Miami Pedestrian Bridge, Part X 50

[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



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[Vance Wiley]

"it is not a small issue that the FIU bridge was a real time, real life experiment" - -
Very well stated. I am not sure you will consider it a compliment, but if an attorney finds your post, it will likely be used in court.
At this point in the engineering and construction technology the workings of a truss should be well enough understood to be considered common practice. The melding of that technology with brittle concrete, on a scale such as this project, then using prestressing (as I tried to describe) and the need to transport the heavy but (as it turned out) delicate structure makes this project particularly risky to all involved. Add to those real and daunting concerns the overlooking of details resulting in the deficient design of the most critical joint (which had no redundancy) and we have seen the results.
Should it have been tested full scale? You bet. When the falsework is removed from CIP work the self weight loads are present and immediately load the structure. If the transporters had remained at the end of this bridge, with PT not required in member 11, it would have likely have failed in lifting onto the transporter, or at least on the trip to its final location.
This structure was a bad idea at the outset, and received horribly deficient execution in the design, review, and construction phases. It is a poor representation of the current state of our knowledge and abilities.
Perhaps it will provide guidelines tor the ABC process. Clear guidelines or requirements for ductility, redundancy, and peer reviews with great attention given to the effects of moving a structure which is intended to serve without moving.

 

[jrs_87]

Can this page help us understand failure? Did FIU bridge have block shear failure? This page is for steel, I don't know if concrete has similar page.

https://www.bgstructuralengineering.com/BGSCM14/BGSCM003/BGSCM00307.htm

OSHA report indicates 2 was deficient. This reinforces past concerns that collapse could have happened any time in the future, for example, with a critical load of students. Another point, by policy OSHA has zero mandate concerning safety of the public - only employees. It will be interesting to see what fines will be levied by OSHA later.

No one here has commented on OSHA's emphasis of lateral support on diaphragm II in casting yard. I think OSHA got that wrong, how could those tiny long pipes participate in load?

 

[MikeW7]

It will be interesting to see what fines will be levied by OSHA later.

OSHA issued some citations and fines on 2018-09-18. Links to the formal citations are included in the news release. The five companies involved are still contesting their fines. No status change in months - I check from time to time.

Will more citations be issued now that the report is out?

 

[jrs_87]

CNN

FIGG Bridge Engineers said in a statement to CNN that they reviewed the report and disagreed with OSHA's conclusions.​

https://www.msn.com/en-us/news/us/f...-before/ar-AACLWea?li=BBnbklE#image=BBKh5Aw|9

 

[jrs_87]

More on Figg's reaction:

https://www.enr.com/articles/47044-osha-investigation-slams-figg-for-fiu-bridge-collapse

Please read all of comment titled OSHA calculations show end diagonal truss member #11anchorage overloaded past failure by 22% and after retensioning by 45% etc. at above link.

 

[samwise753]

From FIGG's response to the OSHA Report:

In a statement to ENR, FIGG disputed OSHA’s findings, calling the report “factually inaccurate and incomplete” with “errors and flawed analyses.”

The OSHA FIU Pedestrian Bridge report “does not include an evaluation of many important factors pertinent to the construction process leading up to the accident. Additionally, it has not been reviewed by any other entities involved in the accident investigation. FIGG disagrees with the conclusions in the OSHA report.”

Um, your bridge is on the ground, bruh. Why even comment? It seems the NTSB report will likely echo the OSHA report, so they'll end up looking like fools.

 

[jrs_87]

samwise753 (Structural)12 Jun 19 20:03

Legal tactic by Figg's counsel. All reports are factually inaccurate and incomplete with errors and flawed analyses if you are arguing in absolute terms.

Gaslighting:

https://thoughtcatalog.com/shahida-...ociopaths-and-psychopaths-use-to-silence-you/

Side note: Louis Berger Inc. as merged with another company and made changes to board last July. Another side note: Louis Berger employees did a nice job helping build a practical footbridge in rural Panama - without heavy equipment.

https://vimeo.com/294241866

 

[jrs_87]

P.S. Unfortunately for the engineering profession, as pointed out, the OSHA report is indeed flawed and it would be prudent for them to amend it.

 

[JStephen]

Somewhere in there, the OSHA report mentioned that the #7 bars sheared off. (Edit: "As a result of the blow-out, three #7 shear reinforcements at the construction joint of diagonal 11 and the deck were sheared but the southernmost shear reinforcement remained intact.", Page 84.)
I agree they should amend as needed.

 

[samwise753]

I can see why an attorney would defend their client using that tactic, but it really looks dumb in light of what went down and how the aftermath is spelling out.

And it's valid that there is that flaw in the report, but that hardly invalidates its conclusions. The 12 conclusions stated in the executive summary are spot on. #12 stands out the most to me.

 

[jrs_87]

Pate's call to FDOT was not a warning as widely reported. He was trying to head-off someone ELSE reporting cracks. ("...because I suspect at some point that’s gonna get to your desk...") Examine every single word of the voicemail transcript.

“Hey Tom, this is Denney Pate with FIGG Bridge Engineers. Calling to, uh, share with you some information about the FIU pedestrian bridge and some cracking that’s been observed on the north end of the span, the pylon end of that span we moved this weekend.

