Miami Pedestrian Bridge, Part VIII 80

[JAE]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.

Part I
thread815-436595

Part II
thread815-436699

Part III
thread815-436802

Part IV
thread815-436924

Part V
thread815-437029

Part VI
thread815-438451

Part VII
thread815-438966



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[TheGreenLama]

hokie66, thanks for that article. It clarifies a lot about the procedure. Those photos are giant FACTS, and would be admissible regardless of when released. It's still strange why they released them now.

 

[TehMightyEngineer]

I wonder if the images were going to come out one way or another and NTSB released them so that they could stay in control of the flow of information? Purely conjecture on my part. Maybe they just wanted to give us more info so they could read more about it in this thread?

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[hacksaw]

On a job interview back in the day, the engineer I chatted with new the two engineers (P.E.'s in Missouri) involved in reviewing the drawings for the Hyatt Reg. design.

They caught the problem, but because of the time pressures brought by their customer, they signed and stamped the drawings...with attached notes of the required changes required...

Those notes were "lost" as can be the case in any construction firm.

The two engineers in question were highly regarded but both lost their licenses to practice, and at one time were facing prison sentences...

Remember, do not sign off on any engineering design that does not meet your design assessment, period.

P.E.

 

[waross]

That would fall under "Punishment of the innocent."

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[human909]

The Hyatt Regency collapse was caused by a fabricator changing the design of the walkway hangers, not a constructability issue:

That is a simplified view and doesn't consider the events before and after. The vast majority of accidents have chains of events that are the cause. No different with The Hyatt Regency nor in the case of this bridge collapse.

Not sure if it is accurate to say that the start of the Hyatt Regency chain of mistakes was constructability since the original design drawings were considered by the structural engineer to be conceptual.

You sound almost as desperate to win an argument as the engineer is to escape blame. Of course the structural engineer is going to claim that! Weasel words to escape blame.

"The engineer of record further contended that it was common practice in the industry for the structural engineer to leave the design of steel-to-steel connections to the fabricator. The original design provided in the structural drawings was intended only to be conceptual."

Yep. But if you design is largely unconstructable and many of the obvious fabricator solutions change the structural loads significantly then there is a problem with supplying "conceptual drawings"....

bimr, human909 is entirely correct that the start of the chain of mistakes was that the original design by Gillum, the EOR, had a long continuous threaded rod assembly for both walkways...very non-constructable.

Thanks.

 

[Archie264]

Regarding the issue of unconstructiblity, I wonder if we’re too quick to accept the popular narrative on that?

The pyramids, Roman aqueducts, the Forbidden City, medieval cathedrals, London Bridge, Manhattan skyscrapers, the Panama Canal, Hoover Dam, etc., etc. were built, to say nothing of the Apollo 11 lunar project or aircraft carriers. And yet steelworkers in Kansas City tell us they were unable to thread some rods through some purlins or run some nuts a long way up a threaded rod? Perhaps either they should take more pride in their craft or engineers are quick to let contractors dictate the design vs. requiring them to build what they bid upon?

 

[JAE]

I don't think it was "we can't do it" but rather "let's do it smarter".


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[3DDave]

I think the expected problem was along the lines of being unable to transport threaded rod that's a bit over one inch diameter and nearly 45 feet long from the fabricator to the job site to the installation without damaging the threads or bending them so much as to be useless. Recall that along with turning nuts halfway up, they would have to slide the cross beams the same distance first. Unlike post-tension rods where only the ends need protection, nearly half the length of the proposed full-length rods would be subject to damage that would prevent them from being usable.

Thread damage could be cleaned up, and probably bent rod as well, but why not avoid those problems entirely?

Looking again at the NTSB report it just looks like no one gave serious consideration to the structural aspects an instead concentrated on making the walkways easier to install, even failing to pre-camber the beams so they would be straight when the concrete load was added, resulting in even more concrete being added to level them.

 

[human909]

Regarding the issue of unconstructiblity, I wonder if we’re too quick to accept the popular narrative on that?

The pyramids, Roman aqueducts, the Forbidden City, medieval cathedrals, London Bridge, Manhattan skyscrapers, the Panama Canal, Hoover Dam, etc., etc. were built, to say nothing of the Apollo 11 lunar project or aircraft carriers. And yet steelworkers in Kansas City tell us they were unable to thread some rods through some purlins or run some nuts a long way up a threaded rod? Perhaps either they should take more pride in their craft or engineers are quick to let contractors dictate the design vs. requiring them to build what they bid upon?

I hope you are being facetious here. Otherwise you are displaying exactly the characteristics that are an issue among some structural engineers.

Yes steelworkers were unable to do this. It was a totally impractical design and if that isn't obvious to you then you need to go out to the fabrication shop and to site a little more often. Perhap you need to take more pride in your craft AND understand how steelwork is constructed.

I don't think it was "we can't do it" but rather "let's do it smarter".

No. It could not be practically done in the way that was proposed. Letting steel fabricators decide on unusual connections is dangerous. They are enough to know what looks right and doesn't. They are not structural engineers. So any abnormal connections really need to be thought out.

 

[hokie66]

Piling on Archie a bit here, but his comment sounds like an architect.

