Miami Pedestrian Bridge, Part XV 15

[Sym P. le]

Please allow me to continue the previous thread (Miami Pedestrian Bridge, Part XIV) as the prior is getting unwieldy.

For those who have lost track of the discussion, my summary is that we have most recently moved into a discussion of the progression of nodal region deterioration of members 11, 12 and the deck as it pertains to the physical placement of the structure in its permanent location, then detensioning of PT rods in member 11, and then prior to retensioning of same. Epoxybot was able to connect the timeline of texts sent by Kevin Hanson inquiring of necessary supplies prior to detensioning with the timestamp on photos indicating significant deterioration prior to detensioning. I was reviewing documentation trying to narrow down on this timeline to confirm this critical detail with the implication that analysis contributed to the NTSB review has conflated events and attributed them to post-detensioning occurrences thus leading further analysis astray.

I have also posted what I consider evidence of compression failure of member 11 as the leading event of the collapse immediately after completion of retensioning PT rods in member 11. This includes questionable reinforcing design and deformation patterns in exposed rebar post-collapse.

To forward my own hypothesis, it is that two failure mechanisms were at play, one was the nodal region degeneration, and the second was the member 11 degeneration as it came into the nodal region. Although they played into each other, the weaker nodal region allowed the deck to detach from the node but the structure was able to rely on the connection of the diaphragm with the repurposed member 12 (i.e. a connection not including the deck). Meanwhile, the demand on the flawed member 11 grew and the structure collapsed when 11 failed just above the node.

P.S. With this new and more nuanced timeline, it allows the identification of three significant events to member 11:

1 - Overloading upon removal of shoring followed by release when mounted on transporters,
2 - Overloading upon setting on piers followed by release with detensioning,
3 - Overloading upon retensioning of PT rods followed by collapse.​

 

[Sym P. le]

Further testimony from ALEXIS MOLINA of Corradino Group (See NTSB Docket HWY18MH009, 17 Corradino Group Witness Interview Transcript)

Page 41

From FHWA Assessment of Bridge Design and Performance (See NTSB Docket HWY18MH009, 98 Bridge Factors Attachment 73 – FHWA Assessment of Bridge Design and Performance)

Page 31

 

[Sym P. le]

Further images in connection with testimony of ALEXIS MOLINA of Corradino Group (See NTSB Docket HWY18MH009, 98 Bridge Factors Attachment 73 – FHWA Assessment of Bridge Design and Performance) indicating what he saw immediately prior to detensioning of PT rods in member 11

Page 29

Page 30

 

[Sym P. le]

Testimony from DENNEY PATE of FIGG Bridge Engineers, Inc. (See NTSB Docket HWY18MH009, 21 FIGG Interview Transcript) indicating that he was aware of likely degradation of the structure from the time that FIGG representatives left the construction site after the move and prior to the detensioning of the PT rods in member 11.

Page 260

Page 261

Page 262 and 263

Page 264

 

[Sym P. le]

Images supporting testimony of DENNEY PATE of FIGG Bridge Engineers, Inc. (See NTSB Docket HWY18MH009, 98 Bridge Factors Attachment 73 – FHWA Assessment of Bridge Design and Performance) indicating that prior to FIGG representatives leaving the site after the placement of the span, significant further damage had not yet occurred.

 

[Sym P. le]

See NTSB Docket HWY18MH009, 98 Bridge Factors Attachment 73 – FHWA Assessment of Bridge Design and Performance

In sections 3.5 SETTING OF BRIDGE SPAN ON PIER 2 SHIM STACKS and 3.6 POST-TENSIONING FORCE IN MEMBER 11 IS REMOVED (starting at Page 19), the FHWA report starts setting out the aforementioned timeline complete with imagery before suddenly making the following incongruous statement and worse, immediately relying upon it to forward a concluding hypothesis:

Page 24

Although it is possible that significant progression did occur post-detensioning, there is an evidence gap because the north face of the diaphragm was not photographed by Alexis Molina and member 11 was not photographed by Kevin Hanson. The evidence only indicates that significant progression occurred prior to detensioning yet this fact seems to be dismissed.

 

[Sym P. le]

Text scroll from Kevin Hanson's mobile device (HWY18MH009, 48 Bridge Factors Attachment 23 – Texts from Mr. Kevin Hanson of Structural Technologies on his mobile device dated March 10, 2018).

If we use the timeline from Alexis Molina's images that detensioning had not yet started even at 3:17 p.m., and that detensioning was completed at 6:30 p.m., that allows over three hours to complete the task and another thirty minutes (or so) to examine the north face of the diaphragm. On hind sight, Hanson may just be reiterating concerns of Molina.

 

[Sym P. le]

I can only wonder why the work crew would stay on the decrepit structure after the Molina images were taken unless they truly believed they were safe and their work necessary for the good of the project. All indications at that point were that the structure could collapse at any moment let alone five days down the road. At that time, the road was already closed and it wouldn't have been a back and forth to irritate the public. They could have just left the road closed and said "Sorry, we're just being safe."

