Miami Pedestrian Bridge, Part I 65

[JohnRBaker]

Multiple Fatalities After Pedestrian Bridge Collapses Near Florida International University

https://www.nbcmiami.com/news/local...orida-International-University-476984523.html

As investigators continue to search the site of a deadly collapse involving a 950-ton pedestrian bridge near Florida International University in Miami Thursday, officials say the death toll has risen.

Early Friday morning, the Miami-Dade Police Department confirmed that six people have died as a result of the collapse....

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[3DDave]

Why the excellent video that was re-recorded on cell phone isn't available:

A county spokeswoman, Karla Damian, said the county's Traffic Management Center in Doral, which monitors more than 100 intersection cameras, found about the collapse through the media. Damian said it too late to preserve the incident before it was erased by new footage in the video system's rolling 30-minute recording loop.

"By the time that staff at the TMC attempted to access the video camera, it was already beyond the 30-minute threshold and our staff could not go back to the time of the collapse," Damian said in a statement Friday

http://www.miamiherald.com/news/local/community/miami-dade/article205443304.html

 

[hokie66]

This U Tube dashcam from the opposite direction shows it better, I think.

https://www.youtube.com/watch?v=Ucflj-MsJBI

 

[Tomfh]

similar driver footage. Hokie66 video above shows more detail

https://www.youtube.com/watch?v=BSq8295GFk4

 

[Tomfh]

Following from the youtuber theory that the rod snapping caused the collapse. If they were aiming to destress the rod in #2 and #11, why would snapping the #11 rod cause the member to fail? Was the temporary rod in #11 inadvertently holding #11 (and the node) together?

 

[XR250]

I am curious how this bridge was to handle unbalanced load effectively - i.e. all pedestrians looking over one side of the bridge? Seems it would not fare that well in torsion.

 

[CWB1]

I'm not saying that. Just pointing out that cracks and tendon issues are pretty common in stressed decks and people don't generally hit the panic button unless it's out of the ordinary. Evidently this guy didn't think it was.

"Didnt think" isnt an excuse when it comes to safety matters bc safety is process driven per engineering ethics. These circumstances should've been considered in a FMEA, circumstances outside the FMEA require the pause button being hit until the process docs are reviewed and updated. If this truly is a matter of someone "didnt think" then hopefully those folks end up in jail and out of the profession.

 

[waross]

A possible scenario:
"Well Harry, how are we supposed to take the nut off that bar?"
"Nothing to it Joe. We use the hydraulic jack to stretch the bar a little and then spin the nut off by hand."

"Okay Joe, the nut should turn off now."
"Gosh Harry, I can't turn it. It seems to be stuck somehow."
"Okay. I'll stretch it a little more and see if it will turn."
"Oops. Too much."

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[3DDave]

There should be two rods in member #11 if they duplicated what was used elsewhere. One rod, accessible from the top near the bottom of the beam and a second one accessible from the end that runs along the top. If the rods were both loaded and one became unloaded then the member is potentially destabilized. The state of member #2 is not considered. The rods in #11 should only have been needed for placing the bridge because the transporter lifted the bridge so that the end of the bridge was loaded opposite to its installed loading.

Thanks for the link. I had seen links to a dashcam, the one in the semi, but it was too low resolution, making the image a blur. In Russia there would might have been 40 videos. It's a shame the crane blocks the view of the anchor plate.

It is either reassuring (privacy) or disappointing (evidence) that the traffic-cam footage is automatically deleted. Good on the operators for having some presence of mind to record it before it was deleted. It had the advantage of not changing perspective, making frame-by-frame comparisons clearer.

 

[haynewp]

I still don’t like the eccentricity that could be created in the web members by having multiple PT bars and no mild rebar. If a PT bar fails/is detensioned, there is a moment created on the diagonal by the remaining PT bar(s) and no mild bars to resist bending.

 

[structuralengr89]

[ul]
[li]I'm really disappointed with FDOT's Bridge Engineer allowing the release of the audio of the Engineer w/FIGG to the media to be broadcast. Maybe there are sunshine laws requiring the release of the info, but they could have fought that with their attorneys. They could have released a transcript of the voicemail. The audio does nothing to help in this situation, I feel for the Engineer and his family.

[/li]


[li]Sure to be used in future Ethics courses...You have a client (FIU) who's claim to fame is accelerated bridge construction...which just means constructing a bridge to minimize downtime of traffic...And you have a problem with your construction...and really should shut traffic down to post-tension an extremely important member in you design...which brings me to the third point[/li]
[/ul]


[ul]
[li]Lack of Redundancy...Most highway bridges in the US are pre-stressed beams or steel with multiple girders....beams are hit by trucks with cranes all the time...sometimes 1 or 2 of the girders are taken out..and the bridge still stands....this design had no redundancy at all...and I would be willing to bet that the design lead engineer and all the senior/junior engineers who did the calcs...were bitting their nails when you have a contractor up their stressing that joint...I know I would[/li]
[/ul]

 

[JLNJ]

The proposal is an incredible document. Very impressive.

I can't help but think that maybe there are things going on in a truss web/chord connection that maybe we don't quite fully understand. Did "graceful" top "robust" in this design?

 

[bridgebuster]

I'm curious about the canopy. I wonder if the designer assumed the entire width was the top chord of the truss.

 

[dik]

Just some ramblings:

This will be winding its way through the courts long after I’m gone. In addition to the fatalities, there are numerous other things. A lot of questions, so far unanswered. What really caused the failure; the video is poor and may not show the initial failure. Did the University really have an agreement with the FDOT regarding review? With construction going over a busy roadway, this seems reasonable. Was the FDOT aware of the construction; it appears to be widely publicised, and maybe a dozen others, but, not suitable for this forum.

