Hyatt Regency Hotel Disaster

[Coleman Smith]

This was the biggest claim of my career as a casualty claim adjuster.

I handled nothing but Hyatt claims for more than a year.

 

[bilby]

I seem to remember reading about that one. If I recall correctly, they had the walkways hanging from the ceiling at two levels, and the structural design called for a single, continuous hangar rod, passing through both walkways with a bolt and bracket supporting each walkway at that point.

The builders installed two hangar rods, one supporting the upper walkway from the ceiling, and the second supporting the lower walkway from the upper walkway.

They reasoned that the total load on the hangar rods was, of course, the same in both cases, so (as the rods were rated for that load) this change didn't require structural engineer approval.

However they failed to consider the load on the bolts. In the original design, each bolt and bracket carried the load of the one walkway it supported; But in the new design, the bolt supporting the upper walkway now carried the full combined load from both walkways. Now under up to twice its design loading, it inevitably failed when fully loaded.

Which is why we don't let unqualified people do structural engineering assessments. This has become a classic example of how easy it is to overlook something critical, and is now used for training builders, engineers and achitects.

As an engineer friend of mine remarked, engineers need to be more careful than doctors, because a doctor who makes a mistake might kill somebody, but an engineer who makes a mistake might kill hundreds.

(I don't watch online video, so my apologies if that's not the same event you are talking about).

 

[Loren Pechtel]

Or look at the Challenger. The fundamental problem is the engineers assumed the joint would always be in compression. Yeah, there's a whole bunch of weight pushing down on it, it's obviously in compression.

Except at the moment the main engines lit. Then the whole rocket twanged (expected), the joints got momentary periods of tension. And the solids were lit before the twang died away. And one cold winter morning an O-ring failed to save the day that nobody knew it had been saving for many previous launches.

 

[Tharmas]

I seem to remember reading about that one. If I recall correctly, they had the walkways hanging from the ceiling at two levels, and the structural design called for a single, continuous hangar rod, passing through both walkways with a bolt and bracket supporting each walkway at that point.

The builders installed two hangar rods, one supporting the upper walkway from the ceiling, and the second supporting the lower walkway from the upper walkway.

They reasoned that the total load on the hangar rods was, of course, the same in both cases, so (as the rods were rated for that load) this change didn't require structural engineer approval.

However they failed to consider the load on the bolts. In the original design, each bolt and bracket carried the load of the one walkway it supported; But in the new design, the bolt supporting the upper walkway now carried the full combined load from both walkways. Now under up to twice its design loading, it inevitably failed when fully loaded.

Which is why we don't let unqualified people do structural engineering assessments. This has become a classic example of how easy it is to overlook something critical, and is now used for training builders, engineers and achitects.

As an engineer friend of mine remarked, engineers need to be more careful than doctors, because a doctor who makes a mistake might kill somebody, but an engineer who makes a mistake might kill hundreds.

(I don't watch online video, so my apologies if that's not the same event you are talking about).

I remember that incident. At the time I was working as a structural steel detailer, which entails translating engineers’ plans into detailed drawings of each piece of steel. For instance, every steel beam in a high-rise building is detailed, showing how many and what size bolts to use and where to drill the holes in the beam, so the building goes together like an erector set. The engineers’ plans give the load and stress for each connection and the size of the beams, and the detailer calculates (using a large book of tables which I assume is digitized these days) the size and number of the bolts etc. Of course all the “drawing” is now computerized as well. But in the days of the above incident it was all still done by hand.

When the above incident happened my boss told me it was a detailing mistake; the detailer should have known better. Sometimes the detailers catch engineers’ mistakes, but in any case the engineers are supposed to review all the detailers’ drawings and approve them. Whoever signed off on the details in the above case was the person who took the blame.

 

[Tharmas]

For those interested in a entertaining book on this general subject, I recommend Why Buildings Fall Down: How Structures Fail, by Levy and Salvadori. It's non-technical but I believe accurate, and as I said, quite entertaining.

 

[Tigers!]

I seem to remember reading about that one. If I recall correctly, they had the walkways hanging from the ceiling at two levels, and the structural design called for a single, continuous hangar rod, passing through both walkways with a bolt and bracket supporting each walkway at that point.

The builders installed two hangar rods, one supporting the upper walkway from the ceiling, and the second supporting the lower walkway from the upper walkway.

They reasoned that the total load on the hangar rods was, of course, the same in both cases, so (as the rods were rated for that load) this change didn't require structural engineer approval.

However they failed to consider the load on the bolts. In the original design, each bolt and bracket carried the load of the one walkway it supported; But in the new design, the bolt supporting the upper walkway now carried the full combined load from both walkways. Now under up to twice its design loading, it inevitably failed when fully loaded.

Reminds me of the Westgate Bridge Collapse. There was a royal commission into the collapse. One recommendation was that the review of all calculations must be more rigorous and use some engineers from outside the main architects and builders.
My father was a mechanical engineer and he was asked to check the calculations on bolt stresses that many others had already checked. All had to agree.
For a couple of decades after my father (and many others) would be checking of calculations on a contract basis. Tedious and time consuming but so important.

My father and a friend were actually at the public viewing site when the bridge collapsed. They did not see it fall, but were knocked over by the air blast as the bridge hit the ground. The friend was a keen photographer and some of his photos of the bridge on the ground and the rescue work appeared all over the world.

As an engineer friend of mine remarked, engineers need to be more careful than doctors, because a doctor who makes a mistake might kill somebody, but an engineer who makes a mistake might kill hundreds.

Indeed they do.

 

[Coleman Smith]

I do not know if this is true or not but I did receive an opinion from an engineer who pointed out that the beams that held up the crosswalks were sea beams that were faced towards each other in an open C configuration. He said that the strongest Part of the sea beam is the back vertical section and if the C beams had been turned so that the open part of the sea was facing away from each other and the rods aligned vertically between them with a steel plate underneath it his opinion is that the crosswalks would not have failed.

I do not remember the engineer's name and I do not know if this is true or not. I find it to be an interesting opinion that was not included in any of the reports that I read.

 

[bilby]

I do not know if this is true or not but I did receive an opinion from an engineer who pointed out that the beams that held up the crosswalks were sea beams that were faced towards each other in an open C configuration. He said that the strongest Part of the sea beam is the back vertical section and if the C beams had been turned so that the open part of the sea was facing away from each other and the rods aligned vertically between them with a steel plate underneath it his opinion is that the crosswalks would not have failed.

I do not remember the engineer's name and I do not know if this is true or not. I find it to be an interesting opinion that was not included in any of the reports that I read.

Was this written using speech-to-text?

There is no such thing as a "sea beam", as you seem to be aware, because you get "C beam" correct once, but (bizarrely) "sea" is written where "C" is meant three times.

I am not an engineer, but my feeling is that if a C-beam is close enough to failure under vertical load for the orientation to matter when mounted with the web (the back of the C) vertical, the structure probably lacks an adequate safety margin.

Mounting the web flush against a supporting structure might help with twisting resistance, but if that kind of torsion is a concern, a C-beam may be the wrong choice altogether.

 

[Coleman Smith]

Was this written using speech-to-text?

Yes, my bad.

Wish I could edit it.