The Hyatt Regency Hotel was built in Kansas City, Missouri in 1978. This hotel consisted of a 40-story hotel tower and conference facilities, which were connected by an open concept atrium. Inside the atrium, there were three walkways that connected the hotel to the conference facilities on the second, third, and fourth floors. The atrium was 145 feet long, 117 feet wide and 50 feet high.
On July 17, 1981, approximately 2,000 people had gathered in the atrium to participate in and watch a dance contest. Dozens stood on the walkways. At 7:05 PM, the walkways on the second, third, and fourth floor were packed with visitors as they watched over the active lobby, which was also full of people. The fourth floor bridge was suspended directly over the second floor bridge, with the third floor walkway set off to the side several meters away from the other two. Construction issues led to a subtle but flawed design change that doubled the load on the connection between the fourth floor walkway support beams and the tie rods carrying the weight of the second floor walkway. This new design could barely handle the dead load weight of the structure itself, much less the weight of the spectators standing on it. The connection failed and both walkways crashed one on top of the other and then into the lobby below, killing 114 people and injuring more than 200 others.
Originally, the 2nd and 4th floor walkways were to be suspended from the same rod (as shown in fig-1) and held in place by nuts. The preliminary design sketches contained a note specifying a strength of 413 MPa for the hanger rods which was omitted on the final structural drawings. Following the general notes in the absence of a specification on the drawing, the contractor used hanger rods with only 248 MPa of strength. This original design, however, was highly impractical because it...