Citigroup Center

Citigroup Center
Citigroup center.jpg
General information
Location 153 East 53rd Street, Manhattan, New York, United States
Status Complete
Constructed 1974-1977
Opening 1977
Use Office
Height
Roof 915 ft (279 m)
Technical details
Floor count 59
Cost $195 million (USD)
Companies involved
Architect(s) Stubbins Associates, Emery Roth & Sons
Structural engineer Le Messurier Consultants, James Ruderman
Developer Boston Properties
Owner Boston Properties

The Citigroup Center (formerly Citicorp 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 is one of the most distinctive and imposing in New York's skyline, with a 45° angled top and a unique stilt-style base. It contains 1.3 million square feet (120,000 m²) of office space, and the 45-degree angle at the top of the building was originally intended to contain solar panels to provide energy; this idea was eventually dropped because the positioning of the angled roof meant that the solar panels would not face the sun directly. It was designed by architect Hugh Stubbins Jr. for Citibank, and was completed in 1977. The building is currently owned by Boston Properties, and is the tallest building that bears the Citigroup name.

Contents

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

Night View of Citigroup Center from GE Building.

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 columns 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.

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, Le Messurier 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.

Base of the Citigroup Center
View from the street

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, and hurricane season began in August. The problem had to be corrected quickly.

It was reported that LeMessurier agonized over how to deal with the problem, and, by making it known to the wider world, 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.[1] 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.[2] 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. The company is also considering selling naming rights to the building.[3]

Notable features

Public lobby

See also

Notes

  1. ↑ Joe Morgenstern (1995), "The Fifty-Nine-Story Crisis", The New Yorker, May 29, 1995. Pages 45–53.
  2. ↑ Eugene Kremer (2002). "(Re)Examining the Citicorp Case: Ethical Paragon or Chimera", Cross Currents, Fall 2002, Vol. 52, No 3.
  3. ↑ BNET Boston Properties to rename 601 Lexington Avenue.
  4. ↑ Greer, William R. (October 24, 1982). "Rx for Swaying Skyscrapers". The New York Times. http://www.nytimes.com/1982/10/24/realestate/rx-for-swaying-skyscrapers.html. Retrieved 2009-07-25. 
  5. ↑ O'Driscoll, Patrick (September 25, 2002). "High-rises remain vulnerable after 9/11". USA Today. http://www.usatoday.com/news/nation/2002-09-25-high-rises-1acov_x.htm. Retrieved 2010-04-11. 

References

External links