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# Miami Pedestrian Bridge, Part VIII76

## Miami Pedestrian Bridge, Part VIII

(OP)

### RE: Miami Pedestrian Bridge, Part VIII

(OP)
hokie66, I'd agree with you that the article seems to be well written for its intended audience.

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### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (Miami-Herald)

FIU had launched and heavily promoted a center for ABC at its engineering school, and explicitly saw use of the technique for its pedestrian bridge as a demonstration of its efficiency.

Such quick-bridge construction effectively ruled out a true cable-stayed bridge. Cable-supported bridges are built in sections and in place, which requires extended road closures. Truss designs, in contrast, are ideal for the accelerated approach, engineers say.

I posted this bridge in Part IV but I'm re-posting it because it demonstrates that the above premise is not valid.

The Mary Ave. (Don Burnett Bicycle-Pedestrian Bridge) is built to withstand SF Bay Area earthquakes. As the photo demonstrates they could have built HALF of this bridge and probably have had plenty of money to dress it up & make it the deck wider, while still employing a method of ABC. This bridge would have needed support briefly. The extra unused lane on the Tamiami Trail/Hwy 41 would have served nicely.

### RE: Miami Pedestrian Bridge, Part VIII

Yes, there are plenty of cable stayed pedestrian bridges built while the roadway below is in use.

And the bridge in Cupertino CA is structurally honest, and IMHO better looking than the Miami bridge was going to be.

### RE: Miami Pedestrian Bridge, Part VIII

I wonder about the difficulties of anchorage to support the asymmetrical weight of a pure cable-stayed bridge and the concentration of the weight on the one central pier that would happen, given the close proximity to the canal. It's also about 12 feet wide, or about 1/3 the width of the FIU bridge and likely a lot more elastic/jouncing making for a less desirable hangout spot.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (hokie66)

This article in the Miami Herald, linked late in the Part VII discussion, would make a good starting point.

http://www.miamiherald.com/news/local/community/mi...

...but that 'undernourished' strut....

It's all okay as long as it's okay.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (thebard3)

...but that 'undernourished' strut....
I'm thinking that is a case of an overly active use of a thesaurus. (Maybe a change from underweight to undernourished?)

### RE: Miami Pedestrian Bridge, Part VIII

I was quite happy to have another structural term in my vocabulary. The bridge was demonstrably understrength, and strength often relates to nourishment, so I give the journalist a bit of leeway.

### RE: Miami Pedestrian Bridge, Part VIII

4
undernourished = lacking sufficient iron

### RE: Miami Pedestrian Bridge, Part VIII

I quite like that description. Not enought "meat on the bones" if you like I think gets the message over very well.

I thought that was a very well written article.

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

### RE: Miami Pedestrian Bridge, Part VIII

I'm feeling confident so here's my two sense on the failure progression:

a) The base of #11 fails early - essentially a column with a wedge shaped base that slips and crushes against #12. This failure is not explosive, rather it is progressive as PT is ratcheted up.
b) The displacement and crushing of the lower end of #11 results in the upper canopy being pinched downwards at the #10/#11 bubble.
c) Further PT on #11 also loads energy into #10 which bows upwards while #11 bows downwards.
d) This deformed system continues to be loaded with PT plus gravity until the upper end of #11 blows apart. This is when we first see the obvious disaster unfold.
e) As #10 is restored, the north end of the #10/#11 bubble is punched out of the failed canopy creating an illusion of time lag in the canopy collapse north/south of the bubble.
f) The lower deck fails across the #9/#10 joint.
g) The north end of the bridge is dragged down, tearing the PT cables out of #11.

Unfortunately, this disaster truly was amateur hour.

My sincerest condolences to the victims and their families.

### RE: Miami Pedestrian Bridge, Part VIII

I'm with you up to d)

Looking at this extensively I think it's the base of no 11/12 which fails first or maybe at the same time as the top. This action is enough to push no 12 off the plinth. If you look closely at the top of 12 during the many slo mo videos, the canopy at the 12 end falls at the same time as the rest for about half its height before the canopy collapse drags it back over the plinth into its final resting position.

One of the survivors quotes a sudden loud noise just before the collapse. Could be either end of 11 IMHO

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

### RE: Miami Pedestrian Bridge, Part VIII

OK - I understand what everyone has explained. And I am not a structural engineer, but I have to ask, what if the joint between diagonal #11 and the deck had not been a "cold joint" but a continuously poured section of concrete (not that that would even have been possible). I might have thought that critical "joints" would have been spec'ed to be completed in a single pour for this reason.
It looks a little to me as if the designer was used to building steel bridges where a properly done weld would be stronger than the base metal. It looks as if concrete bridges may be a different matter.
What does anyone think?

### RE: Miami Pedestrian Bridge, Part VIII

Hello Again,
I have been working (slowly) on a frame by frame of the original dashcam images.
It is easy to draw boxes aligned with the image shapes, the hard part is to align the images frame to frame because of the movement of the truck. It is very clear that the canopy drops at the #10-11 blister before any other movement can be detected at the resolution of the dash cam. #12 appears the remain vertical at this moment. To me this implies a break at the top of #12 and requires #11 to get shorter. There is also an increase in the angle between #10 and 11, so something had to give there.
I'm working in powerpoint 'cause that's what I'm familiar with, but haven't found a way to capture the slideshow. I'll post as soon as I can convert to a reasonable format.
Thank you,

SF Charlie
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### RE: Miami Pedestrian Bridge, Part VIII

SFcharlie - Hence why I think the base of 12 and 11 was initially pushed out just beyond the support (would in essence make no. 11 "shorter").

tomcat - I think many are agreed that the design of the bridge was not standard and that the analysis of the joints and connections between the different elements was a lot more complex than may have been imagined / undertaken. It has also been noted many times that the number of concrete truss like designs is very limited - probably for good reasons.

However we don't have the inside knowledge on the level of analysis and design scrutiny / review which was undertaken.

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

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (LittleInch (Petroleum))

I think the base of 12 and 11 was initially pushed out just beyond the support
I can see the upper part of #12, and it doesn't move. I suspect that the little ~3 inch high bit of concrete between #12 and 11 failed. What happens at the top is confusing since in the aftermath, we see the blister more or less intact, but separated from the canopy, but somehow 11 became hinged re #10. Also in the aftermath, 11 is damaged at both ends. I wish NTSB would release the photos of the elements as they observed during the deconstruction of the north end.
Respectfully,

SF Charlie
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### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (IRstuff (Aerospace))

possible to screen capture the slide show into a video
Thanks!
Yes, I'm sure you're correct. I had hoped that Microsoft would provide a way to export the show as a gif or video file, but I haven't found the correct pulldown. I'll google it.

SF Charlie
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### RE: Miami Pedestrian Bridge, Part VIII

Thanks for the answer. I didn't phrase the question very well. Putting bridges aside for a moment....
Does anyone know if the shear strength of a concrete "cold joint" is different than the shear strength of a solid block of concrete? Intuitively it would seem likely it would not be the same, but I expect it depends on a variety of factors including how much the first pour has cured before the second pour is made. My question stems from the excellent information in this thread about the FIU Bridge construction using a "cold joint" at the junction of the lower end of diagonal 11 and the walkway. It seems essential that the diagonal be properly bonded to the walkway and it would seem to make a difference whether these two pieces were connected with a "cold joint" or a continuous pour. There was a very large horizontal component of force on this joint (the horizontal component of the compression force in diagonal 11) and I am wondering if the engineers over estimated the shear strength of the concrete that composed that joint because they failed to recognize the field construction had to pour the walkway and diagonal in two different pours. Thanks for your patience.

### RE: Miami Pedestrian Bridge, Part VIII

According to the Miami Herald article from June 14, 2018, it's apparent that the Herald's request for additional information from the parties involved was granted, as it's stated within the article that nearly 2,000 pages of calcs were reviewed by several engineers. But where are these calculations? What were the terms of the release? Are there legal restrictions to full disclosure at this time? If this was a freedom of information-like release, why weren't these calcs made public?

Could someone here please explain this to me, or could someone from the Miami Herald please speak to this issue (the Herald article was extremely vague on this point). It seems to me that a perfect way to kill, or control, a story is to request info, then once you've obtained it release it only to a select group of individuals.

### RE: Miami Pedestrian Bridge, Part VIII

TheGreenLama... when this first came out, I sent an eMail to one of the people responsible for the article... no response.

Dik

### RE: Miami Pedestrian Bridge, Part VIII

Andres Viglucci (aviglucci@miamiherald.com) was the guy I sent the query to...

Dik

### RE: Miami Pedestrian Bridge, Part VIII

Tomkat: I can't answer your question about cold joint strength (details outside my field), but it's been discussed. I'd assumed #11/12 slid off the end of deck after breaking at cold joint, but recently someone posted a different view of #12's end that shows it broke below the cold joint (which held). The 'leaked' photo showing cracks at base of #11 after shoring was removed shows a crack traveling along the cold joint.

### RE: Miami Pedestrian Bridge, Part VIII

It sounds like they made a basic public records request for the 2000 pages of calculations.
"The Herald obtained the structural calculations and design plans through a public records request and shared them with the engineers. Howell and Beck, who both have expertise in bridge design and structural engineering, analyzed the plans and calculations independently but came to similar conclusions."

but I'm not sure if this (further down article) means the calcs are no longer accessible by the public:
"Unless you’re part of the investigative team, you may not be privy to all the information.”
"That information is no longer accessible to the public, however. The NTSB has severely restricted access to records related to the accident, leading the Herald to file a lawsuit demanding access to documents that were previously available for public review under Florida public records laws."

This is new from a lawyer. Bottom line is the NTSB is supposed to write a document to say if they want to be party to MH suit, and if not, the judge will rule on whether info between Fed 19 and Mar 15 before the span fell can be released (especially minutes from the meeting about cracks the morning before collapse). Is the same place they were weeks ago when the judge asked NTSB to show up (they didn't but wrote a letter).

### RE: Miami Pedestrian Bridge, Part VIII

Chris,

Thanks for the link to the July 5th article in Roads & Bridges. It reads like the Herald has received documents that were created on or before Feb. 19, and that the lawsuit is to try and gain access to material between Feb. 19 and the collapse. At least that's my interpretation. If so, it implies that they have received the design calculations from FDOT, separate from the lawsuit, and for some reason are only letting select people have access to them. What would be their motivation for doing this?

I believe that the St Augustine article is nothing but a copy of the earlier Herald article.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (FDOT)

DOT produced documents created on or before Feb. 19—a little less than a month before the collapse—but nothing thereafter, including during the crucial days leading up to the collapse. FDOT’s refusal to produce documents originating after Feb. 19 was the result of a written directive it received from the NTSB

Even though they claim 'no involvement'... I betcha they are in it up to their kazoo... Maybe protecting themselves?

Dik

### RE: Miami Pedestrian Bridge, Part VIII

I did a quick critique on an article showing the FDOT's involvement, only to learn that it was for a different project.

Does anyone have a copy of the document that pertains to this project? I couldn't find my reply in the earlier parts of this thread.

Dik

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (chris snyder (Electrical))

recently someone posted a different view of #12's end
This is a frame from Engineer Multiple red flags behind fiu bridge collapse
It looks to me as though the rebar for the tower (or the diaphragm for the north span?) is intact behind #12 lying on the pier?
Thank you Chris for bring this to our attention.

### RE: Miami Pedestrian Bridge, Part VIII

2
It was, and still is a very interesting discussion, but somehow concentrating on the mode of the collapse, instead on the real reasons leading to this tragic accident.
It is obvious that the bridge was under designed as it failed under dead load alone. So, it’s apparent that there was a major design error overlooked by all involved parties.
As I posted before, the code and design guide used to design this bridge were leading to the seriously “undernourished” structure with unacceptable safety factor, or, as proven by the events, to failure under self-weight.
As on the typical well-founded project, a lot of studies were done such as the study of the loading. Unfortunately, no studies were conducted for the load factors to be used in the design, so typical AASHTO's were likely used, applicable to highway bridges and pedestrian crossings with light weight (steel) structures. The attached article presents some thoughts on the subject, as well as commonly used factors for different types of structures, and explains the risks associated with this approach.
Equally critical, in my opinion, was the methodology used in the design for shear stresses. The current code approach is to carry the excess stresses on the steel, using some fancy formulas, where the old approach was to carry all shear forces via reinforcement, when the allowable shear stresses where exceeded, and always use this approach in the support or anchorage zones.
Perhaps that the secret so closely guarded by NTSB? That the bridge was designed as per AASHTO and “Design Guide for Pedestrian Bridges” without major deviations?

### RE: Miami Pedestrian Bridge, Part VIII

3
An important reminder: there is no "slow-motion" video. The original truck-cam video was shot at approximately 5fps, or one frame every 0.2 seconds, and had a resolution of 1280x720 pixels. This video was then processed to CREATE THE ILLUSION of zooming and slow-motion. The "zooming" was performed by CREATING in-between pixels, probably by simple linear interpolation, so a small center section appeared larger. The "slow-motion" was performed by CREATING multiple in-between frames with advanced 3D (X,Y,time) interpolation routines that recognize primative shapes and patterns in consecutive frames.

These techniques can produce a remarkably realistic interpretation of an event, as long as the event being filmed has dynamics that are relatively slow compared to the original video frame rate. When this is true, the CALCULATED in-between pixels and frames will create an ILLUSION that matches up very closely with reality.

In this scenario, however, we are dealing with with an extremely rapid series of explosive non-linear events that occurred on a millisecond or microsecond timescale in which 0.2 seconds is a lifetime. As a simple example, a car traveling at 60 mph, or 88 feet per second, travels 17.6 feet in 0.2 seconds. If you filmed that car driving into a concrete barrier at 5fps, you'd only record one or two frames of the impact, and you simply don't have enough information to process those frames into a video that portrays the crash realistically. That same reasoning should be applied to the truck-cam video.

### RE: Miami Pedestrian Bridge, Part VIII

Has this been suggested yet?
The compressive strength of the diagonal member was exceeded.
The lower part of the diagonal member crumbled under compression.
With part of the diagonal member crumbled, the member ceased to be a viable structural mamber.
Gravity took over.
As the bridge collapsed, the shortened remnant of the diagonal punched into the vertical member inducing the shear failure.
At the same time, more of the diagonal member may have crumbled.
The final position of the hydraulic jack indicates that the diagonal member is considerably shorter than originally.
My main point is that the initial failure may have been compressive failure rather than a shear failure.
This suggestion is supported by reports that the initial failure occured during an operation that increased the compression stress on the diagonal member.

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

### RE: Miami Pedestrian Bridge, Part VIII

waross, in looking at the way the post-tension bars were installed, they acted like anchors in the deck, below the shear line of observed cracks. If one were to put a cable alongside the diagonal for the purpose of pulling it off the end of the deck one would anchor it just the same way. In an early post I took a shot that the compression load in that diagonal was approximately the full weight of the bridge; the total compression stress was from that was in the mid 4ksi range for concrete that was supposed to take 8.5 ksi minimum. The additional tension was 5-10% of the dead load (sofa-cushion estimate).

From this I have since concluded that the most likely failure was to continue to fail the connection that had already failed - the shear line between the diagonal and the deck. Only an inch of relative movement would exceed what the rebar bridging that connection would be able to take. Whether the rebar failed in pure shear or because of excess tension as the embedded ends were displaced, I don't know, but the overall failure looks to be entirely from a loss of shear capability.

### RE: Miami Pedestrian Bridge, Part VIII

From earlier threads and information there are two tensioning bars in member 11, one high and one low. Apparently the top bar had been further tensioned and it was during the tensioning of the lower bar when the failure occurred.

The top bar remained in place, but the bottom bar, which was anchored into the bottom base was ripped out of the member 11 during the collapse thus showing that, at some point during the collapse, member 11 became detached from its connection to the base. This ripping out essentially shortened the bar leading to the tensioner sticking out the top.

Now whether this was cause or effect is not clear, but many here believe that the extra tension on the bottom bar added to the shear load of the joint between 11,12 and the base leading to a shear failure in that joint, perhaps initially only of a couple of inches, which then lead to a sudden failure of the rest of the structure. Now how that complex joint was designed, analysed and reviewed / approved is probably the key design issue here as wiktor states. On the design data available and evidenced by the cracks seen, it looks like the weak point and is not over encumbered with re-bar.

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

### RE: Miami Pedestrian Bridge, Part VIII

The Chirajara bridge in Colombia collapsed on January 15, 2018.

On January 31, fifteen days later, a preliminary report was presented explaining the reasons for the ruling.

The report mentioned the desirability of demolishing the opposite side of the bridge.

On March 15, 2018, the FIU pedestrian bridge collapsed.

Because 120 days later there is no preliminary report?

### RE: Miami Pedestrian Bridge, Part VIII

They already released a preliminary report.

The NTSB typically investigates for systemic causes into failures, not simply immediate causes and this can take longer. There is also no pressing potential of another collapse of a similar structure because there is no other structure built to these plans. I'm pretty sure the NTSB clearly stated that it would take up to a year before their final report would be issued. Even if they did not, that is the amount of time almost every final report takes; they do not issue any intermediate reports.

