Engineering Disasters: The Hyatt Regency Walkway Collapse

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In 1981 interior walkways in the Hyatt Regency hotel in Kansas City Missouri collapsed and killed 114 people and injured 216 people (ref).

Engineering is a very serious matter and making mistakes in this field can get people killed.

In this post I am going to go over a classic engineering mistake that was the Hyatt Regency walkway collapse.

At the time of the collapse a tea dance party was being held in the hotel's lobby and people were crowded onto the walkways above to get a good view of the action.

The lobby featured a large atrium that was spanned by multiple elevated walkways that were suspended from the ceiling above. These walkways were 37 metres long and weighed 29,000 kilograms.

The Original Design

The walkway as originally designed was perfectly acceptable and it would have been able to take the weight of the spectators without any problems.

In the original design (left hand side of the drawing above), each walkway was suspended on three steel crossbeams that were supported by vertical steel tie rods. The steel tie rods were of sufficient strength to handle the load presented by the two walkways.

The crossbeams for each walkway were supported by nuts that threaded onto the rod. The nut and the crossbeam box was adequate to hold the load of the stretch of walkway that it was supporting.

As designed, if each walkway had a weight of 'F' the load on each nut would be 'F' and the load on the upper section of the steel tie rod would be '2F'. There were no problems with this design.

The Modified Design

The design however was modified, apparently to help the construction contractor (Havens Steel Company) avoid the hassle of having to thread the nuts all the way up the steel tie rods and to avoid potential damage to the threads when hoisting the walkways.

Havens proposed the modification as drawn on the right rand side of the drawing above.

In this modification the steel tie rod is broken into two lengths which makes the threading operation much less time consuming.

The fatal flaw in this modification is that this change doubled the load on the nut supporting the upper level walkway. It now had to support both the weight of upper level walkway plus the weight of the lower level walkway.

The force on that upper level nut was now '2F' (outlined in yellow).

The failure point, as can be seem from the image below, appears to be the steel wall in the box of the cross beam. It looks to me like the nut just pulled its way right on through the steel box wall and then I guess just right out the other side.

This caused the upper walkway to drop onto the lower walkway and both then dropped onto the crowd of people below.

Closing Words

The walkways with the modified design were later calculated to barely be able to hold their own self weight let alone the people who unfortunately were standing on these bridges.

The aftermath and the description of the rescue operation are a very gruesome tale to read which underscores the importance of doing the job right.

This failure highlights the critical importance of carefully considering modifications to any design and to understand exactly what it is that you are doing.

Unfortunately accidents like this continue to happen but hopefully at a much reduced rate than in the past.

Post Sources

https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse
https://interestingengineering.com/understanding-hyatt-regency-walkway-collapse
http://www.asce.org/question-of-ethics-articles/jan-2007/
https://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/175/Hyatt-Regency-Walkway-Collapse.aspx

Thank you for reading my post.