Hyatt Regency Kansas City walkway collapse was July 1981. The original design featured threaded rods suspended from above that supported both second and fourth floor walkways. Each walkway connection to the rod only supported its own weight. The design change split the rods in two, with the second floor walkway supported by the fourth floor walkway, doubling the load on the fourth floor walkway connection to its suporting rod.
The original design was only made for about 60% of the required walkway loads under the building code. Two structural engineers lost their licenses over the incident.
A portion of the atrium roof collapsed during construction, and the building owners reportedly told the architects/engineers to recheck all their calculations.
The Kemper Arena roof collapsed in Kansas City in 1979. A number of complicating factors entered into the roof collapse. It occurred during a major rainstorm. The roof drain system was limited in its release rate to the storm sewers and thus retained water, and the wind blew water away from overflow scuppers, increasing the live roof load. If I remember correctly, this collapse and the 1978 Hartford Civic Center Arena roof collapse under snow load led to revisions in the accepted calculations for high-strength structural bolts. Gerald Ford also required a physical load test on the Ford Presidentail Library roof, which used a space truss design similar to the Hartford Arena.