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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[Sym P. le]

I was checking out the on-board video of the move to see if there was any indication of the deck cracking at that stage. Although it is possible, I've decided it's more likely just twine.

 

[Alpha Kai]

As I have always stated, #11 was not capable of shearing #12.
The latest releases prove that by showing it was structurally "unsound".
It appears to exhibit and exterior /outward force from internal to the member; this could be a result of reinforced "rebar" buckling once load was applied to it.
Never the less, as I have stated in my videos, Construction Engineering and Photography, that the failure was a result of loads being directed down member #10 and the "resolving" forces being "taken up"/ transferred through the post tensioning in the canopy and the bridge deck.
That neither could sustain those forces as the "intent" was to have forces go down #11 (number 11, being a "failure" could only, marginally take any loads; putting the load path down #10)...
This is a design, conception failure in which the owner, contractor, Figg, FDOT, FIU had "too much skin in the game"...
They could not come to the public with a bridge and road closure (Another part of the contributing factors.).
Further, the PT cables were not performing to the best of their abilities (they should have checked them after the move and determine if they further elongated; reducing their effectiveness... and their ability to act as a "strongback"... The resulting loads, created this structure to failure... of course because of a failed design and application of materials being of "conflict" with post tensioning and the demand loads...
Thank you, to one of my subscribers to showing me this feed tonight.
My intentions are not to offend anyone in this group, just sharing some love and "direction"... I was the only one who insisted no shear took place at 11 & 12; that forces were going down 10 which caused this "physical failure" (of course this is a design failure AND a "corruption failure")...
I also the only one stating, Denny Pate needs immunity so we can get the truth and all the corruption be exposed!
Surely, the parties involved can NOW speak up about PUBLISHED articles by the NTSB (even if just to that limuted degree...BUT, they ALL are still hiding behind "helping the NTSB! That is b.s.)...
Note, those cracks go much deeper, and even down to the post tensioning...
If, this is the first time watching any of my videos, I apologize to my "aggressive comments" in advance... it is just vindication and disgust in my voice...

https://www.youtube.com/watch?v=Ifj7pxs_bs0

 

[Retiredat46]

One option would be to make the two halves equal in weight. Make the short span really thick to act as a counterweight to the other half.

I like that, and it fits well with my earlier suggestion of having six nearly identical sections (prefabbed nearby) to hang in place while the road is closed for a short time. Real cables, simple engineering, and accelerated construction for the win.

 

[Sym P. le]

I would like to go on eloquently about structural elements, design, failure modes/progression, etc. But I can't hide my disgust in prissy language.

Jacking on the PT rods was no different than taking a jack hammer to #11.

This bridge did not experience structural failure. It experienced demolition.

In that vein, I find the latest report offensive because it just provides cover by suggesting that something went wrong.

 

[3DDave]

To counterbalance, the two halves need equal leverage. One section was about half the length of the other and therefore would apply between two and four times additional force on the central support to produce the same leverage - putting that weight onto a support next to a water filled canal on Florida, which seems to be mostly limestone that is gradually getting eroded away.

https://en.wikipedia.org/wiki/Geology_of_Florida

 

[rebardan]

So, some time after the onboard video recording Linkhttps://www.eng-tips.com/postedit.cfm?id=8378200&action=edit
and before the March 13-14 photos, the fractures, represented as cracks, opened up far beyond those photographed February in the casting location post shoring removal. I wonder if it was a slow propagation or if they suddenly appeared after the PT rod tension was released from #11. The video shows the structure functioning as intended aboard the abutments without sudden failure. I hope more pictures emerge of the failure zone. Very interesting stuff. #11s force cone blowing out the deck and elongating the closest PT strand bundles indicate the failure wasn't as sudden as first thought and progressed over several DAYS!. The failure of the bridge pales in comparison to the glaring human failure. No one who saw the fractures warning of imminent catastrophic failure had the balls to speak up.

I am impressed by the composite concete/steel's lack of sudden failure as mentioned earlier in this thread as one of the material's properties. The span screamed out it's intent for days and no one heeded the call. I'd guess the tradesmen ironworkers, concrete men and operators saw and spoke out the obvious. Cant wait for the final report.

 

[IEGeezer]

I have reread the discussion in Part IV here:

https://www.eng-tips.com/viewthread.cfm?qid=436924

I am including a diagram from a post by SheerForceEng on 25 Mar 18 at 00:42 and comparing it to the picture from Figure 1 of the recent NTSB report that was posted above by Sym P. le on 10 Aug 18 at 22:23.

 

[appster]

If you go to the following Miami Herald web page photos of many large cracks not revealed before can be seen.

https://www.miamiherald.com/news/local/community/miami-dade/article216388430.html

These photos were apparently taken on March 13 or March 14 at least one day before the collapse. This if true would indicate that the work on the day of the collapse did not cause the failure. These are the same photos shown in the second interim NTSB report.

