Miami Pedestrian Bridge, Part IX 33

[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


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[SFCharlie]

Eng-Tips lurker and YouTube conspiracist Construction Engineering, & EQUILIBRIUM is taking credit

added:Thank you for adding the info to your videos!
Yes,
At first, I watched because he was showing photos that I was not aware of...
But then, I realized he could not read blueprints. He was dependant on his readers comments to set him straight.
He has had to change the name of his chanel at least three times.
He is unwilling to share his sources. (Many are seen here.)

 

[Vance Wiley]

TheGreenLama and jrs_87
The Cornell program IS ACI 318 - but it is the only one I found. I figured it would yield a number somewhere in the ballpark to give an indication of the capacity of 11. I certainly would not use it to design a column or critically judge a design.
I was unsure of the phi factor you provided also. And I guessed at load factors for self weight and live load. I should have done more research to make the findings more applicable to this structure. How much reinforcing would you consider requiring in 11?
(I hung my slide rule up 13 years ago, but one does not easily abandon a career of learning and curiosity.)
Also, I was working Thursday on the concept of rotating the structure 90 degrees to better illustrate the importance of node 11/12 to those who may not visualize the workings of a truss and how a joint can fail horizontally from vertical loads.
The load matching the shear in 11 to deck would be that of one end of an equivalent span of about 1160 kips/11 k/ft or 212 feet weighing the same as this structure per foot of length. I was planning to pose the question "Would you stand under something that big with cracks like that ?"
Great minds run together.
Thank you for your comments.

 

[MikeW7]

Possible cause of canopy damage to the 10-11 blister area:
[ul]
[li]During the move the underside of the canopy south of 10-11 was anchored to the "arms" on top of the SPTM movers but the span bottom was resting on cribbing directly beneath the canopy anchor points. This allowed the canopy to move independant of the deck.[/li]
[li]The canopy at 12 was chained directly to the deck edges. The canopy could not sway sideways with respect to the deck.[/li]
[li]When the bridge was moved over the roadway median there were several instances where the south SPMT movers moved independent of the north movers, causing the span to spin and shift on the cribbing (watch the north end of the span).[/li]
[li]If the canopy flexed at all during this, the 10-11 blister area would be near the midpoint of section between fixed end at 12 and the flexed portion chained to the SPMT arms. The 10-11 blister appears to be one of the initial failure points.[/li]
[/ul]

Shortly after spin-and-shift events the move was paused and somebody was taken up in a manlift to have a look around. The moved resumed immediately after the manlift came down - before it was even parked.

 

[SFCharlie]

When the bridge was moved over the roadway median there were several instances where the south SPMT movers moved independent of the north movers, causing the span to spin and shift on the cribbing

The SPMTs axles all go up and down independently, you can see this in the ground level shots and time lapses. So going over the median "should" not of tipped the structure. We do see the structure tip when it is being jacked up and down, but it looks as if the trailing edge is raised first, and then the leading edge, so no twist "should" have been induced. Besides, the cracks were noted while the structure was still on the construction supports before the SPMTs came on site. So whatever broke was starting to break before the move. Could tensioning the PT rods in 2 and 11 have pushed the already weak design over the breaking point?

 

[MikeW7]

SFCharlie - I'm not talking about rocking or tipping the entire structure. The canopy is chained directly to the SPMT arms, but the deck is sitting loosely on top of cribbing. If the deck shifts sideways (as viewed in the Ground Level video) the canopy chains hold the canopy stationary with respect to the SPMT arms, so the truss area between the canopy and deck is being bent - the vertical line of "I" cross section is bending as the bottom line moves but the top line does not. Similarly When the deck spins on the SPMT timbers while the canopy remains stationary with respect to the SPMT, the truss area between the canopy and deck is being twisted - the bottom line of the "I" cross section is rotating about the vertical line, with respect to the fixed top line.

 

[MikeW7]

Based on the original SPMT locations, the north end of the canopy was probably supposed to be chained to some arms on top of the northern-most SPMT, but after the design change that SPMT was moved inward, and Barnhart ended up chaining the north end of the canopy directly to the deck edges.

 

[Vance Wiley]

MikeW7 - It looks like the cables run over the edge of the deck and attach to the transporter beams. I had originally thought they were connected to the deck surface.

 

[MikeW7]

Vance Wiley - Canopy chains attached to deck at span ends, but to SPMT arms at SPMT lift points:

 

[jrs_87]

Re: "Canopy Chains"

This is final plan for move, includes call out for canopy chains.

See jrs_87 (Mechanical)7 Jun 19 19:06 for link:

 

[MikeW7]

EDIT: I re-uploaded the images but they still look like crap. A "feature" of the forum I guess....

Some notes on the SENSOR instrumentation, taken from the Barnhart Movement Plan link provided by jrs_87 (Mechanical) 7 Jun 19 19:06


In the diagram below, columns 10 & 11 were not monitored at all, and rotation sensors were installed at the points marked DISP2, DISP3 and DISP4. These monitor the structure tilt in the lengthwise direction.

