World Trade Center (1973–2001), a ledger of building statistics



 For data on the WTC's origins, general history, social role, facilities, 9\11 deaths and it's destruction see- World Trade Center (1973–2001). 

For the list of tenants see- World Trade Center (1973–2001) tennants during 9\11.

Over view

 *  For data on the WTC's origins, general history, social role, facilities, 9\11 deaths and it's destruction see- World Trade Center (1973–2001). 

The World Trade Center was a large complex of seven buildings in Lower Manhattan, New York City, United States. It was a major twin office block unit owned by the Port Authority of New York and New Jersey that was erected in 1973 in Manhattan's financial district. It was a key fixture of the district for 37 years until it was destroyed by the terrorist attacks of 9\11. It featured landmark twin towers, which opened on April 4, 1973, and were destroyed in the September 11 attacks, with 7 World Trade Center collapsing later that day due to the damage it suffered when the twin towers collapsed that morning. The other buildings in the complex were severely damaged by the collapse of the twin towers, and their ruins were eventually demolished.

At the time of their completion, the "Twin Towers" — the original 1 World Trade Center, at 1,368 feet (417 m); and 2 World Trade Center, at 1,362 feet (415 m) — were the tallest buildings in the world. The other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC, 5 WTC, 6 WTC, and 7 WTC. All these buildings were built between 1975 and 1985, with a construction cost of $400 million ($2,300,000,000 in 2014 dollars). The complex was located in New York City's Financial District and contained 13,400,000 square feet (1,240,000 m2) of office space.

The World Trade Center experienced a fire on February 13, 1975, a bombing on February 26, 1993, and a robbery on January 14, 1998. In 1998, the Port Authority decided to privatize the World Trade Center, leasing the buildings to a private company to manage, and awarded the lease to Silverstein Properties in July 2001.

On the morning of September 11, 2001, fanatical Al-Qaeda affiliated hijackers flew two Boeing 767 jets into the complex, beginning with the North Tower at 8:46 a.m., then the South Tower at 9:03 a.m., in a coordinated act of terrorism. After burning for 56 minutes, the South Tower collapsed at 9:59 a.m. 29 minutes later, at 10:28 a.m. (102 minutes after being struck by the plane), the North Tower collapsed. The attacks on the World Trade Center killed 2,606 people in and within the vicinity of the towers, as well as all 157 on board the two aircraft.

Falling debris from the towers, combined with fires that the debris initiated in several surrounding buildings, led to the partial or complete collapse of all the other buildings in the complex and caused catastrophic damage to ten other large structures in the surrounding area, including the World Financial Center and Deutsche Bank Building; three buildings in the World Trade Center complex collapsed due to fire-induced structural failure, and when the North Tower collapsed, debris fell on the nearby 7 WTC, damaging it and starting fires so that it eventually collapsed. The process of cleaning up and recovery at the World Trade Center site took eight months.

The World Trade Center complex was rebuilt over a span of more than a decade. The site is being rebuilt with six new skyscrapers, while a memorial to those killed in the attacks and a new rapid transit hub have both opened. One World Trade Center, the tallest building in the United States, is the lead building for the defiant new complex, reaching more than 100 stories upon its completion in November 2014.

The buildings involved



 *  For data on the WTC's origins, general history, social role, facilities, 9\11 deaths and it's destruction see- World Trade Center (1973–2001). 

These are the buildings that were directly involved in the incident. Some were destroyed, fatally damaged\burnt out, or repairable after the 9\11 attacks.
 * 1) WTC 2 (South Tower).
 * 2) WTC 1 (North Tower).
 * 3) 7 World Trade Center.
 * 4) St. Nicholas Greek Orthodox Church (WTC).
 * 5) Marriott Hotel (3 WTC).
 * 6) South Plaza (4 WTC).
 * 7) U.S. Customs (6 WTC).
 * 8) The Deutsche Bank Building on 130 Liberty Street (5 WTC).
 * 9) World Trade Center station (PATH).
 * 10) The West Street Building (90 West Street).
 * 11) Borough of Manhattan Community College 's Fiterman Hall.
 * 12) World Financial Center buildings.
 * 13) One Liberty Plaza.
 * 14) The Mall at the World Trade Center.
 * 15) Millenium Hilton.
 * 16) FDNY 10 Firehouse.
 * 17) 90 Church Street.
 * 18) West St/Vesey St. bus stop and shelter.
 * 19) The Verizon Building (140 West Street).
 * 20) The Verizon Building (375 Pearl Street).

