the President and confirmed with the "advice and consent" of the Senate...
refused to accept the case. 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. 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."
Private
real estateReal estate is a legal term that encompasses land along with anything permanently affixed to the land, such as buildings, specifically property that is fixed in location.
"Real estate" The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin...
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. An especially vocal critic was Lawrence A. Wien, owner of the
Empire State BuildingThe Empire State Building is a 102-story landmark Art Deco skyscraper in New York City at the intersection of Fifth Avenue and West 34th Street. Its name is derived from the nickname for the state of New York. It stood as the world's tallest building for more than forty years, from its completion...
, which would lose its title of
tallest building in the world. Wien organized a group of builders into a group called the "Committee for a Reasonable World Trade Center" to demand that the project be scaled down.
In January 1964, the Port Authority inked a deal with the State of New York to locate government offices at the World Trade Center. The Port Authority began signing commercial tenants in the spring and summer of 1964, including several banks. In 1965, the Port Authority signed the
United States Customs ServiceUntil March 2003, the United States Customs Service was an agency of the U.S. federal government that collected import tariffs and performed other selected border security duties....
as a tenant.
A final obstacle for the Port Authority was getting approval from
New York City MayorThe Mayor of the City of New York is head of the executive branch of New York City's government. The Mayor's office administers all city services, public property, police and fire protection, most public agencies, and enforces all city and state laws within New York City.The budget overseen by the...
John LindsayJohn Vliet Lindsay was an American politician,lawyer and broadcaster who was a U.S. Congressman, Mayor of New York City, candidate for U.S...
and the
New York City CouncilThe New York City Council is the lawmaking body of the City of New York. It has 51 members from 51 council districts throughout the five boroughs. The Council serves as balance of power against the mayor in a "strong" mayor-council government model. The council monitors performance of city agencies...
, who 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 , 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. In subsequent years, the payments would rise as the
real estate taxProperty tax, or millage tax, is an ad valorem tax that an owner is required to pay on the value of the property being taxed. Property tax can be defined as "generally, tax imposed by municipalities upon owners of property within their jurisdiction based on the value of such property."There are...
rate increased.
Design
On , the Port Authority announced the selection of
Minoru Yamasakiwas an American architect of Japanese descent, best known for his design of the twin towers of the World Trade Center buildings 1 and 2. Yamasaki was one of the most prominent architects of the 20th century and his firm, Yamasaki & Associates, continues to do business...
as lead architect, and
Emery Roth & SonsEmery Roth was an American architect who designed many of the definitive New York City hotels and apartment buildings of the 1920s and 30s, incorporating Beaux-Arts and Art Deco details...
as associate architects. Originally, Yamasaki submitted to the Port Authority a concept incorporating 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."
To meet the Port Authority's requirement to build 10 million
square feetThe square foot is an imperial unit / U.S. customary unit of area, used mainly in the United States, the United Kingdom, and Canada. It is defined as the area of a square with sides of 1 foot in length...
(930,000 m²) of office space, the buildings would each need to be 110 stories tall. A major limiting factor in building heights is elevators; the taller the building, the more
elevatorAn elevator or lift is a vertical transport vehicle that efficiently moves people or goods between floors of a building...
s are needed to service the building, requiring more space-consuming elevator banks. Yamasaki and the engineers decided to use a new system that included 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 can be stacked 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. The World Trade Center towers were the second supertall buildings to use sky lobbies, after the
John Hancock CenterJohn Hancock Center at 875 North Michigan Avenue in the Gold Coast area of Chicago, Illinois, is a 100-story, 1,127-foot tall skyscraper, constructed under the supervision of Skidmore, Owings and Merrill, with chief designer Bruce Graham and structural engineer Fazlur Khan. When completed in...
in
ChicagoChicago is the largest city in the U.S. state of Illinois, and with more than 2.8 million people, the 3rd largest city in the United States...
. This system was inspired by the
New York City SubwayThe 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, a subsidiary agency of the Metropolitan Transportation Authority and also known as MTA New York City Transit...
system, whose lines include local stations where local trains stop and express stations where all trains stop.
