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Miami Pedestrian Bridge, Part VII 51

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JAE

JAE

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Jun 27, 2000
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A continuation of our discussion of this failure. Best to read the other threads first.

Part I
thread815-436595
Part II
thread815-436699
Part III
thread815-436802
Part IV
thread815-436924
Part V
thread815-437029
Part VI
thread815-438451




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dik (Structural) said:
I don't know how the contract bonding was handled for the 'bridge', but, because it was a 'design-build' effort, bonding could have been waived...
Click to expand...

Here is an example of a design build performance bond that MCM used on another contract. The State of Florida has a copy of the performance bond.


Example of FDOT Design build Performance Bond with MCM:

Example of FDOT Design build Performance Bond with MCM
of

FDOT Design Build Info

There is no way that MCM is going to walk away from this.
 
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jrs87,

In the sense that the problems were in the connections, both the Hartford failure and Bill LeMessurier's averted strength deficiency are classic examples.

The Hartford space frame was a case of axial members not meeting where the analysis required, and that bears some similarity to the Miami collapse.

The CitiCorp Tower may have survived without the modifications. We will never know, but LeMessurier took the right and ethical action, and he is respected in the structural community because of it.
 
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hokie66 (Structural) said:
26 May 18 20:14
That may be the case in aircraft, but in bridge failure investigations, not so much. We will see.
Click to expand...
please search for "i35 ntsb"
I count six releases by the ntsb, including a fifth update.
The "Accident Report" alone is 178 pages (Yes I'm counting the covers).
That's about the size of our first three threads:
Miami Pedestrian Bridge, Part I thread 815-436595
68 Pages​
Miami Pedestrian Bridge, Part II thread 815-436699
55 Pages​
Miami Pedestrian Bridge, Part III thread 815-436802
67 Pages​

They not only identify gussets that were not revised during a design change, but have a photo of the gusset bending during a pre accident inspection.
The "Accident Report" will probably take a long time, because there is so much to dig into, as we have noted here.
Thank you and Thank you all for maintaining this forum, and all yourinsights and cross check and explanations,

SF Charlie
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I may be naive, or worse, but aren't there remedies for cracks in structural concrete, Fiber reinforced polymer wraps?
Couldn't they have used a sample hole saw to drill through the top face of the deck at the 11-12 joint and filled it with something very strong (steel or Fiber reinforced concrete, ?). ...epoxied a steel pin in the hole?
With all the pre and post tensioned precast concrete being installed, there must be industry accepted repairs?

SF Charlie
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SFCharlie,
Yes, I agree that the I35W report was extensive. That one had as much discussion on this site as the Miami bridge.

There are industry accepted repairs for many types of defects in concrete structures. But this failure, although it should have been anticipated, was unprecedented because the concrete truss form of the bridge was itself unprecedented. The other concrete truss examples which have been posted here bear little resemblance to the Miami attempt. Perhaps that is why the cracks were not assessed as serious enough for concern.
 
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hokie66 (Structural) said:
Perhaps that is why the cracks were not assessed as serious enough for concern.
Click to expand...
I'm afraid you're probably right. In the Missouri example I posted above, they found their assumptions were wrong because they instrumented the bajesus out of it. They learned from it, and got a cheaper and much lighter bridge. Again, why wasn't FIU eager to learn and have their students learn from their adventure into innovation?

Thank you for replying to my questions,

SF Charlie
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Following up on the idea that concrete truss bridges are unprecedented, in fact most of the true cable stayed bridges that Figg has designed utilize essentially a concrete truss spanning transversely across the bridge deck. They pioneered the single cable plane design and use concrete “delta frames” to transfer loads in twin box spans to the central stays. See page 4 at the below link for a section of the C&D Canal Bridge which is typical of Figg cable stayed spans.

Link

However these true cable stayed spans are all hyperstatic unlike the FIU single truss design.

 
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I beleive a concrete single axis I-beam bulb truss does not have optimal section-moment-of-inertia:
RUStructural, your link for Pate article proves my point, where are similar articles on the FIU design? I could be wrong, but I don't think design concept was motivated by innovation, FIGG/MCM was simply trying to come up with something to satisfy the selection committee. This in and of itself of course is not unethical.
 
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Tomfh (Structural) said:
Do we know what happened yet? Do we know what failed?
Click to expand...
We have refined, incrementally, what we think happened, Nothing that was not hinted in Part 1.
The NTSB issued a Preliminary report with only info we had already found and posted here.
One thing they did clarify is that the PT rods at 1-2 and 11-12 were Detentioned on the 10th of March and REtentioned on the 15th at the time of the collapse.
But no, we don't know what failed, and it's not the style of the NTSB to state cause until the Accident report, probably in about a year from now.
Regards,
 
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jrs87,

Not sure about the moment of inertia being inadequate, the span to depth looks quite reasonable considering the relatively light nature of the live load but I’ve not made any numbers. My intent was to provide some additional background on concrete trusses, not to defend the concept. It seems to me that the design firm did have some experience with concrete trusses and that the concept was not completely untested.
 
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RUStructural - Live loads is something that has bothered me from the start of this thread. The concept of this Signature Bridge as a Place to linger and meet up with people; a public space. I have visions of the bridge lit up in various colors at night & a couple hundred celebrating, drunk & rowdy college students jumping up & down to music. I think building a bridge as a public space adjacent to a university that isn't built to stadium/arena live loads is just asking for a disaster. While the likelihood is small, I don't think such a circumstance can be discounted as inconceivable.
 
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