Local Geology
The western portion of the World Trade Center site was originally under the Hudson River, with the shoreline in the vicinity of Greenwich Street. It was on this shoreline close to the intersection of Greenwich and the former Dey Street that Dutch explorer Adriaen Block's ship, the Tyger, burned to the waterline in November 1613, stranding Block and his crew and forcing them to overwinter on the island. They built the first European settlement in Manhattan. The remains of the ship were buried under landfill when the shoreline was extended starting in 1797, and were discovered during excavation work in 1916. The remains of a second ship from the eighteenth century were discovered in 2010 during excavation work at the site. The ship, believed to be a Hudson River sloop, was found just south of where the Twin Towers used to stand, about 20 feet below the surface. The old shore line of the southn half of the island was finaly replaced by the crurrent one by the 1920s.

Before the World Trade Center


Later, the area became Radio Row. New York City's Radio Row, which existed from 1921 to 1966, was a warehouse district on the Lower West Side in the Financial District. Harry Schneck opened City Radio on Cortlandt Street in 1921, and eventually the area held several blocks of electronics stores, with Cortlandt Street as its central axis. The used radios, war surplus electronics (e.g., ARC-5 radios), junk, and parts often piled so high they would spill out onto the street, attracting collectors and scroungers. According to a business writer, it also was the origin of the electronic component distribution business.

The idea of establishing a World Trade Center in New York City was first proposed in 1943. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project but the plans were put on hold in 1949. During the late 1940s and 1950s, economic growth in New York City was concentrated in Midtown Manhattan. To help stimulate urban renewal in Lower Manhattan, David Rockefeller suggested that the Port Authority build a World Trade Center in Lower Manhattan.

Plans for the use of eminent domain to remove the shops in Radio Row bounded by Vesey, Church, Liberty, and West Streets began in 1961 when the Port Authority of New York and New Jersey was deciding to build the world's first world trade center. They had two choices: the east side of Lower Manhattan, near the South Street Seaport; and the west side, near the H&M station, Hudson Terminal. Initial plans, made public in 1961, identified a site along the East River for the World Trade Center. As a bi-state agency, the Port Authority required approval for new projects from the governors of both New York and New Jersey. New Jersey Governor Robert B. Meyner objected to New York getting a $335 million project. Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate.

At the time, ridership on New Jersey's 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 had opened across the Hudson River. In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes, the Port Authority offered to take over the Hudson & Manhattan Railroad to have it become the Port Authority Trans-Hudson (PATH). The Port Authority also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH. With the new location and Port Authority acquisition of the H&M Railroad, New Jersey agreed to support the World Trade Center project. In compensation for Radio Row business owners' displacement, the PANYNJ gave each business $3,000 each, without regard to how long the business had been there or how prosperous the business was. After the area had been purchased for the World Trade Center in March 1964, Radio Row was demolished starting in March 1965. It was completely demolished by 1966.

Approval was also needed from New York City Mayor John Lindsay and the New York City Council. Disagreements with the city centered on tax issues. On August 3, 1966, an agreement was reached 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 tax rate increased.

St Nicholas Greek Orthodox Church
The building that came to house the church was built around 1832. It was originally a private dwelling which was later turned into a tavern. In 1916, Greek American immigrants started the congregation of St Nicholas Greek Orthodox Church. Before moving to Cedar Street, its parishioners worshiped in the dining room of a hotel on Morris Street run by Stamatis Kalamarides. In 1919, five families raised $25,000 to buy the tavern and converted it into a church, and started to hold worship services in 1922. The church building was only 22 feet (6.7 m) wide, 56 feet (17 m) long, and 35 feet (11 m) tall and was easily dwarfed by the 110 story Twin Towers, which were completed in 1972 and 1973. Despite its small size and unusual location (all the adjacent buildings had been demolished, making the church be surrounded on three sides by a parking lot), before the attacks the church had a dedicated congregation of about 70 families led by Father John Romas. On Wednesdays, the building was opened to the public and many people, including office workers from the towers and non-Greek Orthodox, would enter the quiet worship space for contemplation and prayer.

Among the church's most valuable physical possessions were some of the relics (remains) of St Nicholas, St Catherine, and St Sava, which had been donated to the church by Nicholas II, the last tsar of Russia. These relics were removed from their safe on holy days for veneration; they were never recovered after the attack.

90 West Street
90 West Street (alternatively West Street Building) is a building in Lower Manhattan, New York City designed by architect Cass Gilbert and structural engineer Gunvald Aus for the West Street Improvement Corporation. When completed in 1907, the building's Gothic styling and ornamentation served to emphasize its 23-story height, and foreshadowed Gilbert's later work on the Woolworth Building. Originally built as an office building, the main tenant was the Delaware, Lackawanna and Western Railroad and the top floor was occupied by Garret's Restaurant, which advertised itself as the "world's highest restaurant".

