THE GUIDE

Citigroup Center (ex Citicorp Building)

Designed by architect Hugh Stubbins and structural engineer William LeMessurier and built in 1977, it is 279 m high with 59 floors and has two particular architectural elements. These are the 45° sloping roof and the four 39 m high support pylons that are not at the corners but at the centre of the sides of the building. The reason why these asymmetrical pylons were built is because of a small church, St. Peter's Lutheran, which stood on that land since 1904. The owners of the church agreed to sell the land to Citigroup on the condition that the church be rebuilt in the same place without being in direct contact with the skyscraper. Since the church was located at one of the corners of the skyscraper, the designers proposed a structure of V-beams that would unload the weight of the building onto the pylons built at the center and not at the corners of the sides.
In 1978 Diane Hartley, an architecture student at Princeton University, was writing her thesis on the Citigroup Center and during her studies found herself with calculations that did not return to her on the building’s resistance in the event of strong winds at 45°. She decided to contact the structural engineer to find out where she was wrong. The designers discovered that she was not wrong at all and this because the engineer had made calculations only for winds that hit the skyscraper at 90° as required by local regulations. All this seriously compromised the stability of the building with winds of over 110 km/h, thanks also to the use of the cheapest bolts instead of welds to stop the joints. After a consultation between Citigroup's managers and the designers, it was decided to intervene with welds and reinforcement plates but at the same time to keep the story hidden from the press. The secret remained until 1995 when The New Yorker told it in a long article.

References

Francis Morrone. The Architectural Guidebook to New York City . Gibbs Smith, 2002. pp. 169-172
Citigroup Center (Wikipedia)
L'edificio che ha rischiato di crollare su Manhattan (Linkiesta.it)