Any engineer looking at these cracks could only conclude that the bridge had basically already failed as far as meeting its intended purpose and needed to be closed until a shoring and remediation or demolition plan could be made. The fact that the bridge was not closed in my opinion amounts to negligence, probably to the point of being criminal. Very sad but what else can I say.

The large cracks also appear to show movement of 11 and 12 together, splitting of member 11 probably due to inadequate confinement and shear styrrups at the deck and rotation of 11 and 12 together clockwise looking towards the canal and 11 rotating away from the deck towards the canal. It appears to me that 11 also appears to have moved along the deck face as 11 and 12 moved.

 

[TehMightyEngineer]

If you go to the following Miami Herald web page photos of many large cracks not revealed before can be seen.

I only see the cracks shown in the NTSB preliminary report, nothing new.

However, that article does answer a few of my questions about the FDOT oversight where it appears they were not made aware of the extent of the cracking or even that it cracked at all. I wonder whether they had an on-site inspector but it sounds like they did not. If this is the case then they may be free from liability. I certainly hope so, any engineer who saw those cracks is going to be in the line of fire.

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

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

 

[epoxybot]

I'm starting to wonder if there wasn't a communication breakdown between the people in the field and the EOR. The cracks could have been very small to begin with and that may have been the status as Denny Pate knew it when he made a phone call to the FDOT. The minutes to the meeting on the day of the collapse might be interesting. Did any of the engineers at the meeting actually visit the site and look at the damage between the 13th & the day of the collapse? I just don't see how one can look at the photos of March 13 & 14 and think that wrenching on the PT rods was a good idea. Wasn't Denny Pate in Texas at the time? I'm curious to know if there are any full section photos. It is easy enough for anyone studied in the bridge to place the locations of the discrete photos but good documentation should include some areal photos too.

 

[chris snyder]

to TME: I just thought about WHO was supposed to inspect this bridge? When I put in underground electric service, the city inspector came out to make sure the trench was 18" deep, then did a final when completed... very simple job with two inspections.
Assuming this bridge had a typical permit, it seems there would have been city/state inspections at "milestones", one of which would be after the span was moved into place.

rebarden wrote: "I'd guess the tradesmen ironworkers, concrete men and operators saw and spoke out the obvious. Cant wait for the final report."
This is why I'm surprised the two workers tightening the PT rods on #11 didn't have their safety harnesses latched (assuming they were held by the crane, as it must've been since one worker credits latching up when he felt/heard a shift/crack for saving his life). I'd think these guys saw the cracks and would know they aren't typical.. it just seems odd they didn't latch up before jacking. We're looking at it from hindsight, but everyone says such cracks means it already failed, just hadn't collapsed yet.

 

[jasm]

FIU releases new video of the bridge collapse, from time-lapse cameras:

https://www.miamiherald.com/news/local/community/miami-dade/article216703455.html

 

[appster]

To TehMightyEngineer (sorry don't know how to do quotes)
To the contrary the article clearly indicates that the FDOT was represented at the morning meeting, it does not indicate if the pictures were shown at the meeting or if only a discussion was held and the FDOT rep. was in a secretarial role as opposed to an engineering or technical role. If the FDOT did not see the photos then it makes me wonder if the photos were kept between the Contractor and the Engineer.

By definition in ultimate design member 11 and 12 had reached technical failure in strain long before the photos of the 13th were taken; the bridge should have been closed and shored until its final fate was decided. In my opinion 11 was overstressed due to axial load and bi-axial bending along with torsion under dead load alone with no applied live (including torsional load imbalance on the bridge) and wind loads. Torsional stability requirements placed significant lateral and torsional load requirements on 11 and joint rigidity placed biaxial moments on 11 and 12.

The only consolation here is that this was probably a more gradual failure than it appeared to be but nobody was listening to the bridge crying out and lives were lost.

Bob App, Retired former PE Ontario

 

[TehMightyEngineer]

it seems there would have been city/state inspections at "milestones", one of which would be after the span was moved into place.

I agree, I'm surprised there wasn't a post-install inspection being performed. Perhaps it was scheduled to be completed after when the collapse occurred? Hard to say, but I'm sure we'll find out.

To the contrary the article clearly indicates that the FDOT was represented at the morning meeting, it does not indicate if the pictures were shown at the meeting or if only a discussion was held and the FDOT rep. was in a secretarial role as opposed to an engineering or technical role. If the FDOT did not see the photos then it makes me wonder if the photos were kept between the Contractor and the Engineer.

That wasn't the conclusion I drew but it's open to interpretation and will definitely need to be clarified.

