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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[samwise753]

Further development from recent court proceedings:

https://www.nbcmiami.com/investigat...Morning-of-FIU-Bridge-Collapse-508394661.html

I find the statement about conflicting meeting minutes troubling:

But FIGG has challenged the accuracy of the minutes of the meeting, prepared by BP&A, and six weeks after the collapse provided its own version of the meeting to the National Transportation Safety Board, calling them "corrected minutes."

FIGG's version made "significant substantive changes" from the original minutes, according to a lawyer for The Louis Berger Group, an engineering firm also being sued in the civil cases.

I would think that all professional engineering companies require the chair of the meeting to send out a draft of the meeting minutes to all attendees for review and update with any comments or missing information. The final draft isn't issued until everyone agrees, so I find it hard to believe "corrected" meeting minutes issued 6 weeks after the collapse to be considered valid once checked against e-mail records provided by the parties involved.

This also highlights the importance of documentation in our profession.

 

[JStephen]

I don't know how they did it there, but most of the meetings I've ever been in, any minutes were pretty rudimentary and were not emailed around until everyone agreed, etc. So I wouldn't doubt that the minutes were incomplete or omitted items that people said, etc., unless they purported to be otherwise.

 

[saikee119]

I don't think the Minutes of the Meeting on the day prior to the collapse carried much weight in the case.

FIGG is the designer. Only the designer has the right to modify or repair the bridge. The designer is also charged to evaluate the severity of the cracks and their impact to the structure. He is the sole party to decide if a repair is needed, when and how it is to be executed.

FIGG proposed to re-tension the truss members. The MCM contractor was executing FIGG's repair scheme and FIGG knew traffic was running underneath and did nothing to halt the remedial work. The bridge collapsed "during" the execution of FIGG's repair scheme.

Whatever written on the Minutes can't change the above.

The NTSB published photos, that shows a tape can be inserted to a depth of 4" and then 6" into the cracks of the slab and Member 11 respectively, were taken by the workmen on 13th and 14th so the participants to the meeting on 15th would know full well the severity of the cracking. If FIGG concluded, there is "no safety concern" as recorded in the voice mail then that is enough to demonstrate FIGG's competency in this project.

 

[hokie66]

Unless the minutes of the meeting were a condensed version of a recording, it is "he said, she said". There were probably notes taken during the meeting, but the minutes would have been prepared and distributed later, presumably after the collapse, so you would have to question their reliability, just as you would question "corrections" made six weeks later.

 

[RolMec]

in order to find core reasons and systemic failures in procedures the true course of actions / nonactions needs to be established
this is beyond the who to blame level,this would save life / health in future

casting of a shadow on things means resources / thoughts are bent elsewhere
engineering maturity is not making the beeline off of the site, not even mentally. but full support to uncover all that may be found out.

in this case, the fact is evident that certain meeting discussions / decisions need to be cast into mutual agreement BEFORE further work is executed.
professionally this should be mandatory for security related issues.



Roland Heilmann

 

[epoxybot]

I thought I had read that the work crew were already up on the bridge while the meeting was taking place. It raises the question whether they on site to perform work based on the smaller cracks and somehow the word wasn't circulated that a re-think was in the works.

Obviously, the meeting minutes would tell us whether the outcome of the meeting was to tighten the rods.

 

[saikee119]

It raises the question whether they on site to perform work based on the smaller cracks and somehow the word wasn't circulated that a re-think was in the works.

The NTSB photos in the 9 Aug 2018 Update were dated 13 and 14 March 2018. It would be unimaginable the last big known cracks were not discussed at the 15 March meeting held five hours prior to collapse. Any engineer who has worked on site for say a few years and have seen strength tests by crashing concrete cylinders would know the bridge has gone just by looking at the cracking severity in the NTSB photos, one of which shows a tape can be inserted to 25% depth of Member 11 two days before the bridge failed!.

NTSB preliminary report shows the cracks before the bridge was relocated. The last known cracks should be those in the NTSB 9 Aug Update. Three photos were sourced from the Contractor MCM and one from BP&A Consultant most likely sometimes after the PT rod tension was removed in Member 11.

