In July 1981, the Hyatt Regency Hotel in Kansas City, Missouri hosted a large party in the atrium area of the hotel. During this event, a pair of suspended walkways on the 2nd and 4th floors collapsed leading to 216 injured and 114 dead. Following investigation, the cause was determined to be resulting from a seemingly minor change in the original design of the walkways proposed by the fabricator and approved by the structural engineering without due process.
The original design had the 2nd and 4th floor walkways supported by box girders suspended from a single pair of hanger rods passing through the 4th and 2nd floors and retained by nuts and washers. Each floor is independently loading the hanging rods. The proposed change split the hanger rods in two sets where the 4th floor was hung on the first set and the 2nd floor suspended from the 4th floor girders. This resulted in the 4th floor nuts and washers supporting the weight of the 2nd floor below.
This loaded the nuts and girders with at least twice its designed loading and subsequently, with a large crowd and live loading, the box girders split, slipped over the nuts and washers to the crowd below.
A good analogy is to consider two people hanging on a rope. In the first case each person is gripping onto the rope but in the second one person is gripping the ankles of the other. There is still the same amount of loading on the rope but the second case is much more precarious.
This seemingly minor change had a catastrophic result which would have been picked up by the engineers had they performed a review of the design or calculations.
As the general public, we don’t have a choice but to trust the constructed environment in which we live is safe and sound. When we as engineers sign off on a design we take on the responsibility for its safety. But to err is human so it is essential that we develop processes to catch the mistakes and reduce this risk.
The views expressed in this article are those of only of the author, Nadav Cohen, not PBC itself.