3DDave... that report and $2.00 will get you a cup of coffee. Report was useless. Taxpayers' money hard (ly) at work. Dik ### RE: Miami Pedestrian Bridge, Part VIII The report was exactly what NTSB can release at this point in their investigation, and it is exactly what they are supposed to release. It sets forth the facts that are knowable by inspection (what happened, when, and where, etc) and lays the groundwork for the ensuing investigation. It does not speculate. ### RE: Miami Pedestrian Bridge, Part VIII hpaircraft... it was pretty light for that even. It did not provide any factual information they had. The information has been specifically held back, so, characters like those on this forum could not come up with 'real' information. To reiterate, the report was useless, and, a waste of paper and manhours. Dik ### RE: Miami Pedestrian Bridge, Part VIII 2 The reason that the NTSB is so backlogged is due to budget cuts. They have only just gotten around to holding the hearings on the train crash outside of Tacoma. They will hold hearings on the FIU bridge and they will leave no stone unturned. Everyone will take their turn being grilled. Be patient. SF Charlie Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII Greetings toall: Regarding the calcs, you can do what I did: contact FIU . It will cost you only 47 bucks to get them. See Below their response to my e-mail request. Good afternoon, We estimate one hour’s worth of personnel time to prepare and provide the structural calculations documents for production, which would be a charge of$47.00 for these documents and a link to download the documents will be provided. Upon receipt of payment for this charge, we will proceed to prepare these documents for production. Please provide the payment in the form of a check made payable to "Florida International University" and remit the check to our office so that we can proceed with providing you with responsive records. Further, please be advised that we will not be gathering any documents until we receive payment. Lastly, you should be aware that if a requesting party fails to respond to inquiries for clarification, cost estimates, or any other communication from the University for 30 days, the request will be closed.

Thank you and have a nice day.
Lizvette Torres, Paralegal
Office of the General Counsel
Florida International University
Modesto A. Maidique Campus
11200 Southwest 8th Street, PC 511
Miami, FL 33199
Direct: 305.348.0382 | Main: 305.348.2103 | Fax: 305.348.3272

https://generalcounsel.fiu.edu/
Florida International University (FIU) is subject to the State of Florida’s public records law under Chapter 119, F.S., which provides that any records made or received by any public agency in the course of its official business are available for inspection, unless specifically exempted by the Florida Statutes and/or other applicable federal laws.

From: Me
Sent: Monday, April 30, 2018 12:40 PM
To: Lizvette Torres <lizvtorr@fiu.edu>
Subject: RE: FIU Pedestrian Bridge Collapse

Greetings from here:

For the purpose of transparency, may FIU post these calcs the same way that the Contract Plans have been posted and now are available to the public:

https://cdn2.fdot.gov/fiu/13-Denney-Pate-signed-an...

Again, just a PDF will do for most of the engineering public because it is critical to us to know if there is something in our standard calculation procedures that we may not be aware and needs to be addressed in the AASHTO and FDOT Codes and Specifications.

Best regards

Me

From: Lizvette Torres [mailto:lizvtorr@fiu.edu]
Sent: Monday, April 30, 2018 9:36 AM
To: You
Cc: Lizvette Torres <lizvtorr@fiu.edu>
Subject: FW: FIU Pedestrian Bridge Collapse

Good morning,

Our office is in receipt of your request dated April 27, 2018, for Public Records. The Office of the General Counsel will be overseeing the University’s response to your request. If a cost is associated with gathering these documents, you will be provided with a good faith estimate of the costs as quickly as possible. If no estimate is necessary, responsive documents will be provided to you within a reasonable period of time.

Thank you and have a nice day.
Lizvette Torres, Paralegal
Office of the General Counsel
Florida International University
Modesto A. Maidique Campus
11200 Southwest 8th Street, PC 511
Miami, FL 33199
Direct: 305.348.0382 | Main: 305.348.2103 | Fax: 305.348.3272

https://generalcounsel.fiu.edu/
Florida International University (FIU) is subject to the State of Florida’s public records law under Chapter 119, F.S., which provides that any records made or received by any public agency in the course of its official business are available for inspection, unless specifically exempted by the Florida Statutes and/or other applicable federal laws.

From: Me
Sent: Friday, April 27, 2018 4:16 PM
To: Office of the General Counsel <generalc@fiu.edu>
Subject: FIU Pedestrian Bridge Collapse

To whom it may concern:

Please provide public access to the signed and sealed structural calculations for the FUI Pedestrian Bridge that recently collapsed. How can a member of the public get that information?

Best regards

### RE: Miami Pedestrian Bridge, Part VIII

Good job - I wouldn't even know who to contact.
This answers a question I had from the long, detailed article. The docs the engineers looked at are still available to the public.. when article said ~"docs not available except to those close to the investigation" it meant those that Miami Herald is suing for (docs between Feb 19 and Mar 15). We were fortunate those photos/memo dated 2/28/18 were "leaked".

Is this the 2000 pages the four engineers in article went through? in what kind of format? (I assume not printed) $47 is cheap... I'm most curious if there are any calculations for connections. All are about the same. ### RE: Miami Pedestrian Bridge, Part VIII Trust me, it is worthy to get the cals. They are in PDF and about 2000 pages. As they are the calcs for the signed and sealed drawings, they contain calcs about the connections. The 47 bucks are a very small price for some answers to many questions. But again, we do not have the info regarding what else it was done to propose to stress those bars the day of the failure. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (The Mad Spaniard) Trust me, it is worthy to get the cals. Pay To Play. I think I'll take a pass. ### RE: Miami Pedestrian Bridge, Part VIII Another preliminary report from NTSB is out. It shows the pics of the cracks after trhe bridge had been moved (and , I guess, the ones tha Pate said to Tom Andres that were nothing to worry about.) THE CRACKS ARE HUGE!!!!! THIS IS CRAZY!!!! THE BRIDGE IS TELLING THAT IT IS IN TROUBLE!!!!! HOW ANYBODY CAN FIX THAT OVER TRAFFIC!!!!!! ### RE: Miami Pedestrian Bridge, Part VIII OMG! With cracks like that in and around a critical member, they didn't shut down traffic while they worked on it? That's beyond unbelievable, it's irresponsible. It may be found to be criminal, but we'll see. ### RE: Miami Pedestrian Bridge, Part VIII Here is that message so you don't have to look for it: “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,” Pate said." “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.” Agree that it is crazy. Did Denny Pate actually inspect the bridge himself or did he send a Newbie to look at it. ### RE: Miami Pedestrian Bridge, Part VIII Unreal. A clear indication to do some serious analysis of the forces at that connection. I wonder if #1-2 cracked at all.. they'd already tightened those rods and it held. Won't do it now, but will go back and see how this fits with GreenLama's theory - these cracks show initial step of failure. https://www.eng-tips.com/viewthread.cfm?qid=438966 6 Jun 18 21:21 I sense the trigger was described by Gwideman way back... tightening the rods pulled #11/12 toward the edge of the deck. https://www.eng-tips.com/viewthread.cfm?qid=436924 23 Mar 18 17:09 Same theory in "Polish guy's" video https://www.youtube.com/watch?v=znzCubAWIeo&fe... Cutterhead had calculated #11/12 would only have to move about 0.024" to weaken the structure to a point of failure - that showed on first crack photos before it was moved. https://www.eng-tips.com/viewthread.cfm?qid=437029 29 Apr 18 02:27 It's amazing (and bad) that the span didn't collapse when they moved it. Tony Pipitone said it was a matter of pride for FIU and FIGG that ABC only required traffic to be stopped when the span was moved into place. I can see them not wanting to say it needed redesign and start over (as one engineer said should have been done), but it's insane that no one said traffic should be stopped. The workers on the canopy would have seen this, but didn't have their safety harnesses hitched.. with their experience, I wonder if they'd seen cracks like this before. ### RE: Miami Pedestrian Bridge, Part VIII The cracks appear faulted too. How did they come to the conclusion that everything was okay? Wowsers. This is a lot worse looking. Diagonal 11 appears to have cracks at the top and bottom of the section, 45º, faulted, and quite large. ### RE: Miami Pedestrian Bridge, Part VIII Hey, aren't those just shrinkage cracks?... all concrete shrinks, and cracks... Dik ### RE: Miami Pedestrian Bridge, Part VIII to RickyTickyTavi: First photos (~2/24/18, pre-move, after shoring removed, only supported at ends as in practice) showed a small diagonal crack on east side of #11 that continued north along the deck. In these photos, that crack expanded and #11 appears to have moved north about 1/2" - #12 was breaking loose from the deck. The rebar was still holding (not sheared yet?), but the concrete must have been tearing up inside the members... it looks like #11's upper PT rod had broken loose. Wonder if they could have xrayed this. Unbelievable they didn't stop traffic. Everyone is silent because they were told to be, but it's hard to imagine someone (intermediate engineer type) wasn't screaming about this. ### RE: Miami Pedestrian Bridge, Part VIII "It's amazing (and bad) that the span didn't collapse when they moved it." The stresses at that connection were opposite while it was being moved, and much smaller. Member #11 was in tension holding up the cantilevered end during transport. In place it was in compression, supporting over half the weight of the bridge. ### RE: Miami Pedestrian Bridge, Part VIII Those images are disturbing! To make matters worse, #11 was covered with a banner while the structure sat in this distressed state and was being worked on. In summary, #11 was no longer functional (as a result of its triple role of compression/tension/(move)/compression) save for the fact that the structure had not already collapsed. Jacking the PT rods just finished blowing the structure apart. This is beyond stupid! That may be harsh with the advantage of hind sight, but knowledgeable and competent engineers have the advantage of education, experience and peer scrutiny. Even my trade workers would not have allowed that I be this stupid. If I've gone too far with this feel free to delete. ### RE: Miami Pedestrian Bridge, Part VIII Also, if the lower deck has become detached from the #11/#12 joint, the resulting deformation would create a hinge effect on the top deck at the #10/#11 joint. In short, this structure was primed for collapse but we already knew that. ### RE: Miami Pedestrian Bridge, Part VIII There would also be a hinge at the bottom of #10, but neither hinge mattered because neither was intended to have enough strength to make any useful moment resisting contribution. Losing the ability to push that end of the bridge up due to losing the attachment at the base of #11 is the only condition that matters. I guess the NTSB is not participating in an effective coverup after all. It is curious they have released this data ahead of a final report. ### RE: Miami Pedestrian Bridge, Part VIII I'm curious as to the scrutiny the #11 PT rods and accompanying hydraulic equipment is getting. They were obviously up to the task of destroying what was left of the bridge. ### RE: Miami Pedestrian Bridge, Part VIII From Part 1: We'll wait and see what the 'official' cause of the collapse was; hopefully it will be similar to this thread. It would be great to have copies of photographs taken of the 'crack', just to see how insignificant it was. The EoR was likely doing 'damage control' in the event others brought up the crack. It will be interesting to see if the project goes ahead, and, if there is any 'political spin'. It would be nice to see if the funding is challenged. I was really surprised that the collapse was 'instantaneous', without warning, other than maybe the earlier crack. The EoR will likely carry his statement about the insignificance of it to his grave... Dik ### RE: Miami Pedestrian Bridge, Part VIII Wow! I may have missed it before (very possible, given that we have now extended to 8 threads of commentary), but I hadn’t appreciated that the photos of the cracks that we have seen for some time (e.g. scroll up to chris snyder’s post above, dated 11 July) were actually taken on or about 24 February – a couple of weeks BEFORE the bridge was moved. I had been under the impression that these were the cracks that were mentioned in the phone calls AFTER the move (for a transcript, see bimr’s post above, dated 9 August) – but no, the cracks that Denney Pate was saying “we don’t see that there’s any issue there so we’re not concerned about it from that perspective” are the ones in the photos dated 13 and 14 March, as shown in the latest NTSB report: https://www.ntsb.gov/investigations/AccidentReport... I’m surprised (but not totally gob-smacked) that they concluded the bridge was safe to move, given the cracking that they had seen BEFORE the move. But I am absolutely astounded that anybody could possibly conclude that there was no safety issue after the move, with cracks like that?! ### RE: Miami Pedestrian Bridge, Part VIII Based on those photos, the structure had failed at least one or two days before it collapsed. Despite knowledge of that, traffic was allowed to proceed below. Beyond comprehension. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (Sym P. le) This is beyond stupid! That may be harsh with the advantage of hind sight... I think you're wrong about that (being harsh, I mean). A crack like that in my home foundation would keep me awake at night. Brad It's all okay as long as it's okay. ### RE: Miami Pedestrian Bridge, Part VIII I do not like to sound to harsh, but these cracks are beyond shrinkage (Dik - you were joking right?), or result of wrong sequence or lack of post-tensioning - for any engineer with a little common sense these were signs of imminent catastrophic failure. Whoever seen and inspected this bridge when cracked, should immediately stopped any intervention, post-tensioning or keeping this already failing structure over traffic lanes without immediate shoring. It is a long overdue result of playing with the load factors (see my previous posts - and the link to an excellent article on the subject), stringent adherence to codes and design guides, but without slightest understanding of the meaning, and in general promotion of pushy but not so engineering-smart administrators to a position of responsibility. The initial cracks are apparent result of the post-tensioning, and lack of strands at the center of the lower deck - as the structure cracked when it was still on the casting bed, prior to lifting for movement. When the structure was loaded with self weight, it cracked more - as cracked concrete has no capacity for shear - and all stresses at the #11 and #12 top and bottom nodes were carried by "undernourished" steel, but sized accordingly to the code, or design guide for pedestrian brides. It seems, that more rigorous analyses of the stresses in the critical nodes were not performed - or not understand for the implication for the safety of the structure, as this was very innovative design. Which brings another question - what was the role and input of the peer review duds - and were they informed about cracks? I somehow understand the secrecy by NTSB in publishing these photographs (these are just beyond my imagination as these were sings of imminent failure) - but I will immediately suspend the usage of "Design Guide for Pedestrian Bridges", and seriously question the approach towards design for the shear stresses in the crucial nodes of non-redundant structures, by both ACI and ASHTO. It may save some lives down the road. The report by NSTB is fine, finally publishing the evidence of the total neglect by all involved parties - because whoever seen this pictures, should ordered immediate shoring of the span, pending safe removal. ### RE: Miami Pedestrian Bridge, Part VIII I wouldn't call it an "innovative design". Maybe you meant "ignorant". ### RE: Miami Pedestrian Bridge, Part VIII @wiktor: You referred to: "undernourished" steel, but sized accordingly to the code, or design guide for pedestrian brides [sic] and I will immediately suspend the usage of "Design Guide for Pedestrian Bridges" I will bet$100 to the charity of your choice that when the NTSB report and other peer reviews are complete, the root cause has little (if anything) to do with the design codes and design guidelines, but are instead due to fundamentally flawed analysis and design which were not in compliance with those codes - or indeed, in accordance with undergraduate-level structural engineering principles.

The biggest mystery to me is how a team of apparently well-credentialed bridge designers and constructors got it so wrong, at so many points of the whole project - from the fundamental design concept of a faux-cable-stayed bridge, to design detailing of the concrete connections, to not recognising the significance of the cracking observed before the bridge was moved into position, to most baffling of all - not acting on the major cracking observed after the move.

There may well be cause for revision of the various codes to try to capture and prevent these sorts of systemic errors - but just how you can codify protection against "wilful ignorance" by qualified professionals is frankly beyond me.

When you asked "what was the role and input of the peer review duds" [sic], I first thought that it was an apt Freudian slip, but in retrospect, it would seem that the whole peer review process was indeed a "dud" in this case.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (wiktor)

Dik - you were joking right?
... could be...

The type of crack is a clear example of something overstressed. A shrinkage crack does not in any manner resemble what has been shown.

Dik

### RE: Miami Pedestrian Bridge, Part VIII

Looks like Figg's insurers are trying to get out of paying:
https://www.law360.com/articles/1058149/insurers-w...

They say they weren't made aware of the lash-up between Figg and MCM for this project, and therefore have no responsibility to provide coverage. It's easy to see why they want out after reading this article about the insurance aspects of the collapse:
https://www.justinziegler.net/fiu-bridge-collapse-...

It's interesting that the NTSB report cannot be used as evidence in a lawsuit, but can be used in negotiations for a settlement.

### RE: Miami Pedestrian Bridge, Part VIII

Has there been any activity from the Florida's professional engineering association?

Dik

### RE: Miami Pedestrian Bridge, Part VIII

This even made the national news tonight, at least it did on the 'NBC Nightly News with Lester Holt'. They talked about the report being released and showed pictures of the cracks and the video 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

### RE: Miami Pedestrian Bridge, Part VIII

To me the real tragedy is that no one needed to die on that Thursday afternoon. Regardless of any shortcomings of the design or construction process to that day, the imperfect structure stood no matter the improbability of that reality. Yet on that Thursday morning someone decided to play a deadly game of chance and no one had the mettle to stop the insanity. Someone knew or ought to have known and everyone knew or ought to have known that the activities of that day were reckless. Did the Engineer need to hold everyone's hand? The construction principal or site supervisor or foreman? The hydraulic operator? Who said "We shouldn't be doing this!" and who said "Never mind!"

The big players could have argued for fifty years whether they threw good money away on an absurd or whimsical project but no one needed to die.

### RE: Miami Pedestrian Bridge, Part VIII

Wow,

Some of those cracks are deep, 4-6 inches min when someone stuck their tape measure in.

The testing of the bars and concrete look like standard testing to be able to rule out

Snapping of the tendon
Excessive force applied by accident by the jacking ram
Poor concrete mix

But how those cracks could be essentially dismissed as not being a safety concern is bordering on criminally negligent. IMHO.

