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7 World Trade Center
The new 7 World Trade Center (view from southeast)
General information
Location	250 Greenwich Street New York City, New York, United States
Height
Roof	750 ft (228 m)
Technical details
Floor count	52
Floor area	1.7 million ft sq. 158,000 m sq.
Design and construction
Architect(s)	David Childs (S.O.M.)
Developer	Silverstein Properties

7 World Trade Center is the name of two buildings in New York City, located in Lower Manhattan across from the World Trade Center site. The original building, developed by Larry Silverstein in the 1980s, was 47 stories tall, clad in red exterior masonry, and occupied a trapezoid-shaped footprint. The building was constructed above a Con Edison power substation, which imposed some unique structural design constraints. An elevated walkway connected the building to the World Trade Center plaza. The original building opened in 1987 and had difficulties attracting tenants at first. In 1988, the Salomon Brothers signed a long-term lease, and became the main tenants of the building. During the September 11, 2001 attacks, this original structure was heavily damaged by debris when the adjacent twin towers collapsed. Its structural integrity was further compromised by fire, and the combined effect of structural damage and fire resulted in its collapse at 5:20 p.m. on September 11.

By 2002, construction of a replacement building was underway. The new building, completed in 2006, is 52 stories and also is above a power substation. It was built on a smaller footprint than the original to allow Greenwich Street to be restored from TriBeCa through the World Trade Center site and south to Battery Park. The new building is bounded by Greenwich, Vesey, Washington, and Barclay streets. A small park across the street, between Greenwich and West Broadway, occupies space that was part of the original building's footprint. The new building's design placed emphasis on safety, with a reinforced concrete core, wider stairways, and thicker fireproofing of steel columns. The new 7 World Trade Center also has numerous environmentally friendly features, which enabled it to gain gold status in the U.S. Green Building Council's LEED program.

1984–2001

The original 7 World Trade Center was a 47-story building, designed by Emery Roth & Sons. The building was 610 ft (185.9 m) tall, with a trapezoid-shaped footprint that was 330 ft (100.6 m) long and 140 ft (42.7 m) wide. Construction began in 1984, and was managed by Tishman Realty & Construction. In March 1987, the building opened, to become the seventh structure of the World Trade Center.

The building was constructed above a Con Edison substation, which had been on the site since 1967. The substation had a caisson foundation designed to carry the weight of a future building on the site, which would be 25 stories and contain 600,000 sq ft (55,700 m²) The final design for 7 World Trade Center was for a much larger building, which also covered a significantly larger footprint than originally planned when the substation was built.

Between floors 5 and 7, the building had a system of gravity column transfer trusses and girders to transfer loads to the smaller foundation. 7 World Trade Center utilized existing caissons installed in 1967, along with new caissons. 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. The roof of the building included a small west penthouse and a larger east mechanical penthouse.

A shipping/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 2-hour fire rating for steel beams, girders and truss, and 3-hour rating for columns.

Mechanical equipment was installed on floors 4-7, including 12 transformers on the 5th floor. Several generators in the building were used by the Office of Emergency Management, Salomon Smith Barney, and others. Storage tanks contained 24,000 gallons (91,000 liters) of diesel fuel to supply the generators. Fuel oil distribution components were located at ground level, up to the 9th floor.

Each floor had 47,000 sq ft (4,366 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 (174,000 m²) of office space. The building was given a red granite façade. Two pedestrian bridges connected the main World Trade Center complex, across Vesey Street, to the 3rd 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. A sculpture by Alexander Calder, called WTC Stabile (also known by other names, The Cockeyed Propeller and Three Wings) was on a plaza in front of the building.

Tenants

Drexel Burnham Lambert originally agreed (June 1986) to lease the entire 7 World Trade Center building for $3 billion over a term of 30 years. In fallout from the Boesky insider-trading scandal, Drexel Burnham Lambert canceled the lease in December 1986, leaving Silverstein to find other tenants. Spicer & Oppenheim agreed to lease 14 percent of the space, but for more than a year Silverstein was unable to find tenants for the remaining space, as Black Monday and other factors adversely affected the Lower Manhattan real estate market. By April 1988, Silverstein had lowered the rent and made other concessions.