In the diagram below, at 5 equally spaced points (labeled 1-2-3-4-5, but the same as DISP1 to DISP5), 3 rotation sensors (labeled A-B-C) were installed at the deck edges and center. These sensors monitor the tilt of the structure across its width. NOTES:
[ul]
[li]The canopy chain is shown on the Twist Angle cross-section diagram as being connected to the deck curb, but as explained in my next section, BRIDGE TWIST is measured at points 2 and 4, where the canopy is chained to the SPMT arms.[/li]
[li]The comment box at the bottom describes how they expect the previously observed cracks to behave.[/li]
[/ul]

In the Testing Notes below:
[ul]
[li]STRUCTURE TILT is defined as the AVERAGE OF SEVERAL ROTATION SENSORS - I assume that will be DISP2-DISP3-DISP4 for the lengthwise tilt, and each set of A-B-C sensors at the cross section points 1-2-3-4-5 for the side-to-side tilt.[/li]
[li]BRIDGE TWIST is defined as the DIFFERENCE BETWEEN ROTATION SENSORS AT LIFT POINTS, which I assume are the A-B-C averages at cross section points 2 and 4.[/li]
[/ul]

My observations:
[ul]
[li]Columns 10 and 11 are devoid of sensors. The sensor record will indicate "nothing happened" to them during the move.[/li]
[li]There are no sensors anywhere on the canopy, and BRIDGE TWIST is defined between two deck cross sections (EDIT: at "floor level") at points 2 and 4. The events I described in my earlier posts involve the canopy area at the 10-11 blister moving/flexing with respect to the deck, which is I assume remains rigid. The sensor record will also indicate "nothing happened" to this area.[/li]
[li]These two facts explain why the on-deck activity during the move "pause" did not seem to involve the area around columns 10-11.[/li]
[/ul]

It's been a long afternoon piecing this all together (and I'm hungry), but hopefully I didn't mis-interpretate anything from the Barnhart document.

One final note: Below is a drawing of the bridge as shown on the cover page of the Barnhart document. I can understand why it shows the exaggerated tilt, but why are the SPMTs not in the same location as they are shown in the sensor location image? They are shifted quite a bit to the north (right). Attention to details....

 

[jrs_87]

Green arrow show possible remnants of 8" PVC pile. While I believe it's unlikely these are actually remnants of drain pipe, I don't have any idea what they might be instead. Other markups apply to another post.

 

[jrs_87]

Still looks like 8" PVC pipe? See attached in next post for larger size.

 

[jrs_87]

Larger size image.

 

[SFCharlie]

a good photo of the top of the deck at the base of 11 and 12

The NTSB report will likely be out this fall. They will have a "Docket" on their website with the Evidence they considered.

 

[Vance Wiley]

MikeW7 re cables and chains bracing canopy during move - I like the chains better. Big chains well anchored. This seems like the place for something with very little stretch under load - so that means large steel areas. Cable is not called wire rope for no reason.
There was a photo of an early crack at the fillet of 11 to the deck, with a path on the east side being a projection of the lower side of 11 to the deck and the cold joint. Across the face of that fillet the crack traveled downward to the west face at an angle - kinda like a tension crack might develop under a lateral force to the west at the top - maybe from some wracking or wobbling during the move.
The NTSB report will be interesting - at least to this group.

 

[Wetlander]

Today's article from the station covering the FIU bridge trial reveals some FIGG text messages, although just one from Denney Pate's phone, as well as some of the differences between the Bolton Perez meeting minutes and the FIGG version of meeting minutes.

https://www.nbcmiami.com/investigat...gineers-Phone-Has-Water-Damage-511067272.html

 

[MikeW7]

Looks like the only thing Pate will be remembered for is his ugly pedestrian overpass and its collapse. What a way to end an otherwise remarkable career:
[ul]
[li]Senior VP and principal engineer in an engineering company with offices in 7 states, involved in the construction of over 200 bridges in 42 states and 6 nations, with a total value of over $14 billion(US).[/li]
[li]P.E. in 16 states[/li]
[li]Designer of over 30 majestic cable-stayed bridges.[/li]
[li]An actual Hall of Fame member (see the video).[/li]
[li]A distinguished alumni of Auburn's College of Engineering.[/li]
[/ul]

 

[3DDave]

If the phone has water damage then iPad reHab could be the solution. Or Louis Rossmann. Or any of the other dozens of phone rebuilders who will repair whatever chip(s) are no longer chipping. For this level of need, data recovery/phone rescue pricing is worth it. It is unlikely that any irreparable harm has been done, especially to the memory chips.

 

[JStephen]

"How did your phone suffer water damage?"
"It fell in the toilet."
"Did you fish it out?"
"No, I couldn't."
"Why not?"
"Because it was in little bitty pieces."
"Why was it in little bitty pieces?"
"Because I'd just spent a half-hour working it over with a ball peen hammer."

 

[3DDave]

My wife lost a phone into a toilet. Before she could decide on calling the building maintenance guys to get it, the auto-flusher sent it on its way. She has a larger phone now.