I think it is now pretty clear that the 11/12 joint either had already failed and the bridge was being held up by the stiffness of the beams or was so close to failure that it didn't take much. Fig 4 is possibly the worse showing the level of stress and movement between no 11 and the base.

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

### RE: Miami Pedestrian Bridge, Part VIII

4
Well then, now that there's further preliminary official reports out I feel there's enough information for me to comment without indiscriminately disparaging the parties involved or without criticizing without sufficient knowledge (for me personally; you folks carry on, I enjoy reading all these comments. I'm being deliberately conservative in not commenting until now given how much public scrutiny this failure has received).

Knowing nothing else, those cracks should have junked the bridge IMO. A flexural, shrinkage, or other crack from casting, moving, or in-service stresses should be partial depth cracks of a hairline nature at worst. Plus, per most standards I've had to design pedestrian bridges to, and per the PCI design handbook which I assume applied to this project, tensile stresses that exceed the modulus of rupture and cause cracking on exposed members should be prevented during moving.

Without mentioning the likely design errors by the EOR, this is troubling from all aspects of the project.

I designed a slab a few years back to span over a trench at a farm. I goofed and forgot to check lifting and handling stresses on the panels for tensile rupture. The panel was completely safe and serviceable but did not meet PCI standards due to these hairline cracks that formed after lifting. The cracks were only 0.010" wide. This is standard industry practice for precast items where I work, this rejection was done on my call with no oversight.

If my cracked panel was a state project then this would have been similarly been rejected right away by the state inspector and I wouldn't have been able to brush it off even if I wanted to. Hairline cracks are not permitted without repair or at least a non-conformance report in our bridge work. I can only imagine that on this bridge there were government inspectors or at least some third-party there inspecting for the owner. This should have instantly been something that the owner and/or the governmental organization overseeing it should have been made aware of, and required a written report from the contractor/engineer on how these cracks should be addressed.

I can't believe that any third-party inspector or overseeing engineer stood by and allowed this to proceed. In my opinion, unless these were hidden from them, they need to share some liability in allowing this to proceed. The engineer should have been required to submit documentation showing that there was no structural issue, that this could be repaired, and that the bridge was not unsafe. I can't see how any of that was done, as it should have identified the impending failure and no work should have been done with traffic under the structure. If these cracks were hidden or their effects minimized in what the third-party inspectors saw then so be it; but assuming they were in the loop I'm very curious to hear what the other officials involved in this project have to say.

I wonder who was pushing for this bridge to go in more; the owner, the governmental organizations, or the EOR/contractor. Sounds like everyone was more than willing to turn a blind eye to this.

Regarding the cracks shown; those are not simple hairline cracks from a bad move of the bridge. That is a failure of the bridge. This is not looking favorable to any involved. I agree with these above who are wondering who gave the "okay" for this and who else was in the background screaming for this to be addressed properly. Could this be the challenger disaster all over again?

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)

### RE: Miami Pedestrian Bridge, Part VIII

Haven't commented thus far for similar reasons to TME. Don't know enough and didn't want to speculate. And still won't speculate.

But those are some big ****ing cracks. Those are so big I really don't want to even call them cracks anymore. All concrete cracks, it's not necessarily a bad thing. We expect most of what we do to crack for one reason or another, that's what the rebar is for. These are in a whole different realm than 'cracking' to me.

### RE: Miami Pedestrian Bridge, Part VIII

I thought one of the outcomes of the Loma Prieta Earthquake was the determination that if cracks are .25 inches/6.35mm or greater, the engineer had to be concerned about rebar dis-bonding and possible rebar deformation.

I went back to look at BDI, the sub-contracting firm who instrumented the bridge for moving. They were hired by Barnhart Crane and Rigging; the SPMT mover. Seems hard to believe they didn't pick up some unusual readings.

I would have thought an engineer would have wanted Impulse Echo testing done ASAP, to get a grasp of the extent of discontinuity resulting from cracking. Maybe Impulse Echo isn't appropriate to prestressed concrete, it that is the case then they should have ordered up Ground Penetrating Radar to map the cracking. It sure seems like they were making decisions in the blind.

As RickyTickyTavi noted, zooming in on Figures 1, 3 & 4 in the NTSB update, one can see faulting & suspect faulting, Vertically, Horizontally & perhaps in Rotation. Finally in Figure 2 we see the diagonal crack in #12 passing through the diaphragm into the #12 buttress column just above the drain pipe where it appears the column ultimately separated from the diaphragm during collapse. It is no small crack, consistently about 20 mils across the section.

A lot of the cracking looks to have taken place when #11 was in tension. I suppose the faulting could have been a result of a change in loading from tension on #11 to compression. If so, that too should have been a huge red flag. Who beside Barnhart Crane and Rigging was privy to the data collected by BDI?

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (3DDave)

I wonder about the difficulties of anchorage to support the asymmetrical weight of a pure cable-stayed bridge and the concentration of the weight on the one central pier that would happen, given the close proximity to the canal.

One option would be to make the two halves equal in weight. Make the short span really thick to act as a counterweight to the other half.

### RE: Miami Pedestrian Bridge, Part VIII

Reports about materials, all fine. Reports about cracks/breaks, terrible. Now for the report about the design, which should be terrible as well.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (epoxybot)

I thought one of the outcomes of the Loma Prieta Earthquake was the determination that if cracks are .25 inches/6.35mm or greater, the engineer had to be concerned about rebar dis-bonding and possible rebar deformation.

I thought it was Northridge, not Loma Prieta. Regardless, the papers I've read which tried to tie crack width to RC performance were not very rigorous. Crack width means something very different for concrete structures designed with proper confinement and detailing to be ductile than it does to structures that were not designed to be ductile. Even then I don't think those papers would apply to PT structures like this bridge.

### RE: Miami Pedestrian Bridge, Part VIII

I was checking out the on-board video of the move to see if there was any indication of the deck cracking at that stage. Although it is possible, I've decided it's more likely just twine.

### RE: Miami Pedestrian Bridge, Part VIII

As I have always stated, #11 was not capable of shearing #12.
The latest releases prove that by showing it was structurally "unsound".
It appears to exhibit and exterior /outward force from internal to the member; this could be a result of reinforced "rebar" buckling once load was applied to it.
Never the less, as I have stated in my videos, Construction Engineering and Photography, that the failure was a result of loads being directed down member #10 and the "resolving" forces being "taken up"/ transferred through the post tensioning in the canopy and the bridge deck.
That neither could sustain those forces as the "intent" was to have forces go down #11 (number 11, being a "failure" could only, marginally take any loads; putting the load path down #10)...
This is a design, conception failure in which the owner, contractor, Figg, FDOT, FIU had "too much skin in the game"...
They could not come to the public with a bridge and road closure (Another part of the contributing factors.).
Further, the PT cables were not performing to the best of their abilities (they should have checked them after the move and determine if they further elongated; reducing their effectiveness... and their ability to act as a "strongback"... The resulting loads, created this structure to failure... of course because of a failed design and application of materials being of "conflict" with post tensioning and the demand loads...
Thank you, to one of my subscribers to showing me this feed tonight.
My intentions are not to offend anyone in this group, just sharing some love and "direction"... I was the only one who insisted no shear took place at 11 & 12; that forces were going down 10 which caused this "physical failure" (of course this is a design failure AND a "corruption failure")...
I also the only one stating, Denny Pate needs immunity so we can get the truth and all the corruption be exposed!
Surely, the parties involved can NOW speak up about PUBLISHED articles by the NTSB (even if just to that limuted degree...BUT, they ALL are still hiding behind "helping the NTSB! That is b.s.)...
Note, those cracks go much deeper, and even down to the post tensioning...
If, this is the first time watching any of my videos, I apologize to my "aggressive comments" in advance... it is just vindication and disgust in my voice...

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (MatthewDB)

One option would be to make the two halves equal in weight. Make the short span really thick to act as a counterweight to the other half.

I like that, and it fits well with my earlier suggestion of having six nearly identical sections (prefabbed nearby) to hang in place while the road is closed for a short time. Real cables, simple engineering, and accelerated construction for the win.

### RE: Miami Pedestrian Bridge, Part VIII

I would like to go on eloquently about structural elements, design, failure modes/progression, etc. But I can't hide my disgust in prissy language.

Jacking on the PT rods was no different than taking a jack hammer to #11.

This bridge did not experience structural failure. It experienced demolition.

In that vein, I find the latest report offensive because it just provides cover by suggesting that something went wrong.

### RE: Miami Pedestrian Bridge, Part VIII

To counterbalance, the two halves need equal leverage. One section was about half the length of the other and therefore would apply between two and four times additional force on the central support to produce the same leverage - putting that weight onto a support next to a water filled canal on Florida, which seems to be mostly limestone that is gradually getting eroded away. https://en.wikipedia.org/wiki/Geology_of_Florida

### RE: Miami Pedestrian Bridge, Part VIII

2
So, some time after the onboard video recording Linkhttps://www.eng-tips.com/postedit.cfm?id=8378200&a...
and before the March 13-14 photos, the fractures, represented as cracks, opened up far beyond those photographed February in the casting location post shoring removal. I wonder if it was a slow propagation or if they suddenly appeared after the PT rod tension was released from #11. The video shows the structure functioning as intended aboard the abutments without sudden failure. I hope more pictures emerge of the failure zone. Very interesting stuff. #11s force cone blowing out the deck and elongating the closest PT strand bundles indicate the failure wasn't as sudden as first thought and progressed over several DAYS!. The failure of the bridge pales in comparison to the glaring human failure. No one who saw the fractures warning of imminent catastrophic failure had the balls to speak up.

I am impressed by the composite concete/steel's lack of sudden failure as mentioned earlier in this thread as one of the material's properties. The span screamed out it's intent for days and no one heeded the call. I'd guess the tradesmen ironworkers, concrete men and operators saw and spoke out the obvious. Cant wait for the final report.

### RE: Miami Pedestrian Bridge, Part VIII

I am including a diagram from a post by SheerForceEng on 25 Mar 18 at 00:42 and comparing it to the picture from Figure 1 of the recent NTSB report that was posted above by Sym P. le on 10 Aug 18 at 22:23.

### RE: Miami Pedestrian Bridge, Part VIII

If you go to the following Miami Herald web page photos of many large cracks not revealed before can be seen. https://www.miamiherald.com/news/local/community/m... These photos were apparently taken on March 13 or March 14 at least one day before the collapse. This if true would indicate that the work on the day of the collapse did not cause the failure. These are the same photos shown in the second interim NTSB report.

Any engineer looking at these cracks could only conclude that the bridge had basically already failed as far as meeting its intended purpose and needed to be closed until a shoring and remediation or demolition plan could be made. The fact that the bridge was not closed in my opinion amounts to negligence, probably to the point of being criminal. Very sad but what else can I say.

The large cracks also appear to show movement of 11 and 12 together, splitting of member 11 probably due to inadequate confinement and shear styrrups at the deck and rotation of 11 and 12 together clockwise looking towards the canal and 11 rotating away from the deck towards the canal. It appears to me that 11 also appears to have moved along the deck face as 11 and 12 moved.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (appster)

If you go to the following Miami Herald web page photos of many large cracks not revealed before can be seen.

I only see the cracks shown in the NTSB preliminary report, nothing new.

However, that article does answer a few of my questions about the FDOT oversight where it appears they were not made aware of the extent of the cracking or even that it cracked at all. I wonder whether they had an on-site inspector but it sounds like they did not. If this is the case then they may be free from liability. I certainly hope so, any engineer who saw those cracks is going to be in the line of fire.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)

### RE: Miami Pedestrian Bridge, Part VIII

I'm starting to wonder if there wasn't a communication breakdown between the people in the field and the EOR. The cracks could have been very small to begin with and that may have been the status as Denny Pate knew it when he made a phone call to the FDOT. The minutes to the meeting on the day of the collapse might be interesting. Did any of the engineers at the meeting actually visit the site and look at the damage between the 13th & the day of the collapse? I just don't see how one can look at the photos of March 13 & 14 and think that wrenching on the PT rods was a good idea. Wasn't Denny Pate in Texas at the time? I'm curious to know if there are any full section photos. It is easy enough for anyone studied in the bridge to place the locations of the discrete photos but good documentation should include some areal photos too.

### RE: Miami Pedestrian Bridge, Part VIII

to TME: I just thought about WHO was supposed to inspect this bridge? When I put in underground electric service, the city inspector came out to make sure the trench was 18" deep, then did a final when completed... very simple job with two inspections.
Assuming this bridge had a typical permit, it seems there would have been city/state inspections at "milestones", one of which would be after the span was moved into place.

rebarden wrote: "I'd guess the tradesmen ironworkers, concrete men and operators saw and spoke out the obvious. Cant wait for the final report."
This is why I'm surprised the two workers tightening the PT rods on #11 didn't have their safety harnesses latched (assuming they were held by the crane, as it must've been since one worker credits latching up when he felt/heard a shift/crack for saving his life). I'd think these guys saw the cracks and would know they aren't typical.. it just seems odd they didn't latch up before jacking. We're looking at it from hindsight, but everyone says such cracks means it already failed, just hadn't collapsed yet.

### RE: Miami Pedestrian Bridge, Part VIII

To TehMightyEngineer (sorry don't know how to do quotes)
To the contrary the article clearly indicates that the FDOT was represented at the morning meeting, it does not indicate if the pictures were shown at the meeting or if only a discussion was held and the FDOT rep. was in a secretarial role as opposed to an engineering or technical role. If the FDOT did not see the photos then it makes me wonder if the photos were kept between the Contractor and the Engineer.

By definition in ultimate design member 11 and 12 had reached technical failure in strain long before the photos of the 13th were taken; the bridge should have been closed and shored until its final fate was decided. In my opinion 11 was overstressed due to axial load and bi-axial bending along with torsion under dead load alone with no applied live (including torsional load imbalance on the bridge) and wind loads. Torsional stability requirements placed significant lateral and torsional load requirements on 11 and joint rigidity placed biaxial moments on 11 and 12.

The only consolation here is that this was probably a more gradual failure than it appeared to be but nobody was listening to the bridge crying out and lives were lost.

Bob App, Retired former PE Ontario

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (chris)

it seems there would have been city/state inspections at "milestones", one of which would be after the span was moved into place.

I agree, I'm surprised there wasn't a post-install inspection being performed. Perhaps it was scheduled to be completed after when the collapse occurred? Hard to say, but I'm sure we'll find out.

#### Quote (appster)

To the contrary the article clearly indicates that the FDOT was represented at the morning meeting, it does not indicate if the pictures were shown at the meeting or if only a discussion was held and the FDOT rep. was in a secretarial role as opposed to an engineering or technical role. If the FDOT did not see the photos then it makes me wonder if the photos were kept between the Contractor and the Engineer.

That wasn't the conclusion I drew but it's open to interpretation and will definitely need to be clarified.

I based my assumption that the key officials and engineers at FDOT hadn't been made aware of the cracking based on this:

#### Quote (Article)

FDOT has said it was not told about “life-safety issues” and did not hear Pate’s message until days later

From: https://www.miamiherald.com/news/local/community/m...

#### Quote (Article)

Also in the statement, FDOT said one of its consultants attended a meeting with the FIU bridge team — including executives from Munilla Construction Management, the contractor, and Figg, the engineering contractor — hours before the collapse that killed at least six people. The statement said no “life-safety issues” were discussed.

From: https://www.miamiherald.com/news/local/community/m...

So, it sounds to me like only an FDOT consultant was at the meeting and that they downplayed the cracking at the meeting. Further, being only hours before the collapse I imagine any images of the cracking had yet to filter up to the engineers in charge oversight for this project at the DOT. As they stated they did not receive Denney Pate's phone call it seems that also didn't reach the FDOT people in time.

But, I of course conclude that this is all preliminary details and likely not the full picture. I'm sure the timeline between FDOT and the bridge cracking being found will be clarified.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)

### RE: Miami Pedestrian Bridge, Part VIII

I don't know if the following has been raised in the discussion yet (there is too much to review) but the use of PT rods in #11 to carry the end of the structure during the move seems to have been too clever by half and may have ultimately led to the disaster (if nothing else, they became a distraction). Use of external strong backs may have been a cosmetic blight on a heavily promoted project, but the additional compression to the already critical #11 and the poorly understood internal stress dynamics from the various stages of this construction process seem to have added a level of complexity that was not overcome.

As suggested by rebardan, the tension release may have resulted in the fracturing. I am curious to know what happens when you place a concrete column under an extreme and complex load and then suddenly introduce an eccentricity by releasing a compression element on one side or by giving a little tug so that you can back off the nut? If cause and effect were conspicuous but did not result in sudden collapse, I suppose some O2 therapy would be permissible as evaluations are made but if these fractures were observed developing over time, would you not come to a not to soon realization that the structure is yielding to gravity and requires immediate intervention (namely shoring)?

I noticed from the time stamp with the images in the Investigative Update that the west side images were taken two hours before the east side images. That's a lot of head scratching. And if I'm not mistaken, that was two days before a two hour meeting on the morning of the catastrophe. I don't wish to make light of a bad situation but rather to shake up the thinking of what was happening with the thinking. This brings me back to my suggestion that the PT rods in #11 were a distraction. Rather than the obvious intervention of shoring up the structure while properly evaluating the damage and conducting remedial work, the focus was on the PT rods. Unfortunately, entropy has a bite and you can't put the genie back in the bottle (See my previous posts).

