Twenty-eight years ago today, the Hyatt Regency walkway collapsed killing 114 people. From Wikipedia:
"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."
Below is a copy of the front page of the Syracuse Herald-Journal from Syracuse, New York. The walkway collapse was the headline for Saturday, July 18, 1981. A sportswriter, Mike McKenzie, of The Kansas City Star was in the Hyatt Regency Hotel when the walkway collapsed. His version of the events is related in the newspaper. Click on the image to view a larger version.
View of the collapsed walkways, during the first day of the investigation of the Hyatt Regency walkway collapse. Source: Wikipedia Commons.
According to matdl.org,
Original and as-built hanger details. Source: matdl.org.
"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 called for a nut 6.1 meters up the hanger rod and did not use sleeve nuts. The contractor modified this detail to use 2 hanger rods instead of one (as shown in fig-2) and the engineer approved the design change without checking it. This design change doubled the stress exerted on the nut under the fourth floor beam. Now this nut supported the weight of 2 walkways instead of just one (Roddis, 1993).
Analysis of these two details revealed that the original design of the rod hanger connection would have supported 90 kN, only 60% of the 151 kN required by the Kansas City building code. Even if the details had not been modified the rod hanger connection would have violated building standards. As-built, however, the connection only supported 30% of the minimum load which explains why the walkways collapsed well below maximum load (Feld and Carper, 1997).
While Kansas City did not convict the Hyatt Regency engineers of criminal negligence due to lack of evidence, the Missouri Board of Architects, Professional Engineers, and Land Surveyors was not as timid. It convicted the engineer of record and the project engineer of gross negligence, misconduct, and unprofessional conduct in the practice of engineering. Both of their Missouri professional engineering licenses were revoked, and they lost membership to ASCE. Also the billions of dollars in damages awarded in civil cases brought by the victims and their families dwarfed the half million dollar cost of the building (Roddis, 1993)."