I based my assumption that the key officials and engineers at FDOT hadn't been made aware of the cracking based on this:

FDOT has said it was not told about “life-safety issues” and did not hear Pate’s message until days later

From:

https://www.miamiherald.com/news/local/community/miami-dade/article216388430.html#storylink=cpy

Also in the statement, FDOT said one of its consultants attended a meeting with the FIU bridge team — including executives from Munilla Construction Management, the contractor, and Figg, the engineering contractor — hours before the collapse that killed at least six people. The statement said no “life-safety issues” were discussed.

From:

https://www.miamiherald.com/news/local/community/miami-dade/article205660334.html#storylink=cpy

So, it sounds to me like only an FDOT consultant was at the meeting and that they downplayed the cracking at the meeting. Further, being only hours before the collapse I imagine any images of the cracking had yet to filter up to the engineers in charge oversight for this project at the DOT. As they stated they did not receive Denney Pate's phone call it seems that also didn't reach the FDOT people in time.

But, I of course conclude that this is all preliminary details and likely not the full picture. I'm sure the timeline between FDOT and the bridge cracking being found will be clarified.

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

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

 

[Sym P. le]

I don't know if the following has been raised in the discussion yet (there is too much to review) but the use of PT rods in #11 to carry the end of the structure during the move seems to have been too clever by half and may have ultimately led to the disaster (if nothing else, they became a distraction). Use of external strong backs may have been a cosmetic blight on a heavily promoted project, but the additional compression to the already critical #11 and the poorly understood internal stress dynamics from the various stages of this construction process seem to have added a level of complexity that was not overcome.

As suggested by rebardan, the tension release may have resulted in the fracturing. I am curious to know what happens when you place a concrete column under an extreme and complex load and then suddenly introduce an eccentricity by releasing a compression element on one side or by giving a little tug so that you can back off the nut? If cause and effect were conspicuous but did not result in sudden collapse, I suppose some O₂ therapy would be permissible as evaluations are made but if these fractures were observed developing over time, would you not come to a not to soon realization that the structure is yielding to gravity and requires immediate intervention (namely shoring)?

I noticed from the time stamp with the images in the Investigative Update that the west side images were taken two hours before the east side images. That's a lot of head scratching. And if I'm not mistaken, that was two days before a two hour meeting on the morning of the catastrophe. I don't wish to make light of a bad situation but rather to shake up the thinking of what was happening with the thinking. This brings me back to my suggestion that the PT rods in #11 were a distraction. Rather than the obvious intervention of shoring up the structure while properly evaluating the damage and conducting remedial work, the focus was on the PT rods. Unfortunately, entropy has a bite and you can't put the genie back in the bottle (See my previous posts).

From Figure #2 in the update, the diagonal crack on #12 below the deck level (and where #12 ultimately failed) indicates that the top of #12 is being pulled toward the centre of the span, perhaps from the structure sagging, though not much, and this too is a clue. Nothing moved much until the end when I believe #11 ruptured under a multitude of funky internal stresses.

Like everyone else, I can't wait to see the final report. I do believe the NTSB does outstanding work.

 

[human909]

This brings me back to my suggestion that the PT rods in #11 were a distraction.

Very true. And I think most people have recognised this, but it is a distraction and it was very likely the straw that collapsed the camel. (The camel's back was already broken.)

I believe that unavoidable fact was member 11 and its connection to deck around member 12 was very poorly designed for the anticipated loads. This is likely the case even without the additional stress of the unorthodox cantilevering during placement and the mucking about with the PT cables.

A very badly designed bridge, a ill considered construction and placement and ignoring ALL the warning signs.

Like most accidents this is multifaceted. There are critical mistakes and there are also lost or ignored opportunities of rectifying those mistakes.

 

[FortyYearsExperience]

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone. Any engineer, even an unqualified one, would have immediately recognized that a collapse was in progress. What he did was he placed a call based on somebody else reporting a "slight cracking" to him. This will have profound implications.

 

[LittleInch]

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone

40YE, Can you elaborate on where this has been made "perfectly clear"? Or is this really just speculation on your part?
Are you Denney Pate?
Unless you have inside knowledge that the rest of us don't have then whilst it might seem to you and me that such an experienced engineer would realize that those cracks were far beyond what could be described as slight cracking, in reality we just don't know, nor, as yet, what pictures or information was available at this meeting which took place prior to the collapse.

If I've missed something in an article or whatever, please let us all know.

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

 

[thebard3]

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone.

He didn't know what the conditions of the crack were, when he was reporting on the conditions to FDOT? Really?

Brad Waybright

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

 

[human909]

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone. Any engineer, even an unqualified one, would have immediately recognized that a collapse was in progress.

You would STRONGLY hope this would be the case.

Except this faith in an engineer of 40 years experience doesn't explain why decision were made to continue to go ahead and play with the PT tendons. Nor is it clear why the engineer thought the cracking was serious enough to report, yet not serious enough to inspect himself.

Those photos were taken by people on site. You would have expected SOME engineers would have seen them given a report was made.