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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[thebard3]

I wonder how insulated FDOT, FIU, and any other authorities and owners are on this?

I would expect that level of insulation to be directly proportional to each organization's level in the government hierarchy.

Brad Waybright

It's all okay as long as it's okay.

 

[LittleInch]

Yes I think many of us here had zeroed in on the 11/12 joint connection.

This is the text from the actual update

"Although the evaluation is ongoing, the assessment has determined that errors were made in design of the northernmost nodal region of the 174-foot-long span, where two truss members were connected to the bridge deck. These design errors resulted in (1) overestimation of the capacity (resistance) of a critical section through the node comprised of diagonal member 11 and vertical member 12; and (2) apparent underestimation of the demand (load) on that same critical section. Additionally, the FHWA evaluation determined that the cracking observed in the node prior to the collapse is consistent with the identified errors."

So basically it got bitten from both ends - not enough capacity to resist the forces they thought were going into it AND underestimate of the forces going into it.

The final report will be interesting to see how they analysed it and how they dealt with the new and unique design issues coming from a concrete truss design.

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

 

[BridgeSmith]

For sure it's an oversimplification, but from my understanding of the process, this seems to illustrate the dangers of checking one 'black box' FEA with another 'black box' FEA.

I suppose the estimation of the actual shear capacity could become very complex, but the loading should have been fairly straightforward with hand comps that would get within a few percentage points. A conservative approximation of the shear capacity of the section would also be fairly straightforward.

 

[epoxybot]

I think there are a lot of political interests in Miami that want to foist a good portion of blame on the FDOT (State purse). The last report I read from the Miami Herald seemed obsessed with communications between the Governor's Office & the FDOT immediately following the bridge collapse.

Florida International University official's response immediately after the collapse was somewhat flatfooted. Their umbrage over the FDOT's statement, in which FDOT distanced themselves from the project, paints FIU officials as, not quite processing the caliber of leadership to have been entrusted with the project, to begin with. FIU was the unquestionable principal authority for the project.

As part of the University Bridge project, FIU applied for and received Local Public Agency (LPA) status, by way of the FHWA & FDOT for this project. This made FIU the governing authority (municipality) responsible for the execution of the project. The way I see it, if a City (FIU) builds a bridge over railroad tracks (FDOT Hwy) and the bridge collapses, it isn't the railroad company that is responsible simply because they enforced certain easement requirements, right-of-way restrictions, a list of safety requirements or gave preliminary commentary on the design of what passes through the airspace immediately over their railroad tracks.

Maybe FDOT has played a deeper role in the project but on the surface, their role was by intent to be the purse keeper & auditor. In essence, the Tiger Program was for the FHWA & in some cases, State DOTs, a Redevelopment Agency (Economic Stimulus) Program for which they were its administrators. Simply because they enforced standards on anything that encroached on their right-of-way, doesn't automatically make them an acting responsible participant.

I'm actually surprised FIU's role hasn't received a lot more scrutiny by the press. If FIU assumed they could manage their LPA status by the purchase of a-la-carte professional services, then maybe they should have left the decision about what bridge was built to a firm experienced in planning. T.Y. Linn was the planning firm that prepared the original areal concept. I wonder what they had to say about the MCM/FIGG submission. I question whether anyone at FIU, with a background in construction, was given charge of the project. The key decision maker seems to have been FIU's head of Finance. FIU officials seemed completely enamored with the bridge design.

 

[Ingenuity]

ENR reported this from FIGG:

A statement from Tallahassee, Fla.-based FIGG Bridge Engineers, the project’s engineer of record, argued that the NTSB’s analysis was based on an early version of the design, and not the final one. “The update refers to the calculations on file, which were done prior to incorporating all final design comments and prior to the production of the construction plans,” the firm explained. FIGG’s statement further stresses that: “The investigative update is just that—an update on certain preliminary facts, and NTSB underscores that no probable cause conclusion should be drawn from the update.”

Source: Link

 

[hokie66]

I just hope that the NTSB does not just focus on the locus of the failure. Rather, the overall concept of building a concrete truss/frame, complicated by post-tensioning of some members, should be closely examined. Unlike a steel bridge, which readily forgives bending in individual members and joints, a rigid concrete frame does not. The shortening of various members by shrinkage and applied axial force would have been resisted by other members, and this resulted in cracking which was observed long before the bridge was erected. The concept doomed the bridge, then stubbornness brought it down.

 

[LittleInch]

So what FIGG seems to be saying is that we did the analysis and calculations, then changed a bunch of stuff to produce some final construction details, but hadn't got round to updating the analysis? Surely FIGG would have supplied the NTSB with the final/latest set of design deliverables and analysis / calculations to review?? This makes no sense to me.

Ultimately though I do think Hokie has it right. This design was fatally flawed from day one as a concept. Quite how it got through any round of reviews or design analysis without someone having the strength or responsibility to truly challenge this design might be its lasting legacy.

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

 

[JStephen]

"The update refers to the calculations on file, which were done prior to incorporating all final design comments and prior to the production of the construction plans..."

Re-read that statement, what it does NOT say is that the calculations pertaining to the point of failure changed in any way from the calculations on file to the final ones.

