Some thoughts on project management (FIU bridge in particular) 9

[spsalso]

I found many good points in this video examining the causes of the bridge failure--the "whys", not the "whats".

https://www.youtube.com/watch?v=YKiyb8S-Dq0

spsalso

 

[RVAmeche]

That's (part of) the problem though. Everyone has schedules and incentives and doesn't want to rock the boat or "be that guy" and normally that's okay. But the construction manager or site safety supervisor or someone at that site should've seen those cracks, the live road beneath, and made that call. The CM's I've worked with have never been shy about calling bullshit on engineers so I find it hard to believe everyone involved just blindly trusted Pate unless he's regarded as a god of bridge design?

The Challenger disaster should've taught us that schedules, delays, optics, etc are not good enough reasons to endanger people when there's a clear risk involved. Granted this is different because the engineer was the one claiming everything was fine, but the point stands.

 

[LittleInch]

unless he's regarded as a god of bridge design?

I think he was. Emphasis on "was".

I agree there are a lot of "noises off" and monetary issues, but there's no way that this should have all been left dependant on one persons judgement and most reports do state that this was a failure by lots of different parties to take responsibility and do the right thing, even if they fear the consequences.

These lessons need to be learnt by every generation it seems. It is very difficult to teach it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

I see multiple issues going on.
One is peer pressure. There were a half-dozen people that could have/should have shut down the road, etc. If any five of them had said "Let's shut it down", it's almost certain the 6th would have voted to do so as well, and would have felt like that was the obvious and only safe choice.
One potential issue is that most design engineers aren't really involved in inspection of deteriorating structures. Had they had people that were more used to seeing failures, they might have recognized it a lot quicker.
One issue is the perception of the consequences. You can have a lot of structures that can get a crack or buckle and it needs repair, but doesn't mean the whole structure's going to fail catastrophically if you don't do it, either. Seeing a crack is one thing, but recognizing that the stability of the entire structure depends on the integrity of that one area is another step beyond that.

 

[3DDave]

They trusted Pate due to lack of a suitable explanation. After Pate, I am most disappointed by the post-tension company as they should have a grasp on how loads are transferred in concrete structures and refused to work on an unstable structure. Clearly the tension rod did not operate across the opening of the crack and was oriented the opposite way.

 

[Tomfh]

The Challenger disaster should've taught us that schedules, delays, optics, etc are not good enough reasons to endanger people when there's a clear risk involved.

The reality is that calculated risks in engineering pay off the other 99.9% of the time. People don’t volunteer that their design doesn’t work until they are 100% sure it doesn’t, and nothing says “my design doesn’t work” like an emergency shut down of a highway.

 

[hokie66]

There were cracks even before they picked it up. That should have led to reexamination of the concept, but hubris...thanks, JLNJ. There was too much emphasis on calculation, not much on concept.

 

[Sym P. le]

I'm struggling with the NTSB not being able to do a rigorous analysis of the failure, and the rest of the engineering community parroting the nonsensical failure mechanism they fluffed up.

Nevermind the "retensioning", it's very bad when engineers can't recognize a lack of appropriate rebar in member 11 nor the resulting compression failure.

Just hoping someone eventually catches on.

 

[Tomfh]

and the rest of the engineering community parroting the nonsensical failure mechanism they fluffed up.

What's the nonsense mechanism you refer to?

 

[Sym P. le]

Experts cite explosive joint failure as cause of Florida bridge collapse

... sliding along the cold joint and punch-out failure in the deck region

These theories are alluring but deeper analysis can't possibly support any of it. They sound good and serve to alleviate the profession of the far more damning criticism that the clown show couldn't design a concrete column (member 11) or recognize its impending failure, let alone accept the fact that "retensioning" squeezed the remaining life out of the member.

Here is one more piece of the puzzle. Member 11 was standing on its toes, so to speak, squeezed into the crook of 12 and the deck. The deck was being pulled opposite 11/12 by the sagging structure though unable to move far. It still supported 11. 12 was bowed north, while buttressing 11.

The following image may actually show the footprint or contact area of 11 on the slab, an indication of the role shear lag played in the redistribution of forces through 11. The redistribution is attributable to the myriad of inclusions isolating 12 from the deck and the underdeveloped theory that the innermost slab tensioning would catch the horizontal truss forces. Regardless of the cold joint, even solid concrete would have opened up around the fringe of the deck/11 interface.

Also, the bridge did sag. I don't have the reference to this transcript excerpt (I clipped it out a while ago) ...

As they retensioned the lower bar, a more sinister situation develops. If there is any shortening between the upper and lower endpoints of the retensioning bar, tension is lost and the hydraulic jack pumps more energy into the system as tension is their only measurement. Eventually the uncontained longitudinal rebar in 11 pop free and 11 no longer exists, the bottom three feet are crumbled. The kinked upper tension rod and patterned rebar failure are evidence of 11 kicking out. The deck, 12, and diaphragm are still in tact at this juncture.

This is distinctly NOT a joint failure. To this point, the bridge remained standing in spite of its shortcomings as it had accommodated the isolation of the deck from the node.

I'll leave the rest unless anyone wants to hear again how the deck rotated the diaphragm off 12 evacuating the cavity in the supposed slab.

