11. The deadliest structural collapse in U.S. history until the World Trade Center, the Hyatt Regency Hotel Walkway Collapse in 1981 resulted in the deaths of 114 people
On July 17, 1981, a tea dance was held at the Hyatt Regency Kansas City hotel, located in Kansas City, Missouri. Attended by approximately 1,600 people, at 7:05 pm the fourth-floor bridge suspended over the dance collapsed onto the second-floor walkway; the second-floor bridge subsequently collapsed under the impact and itself crashed onto the lobby floor below. A total of 111 people were killed, with a further three dying in hospital from injuries sustained at the hotel, whilst an additional 219 suffered injuries of varying severity. A fourteen-hour rescue operation sought to rescue those buried beneath 60 tons of rubble, hampered by the activation of sprinklers which flooded the lobby, successfully recovering 29 people alive.
The incident was caused by inexcusable oversights by the structural engineers behind the hotel. During construction, a design change doubled the load being held by the connection between the fourth-floor walkway’s support beams and rods. As a result, the bridge was barely capable of supporting its own weight; with the guests added, a collapse was inevitable. Investigations revealed that the engineers responsible approved the changes over the phone, without viewing any plans or performing even basic calculations. Despite this, they were ultimately acquitted at trial of gross negligence but were stripped of their licenses and barred from the profession.