It is located on West Street, between Cedar and Albany Streets, just south of the World Trade Center site, the building had a view to the Hudson River before Battery Park City was built on fill across West Street.

90 Church Street
The Federal Office Building at 90 Church Street includes the United States Postal Service's Church Street Station, which is responsible for the 10048 ZIP code in New York City. The building takes up the full block between Church Street and West Broadway and between Vesey and Barclay Streets in the Civic Center neighborhood of Manhattan.

The AIA Guide to New York City says about the building: "A boring limestone monolith that has trouble deciding between a heritage of stripped down neo-Classical and a new breath of Art Deco."

90 Church Street was designed by Cross & Cross, Pennington, Lewis & Mills and Louis A. Simon, who was Supervising Architect of the Department of the Treasury at the time. The architectural style of the building is a mixture of Neo-classicism and Art Deco. It has two towers and the facade is clad in limestone.

The building was completed in 1935, and is listed on the National Register of Historic Places.

In addition to housing the Postal Service, the 90 Church Street building contains offices of the New York State Public Service Commission, the New York State Health Department, and the New York City Housing Authority.

7 World Trade Center
The original 7 World Trade Center was a 47-story building, designed by Emery Roth & Sons, with a red granite facade. The building was 610 feet (190 m) tall, with a trapezoidal footprint that was 330 ft (100 m) long and 140 ft (43 m) wide. Tishman Realty & Construction managed construction of the building, which began in 1983. In May 1987, the building opened, becoming the seventh structure of the World Trade Center.

The building was constructed above a Con Edison substation that had been on the site since 1967. The substation had a caisson foundation designed to carry the weight of a future building of 25 stories containing 600,000 sq ft (56,000 m2). The final design for 7 World Trade Center was for a much larger building than originally planned when the substation was built. The structural design of 7 World Trade Center therefore included a system of gravity column transfer trusses and girders, located between floors 5 and 7, to transfer loads to the smaller foundation. Existing caissons installed in 1967 were used, along with new ones, to accommodate the building. The 5th floor functioned as a structural diaphragm, providing lateral stability and distribution of loads between the new and old caissons. Above the 7th floor, the building's structure was a typical tube-frame design, with columns in the core and on the perimeter, and lateral loads resisted by perimeter moment frames.

A shipping and receiving ramp, which served the entire World Trade Center complex, occupied the eastern quarter of the 7 World Trade Center footprint. The building was open below the 3rd floor, providing space for truck clearance on the shipping ramp. The spray-on fireproofing for structural steel elements was gypsum-based Monokote which had a two-hour fire rating for steel beams, girders and trusses, and a three-hour rating for columns, like in 1 WTC and 2 WTC.

Mechanical equipment was installed on floors four through seven, including 12 transformers on the 5th floor. Several emergency generators installed in the building were used by the Office of Emergency Management, Salomon Smith Barney, and other tenants. In order to supply the generators, 24,000 gallons (91,000 L) of diesel fuel were stored below ground level. Diesel fuel distribution components were located at ground level, up to the ninth floor. After the World Trade Center bombings of February 26, 1993, New York City mayor Rudy Giuliani decided to situate the emergency command center and associated fuel tanks at 7 World Trade Center. Although this decision was criticized in light of the events of 9/11, the fuel in the building is today not believed to have contributed to the collapse of the building. The roof of the building included a small west penthouse and a larger east mechanical penthouse.

Each floor had 47,000 sq ft (4,400 m2) of rentable office space which made the building's floor plans considerably larger than most office buildings in the City. In all, 7 World Trade Center had 1,868,000 sq ft (173,500 m2) of office space. Two pedestrian bridges connected the main World Trade Center complex, across Vesey Street, to the third floor of 7 World Trade Center. The lobby of 7 World Trade Center had three murals by artist Al Held: The Third Circle, Pan North XII, and Vorces VII.

Marriott Hotel 3 WTC
The Marriott World Trade Center was a 22-story steel-framed hotel building with 825 rooms. It had a roof height of 73.7 m (242 ft) and was designed by Skidmore, Owings & Merrill. Its structural engineer was Leslie E. Robertson Associates with Tishman Construction serving as the main contractor. Construction began in 1979. It opened in July 1981 as the Vista International Hotel and was located at 3 World Trade Center in New York City.

The Vista International Hotel was the first hotel to open in Lower Manhattan since 1836. The hotel was originally owned by the Port Authority of New York and New Jersey and KUO Hotels of Korea with Hilton International acting as management agent. It was sold in 1995 to Host Marriott Corporation.