In November 1988, Salomon Brothers agreed to a 20-year lease for the top 19 floors of 7 World Trade Center, after withdrawing from plans to build a large new complex at Columbus Circle in Midtown. The building was extensively renovated in 1989 to accommodate the needs of Salomon Brothers. Most of three existing floors were removed as tenants continued to occupy other floors, and then more than 350 (US) tons of steel were added to construct three double-height trading floors. Nine diesel generators were installed on the 5th floor as part of a backup power station. "Essentially, Salomon is constructing a building within a building - and it's an occupied building, which complicates the situation," said a district manager of Silverstein Properties. The unusual task was possible, said Larry Silverstein, because it was designed to allow for "entire portions of floors to be removed without affecting the building's structural integrity, on the assumption that someone might need double-height floors."

At the time of the September 11, 2001 attacks, Salomon Smith Barney was by far the largest tenant in 7 World Trade Center, occupying 1,202,900 sq ft (111,750 m²), which was 64 percent of the building and included floors 28–45. Other major tenants included ITT Hartford Insurance Group (122,590 sq ft/11,400 m²), American Express Bank International (106,117 sq ft/9,900 m²), Standard Chartered Bank (111,398 sq ft/10,350 m²), and the Securities and Exchange Commission (106,117 sq ft/9,850 m²). Smaller tenants included the Internal Revenue Service Regional Council (90,430 sq ft/8,400 m²), and the United States Secret Service (85,343 sq ft/7,900 m²). The smallest tenants included the New York City Office of Emergency Management, NAIC Securities, Federal Home Loan Bank, First State Management Group Inc., Provident Financial Management, and the Immigration and Naturalization Service. The Department of Defense (DOD) and Central Intelligence Agency (CIA) shared the 25th floor with the IRS. Floors 46–47 were mechanical floors, as well as the bottom six floors and part of the 7th floor.

Collapse

As the North Tower collapsed on September 11, 2001, debris hit 7 World Trade Center "with the force of a volcanic eruption." Much of the bottom 10 stories of the building's south face were destroyed, with damage visible as high as the 18th floor. After the north tower collapsed, some firefighters entered 7 World Trade Center to search the building. They also attempted to extinguish small pockets of fire, but low water pressure hindered their efforts. A massive fire burned into the afternoon on the 11th and 12th floors of 7 World Trade Center, with flames visible on the east side of the building. During the afternoon, fire was also seen on floors 6-10, 13-14, 19-22, and 29-30. Around 2:00 p.m., firefighters noticed a bulge in the southwest corner of 7 World Trade Center, between the 10 and 13th floors, which was a sign that the building was unstable and might collapse. During the afternoon, firefighters also heard creaking sounds coming from the building. Around 3:30 pm, FDNY Chief Daniel Nigro decided to halt rescue operations, surface removal and searches along the surface of the debris near 7 World Trade Center and evacuate the area, due to concerns for the safety of personnel, given that 7 World Trade Center was unstable and would possibly collapse. At 5:20 p.m. EDT on September 11, 2001, 7 World Trade Center collapsed. The building had been evacuated and there were no casualties associated with the collapse.

In May 2002, the Federal Emergency Management Agency (FEMA) issued a report on the collapse, based on a preliminary investigation conducted jointly with the Structural Engineering Institute of the American Society of Civil Engineers, under leadership of Dr. W. Gene Corley, P.E. FEMA made preliminary findings that the collapse was not primarily caused by actual impact damage from the collapse of 1 WTC and 2 WTC, but by fires on multiple stories that were ignited by debris from the other two towers and continued unabated due to lack of water for sprinklers or manual firefighting. Structural elements were exposed to high temperatures for a sufficient period of time to reduce their strength to the point of collapse.

