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Sitting strangely in the New York skyline, the sloped roof of 601 Lexington catches the eye. Not nearly as elegant as the Chrysler Building, or as impressive in height as either the Empire State or the Bank of America, the skyscraper still manages to impose as the tenth tallest building in New York City, and the sixth tallest in Midtown. (Note: 1 WTC, 4 WTC, and the midtown One57 are still in construction but have each passed 601 Lex in height.) Also known as the Citigroup Center, this 59-storey, 915-foot building contains over 1.3 million-square-feet of office space.
The Unique Base
Beyond its 45-degree angled top (originally intended for a solar panel array, but abandoned because the building is not oriented correctly), the building has several histories that make it one of the most curious structures built in the late 1970s. The first has to do with its unique cantilevered base. Unlike so many hulking structures in the neighborhood, the Citigroup building appears to float above a sunken plaza. Under the northwest corner of the building sits a modern church for St. Peter’s Evangelical Lutheran.
The church had been on the site since the mid-1900s, and when the land deal was made for the new banking center, it was contingent on the new church be constructed such that none of the building’s columns would pass through it.
The engineer William LeMessurier decided that by setting the tower in four massive columns, each over 110 feet tall, he could soar above each corner. Rather than support each corner directly like a simple table, the cross-shaped cantilever allowed LeMessurier to span the new church with a system of stacked chevron shaped braces concealed within the building.
Problems
While this technique seemed sufficient to allow for the corners to remain unobstructed, another problem arose soon after.
In June of 1978, one year after the building was constructed, it was discovered that the building was critically under-engineered. When LeMessurier designed the building, he calculated for only straight and perpendicular wind loads, as these were usually the greatest theoretical loads.
However, an engineering student at Princeton, Joel Weinstein, calculating for a school project, used 45-degree quarter loads and discovered that these were unusually greater. He contacted LeMessurier with his discovery, and at first was assured that the welded construction of the corners would sufficiently withstand these excessive loads as well. It was only later that LeMessurier discovered that to save on costs during construction, the welded joints had been replaced with much weaker bolted ones.
The Calm After the Storm
Exasperating the problem further, hurricane season had just begun and any Category 1 storm would be certain to cause serious damage. LeMessurier contacted the owners and convinced them to enact a secret plan to repair the building after work hours and also put in place a plan to evacuate the area in case such a storm came close.
Of course, only six weeks into the repair, with only half of the building corrected, Hurricane Ella was charted to hit the city. Fortunately, in the last minutes, the storm veered off course and the workers were able to complete their secret repairs.
In fact, since there were no incidents, it wasn't until The New Yorker ran a piece on the emergency repairs in 1995 that the story was made public. In the end, the story speaks both poorly and well of the engineer: Though he lacked the proper oversight in construction to have observed the error in the first place, once he was made aware of the problem, he took the necessary steps to correct the mistake.