It is coming up to July 4 week. Cadence will be shut down and Breakfast Bytes will be on hiatus. On shutdowns like this, I traditionally find something that might well interest the sort of people who read Breakfast Bytes but is only peripherally related to semiconductor or design automation. For example, last Thanksgiving I looked at some surprising facts about medical tests in Happy Thanksgiving. Do You Have Toenailitis? . Today an engineering cautionary tale about how late changes to a design can have unfortunate side effects. I'm sure that has never happened to any of us. Those of us that are software engineers are probably all guilty of making a change that is so trivially simple that it doesn't even need testing, just release it. Oops. Kansas City Hyatt Walkway Collapse In 1981, a couple of years before I came to the US, there was a big structural failure in Kansas City. One of the things that I was surprised to learn years ago, when we had to make an unscheduled landing in Kansas City of a San Francisco to London flight, was that Kansas City is not in Kansas but Missouri. I had no idea. It seems they are not just the S how Me state but also the Kansas City state. If you have ever stayed in a Hyatt, you will have noticed that they typically have large atria (I think that must be the plural of atrium) going the entire height of the building.Try the one in Burlingame if you want to see the style. Or look at the above picture, which is the Kansas City Hyatt Regency lobby today. The Kansas City Hyatt Regency was no different. It had some walkways right across the atrium at the second and fourth levels. Unfortunately, the two walkways collapsed onto a dance going on in the lobby underneath, killing 114 and injuring about twice as many again. At the time, it was the deadliest structural collapse in US history, and still is the deadliest accidental one, since it was only surpassed by the collapse of the WTC towers on 9/11, which were anything but accidental. This was not some ancient hotel that had not been upgraded to modern building standards. The Hyatt Regency had been open for less than three weeks when the disaster happened. Why Did It Happen? The immediate reason that it happened is that there were a lot of people on the walkways dancing to the music. This is a sort of worst-case problem from a mechanical point of view since it can put a lot more stress onto the structure than the static load of the same number of people just standing there, or even the same number of people walking around normally. But with music, everyone walks in time. This is the reason that soldiers break step when marching across bridges. But you can hardly ask people to break step when dancing, that's the whole point of dancing. But it wasn't just that a lot of people were dancing. There was a construction flaw. But it is very subtle. The walkways were suspended from long rods from the roof. In fact in the picture above (after the collapse) you can see some of the rods still in place. The original design created by the architects was not very realistic from a construction point of view. In the diagram below, in the picture on the right, you can see the original design. There were two walkways, one above the other, and the design required the rod to run through the upper walkway down to the lower walkway. This would require the rod to be threaded all the way from the lower walkway to the upper, and then a nut to be spun all the way up a couple of storeys under the upper walkway beams to support it. It was changed to be more easily constructed, so that the rod was split in two. That way the rod did not require to be threaded for long distances, just the end so that the nuts could be attached as in the diagram on the left. The Puzzle Do you see now why the walkways collapsed? Like I said, it is subtle. Tomorrow's post will explain it, in case you can't see the answer.
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