The report did not reach final conclusions about the cause of the collapse, but listed several issues requiring further investigation. FEMA made these findings:

Loss of structural integrity was likely a result of weakening caused by fires on the 5th to 7th floors. The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analyses are needed to resolve this issue.

In response to FEMA's concerns, the Commerce Department’s National Institute of Standards and Technology (NIST) was authorized to lead a three-year, US$16 million investigation into the structural failure and collapse of the World Trade Center twin towers, as well as 7 World Trade Center. The investigation, led by Dr S. Shyam Sunder, drew not only upon in-house technical expertise, but also the knowledge of several outside private institutions, including the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), the Society of Fire Protection Engineers (SFPE), the National Fire Protection Association (NFPA), the American Institute of Steel Construction (AISC), the Council on Tall Buildings and Urban Habitat (CTBUH), and the Structural Engineers Association of New York (SEAoNY).

NIST has released a video and still-photo analysis of Building 7 before its collapse that appears to indicate a greater degree of structural damage from falling debris than originally assumed by FEMA. Specifically, NIST's interim report on 7 WTC displays photographs of the southwest façade of the building that show it to have significant damage. The report also highlights a 10-story gash in the center of the south façade,toward the bottom, extending approximately a quarter of the way into the interior. A unique aspect of the design of 7 WTC was that each outer structural column was responsible for supporting 2,000 sq ft (186 m²) of floor space, suggesting that the simultaneous removal of a number of columns severely compromised the structure's integrity. Consistent with this theory, news footage shows cracking and bowing of the building's east wall immediately before the collapse, which began at the penthouse floors. In video of the collapse, taken from the north by CBS News and other news media, the first visible sign of collapse is movement in the east penthouse 8.2 seconds before the north wall began to collapse, which took at least another 7 seconds.

A progress report was released in June 2004, outlining NIST's working hypothesis. The hypothesis, which was reiterated in a June 2007 status update, is that an initial failure in a critical column occurred below the 13th floor, caused by damage from fire and/or debris induced structural damage of a critical column, from the collapse of the two main towers. The collapse progressed vertically up to the east mechanical penthouse. The interior structure was unable to handle the redistributed load, resulting in horizontal progression of the failure across lower floors, particularly the 5th to 7th floors. This resulted in "a disproportionate collapse of the entire structure."

NIST anticipates the release of a draft report of 7 WTC by the end of 2007. The investigation of 7 World Trade Center has been delayed for a number of reasons, including that NIST staff who had been working on 7 WTC were assigned full-time from June 2004 to September 2005, to work on the investigation of the collapse of the twin towers. Regarding the investigation of 7 World Trade Center, Dr S. Shyam Sunder stated in a New York magazine interview in March 2006, "We are studying the horizontal movement east to west, internal to the structure, on the fifth to seventh floors”; he then added, "But truthfully, I don’t really know. We’ve had trouble getting a handle on Building No. 7." In June 2007, he explained, "We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible. The WTC 7 investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."

Despite FEMA's preliminary finding that fire caused the collapse, some conspiracy theorists believe the building seven collapse was the result of a controlled demolition. When asked about controlled demolition theories, Dr. Sunder said, "We consulted 80 public-sector experts and 125 private-sector experts. It is a Who’s Who of experts. People look for other solutions. As scientists, we can’t worry about that. Facts are facts." In answer to the question of whether "a controlleddemolition hypothesis is being considered to explain the collapse," NIST said: "hile NIST has found no evidence of a blast or controlled demolition event, it would like to determine the magnitude of hypothetical blast scenarios that could have led to the structural failure of one or more critical elements."

When 7 World Trade Center collapsed, debris caused substantial damage and contamination to the Borough of Manhattan Community College's Fiterman Hall building, located adjacent at 30 West Broadway, to the extent that the building is not salvageable. As of August 2007, Fiterman Hall is undergoing deconstruction. The adjacent Verizon Building, an art deco building constructed in 1926, had extensive damage to its east from the collapse of 7 World Trade Center, though was able to be restored at a cost of US$1.4 billion.