From Figure #2 in the update, the diagonal crack on #12 below the deck level (and where #12 ultimately failed) indicates that the top of #12 is being pulled toward the centre of the span, perhaps from the structure sagging, though not much, and this too is a clue. Nothing moved much until the end when I believe #11 ruptured under a multitude of funky internal stresses.

Like everyone else, I can't wait to see the final report. I do believe the NTSB does outstanding work.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (Sym P. le)

This brings me back to my suggestion that the PT rods in #11 were a distraction.

Very true. And I think most people have recognised this, but it is a distraction and it was very likely the straw that collapsed the camel. (The camel's back was already broken.)

I believe that unavoidable fact was member 11 and its connection to deck around member 12 was very poorly designed for the anticipated loads. This is likely the case even without the additional stress of the unorthodox cantilevering during placement and the mucking about with the PT cables.

A very badly designed bridge, a ill considered construction and placement and ignoring ALL the warning signs.

Like most accidents this is multifaceted. There are critical mistakes and there are also lost or ignored opportunities of rectifying those mistakes.

### RE: Miami Pedestrian Bridge, Part VIII

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone. Any engineer, even an unqualified one, would have immediately recognized that a collapse was in progress. What he did was he placed a call based on somebody else reporting a "slight cracking" to him. This will have profound implications.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (Fourtyyearsexperience)

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone

40YE, Can you elaborate on where this has been made "perfectly clear"? Or is this really just speculation on your part?
Are you Denney Pate?
Unless you have inside knowledge that the rest of us don't have then whilst it might seem to you and me that such an experienced engineer would realize that those cracks were far beyond what could be described as slight cracking, in reality we just don't know, nor, as yet, what pictures or information was available at this meeting which took place prior to the collapse.

If I've missed something in an article or whatever, please let us all know.

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

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (FortyYearsExperience)

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone.
He didn't know what the conditions of the crack were, when he was reporting on the conditions to FDOT? Really?

It's all okay as long as it's okay.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (FortyYearsExperience)

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone. Any engineer, even an unqualified one, would have immediately recognized that a collapse was in progress.

You would STRONGLY hope this would be the case.

Except this faith in an engineer of 40 years experience doesn't explain why decision were made to continue to go ahead and play with the PT tendons. Nor is it clear why the engineer thought the cracking was serious enough to report, yet not serious enough to inspect himself.

Those photos were taken by people on site. You would have expected SOME engineers would have seen them given a report was made.

### RE: Miami Pedestrian Bridge, Part VIII

I always thought that message from Pate was kind of goofy. When I first heard it, I thought it was from some burnout (forgive me for being judgemental) because there was no "drive" or authority to it like I'm used to hearing from senior engineers.

I'm still not sure what to make of it considering the msg was left after he'd (allegedly) seen the initial #11/12 cracks in Feb (after tensioning, after shoring was removed, but before span was moved), seen the larger cracks (after span was moved), but before the meeting and before the collapse - there seemed to be zero urgency or care... this after everyone else has said it was an "already failed" structure that hadn't fallen yet (a "dead man walking"). I couldn't quickly find the audio, but this with its "uh"s and "um"s makes the point.

"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."

I suspect FYE is being sarcastic, cynical, ??? because it's hard to believe Pate would take responsibility without seeing this.. as if he could say later "I'm not responsible because I was relying on someone else's description".
The part about "something's going to have to be, ya know, done to repair that" sounds ludicrous - I don't see HOW that could be repaired... by injecting epoxy? I questioned if there was any cracking at the south end (#1/2) and just noticed it's not mentioned in the msg, so maybe not. #1/2 was more robust (beefed up on final prints, but not prelims) - maybe because axial forces were higher on 2D analysis... but the 3D (finite element) analysis clearly shows MUCH more strain at the north end. The engineer who ran this (Toomas Kaljas) said it's because of the asymmetric "W" pattern of the trusses.

### RE: Miami Pedestrian Bridge, Part VIII

Seeing those cracks, any responsible engineer would have immediately 'frozen the area of construction and provided temporary shoring.

Dik

### RE: Miami Pedestrian Bridge, Part VIII

chris,

I believe the Toomas Kaljas calculations do not include the post-tension stresses, hence the high tensile stress numbers seen in 10 and 3. They also don't appear to include the pre-loads on the diagonals as a result of the longitudinal post-tensioning on the deck and canopy. I think those loads, carried via shear, were responsible for the cracks seen in some other diagonals spread along their length. I also think the canopy post tensioning was to match the strain in the deck so that the ends of the diagonals moved together, keeping the bridge deck straighter/level.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (FortyYearsExperience)

What is perfectly clear is the Denney Pate (40 years experience) did not see the cracks in person when he reported them by telephone. Any engineer, even an unqualified one, would have immediately recognized that a collapse was in progress. What he did was he placed a call based on somebody else reporting a "slight cracking" to him. This will have profound implications.
After seeing the large cracks, this was my first thought.

It might be that an honest look at the issue of experienced engineers delegating important duties to those with marginal or insufficient experience is the big thing that comes out of this.

#### Quote (LittleInch)

...Are you Denney Pate?
Unless you have inside knowledge that the rest of us don't have then whilst it might seem to you and me that such an experienced engineer would realize that those cracks were far beyond what could be described as slight cracking, in reality we just don't know, nor, as yet, what pictures or information was available at this meeting which took place prior to the collapse. ...
A non-engineer with an average IQ could look at those cracks and realize something was seriously wrong.

#### Quote (thebard3)

He didn't know what the conditions of the crack were, when he was reporting on the conditions to FDOT? Really?
Higher-up engineers are often extremely busy and delegate almost all nuts-and-bolts work to far less experienced underlings, so I'm not sure why this would be surprising.

### RE: Miami Pedestrian Bridge, Part VIII

Hopefully, the judge's ruling will be respected by the FDOT, and their records about the construction, meetings, phone calls, and correspondence included, will be released. This is a state's rights issue, among other things. The NTSB does not need all this information to interrogate the design, which should be their focus. The failure to recognize the imminent collapse of the structure, and then protect the public, should be separated from the technical investigation.

### RE: Miami Pedestrian Bridge, Part VIII

If any of you here ever watch the "Mayday" series which shows many types of NTSB investigations (mainly aircraft accidents but also railway, highway, bridges etc.) they always look into the human factors which may lead to an accident or make an accident worse. They will undoubtedly look into why cracks were ignored or downplayed and why the bridge was not closed.

They also go above and beyond to find the root design, material, and other causes of an accident to pin down the cause or causes and the string of events that led to the accident. This should not prevent the FDOT or any other party releasing information that by law is public. According to an earlier post one may receive copies of the original detailed design calculations for a nominal fee for reproduction costs. Engineers not party to the NTSB investigation have publicly stated in the Miami Herald that the think that the design was deeply flawed; many here have given the same opinion (including myself). Is it ethical to give an opinion in many jurisdictions probably not but it is an engineers nature to look for why something failed and we feel free to speculate based on calculations and our experience.

### RE: Miami Pedestrian Bridge, Part VIII

SFCharlie... the documents held by the FDOT may shed light on the extent of their involvement. For exposure and legal reasons, they may want to appeal the release. NTSB, for sure would want to appeal this... it erodes their being able to 'put a lid on things'.

Dik

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (271828)

Higher-up engineers are often extremely busy and delegate almost all nuts-and-bolts work to far less experienced underlings, so I'm not sure why this would be surprising.
We do understand that, but as the engineer of record, it is incumbent on him to know exactly what the condition is that he is reporting. The now-well-documented discussions that he had with FDOT to imply there was nothing of immediate concern (paraphrasing) should be backed by his explicit knowledge of the condition of the cracks, including some empirical evidence, not by some nebulous assurance of an 'underling' that everything was okay. It will be interesting to learn if he did or did not have the pictures of the 'cracks' prior to this discussion.

It's all okay as long as it's okay.

### RE: Miami Pedestrian Bridge, Part VIII

I really have a hard time seeing the Florida DOT's exposure on this project. Maybe they have a public perception concern or a political concern but unless there is some flaw in their assessment of FIU as an acceptable participant in the Local Agency Program, or there are emails and the like that express concern for the performance of FIU, FIGG and/or MCM or any of the other parties, I just don't see where the FDOT bears much blame. There are so many politicians involved, it may just be they've been told to circle the wagons.

The bridge could just as easily have been a City of Sweetwater project as opposed to FIU. Just like FIU, the City of Sweetwater would have had to apply via the Local Agency Program. The federal statutes state that State Transportation Departments have to maintain chief responsibility for the project but when you read further, it demonstrates how that responsibility is maintained while being delegated to DOT certified contracting entities. So when you look at who was responsible for preforming the design review in lieu of the FDOT, that was Louis Berger. When you look at who was responsible for inspections in lieu of the FDOT, that was the CEI - Bolton, Perez & Associates. This is how the Local Agency Program works, participants can contract out the functions they don't have the expertise to provide. Just like a Municipal Building Dept. may contract out engineering reviews to a private firm. In this sense the FDOT followed the statutes regarding the FHWA & Local Agency Programs. Ultimately, what the federal statues really only require that the State DOTs maintain control of the purse. They can't outsource the oversight to a private firm. The FDOT's role in LAP projects is very much like a Building Dept. that contracts out the engineering & inspection work to private firms. They merely perform the administration, making sure that the work has been reviewed and accepted by the parties charged with these responsibilities.

It would be interesting to know what time of day Denny Pate contacted Tom at the Florida DOT on the 13th, was it before or after the photos were taken. Assuming Tom is the Chief Engineer for FDOT assigned to the project, Tom..., who? Who took the photos? I assume it was a Bolton, Perez & Associates, inspector.

Bolton, Perez & Associates was under contract to FIU, not to FIGG or MCM. What communication structure existed? One would assume any communications by Bolton, Perez & Associates to FIU would automatically be communicated to FIGG & MCM. Rafeal Urdaneta, a Bolton Perez & Associates employee is the one who contacted Alfredo Reyna, the FDOT's Assistant LAP Coordinator notifying him on the 14th of the meeting, the following day. A Bolton, Perez & Associates Newsletter in the Summer of 2015, reports him as a new hire to their CEI team stating, Mr. Urdaneta has over 27 years of experience in civil engineering construction management projects. His experience in public and private projects include: roadways, utilities, wastewater facilities, stormwater and drainage systems, water distribution, high-rise buildings, petroleum platforms, subdivisions and medical centers. Rafeal Urdaneta isn't on the Florida Licensed Professional registry. Assuming Rafeal Urdaneta was the day-to-day on-site inspector for Bolton, Perez & Associates, is there a point that Bolton, Perez & Associates had the responsibility to send a qualified Licensed Engineer to the job site? They were after all, as the FDOT certified CEI, responsible for being the FDOT's eyes on the project.

Alfredo Reyna, the FDOT's Assistant LAP Coordinator, is a Licensed Engineer, yet he states when he attended the meeting on the 15th, which occurred shortly before the bridge failure and collapse that he was not notified of any life-safety issue. It doesn't seem possible that there wasn't any discussion of the cracks, unless he wasn't present for the whole meeting or the matter was discussed separate from the meeting. Alfredo Reyna's job as FDOT's Assistant LAP Coordinator, was to make sure that the money was being spent on work & materials approved by the program & that any changes were applicable for LAP funds or out of program. For instance, he was responsible for determining if the cost of relocating the bridge pylon from the roadway to the canal position fell within the LAP/Tiger Program funding. Essentially his role was as a Civil Works Program examiner. The project inspection criteria for his job is almost entirely based on administrative review of process flow. His attendance at meetings is to determine whether work discussed falls within the program and that the project is meeting the funding timeline.

Assuming my characterization of Bolton, Perez & Associates is accurate, did they not have a responsibility independent of FIGG to determine if the bridge was a hazard to the public? There presence on the canopy at the time of collapses, suggests they were performing the kind of special inspection work often called out by Building Depts. but were they doing the work that the FDOT designates as the CEI responsibility in lieu of FDOT inspections? It is troubling that at the time of the collapse there should have been two people on-site that knew, they needed to abort what they were doing, one was the Bolton, Perez & Associates staffer and the other should have been one of the Structural Technologies staff.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (epoxybot)

Assuming Rafeal Urdaneta was the day-to-day on-site inspector for Bolton, Perez & Associates, is there a point that Bolton, Perez & Associates had the responsibility to send a qualified Licensed Engineer to the job site? They were after all, as the FDOT certified CEI, responsible for being the FDOT's eyes on the project.

For better or worse this is done frequently, at least in my experience. Have not done bridge work or Florida work. Have done a couple of DOT building projects. The 'inspector' usually has to be operating under the supervision of a licensed professional (or structural) engineer. But they themselves do not have to be licensed. Just like most engineering work, the actual work does not have to be done by a licensed engineer, just under the supervision of a professional engineer. For my projects the inspector has usually been an older construction management type or perhaps even a former contractor. Someone who has been around long enough to know how things are supposed to be done and have enough confidence to speak up to contractors who may also have been around forever. But not licensed. Sounds like this case was similar.

Knowing the types that have worked on my job, I would have expected them to speak up on something like this. Those guys tended to speak up about EVERYTHING when I would visit the site, no matter how minute. However that was only when I was actually visiting the site. When I wasn't on site I'd get reports but because there's so much bureaucracy between the inspector and me (the engineer), I wouldn't see their reports until weeks after the fact AT BEST. Usually it was months after the fact before the reports would go from inspector to his bosses at the construction management company to the DOT to the design-build contractor to the architect and then finally to me.

### RE: Miami Pedestrian Bridge, Part VIII

MrHershey,
That is an improper channel for such reports, and can not be expected to work. Reports from the site should reach the design engineer quickly.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (hokie66)

MrHershey,
That is an improper channel for such reports, and can not be expected to work. Reports from the site should reach the design engineer quickly.

I wholeheartedly agree and wish anyone the best of luck in trying to get this particular DOT to change the way they do things. Getting reports months after the fact isn't much better than getting no reports at all.

For what it's worth, that was just the chain of communication for the DOT's inspector, which is the role epoxybot was talking about. There were also typically special inspectors under the contractor in addition to the DOT's inspector. We got those reports a lot quicker since they weren't sitting on the desk of someone at the DOT for weeks/months. Special inspector being under contractor technically isn't allowed by IBC but that's the arrangement the DOT wanted and they're the code authority for their own projects.

### RE: Miami Pedestrian Bridge, Part VIII

(OP)
I might throw in a couple of observations about the inspections:

1. "Special Inspections" is purely an IBC term for buildings - I don't think it applies in any way to bridges. Yes there are bridge inspectors and inspections, but don't confuse the language, contractual restrictions, etc. in the IBC with bridge work....not related at all.

2. Inspectors should and do report up the chain things that appear extraordinary, like large cracks. But their primary focus is on comparing work performed vs. work required by the plans and specifications. It may be that, despite the huge, ugly crack, that the inspector(s) resolved that the engineers knew about it and didn't need their reporting. Or, the work in that vicinity of the bridge was essentially complete and there was no need to get up there to observe how the structure was behaving since they had already reviewed the performed-vs-required aspects of the rebar, concrete placement, curing, etc.

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### RE: Miami Pedestrian Bridge, Part VIII

The responsibilities of the construction inspector is included in the contract documents and the construction inspector responsibilities will be enforced by contract law. I am not aware that a link to the contract documents has ever been posted in this forum. I looked online for the Contract some time ago and was not successful in finding the Contract.

I am not an advocate of engineering (by FIGG Bridge Engineers, Inc.) and inspection (by Bolton, Perez & Associates) being done by different organizations as their tends to be little communication between the parties until something goes wrong.

### RE: Miami Pedestrian Bridge, Part VIII

2
bimr - I've had the same experience in mechanical engineering - when the QA department reports to the head of Manufacturing instead of the head of Engineering, a lot gets swept under the rug where it sometimes festers into a huge problem.

Still, it would not seem as if there needs to be much communicated if nothing is going wrong. There were reports made when some of the reinforcement was found to be out of place prior to pouring the deck, so it's not as if the inspection team was just phoning it in based on casual observation.

I would expect any inspector to make an immediate report where a previously OK portion was suddenly not OK, but I would not expect the bridge to get 24 hour construction site inspection oversight.

Much of the externalization of this event (where this thread stands) has moved into an academic phase, awaiting the transition into legal (lawsuit and possible prosecution) and regulatory participation. I think it is clear there was a design defect and not a materials or workmanship problem. I think it is also clear there was nothing impeding adequate investigation of the discovered defect before selecting a way to deal with it, but there is a lack in public knowledge of who knew what, when they knew it, and how it was determined to proceed. There is a clear line of responsibility for the design, but not a clear chain for what to do for defects of this type.

In this respect the failure is somewhat similar to the Hyatt Regency walkway failure, where those working on site knew the bridge was too flimsy and work crews were told to avoid taking construction materials over it. It isn't identical because the reason it was flimsy was due to a fabricator mod to the design which the fabricator communicated over the phone; there was apparently no analysis**. There were enough irregularities in the rest of the building design that their licenses were pulled anyway. No criminal prosecutions were made.

I think that leaves two avenues for consideration:

1) What sanity checks should be in place for structural calculations that not only ensure those calculations that are performed are done correctly and that all areas of a structure are correctly dealt with?***

2) What system should be in place for directly reporting to emergency personnel that there is an unexpected failure of a major structure, even if the failure has not had an immediate catastrophic result? This reporting should not require any other level within a construction or design firm to authorize or review before making the report. It also requires considering what evidence the construction firm or design firm should have to provide to show the situation has been adequately dealt with. And it requires a means to deal with anti-whistleblower actions by employers and malicious reporting by anyone.

