The Unseen Peril of a Skyscraper
In 1977, the Citigroup Center in New York City opened as the tallest new skyscraper since the 1930s. Its unique design, with a sloped roof and a sunken public plaza, made it an architectural marvel. However, beneath its impressive exterior lay a hidden vulnerability that could have led to catastrophic consequences.
The tower’s unusual structure was a result of a negotiation with St. Peter’s Lutheran Church, which had refused to sell its land. Instead, the church agreed to sell air rights, allowing the construction of a new church on the same corner. This led to the design of a building that appeared to levitate above the plaza, supported by four main columns running through the middle of each face rather than the corners.
This unconventional approach created inherent instability. To counteract this, engineer William LeMessurier developed a structural bracing system with V-shaped chevrons and mast columns. Additionally, a tuned mass damper was installed to reduce movement during strong winds. Despite these measures, the building was not immune to potential failure.
A Fateful Discovery
In 1978, two college students unknowingly uncovered a critical flaw in the building’s design. Diane Hartley, a Princeton University student, was researching tall buildings for her thesis when she noticed discrepancies in the wind load calculations. Her findings suggested that diagonal winds could exert significantly more stress on the building than previously accounted for.
Hartley contacted LeMessurier’s office, but her concerns were dismissed. She later forgot about the interaction until a documentary in the 1990s mentioned a mystery student who had raised the alarm. While it remains unclear if she directly influenced LeMessurier, her work is credited with initiating a chain of events that led to the discovery of the potential disaster.
Another student, Lee DeCarolis, also reached out to LeMessurier around the same time, highlighting concerns about the placement of the columns. Although the exact impact of their communications is uncertain, both students played a role in prompting LeMessurier to re-evaluate his calculations.
The Engineer’s Dilemma
LeMessurier, a Harvard educator and renowned structural engineer, began re-examining his wind load calculations after the students’ concerns. He discovered that the building’s bracing system was more susceptible to quartering winds than initially believed. These diagonal gusts could cause significant stress on half of the exoskeleton’s bracing members, leading to potential failure.
Further investigation revealed that the building’s bracing had been bolted together instead of welded, a decision made to save time and money. This compromised the structural integrity, as each splice only had four bolts instead of the required 14. LeMessurier realized the tower was in real trouble, with a 1-in-16 chance of collapse under certain conditions.
Ethical Challenges and Crisis Management
Faced with the possibility of a catastrophic failure, LeMessurier grappled with the ethical implications of his actions. He considered the personal and professional consequences of revealing the flaw, even contemplating suicide. Ultimately, he chose to disclose the issue, knowing it could ruin his career.
LeMessurier worked with colleagues and the bank to address the problem. Steel plates were welded over the bolted joints, and emergency plans were put in place. A private weather forecasting company monitored potential storms, and gauges were installed to detect dangerous movements in the building.
Despite the urgency, the repairs were carried out discreetly due to a newspaper strike, keeping the public unaware of the danger. When Hurricane Ella threatened New York, the storm veered away, offering temporary relief. The crisis remained largely hidden until the mid-1990s, when a detailed article in The New Yorker brought the story to light.
Legacy and Lessons Learned
The incident with Citicorp Center became a landmark case in engineering ethics. LeMessurier’s actions are now studied as a model for professional responsibility. His story highlights the importance of transparency and the need for engineers to prioritize safety over cost-saving measures.
The book “The Great Miscalculation: The Race to Save New York City’s Citicorp Tower” by Michael M. Greenburg provides a comprehensive account of the events, emphasizing the human stories behind the technical challenges. It serves as a reminder of the critical role engineers play in ensuring public safety.
