More information on the Miami Bridge failure!!!

JD Seller

Well-known Member
Mr. Brown has posted another video with more details on the Miami bridge failure. This includes dash cam footage of the actual failure. It shows the failure at the support the construction company was adjusting. This video is loaded with good factual information.

Miami Bridge failure

https://www.youtube.com/watch?v=GxQJj8D_FE0
Maiami Bridge failure update
 
Ohiojim: Mr. Brown does a great job presenting facts not fiction or opinion on these type of things. He really is doing us a great service that none of the new services do anymore. They "create" news and spout opinion as fact too much of the time.
 
37chief: I have to agree with you. The biggest screw up I see out of this is not shutting down traffic while they were working on the bridge.

Some things to think about:
1) The motivation for this bridge was the single death of a student. Now we have six dead because of the bridge. No point just an observation.
2) I am not any type of engineer. I just do not see any common sense in having a 1000 ton bridge to span only 175 feet. I would bet that a steel bridge could have been built that was much lighter and cheaper/faster to build.
3) I am betting that several egg heads and politicians pushed this bridge design because it was "pretty" and would be "ground breaking". All while spending other people's money, TAX payers.
4) I wonder if the same wizards of smart will try to just change the design a little bit and rebuild it like the one that failed????
5) I bet there are prefabbed steel bridges that could be build entirely off site and trucked in within a short time frame. You not redesigning the wheel here folks. I know of several walk bridges that span much longer distances and they are simple steel structures built in sections and bolted/welded together.
 
I designed bridges on Long Island NY--Our preferred material was concrete if say within 1 mile of salt water. The dampness and salt air deteriorated the steel bridges at a very fast rate. Of course we always budgeted maintainous funds to have an appropriate schedule of maintaining and painting them.More often than not the politicians would appropriate those funds to build new pet projects in their districts to impress the voters.
 
I thought pre-cast concrete was post stressed at the plant before erection.

The erection crew was in-experienced and non-union. This right here would explain most of the problem.
 
wgm: I wondered about that too. My exact thought was the guys took the nut off rather than tightened it. If you follow along close they state that they tightened the bolts more before the move to carry the load since the movers where closer to the middle than the original plan/design. So it would make sense to me they where lowering the tension back to what it should have been for the design. In the one picture you can see the thightener still attached to the rod. The rod is shot out of the concrete beam. Did the rod break or where they loosening it and the bottom nut came off????

I do not know if you caught it but they even could not use their safety harnesses correctly. The crane was setting there just so the workers on the roof could tie off to the crane. IF you watch the video real close you can see that the harness/crane failed to catch the worker. If you can not use a fall protection harness correctly should you be working on a bridge?????

So is worker/contractor error going to be the cause????

The NSB will find out what actually happened. They are very good at ferreting out the cause of this type of stuff.
 
JD--we were once tightening a post tension rod and the damn nut stripped out! thank God it had no affect on the strength of the bridge!
 
Good One JD
As a GeoTech and Construction Materials Engineer, I putting my "money" on defective concrete and/or defective cable ancorhage or integrity.
Will probably be reading about this failure soon.
Jim
 
Has anyone else heard this? "If a thousand ants were to walk across the Golden Gate bridge in perfect unison, the bridge would collapse before they reached the other side" Does that sound right?
 
NO
There is Prestressed Concrete at the plant
And Post Tensioned Concrete when the members are placed and subjected to the required tension forces to support the loads.
The more I think about it, I think the concrete failed due to the concrete "creep" cracks observed before the bridge failure.

That's my story and I'm sticking to it (for now) !!!
 
What they are talking about is people/animals walking start a rhythm or harmonic that can cause a structure to fail. So it is not a weight facture. Walk bridges have to take this into consideration. Have you ever walked across a rope bridge??? They will get hopping as you walk.

Lay a 2x12 down across two saw horses and walk across it. The rhythm of you walking with make it bounce.
 
kruser
I'm a junior civil engineer and ran a QC lab at a precast plant doing pre and post tensioning.
In the video it looks like a hydraulic tensioner.

So this is my professional guess. It was over stressed for the cantilever. I think they came close to the ultimate strength.Then they had to destress it. When you destress you have to put more tension on it to loosen the chuck.I think the rod or one of the end plates broke. One other thing is the chucks could have failed while relieving the pressure. I have seen chucks fail. 450' of strand flying to other end of the building in a blink of a eye.We stressed 1/2" strand to 28,000 psi.
 
I wasn?t aware that not being in a union made you less of a tradesman. Seems like a stretch, no?
Inexperience, that?s not hard to see as being a factor, but non union, that?s almost insulting.
 
