Miami Pedestrian Bridge, Part X 50

[JAE]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.

Part I
thread815-436595

Part II
thread815-436699

Part III
thread815-436802

Part IV
thread815-436924

Part V
thread815-437029

Part VI
thread815-438451

Part VII
thread815-438966

Part VIII
thread815-440072

Part IX
thread815-451175



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[Sym P. le]

Even if a suitable strategy were undertaken with urgency, it would be reckless to permit traffic to continue or to leave workers vulnerable to a poor outcome.

The issue of the phone is whether a legal directive to preserve evidence was followed.

 

[SFCharlie]

I am most grateful and have the highest admiration for Tom Andres. I can't let FDOT off the hook. They had the bridge moved over one lane one month before construction was supposed to start. Imagine having to rerun all the checks and balances. Yes, FIGG got a one hundred and eighty day extension and a chunk of money to do it, but all the adding PT bars and everything that precipitated from that was an afterthought. I don't know that the FE modeling was bad, but many of you suspect the highway span was never modeled separately. I don't know if they modeled the cold joints correctly. (We hope the NTSB will clarify this.) I also am having a hard time with the lack of academic participation in this. Did FIGG insist on "No students"? I feel like an incredible opportunity was lost and an extra set of eyes might have helped. I know explaining my thinking to others often causes me to realize fallacies as I'm trying to explain myself. Where was FIU's participation?
(Sorry for the earlier misspellings...)

 

[jrs_87]

How to Model Concrete using Finite Elements

https://caeai.com/blog/how-model-concrete-using-finite-elements

EARLY FINITE ELEMENT RESEARCH AT BERKELEY by Ray W. Clough Nishkian Professor of Structural Engineering, Emeritus University of California, Berkeley and Edward L. Wilson T. Y. Lin Professor of Structural Engineering, Emeritus University of California, Berkeley

http://www.ce.memphis.edu/7111/notes/class_notes/papers/fe-history.pdf

 

[epoxybot]

I can't find an update to this story, but the pictures taken by Kevin Hanson immediately after the de-tensioning on 2018-03-10 have never been released because possession of his phone is tied up in a court battle.

Kevin Hanson's sent two photo's on March 10, 2018 to his supervisor at VSL, which appear on page 49 of the OSHA report.

 

[Vance Wiley]

You have drawn a little green rectangle on the three photos - I think those are around the visible remains of a top interior diaphragm reinforcing bar. If I am correct in that thought, that bar would be maybe 3 inches inside (north of) the south face of diaphragm 2.
Sorry I am not adept at images and computers, so I must try to describe with words.
Tomfh has addressed the triangular fillet well and I could not agree more.
The cold joint appears to define the shear plane until it passes over the rebar in your green boxes, with the exception of the divot around the PT rod, which I suggest was caused by the prying action of the PT rod as the deck and 11/12 parted company.
I cannot determine if the PT rod anchor plate was disturbed by everything going on, but there certainly was that opportunity. It appears like the diaphragm bar sorta shielded the PT anchor plate and the break-away passed over the anchor plate. The plate would have created a "no shear no tension" zone or a weakened zone in the concrete for things moving essentially perpendicular to and away from the backside of the anchor plate.
With everything going on during the collapse it is not unthinkable that the PT anchor plate was unseated by some distance then pulled back into position. At some point about 4 feet of member 11 went somewhere and the dimension between node 10/11 and node 11/12 could have decreased, pushing the anchor plate away from the deck for an instant.

EDIT In looking closer the rebar in the green box may be transverse reinforcing in the deck and so may be farther south than I originally thought. See Half Plan, sheet B-47. It appears to be PT anchor distribution reinforcing.
Interestingly, that reinforcing could have "stolen" some of the "clamping" forces from the transverse PT which FIGG was counting on.

 

[MikeW7]

The last section of the FDOT Preliminary Fact Sheet

[highlight #FCE94F]FDOT’s involvement was limited to[/highlight]:
[ul]
[li]issuing a permit for traffic control during installation of the structure last Saturday;[/li]
[li]acting as a pass-through for federal funding and providing $57,000 in state funding for this $16.5 million project;[/li]
[li]conducting a routine preliminary review to ensure this project complied with the terms of the agreement with the state. This is a standard process FDOT conducts for projects like this; and[/li]
[li][highlight #FCE94F]authorizing FIU to utilize the aerial space above the state road to build a structure, which FIU and its contractors are solely responsible to inspect and maintain at the university’s sole expense[/highlight][/li]
[/ul]

The wording of FDOT's fact sheet seems to indicate they knew immediately how the blame game was going to pan out, and they pushed out a public statement to declare their limited involvement. But as epoxybot (Structural) 21 Jun 19 03:57 previously noted, there was a lot of political weight behind this project, and FIU's role is being diminished (to almost zero it appears) and more of the blame directed toward FDOT.

