Miami Pedestrian Bridge, Part VII 51

[JAE]

A continuation of our discussion of this failure. Best to read the other threads first.

Part I
thread815-436595
Part II
thread815-436699
Part III
thread815-436802
Part IV
thread815-436924
Part V
thread815-437029
Part VI
thread815-438451




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[Sparweb]

Live load due to "a couple hundred celebrating, drunk & rowdy college students jumping up & down to music" is [highlight #FCE94F]>>[/highlight] Live load due to "Pedestrians" isn't it?

STF

 

[hokie66]

Probably not, SparWeb, but the impact and vibrations would have to be considered. But I doubt that scenario was contemplated, and the University could undoubtedly provide better venues for that type activity.

 

[jrcooper80]

I just came across this old article on the Chronicle of Higher Education: Link. It does appear that FIU dictated the overall design of the bridge that probably sealed the fate of the bridge from the beginning. According to the article, FIU wanted it to be cable-stayed for its looks (opting for aesthetics over safety?). It is not clear why they ended up with a truss bridge with decorative cables. Then they also decided to go with the heavy and fragile concrete over the lightweight, cheaper and safer steel. The irony is that the researcher in the article actually specializes in steel bridge, but chose to give concrete a shot for both aesthetics and longer service life. According to the article, the researcher had just finished a major project on bridge service life and wanted to use the bridge for experiment and to verify research results (re the last paragraph of the article). Perhaps the final nail in the coffin was FIU's decision to also use the ABC method advocated by the researcher. Combining ABC with the long, heavy and fragile concrete slab may have turned a usual over-engineered bridge to one that was under-engineered in terms of withstanding construction/design errors. Shouldn't experiments belong in labs? Sadly, these decisions may have cost six lives.

 

[RUStructural]

The AASHTO pedestrian bridge live load is 90psf nominal and gets a 1.75 load factor for 158psf factored LL. To get that density of people no one will have space to jump or really move at all.

 

[SFCharlie]

(opting for aesthetics over safety?)

Thanks for finding this.
Please see my reply (26 May 18 23:42) to Retiredat46 (Aeronautics) 26 May 18 17:10 above.
The link is to an article in FIU Magazine reaffirming your analysis.

Yes, but aren't experiments supposed to have criteria and instrumentation and findings?

 

[bridgebuster]

NTSB releases preliminary report

Link

 

[bridgebuster]

of course it doesn't say much.

 

[chris snyder]

Not sure if NTSB error, but the prelim report said the photos were from 2/24/18, but the created date of the six photos was 2/28. The accompanying Crack Report memo from Jose Morales was also dated 2/28 and just noticed that Carlos Chapman was copied (the worker on canopy who latched his harness before it fell), so maybe he was a senior guy w/Structural Technologies.

Problem is they had warning that something was wrong (per cracks) 10-14 days before they moved the span and nothing was said until after the move. Before moving, the span was supported only at ends as it would be on the piers, so they could have done 'real world' tests/adjustments. Many here say the 11/12/deck connection was weak, Toomas Kaljas ran FEA that showed high 3D stress there, but no one's estimated the strength of the connection (maybe not so easy). The 1/2/deck connection held after the collapse, as did vertical #1, LONG members 4 (no PT rods) and 2 held, but member 3 had much damage even though it was ~vertical - just correlated this with being the only other member with odd/high 3D stress.

Warning signs were missed/ignored. Is similar to the Hartford Civic Center where bending of girders was evident on the ground, but they hoisted up the sections and continued building. And like the WestGate Bridge, they didn't clear out underneath while working on it - Wikipedia said "Many of those who perished were on lunch break beneath the structure in workers' huts, which were crushed by the falling span." (this after they'd put 80 tons on it and had removed 37 bolts to change camber/match sides).

 

[3DDave]

I expect that when tension was applied to #11 as part of the move it eased back on the crack and then when the post-tensioning was relieved the joint opened again; so they thought that re-applying the tension would close the crack.

In the pictures in the FEA stress analysis, the diagonals should all end flush with the top of the deck as the deck was poured first and only re-bar and friction was holding the diagonals in place. The stress analysis does not show the finished size of #2, which nearly doubled in depth and probably accounted for its survival.

 

[Retiredat46]

Would it have made any difference if they had made a raised pedestal as part of the deck pour below 11 and 12 so the construction joint on 11 would have been perpendicular to the axis of 11? I'm assuming no change to the rebar placement. The bottom of the pedestal would still see significant shear, but at least it would be one solid piece of concrete.

I'm just really bothered by a construction joint passing at an angle through the area with the highest loading. Is that an unjustified concern?

 

[jrs87]

Retiredat46,

This may help:

Summary of Cast-In-Place Concrete Connections for Precast Deck Systems (2011)
Chapter: Summary of Cast-In-Place Concrete Connections for Precast Deck Systems

https://www.nap.edu/read/14556/chapter/1

See this article for serious rebar placement.

http://www.constructionenquirer.com/2017/08/25/mersey-gateway-bridge-set-to-open-early/

 

[CCW1]

Here is Boston Big Dig Tunnel Ceiling panel collapse litigation compass rose.
Two people were killed: driver and passenger of car the panel fell on.
The courts and officers of the court (lawyers) took two years to get to
the bottom of it. By process of elimnation, the supplier of the adhesive
for the ceiling anchors was held responsible, although they claimed it was
the field contractor who mishandled the adhesive who was responsible.