 

[3DDave]

Was the bridge safe to use except for the retensioning?
Was the 11-deck joint completely fine?

The NTSB cause stops when the bridge is not structurally sound.

The probable cause of the FIU pedestrian bridge collapse
was the load and capacity calculation errors made by FIGG
in its design of the main span truss member 11/12 nodal
region and connection to the bridge deck. Contributing to
the collapse was the inadequate peer review performed by
Louis Berger, which failed to detect the calculation errors
in the bridge design. Further contributing to the collapse
was the failure of the FIGG EOR to identify the significance
of the structural cracking observed in this node before the
collapse and to obtain an independent peer review of the
remedial plan to address the cracking. Contributing to the
severity of the collapse outcome was the failure of MCM;
FIGG; Bolton, Perez; FIU; and FDOT to cease bridge work
when the structure cracking reached unacceptable levels
and to take appropriate action to close SW 8th Street as
necessary to protect public safety

That the follow-on led to uncontrolled collapse is insignificant to the avoidance of getting anywhere near that point. NTSB is going after the first domino, not the last one. Sure, grabbing the tensioner was the final step, but the bridge was unlikely to be remediated if the defect was correctly identified before then.

"Sagging" is a symptom, not a cause, but it has been taken by some to suggest that it was the function of the deck cantilevered from the deck-10 node to support the bridge at the pillar, making 11 not required and taking no load. "If the deck didn't fail by sagging..." is a common misunderstanding that I dislike giving the slightest oxygen to.

 

[1503-44]

You definitely want to stop work when someone says "let's just hang 10 concrete blocks on it to level it out.

West Gate Bridge, Melbourne 1970

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

I don't think we want to start getting into the causes and reason all over again as the 10 or more threads of 300+ posts have done that to death.

It's clear that this bridge did not get the attention it deserved and numerous errors were made, both in design, review, construction and oversight by those who had responsibility for public safety (Florida DOT in particular here). I've always thought that the bridge did not get the design review it deserved as it was only half built and suspect this intermediate stage was overlooked to a certain extent compared to the full design which included sections butting up against it thus reducing the potential for the punch out effect (maybe). That and the plethora of additional tubes, cables, and obstructions in that crucial 11/12 node area reduced the strength of that joint well below what was initially designed when those things didn't exist.

However, lets not get into all of that again and I think it would be good for someone who sat through the 20min video in the OP to actually list the key "Whys" for everyone else?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sym P. le]

The same human factors that led to the failed structure also impede the investigation, tunnel vision on an errant hypothetical.

We all know the "load and capacity calculation errors" refer to the shear plane at the surface of the deck. The NTSB has it under performing as a whole and had the structure been able to withstand the jackhammer, we would instead see the structure collapse as 11 slid to the North Pole.

Remarkably, that same interface over performs within the confines of 12, allowing a redundant load path to catch the horizontal truss forces. The NTSB cannot square this contradiction so they envisioned a series of shear plane deflections, a fantasy of delusion.

I can go on, but --> first sentence.

It would be a shame to toss out this construction technique because stupid ego designed it and stupid ego couldn't analyze it.

 

[spsalso]

"...I think it would be good for someone who sat through the 20min video in the OP to actually list the key "Whys" for everyone else?"

I s'pose that would/should be me.

The key "whys" would be hubris, complacency, incompetence, and lack of accountability. This was generally spread among all the actors.

That said, I strongly recommend sitting through the video to get the full flavor.


And, speaking of hubris. I do fail to see why the federal government should provide $20 million (according to the video) to build that bridge. It was completely unnecessary, as there was, and still is, a protected crosswalk approximately 50 feet away:

Who asked for money for this bridge? Who decided it should be given? It would be interesting to read the proposal submitted to the feds.


spsalso

 

[CWB1]

It surprises me that no one is charges with criminal negligence.

In other industries this would've been an easy criminal case against the EOR, approving regulator, and others but sadly, a large portion of the CE/SE industry stateside (industry and regulators alike) has normalized skipping standard engineering quality process steps to maximize profit and minimize regulators' workload and personal liability. They constantly excuse criminal-negligence as "mistakes" as-in the garbage NTSB report. The fact that this team needed an engineer to review the cracking and determine a path forward rather than following a predetermined, reviewed, and team-approved quality plan shows that they have no regard for a century of quality studies, public safety, or the profession - that alone should be enough to revoke every engineering license involved. The fact that they sent their top engineer to do so is comically absurd.

I applaud the creator of the video posted for trying to bring attention to this disaster but found the commentary rather strange and missing the forest for the trees or more accurately, quality process for ego. I've worked with many big egos but have never known anyone who lasted more than a few months as a junior engineer without being quick to admit the frequency of their own mistakes. Design reviews very quickly humble juniors and even among seniors, bigger egos make bigger mistakes bc they're willing to take bigger risks and regularly have to eat crow for it. The bottom line tho is that this disaster wasn't caused by an engineering mistake nor human nature, it occurred bc every member of the design team top-bottom chose to ignore their ethical and legal duty to protect public safety by following a crap quality process and local regulators failed to stop it.

 

[Sym P. le]

Back to you Steve ... we all gonna have to admit to some stuff!

That's all i got