If that voice phone message is correct, then, there may have been a precursor to the collapse that was not followed through. There is also a reference to a ‘pinging’ sound a couple of hours before the collapse. If acted on, several lives may have been saved.

I’m not a big fan of design-build because the owner is ‘short changed’ in the QA/QC of the project. Additional review may have been useful.

The cable stayed structure, from the renderings, appears to be an attractive structure. A lot of work went in to providing these asthetics. I don’t know why it was chosen. It is likely a very costly undertaking. I think steel would have been more economical and would offer greater ductility. The spans are not excessive. The depth to span appears to provide sufficient depth to use a 2-span structure, in concrete or steel, without cable stays. I’m not familiar with the quakes and/or hurricanes that Florida can expect. It may be that construction has to be more robust than what I’ve normally encountered. For hurricanes, I would consider that a massive, albeit ‘brittle’ structure, would have merit; I’m not so sure about a seismic environment.

I don’t know what the intended support at the ‘free’ ends of the cable stayed span. I couldn’t gather this from the drawings and it has a major impact on forces/stress throughout the structure. The sequence of stressing and relaxing the strand or bars has a major impact on the resulting stresses in the structure. As noted, some of the details don’t make sense for a cable stayed structure, in particular, how will it be ‘adjusted’ after erection.

[Added] I didn't know at the time of this post that the 'cable stays' were decoratively only.

I’ve taken a cursory look at the structural information. Some of it makes little sense. Not knowing the intent of the design, it may be that this could be rationalised. I just don’t know. As I noted earlier the compression force in the end diagonal may very well be a tension member in the final configuration. Just so many unknowns.

In these environs, a ‘dash’ in a table is regarded as ‘nothing’, not a ‘ditto’ or a “do”. Having no information in these spaces makes little sense, IMHO. It could be that the ‘dash’ means to repeat. One thing about-design build is that this type of notation may mean ‘whatever it should mean’ and can be easily interpreted. This reasoning applies to sections and details. ‘As Built’ drawings or record drawings may be a little different.

Will the city proceed with this work? It looks like the schedule is ‘shot’.

 

[epoxybot]

It irks me that an agency that employs video surveillance doesn't make use of screen recording software in the first instance and retrieval from the server in the second.

The bridge was built over Southwest 8th St. which is US Hwy 41. During the bridge move the site would have been crawling with FDOT engineers. The call from FIGG was simply good conduct to the Chief FDOT Engineer for the project.

Since the first line in the table of PT members has dashes, I would interpret the dashes to me NO PT.

According to the initial proposal, the bridge over Hwy 41 was essentially structurally complete when it was moved. The faux stay cables would add stiffness that would dampen harmonic ~play~ caused synchronous pedestrian foot traffic.

The project was a ridiculous amount of money for the FHWA to be spending on a pedestrian bridge. The entire idea of making this area into a public space was delusional. Who in their right mind wants to hang out next to 40 mph noisy traffic on a road that has little to none in the way of sound damping foliage? All the hard surfaces would have made it even worse from a noise perspective.

The bridge is, for all intents, on the back side of the university. There is nothing over in this area but parking garages. The city of Sweetwater is only 15000 residents. 74% foreign born, it is known as "Little Managua". When you do the projections, it really doesn't pencil out to spend this kind of money for a pedestrian bridge, so why?

Here is why: Link
A private development, that's why. This whole project stinks of politics, using Federal money to build a bridge for the benefit of private investors. The poor people of Sweetwater are going to see their city bulldozed in the next decade. The developer/s have already torn down the two story condos that were adjacent to the bridge, to build the tower. They call the tower "University Bridge" and it was originally suppose to be half condo half apartments. With the tax changes it is now to be all apartments.

They obviously would need a pedestrian bridge BUT if the university & Miami County wanted a signature bridge, then they should have been on the hook for at least HALF the cost, instead of the FHWA paying for 80% of the project.

 

[slickdeals]

What does 74% foreign born or "Little Managua" have to do with the pedestrian bridge?

 

[dik]

Slickdeals... maybe the demographics didn't justify the bridge, and it was politically motivated.

Dik

 

[epoxybot]

I'm saying they are typically a less informed and vulnerable population that have founded a community that by City Data standards is a nice affordable low crime place to live. I also think that big developers and FIU with 54,000 students sees Sweetwater as ripe for the pickings.

 

[BAretired]

I have not read all of the above comments. The attached video may have been mentioned before...one guy's explanation for the collapse.

https://www.youtube.com/watch?v=KtiTm2dKLgU

BA

 

[EPCI-Steel]

I know we are all very curious to know what exactly happened, so here is my 2 cents.
I have very little experience with concrete, and none with pre/post tensioned concrete structures, but it appears to me from the dashcam video and the method of collapse that the first compression member's connection (where the alleged de-tensioning or tensioning operation was occuring) to the upper chord failed in shear.

If AVE's assertion is correct that the PT rod and ram being ejected some distance out of the conduit is evidence that the construction crew tensioned beyond the Fu of the rod, why would this cause a collapse of the entire structure? (being as it is a compression member and all)

What levels of redundancy are typical for a structure of this type?

 

[Tomfh]

I'm really disappointed with FDOT's Bridge Engineer

That's how it goes when things go badly wrong. You do someone else over so you don't get done over (that's an observation, not an endorsement). Evidently the strategy is working given the comments even in this forum here.