The hotel was connected to the North and South Towers, and many went through the hotel to get to the Twin Towers. The hotel had a few establishments including The American Harvest Restaurant, The Greenhouse Cafe, Tall Ships Bar & Grill, a store called Times Square Gifts, The Russia House Restaurant and a Grayline New York Tours Bus ticket counter, a gym that was the largest of any hotel in New York at the time, and a hair salon named Olga's. The hotel also had 26,000 square feet (2,400 m2) of meeting space on the entire 3rd floor along with The New Amsterdam Ballroom on the main floor, and was considered a four-diamond hotel by AAA.

The Mall at the World Trade Center
Westfield World Trade Center is a shopping center at the World Trade Center complex which is operated and managed by Westfield Corporation. The mall opened on August 16, 2016. It replaces an earlier shopping center called The Mall at the World Trade Center, which was located in the concourse area of the original World Trade Center until it was destroyed on September 11, 2001.

Prior to 9/11, the mall had been leased to the Westfield Group by the Port Authority of New York and New Jersey, the owner of the complex. Westfield intended to rename the mall Westfield Shoppingtown World Trade Center, and embark on a major expansion and renovation program. Plans called for the addition of 200,000 square feet (19,000 m2) of new mall space and a few well-known sit-down restaurants. This renovation never happened due to its destruction.

Architectural design



 * For data on the WTC's origins, history, faciltys and destruction see- World Trade Center (1973–2001).

Design announced
On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect, and Emery Roth & Sons 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." Yamasaki's design for the World Trade Center was unveiled to the public on January 18, 1964, 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 inches (45 cm) wide, which reflected on Yamasaki's fear of heights and desire to make building occupants feel secure. Yamasaki's design called for the building facades to be sheathed in aluminum-alloy.

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 is elevators; the taller the building, the more elevators 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 Center in Chicago. 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.

Original architectural and engineering model. This model is now on permanent display at the National September 11th. Memorial and Museum in NYC. Yamasaki, who had previously designed Saudi Arabia's Dhahran International Airport with the Saudi Binladin Group, incorporated features of Arabic architecture into the design of the World Trade Center. The plaza was modelled after Mecca, incorporating features such as a vast delineated square, a fountain, and a radial circular pattern. Yamasaki described the plaza as "a mecca, a great relief from the narrow streets and sidewalks of the Wall Street area." He also incorporated other features of Arabic architecture into the building design, including pointed arches, interweaving tracery of prefabricated concrete, a minaret like flight tower, and arabesque patterns.

The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups. 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." 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. 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 History also opposed the Trade Center project, citing hazards the buildings would impose on migrating birds.

The structural engineering firm Worthington, Skilling, Helle & Jackson 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.

Architecture used
They wanted and succeeded in creating a utilitarian and functional, yet user friendly and iconic modernist oblong tower block format on the Twin Towers and WTC 7.

Designer's planning philosophy


They wanted and succeeded in creating a utilitarian and functional, yet user friendly and iconic modernist oblong tower block format on the Twin Towers and WTC 7.

Sky Lobbies we used as a way of interchanging people between local and express lifts at strategic points up the Twin Towers rather than having long cues out side a normal number of lifts or even more lift shafts funning the full length of in the building in order to cope with the number of people using it.

The plans and technology used
The fire resistant cladding on the metal core, anti-sway devices, aircraft impact proofing and sky-lobbies were a technological marvel of the time.

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 still in place. The structural engineers ended up following draft versions of the new 1968 building codes, which incorporated "advanced techniques" in building 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, earlier introduced by Fazlur Khan, 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 60 perimeter columns, narrowly spaced, on each side of the buildings. In all, the perimeter walls of the towers were 210 feet (64 m) on each side, and the corners were beveled. 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 1620.

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 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 steel varied over the height of the tower, ranging from 36,000 to 100,000 pounds per square inch. 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 bedrock, 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 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 floors where the two outside stairwells temporarily left the core in order to avoid the express elevator machine rooms, and then rejoined the core by means of a transfer corridor. It was this arrangement that allowed Stairwell A of 2 WTC to remain passable after the aircraft impact on September 11, 2001.

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 with shear connections for composite action. A grid of lightweight bridging trusses and main trusses supported the floors. The trusses had a span of 60 feet (18 m) in the long-span areas and 35 feet (11 m) in the short span area. The trusses connected to the perimeter at alternate columns, and were on 6-foot-8-inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers, which helped reduce the amount of sway felt by building occupants.

