Miami pedestrian bridge collapse

[Redlands Okie]

Negligence or poor design?

"Florida's Department of Transportation says an engineer left a voicemail two days before a catastrophic bridge failure to say some cracking had been found at one of the concrete span.

However, the agency says the voicemail left on a landline wasn't heard by a state DOT employee until Friday because the employee was out of the office on an assignment."

The Latest: Caller reported cracks in bridge before collapse


more -

"A construction firm involved in this week's fatal bridge collapse in Florida was accused previously by a subcontractor of failing to properly design a bridge construction system after an accident in Virginia.

The allegations were made in a lawsuit that was later settled. A confidentiality agreement bars the release of details.
The lawsuit stemmed from FIGG Bridge Group's building of the Southern Norfolk Jordan Bridge in 2012. During construction in Chesapeake, a 90-ton segment fell onto railroad tracks below."

That recorded phone call warning of a potential problem has one small issue. The caller said it looked cracks but not a major issue. Oops. However I suspect that that phone call will be worth a lot of money and jail time since it will give the defense some excuses.

 

[Todd727]

I'm trying to understand the mythical center support. From the drawings I've seen, this was only half of the finished bridge and the center support that is referred too is actually the support on the end nearest the break. Is that correct?

 

[California]

Yes correct.

This segment of the bridge went to the pylon at the the edge of the ditch. The future segment starts there and crosses the ditch. The future tower would be above that pylon.

====Major edit==== I'll paste in here a simplified drawing similar to an engineering drawing described on Welding Web. The bridge broke below the upper end of the chord (diagonal) nearest the tower. The underside of the bridge at the break point is where the bridge was supported by the truck that moved the bridge into place.

Below is the engineering drawing posted on Welding Web. Here are alternate sources for the drawing:

The original drawing is on page 115 of the project proposal
https://facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf
... following many pages of fluff - biographies, landscaping etc.

The engineering drawing is also shown and described at 3:14 in Juan Browne's excellent second video on the subject:
YouTube - Miami Bridge Failure Update 18 March 2018


==== end edit===

The bridge broke at a point below the top of of chord #11 shown in the engineering drawing.

The chart in that drawing doesn't list rods in some of the chords. WTH??? Hypothesis: Maybe chord #11 [nearest the pylon] got stretched while the bridge was supported 20 ft from its end while it was transported into place.

 

[Streetcar]

California
Link does not work

 

[MossRoad]

Or steel and steal

Foreign beer in chinese metal cans.... :confused3:

 

[MossRoad]

From the articles I have seen, the bridge was a post tensioned beam. The canopy and diagonals were bracing to stiffen the beam . The cables were decorative.
It is common to tension beams that are over live traffic.
It does not appear to be any post tensioning in the canopy or diagonals

The bridge was a truss bridge. From here:
Miami bridge collapse: Truss design, despite suspension appearance

Those concrete trusses were structural. The main walkway couldn't have supported itself without them and the canopy.

 

[California]

California
Link does not work

Sorry, I see you need to be logged in over there.

I'm looking for a copy of that engineering drawing, haven't found it yet. Meanwhile here's a thread on an engineering forum with lots of diagrams and discussion - but also containing some statements that are later corrected by other posts. The diagrams are valuable.

CR4 - Thread: Miami Bridge Collapse

And here's a simple diagram. (I'm still looking for the engineering drawing in a form I can link here).
I went back and edited post#43 above, hope it's useful now.

 

[KennyG]

As an engineer, this boggles my mind. Who, other than a government agency would spend that kind of money to make a structure look like something it is not. And who would think that that volume of concrete would be the smart way to build a pedestrian bridge.

 

[bigdeano]

I suspect the tower and cables would have been structural when it was completed. The truss bridge was barely able to support itself, much less possibly hundreds of people that would fit on the walkway. They were apparently tightening cables when something broke. Maybe overtightened or a defective part.

 

[ruffdog]

So this guy is under the bridge when it makes a snapping noise 5 hours before it fell. Then, there was a meeting of the minds 2-3 hours before it fell. Was there ANYONE worried about the cracks?
Miami FIU bridge collapse: Man hears crack before collapse | Miami Herald