** What I don't understand is if the original walkway rods were too long to easily manage and adding the threads to the middle too difficult, why they didn't propose using a coupler nut instead of offsetting the rods. I also don't understand why the fabricator didn't run the numbers or do a test before proposing the change. Maybe this is a case where Virtual Reality will be useful - if the fabricator saw the installation, perspective corrected, from the top walkway they might have given some consideration to the potential for plummeting all the way to the floor below.

*** In the I35W collapse it is clear there was never a full analysis found for buckling on the gusset plates and only a preliminary check done on the rivets that went through them.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (3DDave)

** What I don't understand is if the original walkway rods were too long to easily manage and adding the threads to the middle too difficult, why they didn't propose using a coupler nut instead of offsetting the rods. I also don't understand why the fabricator didn't run the numbers or do a test before proposing the change. Maybe this is a case where Virtual Reality will be useful - if the fabricator saw the installation, perspective corrected, from the top walkway they might have given some consideration to the potential for plummeting all the way to the floor below.

My sense is that, like too many engineering failures, the Skywalk collapse was more a failure of imagination than a failure of calculation. Nobody who looked at the revised connection scheme had that little spark of intuition that told them that the forces applied to the nuts on the upper rods were doubled. They were fooled by the fact that they looked just like the other joints in the system, and they failed to imagine that they might be loaded differently. And so they didn't even bother to calculate what the difference might be.