 

[MikeW7]

Kevin Hanson's sent two photo's on March 10, 2018 to his supervisor at VSL, which appear on page 49 of the OSHA report.

I missed the screenshot in the OSHA report.
Hanson's original photos (unknown number) have never been released as far as I know. I don't think it's even known if he sent other emails.

EDIT ADD: What is the proper name for the area depicted in Hanson's photos. I will use it to rename the the two drone videos (... pylon drain 1 and ...pylon drain 2) on Whirled Gnus. I included those videos because I thought I saw a crack radiating from the drain into that area, but it appears from Hanson's pictures that the dark line I saw was just a filament of fabric or tape.

 

[JStephen]

I think keeping FIU faculty and students un-involved with the project was appropriate. The usual problem on something like this is having too many people involved, and throwing in a few dozen extras with zero experience in the work would not have been helpful.
On the fate of that phone, it is very possible that there is practically nothing on it, or it could be very damning. If he had texted someone and said "This bridge is about to go any second!", sure that'd be helpful to know. But, some people just don't use text messaging much. Presumably the investigators have the opposite sides of any text exchanges, and they may actually rank that phone as a low-priority item. The report was, he didn't take any photos with it, and if that were untrue, it would be enlightening.

 

[Vance Wiley]

FIGG did not have to follow FDOT suggestion and could have strengthened Member 11 with a different scheme of its own. How much the legal people would use FDOT's good will to evade FIGG's accountability remains to be seen. I am sure they will a have a go at it.

The concerns of Andres have been in my mind for days - and apparently he was cut out of the final review?
Sadly, attorneys will use the suggestion of PT for 11 as a directive, but hopefully that will get them nothing. The exposure is that he made a specific suggestion instead of posing a question and pointing out something that was not yet addressed. From his position it is not good to help too much.
Not helping is a problem to engineers. Remember the joke about the French guillotine?

 

[Earth314159]

Where does this compression come from? If the mainspan is supposed to be a stand alone structure and was simply set on the pylon, it can have no free forces to create external compression. The compression of 11 is supposed to be resisted internally, but has failed. The backspan is cast in place so the wet concrete will not create free forces. Removing falsework would load 14 in compression but in my mind intelligent design would have that force resisted internally also. When the thing fails, of course you reach for anything.
Since node 11/12 was failing, how much capacity is left? (Assuming you get there before it colllapses).
Anything relied on would have been an assumption. FIGG advanced an idea to restrain (capture) 11/12 with channels extending to 9/10 at the deck level. We will never know if they intended those tiebacks to be temporary. Then they said the backspan would do the job so it appears they intended the ties to be temporary.
Here is a previous post:
Vance Wiley (Structural)18 Jun 19 18:27
Quote:
saikee119 (Structural)18 Jun 19 17:23 quoting "The fact the bridge collapsed before FIGG’s strengthening scheme could be devised is a good testimony on the technical competency of FIGG on the matter."

"Being sarcastic, right?
I still question this statement/position by FIGG: "Such restraint would of course be provided by the erection of the side span had the bridge been able to achieve completion. "
Could someone identify the elements/parts in the closure strip over the Pylon which will provide 2000 kips of tension tie between the north and main {deck ?}."

I was thinking the compression would come from the internal hogging moment over the support. My understanding is the C1 and C4 run through the joint. Tr=0.9x48x58.6Kips=2500 Kips. These would also be grouted. The pipe stays would also contribute.

 

[epoxybot]

When it comes to FIU Engineering students participating in construction projects, it all comes down to funding. FIU Engineering Dept's participation in projects (instrumenting bridges) has been FHWA/FDOT work through multi-year grants.

In this case, that work/cost might have been required to be a component of the TIGER Grant. FIU was nothing, if not tight with its own purse on this project.

 

[SFCharlie]

FDOT Preliminary Fact Sheet

Funny, I don't see anything in here about adding lanes to the Tamiami Trail (8th)...


SF Charlie
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[SFCharlie]

epoxybot you are so spot on as usual, funny way to "own" a project?

SF Charlie
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[MikeW7]

SFCharlie (Computer) 21 Jun 19 18:10

My deepest apologies. My assumption was that the lane move took place in the TY lin 2015 revision, which actually moved the north elevator tower. I have no memory of reading about the 2016 FDOT request.