(quoted from post at 19:55:59 03/18/18) Has anyone else heard this? "If a thousand ants were to walk across the Golden Gate bridge in perfect unison, the bridge would collapse before they reached the other side" Does that sound right?
No it would take several million ants at least?
 
was that type 270k stress relieved strands? we always used them for the design of prestress concrete products
its very exciting when your tensioning the strands and one breaks--that steel wall barrier that you work behind was really necessary
 
Yes I believe we used 270k stress relieved strands. It has been a few years since I worked their. We made spancrete in one building. The stressing block was 2"x24" plates stacked up with a 1" continuous space for your strand. One time the operaters of the machine started a new production line. The strand did not line up. He was tapping on the chuck to line it up.He tapped it to high or to low and that chuck went into the 1" hole. That caused the top and bottom plate to fail. It bent both plates and made the space 2"wide. That caused a couple injures.
 
Source for the claim the crew was inexperienced and nonunion? Given the job it was a David-Bacon project with union wages required. They hold the record for the largest precast construction projects.

Usually on a project like this the engineer is the one at fault. They designed the project, they oversee the construction to ensure the contractor builds it to their specifications. The ensure the metal content, they test the concrete used to ensure it meets their specifications. The engineer gets paid a huge percentage of the contract for their services during the construction faze of the project. And as usual when their design fails they blame the contractor.
 
What about couple yrs ago they had a celebration of the Golden Bay Bridge and it was loaded with thousands of people wall to wall and they did a quick figure about all that wt which was much more that if it was loaded with cars traveling and then said it weould be OK The bridge had never had that much wt at one time since it was built and it passed with flying specs.
 
The FIU bridge was built using Accelerated Bridge Construction (ABC) technology.
Which means that in no way could it be a "union job". Otherwise it would be called De-Accelerated Bridge Construction (DABC) technology.
Otherwise known as "How to do something as slow as possible for the most dollars per hour possible".
 
(quoted from post at 11:07:23 03/19/18) The FIU bridge was built using Accelerated Bridge Construction (ABC) technology.
Which means that in no way could it be a "union job". Otherwise it would be called De-Accelerated Bridge Construction (DABC) technology.
Otherwise known as "How to do something as slow as possible for the most dollars per hour possible".

By that line of reasoning unions shops would have been forced out of business decades ago. Non union shops take the scab jobs that won’t Pay for safety and training.
 
To add to JD Sellers, its called resonance. The unison part is more important than the weight. They would all have to be marching in a rhythm to match the natural frequency of the bridge as well. In some situations, even wind can cause this. The Tacoma Narrows bridge in the 1930's came apart when a wind caused the bridge to sway at its natural frequency, the sways amplified until the bridge collapsed.
 
(quoted from post at 11:54:18 03/19/18) No the policy is called work or get fired. Union labor is too expensive for slackers.
Have you ever been inside a union auto plant trying to install equipment?
Need power turned off?
Wait an hour or to for the union electrician to pull and lock out the switch.
Need to more a pallet of parts from the dock to the work site within the plant?
wait an hour or two for the unionized forklift operator.
Same scenario for:
getting compressed air hooked up.
getting natural gas hooked up.
getting electric power hooked up.
on and on and on.
but then it is break time when they show up.
Then before the task is completed it is shift change and the above starts all over again from scratch.
 
That was in 1987, the 50 year celebration....The bridge was opened in 1937. My wife and I were living in San Jose and we went up there. We went up to San Francisco pretty early and parked within about a mile from the south anchorage and managed to get nearly on the bridge as far as under the south tower. There was one huge crowd there. Pictures taken showed the arch of the bridge deck was somewhat flattened by the load of people, more than had ever been noticed with a heavy vehicle load.
 
Used to be that army troops were instructed to break step (break stride) when crossing a bridge. Probably obsolete idea now but ....

"If soldiers march in unison across the structure, they apply a force at the frequency of their step.

If their frequency is closely matched to the bridge's frequency, the soldiers' rhythmic marching will amplify the vibrational frequency of the bridge. If the mechanical resonance is strong enough, the bridge can vibrate until it collapses from the movement".
On an early 1900's bridge at Harrisburg,PA, if enough people are running on it, you can feel it vibrate.
 
Thanks Guys for opening this discussion , I just hope it Stays out of the hands and minds of those who care nothing about learning from this terrible failure that killed 6 and possibly more people . the fact these deaths occurred should silence anyone from making less than a caring intelectual comment.. . i too have been sifting thru all the news and whatever pix and design engineering flaws, to grasp what really happened . Today I learned that the center pole and the suspension legs were designed with the lesser intent of stabilizing the bridge and the greater intent of making a pretty picture for yrs to come. Not Until i Realized that fact , I too , Believed that allowing the public under a bridge while under construction without the main suspension arms in place was extremely negligent .Others stated and I agree , The Supports were not placed as the engineers had originally intended.. some one barn yard engineered figured and reasoned they could adjust load tensioners and all would be well,.As Soon as that thought became reality , all traffic beneath the bridge should had been re routed ,,BECAUSE , BY adjusting YOU are Really testing Loads that have YET to be PROVEN . THIS is Where and when The Health Safety and welfare of the public was left wide open ,. LOTS of Questions here,.sadly the families will sue. As They Should.. But in the End , We Should all be able to understand this tragedy and LERN From it , So Failures like this will not kill in the future.
 

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