May be I am among the minority disturbed by the magnitude of the cracks. However the majority of the large cracks photos were taken by the workman who carried out work on the PT rods. My speculation is that he was equally surprised too and had gone out his way to record the evidence rather professionally, with a tape inserted as a comparison. He must have been deeply worried if he had done something wrong and the photos were his protection to show the end result of his work was as per instructions/commands. Sadly his employer still sent him out to do more work on the PT rods and he was seriously injured at the end.

 

[MikeW7]

Don't think this has been mentioned before, but the bridge may have been unknowningly damaged during the move. From the NBC Timeline:

March 10th:

"A document prepared by the claims administrator for the insurer of Bridge Diagnostics Inc. (hired to install and monitor sensors tracking the bridge's position, rotation, strain, tilt and twist during the move) states that the movement had to be stopped 10 to 15 times because the span twisted greater than one half of one degree -- requiring workers to readjust rigging supports each time."​

March 15th:

Shortly after the bridge collapsed a Bridge Diagnostics Inc. engineer was called by Barnhart, the company that moved the bridge. The BDI engineer was working on a final report, and told Barnhart that evidently after a work break their monitoring software failed to reload it's stored offset measurements when the computer was turned back on. NBC noted that because the NTSB has prevented all parties from commenting, it's unknown if this malfunction only affected the BDI final report, or if BDI gave the Barnhart engineers corrupted sensor data during the move.
​

 

[saikee119]

Let's see how damage could have inflicted to the bridge during the move.

The FIU bridge has a dead weight of 950 ton. It has 5 bays so roughly each bay weighs about 190 ton. During the move the two end bays were cantilevered out so each might have a maximum of 190 ton hanging freely.

Member 11 has two PT rod each stressed to 280 kips so together the two rods offer about 250 ton resistance.
Since the bridge was tightly monitored and fully rigged with strain gauges I doubt much damage could have occurred.

The Member 11 has a slope of 35 degree (1 vertical:1.427 horizontal:diagonal 1.74) so if the reaction at the support were to be 475 ton then the axial compression in Member 11 due to the dead weight could have been about 950/2*1.74 = 826 ton

To me a real killer could be the omission or the lack of consideration of 250 ton from the PT rod stress, required only during the move, in rebar design of Member 11. 250 ton is an increase of 30% load to member 11.

FDOT had hand written the need of temporary PT rods on FIGG's drawing on 15 Sept 2016. Any engineer looking at the rebar inside Member 11 would know it could not possibly take 1/5 of the bridge dead weight. This raises the alarm about FIGG's competency have to rely on FDOT to tell them something so fundamental. If FIGG had implemented FDOT suggestion of the extra PT rods but did not follow through with the rest of the structure especially the connection design of Member 11 to take the extra 30% load then that might be the smoking gun everybody been looking for.

 

[SFCharlie]

It was FDOT, that asked them to add room for an extra lane just before construction was due to start. I wouldn't have been real happy having to deal with that at the last minute. What I find mysterious is that members one and two were beefed up, but not eleven and twelve?

SF Charlie
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[MikeW7]

The strain gauge data may have been corrupted, allowing the bridge to be over-stressed without a warning indicator. BDI was responsible for installing and monitoring the strain gauges. They acknowledged to the bridge mover, Barnhart, that at one point a computer was turned off and on during a work break, and all their gauge readings were reset to zero instead of reloading the stored values that were present before the break. [highlight #FCE94F]EDIT ADD: After re-reading the Timeline description, what may have been lost were the inital calibration offsets that were used to zero the gauge readings before the move began.[/highlight] This implies that many of the monitored areas could have exceded 100% of the safety threshold during the remainder of the move, and at least one of the monitored areas may have experienced close to 200%. It's also possible that the lack of concern about the cracks after the move may have been partly influenced by the "good data" provided by BDI showing the bridge hadn't been overly stressed during the move.

