Citigroup Center
Encyclopedia
The Citigroup Center is one of the ten tallest skyscrapers in New York City
, United States, located at 53rd Street
between Lexington Avenue and Third Avenue
in midtown Manhattan
. The 59-floor, 915-foot (279-m) building contains 1.3 million square feet (120,000 m²) of office space, and is one of the most distinctive and imposing in New York's skyline, thanks to a 45° angled top and a unique stilt
-style base. It was designed by architect Hugh Stubbins Jr.
for Citibank
, and was completed in 1977. The building is currently owned by Boston Properties
, and in 2009, was renamed 601 Lexington Avenue.
From the beginning, the Citigroup Center was an engineering challenge. When planning for the skyscraper began in the early 1970s, the northwest corner of the proposed building site was occupied by St. Peter's Lutheran Church. The church allowed Citicorp to demolish the old church and build the skyscraper under one condition: a new church would have to be built on the same corner, with no connection to the Citicorp building and no column
s passing through it, because the church wanted to remain on the site of the new development, near one of the intersections. Architects wondered at the time if this demand was too much, and if the proposal could even work.
Structural engineer William LeMessurier
set the 59-story tower on four massive 114-foot (35-m)-high columns, positioned at the center of each side, rather than at the corners. This design allowed the northwest corner of the building to cantilever
72 feet (22 m) over the new church. To accomplish these goals LeMessurier designed a system of stacked load-bearing braces, in the form of inverted chevrons. Each chevron would redirect the massive loads to their center, then downward into the ground through the uniquely positioned columns.
Later that month, LeMessurier met for an inquiry on another job where he mentioned the use of welded joints in the Citicorp building, only to find a potentially fatal flaw in the building's construction: the original design's welded joints were changed to bolted joints during construction, which were too weak to withstand 70-mile-per-hour (113 km/h) quartering winds. While LeMessurier's original design and load calculations for the special, uniquely designed "chevron" load braces used to support the building were based on welded joints, a labor- and cost-saving change altered the joints to bolted construction after the building's plans were approved.
The engineers did not recalculate what the construction change would do to the wind forces acting on two surfaces of the building's curtain wall
at the same time; if hurricane-speed winds hit the building at a 45-degree angle, there was the potential for failure due to the bolts shearing. The wind speeds needed to topple the models of Citigroup Center in a wind-tunnel test were predicted to occur in New York City every 55 years. If the building's tuned mass damper
went offline, the necessary wind speeds were predicted to occur every 16 years.
This knowledge, combined with LeMessurier's discovery that his firm had used New York City's truss safety factor of 1:1 instead of the column safety factor of 1:2, meant that the building was in critical danger. The discovery of the problem occurred in the month of June, the beginning of hurricane season. The problem had to be corrected quickly.
It is reported that LeMessurier agonized over how to deal with the problem. If he made it known publicly, he risked ruining his professional reputation. He approached Citicorp directly and advised them of the need to take swift remedial action, ultimately convincing the company to hire a crew of welders to repair the fragile building without informing the public, a task made easier by the press strike at that time.
For the next three months, a construction crew welded two-inch-thick steel plates over each of the skyscraper's 200 bolted joints during the night, after each work day, almost unknown to the general public. Six weeks into the work, a major storm (Hurricane Ella) was off Cape Hatteras
and heading for New York. With New York City hours away from emergency evacuation, the reinforcement was only half-finished. Ella eventually turned eastward and veered out to sea, buying enough time for workers to permanently correct the problem.
Because nothing happened as a result of the engineering gaffe, the crisis was kept hidden from the public for almost 20 years. It was publicized in a lengthy article in The New Yorker
in 1995. LeMessurier was criticized for insufficient oversight leading to bolted rather than welded joints, for misleading the public about the extent of the danger during the reinforcement process, and for keeping the engineering insights from his peers for two decades. However, his act of alerting Citicorp to the problem inherent in his own design is now used as an example of ethical behavior in several engineering textbooks.
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
, United States, located at 53rd Street
53rd Street (Manhattan)
53rd Street is a midtown cross street in the New York City borough of Manhattan, that contains buildings such as the Citicorp Building. It is 1.83 miles long. The street runs westbound from Sutton Place across most of the island's width, ending at DeWitt Clinton Park at Eleventh Avenue...
between Lexington Avenue and Third Avenue
Third Avenue (Manhattan)
Third Avenue is a north-south thoroughfare on the East Side of the New York City borough of Manhattan, running from Cooper Square north for over 120 blocks. Third Avenue continues into The Bronx across the Harlem River over the Third Avenue Bridge north of East 129th Street to East Fordham Road at...
in midtown Manhattan
Manhattan
Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...
