BOMB-PROOF STRENGTHENING is being carried out to a landmark New York skyscraper on what is believed to be the first project of its kind in the city since last year's World Trade Center attacks.
The 59 floor, 279m tall Citigroup Center, with its distinctive triangular wedge-shaped roof, is being strengthened.
Studies by consultant Thornton Tomasetti subsidiary LZA Technology revealed the building's stability could be at risk from a street-level car bomb.
The steel-framed structure built between 1974 and 1977 is partially supported on four huge nine-storey high columns. Each is located at the midpoint of the building's sides with one standing in a busy street. The supports comprise an arrangement of braced steel columns.
Studies ordered by owner Boston Properties on the Manhattan landmark revealed that strengthening would be required to protect against a possible car or truck bomb.
No details are being made public about the work, but it is believed the strengthening includes installation of steel plates to shield against explosive forces, mounted on copper sleeves which crumple like shock absorbers in a blast.
Column elements will also be stiffened.
The building, designed by engineer Le Messurier, previously had major retrofitting carried out to improve its wind resistance after construction was complete.