Poor, spotty memory kept me from working as a professional. I try to compensate by double checking everything before I post, but in this case I was so "certain" I had the facts straight that I neglected to do so. It's not the first time it's happened. I try....

ADD: I edited my original post...

 

[LionelHutz]

saikee119,
The phone - First off, the voice message wouldn't be on his phone. Secondly, how do you know that voice message is the only important piece of evidence that could come from his phone? The combined facts of him claiming it was damaged and him not allowing anyone else (relevant authorities or investigators) to possess it is what stinks.

The fantasy - The morning briefing said the tie back to 9/10 would be temporary until the rest of the bridge was built at which point the other parts of the bridge would somehow hold 11/12 in place. The second part is the fantasy I was referring to. I'll re-word what I wrote before - the "truss" they poured off site and moved onto the piers MUST be capable of holding itself together and supporting itself for the completed bridge to have any chance of surviving long term.

jrs_87
Interesting notes on the subpoena ability. I haven't seen anything about the phones of key personnel being subpoenaed but given how much texting and emailing is done via cell phones these days I would have thought that would be part of the standard procedure.

I wonder if it was Apple or Android. I know when you replace an Apple phone the new one comes out data and app wise to match exactly like the old one, assuming that cloud backups are turned on. I'm told the same applies with Android phones, but work won't supply Android phones so I've never tried it myself.

MikeW7
The battle over Hanson's phone smelled like greed to me, as in the people fighting for possession were hoping to get paid for right or access to the phone.

 

[SFCharlie]

MikeW7 you have nothing to apologize for...

SF Charlie
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[saikee119]

Has anyone had a view on the collapse based on the historical formation of cracks reported by OSHA?

To summarize:

There were some minor cracks in various locations recorded prior to the span being moved to its final position. The extent and severity of these cracks then did not alarm FIGG. I also did not find these cracks a concern before March 10.

During the bridge migration on March 10 and before the PT rod stress release there was no photo available on the existing or any new crack. OSHA report states "Truss was transported by SPMT and placed on the pier and the pylon, and were generally free of cracks other than those mentioned above"

First knowledge of significant cracks occurred on March 10 2018 immediately after the PT stress released in Member 2 and 11 when the span was already at its final position. Photos were taken by the VSL crew with comment "It cracked like hell". More photos were taken later and they generally show the cracks at 11/12 were growing. The span was apparently "damaged" simply by removing the temporary tension in Member 2 and 11 installed there purely for structure migration purpose.

Would the formation of these alarming cracks, ranging 3" to 7" deep developed only after the PT rod destressed in Member 2 and 11, not the very evidence that the span was underdesigned and cracked under its own weight. These cracks did not developed initially because the temporary PT rod tension helped to hold structure together.

OSHA report now confirmed on March 15 2018 the bridge collapsed at the exact moment when 280kips had just been fully restored in the upper PT bar and the last 50kips was introduced to the low bar of Member 11 (already had 230kips restored and 50kips were applied alternately).

Would the re-tensioning of PT rods back to previous construction phase inside Member 11 the very trigger to cause the collapse? If this were the case then the re-application of the PT rod stress pushed the span to collapse.

A possible explanation why the initial tension caused no cracks but its re-introduction destroyed the bridge could be the bridge was permanently damaged after the stress release. The photos show the 11/12 had moved outward by as much as 5mm or 1/4" and so the sections would have already partially separated but were retained in position possibly by rebar. The re-application of the PT tension did not pull the sections back together because high shear friction, between cracked concrete, would have to be overcome to re-align the moved surfaces. The re-introduction of the PT tension finally broke off the section and shear off the remaining rebar across the shearing plane.

To pin point the exact failure would require more photos evidence than the NTSB and OSHA reports currently provide. However the historical development of the cracks shows the span was damaged beyond repair under its own weight and it was the re-introduction of PT rod stress that killed the bridge.

 

[MikeW7]

During the bridge migration on March 10 and before the PT rod stress release there was no photo available on the existing or any new crack.

In these two videos gawkers 1 and gawkers 2, it's not clear if the crowd is admiring the rebar work of if they're concerned about something they see in the area Hanson photographed later that day. You can see several people taking phone pictures, but I have no idea if OSHA/NTSB even knows they exist.

The move was stopped numerous times, but this is undoubtably the best position for quality photos of Hanson's "cracked like hell" area.

 

[Sym P. le]

Please, do tell! Who is taking pictures? Screen grab please.

 

[saikee119]

MikeW7 (Electrical)

I was careful to use the word "no photo available" during that period.

Video cannot show details of cracks.

Photo is the only evidence we could rely on to find out what happened.