So, Hokie66 nailed it. With the list of cast of suspects already growing, and without an obvious cause-effect chain discovered, it will take a while.

 

[jrs87]

February 2015 Cable Stayed Pedestrian Bridge Collapse:
(You may wish to translate in browser)

http://www.eltiempo.com/archivo/documento/CMS-15182335

http://www.eltiempo.com/archivo/documento/CMS-15179976

Mast failed in load test.

 

[jrs87]

Yet another collapse:

https://estudiosassani.wordpress.com/2017/04/10/fallas-en-las-construcciones-de-puentes/

Twin spans, one failed, the other did not.

 

[epoxybot]

CCW1 - I don't think a process of elimination in the courts actually defines who is principally responsible unless the actions taken were done so without any knowledge of the parties producing the materials & assembly. Both SIKA & Power Fasteners should have shut down any consideration of using an adhesive for suspending concrete panels over any area that humans might pass under or anywhere that might create an attending hazard to structures/infrastructure. They are suppose to be the experts on adhesives. Not the engineers, the suppliers or the contractors.

This is when companies like SIKA & Power Fasteners are suppose to say, "You can't do that and even if you decide to do it, we will not supply the material" and then you follow up with a letter making your declaration clear. Things have changed a lot since the cost of ICBO Reports have eliminated a lot of very good adhesive manufacturers from anchoring applications. There is a much smaller circle of input as to what is an acceptable risk. Hilti has done a great job of specializing the adhesive anchor business and deserves their reward for doing the R&D. The companies in the adhesive anchor business today enjoy limited competition and should find it easy to JUST SAY NO to request for an overhead applications. If hundreds of adhesive manufacturers would not allow it (and didn't), there isn't any better thinking that applies to overhead/suspended adhesive applications now ICBO has entered the game.

Prior to the Big Dig the only applications that I was aware of where adhesive anchors had been used in overhead/suspended applications, was for temporary rock screens in mining & tunneling work. From the point of conception for this work on the Big Dig, it is the adhesive manufacturers who knew they were treading where other manufacturers would have stopped. Having worked for a former Chairman of ACI Committee 503 & a former Chairman of ASTM C-881, if I had walked the question of the use of adhesives to suspend the concrete panels on the Big Dig Tunnels, to either of their office doors, they would have responded with a definitive NO. In my personal judgement I find SIKA & Power Fasteners participation contemptible. More so since like most manufacturers, they should have known the frequency of how often installation via cartridges with static mixing elements were poorly understood & executed by ordinary tradesmen, at that time.

 

[hokie66]

Hear, hear, epoxybot.

 

[CCW1]

Big Dig was the black hole granddaddy of all public works projects that formed over the northeast seaboard 1992-2007 (for the youngsters here). Everything associated with it was ground breaking, new technology on a scale never done before. You can read about it from many sources, maybe in your text books by now. Here is just one

https://www.nasa.gov/pdf/469423main_ASK_39s_big_dig.pdf.

Probably some of the folks on here worked on the project, something for everybody including engineering the widest cable-stayed bridge in the world, at the time.
Excerpt:
Boston’s Central Artery/Tunnel Project, commonly known as the Big Dig, was the largest, most complex, and most technically challenging highway project in American history. Larger than the Panama Canal, the Hoover Dam, and the Alaska Pipeline projects, it was built through the heart of one of the nation’s oldest cities. Its list of engineering firsts include the deepest underwater connection and the largest slurry-wall application in North America, unprecedented ground freezing, extensive deep-soil mixing programs to stabilize Boston’s soils, the world’s widest cable-stayed bridge, and the largest tunnel-ventilation system in the world.

One of the photographs in the reference shows the flat roof of the 10 lane tunnel ceiling, also a photo of the big Bunker Hill Cable-Stayed bridge.

Epoxybot do you know if they went back and replaced all the adhesive anchors on the ceiling panels or what?

 

[CCW1]

Speaking of Impact and vibration criteria. How would AASHTO LRFD Section 3.6.5 apply to this Miami Ped. Bridge?

 

[hokie66]

CCW1,
We had an extensive discussion about the Big Dig ceiling failure when it happened, and looking back, that was 12 years ago.

My recollection is that all the ceiling hanging bolts were replaced or supplemented with Hilti mechanical undercut anchors.

 

[TheGreenLama]

Nothing new here. Just wanted to get a better picture of the FIGG design team. Denny Pate was the engineer of record, but others help craft this hybrid. Pate stamped the drawing. He's responsible. But it doesn't mean he designed the bridge. This was a team failure. These were cut from the "MCM FIGG Proposal for FIU Pedestrian Bridge," 9-30-2015 [Link].
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