Yamasaki's design for the World Trade Center was unveiled to the public on , with an eight-foot model. The towers had a square plan, approximately 207 feet (63 m) in dimension on each side. The buildings were designed with narrow office windows, only 18
inchAn inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
es (45 cm) wide, which reflected on Yamasaki's
fear of heightsAcrophobia is an extreme or irrational fear of heights. It belongs to a category of specific phobias, called space and motion discomfort that share both similar etiology and options for treatment.Acrophobia can be dangerous, as sufferers can experience a panic attack in a high place and become too...
and desire to make building occupants feel secure. Yamasaki's design called for the building facades to be sheathed in aluminum-alloy. In all, the World Trade Center complex contained six buildings within the superblock.
The World Trade Center design brought criticism of its aesthetics from the
American Institute of ArchitectsThe American Institute of Architects is a professional organization for architects in the United States. Headquartered in Washington, D.C., the AIA offers education, government advocacy, community redevelopment, and public outreach to support the architecture profession and improve its public image...
and other groups.
Lewis MumfordLewis Mumford was an American historian and philosopher of technology and science. Particularly noted for his study of cities and urban architecture, he had a tremendously broad career as a writer that also included a period as an influential literary critic...
, author of
The City in HistoryThe City in History: Its Origins, Its Transformations, and Its Prospects is a 1961 National Book Award winner by American historian Lewis Mumford.It was first published by Harcourt, Brace & World ....
and other works on
urban planningUrban, city, and town planning is the integration of the disciplines of land use planning and transport planning to explore a very wide range of aspects of the built and social environments of urbanized municipalities and communities...
, criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets."
TelevisionTelevision is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission...
broadcasters raised concerns that the World Trade Center twin towers would cause interference in television reception for viewers in the
New York City areaThe New York metropolitan area, also known as Metropolitan New York, Greater New York, or the Tri-State Region, is the most populous metropolitan area in the United States and is also one of the most populous in the world. The metropolitan area is defined by the U.S...
. In response to these concerns, the Port Authority offered to provide new television transmission facilities at the World Trade Center. The Linnaean Society of the
American Museum of Natural HistoryThe American Museum of Natural History , located on the Upper West Side, Manhattan, New York, USA, is one of the largest and most celebrated museums in the world...
also opposed the Trade Center project, citing hazards the buildings would impose on
migrating birdBird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. These however are usually irregular or in only one direction and are termed variously as nomadism, invasions,...
s.
The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing the
tube-frame structural systemIn structural engineering, the tube is the name given to the systems where in order to resist lateral loads a building is designed to act like a three-dimensional hollow tube, hence the name, cantilevered perpendicular to the ground. The system was introduced by Fazlur Rahman Khan while at...
used in the buildings. The Port Authority's Engineering Department served as
foundation engineersGeotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering includes investigating existing subsurface conditions and materials; determining their physical/mechanical and chemical properties that are relevant to...
, Joseph R. Loring & Associates as
electrical engineersElectrical engineering, sometimes referred to as electrical and electronic engineering, is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after...
, and Jaros, Baum & Bolles as
mechanical engineersMechanical Engineering is an engineering discipline that was developed from the application of principles from physics and materials science. Mechanical engineering involves the analysis, design, manufacturing, and maintenance of various systems...
. Tishman Realty & Construction Company was the
general contractorA general contractor is a group or individual that contracts with another organization or individual for the construction, renovation or demolition of a building, road or other structure...
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.
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 codeA 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. The main purpose of the building codes is to protect public health, safety and general welfare as they relate to the...
s. 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 still in place. The structural engineers ended up following draft versions of the new 1968 building codes, which incorporated "advanced techniques" in
building designBuilding design refers to the broadly based architectural, engineering and technical applications to the design of buildings. All building projects require the services of a building designer, typically an architect on all but the simplest of projects...
.
The World Trade Center towers included many
structural engineeringStructural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads. Structural engineering is usually considered a specialty within civil engineering, but it can also be studied in its own right....
innovations in
skyscraper design and constructionThe design and construction of skyscrapers involves creating safe, habitable spaces in very tall buildings. The buildings must support their weight, resist wind and earthquakes, and protect occupants from fire. Yet they must also be conveniently accessible, even on the upper floors, and provide...
, which allowed the buildings to reach new heights and become the
tallest in the world. Traditionally,
skyscraperA skyscraper is a tall, continuously habitable building. There is no official definition or height above which a building may clearly be classified as a skyscraper...
s used a skeleton of columns distributed throughout the interior to support building loads, with interior columns disrupting the floor space. The tube-frame concept, earlier introduced by
Fazlur KhanFazlur Rahman Khan , born in Dhaka, Bengal , was a Bangladeshi-American architect and structural engineer. He did the structural engineering" of the Willis Tower and John Hancock Center...
