Welp, it looks like it’s just about time for another architectural fact. This fact is the tragic tale of a lovely tea party in Kansas City that went horribly wrong due to a seeming insignificant nut.
In 1980, The Hyatt Regency hotel in Kansas City, Missouri opened for business. Designed by Edward Larrabee Barnes and the firm BNIM (Berkebile Nelson Immenschuh McDowell, Inc.), the hotel housed over 700 guests, had 42 suits, an exhibit hall, and a rooftop revolving restaurant. It also had a ballroom. Now Hyatt wanted the ballroom to have all the bells and whistles, so the architects designed a multi-story atrium spanned by elevated walkways suspended from the ceiling. Made of concrete and cladded in glass, the walkways looked beautiful. Until it collapsed.
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So, what happened? In short: one long rod was replaced by two short ones.
If there's one principle consistent across all human nature, it's that we will always prefer the path of least resistance (i.e., "if you can get away with a half-assed job, do it"). The original plan was for two walkways that were directly on top of one another to both be supported by one very long rod that would anchor into the ceiling. Like so:
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Simple right? One long rod hangs from the ceiling, is threaded all the way through the upper walkway, which is held with a nut, then continues down to the lower walkway where it’s attached with another nut. This assembly was a good design and would have easily held up both walkways no problem. But remember what I said about people being lazy.
The contractors saw this plan and realized that it required them to:
- Transport a bunch of 75’+ (22 m) rods to the site
- Thread it up to the fourth floor level (where the upper walkway was)
- Raise the walkway up and hold it in place
- Spend a bunch of time slowly screwing the nut up the rod for 24’ (7.3 m) until it hit the bottom of the upper walkway
- Then attach the bottom walkway.
It was too much work for their liking, so they asked the engineers if they could change it and the engineer agreed. Their new design was to have one rod from the ceiling support the upper walkway, then come back later and attach a second rod to that upper walkway’s support beam that would go down to the lower walkway to support it. Easy right?
Here was the revised design. Please direct your attention to the nut labeled “Oh Shit!”
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That nut is responsible for the deaths of 114 people, the injuries of 216 more, and resulted in $140 million ($334 million in today’s dollars) worth of lawsuits. It was the deadliest structural collapse in US history at the time and would not be surpassed until 20 years later with the World Trade Centers collapse on 9/11.
You see, in the original design each nut was only responsible for holding up the weight of its own walkway. That’s a good thing, because each nut is only rated to carry the weight of ONE platform. In the revised plan, the upper walkway nut was now responsible for holding up the weight of TWO platforms. They changed the rods but didn’t change the nuts or the support beam to compensate.
Cut forward to July 17, 1981. Approximately 1,600 people gathered into the atrium of the Hyatt Regency to attend a Tea Dance venue. Everyone was having a good time, sipping tea, eating tiny sandwiches, and dancing the night away. 20 people were standing on the upper walkway with an additional 40 standing on the lower. At 7:05pm, the guests on the upper level heard a loud pop then dropped several inches. This was followed by a second loud pop and the platform fell 24’ into the lower level, sending both walkways crashing to the floor. The nut that was holding everything up cleaved right through the support bar by the sheer weight of both platforms.
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During the investigation, it came out that neither the steel company nor the engineering firm had done an evaluation of the design change. That evaluation would have shown the error and prevented the inevitable collapse.
Hindsight is 20/20. It’s only obvious now that the altered design was flawed from the beginning, but back then it was such a small detail that it seemed fine. Architects and engineers must balance a thousand different systems designed by a half dozen contractors who, in turn, each have a dozen sub-contractors, just to construct one building. Project Managers cannot allow even a seemingly small things, like a threaded rod and a nut, to go unchecked. The Hyatt collapse stands as an example of the importance of engineering safety, oversight, and ethics.