Hat trusses (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building. Only 1 WTC (north tower) actually had 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 Building that have thick, heavy masonry for fireproofing of steel structural elements During the design process, wind tunnel tests were done at Colorado State University and at the National Physical Laboratory in the United Kingdom 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 dizziness and other ill effects. One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of 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. Wind is always an issue with tall structure.

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 78th and 79th floors of the Empire State Building. A year later, another airplane nearly crashed into the 40 Wall Street building, and there was another close call 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 707, which might be lost in the fog, seeking to land at JFK or at Newark airports. The National Institute of Standards and Technology (NIST) found a three-page white paper that mentioned another aircraft impact analysis, involving impact of a jet at 600 mph (970 km/h), was indeed considered, but NIST could not locate the documentary evidence of the aircraft impact analysis.

Fire protection
Sprayed-fire resistant materials (SFRMs) were used to protect some structural steel elements in the towers, including all floor trusses and beams. Gypsum wallboard in combination with SFRMs, or in some cases gypsum wallboard alone, was used to protect core columns. Vermiculite 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. The spray-on fireproofing for structural steel elements was gypsum-based Monokote which had a two-hour fire rating for steel beams, girders and trusses, and a three-hour rating for columns on 1 WTC, 2 WTC and 7 WTC.

More fireproofing was added after a fire in February 1975 that spread to six floors before being extinguished. After the 1993 bombing, 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 11, 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 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. 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.

Sky Lobbies
A sky lobby is an intermediate interchange floor where people can change from an express elevator that stops only at the sky lobby to a local elevator which stops at every floor within a segment of the building. When designing very tall (supertall) buildings, supplying enough elevators is a problem – travellers wanting to reach a specific higher floor may conceivably have to stop at a very large number of other floors on the way up to let other passengers off and on. This increases travel time, and indirectly requires many more elevator shafts to still allow acceptable travel times – thus reducing effective floor space on each floor for all levels. (The other main technique to increase usage without adding more elevator shafts is double-deck elevators.)

Early uses of the sky lobby include the original Twin Towers of the World Trade Center and the John Hancock Center in Chicago.

Mechanical floors


A mechanical floor, mechanical penthouse, or mechanical level is a story 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. They are present in all tall buildings including the world's tallest skyscrapers with significant structural, mechanical and aesthetics concerns.

While most buildings have mechanical rooms, typically in the basement, tall buildings require dedicated floors throughout the structure for this purpose, for a variety of reasonsw. Because they use up valuable floor area (just like elevator shafts), engineers try to minimize the number of mechanical floors while allowing for sufficient redundancy in the services they provide. As a rule of thumb, skyscrapers require a mechanical floor for every 10 tenant floors (10%) although this percentage can vary widely. In some buildings they are clustered in groups that divide the building into blocks, in others they are spread evenly through the structure, while in others still they are mostly concentrated at the top or in a few cases mostly in the bacement levels. Lift (elevator) winding gears, major aircon units and water tanks have  traditonaly been on the top floor or roof under a protective hood for obvise reasons.

Mechanical floors are generally counted in the building's floor numbering (this is required by some building codes) but are accessed only by service elevators. In some legislations they have been excluded from maximum floor area calculations, leading to significant increases in building sizes; this is the case in New York City. Sometimes buildings are designed with a mechanical floor located on the thirteenth floor, to avoid problems in renting the space due to superstitions about that number.

Most mechanical floors require external vents (louvers) for the office ventilation and heat rejection systems along most or all of their perimeter, precluding the use of glass windows. The resulting visible "dark bands" can disrupt the overall facade design especially if it is fully glass-clad. Different architectural styles approach this challenge in different ways.

The South Tower's helipad
On the 107th floor of 2 WTC was a popular tourist attraction called Top of the World Trade Center Observatories. On the roof was an observation deck accessible to the public and a disused helipad at the center.

The North Tower's communications mast


1 WTC gained a 360-foot (110 m)-tall communications antenna in 1978. The basic fact is that communications masts need to be on the high-ground, which includes tall buildings, especially if the building below has a communications center and TV station in it.

Environmental awards
The towers were praised for their wind stability factor at the time by many structural experts. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants.

The technology used
It was cutting edge for it's time. The towers were designed as framed tube structures, giving tenants open floor plans, unobstructed by columns or walls. This design was accomplished by using many closely spaced perimeter columns, providing much of the structure's strength, with the 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 used for office purposes by making the structural core smaller. The design and construction of the towers involved many other innovative techniques, such as wind tunnel experiments and the slurry wall for digging the foundation.

Construction


In March 1965, the Port Authority began acquiring property at the World Trade Center site. Demolition work began on March 21, 1966, to clear thirteen square blocks of low rise buildings in Radio Row for construction of the World Trade Center. Groundbreaking for the construction of the World Trade Center took place on August 5, 1966. 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.