, was a major innovation, allowing open floor plans and more space to rent. The buildings used high-strength, load-bearing perimeter
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
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. In all, the perimeter walls of the towers were on each side, and the corners were
bevelA beveled edge refers to an edge of a structure that is not perpendicular to the faces of the piece. The words bevel and chamfer overlap in usage; in general usage they are often interchanged, while in technical usage they may sometimes be differentiated as shown in the image at right.-Cutting...
ed. The perimeter columns were designed to provide support for virtually all lateral loads (such as wind loads) and to share the gravity loads with the core columns. Structural analysis of major portions of the World Trade Center were computed on an
IBM 1620The IBM 1620 was announced by IBM on October 21, 1959 and marketed as an inexpensive "scientific computer". After a total production of about two thousand machines, it was withdrawn on November 19, 1970...
.
The perimeter structure was constructed with extensive use of prefabricated modular pieces, which consisted of three columns, three stories tall, connected 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. The thickness of the plates and grade of
structural steelStructural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and strength...
varied over the height of the tower, ranging from 36,000 to 100,000 pounds per square inch (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. The tube-frame design required 40 percent less structural steel than conventional building designs. From the 7th floor to the ground level, and down to the foundation, the columns were spaced 10 feet (3 m) apart. All columns were placed on
bedrockIn stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
, which, unlike that in Midtown Manhattan, where the bedrock is shallow, is at 65–85 feet (20–26 m) below the surface.
The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop. The modular pieces were typically 52 inches (1.3 m) deep, and extended for two full floors and half of two more floors. 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 stressA shear stress, denoted , is defined as a stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly.-General shear stress:...
between columns, 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.
The building's core housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m), and contained 47 steel columns running from the bedrock to the top of the tower. The columns tapered after the 66th floor, and consisted of welded box-sections at lower floors and rolled wide-flange sections at upper floors. The structural core in 1 WTC was oriented with the long axis east to west, while that of 2 WTC was oriented north to south. All elevators were located in the core. Each building had three stairwells, also in the core, except on the
mechanical floorA mechanical floor, mechanical penthouse, or mechanical level is a storey of a high-rise building that is dedicated to mechanical and electronics equipment. "Mechanical" is the most commonly-used term, but words such as utility, technical, service, and plant are also used...
s where they were located outside the core.
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 thick lightweight
concreteConcrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, aggregate , water, and chemical admixtures...
slabs laid on a fluted steel deck with shear connections for
composite actionComposite construction is a generic term to describe any building construction involving multiple dissimilar materials. It is not to be confused with the Composite order which is a specific order of classical architecture that combines elements of the Ionic and Corinthian orders.- Structural...
. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses had a span of in the long-span areas and in the short span area. The trusses connected to the perimeter at alternate columns, and were on 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
viscoelasticViscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...
dampers, which helped reduce the amount of sway felt by building occupants.
Hat
trussIn architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight slender members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and...
es (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communication
antennaAn antenna is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless...
on top of each building. Only 1 WTC (north tower) actually had an antenna fitted, which was added in 1978. 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 the transmission tower.
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 BuildingThe Empire State Building is a 102-story landmark Art Deco skyscraper in New York City at the intersection of Fifth Avenue and West 34th Street. Its name is derived from the nickname for the state of New York. It stood as the world's tallest building for more than forty years, from its completion...
that have thick, heavy
masonryMasonry is the building of structures from individual units laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone such as marble, granite, travertine, limestone; concrete block, glass block, and...
for
fireproofingFireproofing, a passive fire protection measure, refers to the act of making materials or structures more resistant to fire, or to those materials themselves, or the act of applying such materials. Applying a certification listed fireproofing system to certain structures allows these to have a...
of steel structural elements. During the design process,
wind tunnelA wind tunnel is a research tool used in aerodynamic research. It is used to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
tests were done at
Colorado State UniversityColorado State University is a public institution of higher learning located in Fort Collins, Colorado in the United States. Colorado State University is the state's land grant university and the flagship campus university of the Colorado State University System. The enrollment is approximately...
and at the
National Physical LaboratoryThe National Physical Laboratory is the national measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington, London, England. It is the largest applied physics organisation in the UK....
in the
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces. 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. Many subjects did not respond well, experiencing
dizzinessDizziness refers to an impairment in spatial perception and stability. It is considered imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or for a non-specific feeling such as giddiness or foolishness....
and other ill effects. One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic
dampersIn physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
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.
