Miami Pedestrian Bridge, Part XIV 78

[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

Part IX
thread815-451175

Part X
thread815-454618

Part XI
thread815-454998

Part XII
thread815-455746

Part XIII
thread815-457935

 

[epoxybot]

Is there a way to explore a thin crack to determine it's depth?

Impact-echo, ultrasonic impulse-echo.
Impact-Echo is a nondestructive test method for evaluating concrete and masonry structures. The test utilizes stress waves (sound) that is normally generated through striking concrete by an impactor (Impact), and recording the reflections and refraction from internal flaws and other boundaries (Echo).

 

[SFCharlie]

epoxybot (Structural) Thank you!

SF Charlie
Eng-Tips.com Forum Policies

 

[charliealphabravo]

I think ultrasonic methods are unwieldy for most in-situ applications. Maybe someday we will be able to use nanobots for mapping cracks.

 

[Lomarandil]

CAB -- surely if there was a proactive attempt to determine the extent of cracking (rather than waving a hand over it in blessing as happened, or scrapping and recasting as some are suggesting), this would be a prime case to have employed some more advanced methods.

I'm speaking out of ignorance, as I'm not familiar with the process for concrete. But it's hard to imagine the procedure being that much more unwieldy than ultrasonic weld testing, which is completed regularly for major bridge structures under construction.

----
just call me Lo.

 

[ImminentCollapse]

Those cracks were so bad that NDT, advanced or basic, was unnecessary.

IC

 

[human909]

You're right. It seemed they forgoed non destructive testing and went straight to destructive testing.

 

[LittleInch]

After going through everything in the docket, watching the October 22nd meeting twice and reading the final report, I can only conclude that for all that this was a special, novel project for FIU, to FIGG and MCM it was just a little pedestrian bridge. It did not get the attention it needed from the design or construction firms.

Sometimes it takes a moment to consider this from a higher level and in two sentences I think you've captured the essence here about what went wrong.

The cult of the FIGG EOR also looms large in this disaster and hopefully in the future it will embolden some of the others in the next meeting to step up to the plate and demand action (or inaction) despite what "the mighty EOR" says.

I think (hope) state highways departments will already be preaching the safety first philosophy more than they already did.

To go through that amount of data must have taken you days so congratulations for that assessment.

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

 

[Denial]

Dummy post to boost this current one (Part XIV) back up above its predecessor (Part XII) in the presentation order.

 

[Vance Wiley]

Hi - help me here. I scanned XII and did not find a post by you.
Perhaps a link to where we should go? Then maybe a return link?
Thanks,

 

[SFCharlie]

from Miami Pedestrian Bridge, Part XIII

Earth314159 - please stop posting here - go to Part IV. Thanks.

JAE's instruction should read:
G O T O P A R T X I V

(...just the facts mam)

 

[LittleInch]

Vance,

All that has happened is that someone posted in Part XIII (or 13 in most peoples language) and shouldn't have been. Hence the post above by Denial just put part XIV back as the top listing.

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

 

[JAE]

Ya I screwed up. Thanks Denial for the clarification.

 

[Vance Wiley]

Thank you. Happy Thanksgiving to all!

 

[Earth314159]

Is there a way to explore a thin crack to determine it's depth?

I haven't checked in a long time but I read a few of the latest posts.

Cracks usually go straight through a member. In the NTSB board meeting, they mentioned a standard that considers cracks to be an issue if they are more than 0.5" deep. 99.9% of cracks are more than 0.5" deep. So I don't know where that standard originated from but it makes no sense. The width of the crack is more critical. Also the consistency (does the width vary and how), shape, location of the crack are all more important than the depth. You can usually determine what is happening by an external review of the crack. Even in research, you usually don't look at the internal shape (probably too difficult). You can in theory use ground penetrating radar (GPR) to determine the internal shape. We used to use x-rays for locating rebar and PT (We use GPR now) but I don't ever recall seeing an x-ray and being able to identify the shape of a crack (I am not saying it can't be done) but likely at least as difficult to identifying bone fracture shapes on x-ray (not that easy).

 

[jhardy1]

When they talk about cracks less than 1/2" deep (12 mm), they are talking about normal flexural and shrinkage surface cracks in the cover concrete, which don't reach down to the embedded rebar (or only just), so the "core" of the section is intact, and all rebar is encased in sound concrete. Such surface cracks also typically have a very small surface width - less than 10/1000" or so (0.3 mm) at the surface, tapering to effectively zero width at or near the outer face of the embedded rebar, so do not generally pose a risk for moisture ingress and rebar corrosion etc (although the permissible crack width will be smaller in aggressive environments). Surface cracks of this type are expected in normal reinforced concrete design. One of the common aims of post-tensioned concrete design is to close up even these fine surface cracks, through the application of compression on the whole section, overcoming the flexural and shrinkage tensile stresses.

When we see full-section cracking, with crack width such that you can insert your fingers, then we are looking at a whole different situation.

http://julianh72.blogspot.com

 

[Vance Wiley]

Good description.
And to comment on your last sentence, particularly cracking of that magnitude in an area having designed (??) and purposeful reinforcing. Put simply, if the designer put reinforcing there for a purpose and it cracks that badly, it is time to consider the total consequences of a failure.
Thanks,

 

[JAE]

A very short ENR article (Link):
Seems that Figg now brings with them a skeptical reputation.

[blue]FIU Collapse Report Spurs Texas Bridge Design Review
The Texas Dept. of Transportation has suspended design work on Corpus Christi’s Harbor Bridge pending a safety review of plans prepared by FIGG Bridge Group, one of the firms faulted by the National Transportation Safety Board for last year’s deadly pedestrian bridge collapse at Florida International University. Although construction of the $803-million cable-stayed structure’s initial phase remains unaffected, the review, expected to take at least 30 days, could further delay a project already behind on its original 2021 completion schedule. Tests of elements already in place have revealed no issues.[/blue]

 

[jrs_87]

Re: Corpus Christi Harbor Bridge. Does anyone here know what kind of waiver or exemption allows children to be in construction yard? See photo gallery here:

https://harborbridgeproject.com/gallery/

 

[JStephen]

I'm not aware of any prohibition of children in construction yards that would require a waiver or exemption. But it looks like a public event, similar to groundbreaking, ribbon cutting, etc.- not just kids but other non-construction workers there.

 

[hokie66]

Yes, looks like a good day out to me. There should be more events like this. Otherwise, how does the public, especially the next generations, learn a bit about construction?