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Miami Pedestrian Bridge, Part VI 31

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Update on post jrs87 (Mechanical) 1 May 18 23:35

Upon closer inspection of linked document, these are cracks that were found after shoring was removed, and before bridge was moved.
 
3DDave said:
"...expunged"
Click to expand...

Please explain, still works for me. We now have reports of cracking when forms were removed, when 2 and 11 were first stressed, and when shoring was removed. Do I got that right?
 

jrs87, It works now. It previously reported that the content had been removed with a great big graphic that was quite unmistakable. It's Sharepoint, so who knows.
 
Pictures post shoring removal, pre move #4, #5, #6 tells me the story.
The cracking evidence is that the bottom of #11 slid across the deck, while the lower (4" tall?) side was being held back by a stirrup. Then they prestressed #11 to 560kips, & transported. The next step would place the bridge on pier with full 2,000 kips load at small 1/2 size #11 fillet block. #12 held tight, & #11 slid to crush small undersized fillet. The #4 pict crack is probably 2x the .024" travel I figured was needed to explode fillet.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1525232520/tips/CRACKS_REPORT_AFTER_SHORING_REMOVAL_tcq1tk.pdf[/url]
 
jrs87 -- agreed, odd premise. While the author ponders the merits of slow engineering, I'm happy to snap up jobs relying on quality technical and project engineering instead. Not bending to the perpetual time crunch pressures, but acknowledging the value of timeliness (to the client, end users, and the traveling public).

Also, yet another academic who missed the aesthetic nature of the "stays".

----
The name is a long story -- just call me Lo.
 
I tried to correlate the photo numbers to span locations - 1,2 match page 4 diagram - 3,4,5,6 don't.

Just throwing this out there..
A) Photo 3 at west #12 base? (does #1/2/base have PVC pipe sticking out?)
B) Photo 4 definitely looks like #11 (good input Cutterhead/0.024"), but there appears to be a hole in deck that I can't see elsewhere
C) Photo 5 IS #11/12 (can see the rod sticking out elsewhere)
D) Photo 6 is what I'd expect to see on the opposite side of Photo 4 for #11, but the angle looks steeper - both in crack and bit of diagonal member at top. Angle ~like #7

Attached is an enhanced photo 4. There are parallel hairline cracks that match PT rod angle and angle of large crack that appears to continue along deck. With rods in ducts, there's not a lot of surrounding concrete in these rodded members (as there'd be in #2).
 
 https://files.engineering.com/getfile.aspx?folder=2e1e6ddf-7aef-4a9a-b7af-36232dd3505a&file=4j-bcs-2.jpg
#4, #5, #6 are all at base of #11. The diagram shows them at the bottom of deck, but it isn't so.
One thing that I take from picts, is that some cracks were surfaced over, & some cracks were after surfacing. In other words, there was a lot of movement from #11 to deck.
It was stated by Pate that they were going to tighten the tendons to close the crack. That might have worked if the bottom #11 anchor was above the deck, but they weren't. Applying more tension on tendons only added to the slide, & hence short fillet failure.
I'm guessing the hole is to aid grouting in #11 tendons.
 
Number 11 diagonal was never planned to be grouted.
 
Has all work on the bridge project at FIU come to a halt pending the outcome of the NTSB investigation?

Did the support structures on the ROWs get demolished as part of the cleanup of the accident scene? If not, are they usable or repairable?

Obviously, they still need a pedestrian bridge. Have FIU, Florida DOT, and community leaders publicly discussed or decided on a path forward?

If the NTSB finds that the design was fatally flawed, what effect will that have on Denny Pate, FIGG, and the others involved?

What is the likelihood that the concept bridge can/will be redesigned to overcome its flaws, and eventually be built?

 
If the anchor for #11 were above the deck it could not have carried the necessary tension to the deck during the bridge movement when it was a tension member. In place, on the piers, it became a compression member as it was originally planned. Why did this cracked compression member fail? I have concerns for the anchor design but we do no have those as they are assigned to the post tension company and not part of the plans.

A lot of good thoughts and information here. Thanks to all.

 
To Mr. MOJOJOHN

If you are talking about the PT bars (2) stressed in member 11, for me they make sense to accommodate the tensile force in member 11 during bridge movement. That member only has 8 #7 bars and whatever compression it gets from the tensioning of the deck tendons (minus, probably, some tension from the stressing of the canopy tendons.

After the span is set on the piers (and we, BTW, do not clearly know from the plans the layout of the shims at the piers), that strut gets into real compression (and some additional bending from the stressing of the longitudinal tendons in the canopy and the deck). Now, what?

My interpretation of the contract plans is that the 2 PT bars, which are not needed now for tensile effects, are requested to be removed . AND THIS IS THE OPERATION BEING DONE THE DAY OF THE EVENT (my guess). It does not make sense to add more force to a member that is in compression already.

But, guess what, these PT bars are anchored at the deck, and, therefore, are probably clamping the shear horizontal interface between member 11(and 12) and the deck. If there is lack of shear interface capacity (shear friction), provided by the concrete area or the rebar crossing that plane from member 11 and member 12, now we have a potential failure mode. This has been pondered by members of this group before.

One has to see the EOR calculations to see how that potential failure mode was evaluated. With that, we have to remmember that the constants in the AASHTO code depend on the roughness of the shear plane (about 76"x21", I am guesing). The constant of 1.0 applies to 0.25" "roughness". Has anybody seen in the plans a note requesting that those "cold joints" be roughen to 0.25"? Otherwise, we may have to assume a 0.6 factor. Are the FDOT specifications regarding cold joints ensure a 1.0 factor or a 0.6 factor?

Good hunting

Live long and prosper.

 
Answers to Retiredat46 Aeronautics - 3 May 18 08-25
Has all work on the bridge project at FIU come to a halt pending the outcome of the NTSB investigation?
Yes, it is halted. A video on YouTube shows the the site devoid of activity (Published on Apr 25, 2018).
Besides, the contractors are not getting paid, so do not want to “run-up” their payroll.

Did the support structures on the ROWs get demolished as part of the cleanup of the accident scene? If not, are they usable or repairable?
They where dismantled.

Obviously, they still need a pedestrian bridge. Have FIU, Florida DOT, and community leaders publicly discussed or decided on a path forward?
Yes, they have had meetings and the community still wants a bridge.

If the NTSB finds that the design was fatally flawed, what effect will that have on Denny Pate, FIGG, and the others involved?
Denney Pate (2nd e in Denney) will have to repair his image or retire.

What is the likelihood that the concept bridge can/will be redesigned to overcome its flaws, and eventually be built?
That image will be too painful to the community and a detriment to FIU's image as “We Build Bridges”
I would build a steel bridge with curving members and soaring design as a memorial (That's what Figg pitched after the twin cities bridge disaster).
Thanks for your questions,
Charlie
 
If the NTSB finds that the design was fatally flawed, what effect will that have on Denny Pate, FIGG, and the others involved?
Denney Pate (2nd e in Denney) will have to repair his image or retire.
Click to expand...

Well, if the DESIGN was flawed then yes. But after over 1000 posts on this set of threads there is still a lot unknowns and the investigation could possibly result in a sequence, stressing, construction, contractor error vs. an engineer error. We'll see I guess.

If it was a construction error (vs. design) then perhaps Mr. Pate will be in better shape career-wise.

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