The site of the World Trade Center was located on landfill with the bedrock located 65 feet (20 m) below. To construct the World Trade Center, it was necessary to build a "bathtub" with a slurry wall around the West Street side of the site, to keep water from the Hudson River out. The slurry method selected by Port Authority's chief engineer, John M. Kyle, Jr., involved digging a trench, and as excavation proceeded, filling the space with a "slurry" mixture composed of bentonite and water, which plugged holes and kept groundwater out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the "slurry" out. It took fourteen months for the slurry wall to be completed. It was necessary before excavation of material from the interior of the site could begin. The 1,200,000 cubic yards (920,000 m3) of material excavated were used (along with other fill and dredge material) to expand the Manhattan shoreline across West Street to form Battery Park City.

In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers, and Karl Koch was hired to erect the steel. Tishman Realty & Construction was hired in February 1967 to oversee construction of the project. Construction work began on the North Tower in August 1968; construction on the South Tower was underway by January 1969. The original Hudson Tubes, carrying PATH trains into Hudson Terminal, remained in service as elevated tunnels during the construction process until 1971 when a new PATH station opened.

The topping out ceremony of 1 WTC (North Tower) took place on December 23, 1970, while 2 WTC's ceremony (South Tower) occurred later on July 19, 1971. The first tenants moved into the North Tower on December 15, 1970; the South Tower accepted tenants in January 1972. When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million. The ribbon cutting ceremony was on April 4, 1973.

In addition to the twin towers, the plan for the World Trade Center complex included four other low-rise buildings, which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s, to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16-acre (65,000 m2) superblock.

Corporate plots
Plans to build the World Trade Center were controversial. The site for the World Trade Center was the location of Radio Row, home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents, many of whom fiercely resisted forced relocation. A group of small businesses affected filed an injunction challenging the Port Authority's power of eminent domain. The case made its way through the court system to the United States Supreme Court; the Court refused to accept the case.

Private real estate developers and members of the Real Estate Board of New York, led by Empire State Building owner Lawrence A. Wien, 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. The World Trade Center itself was not rented out completely until after 1979 and then only due to the fact that the complex's subsidy by the Port Authority made rents charged for its office space relatively cheaper than that of comparable office space in other buildings. Others questioned whether the Port Authority should have taken on a project described by some as a "mistaken social priority".

The 'ugly' appearance
The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups. 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".

The Twin Towers them selves were described as looking similar to "the boxes that the Empire State Building and the Chrysler Building came in". The twin towers' narrow office windows, only 18 inches (46 cm) wide and framed by pillars that restricted views on each side to narrow slots, were disliked by many. Activist and sociologist Jane Jacobs also criticized plans for the WTC's construction, arguing that the waterfront should be kept open for New Yorkers to enjoy.

The trade center's "superblock", replacing a more traditional, dense neighborhood, was regarded by some critics as an inhospitable environment that disrupted the complicated traffic network typical of Manhattan. For example, in his book The Pentagon of Power, Lewis Mumford denounced the center as an "example of the purposeless giantism and technological exhibitionism that are now eviscerating the living tissue of every great city".

Wind problems
For many years, the immense Austin J. Tobin Plaza was often beset by brisk winds at ground level owing to the Venturi effect between the two towers. In fact, some gusts were so high that pedestrian travel had to be aided by ropes. In 1999, the outdoor plaza reopened after undergoing $12 million renovations, which involved replacing marble pavers with gray and pink granite stones, adding new benches, planters, new restaurants, food kiosks and outdoor dining areas.

Most New Yorkers liked the congested, low-rise of yesteryear and thus hated the Twin Towers and everyone hated Venturi effect events. Many Western Europeans felt jealous that the USA had set a new world record.

Dead birds
Bird-skyscraper collisions are a problem in urban areas. Several major cities like Toronto in Canada and New York City in the United States have programs to abate this, such as Toronto's Fatal Light Awareness Program (FLAP) and New York City's Lights Out New York, a program of New York City Audubon an environmental organization. According to FLAP, between one and nine million birds die each year in the city from hitting skyscrapers due to mistaking reflective windows for open sky, or being drawn to lights at night.

Legislation
Governments of Canada and the United States have recently introduced legislation to make new and existing buildings bird friendly. Examples include Toronto's Bird-Friendly Development Guidelines that requires new buildings to be bird friendly, Chicago's Design Guide For Bird-Safe Buildings New Construction And Renovation, New York's Bird Friendly-Buildings Act that will require new and existing building be bird friendly effective Jan 1, 2012. On the Federal level the Federal Bird-Safe Buildings Act of 2011 calls for each public building constructed, acquired, or altered by the General Services Administration (GSA) to incorporate bird-safe building materials and design features. The legislation would require GSA to take similar actions on existing buildings, where practicable.

