The Change Nobody Rechecked
Two walkways fell in the Kansas City Hyatt Regency in 1981 after a small redraw doubled the load on one connection. The change was stamped as reviewed by the contractor, the engineer and the architect - and nobody asked what carries the load now.
In July 1981 two walkways collapsed in the atrium of the Hyatt Regency in Kansas City. More than a hundred people died. The US National Bureau of Standards investigated, and its report is plain about what went wrong. As an engineer, what stays with me is how ordinary the mistake was.
The drawings showed one long steel rod from the roof, through the fourth floor walkway beams, down to the second floor beams. Each walkway hung from that rod. Then the steel fabricator drew it differently. Two sets of rods: one from the roof to the fourth floor beams, another from the fourth floor beams down to the second floor. A small redraw. But now the fourth floor connections carried both walkways. The report says the change essentially doubled the load on them.
Here is the part I keep coming back to. The report says those shop drawings were stamped as reviewed by the contractor, the structural engineer and the architect. So the change was seen. Nobody hid it. A stamp tells you someone looked. It says nothing about what they were looking for.
There is a second finding that is easy to miss. Even the original single-rod design would have reached only about 60 percent of the capacity the Kansas City Building Code expects. The first design was already weak, and the change made it worse. When the walkways fell, the load on the connection was about 31 percent of what the code expects it to carry. There was almost no margin.
None of this is about blaming people. What worries me is how familiar it is. A drawing changes, and somebody files the change under fabrication detail. The question that matters never gets asked: what carries the load now?
What I would take from this is simple. If a design changes late, treat it as a new design. Don't treat it as an edit to the old one. Ask someone to trace the load path again from the top, even when the change looks small and three people have already signed. A change costs nothing on paper. Finding out it was wrong after the building is up costs a great deal.
Most of us are not designing walkways. But the same thing happens in a budget, a project plan or a contract. One number moves, and everyone checks that the new number was typed in correctly. Few people check what else now depends on it.