# How They Prevented The Citicorp Disaster Source: https://www.youtube.com/watch?v=w2TLv30F6UU Recap page: https://rapidrecap.app/video/w2TLv30F6UU Generated: 2026-03-24T02:36:29.442+00:00 --- ## Quick Overview Structural engineers discovered that the Citicorp Center's tuned mass damper was inadequately secured, requiring emergency nighttime welding of over 200 joints using 5 cm thick, 2-meter long steel plates, described as "literally Band-Aids," to prevent the building from toppling due to wind forces. **Key Points:** - The structural flaw in the Citicorp Center involved the tuned mass damper (TMD) mounting, which was originally designed only for comfort stabilization but became critical for structural integrity. - Engineer William LeMessurier acquired emergency generators to power the necessary welding operations for the structural repairs. - Welders worked nightly after hours to rip off sheet rock and weld two 5 cm thick, 2-meter long steel plates onto each of the over 200 critical joints. - The repairs focused first on the most important joints, starting with those on the 30th floor, because the work needed to be completed before hurricane season. - To avoid mass panic, the structural issue and the urgent repairs were kept secret from the public and even the building's office workers. - String gauges were fitted on important structural members to monitor every bend and twist of the skyscraper, with data relayed from a communications center eight blocks away. - If the building had failed, it would have toppled into an adjacent building, continuing a chain reaction of catastrophic structural failure, the ultimate effects of which were untold. ![Screenshot at 00:02: 32:A 3D model illustrates the location of the Tuned Mass Damper \(TMD\) on the roof of the skyscraper, which required emergency generators to power the subsequent repair welds.](https://ss.rapidrecap.app/screens/w2TLv30F6UU/00-00-02.jpg) **Context:** The video details the near-catastrophe involving the Citicorp Center (now Citigroup Center) in New York City, a landmark skyscraper designed by William LeMessurier. The building utilized a Tuned Mass Damper (TMD) at its apex, initially intended only to mitigate sway for occupant comfort. However, a structural analysis revealed that the bolted connections securing this massive damper system were dangerously inadequate to withstand high winds, turning the TMD from a comfort device into a critical support structure that, if it failed, could cause the entire tower to collapse. ## Detailed Analysis The video explains how structural engineer William LeMessurier discovered a critical flaw in the Citicorp Center's design: the bolted connections for the tuned mass damper (TMD) were insufficient to handle high wind loads, meaning the TMD, meant only for comfort, was essential for stability. Fearing a collapse, especially with hurricane season approaching, LeMessurier decided on a covert repair operation. Emergency generators were acquired to power the welding equipment. Welders worked nightly after occupants left, removing sheet rock around the chevron beams and welding two 5 cm thick, 2-meter long steel plates onto each of the more than 200 critical joints, treating these additions like "Band-Aids." The repairs were prioritized starting from the 30th floor joints. To prevent mass panic, the engineers and Citicorp kept the danger secret from the public and the building's tenants. String gauges were installed on key structural members to monitor the building's movement, with data transmitted from a communications center eight blocks away, providing a small warning buffer. The failure of the structure would have resulted in the tower toppling into an adjacent building, creating a horrific, untold chain reaction of destruction. ### Structural Discovery - The TMD was originally designed for comfort stabilization, but engineers found it became the "crutch that the tower leaned on" due to flawed connections - Welders were brought in nightly to perform emergency repairs. ### Repair Execution - Welders removed sheet rock around chevron beams and welded two 5 cm thick, 2-meter long steel plates on each of over 200 joints, prioritizing those on the 30th floor. - Emergency generators were acquired to power the necessary work. ### Secrecy and Monitoring - The risk was kept secret from the public and office workers to avoid mass panic, despite the danger that the building could topple into another structure. - String gauges monitored the skyscraper's every bend and twist, relaying data from a comms center eight blocks away to provide a warning buffer. ![Screenshot at 00:00: 03:A 3D model showing the exterior of the skyscraper and highlighting the tuned mass damper mechanism on the roof.](https://ss.rapidrecap.app/screens/w2TLv30F6UU/00-00-00.jpg) ![Screenshot at 00:00: 11:A sketch illustrating the interior where a chevron beam is shown leaning precariously, indicating the area where welds were being performed.](https://ss.rapidrecap.app/screens/w2TLv30F6UU/00-00-00.jpg) ![Screenshot at 00:00: 33:A structural diagram highlighting the chevron bracing pattern \(in orange\) that required reinforcement across multiple floors.](https://ss.rapidrecap.app/screens/w2TLv30F6UU/00-00-00.jpg) ![Screenshot at 00:01: 11:An archival image showing people casually dining in the building's atrium, contrasting with the hidden structural danger.](https://ss.rapidrecap.app/screens/w2TLv30F6UU/00-00-01.jpg)