Solutions
Recent developments in legislation necessitate architects and property managers to take mitigating measures to combat the bird collision issue. There are a variety of different solutions including special window film, specialized glass, decals, screens and external shutters. Some of these solutions have been proven to significantly reduce bird collisions with buildings, but some are unproven and testing is required to prove the claims made for some.

Renovation

 * For data on the WTC's origins, history, faciltys and destruction see- World Trade Center (1973–2001).

Original issues
Wind and fire were major issues.

1979
The fire fighting equipment and elevators were up-graded.

1983
Entrance video surveillance was added. The lift winding gears and firefighting equipment were upgraded.

1993-1994
The bomb damage was repaired and many places strengthened against any future attack. The ambient lighting upgraded in the car parks, basements, emergency stairwells, lifts and the PATH station. Part of the Marriot Hotel and all of it's car park and basement were also heavily reinforced with high grade steel trusses and heavier grade cement.

1999
For many years, the immense Austin J. Tobin Plaza was often beset by brisk winds at ground level owing to the Venturi effect between the two towers. In fact, some gusts were so high that pedestrian travel had to be aided by ropes. In 1999, the outdoor plaza reopened after undergoing $12 million renovations, which involved replacing marble pavers with gray and pink granite stones, adding new benches, planters, new restaurants, food kiosks and outdoor dining areas.

Most New Yorkers liked the congested, low-rise of yesteryear and thus hated the Twin Towers and everyone hated Venturi effect events. Many Western Europeans felt jealous that the USA had set a new world record.

Environmental awards
Non were issued for it.

The technology used
The usual stuff used in office blocks and their plazas.

WTC 1

 * Tallest building in the USA (both including and exclude the communication's mast)- 1972–1974
 * Tallest building in New York State 1971 (both including and exclude the communication's mast)- 2001.
 * Tallest building in New York City 1971 (both including and excluding the communication's mast)- 2001.
 * Tallest building in the world (both including and exclude the communication's mast)- 1971 to 1974.

WTC 1 and 2 jointly

 * Fist place to be 'plane slammed', that is deliberately hit by a civil liner as a act of war or terrorism!
 * The fact that is stayed up any time after having such heavy damage as 9/11. The 1970s engineering was obviously of a good quality since they could not have foreseen 9/11 or been up to preparing for such an event with only 1970s technology, yet they made it strong enough not to instantly collapses on impact with the jets flown in to it!
 * Most 'sky lobbies'- 1971 to 1974.
 * Most elevators- 1971 to 1974.
 * Building with the most floors- 1972–2001.
 * Tallest twin towers in the world- 1972–1998.
 * Building with the most toilets 1972–2001

The Verizon Building (140 West Street)
The building has been called "one of the most significant structures in skyscraper design" through out it's history.

The Verizon Building (375 Pearl Street)
Paul Goldberger decried it at the time as the “most disturbing” of the phone company’s new switching centers because it “overwhelms the Brooklyn Bridge towers, thrusts a residential neighborhood into shadow and sets a tone of utter banality.” On April 3, 2012, the UK's online version of the Daily Telegraph showed 375 Pearl Street ranked 20th in a series of "the ugliest buildings in the world".