“Um, so, uh, we’ve taken a look at it and, uh, obviously some repairs or whatever will have to be done but from a safety perspective we don’t see that there’s any issue there so we’re not concerned about it from that perspective although obviously the cracking is not good and something’s going to have to be, ya know, done to repair that. At any rate, I wanted to chat with you about that because I suspect at some point that’s gonna get to your desk. So, uh, at any rate, call me back when you can. Thank you. Bye.”​

Message contains subtle tells. "whatever", "at any rate" (twice, equivocation), "we/we've" (mouse in pocket), "chat" (no urgency), stumbles after "although", "some information" (dilutes "some cracking"), "been observed" (to distract that it's ongoing), "taken a look" (past tense again, no mention of further analysis, just repair) I'm not implying or saying he was lying, I'm looking for something else than that here.

*Source of transcript:

https://www.equipmentworld.com/insurers-covering-figg-bridge-engineers-bridge-collapse/

 

[gwideman]

OSHA states the 45 degree influence of PT each side of 11/12 in the deck leaves 11/12 outside the shear lag zone so the horizontal force is not restrained by the PT.
As I recall, "40YearsExperience" was addressing exactly that in his posts, and suggested reinforcing wrapping behind 11/12 and extending into the PT compressed zones.

It think you may be referring to this informative post by SheerForceEng in thread part IV, 24 Mar 2018 22:40, responding to my questions as to whether the diagrams I sketched represented principles we would expect to see in the 11-12-deck connection, conveying the horizontal load of #11 to the deck's longitudinal PT bars.

 

[hpaircraft]

Skimming the OSHA report, it appears that Figg had intended to join the main span to the back span in such a way as to resist the sort of tear-out failure that caused the collapse. However, I haven't seen any signs of this plan in the materials so far released. Did I miss something? Were they going to connect something to the ends of the longitudinal PT tendons where they came through the diaphragm? I saw one passing reference to this in regards the tendons in the canopy, but if there were references to doing that with the tendons in the deck I missed them.

If this is actually the case, it might explain earlier commentary about "capturing the node." Maybe they were planning to build an appliance that they could attach to the ends of the PT tendons to simulate the presence of the back span and resist tear-out at the 11/12 node.

 

[jrs_87]

Another angle. Note large size of concrete chunks.

 

[gwideman]

[comments on OSHA report mislabeling direction of views on some photos]

The north-south swap is annoying, but probably results from confusing wording of previous view direction statements on preceding photos.

More concerning is their assertion on one of the photos that #11's lower PT bar sheared off, when photos at the scene show it attached to the deck, which is a highly important piece of evidence implicating the tensioning of this PT bar as the final factor precipitating the collapse.

 

[gwideman]

Were they going to connect something to the ends of the longitudinal PT tendons where they came through the diaphragm? [...] If this is actually the case, it might explain earlier commentary about "capturing the node."

That "capturing the node" discussion stems from the "cracks" meeting just prior to the collapse. From that meeting: "Steel channels to 10/9 node & PT Bars to capture some of that force which is better than vertical support.". So something like this:

This was deemed "better than vertical support", because just supporting near the end of bridge, does not deal with the horizontal component of #11's compression.

 

[Vance Wiley]

I believe OSHA is correct. Those members were 21" wide

You are so correct - and thank you. I just embarrassed myself bigtime. And I have deleted the post and can only hope you were the only one to notice. In my defense - I was only 90 degrees disoriented, N vs S is 180 degrees. Not a lot to hold onto, but that's all I have at this time.
Thanks again.
Regarding the 45 degree shear lag and transferring the horizontal force from 11 to the PT -
I had forgotten the post you reference but I thought a similar post with "V" shaped diagonals wrapping the 11/12 node had been posted by 40YE. Now I see he has apparently removed his posts - I did a search and did not find one. I agree with the reinforcing - but it would take a lot to develop the 1300 kips (DL) and more to be safe for TL.

 

[Vance Wiley]

it appears that Figg had intended to join the main span to the back span in such a way as to resist the sort of tear-out failure that caused the collapse

I too have trouble with that statement.
I have only seen details that anchor the concrete closure between the diaphragms to the pier cap, and a couple of PT rods down into the pier. Also some delayed placement of PT in the canopy to tie the tops together. And the casting of the 109 foot spire to support the fake "strands". Has anyone seen more ties detailed? Anything that could develop 2000 kips?

 

[gwideman]

So, how did all this go down? Did this relatively "simple" pedestrian bridge get a quick glance over for the calculations and analysis? Hey, it is only a pedestrian overcrossing. Did the hope and interests of FIU to promote their ABC engineering program cause their peer review to take a back seat to getting a landmark iconic bridge - even if the design is a risky concrete truss? Isn't there a term or theory for no one willing to challenge a perceived expert or group of experts? I see this not as a lesson for pointing a finger at a villain, but as a lesson for learning to not to get lulled into complacency.

Your entire post is spot on.

For example, while it's important for OSHA or NTSB to use alternative software to cross-check the strength of the design, I hope that one of these bodies reconstructs how FIGG performed the design. I want to understand whether the errors are as simple as discussions in Part IX of this thread suggest. Because if so, then your other points about the efficacy of all the checks and reviews etc are not about some obscure technical detail being missed, they are about how the process failed to stop even a design with problems that were about as conspicuous as possible. (And of course then failed to shut down a structure whose physical symptoms of imminent collapse were also about as conspicuous as possible.) Whatever is behind that part of the failure needs urgent attention.

 

[gwideman]

You are so correct - and thank you.

No worries. I've deleted my comment to you as well.