Aircraft impact
The structural engineers on the project also considered the possibility that an aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in the fog had crashed into the 79th floor of the
Empire State BuildingThe Empire State Building is a 102-story landmark Art Deco skyscraper in New York City at the intersection of Fifth Avenue and West 34th Street. Its name is derived from the nickname for the state of New York. It stood as the world's tallest building for more than forty years, from its completion...
. A year later, another airplane nearly crashed into the
40 Wall Street40 Wall Street is a 70-story skyscraper located in New York City. Originally known as the Bank of Manhattan Trust building, it was later known by its street address when its founding tenant merged to form the Chase Manhattan Bank and today is known as the The Trump Building.The building, located...
building, and there was another near-miss at the Empire State Building. In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner, the
Boeing 707The Boeing 707 is a four-engine commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven"...
, which might be lost in the fog, seeking to land at
JFKJohn F. Kennedy International Airport is an international airport located in Queens County, New York in southeastern New York City about 12 miles from Lower Manhattan...
or at
NewarkNewark Liberty International Airport , first named Newark Airport and later Newark International Airport, is an international airport within the city limits of both Newark and Elizabeth, New Jersey, United States...
airports. The
National Institute of Standards and TechnologyThe National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce...
(NIST) found a three page
white paperA White paper is an authoritative report or guide that often addresses issues and how to solve them. White papers are used to educate readers and help people make decisions...
that mentioned another aircraft impact analysis, involving impact of a jet at , was indeed considered, but the original documentation of the study was lost when Port Authority offices were destroyed in the collapse of the World Trade Center. In 1993, John Skilling recalled doing the analysis, and remarked, "The building structure would still be there."
Fire protection
Sprayed-fire resistant materialFireproofing, a passive fire protection measure, refers to the act of making materials or structures more resistant to fire, or to those materials themselves, or the act of applying such materials. Applying a certification listed fireproofing system to certain structures allows these to have a...
s (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams.
GypsumGypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO
4·2H
2O.-Crystal varieties:...
wallboard in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns.
VermiculiteVermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by hydration of certain basaltic minerals...
plaster was used on the interior-side and SFRMs on the other three sides of the perimeter columns for fire protection. 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.
In April 1970, the New York City Department of Air Resources ordered contractors building the World Trade Center to stop the spraying of asbestos as an insulating material.
More fireproofing was added after a fire in February 1975 that spread to six floors before being extinguished. After the
1993 bombingThe 1993 World Trade Center bombing occurred on February 26, 1993, when a car bomb was detonated below the North Tower of the World Trade Center in New York City. The 1,500 lb urea nitrate–hydrogen gas enhanced device was intended to knock the North Tower into the South Tower , bringing both...
, inspections found fireproofing to be deficient. The Port Authority was in the process of replacing it, but replacement had been completed on only 18 floors in WTC 1, including all the floors affected by the aircraft impact and fires on September 11th, and on 13 floors in WTC 2, although only three of these floors (77,78, and 85) were directly affected by the aircraft impact.
The 1968 New York City building codes did not require
sprinklerA fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected...
s for
high-riseA high-rise is a tall building or structure. Normally, the function of the building is added, for example high-rise apartment building or high-rise offices. Compare: low-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. Following a major fire in February 1975, the Port Authority decided to start installing sprinklers throughout the buildings. By 1993, nearly all of 2 WTC and 85 percent of 1 WTC had sprinklers installed, and the entire complex was retrofitted by 2001.
Construction
In March 1965, the Port Authority began acquiring property at the World Trade Center site. The Ajax Wrecking and Lumber Corporation was hired for the demolition work, which began on to clear the site for construction of the World Trade Center.
Groundbreaking was on , marking the beginning of construction of the World Trade Center's foundations. The site of the World Trade Center was located on
landfillA 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...