. The 59-floor, 915-foot (279-m) building contains 1.3 million square feet (120,000 m²) of office space, and is one of the most distinctive and imposing in New York's skyline, thanks to a 45° angled top and a unique stilt
Stilts
Stilts are poles, posts or pillars used to allow a person or structure to stand at a distance above the ground. Walking stilts are poles equipped with steps for the feet to stand on, or straps to attach them to the legs, for the purpose of walking while elevated above a normal height...
-style base. It was designed by architect Hugh Stubbins Jr.
Hugh Stubbins Jr.
Hugh Asher Stubbins Jr. was an architect who designed several high profile buildings around the world.-Biography:...
for Citibank
Citibank
Citibank, a major international bank, is the consumer banking arm of financial services giant Citigroup. Citibank was founded in 1812 as the City Bank of New York, later First National City Bank of New York...
, and was completed in 1977. The building is currently owned by Boston Properties
Boston Properties
Boston Properties, Inc. is a self-managed real estate investment trust based in Boston, Massachusetts. Its primary focus is "Class A" office space which it acquires, develops, and manages in the major markets of Boston, New York City, Washington, D.C., and San Francisco...
, and in 2009, was renamed 601 Lexington Avenue.
History
The northwest corner of the site was originally occupied by St. Peter's Evangelical Lutheran Church which was founded in 1862. In 1905, the church moved to the location of 54th Street and Lexington Avenue.Early engineering details
Column
A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...
s passing through it, because the church wanted to remain on the site of the new development, near one of the intersections. Architects wondered at the time if this demand was too much, and if the proposal could even work.
Structural engineer William LeMessurier
William LeMessurier
William James LeMessurier was a prominent American structural engineer.Born in Pontiac, Michigan, LeMessurier graduated with an AB from Harvard, went to Harvard Graduate School of Design and then earned a master's degree from Massachusetts Institute of Technology in 1953. He was the founder and...
set the 59-story tower on four massive 114-foot (35-m)-high columns, positioned at the center of each side, rather than at the corners. This design allowed the northwest corner of the building to cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
72 feet (22 m) over the new church. To accomplish these goals LeMessurier designed a system of stacked load-bearing braces, in the form of inverted chevrons. Each chevron would redirect the massive loads to their center, then downward into the ground through the uniquely positioned columns.
Engineering crisis of 1978
Changes during construction led to a finished product that was structurally unsound. In June 1978, prompted by discussion between a Princeton University engineering student and design engineer Joel Weinstein, LeMessurier recalculated the wind loads on the building. In the original design, the engineer calculated for wind loads that hit the building straight-on, but he did not calculate for quartering wind loads, which hit the building at a 45-degree angle. This oversight revealed that quartering wind loads resulted in a 40% increase in wind loads and a 160% increase in the load at all connection joints. While this discovery was disturbing, LeMessurier was not overly concerned because the original design was padded by a safety factor (which in most cases was 1:2) and the design allowed for some leeway.Later that month, LeMessurier met for an inquiry on another job where he mentioned the use of welded joints in the Citicorp building, only to find a potentially fatal flaw in the building's construction: the original design's welded joints were changed to bolted joints during construction, which were too weak to withstand 70-mile-per-hour (113 km/h) quartering winds. While LeMessurier's original design and load calculations for the special, uniquely designed "chevron" load braces used to support the building were based on welded joints, a labor- and cost-saving change altered the joints to bolted construction after the building's plans were approved.
Curtain wall
A curtain wall is an outer covering of a building in which the outer walls are non-structural, but merely keep out the weather. As the curtain wall is non-structural it can be made of a lightweight material reducing construction costs. When glass is used as the curtain wall, a great advantage is...
at the same time; if hurricane-speed winds hit the building at a 45-degree angle, there was the potential for failure due to the bolts shearing. The wind speeds needed to topple the models of Citigroup Center in a wind-tunnel test were predicted to occur in New York City every 55 years. If the building's tuned mass damper
Tuned mass damper
A tuned mass damper, also known as an active mass damper or harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure...
went offline, the necessary wind speeds were predicted to occur every 16 years.
