New York City is famous for its fantastic skyline, with countless buildings stretching hundreds of feet into the air. Architects and engineers design these structures meticulously, so they provide safe shelter to their occupants. These structural considerations also exist to protect the people living around these massive buildings. Every detail, from materials to construction, must be considered and evaluated with utmost care if these towering buildings are to stay upright.
But one mistake could turn a skyscraper, in fact, any building, into a disaster. For example, the wrong kind of wood can turn a treehouse into an accident waiting to happen. Without waterproof decking options, concrete floors can crack from water. No structure in Manhattan can epitomize this statement more than Citibank’s Citicorp Center Tower.
Citicorp Center’s potentially disastrous design flaw stems from the tower’s unusual origins. The plot Citibank had planned to build their skyscraper in the early 1970s already had a preexisting structure: St. Peter’s Lutheran Church. The parishioners weren’t going to move, so architect William LeMessurier came up with an equally unusual structural design.
LeMessurier built the skyscraper on four stilts at the center of the building. This allowed construction to begin over a hundred feet above the small church. However, stilts are supposed to be built on the corners of a structure. So LeMessurier created an array of steel chevrons to be the building’s framework. The building also included an electrical mass damper to stabilize it further. The building was completed in the late 70s without incident.
The Fatal Flaw
The problem with Citicorp Center was discovered when an engineering student called LeMessurier a year later to ask if putting stilts in the center of the building was the wisest choice. The architect defended his decision but was rattled by the inquiry. He double-checked the plans and discovered a horrifying mistake.
The chevron array was designed to withstand winds that would hit the tower from corners, which it was more susceptible to because of the stilt placement. However, the strength of the chevrons depended on the way their joints connected. Instead of being welded, as LeMessurier instructed, the construction crews had bolted them instead, significantly reducing their strength against vicious corner winds from storms.
The chevrons alone weren’t the only safety feature of Citicorp Center. The electrical mass damper acted as secondary protection. However, they relied entirely on electrical power, which could be disrupted by a storm that had strong enough winds to knock down the tower. Experts estimated that New York could be slammed with such a storm every 16 years.
What kind of effect would the 900-foot Citicorp Center crashing down have on the city? According to experts such as the Red Cross, the collapse of the tower would affect over 150 city blocks, leveling untold structures, and kill as much as 200,000 people.
When LeMessurier revealed the structural flaw to the building’s owners, they immediately launched into action, hiring crews to solder the joints every night, every day, for months. Thanks to the tireless efforts of these construction workers and the meticulous attitude to the architects and engineers involved, the Citicorp Center tower remains upright to this day.