, with the bedrock located below grade. In order to construct the World Trade Center, it was necessary to build the "bathtub", with the
slurry wallA slurry wall is technique used to build reinforced-concrete walls in areas of soft earth close to open water or with a high ground water table. This technique is typically used to build diaphragm walls surrounding tunnels and open cuts, and to lay foundations.A trench is excavated to create a...
along the
West StreetThe West Side Highway is a mostly-surface section of New York State Route 9A that runs from West 72nd Street along the Hudson River to the southern tip of Manhattan...
side of the site, to keep water from the
Hudson RiverThe Hudson River is a river that flows from north to south through eastern New York. It rises at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains, flows past Albany, and finally forms the border between New York City and New Jersey at its mouth before emptying into...
out. This method was used in place of conventional dewatering methods because lowering the groundwater table would cause large
settlementsGroundwater-related subsidence is the subsidence of land resulting from groundwater extraction, and a major problem in the developing world as major metropolises swell without adequate regulation and enforcement, as well as a being a common problem in the developed world...
of nearby buildings not built on
deep foundationA deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a...
s. The slurry method involves digging a
trench-Agriculture:Trenches have long been used to carry water. Trenches can be used for draining purposes, leading water away from a swamp or wetland that is to be dried out. Likewise they can be used for irrigation purposes, directing water into dry areas...
, and as excavation proceeds, filling the space with a "slurry" mixture, composed of
bentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
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
MontrealMontreal is the second-largest city in Canada and the largest city in the province of Quebec. Originally called Ville-Marie , the city takes its present name from Mont-Royal, the triple-peaked hill located in the heart of the city, whose name was also initially given to the island on which the...
-based Icanda, a subsidiary of an Italian engineering firm, Impresa Costruzioni Opere Specializzate (I.C.O.S.). 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. The original
Hudson TubesThe Downtown Hudson Tubes are a pair of tunnels that carry PATH trains under the Hudson River between New York City and Jersey City in the United States. In lower Manhattan the trains travel to and from the World Trade Center station. In Jersey City the trains stop at the Exchange Place station...
, which carried PATH trains into Hudson Terminal, remained in service as elevated tunnels until 1971 when a new
PATH stationThe World Trade Center PATH station originally opened on July 19, 1909 as the Hudson Terminal. When the Hudson Terminal was torn down to make way for the World Trade Center, a new station was built, which opened in 1971...
was built.
Construction work began on the North Tower in August 1968 with construction beginning on the South Tower by January 1969. In January 1967, $74 million in contracts were awarded to the
Pacific Car and Foundry CompanyPaccar Inc is the third largest manufacturer of heavy-duty trucks in the world , and has substantial manufacture in light and medium vehicles through its various subsidiaries.-History:...
, Laclede Steel Company,
Granite City Steel CompanyThe United States Steel Corporation , more commonly known as U.S. Steel, is an integrated steel producer with major production operations in the United States, Canada, and Central Europe. The company is the world's tenth largest steel producer ranked by sales...
, and
Karl Koch Erecting CompanyKarl Koch Steel Consulting is a steel construction firm, based in Oyster Bay, New York. The company was established in the 1950s as Karl Koch Erecting Company, Inc., of Carteret, New Jersey. The Karl Koch Erecting Company was hired by the Port Authority of New York and New Jersey as one of the...
to supply
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
for the project. 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 SteelThe Bethlehem Steel Corporation , based in Bethlehem, Pennsylvania, was once the second-largest steel producer in the United States, after Pittsburgh, Pennsylvania-based U.S. Steel. After a decline in the U.S...
or
U.S. SteelThe United States Steel Corporation , more commonly known as U.S. Steel, is an integrated steel producer with major production operations in the United States, Canada, and Central Europe. The company is the world's tenth largest steel producer ranked by sales...
as a cost-saving measure. 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 Americathe river: Alcoa RiverAlcoa, Inc. is the world's third largest producer of aluminum, behind Rio Tinto Alcan and Rusal. From its operational headquarters in Pittsburgh, Pennsylvania, Alcoa conducts operations in 44 countries...
.
Tishman Realty & ConstructionTishman Realty & Construction is corporation that owns and operates:Tishman Construction Corporation is a privately-held firm headquartered in New York City with operating subsidiaries located across the United States. It provides a wide range of construction and construction-related services for...
was hired in February 1967 to oversee construction of the project.
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 controlIn engineering and manufacturing, quality control and quality engineering are used in developing systems to ensure products or services are designed and produced to meet or exceed customer requirements....