 

[Compositepro]

It is a matter of perspective. If instead of using a 40 ft. 1" diameter threaded rod to hang the walkway, the designer used a 40 ft. steel column for support, no one would have complained about constructability, even though the column would be far more expensive and laborious to transport and install.

 

[JAE]

Human909
My comment that you quoted isn’t in disagreement with your answer so I’m not sure why you quoted me. ??

I was simply asserting that it was POSSIBLE to construct it as originally designed...just a very poor design with other BETTER ways to do it smarter.

I agree with what you said...why pick on me?

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[jhardy1]

@Archie264:

Yes, long threaded rod can be obtained (e.g. threaded stress-bar), but in general, only the ends of the cut lengths are used for turning nuts - I don't think I have ever seen a job where a nut was required to be run half way or more along the bar during installation. The idea of doing this on a hanging 40-foot threaded rod, having first slid up and supported the beam which the nut will ultimately support (without damaging the threads for the nut which must follow), sounds pretty diabolical to me.

Yes, almost anything is in principle "constructable", but when I think about "constructability", and when my team conducts "Constructability Reviews", these sorts of details would be eliminated as not being practically or economically or safely constructable.

http://julianh72.blogspot.com

 

[human909]

It is a matter of perspective. If instead of using a 40 ft. 1" diameter threaded rod to hang the walkway, the designer used a 40 ft. steel column for support

A 40ft column is relatively simple to fabricate, transport and install. If for whatever reasons the fabricators desire to splice or butt weld it then these are known techniques.

even though the column would be far more expensive and laborious to transport and install.

I dispute that. (But even on the expensive but because the difficulties discussed will eventually lead to longer man hours and possibly custom production. If thread damage occurs then the headaches just get bigger.)

Fabricating and erecting long columns is in the standard experience of fabricators and steelworkers. Dealing with extremely long threaded rod is not. To get continuous threaded rod of that length is likely to be a custom order. The difficulty starts at procurement and continues from there...

It is entirely impractical.


Threaded collars joining the threading rods seems a possible solution. But so does the proposed solution to a non structural engineer. How is the fabricator meant to know?

 

[Archie264]

Piling on Archie a bit here, but his comment sounds like an architect.

That’s not piling on, Hokie, as Alpha Dog here, which you most emphatically are, directing a comment about me instead of to me is simply a signal to attack. No big whoop; that’s how these forums work.

But the (shall we say?) “enthusiasm” of the responses somewhat illustrates my point, which is, that engineers are too often browbeaten into conformity by the consensus of the project team. In the KC project surely a properly-sized coupling nut would have worked? But that probably never even entered into the reviewing engineer’s mind as the fabricator simply told him his design wouldn’t work and that the fabricator’s design would. That’s not something that would slip by a seasoned engineer such as yourself, of course, but that’s not who was reviewing it.

I contend that imbuing a culture of submitting to the consensus of the project team (not the design team) as the default position, instead of first trying to defend one’s design, either explicitly or by example, is dangerous.

 

[bimr]

"Had this change in hanger rod detail not been made, the ultimate capacity of the box beam-hanger rod connection would still have been far short of that expected of a connection designed in accordance with the AISC Specification."

"The box beam-hanger rod connection would not have satisfied the Kansas City Building Code under the original hanger rod detail (continuous rod)."

Link

The NIST report clearly states that the original design of the Hyatt walkway was deficient. The changed design was also deficient.

The focus on whether or not the design was impractical is misplaced. The actions of the structural engineer of record to seal the design documents without verifying the soundness of the structural design was considered to be unethical.

 

[TheGreenLama]

Browbeating. Think any of that happened within the trailers surrounding the FIU bridge immediately prior to the collapse?

 

[human909]

But the (shall we say?) “enthusiasm” of the responses somewhat illustrates my point, which is, that engineers are too often browbeaten into conformity by the consensus of the project team. In the KC project surely a properly-sized coupling nut would have worked? But that probably never even entered into the reviewing engineer’s mind as the fabricator simply told him his design wouldn’t work and that the fabricator’s design would. That’s not something that would slip by a seasoned engineer such as yourself, of course, but that’s not who was reviewing it.

I contend that imbuing a culture of submitting to the consensus of the project team (not the design team) as the default position, instead of first trying to defend one’s design, either explicitly or by example, is dangerous.

Browbeaten to conformity? I'm sorry you feel that way. Though I'd say in this case it is less of an 'engineers' thing and more of a human and internet forums thing. And it definately can be an issue. However there is no evidence that browbeating was an the issue in the Hyatt Regency being designed initially in an unconstructable manner.

 

[charliealphabravo]

I learned early in my career that 9/10 when a contractor calls you up asking for a change after the contract has been awarded it is because they didn't bid the contract the way it was designed and are hoping to increase their margin.

 

[Agent666]

Round these parts, if there's a change proposed it better come with a saving passed onto the client for it to be considered, but 9/10 times the contractor doesn't understand the engineering principles at play and why it was the way it was. We've generally done all the hard thinking for them, it's a hard lesson I've learnt over time, you cannot leave options open to them to fill in the gaps with the way they would rather detail or build critical elements. Missing or poor detailing always comes back to get you.