Citicorp Center: How an Impending Disaster Forged Lessons for the BIM Era

The Citicorp Center (now Citigroup Center) opened in New York in 1977, a 59-storey, 279-metre skyscraper, a symbol of engineering innovation. But behind its facade, a structural vulnerability threatened catastrophe a year after its opening, putting thousands at risk.

This is the story of a colossus on the brink, of the ethical dilemma of its engineer, William LeMessurier, and the secret efforts to save it. And the question arises, how might BIM (Building Information Modelling) methodology have changed this architectural drama?

An Unconventional Design: Engineering Marvels and Unforeseen Challenges

The design of the Citicorp Center, by Hugh Stubbins and engineer William LeMessurier, faced an initial challenge: St. Peter’s Lutheran Church, which had to remain on its corner. LeMessurier innovated by raising the tower on four 34-metre pillars located in the centre of each facade, not at the corners, allowing them to cantilever 22 metres over the church.

To transfer wind loads to these supports, he devised a diagonal bracing system in the form of inverted chevrons. This design lightened the tower but made it more susceptible to swaying. To counteract this, the first tuned mass damper (TMD) in a skyscraper was installed: 400 tonnes of concrete at the top, designed for comfort, not critical structural stability.

The 45-degree sloping roof, initially for solar panels, was retained for aesthetic reasons. This solution for the church generated unconventional load paths, the future Achilles’ heel of the building. The lightness required the adaptation of a TMD that relied on electricity, which would become another point of vulnerability. The design pushed the boundaries of engineering and the codes of the time.

A Student’s Question was an Engineer’s Crisis

In June 1978, Diane Hartley, an architecture student at Princeton, questioned the stability of the Citicorp Center against diagonal winds (quartering winds) for her thesis. The New York code of 1970 did not require consideration of these winds for such a design, and LeMessurier initially defended his work, but doubt lingered.

Upon recalculating, he discovered that diagonal winds increased the stress on the V-braces by 40%. The problem was compounded by a construction change: the chevron joints, originally welded (stronger), were replaced with bolted joints (cheaper) at the suggestion of Bethlehem Steel, with the approval of LeMessurier’s office, but without him fully evaluating the change until shortly before Hartley’s call.

His firm did not recalculate the bolted joints for corner winds. The combination was critical: 40% more stress from diagonal winds implied 160% more load on the bolted joints, which were weaker. The building was vulnerable to a storm that could occur every 16 years. Wind tunnel tests by Alan Davenport confirmed and even aggravated the fears. An innovative design, limited codes, a cost-driven construction change, and a lack of thorough re-analysis converged into the crisis.

Responsibility, Ethics, Secrecy and a Race Against Time

At the end of July 1978, LeMessurier faced a monumental crisis. He chose responsibility over silence or ruin, stating his “social obligation”. He informed his insurers, Stubbins, and, in early August, Citicorp executives John Reed and Walter Wriston, who supported the repairs.

It was decided to repair in secret to avoid panic. Project SERENE involved welding steel plates onto the 200 defective bolted joints. Welders worked at night, from August to October 1978, with the building operating during the day. Tension rose in early September as Hurricane Ella threatened New York while repairs were halfway complete.

Secret evacuation plans were prepared, and fortunately Ella veered away. A New York press strike helped maintain secrecy, and the full story was not known until Joe Morgenstern’s article in The New Yorker in 1995.

LeMessurier was praised for his ethics, and his reputation was strengthened. However, the nearly two decades of secrecy delayed valuable lessons for the industry. Luck, with Ella’s diversion and the strike, was also a factor.

Reimagining the Past: Could BIM Have Prevented or Mitigated the Crisis?

The Citicorp story is an analogue drama. What would have happened with BIM? BIM creates a centralized digital 3D model, a “single source of truth” with parametric objects containing data and relationships. It could have influenced early detection of the failure (Corner Winds, as a comprehensive structural analysis would have allowed all winds to be simulated exhaustively in the design phase). In the management of joint changes, the switch to bolted joints would be formally recorded, and the strength properties of the joints would be updated. This change would be visible to everyone, including LeMessurier, and re-running structural analyses with the new properties would likely have revealed the 160% increase in stress before construction. Having a common data environment (CDE) would have ensured that LeMessurier, his office, and Bethlehem Steel worked with the same information, and the approval of the change would be documented, facilitating review. A detailed Building Execution Plan (BEP) that would have defined the responsibility of each person involved and, last but not least, could have performed a rule-based detection of structural ‘lashes,’highlighting elements that exceeded stress tolerances, acting as detectors of ‘structural integrity conflicts.

BIM would have made critical information visible, traceable, and proactively analysable. Its collaborative aspect could have prevented the communication gap. BIM is a process and a tool; its effectiveness depends on correct data and sound engineering principles; it does not replace critical thinking. Although building codes were deficient, BIM could have provided data to challenge them. Detecting the failure in design would have changed LeMessurier’s ethical dilemma, facing him with correcting an error before construction.

Echoes of Citicorp: Lasting Lessons for a Digitally Transformed Industry

The saga of the Citicorp Center is a testament to professional integrity. LeMessurier’s ethics, prioritising public safety, is a benchmark. The case underscores the need for rigorous design review and questioning assumptions.

Diane Hartley’s question was vital. Today, BIM offers powerful tools to enhance this rigour: comprehensive simulations, better collaboration, and transparent change management. But the human factor —diligence, ethical judgement, and willingness to ask questions— remains crucial.

The Citicorp crisis, ironically, may have strengthened the profession as a case study in ethics and oversight. It also shows that codes are often reactive; the omission of corner winds in the New York code of 1970 was a systemic failure.

BIM helps engineers go beyond code minimums, fostering a proactive approach to safety. By learning from these events and adopting BIM, the AEC industry can improve safety and efficiency.

The lesson is the synergy between human intelligence, ethics, and technology. BIM is not a panacea but an amplifier of good practices. The goal: robust buildings by design and transparent by process, protecting lives.