Multiple problems with the data collection process. The BDI software apparently wasn't configured to auto-resume after a reboot, or at least indicate a warning. The "meter reader" didn't notice the gauge readings were reset after the work break, possibly because a "new guy" took over. In either case BDI should have anticipated such a problem and trained their personnel. The data discontinuity at the break should have been clearly evident in the charts or readouts, and somebody from BDI or Barnhart should have noticed it during a post-move data review.

 

[LittleInch]

Given that there were only two load points on the bridge I don't think their issue was changes to the bending of the bridge and in any event the final two bays were hanging off the end so not really impacted by changes in elevation at the support points.

The single line of the columns but wide bottom flange gives rise to twisting of the bridge if the trailers encounter changes to the elevation which as they had to negotiate a verge and the central reservation is not surprising. Hence the limit of 1/2 degree of flex.



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

 

[saikee119]

It was FDOT, that asked them to add room for an extra lane just before construction was due to start. I wouldn't have been real happy having to deal with that at the last minute.

From record the bridge was moved as one complete unit by 11' to the North. The span was not changed so structurally the structure was the same as before. As construction had not started yet so the impact to the cost should be minimal.

 

[SFCharlie]

The span was not changed so structurally the structure was the same as before

That's the point: The span wasn't changed (enough) but the support during the move was changed fundamentally. Also the construction was scheduled to start within a month. All the adding the PT rods in 11 etc. happened after the support during the move was changed to accommodate the 11 feet of dirt adjacent to the center pier.

SF Charlie
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[SFCharlie]

There was a non-trivial charge for the extra engineering for the 11 feet for the extra lane. Moving the center pier closer to the canal required driving extra piles taking more time and delaying the start of pouring the piers, putting the schedule in a time bind with the end of the money availability running out causing the rush at the end causing the panic which may have affected the critical thinking at the time of the move.

SF Charlie
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[epoxybot]

MCM asked for an additional 180 days & $1.7M to effect the shift of the bridge.

The timeline was helpful to resolve my impressions that workers were up on the bridge while the meeting was ongoing. They were on the bridge at 10:40AM, with the meeting concluding at 11:00AM. What is concerning, is the anecdote that engineers were seen on the bridge, in the hour prior to the 9:00am meeting, at which Denny Pate gave a presentation and presumably stated; there were no safety concerns & the cracking did not compromise the structural safety of the bridge. Just who at the meeting was up on the bridge?

FDOT engineer Tom Andres' name has been dragged through this disaster by the media & by inference by FIU's finger pointing at FDOT but when he sent an email confirming all his concerns had been resolved, including the positioning of the SFMT transporters, the SMFT transporters were positioned differently under the 2-3 & 10-11 nodes. There isn't any source showing he was informed or approved the repositioning of the SMFT transporters further inboard from both ends of the bridge. No reason has been given for the changed positioning of the SMFT transporters. If he wasn't notified, I imagine having his name dragged through the press does not make him very happy. The timeline shows he doggedly pursued each of his original concerns to a conclusion.

Since we now know the bridge was UNDERNOURISHED, the real tragedy is that the telltale signs were present from the time the bridge was set to the time of its collapse and good people failed to act.

 

[MikeW7]

Does anyone know why the move was halted just before dawn? Stuart Grant took several time-lapse videos from different viewpoints as the bridge was moved, but this ground-level video, credited to Grant, no longer appears on his YT Videos page. It shows several instances of the bridge shifting on the north movers as the south movers were repositioned, then the move being stopped while the north mover is still partly on the center divider. After a short pause someone is lifted up to the center of the span, and the move continues immediately after he is brought down. This video shows the person making several trips to the south end of the span.

 

[epoxybot]

Does anyone know why the move was halted just before dawn?

.

Most likely, the move was halted to await the arrival of dignitaries.

 

[MikeW7]

epoxybot - They paused while the bridge was it still partly on the center divider and before it was aligned North-South. If they were concerned about Show-N-Tell they would have waited until it was squared up with only a few feet to go. Looks like they encountered a problem, stopped to discuss it, then sent somebody up to have a look. If it was BDI checking their instrumentation, this may have been when their computer was shut off. Odd that they only checked the south end even though hairline cracks were previously found on both ends (members 3 and 10).