Rebuilding 7 World Trade Center

Design

The new 7 World Trade Center has 52 stories and is 750 ft (228 m) tall. The building has 42 floors of leasable space, starting at the 11th floor, with a total of 1,700,000 sq ft (158 000 m²) of office space. The first ten floors house an electrical substation, which provides power to much of Lower Manhattan. The office tower has a narrower footprint at ground level than its predecessor, so that the course of Greenwich Street could be restored in an effort to reunite TriBeCa and the Financial District.

David Childs worked in conjunction with glass artist and designer James Carpenter to create a design that uses ultra-clear, low-iron glass to provide reflectivity and light, with stainless-steel spandrels behind the glass to help reflect sunlight. Stainless steel used in the building façade is molybdenum-containing Type 316, which provides improved resistance to corrosion. To enclose the power substation, the base of the building has a curtain wall with stainless steel louvers that provide ventilation for the machinery. During the day, the curtain wall reflects light, while at night it illuminates with blue LED lights. The curtain wall around the lobby uses heavily laminated, heat-strengthened glass that meets high standards for blast resistance. Inside the main lobby, artist Jenny Holzer created a large light installation with glowing text moving across wide plastic panels. The entire wall, which is 65 ft (19.8 m) wide and 14 ft (4.3 m) tall, changes color according to the time of day. Holzer worked with Klara Silverstein, the wife of Larry Silverstein, to select poetry for the art installation. The wall is structurally fortified as a security measure.

The building is being promoted as the safest skyscraper in the U.S. According to Silverstein Properties, the owner of the building, it "will incorporate a host of life-safety enhancements that will become the prototype for new high-rise construction." The building has 2 ft (60 cm) thick reinforced-concrete and fireproofed elevator and stairway access shafts, whereas the original building used only drywall to line these shafts. The stairways are wider than in the original building to permit faster egress. Steel columns are encased in much thicker fire protection, which consists of a medium-density, portland cement-based product that adheres well to the steel columns, among other advantages over other types of spray-applied fire-resistive material.

7 World Trade Center is equipped with Otis destination elevators. After pressing a destination floor number on a lobby keypad, passengers are grouped and directed to specific elevators that will stop at the selected floor (there are no buttons to press inside the elevators). This system is designed to reduce elevator waiting and travel times. The elevator system is integrated with the lobby turnstile and card reader system, which identifies the floor on which a person works as he/she enters and can automatically call the elevator for that floor.

The building is considered New York City's first "green" office tower, and gained gold status in the U.S. Green Building Council's LEED program. Nearly 30 percent of structural steel used in the building consists of recycled steel. Rainwater is collected and used for irrigation of the park and to cool the building. The building is designed to allow in plenty of natural light, power is metered to tenants to encourage them to conserve energy, heating steam is reused to generate some power for the building, and recycled materials are used for insulation and interior materials, along with other sustainable design features.

Construction

Construction of the new 7 World Trade Center began in 2002, soon after the site was cleared of debris. Restoring the Con Ed electrical substation was an urgent priority to meet power demands of Lower Manhattan. Because 7 World Trade Center is separate from the main 16 acre (6.5 ha) World Trade Center site, Larry Silverstein required approval only from the Port Authority, and rebuilding was able to proceed quickly. Building Seven was not included in the original World Trade Center master plan by Daniel Libeskind, but was designed by Skidmore, Owings & Merrill under the leadership of David Childs, who largely redesigned the Freedom Tower.

Once construction of the power substation was complete in October 2003, work proceeded on building the office tower. An unusual approach was used in constructing the building, erecting the steel frame before adding the concrete core. This approach allowed the construction schedule to be shortened by a few months. Construction was completed in 2006 at a cost of $700 million. Costs to rebuild were covered by $475 million in Liberty Bonds, which provide tax-exempt financing to help stimulate rebuilding in Lower Manhattan, along with insurance money.