This knowledge, combined with LeMessurier's discovery that his firm had used New York City's truss safety factor of 1:1 instead of the column safety factor of 1:2, meant that the building was in critical danger. The discovery of the problem occurred in the month of June, the beginning of hurricane season. The problem had to be corrected quickly.
It is reported that LeMessurier agonized over how to deal with the problem. If he made it known publicly, he risked ruining his professional reputation. He approached Citicorp directly and advised them of the need to take swift remedial action, ultimately convincing the company to hire a crew of welders to repair the fragile building without informing the public, a task made easier by the press strike at that time.
For the next three months, a construction crew welded two-inch-thick steel plates over each of the skyscraper's 200 bolted joints during the night, after each work day, almost unknown to the general public. Six weeks into the work, a major storm (Hurricane Ella) was off Cape Hatteras
Cape Hatteras
Cape Hatteras is a cape on the coast of North Carolina. It is the point that protrudes the farthest to the southeast along the northeast-to-southwest line of the Atlantic coast of North America...
and heading for New York. With New York City hours away from emergency evacuation, the reinforcement was only half-finished. Ella eventually turned eastward and veered out to sea, buying enough time for workers to permanently correct the problem.
Because nothing happened as a result of the engineering gaffe, the crisis was kept hidden from the public for almost 20 years. It was publicized in a lengthy article in The New Yorker
The New Yorker
The New Yorker is an American magazine of reportage, commentary, criticism, essays, fiction, satire, cartoons and poetry published by Condé Nast...
in 1995. LeMessurier was criticized for insufficient oversight leading to bolted rather than welded joints, for misleading the public about the extent of the danger during the reinforcement process, and for keeping the engineering insights from his peers for two decades. However, his act of alerting Citicorp to the problem inherent in his own design is now used as an example of ethical behavior in several engineering textbooks.
Name change
In 2008, building owner Boston Properties began planning to rename the tower 601 Lexington Avenue. Renovation of the lobby resulted in relocation of the tower's entrance from 53rd Street to Lexington Avenue. All signage for Citigroup was removed from the building and surrounding block. The name change became effective in 2009. The company is also considering selling naming rights to the building.Notable features
- The roof of Citigroup Center slopes at a 45-degree angle because it was originally intended to contain solar panelsPhotovoltaic moduleA solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...
to provide energy. However, this idea was eventually dropped because the positioning of the angled roof meant that the solar panels would not face the sun directly. - To help stabilize the building, a tuned mass damperTuned mass damperA tuned mass damper, also known as an active mass damper or harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure...
was placed in the mechanical space at its top. This substantial piece of stabilizing equipment weighs 400 tons (350 metric tons). The damper is designed to counteract swaying motions due to the effect of wind on the building and reduces the building's movement due to wind by as much as 50%. Citigroup Center was the first skyscraper in the United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
to feature a tuned mass damper. - The building features double-deck elevatorDouble-deck elevatorDouble-deck elevators are designed with two elevator cars that are attached, one on top of the other. This allows passengers on two consecutive floors to be able to use the elevator simultaneously, significantly increasing the passenger capacity of an elevator shaft...
s, which are separated to serve only odd or even floors. - The corporate headquarters of Citigroup, contrary to popular perception, are not located in the building, but across the street in 399 Park Avenue399 Park Avenue399 Park Avenue is a 41-story office building that is the world headquarters of Citigroup in New York City, United States.Citigroup's chairman and chief executive officer operate from the building's second floor...
. - The building is visible in numerous television shows and movies (often as part of a wider panoramic shot of New York City), notably during the opening credits of the long-running NBCNBCThe National Broadcasting Company is an American commercial broadcasting television network and former radio network headquartered in the GE Building in New York City's Rockefeller Center with additional major offices near Los Angeles and in Chicago...
police procedural and legal drama Law & OrderLaw & OrderLaw & Order is an American police procedural and legal drama television series, created by Dick Wolf and part of the Law & Order franchise. It aired on NBC, and in syndication on various cable networks. Law & Order premiered on September 13, 1990, and completed its 20th and final season on May 24,...
. - In 2002, one of the columns was reinforced with blast resistant shields of steel and copper as well as steel bracing to protect the building due to the possibility of a terrorist attack.
See also
- Citicorp Building
- Citicorp CenterCiticorp CenterCiticorp Center can refer to several skyscrapers named after banking conglomerate Citigroup.* Citigroup Center , formerly Citicorp Center* Citigroup Center , formerly Citicorp Center...
- List of tallest buildings in New York City
- List of tallest buildings in the United States