. Steel components were freighted into a
Penn CentralThe Penn Central Transportation Company, commonly abbreviated to Penn Central, was an American railroad company that operated from 1968 until 1976. It was created by the merger on February 1, 1968, of the Pennsylvania Railroad and the New York Central Railroad...
yard in
Jersey CityJersey City is a city in Hudson County, New Jersey, United States. As of the United States 2000 Census, the population of Jersey City was 240,055, making it New Jersey's second-largest city, behind Newark. As of the Census Bureau's 2007 estimate, the population had grown to 242,389...
. From there, they were brought in early morning hours through the
Holland TunnelThe Holland Tunnel is a highway tunnel under the Hudson River connecting the island of Manhattan in New York City with Jersey City, New Jersey at Interstate 78 on the mainland. Unusually for an American public works project, it is not named for a government official, politician, or local hero or...
to the construction site, and lifted into place by a
craneA crane is a lifting machine, generally equipped with a winder , wire ropes or chains and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...
. Larger pieces were brought to the construction site by
tugboatA tugboat is a boat that maneuvers vessels by pushing or towing them. Tugs move vessels that should not move themselves alone, such as ships in a crowded harbor or a narrow canal, or those that cannot move themselves, such as barges, disabled ships, or oil platforms. Tugboats are powerful for...
s. A special type of crane, suitable for constructing such tall buildings, that used
hydraulicsHydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...
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 WalesNew South Wales is Australia's most populous state, located in the south-east of the country, north of Victoria, south of Queensland and east of South Australia...
, Australia was informally called a "
kangarooA kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern and Western Grey Kangaroo...
crane".
In 1970, tugboat workers went on
strikeStrike action, often simply called a strike, is a work stoppage caused by the mass refusal of employees to perform work. A strike usually takes place in response to employee grievances. Strikes became important during the industrial revolution, when mass labour became important in factories and mines...
, halting the transport of material to the construction site. The Port Authority attempted other means of transporting material, including via
helicopterA helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter achieves lift with the...
. When this method was tried, the helicopter lost its load of steel into the
Kill Van KullThe Kill Van Kull is a tidal strait approximately long and wide separating Staten Island and Bayonne, New Jersey, USA. The name kill comes from from the Middle Dutch word kille, meaning "riverbed" or "water channel."...
. Some other mishaps occurred during the construction process, including disruption of
telephoneThe telephone is a telecommunications device that transmits and receives sound, most commonly the human voice. It is one of the most common household appliances in the developed world, and has long been considered indispensable to business, industry and government...
service in Lower Manhattan when telephone cables were crushed by
pile driverA pile driver is a mechanical device used to drive piles into soil to provide foundation support for buildings or other structures. The term is also used in reference to members of the construction crew that work with pile-driving rigs....
s. On , an explosion injured six workers when a truck hit a
propanePropane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing...
tank. In all, 60 workers were killed in construction accidents while the World Trade Center was being built.
The
topping outIn building construction, topping out, or topping off, is a ceremony held when the last beam is placed at the top of a building. The term may also refer to the overall completion of the building's structure. A topping out ceremony is usually held to commemorate the event.While common in England,...
ceremony of 1 WTC (North Tower) took place on , with 2 WTC's ceremony (South Tower) occurring later on . The first tenants moved into the North Tower in December 1970, and into the South Tower in January 1972. The buildings were dedicated on ; Tobin, who had resigned the year before, was absent from the ceremonies.
Building the World Trade Center involved excavating of material. Rather than transporting this material at great costs out to sea or to landfills in
New JerseyNew Jersey is a state in the Mid-Atlantic region of the United States. It is bordered on the north by New York, and to the east by the Hudson River, Upper New York Bay, the Kill Van Kull, Newark Bay, the Arthur Kill, Raritan Bay, Sandy Hook Bay, Westchester County, New York City, Long Island, and...
, the fill material was used to expand the
ManhattanManhattan is one of the five boroughs of New York City, located primarily on Manhattan Island at the mouth of the Hudson River.New York County, which has the same boundaries as the Borough of Manhattan , is the most densely populated county in the United States, with a 2008 population of 1,634,795...
shoreline across West Street. Work to demolish the
pierA pier is a raised walkway over water, supported by widely spread piles or pillars. The lighter structure of a pier allows tides and currents to flow almost unhindered, whereas the more solid foundations of a quay or the closely-spaced piles of a wharf can act as breakwaters, and are consequently...
s began on , including Pier 7 to Pier 11 which were all constructed around 1910. The demolition work moved forward, despite conflicts between
David RockefellerDavid Rockefeller Sr. is an American banker, statesman, globalist, and the current patriarch of the Rockefeller family. He is the youngest and only surviving child of John D. Rockefeller Jr. and the only surviving grandchild of billionaire oil tycoon John D. Rockefeller, founder of Standard Oil. ...