A 15,000 sq ft (1,400 m²) triangular park was created between the extended Greenwich Street and West Broadway by David Childs with Ken Smith and his colleague, Annie Weinmayr, of Ken Smith Landscape Architect. The park comprises an open central plaza with a fountain and flanking groves of sweetgum trees and boxwood shrubs. As the seasons change, so will the colors in the park, providing a natural complement to the adjacent tower. At the center of the fountain, sculptor Jeff Koons created Balloon Flower (Red), whose mirror-polished stainless steel represents a twisted balloon in the shape of a flower.

Building opened

The building was officially opened at noon on May 23 2006 with a free concert that featured Suzanne Vega, Citizen Cope, Bill Ware Vibes, Brazilian Girls, Ollabelle, Pharaoh's Daughter, Ronan Tynan (of the Irish Tenors), and special guest Lou Reed. In March 2006, before the building opened, the new 7 World Trade Center frontage and lobby were used in scenes for the movie Perfect Stranger with Halle Berry and Bruce Willis.

Since the building opened, several unleased upper floors have been used for events such as charity lunches, fashion shows, and black-tie galas. Silverstein Properties initially allowed space in the new building to be used for such events as a means to draw people to see the building. From September 8 to October 7, 2006, the work of photographer Jonathan Hyman was displayed in "An American Landscape," a free exhibit, hosted by the World Trade Center Memorial Foundation, at 7 World Trade Center. The photographs captured the response of people in New York City and across the United States after the September 11, 2001, attacks. The exhibit took place on the 45th floor, while the space remained available for lease.

As of March 2007, 60 percent of the building had been leased. In September 2006, Moody's signed a 20-year lease to rent 15 floors of 7 World Trade Center. Other tenants that had signed leases in 7 World Trade Center, as of May 2007, include ABN Amro, Ameriprise Financial Inc., Darby & Darby P.C., Mansueto Ventures LLC, business publisher of Fast Company and Inc., and the New York Academy of Sciences. The space occupied by Mansueto Ventures has been designed to use the maximum amount of natural light, and retains an open floor plan. Silverstein Properties also has offices in 7 World Trade Center, along with office space used by the architectural and engineering firms working on the Freedom Tower, 150 Greenwich Street, 175 Greenwich Street, and 200 Greenwich Street. As of July 2007, space remains available on the ten uppermost floors of 7 World Trade Center, as well as the 35-37th floors.

See also

• List of tallest buildings in New York City
• World Trade Center in popular culture

References

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71. Pristin, Terry (February 28, 2007). "Lower Manhattan: A Relative Bargain but Filling Up Fast". The New York Times.
72. "Ameriprise Financial to lease 20,000 SF at 7 WTC" (Press release). Silverstein Properties. January 4, 2006.
73. "Darby & Darby P.C. to move headquarters to 7 WTC" (Press release). Darby & Darby. August 24, 2006.
74. "Mansueto Ventures signs lease at 7 World Trade Center to become the first corporate tenant to locate its national headquarters in the building" (Press release). Silverstein Properties. July 26, 2006.
75. "New York Academy of Sciences Signs Lease at 7 WTC". New York Academy of Sciences. December 16, 2005.
76. Wilson, Claire (May 13, 2007). "An Open, Sunlit Space At 7 World Trade Center". The New York Times.
77. Dunlap, David W. (January 25, 2007). "What a View to Behold, And It's Really Something". The New York Times.
78. Dunlap, David W. (January 18, 2007). "Behind the Scenes, Three Towers Take Shape". The New York Times.
79. "7 World Trade Center - Current Space Availabilities". Silverstein Properties. Retrieved 2007-07-27.

External links

• World Trade Center
• Silverstein Properties

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• 1987 architecture
• 2006 architecture
• Former buildings and structures of New York City
• Skyscrapers in New York City
• Skyscrapers between 200 and 249 meters
• World Trade Center
• LEED gold certified buildings