If somebody criticizes your work, and you say "But we did it just right- and there's the bridge to prove it!"- that's great. But after the bridge falls down, anything said to justify your work carries very little weight. (no pun intended).

 

[IEGeezer]

"... flawed from day one ..."
And then the holes in the swiss cheese lined up leading to loss of life. I think it is going to be interesting reading the final report where they detail all the events that led to this tragedy.

 

[Sym P. le]

A few notes from the second update:

1) ... errors were made in design of the northernmost nodal region ...
2) ... the cracking observed in the node prior to the collapse is consistent with the identified errors.
3) ... The investigation continues to examine the design, review, and construction processes as well as the actions taken once the cracking was observed.

This still leaves room for a flawed design that remained spanning until its demise was hastened by unwitting activity.

It is reassuring to know that construction materials (concrete, rebar, PT rods, etc.) were fully adequate for their specified properties and these suppliers should not be tarnished by their association with this project.

 

[pmover]

not surprising . . .

https://www.msn.com/en-us/news/us/c...r-bankruptcy-protection/ar-BBUh4Bk?li=BBnbfcL

 

[SFCharlie]

Thanks for bringing this to our attention.
The direct link to the Miami Herald article is:
MCM, the contractor behind FIU bridge that collapsed, files for bankruptcy protection


SF Charlie
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[epoxybot]

There are 18 lawsuits against 25 firms. Apparently, even the firm that supplied mats for the bridge mover is included. The judge won't let any of the company's out of the lawsuits, yet. Meanwhile, the lawyers are feasting and there is real concern that the attorneys' fees will eat up the money the insurance companies will pay out. It is Miami-Dade County Court.

NBC: Victim’s Father Frustrated As FIU Bridge Litigation Drags On Link

 

[hokie66]

The NTSB is taking too long. That is part of the problem. And the court is the other part...it should release many of the defendants, e.g. the mat supplier.

 

[thebard3]

From the MSN article--
"where the reliable donor to local races has won contracts for projects at PortMiami and Miami International Airport".
Sounds like quid-pro-quo.

Brad Waybright

It's all okay as long as it's okay.

 

[BridgeSmith]

FDOT was apparently more involved than we've been led to believe. Another revelation is that an engineer at FDOT questioned the adequacy of the north end of the span for shear, in March of 2016. The answer - 'it'll be fine'.

FDOT Needs to Come Clean About Its Role in FIU Bridge Construction

 

[epoxybot]

I don't see much that is new information in the ENR Editorial submission. What is becoming conspicuous is the omission of FIU as the governing body responsible for the entire project. It can't be overlooked that the political powers of greater Miami & FIU would not care for the Miami Herald to shine the spotlight in FIU's direction. Likewise FIU seems a bit disoriented by the idea that they took upon themselves the role of a DOT. Maybe they thought they were an Arms-Length DOT because they hired lots of companies to execute the plan but they nonetheless bear the responsibility of functioning as a Municipality, that asked for & received permission to act on their own.

 

[MikeW7]

The editorial is from the Miami Herald, March 17

Another story from March 15 about Kevin Hanson, the guy who took the pictures and passed them to higher-ups. He was on top of the bridge when it came down and was in a coma for 5 months, and is brain damaged. The story says the probe was held up during the Government Shutdown. Big argument about Hanson's pictures, which are different than those from NTSB.

EDIT: The article also contains videos with comments from Hanson's kids and the widow of the construction worker who died, Navarro Brown.

Many more recent stories - only so many free views per month, but this can be bypassed in Firefox by right-clicking a link and opening it in a New Private Window.

 

[saikee119]

It may be surprise to know that it is common for concrete to crack. In the best concrete show pieces, say the Charles De Gaulle airport, you can still find cracks among the best concrete finishes when you look out for them. Concrete surface will crack easily during its curing stage when the heat hydration given out by the cement's chemical action with water after pouring. The heat hydration can cause uneven temperatures and differential stress in the concrete body, say the concrete near the formwork is unavoidably cooling faster than its interior. Concrete would be still green, plastic and has not developed the strength to resist the large temperature variations. To control crack development the green concrete needs to be dampened continuously and if required insulated.

What is important is the type and the extent of the cracks. Structural cracks caused by bearing unexpected higher load are dynamic as cracks can progressively get worse. Thus the cracks discovered 5 days before the collapse will be less severe than those recorded just the day before. The NTSB first update on 9 Aug 2018 shows the cracks, taken 1 to 2 days before the collapse, were in considerably worse condition than those report in the earlier Preliminary Report.

To a trained engineer the cracks reported om 9 August 2018 by NTSB are sufficient to support the root cause of the collapse as they show part of the structure, Member 11 & 12 in unison as one body, was slowly separating away from the deck. The bridge then was held together, not by the concrete, but by the embedded rebar which would be visible in some of the cracks which appeared to be up to or even over an inch wide. There is no way for any professional engineer to argue that these cracks are not destructive and dangerous.

 

[Sym P. le]

As I reviewed the collapse video once again, I couldn't help but wonder why the truss elements, and particularly 10 and 11, were still wrapped in the promotional banners. Given the obvious distress that these elements were experiencing, wouldn't they have been exposed for evaluation and observation?