Skyscraper puts on armor in Manhattan

59-story Citigroup Center on East 53rd Street has legs strengthened

August 22, 2002|By James Glanz and Eric Lipton | James Glanz and Eric Lipton,NEW YORK TIMES NEWS SERVICE

NEW YORK - Since Sept. 11, the owners of signature skyscrapers have been trying to find ways to calm jittery tenants and make the buildings more durable if catastrophe strikes. Perhaps nowhere has anyone thought longer and harder about that challenge than at Citigroup Center, the 59-story tower on East 53rd Street in Manhattan with the distinctive triangular top and a troubled history involving secretive structural repairs, which were begun 24 years ago to keep the building from toppling in hurricane-force winds.

Now the building's owner, Boston Properties, has undertaken an ambitious - and similarly secretive - project to strengthen the most exposed of the four stiltlike legs that support the bulk of the building nine stories above a plaza and, in one corner, St. Peter's Church.

The leg, composed of interconnected steel columns that are normally wrapped in a burnished aluminum facing, sits in a spot that looks highly vulnerable - only a few feet from traffic rumbling along 53rd Street.

A plywood enclosure, discreetly painted to match the aluminum, now shrouds the leg on three sides. Permits filed at the Department of Buildings in February and March indicate that over a 42-foot segment within the enclosure, crews are making major structural improvements designed to ward off the kind of forces that would be produced not by wind, but by a street-level explosion, according to experts who have seen the plans.

Vertical steel-and-copper shields are being put in place to fend off such a blast, and heavy structural plates are being fitted into place to help keep the columns from buckling in the concussion a blast would produce.

For all its secrecy, the project is a vivid example of a highly focused, structurally sophisticated and quite expensive effort - the cost could be several million dollars - to buttress a building against threats that suddenly seem to be everywhere, from the sky to the street, in the post-Sept. 11 world.

Citigroup, which is still a principal tenant of the building and remains one of the premier international symbols of American finance, may be especially sensitive to those threats. Branches of the company have suffered rocket and bomb attacks by terrorists in Europe, including in Greece in 1995, 1998 and 2000.


Engineers at LZA Technology, whose seal appears on the plans at the Buildings Department, would not comment on what was taking place behind the painted plywood box in the middle of Manhattan. But a structural engineer who is not involved in the work, Ramon Gilsanz, a managing partner at Gilsanz Murray Steficek, inspected the plans and confirmed that they involve structural reinforcements. "This is a strengthening for a blast or an impact load," Gilsanz said.

The design, which includes clever details such as copper sleeves behind the shields which would presumably crumple in an explosion and act like shock absorbers, "is a nice job," Gilsanz said.

A senior vice president and manager of the New York office at Boston Properties in New York, Robert Selsam, would say only, "We have an ongoing program to improve the safety and security of all of our buildings." When asked specifically about Citigroup Center, Selsam said, "It doesn't serve the interest of us or the tenants or the city to go into details."

Several company spokesmen emphasized that despite earlier structural questions, the building was entirely stable against ordinary natural forces like wind or the rare, mild earthquakes felt in New York. Selsam would not say whether the carefully constructed enclosure was part of a plan to keep the work quiet. But the plywood's mimetic coloring seems to have succeeded in doing so when it comes to office workers in the building, few of whom were aware of the nature of the work when asked about it by a reporter outside the building on Tuesday afternoon.

Nigel Hughes, an employee at Sun Microsystems, which moved its offices to Citigroup Center from the World Trade Center, said he had not even noticed the construction. Though Hughes said he was glad the owner was reinforcing the building, he added that office workers should have been told what was being done.

The problems that the 1.6 million-square-foot Citigroup Center faced in the summer of 1978 were frightening. A year after tenants moved into the new skyscraper, its main structural engineer discovered a design flaw that could have caused the entire structure to topple like a rotten oak tree in high winds. The engineer, William J. LeMessurier, made the discovery in July, just as the peak of the hurricane season was approaching.

Air rights

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.