Miami Pedestrian Bridge, Part IX 33

[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

Part VIII
thread815-440072


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[MikeW7]

Here's a compilation video posted 2018 March 15 that includes extensive drone footage of the entire bridge move, Stuart Grant's ground-level time lapse of the move, and high-definition helicopter footage of the north end immediately after the bridge fell.

 

[epoxybot]

Looks like MCM Construction has settled with the vitim's families for $42 million. Link

 

[SFCharlie]

From the local miami news:
Construction company reaches deal to pay up to $42M to victims of FIU bridge collapse

SF Charlie
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[JAE]

Maybe I'm not understanding the legal strategies here - but if the NTSB hasn't determined the cause of it - why, as a contractor, would you settle for $42 million if the cause might end up being totally on the designers?



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[Ingenuity]

Maybe I'm not understanding the legal strategies here - but if the NTSB hasn't determined the cause of it - why, as a contractor, would you settle for $42 million if the cause might end up being totally on the designers?

Yes, I agree, however, it is not like the contractor really has a role in accepting or rejecting a settlement. Once the insurance co's get hold of the case they and their legal team take it over, and the contractor just follows the lead. Bankruptcy of MGM may have also lead them to this settlement too.

 

[MikeW7]

This March 14 ENR.com article says MCM had been operating at a loss since 2016 but wanted to make sure they were able to pay out settlements, so they established a trust/fund to cover all claims as part of their bankruptcy reorganization. The $42 million figure was the maximum amount they estimated could be secured from their insurance policies.

EDIT ADD: Based on this May 03 Miami Herald article MCM reached an agreement with their insurers, not the families. My impression is that because of their ongoing bankruptcy problems, they wanted to make sure money is available in the future if any claims are eventually settled against them.

 

[hpaircraft]

Maybe I'm not understanding the legal strategies here - but if the NTSB hasn't determined the cause of it - why, as a contractor, would you settle for $42 million if the cause might end up being totally on the designers?

Not a lawyer, but based on what I've seen of past cases I think there's a couple things at work here:

* The NTSB report is pretty much a foregone conclusion at this point. Pretty much everyone who matters knows that it will demonstrate that the bridge was designed with inadequate shear margin to prevent what was essentially a tear-out failure of the 11/12 node. It will probably also demonstrate that it was built as designed, although that is unlikely to provide the builders much cover.

* Early settlement is in accord with two ancient axioms: "The bird in the hand is worth two in the bush," and "The first loss is always the smallest." Dragging this thing out is only going to make it uglier and more expensive to everybody on all sides (excepting perhaps the attorneys), and decrease the amount of money available to compensate survivors.

* Pure speculation, but similar past cases suggest that all involved in the design and construction and underwriting have gotten together, gotten their stories as straight as can be managed, and will present a united front that will limit further culpability to the degree practical.

 

[3DDave]

I have the most scorn for those on site who saw the concrete fracturing off in huge chunks and did not declare an emergency, close the road and bail off that bridge. Shades of the Quebec bridge collapse where the on-site engineer kept piling up steel as compression members bowed. After that Wassisname who gave the order to proceed without going on-site and also not pulling everyone off the bridge and closing the road.

 

[hokie66]

The contractor's insurance probably settled relatively quickly to avoid litigation. They had liability, so why prolong the proceedings with the attendant costs? As to the designers, I think they were working for the contractor, so that was not an available dodge for the contractor. Typically, construction litigation proceeds with a number of settlements before any remaining defendants have their days in court. There were earlier reports that the insurers of the designers were denying liability, so that will be more complicated to resolve. And then there will be a host of other defendants.

 

[ImminentCollapse]

https://www.miamiherald.com/news/local/community/miami-dade/article230079344.html

More news, looking now for the 44 page document referenced in the article.

IC

 

[dylansdad]

Latest from AP.

 

[samwise753]

The 44-page document was released by FDOT:

https://cdn2.fdot.gov/fiu/14-FIGG-Structural-Analysis-Presentation-Meeting-Minutes.pdf

Some interesting stuff. I wonder what exactly FIGG thinks they can dispute in the meeting minutes that look to match up with the presentation. I suppose they could try and take somebody along with them or possibly deny the presentation (initially) since the .pdf doesn't show their name on any of it.

 

[TehMightyEngineer]

This whole presentation shows a scary reliance on their modeling and calculations. I don't care what any of the math says, the bridge is screaming for help and they state there's no safety concern in the same presentation where they say it's not clear how the cracks formed. I'm going to double down on caution if a structure is behaving unexpectedly.

I didn't go through the full presentation but it didn't appear to me that they had any checks of the longitudinal reinforcement anchorage resisting the thrust from the diagonal. I got the distinct impression that they checked most everything but the most obvious limit state.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Sym P. le]

It's difficult to endure the presentation knowing that they completely lost the understanding of basic structural principles while ensconced in the defence of their position.

Shame on anyone that utters the term re-tensioning with regards to the work that was being done. What were they really trying to accomplish? Hang the bridge from itself to relieve the stress?

 

[3DDave]

They were trying to use the PT bar to pull the broken sections back together without ever making a diagram that showed the PT line of action would do the opposite. Since the fracturing didn't happen until after the PT load was removed the naive choice was to put it back to stop the fracturing.

Such reliance on the LRFD and not a free-body diagram in sight.

Is there any surprise at the line in the chart "And therefore the is no safety concern ..." An obvious typo and sign of not paying attention to detail?

 

[RVAmeche]

But they had fancy FEA screenshots
(/s)

 

[hpaircraft]

Looking at pages 27 and 28, they clearly gave some thought to shear tear-out of the 11/12 node.

I don't know what went wrong, but I don't think I'm going too far out on a limb to make this guess based on the table on page 28: In assessing the shear resistance contributed by the rebar crossing the shear plane, they assumed that all members were loaded equally in shear. However, the evidence of the cracking shown in the photos suggests that the loading was not uniform; that members were sequentially overloaded and yielded, resulting in even greater loading of the next member along, and its subsequent failure, until the whole thing zippered off the end.

 

[epoxybot]

I wonder if FDOT engineer Tom Andres' notes were ever seen by the PEER review team.

 

[TheGreenLama]

They completely missed a potential failure plane in their presentation.

On page 30 a total shear surface area is shown of 23.62 SF. This whole presentation is made assuming shear failure will occur WITHIN the deck, thus the multiple of 2 being used on 11.81 SF. In this presentation they did not check a shear plane happening along surface of deck. Shear surface area in this instance would be roughly 1.75' (width) x 6.33' (length) = 11.1 SF. This is under half of what they've assumed. And, for this failure plane, there will be NO nodal confinement force from transverse PT, as failure plane is deck surface. I didn't run the numbers for the steel--no shop drawings, and I'm just too lazy at this point--but they're likely to be equally worrisome.

 

[3DDave]

epoxybot, if you are referring to the suggestions that cracks could form, I think that was due to the observation that differential loading of the various portions from the PT bars would create too much strain in the tension sections in combination with differential shrinkage as the concrete cured.

I don't feel there was worry about immediate catastrophic failure because of the lack of adequate reinforcement but concern about exposure of internal reinforcement to corrosive elements.

Greenlama - that answers a question I would have asked - where did the multiplier come from. How did they not know about the cold-joint between the deck and the truss? For certain the photographs they had access to showed shear displacement along the deck and not damage within the deck beyond the spall-out on the end. It's like they determined at some time that the fracture at the deck end was because of transverse bending of the diaphragm, hence the concentration on the pads underneath.