On July 17, 1981, the Hyatt Regency Hotel in Kansas City was hosting a Friday evening dance party. Above the lobby, two walkways supported dozens of party goers overlooking the festivities. Suddenly the walkways collapsed, killing 114 people. The hotel had just been in operation a little over a year at the time of the accident.
The determination of what happened focused on the design and construction of the walkways. Exponent engineers sifted through the wreckage for four days and concluded that the collapse occurred when a welded beam which supported one of the walkways failed.
The 40-story complex featured a unique main lobby design consisting of a 117-foot by 145-foot atrium that rose to a height of 50 feet. Three walkways spanned the atrium at the second, third, and fourth floors. The second-floor walkway was directly below the fourth, and the third was offset to the side of the other two walkways. The third and fourth-floor walkways were suspended directly from the atrium roof trusses, while the second-floor walkway was suspended from the fourth-floor walkway. During construction, the design, fabrication and installation of the walkway hanger system was changed. Instead of one hanger rod connecting the second- and fourth-floor walkways to the roof trusses, two rods were used—one to connect the second- to the fourth-floor walkway, and another to connect the fourth-floor walkway to the roof, which doubled the stresses in the ill-conceived connection.
Just prior to the collapse about 2,000 people had gathered in the atrium to participate in and watch a dance contest, including dozens who filled the walkways. At 7 p.m., the walkways on the second, third, and fourth floor were packed with visitors as they looked down to the lobby, also full of people. It was the second- and fourth-floor walkways—the ones that experienced the design changes—that collapsed. Speculation that the accident had been the result of "harmonic vibrations" caused by dancers on the walkway was disproved by Exponent's mathematical models of the walkways and the sequence of events. The models were then double-checked for clues to the particular combination of the stresses that caused the collapse.
The case remains one of America’s most devastating structural failures and is cited as an example case in most engineering curricula taught around the world.