, Governor
Nelson RockefellerNelson Aldrich Rockefeller was the 41st Vice President of the United States, the 49th governor of New York, a philanthropist, and a businessman....
, and Mayor
John LindsayJohn Vliet Lindsay was an American politician,lawyer and broadcaster who was a U.S. Congressman, Mayor of New York City, candidate for U.S...
regarding plans for
Battery Park CityBattery Park City is a 92-acre planned community at the southwestern tip of lower Manhattan in New York City, United States. The land upon which it stands was created on the Hudson River using 1.2 million cubic yards of dirt and rocks excavated during the construction of the World Trade Center...
. Landfill material from the
World Trade CenterThe World Trade Center was a complex in Lower Manhattan in New York City whose seven buildings were destroyed in 2001 in the September 11 terrorist attacks...
was used to add land, and a cellular
cofferdamA cofferdam is an enclosure within a water environment constructed to allow water to be displaced by air for the purpose of creating a dry work environment. Commonly used for oil rig construction and repair, bridge and dam work, the cofferdam is usually a welded steel structure that is temporary,...
was constructed to retain the material. The result was a extension into the Hudson River, running six blocks or . This land was a "gift" to New York City, allowing more
taxTo tax is to impose a financial charge or other levy upon a taxpayer by a state or the functional equivalent of a state such that failure to pay is punishable by law.Taxes are also imposed by many subnational entities...
-generating developments in Battery Park City.
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. In December 1966, the Port Authority announced increased cost estimates, bringing the estimated total to $575 million. This announcement brought criticism of the project from private real estate developers,
The New York TimesThe New York Times is an American daily newspaper founded in 1851 and published in New York City. The largest metropolitan newspaper in the United States, "The Gray Lady"—named for its staid appearance and style—is regarded as a national newspaper of record...
, and others in New York City. The critics charged that the Port Authority figure was an unrealistically low estimate, and they estimated the project would end up costing $750 million. When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million. The project was financed through
tax-exemptA tax exemption is an exemption from all or certain taxes 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....
bondIn finance, a bond is a debt security, in which the authorized issuer owes the holders a debt and, depending on the terms of the bond, is obliged to pay interest and/or to repay the principal at a later date, termed maturity...
s issued by the Port Authority.
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 MerrillSkidmore, Owings and Merrill LLP is a Chicago-based architectural and engineering firm that was formed in 1936 by Louis Skidmore and Nathaniel Owings; in 1939 they were joined by John O. Merrill. They opened their first branch in New York City, New York in 1937. SOM is one of the largest...
in 1978–79. 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.
7 World Trade Center7 World Trade Center is a building in New York City located across from the World Trade Center site in Lower Manhattan. The name "7 World Trade Center" has referred to two buildings: the original structure, completed in 1987, and the current structure...
was built in the mid-1980s, just 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
substationSubstation can refer to:*Electrical substation*A police substation *The Substation, a Singaporean contemporary arts centre...
.
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. In many instances, openings were cut in the floors to accommodate new stairways 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.
Repairs to structural elements on the lower levels of 1 WTC were made following the
1993 bombingThe 1993 World Trade Center bombing occurred on February 26, 1993, when a car bomb was detonated below the North Tower of the World Trade Center in New York City. The 1,500 lb urea nitrate–hydrogen gas enhanced device was intended to knock the North Tower into the South Tower , bringing both...
. The greatest damage occurred on levels B1 and B2, with significant structural damage also on level B3. Primary structural columns were not damaged, but secondary steel members experienced some damage. 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 loss of the floor slabs which provided lateral support to counteract pressure from Hudson River water on the other side. The
refrigerationRefrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable. The primary purpose of refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature.The term...
plant on sublevel B5, which provided
air conditioningAn air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area, or provide heat to an area. The cooling is done using a simple refrigeration cycle...
to the entire World Trade Center complex, was heavily damaged and replaced with a temporary system for the summer of 1993. 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 attacksThe September 11 attacks were a series of coordinated suicide attacks by Al-Qaeda upon the United States on September 11, 2001. On that morning, 19 Al-Qaeda terrorists hijacked four commercial passenger jet airliners...
.
External links