As to why they didn't just use coupling nuts out of hand, my guess is that it might have been simple penny pinching. Looking in the McMaster catalog, Grade 8 nuts 1-1/4"-7 are about 2.40 each, while a Grade 8 coupling nut in that size is about fifty bucks--and they would have needed six of them for the project. Of course, that's almost nothing in the overall scheme of a project like that, but I'd guess that someone thought they had a better and cheaper way to skin that cat, and didn't stop to imagine how they might be mistaken. --Bob K. ### RE: Miami Pedestrian Bridge, Part VIII .....and why didn't the flight engineer on KLM 4805 speak up? why were they running a low-power non-standard test on unit 4? how did water get into a methyl isocyanate tank? clearly the o-ring was bad, Eastern Flight 401................. History is littered with the victims of tragedies due to smart people caught in negative feedback loops when they just can't see the obvious. We're always shocked after the fact. It may have happened here too. I pray it never happens to me. IC ### RE: Miami Pedestrian Bridge, Part VIII In reference to the Skywalk collapse, there were several ways it could have been easily prevented - the addition of plate washers, having the channels back to back (which is the typical way to detail something like that, if I'm not mistaken), or using coupling nuts. (Were there really only 3 pairs of suspension rods?) Even after so many years, there seems to be some disagreement (conspiracy theory?) concerning whether or not the altered detail was reviewed at all by an engineer at the design firm, or that they were even made aware that the change was made. ### RE: Miami Pedestrian Bridge, Part VIII ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (ImminentCollapse) .....and why didn't the flight engineer on KLM 4805 speak up? why were they running a low-power non-standard test on unit 4? how did water get into a methyl isocyanate tank? clearly the o-ring was bad, Eastern Flight 401................. This is way off topic, however, you mention methyl-isocyanate, and Bhopal, I presume. Methyl-isocyanate can be safely stored if its temperature is kept below 4°C. This is a tricky thing to do in India. The refrigeration was an active safety system. There was no fail-safe. Apparently, other manufacturers of insecticide generated their methyl-isocyanate as part of the process. There was no attempt to store it. -- JHG ### RE: Miami Pedestrian Bridge, Part VIII This struggle over records highlights a peculiar legal problem - the balance between rapid and effective compensation for victims and criminal prosecution of the guilty for past problems versus wanting better policies that would preclude future problems. I think the court's interest would be in knowing where NTSB feels the investigation stands. It would be a shame to cripple a potential long term solution to move the monetary settlement up a bit. OTOH it would be good if FDOT had a victim's fund to make up for immediate expenses with the expectation of reimbursement from future settlements. And if FDOT doesn't then the Florida state government is capable of special legislation to cover it (I know, I'll see Santa in person first.) drawoh - have a read of https://en.wikipedia.org/wiki/Bhopal_disaster#Caus... Both explanations seem reasonable and both are horrific. As bad as it was, it so clearly could have been worse. ### RE: Miami Pedestrian Bridge, Part VIII (OP) I think the legal problem is that one side wants to keep all the data under wraps to ensure a complete, accurate, and effective process in getting to the true cause. The other side wants the data out in the open NOW rather than later. The Pros of delaying release of the information: 1. Ensures a logical flow of review 2. Eliminates or reduces fear in witnesses and participants from testifying if they don't know whether they will be eventually blamed. 3. Reduces the potential for possible responsible actors from destroying evidence. 4. Avoids a media frenzy based on limited or incomplete information. 5. Avoids a media frenzy based on limited media understanding of engineering principles and processes. 6. Still allows for eventual release of all material to the public, which is a must. The Pros of releasing the information NOW: 1. None that I can think of....perhaps others have some ideas? Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII I do disagree, JAE. See my comment of 22 August, 0046. The NTSB should focus on the technical investigation, and let the chips fall where they may legally. Amendment X of the US Constitution. ### RE: Miami Pedestrian Bridge, Part VIII Agree with JAE (Structural). Unfortunately, the wheels of justice turn very slowly. There is a reason for non-disclosure. Nobody will freely provide information that will prevent a future problem if they are concerned with being sued. The delay in waiting for the NTSB report does not prevent the Owner from moving forward and replacing the bridge. ### RE: Miami Pedestrian Bridge, Part VIII (OP) hokie66, I think if the NTSB is charged only with determining the technical cause of the collapse - and is not focused on the human interactions, processes, sequences, obligations, duties, etc. then they could proceed with publishing it all immediately. But honestly, hokie, I don't know the actual mandate placed on the NTSB with regard to all that human interaction stuff. It seems like they are taking a holistic approach and wanting to ensure that their human interviews are kept uninhibited by fears of prosecution should the public start pointing fingers at particular players....similar to what has been going on in these threads with respect to Mr. Pate. I am a big state's rights guy - and the state has a right to publish this information as it is "public"...the question may be exactly when they publish. Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII Factual information should be available for anyone to do whatever they want with it. This will not change the outcome of the NTSB report or add confusion to what the NTSB is working on. It will, however, allow others to review the material as they see fit. Dik ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (hpaircraft) My sense is that, like too many engineering failures, the Skywalk collapse was more a failure of imagination than a failure of calculation. Agreed. Little thought was given. And at initial glance the connection didn't seem materially different for those who haven't seen similar examples. In my experience there are plenty of mediocre engineers who give little or ZERO thought to construction. (Probably not the case for bridge engineers.) I was once on site when the engineer responsible halted work because a suspended concrete slab on steel didn't have appropriate lateral support. (IMO tilt panels on two perpendicular sides was enough, but I never did the calculations.) The absurdity of it all was the finger pointing at the steel fabricators. Asking them why the lateral steel wasn't installed? The engineer obviously hadn't looked at his own drawings the that steel all attatched to members sitting upon the suspended slab.. The point is too often engineers just focus on the completed structure and don't for a second consider how it is to be built and connection details sometimes seem to be an afterthought. Yet it is connection details that are often the most critical. ### RE: Miami Pedestrian Bridge, Part VIII human900... I'm not sure that's correct. Most engineers I've met are concerned about how the things assembled and the constructability has to/ and is considered. Dik ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (dik) Most engineers I've met are concerned about how the things assembled and the constructability has to/ and is considered. Depends on the task.... Bridges, tunnels, mega highrise etc... For sure the constructability is often considered from the very beginning. Though for more mundane sections of structural engineering it often isn't. Case in point is the Hyatt Regency. The start of the chain of mistakes was the engineer designing something that was eminently not constructible. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (human909 (Structural) ) Case in point is the Hyatt Regency. The start of the chain of mistakes was the engineer designing something that was eminently not constructible. The Hyatt Regency collapse was caused by a fabricator changing the design of the walkway hangers, not a constructability issue: Hyatt Report ### RE: Miami Pedestrian Bridge, Part VIII 3 (OP) bimr, human909 is entirely correct that the start of the chain of mistakes was that the original design by Gillum, the EOR, had a long continuous threaded rod assembly for both walkways...very non-constructable. This led to the change in the design of the hangers. Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII This paper (free to ASCE members) provides a good timeline for the Hyatt design and subsequent collapse, and also a lot of precursors including the collapse of part of the roof during construction. There were lots of warning signs that were missed in the process by the designers/constructors, and this paper sums them up quite concisely. CHRONOLOGY AND CONTEXT OF THE HYATT REGENCY COLLAPSE ### RE: Miami Pedestrian Bridge, Part VIII Not sure if it is accurate to say that the start of the Hyatt Regency chain of mistakes was constructability since the original design drawings were considered by the structural engineer to be conceptual. Miscommunication appears to be the start. Nobody working on the project followed through to prepare design calculations of the connections, and review and approve the construction drawings. Link Miscommunication appears to be rearing its ugly head again on the Miami pedestrian bridge project. ### RE: Miami Pedestrian Bridge, Part VIII (OP) After hearing Jack Gillum talk to one of our local groups a while back - his drawings were not simply conceptual - the hotel was being built off them...what happened was that in that era in KC it was very common and typical for the EOR to leave ALL connection design to the fabricator. In this case, the connection wasn't typical yet was pawned off to others. The fabricator started working on it and either they, or the GC, determined that the single line of rod wasn't feasible/constructable and requested the change to the split rods. The fabricator then was awarded a much larger contract elsewhere and sub-contracted the shop drawings to another fabricator who, upon observing the split hanger design assumed wrongly that the connection had been engineered and completed the drawings for fabrication. Gillum's own EIT had "reviewed" them but didn't realize the problem with a split rod assembly doubling the load on the box channel connections and passed them back as OK. Gillum stated that his first comment upon arriving at the collapse scene was "where's the stiffeners?". He saw right away that the two box channel welds had failed at the rods. Edward Phrang (National Bureau of Standards), the principle investigator for the collapse stated to us also that even without the split in the rods, the connections were still barely able to support the required loads of the walkways in their physical test mock-ups and calculations. bimr - I think your thought that "miscommunication" is the primary culprit is probably accurate - miscommunication and a systemic flaw in the practice of EOR's delegating design tasks to fabricators for unique connection designs. But I think the constructability was the first step in magnifying the flaws in the then current practices. Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII I haven't read it it some years now, but To Engineer Is Human: The Role of Failure in Successful Design by Henry Petroski goes into decent detail on the Hyatt Regency walkway and other failures. https://www.amazon.com/Engineer-Human-Failure-Succ... ### RE: Miami Pedestrian Bridge, Part VIII Wow! Just reviewed the NTSB "updated preliminary report." NTSB didn't have to release these additional photos at this time, yet they did. Surely they knew how damning they'd be. A question for the legal minded: Would releasing them now place the photos in different legal status (w.r.t. lawsuits) than if they were held until the final report is issued? There was some mention earlier that a "NTSB report cannot be used as evidence in a lawsuit." Why release these photos, then turn around and fight tooth-and-nail to block the judge's request for a records release? ### RE: Miami Pedestrian Bridge, Part VIII I suspect it's because the NTSB wants to avoid having newspapers yanking them around. Wouldn't the inability to use the report have more to do with NTSB employees being free from being called to testify as to the contents of the report? Outside litigators should be able to use the evidence in the report as long as it can be independently verified. ### RE: Miami Pedestrian Bridge, Part VIII Admissibility is not cut and dried. As long as it is factual, it should be admissible. But the line between fact and expert opinion is often obscure. https://www.wilsonelser.com/writable/files/Attorne... ### RE: Miami Pedestrian Bridge, Part VIII hokie66, thanks for that article. It clarifies a lot about the procedure. Those photos are giant FACTS, and would be admissible regardless of when released. It's still strange why they released them now. ### RE: Miami Pedestrian Bridge, Part VIII I wonder if the images were going to come out one way or another and NTSB released them so that they could stay in control of the flow of information? Purely conjecture on my part. Maybe they just wanted to give us more info so they could read more about it in this thread? Ian Riley, PE, SE Professional Engineer (ME, NH, MA) Structural Engineer (IL) American Concrete Industries https://www.facebook.com/AmericanConcrete/ ### RE: Miami Pedestrian Bridge, Part VIII On a job interview back in the day, the engineer I chatted with new the two engineers (P.E.'s in Missouri) involved in reviewing the drawings for the Hyatt Reg. design. They caught the problem, but because of the time pressures brought by their customer, they signed and stamped the drawings...with attached notes of the required changes required... Those notes were "lost" as can be the case in any construction firm. The two engineers in question were highly regarded but both lost their licenses to practice, and at one time were facing prison sentences... Remember, do not sign off on any engineering design that does not meet your design assessment, period. P.E. ### RE: Miami Pedestrian Bridge, Part VIII That would fall under "Punishment of the innocent." Bill -------------------- "Why not the best?" Jimmy Carter ### RE: Miami Pedestrian Bridge, Part VIII 2 #### Quote (bimr) The Hyatt Regency collapse was caused by a fabricator changing the design of the walkway hangers, not a constructability issue: That is a simplified view and doesn't consider the events before and after. The vast majority of accidents have chains of events that are the cause. No different with The Hyatt Regency nor in the case of this bridge collapse. #### Quote (bimr) Not sure if it is accurate to say that the start of the Hyatt Regency chain of mistakes was constructability since the original design drawings were considered by the structural engineer to be conceptual. You sound almost as desperate to win an argument as the engineer is to escape blame. Of course the structural engineer is going to claim that! Weasel words to escape blame. "The engineer of record further contended that it was common practice in the industry for the structural engineer to leave the design of steel-to-steel connections to the fabricator. The original design provided in the structural drawings was intended only to be conceptual." Yep. But if you design is largely unconstructable and many of the obvious fabricator solutions change the structural loads significantly then there is a problem with supplying "conceptual drawings".... #### Quote (JAE) bimr, human909 is entirely correct that the start of the chain of mistakes was that the original design by Gillum, the EOR, had a long continuous threaded rod assembly for both walkways...very non-constructable. Thanks. ### RE: Miami Pedestrian Bridge, Part VIII Regarding the issue of unconstructiblity, I wonder if we’re too quick to accept the popular narrative on that? The pyramids, Roman aqueducts, the Forbidden City, medieval cathedrals, London Bridge, Manhattan skyscrapers, the Panama Canal, Hoover Dam, etc., etc. were built, to say nothing of the Apollo 11 lunar project or aircraft carriers. And yet steelworkers in Kansas City tell us they were unable to thread some rods through some purlins or run some nuts a long way up a threaded rod? Perhaps either they should take more pride in their craft or engineers are quick to let contractors dictate the design vs. requiring them to build what they bid upon? ### RE: Miami Pedestrian Bridge, Part VIII (OP) I don't think it was "we can't do it" but rather "let's do it smarter". Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII I think the expected problem was along the lines of being unable to transport threaded rod that's a bit over one inch diameter and nearly 45 feet long from the fabricator to the job site to the installation without damaging the threads or bending them so much as to be useless. Recall that along with turning nuts halfway up, they would have to slide the cross beams the same distance first. Unlike post-tension rods where only the ends need protection, nearly half the length of the proposed full-length rods would be subject to damage that would prevent them from being usable. Thread damage could be cleaned up, and probably bent rod as well, but why not avoid those problems entirely? Looking again at the NTSB report it just looks like no one gave serious consideration to the structural aspects an instead concentrated on making the walkways easier to install, even failing to pre-camber the beams so they would be straight when the concrete load was added, resulting in even more concrete being added to level them. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (Archie264) Regarding the issue of unconstructiblity, I wonder if we’re too quick to accept the popular narrative on that? The pyramids, Roman aqueducts, the Forbidden City, medieval cathedrals, London Bridge, Manhattan skyscrapers, the Panama Canal, Hoover Dam, etc., etc. were built, to say nothing of the Apollo 11 lunar project or aircraft carriers. And yet steelworkers in Kansas City tell us they were unable to thread some rods through some purlins or run some nuts a long way up a threaded rod? Perhaps either they should take more pride in their craft or engineers are quick to let contractors dictate the design vs. requiring them to build what they bid upon? I hope you are being facetious here. Otherwise you are displaying exactly the characteristics that are an issue among some structural engineers. Yes steelworkers were unable to do this. It was a totally impractical design and if that isn't obvious to you then you need to go out to the fabrication shop and to site a little more often. Perhap you need to take more pride in your craft AND understand how steelwork is constructed. #### Quote (JAE) I don't think it was "we can't do it" but rather "let's do it smarter". No. It could not be practically done in the way that was proposed. Letting steel fabricators decide on unusual connections is dangerous. They are enough to know what looks right and doesn't. They are not structural engineers. So any abnormal connections really need to be thought out. ### RE: Miami Pedestrian Bridge, Part VIII Piling on Archie a bit here, but his comment sounds like an architect. ### RE: Miami Pedestrian Bridge, Part VIII It is a matter of perspective. If instead of using a 40 ft. 1" diameter threaded rod to hang the walkway, the designer used a 40 ft. steel column for support, no one would have complained about constructability, even though the column would be far more expensive and laborious to transport and install. ### RE: Miami Pedestrian Bridge, Part VIII (OP) Human909 My comment that you quoted isn’t in disagreement with your answer so I’m not sure why you quoted me. ?? I was simply asserting that it was POSSIBLE to construct it as originally designed...just a very poor design with other BETTER ways to do it smarter. I agree with what you said...why pick on me? Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII @Archie264: Yes, long threaded rod can be obtained (e.g. threaded stress-bar), but in general, only the ends of the cut lengths are used for turning nuts - I don't think I have ever seen a job where a nut was required to be run half way or more along the bar during installation. The idea of doing this on a hanging 40-foot threaded rod, having first slid up and supported the beam which the nut will ultimately support (without damaging the threads for the nut which must follow), sounds pretty diabolical to me. Yes, almost anything is in principle "constructable", but when I think about "constructability", and when my team conducts "Constructability Reviews", these sorts of details would be eliminated as not being practically or economically or safely constructable. http://julianh72.blogspot.com ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (Compositepro) It is a matter of perspective. If instead of using a 40 ft. 1" diameter threaded rod to hang the walkway, the designer used a 40 ft. steel column for support A 40ft column is relatively simple to fabricate, transport and install. If for whatever reasons the fabricators desire to splice or butt weld it then these are known techniques. #### Quote (Compositepro) even though the column would be far more expensive and laborious to transport and install. I dispute that. (But even on the expensive but because the difficulties discussed will eventually lead to longer man hours and possibly custom production. If thread damage occurs then the headaches just get bigger.) Fabricating and erecting long columns is in the standard experience of fabricators and steelworkers. Dealing with extremely long threaded rod is not. To get continuous threaded rod of that length is likely to be a custom order. The difficulty starts at procurement and continues from there... It is entirely impractical. Threaded collars joining the threading rods seems a possible solution. But so does the proposed solution to a non structural engineer. How is the fabricator meant to know? ### RE: Miami Pedestrian Bridge, Part VIII 2 #### Quote: Piling on Archie a bit here, but his comment sounds like an architect. That’s not piling on, Hokie, as Alpha Dog here, which you most emphatically are, directing a comment about me instead of to me is simply a signal to attack. No big whoop; that’s how these forums work. But the (shall we say?) “enthusiasm” of the responses somewhat illustrates my point, which is, that engineers are too often browbeaten into conformity by the consensus of the project team. In the KC project surely a properly-sized coupling nut would have worked? But that probably never even entered into the reviewing engineer’s mind as the fabricator simply told him his design wouldn’t work and that the fabricator’s design would. That’s not something that would slip by a seasoned engineer such as yourself, of course, but that’s not who was reviewing it. I contend that imbuing a culture of submitting to the consensus of the project team (not the design team) as the default position, instead of first trying to defend one’s design, either explicitly or by example, is dangerous. ### RE: Miami Pedestrian Bridge, Part VIII "Had this change in hanger rod detail not been made, the ultimate capacity of the box beam-hanger rod connection would still have been far short of that expected of a connection designed in accordance with the AISC Specification." "The box beam-hanger rod connection would not have satisfied the Kansas City Building Code under the original hanger rod detail (continuous rod)." Link The NIST report clearly states that the original design of the Hyatt walkway was deficient. The changed design was also deficient. The focus on whether or not the design was impractical is misplaced. The actions of the structural engineer of record to seal the design documents without verifying the soundness of the structural design was considered to be unethical. ### RE: Miami Pedestrian Bridge, Part VIII Browbeating. Think any of that happened within the trailers surrounding the FIU bridge immediately prior to the collapse? ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (Archie264) But the (shall we say?) “enthusiasm” of the responses somewhat illustrates my point, which is, that engineers are too often browbeaten into conformity by the consensus of the project team. In the KC project surely a properly-sized coupling nut would have worked? But that probably never even entered into the reviewing engineer’s mind as the fabricator simply told him his design wouldn’t work and that the fabricator’s design would. That’s not something that would slip by a seasoned engineer such as yourself, of course, but that’s not who was reviewing it. I contend that imbuing a culture of submitting to the consensus of the project team (not the design team) as the default position, instead of first trying to defend one’s design, either explicitly or by example, is dangerous. Browbeaten to conformity? I'm sorry you feel that way. Though I'd say in this case it is less of an 'engineers' thing and more of a human and internet forums thing. And it definately can be an issue. However there is no evidence that browbeating was an the issue in the Hyatt Regency being designed initially in an unconstructable manner. ### RE: Miami Pedestrian Bridge, Part VIII 3 I learned early in my career that 9/10 when a contractor calls you up asking for a change after the contract has been awarded it is because they didn't bid the contract the way it was designed and are hoping to increase their margin. ### RE: Miami Pedestrian Bridge, Part VIII Round these parts, if there's a change proposed it better come with a saving passed onto the client for it to be considered, but 9/10 times the contractor doesn't understand the engineering principles at play and why it was the way it was. We've generally done all the hard thinking for them, it's a hard lesson I've learnt over time, you cannot leave options open to them to fill in the gaps with the way they would rather detail or build critical elements. Missing or poor detailing always comes back to get you. ### RE: Miami Pedestrian Bridge, Part VIII I may have missed it, but has the bridge transport procedure been fully addressed? The original plans showed an idealized continuous ramp that allowed the movers to gracefully swing and move the bridge from the construction area to the installation site, but videos and images clearly showed that several short ramps were used to run both ends of the bridge off the curb, and awkwardly jump the far end over the highway center divider, at an angle. I realize the movers had built-in height adjusters, but that move over the divider has always bothered me because it looked like it would be very easy to flex and/or twist the bridge as it went over the divider, or bounce the cantilevered end with a sudden vertical adjustment. ### RE: Miami Pedestrian Bridge, Part VIII There are photos showing that the concrete had only minor cracks after it was set in position and that only after the post-tensioning was relieved on member #11 (the diagonal nearest the canal) did the significant amount of spalling and rupture seem to occur. While transport damage might have occurred, my opinion is that the final straw was the choice to try to restore the positions of #11 and #12 by restoring tension in the threaded bars in the diagonal without appreciating that tensioning would only make the positions worse. Sort of like saying - "His sedentary lifestyle and fondness for high calorie snacks contributed to his death, but his inability to out run the bulls at Pamplona was literally the final step in a long journey that started with his first cupcake at age 5 that later joined a love for Hemingway novels." ### RE: Miami Pedestrian Bridge, Part VIII You have a way with words, Dave. grin Bill -------------------- "Why not the best?" Jimmy Carter ### RE: Miami Pedestrian Bridge, Part VIII Hemingway resolves dramatic tension a helluva lot better than this bridge did. ### RE: Miami Pedestrian Bridge, Part VIII Just saw this about OSHA fines. Still thinking how Navarro Brown wasn't hooked to safety harness, and the other worker hooked up when he heard/felt movement. I can't imagine people working up there with those big cracks at 11/12/deck without ensuring they were hooked up safely. https://www.local10.com/news/florida/miami-dade/mu... ### RE: Miami Pedestrian Bridge, Part VIII Those fines are peanuts, but it's likely just the beginning of what it will cost them, moneywise. The damage to the reputations of the people and firms involved will be far more costly, though. ### RE: Miami Pedestrian Bridge, Part VIII Tried looking for the actual OSHA reports on OSHA's website. No luck. But their search system kind of sucks. ### RE: Miami Pedestrian Bridge, Part VIII Apologies in advance for forgetting how to post links. Here is a news release dated September 18 that contains links to citations (in PDF form) for each of the 5 companies: Link. Each citation includes an "Inspection Number" that might be of use. I tried using one of the Inspection Numbers in the OSHA accident search page Link in the "Insp Nr:" box with no results, so maybe the reports aren't publicly available yet. If a site's built-in search engine is crappy, try using Google's "search-string site:URL" search function: "miami bridge site:https://www.osha.gov/". This allows you to use all of Google's search functions on the site's contents. Apparently the reports are not stored on-site as searchable items. ### RE: Miami Pedestrian Bridge, Part VIII Judge Orders State To Turn Over FIU Bridge Records #### Quote (CBS 4 Miami) Siding with the Miami Herald, a Tallahassee judge Tuesday ordered state transportation officials to hand over records related to a March bridge collapse at Florida International University that resulted in six deaths. Matt Yurus reports. SF Charlie Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII The Miami Herald is oddly silent on this? Ahh! digging deeper reveals This is old news (from August) Sorry. ### RE: Miami Pedestrian Bridge, Part VIII I found the OSHA Inspection Detail Page that accepts the "Inspection Number" taken from each PDF citation noted in my post of 20 Sep 18 21:03 - Link. The Insp Nrs are: • 1306456 Figg Bridge Engineers • 1304055 Network ESI • 1303015 Structural Technologies • 1304240 Munilla Construction Management • 1304351 Structural Group of S. Florida and the completed Detail Pages for all of the inspections are here: Link. Each entry includes a "Related Activity" at the end that has an Inspection Number for a similar incident. These Inspection Numbers can also be used to search for "Fatality and Catastrophe Investigation Summaries" on this page: Link. The five Insp Nrs all return 0 search results, probably because the cases are still open - the Case Status for each of the citations are listed as either "Open" or "Pending Abatement". Each Detail Page also lists a common "Report ID" of 0418800 at the top, but a Google Search for it indicates it is a generic report number that has been applied to multiple incidents spanning many years. ### RE: Miami Pedestrian Bridge, Part VIII This is a followup to my post of 22 Sep 18 05:35 - apologies for any thread protocol violations - this is all new to me and I'm just wingin' it! The Case Status for all five Inspection Numbers are now listed as "Pending Abatement". The Detail Page for Insp. Nr. 1303015 (Structural Technologies - Link) includes a "Related Activity - Accident ID" of 1318855, with keywords "bridge, fall, collapse" and a summary of: At 2:00 p.m. on March 15, 2018, a crew of six employees were working on a bridge and were tightening post tensioning rods when it collapsed. One employee was killed and the other five employees were hospitalized with multiple injuries. I couldn't find any info on Accident 1318855, but I did a search in the "Fatality and Catastrophe Summaries" page for "bridge collapse" and found an "Accident Report Detail" for - Accident: 104149.015: Link. It includes the same summary shown above. I assume more information will be available when the Case Status for Insp. Nr. 1303015 is marked as "Closed". ### RE: Miami Pedestrian Bridge, Part VIII Unrelated to the FIU bridge, but compare the reactions and closures after finding a cracked beam in this SF structure to not even closing the road under the FIU span with MAJOR cracks. Another article said the total shutdown was "out of an abundance of caution" - caution was completely missing in FL. "Cracked steel beam shuts down SF’s new Transbay Transit Center" https://www.sfchronicle.com/bayarea/matier-ross/ar... Interesting above. I'd only heard about two people on the canopy, but did see more in a recently posted video or photo. Wondering if the others used safety harnesses. ### RE: Miami Pedestrian Bridge, Part VIII Regarding my post of 26 Sep 18 04:00, the OSHA summary says one worker was killed and five others were hospitalized, but the news reports at the time only mention one dead and four injured. This March 17 ABC News article - Link - states one employee of VSL Structural Technologies (Navaro Brown) was killed and his two co-workers were hospitalized, then later in the article it says first responders pulled "four unconscious construction workers" from the rubble but it was unclear if that total included the VSL workers. Brown died after being transported to a hospital, so perhaps the OSHA summary is mistakenly including his hospitalization among the "five others". Also, in the OSHA news release of September 18 - Link - two of the five companies (Structural Technologies and Munilla Construction) received identical citations that mention 5 workers (Navaro plus the 4 others?): ... employees had installed a single rope lifeline on the canopy of a pedestrian bridge for five employees who were all connected to the same horizontal lifeline ... ### RE: Miami Pedestrian Bridge, Part VIII Well in bridge engineering cracks in steel beams are much more serious than cracks in concrete beams. However, the cracks in the FIU bridge where they can slide a folding rule in are alarming to me. I have designed highway bridges for years before stepping into my current role of inspecting the fabrication of steel and P/S concrete members for the DOT. Considering the factor of safety that is inherent in the AASHTO Code, something very basic had to have been overlooked to have a bridge fail under essentially its own selfweight. In concrete, a new approach to analyzing tricky concrete design problems is the Strut-And-Tie modeling. I wonder if there was something there related to S-A-T that was missed? ### RE: Miami Pedestrian Bridge, Part VIII 2 #### Quote (Dinosaur) ...I wonder if there was something there related to S-A-T that was missed? Probably the "tie" part. ### RE: Miami Pedestrian Bridge, Part VIII 2 Having read the 9 Aug NTSB update which contains 5 photos on the cracked joint at the bottom of Member 11 taken a few days prior to the collapse I cannot help but to put forward my own opinion after working in the civil engineering industry for 54 years. (1) The persons who have access to the photos showing the locations, severity and and extents of the cracks would appear to have inadequate knowledge of structural engineering if they were party to permitting the bridge to be fixed in situ with live traffic flowing underneath. (2) The cracks are sufficient indications confirming a major connection failure/under-design was taking place/present at the bottom of Member 11 which carried one of the heaviest loads. Diagonal member 11 could only perform its structural duty if it could be adequately restrained by the horizontal deck by counterbalancing its huge axial force, thereby putting the deck in large tension. The deck showed cracking spreading 45 degree on both side to the back which has nothing but air to stop the diagonal member 11 from pushing outward. The first four photos in NTSB8 Aug Update clearly indicate the deck was incapable of holding the Member 11 in place resulting the alarming separations of concrete. (3) The pattern, extent and severity of the cracks are enough to halt the construction process immediately it requires a permanent cure. The cracks are major, structural and requiring a substantial rectification and/or possibly a local joint strengthening. If the same bridge were to rebuilt to the same design with the same materials it would simply collapse again. (4) The cracks discovered before the collapse are so severe that finding out the root cause had to be more important than completing the construction as further construction activities could make the bridge less safe. In the end it was the adjustment of the tension in the bridge that triggered its collapse. In the 9 Aug NTSB update Figure 4 shows a small triangular piece of Member 11 was still attached to the deck with the rest of Member 11 totally sheared off horizontally. Figure 1 and 2 show the deck on the left and right side of Member 11 "had" sheared off and totally separated from the rest of the deck at the deck level. The sheared off portions were monolithic with the vertical member 12 but there was nothing but air to prevent the cracked portion of the bridge from moving further away. Are these four photos on their own not enough to tell every structural engineer that something huge is going to pop? ### RE: Miami Pedestrian Bridge, Part VIII ### RE: Miami Pedestrian Bridge, Part VIII Thank you, Pete. That appears to make it official; the failure of this bridge is due to engineering design errors. Even if the contractor(s) also messed something up they've confirmed what I believe we all suspected; that there were design errors in both capacity and load at that end joint. Given the convoluted nature of the liable parties and timeline of events combined with the very alarming photos and reports; I would reason this could have very far reaching consequences for the structural engineering industry. I wonder how insulated FDOT, FIU, and any other authorities and owners are on this? Ian Riley, PE, SE Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL) American Concrete Industries https://www.facebook.com/AmericanConcrete/ ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (TehMightyEngineer) I wonder how insulated FDOT, FIU, and any other authorities and owners are on this? I would expect that level of insulation to be directly proportional to each organization's level in the government hierarchy. Brad Waybright It's all okay as long as it's okay. ### RE: Miami Pedestrian Bridge, Part VIII Yes I think many of us here had zeroed in on the 11/12 joint connection. This is the text from the actual update "Although the evaluation is ongoing, the assessment has determined that errors were made in design of the northernmost nodal region of the 174-foot-long span, where two truss members were connected to the bridge deck. These design errors resulted in (1) overestimation of the capacity (resistance) of a critical section through the node comprised of diagonal member 11 and vertical member 12; and (2) apparent underestimation of the demand (load) on that same critical section. Additionally, the FHWA evaluation determined that the cracking observed in the node prior to the collapse is consistent with the identified errors." So basically it got bitten from both ends - not enough capacity to resist the forces they thought were going into it AND underestimate of the forces going into it. The final report will be interesting to see how they analysed it and how they dealt with the new and unique design issues coming from a concrete truss design. Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Miami Pedestrian Bridge, Part VIII For sure it's an oversimplification, but from my understanding of the process, this seems to illustrate the dangers of checking one 'black box' FEA with another 'black box' FEA. I suppose the estimation of the actual shear capacity could become very complex, but the loading should have been fairly straightforward with hand comps that would get within a few percentage points. A conservative approximation of the shear capacity of the section would also be fairly straightforward. ### RE: Miami Pedestrian Bridge, Part VIII I think there are a lot of political interests in Miami that want to foist a good portion of blame on the FDOT (State purse). The last report I read from the Miami Herald seemed obsessed with communications between the Governor's Office & the FDOT immediately following the bridge collapse. Florida International University official's response immediately after the collapse was somewhat flatfooted. Their umbrage over the FDOT's statement, in which FDOT distanced themselves from the project, paints FIU officials as, not quite processing the caliber of leadership to have been entrusted with the project, to begin with. FIU was the unquestionable principal authority for the project. As part of the University Bridge project, FIU applied for and received Local Public Agency (LPA) status, by way of the FHWA & FDOT for this project. This made FIU the governing authority (municipality) responsible for the execution of the project. The way I see it, if a City (FIU) builds a bridge over railroad tracks (FDOT Hwy) and the bridge collapses, it isn't the railroad company that is responsible simply because they enforced certain easement requirements, right-of-way restrictions, a list of safety requirements or gave preliminary commentary on the design of what passes through the airspace immediately over their railroad tracks. Maybe FDOT has played a deeper role in the project but on the surface, their role was by intent to be the purse keeper & auditor. In essence, the Tiger Program was for the FHWA & in some cases, State DOTs, a Redevelopment Agency (Economic Stimulus) Program for which they were its administrators. Simply because they enforced standards on anything that encroached on their right-of-way, doesn't automatically make them an acting responsible participant. I'm actually surprised FIU's role hasn't received a lot more scrutiny by the press. If FIU assumed they could manage their LPA status by the purchase of a-la-carte professional services, then maybe they should have left the decision about what bridge was built to a firm experienced in planning. T.Y. Linn was the planning firm that prepared the original areal concept. I wonder what they had to say about the MCM/FIGG submission. I question whether anyone at FIU, with a background in construction, was given charge of the project. The key decision maker seems to have been FIU's head of Finance. FIU officials seemed completely enamored with the bridge design. ### RE: Miami Pedestrian Bridge, Part VIII ENR reported this from FIGG: #### Quote (ENR) A statement from Tallahassee, Fla.-based FIGG Bridge Engineers, the project’s engineer of record, argued that the NTSB’s analysis was based on an early version of the design, and not the final one. “The update refers to the calculations on file, which were done prior to incorporating all final design comments and prior to the production of the construction plans,” the firm explained. FIGG’s statement further stresses that: “The investigative update is just that—an update on certain preliminary facts, and NTSB underscores that no probable cause conclusion should be drawn from the update.” Source: Link ### RE: Miami Pedestrian Bridge, Part VIII I just hope that the NTSB does not just focus on the locus of the failure. Rather, the overall concept of building a concrete truss/frame, complicated by post-tensioning of some members, should be closely examined. Unlike a steel bridge, which readily forgives bending in individual members and joints, a rigid concrete frame does not. The shortening of various members by shrinkage and applied axial force would have been resisted by other members, and this resulted in cracking which was observed long before the bridge was erected. The concept doomed the bridge, then stubbornness brought it down. ### RE: Miami Pedestrian Bridge, Part VIII So what FIGG seems to be saying is that we did the analysis and calculations, then changed a bunch of stuff to produce some final construction details, but hadn't got round to updating the analysis? Surely FIGG would have supplied the NTSB with the final/latest set of design deliverables and analysis / calculations to review?? This makes no sense to me. Ultimately though I do think Hokie has it right. This design was fatally flawed from day one as a concept. Quite how it got through any round of reviews or design analysis without someone having the strength or responsibility to truly challenge this design might be its lasting legacy. Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Miami Pedestrian Bridge, Part VIII "The update refers to the calculations on file, which were done prior to incorporating all final design comments and prior to the production of the construction plans..." Re-read that statement, what it does NOT say is that the calculations pertaining to the point of failure changed in any way from the calculations on file to the final ones. If somebody criticizes your work, and you say "But we did it just right- and there's the bridge to prove it!"- that's great. But after the bridge falls down, anything said to justify your work carries very little weight. (no pun intended). ### RE: Miami Pedestrian Bridge, Part VIII "... flawed from day one ..." And then the holes in the swiss cheese lined up leading to loss of life. I think it is going to be interesting reading the final report where they detail all the events that led to this tragedy. ### RE: Miami Pedestrian Bridge, Part VIII A few notes from the second update: 1) ... errors were made in design of the northernmost nodal region ... 2) ... the cracking observed in the node prior to the collapse is consistent with the identified errors. 3) ... The investigation continues to examine the design, review, and construction processes as well as the actions taken once the cracking was observed. This still leaves room for a flawed design that remained spanning until its demise was hastened by unwitting activity. It is reassuring to know that construction materials (concrete, rebar, PT rods, etc.) were fully adequate for their specified properties and these suppliers should not be tarnished by their association with this project. ### RE: Miami Pedestrian Bridge, Part VIII There are 18 lawsuits against 25 firms. Apparently, even the firm that supplied mats for the bridge mover is included. The judge won't let any of the company's out of the lawsuits, yet. Meanwhile, the lawyers are feasting and there is real concern that the attorneys' fees will eat up the money the insurance companies will pay out. It is Miami-Dade County Court. NBC: Victim’s Father Frustrated As FIU Bridge Litigation Drags On Link ### RE: Miami Pedestrian Bridge, Part VIII The NTSB is taking too long. That is part of the problem. And the court is the other part...it should release many of the defendants, e.g. the mat supplier. ### RE: Miami Pedestrian Bridge, Part VIII From the MSN article-- "where the reliable donor to local races has won contracts for projects at PortMiami and Miami International Airport". Sounds like quid-pro-quo. Brad Waybright It's all okay as long as it's okay. ### RE: Miami Pedestrian Bridge, Part VIII FDOT was apparently more involved than we've been led to believe. Another revelation is that an engineer at FDOT questioned the adequacy of the north end of the span for shear, in March of 2016. The answer - 'it'll be fine'. FDOT Needs to Come Clean About Its Role in FIU Bridge Construction ### RE: Miami Pedestrian Bridge, Part VIII 2 I don't see much that is new information in the ENR Editorial submission. What is becoming conspicuous is the omission of FIU as the governing body responsible for the entire project. It can't be overlooked that the political powers of greater Miami & FIU would not care for the Miami Herald to shine the spotlight in FIU's direction. Likewise FIU seems a bit disoriented by the idea that they took upon themselves the role of a DOT. Maybe they thought they were an Arms-Length DOT because they hired lots of companies to execute the plan but they nonetheless bear the responsibility of functioning as a Municipality, that asked for & received permission to act on their own. ### RE: Miami Pedestrian Bridge, Part VIII The editorial is from the Miami Herald, March 17 Another story from March 15 about Kevin Hanson, the guy who took the pictures and passed them to higher-ups. He was on top of the bridge when it came down and was in a coma for 5 months, and is brain damaged. The story says the probe was held up during the Government Shutdown. Big argument about Hanson's pictures, which are different than those from NTSB. EDIT: The article also contains videos with comments from Hanson's kids and the widow of the construction worker who died, Navarro Brown. Many more recent stories - only so many free views per month, but this can be bypassed in Firefox by right-clicking a link and opening it in a New Private Window. ### RE: Miami Pedestrian Bridge, Part VIII It may be surprise to know that it is common for concrete to crack. In the best concrete show pieces, say the Charles De Gaulle airport, you can still find cracks among the best concrete finishes when you look out for them. Concrete surface will crack easily during its curing stage when the heat hydration given out by the cement's chemical action with water after pouring. The heat hydration can cause uneven temperatures and differential stress in the concrete body, say the concrete near the formwork is unavoidably cooling faster than its interior. Concrete would be still green, plastic and has not developed the strength to resist the large temperature variations. To control crack development the green concrete needs to be dampened continuously and if required insulated. What is important is the type and the extent of the cracks. Structural cracks caused by bearing unexpected higher load are dynamic as cracks can progressively get worse. Thus the cracks discovered 5 days before the collapse will be less severe than those recorded just the day before. The NTSB first update on 9 Aug 2018 shows the cracks, taken 1 to 2 days before the collapse, were in considerably worse condition than those report in the earlier Preliminary Report. To a trained engineer the cracks reported om 9 August 2018 by NTSB are sufficient to support the root cause of the collapse as they show part of the structure, Member 11 & 12 in unison as one body, was slowly separating away from the deck. The bridge then was held together, not by the concrete, but by the embedded rebar which would be visible in some of the cracks which appeared to be up to or even over an inch wide. There is no way for any professional engineer to argue that these cracks are not destructive and dangerous. ### RE: Miami Pedestrian Bridge, Part VIII As I reviewed the collapse video once again, I couldn't help but wonder why the truss elements, and particularly 10 and 11, were still wrapped in the promotional banners. Given the obvious distress that these elements were experiencing, wouldn't they have been exposed for evaluation and observation? ### RE: Miami Pedestrian Bridge, Part VIII Apparently when first discovered the cracking problem was at its early stage and progressively got worse with time. The post-tensioning adjustment work carried out prior to the collapse could have exacerbated the situation too. On the last day when photographs were take if a competent PE were to examine the crack width on the deck at the location with Member 11&12 (say it is just 1"), ascertain the maximum thickness he could measure the deck (which is about 48.875" according to the drawings available publicly now) and calculate the strain=deflection/thickness to arrive at the cracking strain of 1/48.875= 0.020 he would be able to stop the construction work citing the maximum strain of 0.003 for concrete at the ultimate limit state of collapse had been exceeded. 0.003 maximum concrete strain at collapse limit state is used by all ACI reinforced concrete codes say 318, 349 and 350. European codes uses 0.0035 so the magnitude is pretty universal. The cracking location did not failed by pure compression but a combination of tension and shear. However there is little possibility that the bridge at the cracking location, which right at the bearing support, could still be deemed serviceable. To me the failing of the design isn't much to do with the amount of tendons and reinforcement in the Members 11&12 or in the deck but the assumption that the connection point would be rigid in the structural analysis not being realized or achieved in the field. The design does not allow sufficient space to deploy enough concrete and reinforcement there to ensure the two to remain monolithically connected when under load. The photographic evidence shows the Member 11&12 sheared off over the top of the longitudinal post tensioning tendons system of the deck which dropped to the ground with little damage. ### RE: Miami Pedestrian Bridge, Part VIII I'm following this story from the very beginning - and my opinion do not change - the bridge was under designed, with way too low safety factors used in the calculations or computer model, and with apparent gross error in the design, which is missing analyses of the truss in the construction stage, i.e. long truss erected and supported, without short truss in place. The short truss, abutting the long one, is taking the horizontal load off the critical node, and reducing the shear to the level which it was designed for, but unfortunately not for the shear during movement and placement on the piers. The photographs of the cracks taken prior to the collapse are the most disturbing, as any marginally competent engineer should know that the reinforcement was already yielding, so the collapse was imminent. Which brings another very disturbing question - who had seen these "secret" photographs, and what was their action? Perhaps answering this is a subject of ongoing investigation? ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (wiktor) missing analyses of the truss in the construction stage Since the bridge has high strength tendons inside the vertical and sloping truss members and a table is enclosed in the MCM/FIGG proposal document, based on which the bridge contract was awarded, it would be difficult for the public to suggest the major calculation is lacking during construction. The above tendon forces are expected to be installed in the bridge at its final position for the working condition. Before the bridge was lifted off its casting position part of the tendon forces would have been applied to give strength to the bridge for its relocation operation. When the bridge had been lowered into the abutments the tendon forces would have to be adjusted. Indeed the bridge collapsed during the tendon adjustment phase. It would be unimaginable that calculation was not performed in each stage to arrive at the amount of tendon forces needed. Thus the investigator can anticipate there will be essential calculation performed. Whether the computation is correct or adequate for the purpose is another matter. Personally the evidence of cracks, by the geometrical formation, extent, severity and location, indicate a connection failure. Unlike structural steel, where one can perform calculation on each connection, in reinforced concrete the connection calculation is rarely done. It is like forming a hole in a concrete slab the designer is expected to detail four trimmer bars across the corners. An experienced designer would know something is needed to beef up this connection if one examines its stress path. Whenever structural calculation is performed on reinforced concrete each joint will have to be assumed rigid and monolithic so that the forces, bending moments and shears are held in equilibrium by the members at that nodal point. I expect the designer in this case to be criticized for failing to realize the basic design assumption in the field. I do have sympathy for the designer as checking the structural adequacy of a connection is not routine in reinforced concrete design. The design with both reinforcing steel and post tensioning tendons is respectable, the bridge arrangement is elegant and the fake stayed cable (using steel pipes) is innovative. The bridge would have worked if the designer was given more room to put a bit more concrete and rebar at the cracked location to dissipate the highest stresses in the structure. He could also had insisted the post tension anchors of the Member 11&12 and the deck to be structurally linked to those in the deck locally, say by a gusset plate or by welding. Engineers learn from mistakes. There are many good lessons to be learned from this bridge. ### RE: Miami Pedestrian Bridge, Part VIII 6 #### Quote (saikee119) I do have sympathy for the designer as checking the structural adequacy of a connection is not routine in reinforced concrete design. I've stopped commenting on this thread, but I couldn't let this pass. This is complete BS! Any qualified bridge engineer does this routinely. ### RE: Miami Pedestrian Bridge, Part VIII Just to be sure we are on the same wave length I am talking the rebar inside Member 11&12 having sufficient development length in the deck and vice versa. The deck has horizontal rows of post tensioning tendons in two directions so the concrete is under high compression axially and transversely making it a stiff 2D plate. Similarly Member 11 is axially compressed to be a lot stiffer than normal reinforced concrete. During the relocation operation the bridge was supported with the two ends as cantilevers making Member 11 a tension member temporarily so stress reversal occurred too and that I suspect is the basis for post tension adjustments. However there is a thin layer of concrete in the deck above the post tension tendons connecting with the Member 11&12. This reinforced concrete layer is relatively free from the post tensioning effect and not subjected to the same stress intensity as the Member 11 or the main deck. Member 11&12 pushes this layer outward while the deck's post tensioning tendons pulls it inward. To analyse this connection properly one will need to assume several modes of failure and compute the shear and tensile resistances of the concrete and rebar across the breaking surfaces. The capacity of the connection is the mode that requires the least breaking force or along the line of the least resistance. May be it is done routinely but it isn't a topic I am familiar with in the ACI or AASHTO codes in USA or the EU codes, other than checking the development lengths of the embedded rebar which tells us only the tensile contribution from the reinforcement at limit state. To make it more interesting there is a large diameter 8" drainage pipe embedded with a number of grouting ducts making the continuity of rebar very challenging at this location. The failed bridge has evidence suggesting these embedded items could have been points of weakness. If the above connection has enough concrete or rebar it would not have sustained the cracks well exceeding the limit state collapse strain. ### RE: Miami Pedestrian Bridge, Part VIII @saikee119 Just to be on the same wave length - I'm 100% sure that something was amiss in the analyses of the temporary condition. The proof landed on the highway, so the only question is how it happened. The bottom deck tendons were to far away from member 11 to contain the horizontal force from #11 (i.e. shear in between diagonal and the deck) - actually depending on the actual sequence of tensioning, this shear could be increased as result of post-tensioning. " May be it is done routinely but it isn't a topic I am familiar with in the ACI or AASHTO codes in USA or the EU codes, other than checking the development lengths of the embedded rebar which tells us only the tensile contribution from the reinforcement at limit state." Both ACI and AASHTO, and Eurocodes are great "cookbooks". Unfortunately, the familiarity with the cookbook doesn't make a great chef. "Personally the evidence of cracks, by the geometrical formation, extent, severity and location, indicate a connection failure. Unlike structural steel, where one can perform calculation on each connection, in reinforced concrete the connection calculation is rarely done." The connections are always analysed, when design is done by a competent engineer - period. ### RE: Miami Pedestrian Bridge, Part VIII Wiktor, I like the word "competent" used by you. I am not sure your definition of temporary condition as I thought the bridge was already in its final position and structurally independent. I suppose we could classify it as one of the construction phases because once the rest of the abutments are constructed and the fake stay cables fitted the bridge might survive with the benefit of additional restraints and some small structural contribution from the steel pipes. The cracked section would then be constrained and requires a local but substantial strengthening scheme. Bearing in mind Member 11 had a complete stress reversal from being in pure tension, as a cantilever during the transportation, changed to 100% compression after being dropped onto the abutment there could be some dynamic stresses overlooked. My point is the bridge was in its final position and had survived all the previous temporary conditions. It would be nearly impossible to find which temporary condition had gone amiss. We all know design codes are just good engineering practice to follow. We can put in more than the code mandates but not less. If we follow the code to the full and interpret it as every competent designer a failure is not our fault but state of our knowledge needs to be improved. In that way the code protects us. As an example we specify the adequate cover and use the right mix to protect the rebar to withstand a 1 hour fire but the component fails then we do not expected to be prosecuted if the materials were up to the standard. My respect of the design codes is probably due to having used about a dozen of national reinforced concrete design codes in my time and did not find them vary significantly from each other. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (Wiktor) ...The short truss, abutting the long one, is taking the horizontal load off the critical node, and reducing the shear to the level which it was designed for, but unfortunately not for the shear during movement and placement on the piers... The bridge looks like this should be so on the outside, but I don't think that there is much evidence that it was actually designed to work like that. The construction drawings so far available appear to show that the two trusses are structurally independent of each other. I think that it is likely that, had the long truss lasted until the short one was in place, its eventual failure would have just kicked the short truss off of the central pier, and both would have fallen. --Bob K. ### RE: Miami Pedestrian Bridge, Part VIII ### RE: Miami Pedestrian Bridge, Part VIII With regard to NTSB finding (2) the public like ourselves do not have access to the design calculation and wouldn't know what demand (load) was estimated by the designer at the above nodal point. One would have thought the dead weight of the structure is hard to underestimate whereas the wind, snow, thermal, shrinkage, creep, pedestrian traffic and seismic loads were not playing much a role at the time of collapse a probable culprit of load underestimation could be construction-induced stress sustained when the bridge was moved from the casting position to the collapsed position. The final report takes time because it has to demonstrate no stone unturned and for completeness like the materials tested are in compliance or not, explanation of failures of other parts could be consequential , a list of contributory or non-threatening construction defects found, certain minor oversights or omissions in the design discovered here or there etc, etc. The combination of Finding (1) and (3), to some of us, has already defined the root cause of failure. The discussion of the last few posts is on the subject whether the failed critical section, as stated in NTSB Finding (1), is routinely analysed by a competent bridge designer or not. ### RE: Miami Pedestrian Bridge, Part VIII saikee119 (Structural, Thank you for your clarification. SF Charlie Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII 2 (OP) #### Quote: ...whether the failed critical section, as stated in NTSB Finding (1), is routinely analysed by a competent bridge designer or not. With a totally unique bridge like this, there is no "routine" about the design at all. So asking if engineers routinely check a non-routine connection is a bit of a weird question. The question should be: Did the design engineer perceive that the diagonal/vertical strut connection to the horizontal deck was very unique and therefore demanded very focused and special design attention? Check out Eng-Tips Forum's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ### RE: Miami Pedestrian Bridge, Part VIII Too much focus on the node where the collapse initiated, and too little focus on the structural concept. This was not just a truss with axial members, it was a concrete frame, and the flexural behavior of the members and joints was not understood by the designers. As well, internal restraints led to cracking which was ignored. Shrinkage cracking is often inconsequential to strength, but that was not the case here. The critical mistake which was made was not to load test the structure while they had it on the ground. For a structural type which was unprecedented, that should have been obvious, at least it is in hindsight. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (saikee119) When the bridge had been lowered into the abutments the tendon forces would have to be adjusted. Indeed the bridge collapsed during the tendon adjustment phase. You're way late and seem to have missed a lot of important information that has already been covered. The PT rods in 2 and 11 were there to support the cantilevered ends of the bridge during movement. The first thing they did after placing the bridge was removing the tension in the rods inside those members. The general wisdom is that the crew was re-tightening the PT rods in member 11 when failure occurred, even though those rods were never supposed to be tensioned once the bridge was in position. In other words, they had placed the bridge and released the tension in the PT rods as per the design and then decided later to re-tension them again, allegedly with the intent to see if it would close the cracks. ### RE: Miami Pedestrian Bridge, Part VIII LionelHutz, While I admit not having read the post but I did start when the thread first commenced and occasionally came back when NTSB released the findings periodically. To make sure no misinterpretation I have never implied the tendon adjustment in Member 11 causing the failure because I used the word "tendon adjustment phase". The video everybody can see when the bridge collapsed had a workman adjusting the tendon at the opposite end of Member 11. As regard to whether the tendon forces were removed, relaxed or re-applied I can only go about it according to the table in the drawing showing the PT Bar tension requirement I posted on 26 Mar 19 12:09. In it Member 11 show no force required. Thus if force were applied and then removed in any member that to me is the tension adjustment phase. The FIU bridge collapse has the hallmark of the West Gate Bridge collapse in Melbourne Australia in 1970. It was a steel box girder bridge with a large misalignment when two parts joined together. The workmen placed heavy concrete blocks to force the two parts together and the bridge collapsed as a consequence. Another attempt by the site people doing their own things not in accordance with good engineering practice or per design drawing. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (hokie66) ...The critical mistake which was made was not to load test the structure while they had it on the ground. For a structural type which was unprecedented, that should have been obvious, at least it is in hindsight. That sounds like a no-brainer in, as you say, hindsight. But I wonder what that static testing might have looked like in practice. Clearly they'd support the bridge at each end to simulate the actual abutments. For the mass, would they use gravel or sandbags or water bladders? I can imagine that the idea of a static test would be somewhat unpalatable to the developers. For one, the idea that it needs testing at all kind of casts doubt on the design--aren't these the world experts in ABC bridge designs? For another, it would inevitably become a public spectacle, and anything less than resounding success would reflect poorly on all involved. Of course, both of these rationales are in fact excellent reasons to conduct such a test. Anything that can be destroyed by the truth deserves to be destroyed. Oddly enough, when I google "bridge static load test," one of the strongest hits is for this paper on a mobile testing system developed by--wait for it--the Florida DOT. Another interesting hit was this paper about using, among other things, US Army M60 battle tanks. Which suggests that the guy who crashed a Bobcat skid-steer loader through the deck of a different pedestrian bridge might have been on the right track. ### RE: Miami Pedestrian Bridge, Part VIII saikee119 - Well, they reported that the PT rods were adjusted to their final tensions on the same day they placed the bridge, so the only direction they could be going on the day of the failure was to be applying tension again. This was all covered in the threads. ### RE: Miami Pedestrian Bridge, Part VIII hpaircraft, Yes, they could have used water or sand. Plenty of both in Miami. The load testing in the FDOT paper is really a load rating test. They are not fully loading these existing bridges, but rather using instrumentation to rate the capacities. The M60 tanks are a bit of a reach. Another thread here about a bridge in Colombia shows them driving a line of loaded dump trucks onto a completed cable stayed highway bridge. That's a real test, but not what I was looking for. ### RE: Miami Pedestrian Bridge, Part VIII I think if you look at dollars/pound to get weight on a bridge, you'd find loaded dump trucks were way cheaper than army tanks. ### RE: Miami Pedestrian Bridge, Part VIII The configuration of this bridge would preclude the use of tanks or trucks. Of course, for a pedestrian bridge either would be significantly more concentrated load than it was designed for. Very few bridges are ever tested for capacity. A few are tested for deflection at something well below the expected capacity, to estimate their capacity, usually after many years of service and significant deterioration. ### RE: Miami Pedestrian Bridge, Part VIII I didn't suggest trucks or tanks. What should/could have been done is a load test with static mass, such as sand or water as suggested. This is quite common in building structures, if not for bridges. This was not just a bridge, it was a never before attempted structural design. ### RE: Miami Pedestrian Bridge, Part VIII The bridge, according to the design brief, is to carry a live load of 90 psf (pound per sq ft). Since water has a unit weight of 62.4 pound per cubic ft the pedestrian traffic this bridge can carry is equivalent to a layer of water of just 17" deep. Forget about the load test, army tank, lorries.... ### RE: Miami Pedestrian Bridge, Part VIII Why do you say that, saikee? I suspect that 17" of water would have told the story easily, as the bridge actually failed under its own load. But the load test would have needed to be conducted in accordance with US standards for load testing. ### RE: Miami Pedestrian Bridge, Part VIII hokie66, Like HotRod10 said we would test a whole bridge if we need to ascertain its capacity. This is usually done if understrength or defective construction, say a wrong mix has been poured or the rebar fails the strength test, is suspected or its structural details unavailable due to old age. If we do want to test this bridge all we need is to erect a 24" high watertight barrier and pour water to a depth of 17". Is that the information everybody is seeking? Like you said this bridge couldn't even support itself let alone put anything on it. I am just being practical. This bridge cannot be tested at its casting position because when it is transferred its final position the lifting operation can inflict damage after it has passed the load test. The bridge could have been tested if it didn't collapse. However by then who would bother if it works? There exists procedures with which we can test a bridge structure but that is not a normal requirement in any bridge construction as it will be expensive relative to the cost of the structure. Let's say FIU is clever enough to write a clause in the contract to mandate the builder to carry out a load test. We still be exactly what we are today because the load test would only be of value to FIU when it is fully complete and not just one span when it collapsed. ### RE: Miami Pedestrian Bridge, Part VIII There is no reason why it could not have been tested where it was built. Damage by transport is highly speculative. And this span had to work on its own, not as part of a continuous bridge. ### RE: Miami Pedestrian Bridge, Part VIII #### Quote (hokie66) Damage by transport is highly speculative It is speculative but not highly because had the bridge been transported as per original design the Member 11 and 2 would always be in compression, have no stress reversal and no need of any PT rod tension adjustment. It can be argued that the original scheme may be impractical as some transporter wheels must travel onto the unpaved areas adjacent to the abutments. This will cause unwarranted if not uncontrollable settlements or movements of the wheels and endanger the temporary supports of the bridge. Comparing the original with the actually executed scheme it would be obvious there had been a design change in the temporary work resulting the two end bays to have the ability to withstand as cantilevers not envisaged in the original design. In the original scheme it would be more difficult to manoeuvre the transporters into position, the rigid linkage between the four transporter supports would have to be more substantial(the original 4 separated supports were in the end bolted together to form just 2 supports), the cost has to be higher (unpaved areas to be concreted over, traffic barriers removed and then reinstated) and the worst of all is the longer construction time. The bottoms of Member 2 and 11 are taper and not intended as support points in the design. Were the two temporary support points structural adequate or suitably strengthened for this purpose? If one looks at the centre divider kerb one may wonder if the design has the dynamic forces considered when the transporters crossed over it. The Google map does show several newly patched areas at the position where the transporters had to cross over and a long unpatched damaged kerb section possibly sustained during the removal operation of the collapsed bridge. It is common in the construction industry for the scheme proposed to win a job to have minor deviations in the final execution. Thus attention to details is the key. The evidence above is just a few need to be considered if the bridge were to be satisfactorily delivered. ### RE: Miami Pedestrian Bridge, Part VIII A while back there was a push to have the design calculations made public. If I remember correctly, they were, however, you had to pay a fee\$ to get a copy. After that I expected to see bits and pieces of those calcs, along with a running commentary, appear in this thread. That hasn't happened. I'm assuming the reason why that hasn't happened is that there is some legal contract that all parties, who receive a copy, must sign that restricts them from making public any info contained within. So a couple of questions:

1) May we expect that after the NTSB releases it's final report this contract will be voided and we will begin to see commentary on the calcs begin to appear in this thread?
2) Or will the calcs be eternally sealed and hidden from the public?
3) In general, calcs are not public documents. So why should we expect them to made public in this case?

The reason I ask is that I would be very disappointed if all we get from the NTSB is a video animation of the collapse, along with a bulleted list of findings, such as insufficient this at node 11-12, or failed to adequately address that at node 11-12. There are a host of other design concerns, not directly related to the collapse, that could've played a role in determining the long term safety of the bridge, some of which are:

2) Were moments foreseen to develop in the diagonals?
3) How were the diagonals designed?
4) How was node 1-2 designed for DL + LL + (C, S, T)?

I suppose we can't expect the NTSB to redesign the entire bridge. Maybe that's something left to academia. Seeing the calcs would bring out into the open some of these issues. I guess I'm just preparing myself for the release of the report, and being left with a lot of unanswered questions.
>

On a separate note, Were any VSL engineers present during stressing? From my recollection the answer is no. This was a small job with relatively simple PT, so it may have just been the crew working the jacks. My sense is that if VSL engineers were involved--as a separate set of eyes--we'd be having a vastly different conversation today. Or maybe this is just wishful thinking.

### RE: Miami Pedestrian Bridge, Part VIII

This March 15 Miami Herald story noted that the report was delayed because of the government shutdown, but it's expected to be completed by late Summer to early Fall.

### RE: Miami Pedestrian Bridge, Part VIII

#### Quote (Green Lama)

Were any VSL engineers present during stressing?
- No but an inspector from Bolton, Perez & Associates (Engrs) was up on the canopy when it collapsed.

### RE: Miami Pedestrian Bridge, Part VIII

Thanks for the note about Bolton. The Miami Herald story mentions the jacking crew as working for Structural Technologies, not VSL. I guess I was mistaken.

Here's a link to a March 26th report about how Bolton and FIGG cannot now agree as to what was said during the trailer meeting minutes before the collapse.
https://www.nbcmiami.com/investigations/Companies-...

### RE: Miami Pedestrian Bridge, Part VIII

The MH story I cited a few spots above said there were at least two ST employees on the canopy. Kevin Hanson, who took cellphone pics of the widened cracks right after after the bridge was moved and forwarded them to higher ups, and Navaro Brown. ST called Hanson back the day before the collapse, and Brown was called away from another job the night before the collapse. Hanson's girlfriend said she was nervous about the cracks and didn't want him to go back the second day. Brown was killed, and Hanson was buried in rubble and ended up brain damaged.

### RE: Miami Pedestrian Bridge, Part VIII

Thanks again. I knew I'd seen VSL mentioned somewhere. Hell, I'd even linked earlier in this thread to a PDF technical report, "Detailing for Post-Tensioned," which can be found on the ST link above, however I'd gotten it straight from VSL. I must have just glossed over the Structural Technologies reference and connection.

It's so sad about all who were killed and injured. NTSB identified "design errors" and a construction site timetable are a toxic combination.

### RE: Miami Pedestrian Bridge, Part VIII

There is a video news story on the NBC Miami page linked above by TheGreenLama. This may have already been discussed in the thread, but in that news video, it is intimated that an FDOT engineer identified the potential failure planes in the concrete as early as 30% review documents prepared by FIGG. The video news story shows still shots of the bridge plans (presumably the 30% review set) with the FDOT engineer's red-line markups indicating where the bridge would crack. It is the same engineer who's voicemail box received the voicemail from the FIGG engineer about the cracks 2 days before the collapse. Pretty telling that the problem was identified so early in the process.

### RE: Miami Pedestrian Bridge, Part VIII

On March 14, Tony Pipitone posted a MASSIVE timeline of NBC 6 Miami's investigation of the disaster. The left side is interactive: documents can be scrolled page by page and videos can be played.

EDIT ADD 1: At least in FireFox, if you right-click inside the window and select "This Frame" -> "Open frame in a new tab/window)" the frame will expand to fit your browser window edge-to-edge. In Firefox, you can full-screen the window by using Ctrl-B to close the bookmark sidebar and F11 to eliminate everything else. Reverse with a second Ctrl-B or F11.

EDIT ADD 2: When a document is displayed, click the 4-arrow button at bottom left to open document in a full screen viewer that has an "Original Document (PDF)" link in right sidebar. From there you can print/save the PDF. If you hover over videos and some images, an arrow button appears in upper right corner than can full-sreen the video/image. If no arrow, right-click the image and select "view image".

On March 15 Pipitone posted a news report with a link to the timeline plus several videos. Parts of this post were reused in the March 26 story noted by The Green Llama.

### RE: Miami Pedestrian Bridge, Part VIII

Thanks MikeW7 (Electrical)
30-Plans-Review
Hint: search for "tricky"

### RE: Miami Pedestrian Bridge, Part VIII

Wow, thanks MikeW7, that massive timeline put together by NBC6 Miami is a nice summary of events.

### RE: Miami Pedestrian Bridge, Part VIII

Thanks MikeW7 for pointing out the NBC 6 Massive timeline which was also mentioned by gte447f

The following may have been covered here and there but I just put them together.
(1) As gte447f said the FDOT engineer has asked many questions about Member 11 specifically on the risk of cracking. The NBC6 timeline indicates on 15 Sept 2016 meeting, or 1.5 years before the collapse, FDOT suggested Member 11 needed to have PT rod to withstand the force when the bridge was lifted. He wrote "Cracking will occur here!" on several drawings. One of them is on the short span a connection similar to Member 11&12 with the deck

The two photos released by NTSB on 9 Aug update have the similar 45 degree cracks spread out as predicted on both sides of Member 11&12. One photo has been rotated to show the 45 degree crack is almost a mirror image of the other side.

(2) NBC6 has a complete set of the FDOT approved drawings for construction. I post a couple below showing weakness which would be apparent to every reinforced concrete designer. This first depicts the Member 11 having very little concrete continuity vertically with the deck due to the presence of a 8" rainwater pipe.

The drawing below depicts on either side of Member 11&12 there were 4 No. of 4" reinforcement tubes and a number of PVC cable ducts. Thus the horizontal continuity of Member 11&12 with the deck will also be compromised. In fact the second NTSB photo shows the crack crosses one of the cable duct.

The interference of the embedded items can be seen from the photo below which has been posted previously here. Note that the bridge at that time was being hoisted and had not yet dropped onto the support so the severity of the cracks was not yet serious. Member 11 was in tension then.

(3) Finally in NBC6 the descriptions of the photos taken by the workman, who fell but survived in the accident, alert me the severity of these cracks which I missed out. The first NTSB photo has been described as "4-inch crack" because the tape managed to dip 4" into the crack!

This photo also used by NTSB in the 9 Aug 18 Update and was described as "6-inch crack" because the crack has swallowed a section of the tape of 6" long.

Any professional engineer, who had access to these photos showing the most critical structural connection of the bridge has cracked and separated to a depth of 4" to 6", and did nothing to halt the construction or traffic deserves what is coming to him/her.

### RE: Miami Pedestrian Bridge, Part VIII

(OP)
Please discontinue posting in this thread. Go to Part IX thread815-451175: Miami Pedestrian Bridge, Part IX for any further posts.

This topic is broken into multiple threads due to the long length and many images creating longer load times for some. If you are NEW to this discussion, please read the following threads prior to posting to avoid rehashing old discussions.

Part I
thread815-436595: Miami Pedestrian Bridge, Part I

Part II
thread815-436699: Miami Pedestrian Bridge, Part II

Part III
thread815-436802: Miami Pedestrian Bridge, Part III

Part IV
thread815-436924: Miami Pedestrian Bridge, Part IV

Part V
thread815-437029: Miami Pedestrian Bridge, Part V

Part VI
thread815-438451: Miami Pedestrian Bridge, Part VI

Part VII
thread815-438966: Miami Pedestrian Bridge, Part VII

Part VIII
thread815-440072: Miami Pedestrian Bridge, Part VIII

Part IX
thread815-451175: Miami Pedestrian Bridge, Part IX

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