The Untold Story of Citicorp Center: Engineering Marvel, Near Disaster, and Ethical Triumph
In the heart of Manhattan stands the Citicorp Center, a striking skyscraper completed in 1977 that was hailed as an architectural and engineering marvel. Yet, behind its sleek design lies one of the most dramatic and ethically challenging engineering stories of the 20th century—one that nearly ended in catastrophe but ultimately became a testament to professional integrity and innovation.
A Bold Architectural Challenge: Building Around a Church
In the 1960s, Citicorp sought to build a new headquarters in Manhattan. The site posed a unique challenge: an entire city block was available for development—except for Saint Peter’s Church, whose pastor insisted it remain physically distinct and maintain its own identity. The solution was unprecedented: design a skyscraper that would stand on stilts, with the church occupying the ground space beneath it.
Architect Hugh Stubbins and structural engineer Bill LeMessurier collaborated to create a tower supported on four stilts placed at the midpoints of each side, rather than the corners as in typical buildings. This created a complex engineering problem: how to transfer the building’s gravity load and resist wind forces without the usual corner columns.
The Ingenious Structural Solution: Chevron Bracing and Tuned Mass Damper
LeMessurier’s flash of inspiration was the introduction of six layers of diagonal chevron braces on each face of the building. These massive braces—some nearly 40 meters long—channeled gravity and wind loads from the upper stories down to the stilts. Because transporting braces this large was impossible through Manhattan’s streets, they were fabricated in pieces and welded on-site.
While this design saved considerable weight and cost, it made the building more flexible, causing noticeable sway in strong winds. To address this, LeMessurier incorporated a tuned mass damper (TMD)—a massive 400-ton concrete block mounted atop the building, suspended on springs and viscous dampers. This device oscillates out of phase with the building’s sway, dissipating energy and reducing motion by about 50%. This was the first use of a TMD in a skyscraper, pioneering a technology now standard in tall buildings worldwide.
The Terrifying Discovery: A Fatal Structural Flaw
About a year after opening, in 1978, LeMessurier received a phone call from a student questioning the building’s design regarding wind forces hitting its corners, known as quartering winds. Intrigued and concerned, LeMessurier re-examined the calculations and discovered a grave oversight: the building’s bolted braces—installed instead of the originally designed welded ones—were insufficient to handle the increased stress from quartering winds.
The original design called for four bolts per joint, but under quartering winds, some braces required as many as 14 bolts for safety. Furthermore, dynamic wind effects could increase stresses by up to 60%, and if the tuned mass damper failed (for example, due to power loss), winds as “low” as 110 km/h could cause catastrophic failure.
The Ethical Dilemma and Heroic Response
LeMessurier faced a profound ethical crisis: stay silent and risk thousands of lives or act immediately and face potential professional ruin. After consulting experts and informing Citicorp executives, he orchestrated a secret, round-the-clock repair operation—Project Serene.
Workers welded steel plates over more than 200 critical joints after hours, reinforcing the structure without disrupting tenants. Emergency systems were put in place, including backup power for the tuned mass damper and a 10-block evacuation plan formulated with the Red Cross.
The Close Call: Hurricane Ella and the Repair Completion
As repairs were underway, Hurricane Ella approached New York in September 1978 with winds reaching 200 km/h. The city prepared to evacuate thousands, but at the last moment, the hurricane veered out to sea. Repairs were completed shortly thereafter, making the building capable of withstanding storms far stronger than any previously recorded.
Legacy: Engineering Ethics, Innovation, and Continuing Impact
Though initially kept secret, the story emerged publicly in the 1990s, with LeMessurier praised for his courage and integrity. The incident became a landmark case study in engineering ethics worldwide.
The Citicorp Center also set a precedent for the use of tuned mass dampers, now used in many of the tallest buildings globally, from Taipei 101 to Tokyo’s skyscrapers, enhancing safety in wind- and earthquake-prone regions.
Lessons Learned
- Innovative engineering requires rigorous, continual review: Even groundbreaking designs must anticipate all environmental forces, including less obvious ones like quartering winds.
- Ethical responsibility outweighs personal risk: LeMessurier’s decision to disclose and fix the flaw highlights the paramount duty engineers have to public safety.
- Transparency and communication are critical: While secrecy helped prevent panic, the eventual sharing of this story educates future engineers and the public.
- Technological advances like tuned mass dampers are invaluable: They allow architects to push boundaries while maintaining safety and comfort.
Conclusion
The Citicorp Center story is more than an engineering case; it is a powerful narrative about courage, responsibility, and innovation. It reminds us that behind every skyscraper, there are engineers whose decisions can literally hold up—or bring down—entire cities. Bill LeMessurier’s legacy endures not only in steel and concrete but in the ethical standards that guide the profession today.
If you found this story inspiring and want to learn more about engineering marvels and ethics, stay tuned for more deep dives into the world of structural innovation and human courage.