 

[Sym P. le]

The attached file is a clip from a time lapse video showing the detensioning operation. Member 11 was detensioned first and then Member 2.

This copy is 6.2 MB size.

 

[Sym P. le]

A larger copy of previous post, 17.3 MB size.

 

[Sym P. le]

Some excepts from FIGG Bridge Engineers, Inc. Photo Submission (HWY18MH009, 101 Bridge Factors Photographs - FIGG Bridge Engineers, Inc. Submittal of Photographic Evidence) with real time stamps and frame references to above posted video.

Page 109

Page 112

Page 119

Page 121

 

[Sym P. le]

In the video, from 9 sec +22 to 12 sec +28 I can see someone inspecting the deck, Members 1/2, and 11/12 while there is a lull in the activity on the canopy. Detensioning work appears to start on Member 11 at 17 sec +4 and finishes by 18 sec +4. This time frame does not seem to support gradual alternate release of the upper and lower PT rods. The work then shifts to Member 2 and completes by 23 sec +27. At the tail end of the video after everything appears to be tidied up, someone gets back on the man lift and goes up to inspect the north face of the diaphragm one more time.

I was not able to correlate the time stamps from the FIGG images (even though the time stamps are rough extrapolations from FIGG's presentation) with the video. Perhaps the cadence of the time lapse varies throughout but I'm not familiar with this aspect of video recording. The frames that I have identified above are accurate, I just don't know if I've assigned the correct time stamp.

It does seem that the video supports the above evidence of Molina and that Hanson was only the first to see the diaphragm because until detensioning was complete, the man lift was prioritized for that work.

 

[Sym P. le]

I've attached a cropped and zoomed video of the detensioning work on Member 11 (size 11.0 MB). The upper PT rod was detensioned first. If any work was done to detension a PT rod prior to Hanson requesting oil for the jack, and hence, Molina taking his photos, it was to the upper PT rod. Very little time was spent on the lower PT rod just at the end of the video. Again, I don't know the cadence of the time lapse or if it is steady through the whole video.

Early Frame

Late Frame

Animated GIF of the two frames

 

[dik]

It's terrible that this project was badly designed and failed catastrophically... I thought it was quite an attractive structure... and likely one that will not be duplicated.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Sym P. le]

It's terrible that this project was badly designed and failed catastrophically... I thought it was quite an attractive structure... and likely one that will not be duplicated.

I agree.

I'm also disappointed in the NTSB/FHWA/OSHA reviews as the closer I look, the more amateurish the design seems and the more disappointing the reviews seem, at least so far as identifying the trigger for the collapse. That's not to say that their findings of responsibility were necessarily wrong. It is patently obvious that Member 11 failed in compression below the last full column tie and above the 11/12/deck node.

A few more images to illustrate the point. In the 3D perspective, I've erased the far side longitudinal rebar (west side and bottom face, including the lower PT rod), hopefully to reduce the confusion of how much rebar exists and to illustrate how vulnerable the upper surface of Member 11 is. Again, the skewed U shaped tie is practically useless.

):

 

[epoxybot]

Thanks for digging up Denny Pate's interview. It really is stunning that he was aware that the bridge was failing under its own weight but didn't seem troubled with what was happening. I suppose he chalked it up to the concerns of the Peer Reviewer, regarding the expeditious detentioning of the PT bars, perhaps not occurring quickly enough.

The PT Hydraulic Jack had a separate reservoir/pump. One of VSL's junior field techs during his interview, stated it was his & usually another junior field tech's job to mobilize the equipment to the location where work was to be done. So it is entirely possible, they had the jack mounted on the PT bar before they realized the reservoir needed hydraulic oil.

 

[Sym P. le]

The timing of the detensioning/jacking could use a definitive answer. I suspect they would have to give a little tug on the PT rod in order to release the nut. Is it possible that they engaged the jack before realising oil was required and if so did that trigger the cracking? Why did Molina do his inspection when he did? Did something raise concerns?

As I reviewed Molinas images some more, it became clear that the deck surface cracks that he caught at the corners of his images could only be part and parcel of the north face cracking later imaged by Hanson.

It all seems that the investigators were steering the investigation to a predetermined conclusion.

 

[Sym P. le]

Denny Pate appears rather defensive in his interview yet all the while admitting he knew what he knew when he knew it.

 

[Rabbit12]

Just read Pate's interview and the interview of Jason Stauffer after Denney's. Is it a strategy to come into these interviews without any info so you can play dumb? The Stauffer guy could answer almost no questions including who provided him the loads to design the substructure. How do you not remember that or at least do enough refresher work to know that answer?

 

[SwinnyGG]

Is it a strategy to come into these interviews without any info so you can play dumb

Yes, it absolutely 100% is.

There are some people who won't email critical information because they don't want a subpoena-able record to ever be available. If you are under subpoena, anything in writing is obtainable.

Go read Manual Feliciano's interview where he states he was instructed after the collapse not to do any engineering evaluation or perform any calculations. I can almost guarantee that was direction all the way from the top of their leadership and/or legal counsel, to avoid any internal documentation creating a paper trail that indicated they were aware of mistakes that may have been made.