This video recounts the engineering crisis of the Citicorp Center in the late 1970s. Designed with a unique structure featuring columns at the center of each face to accommodate an existing church, chief engineer Bill LeMessurier employed innovative chevron bracing and a tuned mass damper. However, a design change substituting welded joints for bolts on the braces, combined with an oversight in calculating strength under "quartering winds" (hitting the building diagonally), left the skyscraper vulnerable to collapse in a severe storm. LeMessurier's discovery of this potentially fatal flaw led to a critical ethical dilemma. Choosing public safety over professional reputation, he initiated a secret repair operation (Project Serene) to weld reinforcement plates onto the vulnerable joints, working against the clock during hurricane season. The building narrowly avoided disaster during Hurricane Ella. The story highlights LeMessurier's integrity and has become a celebrated case study in engineering ethics, leading to changes in building codes regarding wind load calculations.
The Citicorp Center Crisis: A Near Disaster and an Ethical Triumph
0:00 The Citicorp Center, opened in 1977, was an engineering marvel with a hidden fatal flaw discovered in the summer of 1978 by engineer Bill LeMessurier.
1:05 The building's unique design was necessitated by an agreement with Saint Peter's Church (0:01:16), requiring the tower's base to be open, leading to the placement of supporting columns at the center of each side rather than the corners.
3:19 LeMessurier designed a chevron bracing system to transfer gravity loads to the central columns and withstand wind loads, a unique solution for a skyscraper.
7:50 To mitigate swaying due to the relatively light structure, a novel tuned mass damper (TMD) was installed on the top floor (0:09:49), weighing 400 tons.
11:18 The critical flaw was discovered after LeMessurier learned that welded connections on the chevron braces had been substituted with bolts (0:11:45) to save costs.
13:59 While rechecking calculations, LeMessurier realized that the bolt connections had only been analyzed for straight-on winds, not "quartering winds" hitting the building diagonally (0:14:06).
14:17 Calculations showed that quartering winds could increase forces on some braces by 40%, and dynamic analysis (considering building movement) revealed even higher stresses (0:18:09), potentially exceeding the strength of the bolted joints.
17:22 Compounding the issue, the firm had used an incorrect factor of safety and underestimated gravity loads when calculating the required number of bolts, resulting in far fewer bolts (four) than needed (up to ten or more) at critical joints (0:17:00).
18:39 LeMessurier calculated that a storm occurring every 67 years could cause collapse, or every 16 years if the TMD lost power (0:19:06). He believed it could fall in his lifetime.
19:51 Facing potential professional ruin, bankruptcy, or even considering suicide, LeMessurier chose to inform Citicorp executives (0:20:34) about the risk to public safety (0:20:25).
20:41 Citicorp's chairman, Walter Wriston, immediately approved emergency measures, including generators for the TMD (0:20:42) and a secret repair plan called Project Serene (0:20:55).
21:10 Project Serene involved welding large steel plates onto over 200 vulnerable joints, working overnight to minimize disruption (0:21:15).
21:41 An evacuation plan for a 10-block radius was developed with the Red Cross, though kept secret from the public to avoid panic (0:22:25). Strain gauges and dedicated phone lines were installed for monitoring (0:22:31).
25:02 A remarkable coincidence occurred when LeMessurier tried to call The New York Times, only to find the newspaper staff were on strike (0:25:06), resulting in a press blackout that aided the secrecy of the repairs.
25:42 The project faced a major threat when Hurricane Ella, a strong storm, headed towards New York in September 1978 (0:25:42). The city prepared for evacuation (0:26:20), but the hurricane turned out to sea at the last minute (0:26:37), narrowly avoiding disaster.
26:59 Repairs were completed in October 1978 at a cost of $4-5 million. The building is now considered safe enough to withstand a "one in 1000" storm (0:27:04).
27:24 The crisis remained largely secret for almost two decades until a 1995 "New Yorker" article (0:27:29). LeMessurier was widely praised for his ethical conduct (0:27:35).
27:42 New York City updated its building code to include requirements for quartering wind calculations (0:27:42).
28:08 Tuned mass dampers, pioneered in this skyscraper, are now common in tall buildings worldwide (0:28:08).
28:37 The legacy includes controversy over the identity of the student who first raised concerns about the quartering winds (0:28:39), often attributed to Diane Hartley (0:28:51) or Lee DeCarolis (0:31:00), though the exact interaction with LeMessurier remains debated.
32:20 The Citicorp Center crisis is widely taught as a prime example of engineering ethics and the professional responsibility engineers have for public safety (0:32:23).