90 West Street
The "world's highest restaurant" in 1907.

Their individual fates



 * 1) WTC 2 South Tower- Catastrophic upper boddy damage and then a total collapse.
 * 2) WTC 1 North Tower- Catastrophic upper boddy damage and then a total collapse.
 * 3) 7 World Trade Center- It can be assumed that heavy blast damage compromising the structural integrity of the building, which in turn lead to it's collapsed. Many windows were blown in, but otherwise there was only minimal visible damage and modest fires.
 * 4) St. Nicholas Greek Orthodox Church (WTC)- Crushed under debris and aicraft wrekage.
 * 5) Marriott Hotel 3 WTC- Crushed under debris.
 * 6) South Plaza 4 WTC- Slightly damaged, some fires and many windows blown in by the blast.
 * 7) U.S. Customs 6 WTC- Reduced to ruins by falling debris and later demolished.
 * 8) The Deutsche Bank Building (130 Liberty Street)- Initially is sustained major impact damage from falling debris. It soon partly caught fire and was also slightly damaged in places by the fairs involved. It was later condemned as uninhabitable because of toxic conditions relating to levels chemicals, dust, water and mold inside the office tower. It was later deconstructed.
 * 9) The Verizon Building (375 Pearl Street)- suffered minor accidental fire damage but have been repaired.
 * 10) The Mall at the World Trade Center- Crushed by falling debris.
 * 11) World Trade Center station (PATH)- Crushed under debris, but later rebuilt.
 * 12) 90 West Street- suffered major impact damage but have been restored.
 * 13) Borough of Manhattan Community College's Fiterman Hall- condemned due to extensive damage after being crushed by debris in the attacks, and is being rebuilt.
 * 14) World Financial Center buildings- had moderate damage and have since been restored.
 * 15) One Liberty Plaza- had moderate damage and have since been restored.
 * 16) Millenium Hilton- had moderate damage and have since been restored.
 * 17) 90 Church Street- had moderate damage and have since been restored.
 * 18) West St/Vesey St. bus stop- Crushed by falling debris.
 * 19) FDNY 10 Firehouse- closed for a couple of days as the roof and garage were cleared of dust, rubble, glass and other minor debris. It closed for about 1.5 years soon after when surveyors found impact related structural damage in the building that needed to be repaid. A memorial wall was added to the building when it was partly re-built.
 * 20) The Verizon Building (140 West Street)- suffered major impact damage but have been restored. The underground cable vaults belonging to Verizon, along with other underground utility infrastructure were also heavily damaged from water and debris.

Lost artworks


Many works of art were destroyed in the collapse.
 * Ideogram (1967) stainless steel sculpture by James Rosati
 * Cloud Fortress (1975) a large, black granite piece by Japanese artist Masayuki Nagare, destroyed in the 9/11 rescue and recovery efforts.
 * The World Trade Center Tapestry a 20' x 35' tapestry by Joan Miró that hung in the South Tower Lobby.
 * Sky Gate, New York (1977–78) large wooden sculpture by Louise Nevelson
 * A memorial fountain for the victims of the 1993 World Trade Center bombing by Elyn Zimmerman
 * World Trade Center Stabile (1971) a 25' red steel sculpture by Alexander Calder. Approximately 30% of the sculpture was recovered.
 * Some 300 sculptures and drawings by Auguste Rodin, part of the Cantor Fitzgerald collection.
 * Needle Tower (1968) by Kenneth Snelson.
 * Recollection Pond, a tapestry by Romare Bearden.
 * Path Mural, by Germaine Keller.
 * Commuter Landscape, a large mural by Cynthia Mailman.
 * Fan Dancing with the Birds, a mural by Hunt Slonem.
 * The Entablature Series by Roy Lichtenstein
 * Approximately 40,000 negatives of photographs by Jacques Lowe documenting the presidency of John F. Kennedy.
 * The Sphere, an abstract sculpture by Fritz Koenig, survived the collapse but was seriously damaged, and now serves as a memorial. The Sphere  is 25 feet (7.6 m) high and cast in 52 bronze segments. Koenig considered it his "biggest child". It was put together in Bremen, Germany and shipped as a whole to Lower Manhattan. The artwork was meant to symbolize world peace through world trade, and was placed at the center of a ring of fountains and other decorative touches designed by trade center architect Minoru Yamasaki to mimic the Grand Mosque of Mecca, Masjid al-Haram, in which The Sphere stood at the place of the Kaaba The structural engineers who took a part on this project was  Leslie E. Robertson Associates  (LERA), who helped make the globe possible to rotate once every 24 hours.

Many other works of art and valuable artifacts, found in safe deposit boxes located throughout the towers, were also destroyed. Two other sculptures were damaged, but not destroyed by the attacks. These are Red Cube by Isamu Noguchi and Joie de Vivre by Mark di Suvero, located down the street from the World Trade Center. They were repaired and still stand today.

Tenants at the time of the attacks

 * For the list of tenants see- World Trade Center (1973–2001) tennants during 9\11

The tenant list below was compiled from the original list provided by CoStar Group (a provider of electronic commercial real estate information), and quoted by CNN and most media. It was amended using UnBlinking.com. Entries unique to UnBlinking are in italics, marked (?UB) if uncertain. Companies listed on different floors by each source are marked (CS) at their position in CoStar, and (UB) at their position in UnBlinking. Special cases link to footnotes for more explanations. Cantor Fitzgerald's corporate headquarters were located in One World Trade Center.

6 plausible conspiracy theories

 * For data 9\11 conspiracy theories see- World Trade Center (1973–2001).

Also see

 * 1) World Trade Center (1973–2001)
 * 2) CIS Tower
 * 3) Terrorism
 * 4) Terrorist organisations
 * 5) Famous buildings
 * 6) World Trade Center (1973–2001) tennants during 9\11