Florida Bridge Collapse

mikeg2015

Well design might not have been wrong, but I’ve seen really poorly written specifications and details especially with instructions for assembly. Plus contractors are not always good ablutn usliry control.

The key will be the 3rd party material testing and the company that was performing the project management and overall oversight. Did they allow any deviations to avoid rework or increased costs.

What’s amazing is that the community college inwork at hired the GC to also perform project management. Nobody from the college provided any real oversight except budget, timeline and changes to scope or addendums.

Gordy

Self perform is not as most people think. Most times third party testing, and engineering firms are hired outside the GC for testing, and inspections.

However some parts of the special provisions for the job can be misinterpreted by the novice. Special attention to detail, and punctuation in the framework of the wording is key, and at times can be argued in favor of the contractor by the contractor.

I’m quite sure the designers were not looking the other way on a unique design by themselves as this one. Not a cookie cutter bridge design. Even though it’s a pedestrian bridge it was still over six lanes of traffic. Anything is possible though.

Gordy

I’m not sure how Florida’s FDOT operates, but most private owner build special provisions would follow FDOT’s , or what ever state construction resided ins spec book as a minimum standard.

EBEBRATT-Ed

@hot rod is right and others have mentioned as well concrete has no tensile strength but has massive compression strength.

If they plunked it down without it's support structure I can see it buckling in the middle, half the deck thickness in compression and half in tension. Should have been set on temporary intermediate supports until the support structure was in place.

You can design anything on paper and make it work. Dosen't mean it will work in the real world.

Just picking it up wrond and setting it could have stressed that POS

And it was supposed to take a hurricane load as well as people, bicycles and god knows what else.

Anybody here the words "safety factor"

Oh yeah, I forgot that costs money.

They sure save a lot of $$$$on this job

Gordy

Yeah, and it sure kept traffic moving do to construction inconvenience......how many days before that detour is opened up again?

Gordy

Interestingly the superstructure was set in place on Saturday. It collapsed yesterday. Usually failure is designed in to be a slow process, and not instantaneous.

Fred

Latest update, the lead Engineer on the job called the DOT two days before the collapse and reported that there was some cracking in the concrete at one end of the bridge and said that while it would require some repair, he did not believe there was a safety issue.

Gordy

This much I know. No one is that stupid to set 950 tons of concrete over six lanes of live traffic with out complete confidence in its design.

There are layers of control in that process. The contractor, on site engineering, and design, and owner of the road it’s going over.

So the contractor certainly did not do it with out the knowledge, and consent of the other three entities. The onsite engineering firm didn’t allow it with out the okay of the designers. FDOT wouldn’t allow it over their Highway with out the designers okay.

skalor

Check out AvE on YouTube. He's posted a couple interesting videos about this.

Gordy

Lol.

He has a general understanding.

False work was not apart of the erection process. I guarantee that it was engineered that way.

Post tensioning is done after casting, and concrete curing, and strength results are met. The cables are in ducts, and not poured into the concrete.

Then post tensioning proceeds. The whole structure, top ,and bottom is brought under tension. This results in the concrete being preloaded in compression, while still on the casting bed.

When set on the mobile erection assemblies the bearing points were at 1/4 points in the span. This resulted in partial tension on the bottom, and partial compression on the top.

Once set in place, and comes to rest at the end bearing points the structure is then in full compression on top, and tension on the bottom.

The post tensioning cables on the bottom are designed for the load with a set amount of deflection. The cables were never under their designed load until the section was set in place.

The maker of the video also misses the point that one end is a fixed bearing point, and the other is not fixed so expansion, and contraction happens at the expansion end. This why the fixed end of the section was still on top of the pier. Being fixed the failure resulted in pulling the section off the expansion pier because it is not fixed to the pier.

The more I see the more I believe the problem was in the post tensioning cables. Either they weren't big enough in diameter, or they weren't equally tensioned to equally carry the load.

To come to rest as it did all the cables had to of either failed completely together, or pulled through the dogs that hold them in the tensioning blocks.

If the cables would have failed from say one side the section would have fallen in a more twisting motion. Buckling side ways not straight down.

Fred

@Gordy, the Engineer made a call that the cracks were not a safety issue and maybe they weren't but something caused the colapse and it was noteworthy enough that he called it in the FDOT. His judgement maybe was correct but maybe wasn't. One thing for sure, the FDOT, this morning said yes, he called in but had to leave a Voicemail, two days before the collapse but they did not listen to the voicemail until a day after the collapse, which means they did not provide any direction. At the end of the day, no matter what the design/construction/safety measures are, it boils down to human decisions and judgement. In this case, several lives were lost.

Gordy

He called looking for backup of his observations. Shame on FDOT for not being there. During the week no less. At least maybe traffic could have been detoured until confirmation of the problem was made that it was not structurally critical.

Gordy

I will add that the on site engineer should have called, and included the designers of the structure in that chain.

After all who else would know better? FDOT certainly would not. They didn't design the bridge. Probably knew very little about it. Especially the little bit of info provided. Crack? Where? How big? Is it progressive? Etc.
That would be like calling lochinvar about a crack in your HTP UFT HX. They would know it wasn't good, but didn't design it there fore can't explain why, or how it happened because it's a different firetube design by someone else.

Fred

At the end of the day, all of our opinions, experience and perspectives are just conjecture. My point it not to try to place blame, the final investigation, by those onsite and studying all the facts will do that, as best they can. The failure may well be the result of a collection of flaws, maybe in design, maybe in construction, maybe in materials, maybe in judgement but clearly this did not go as planned. This lead Engineer most likely followed protocol by calling the FDOT. That does not suggest that he did not inform others as well. It was still left to human judgement, right down to the decision to not close off the road to traffic.

Gordy

I'll blame computer design programs also, and the ones that place complete confidence in their reliability.

Most seasoned older generation engineers, and designers that go through or have gone through calculations by hand through successive steps to get the result will have better perspective as to where an error in the calculations of the final design can be.

Punching numbers into a software program, and it saying this will, or will not work is becoming the norm with new generation engineers, and designers. That norm is a slippery slope to follow. I say that because with out at least understanding how to get the resulting answer you have no idea if it will work, or where the error may be.

Like using a heat loss program. A seasoned designer can pick out a heatloss that's over, or under what it should be. and where the error may be in the program. Because he has a great understanding of building envelopes, and materials. We see this all the time where homeowners use them.

Vinny_5

I hope this doesn't offend anyone, but this is dash cam video of the collapse at street level:
https://www.youtube.com/watch?v=Ucflj-MsJBI
Seems to initially buckle right by the crane.

Fred

Wow, just a sudden collapse. Didn't buckle, lean or sway at all. Appeared to be just a sudden clean failure across the width of the bridge a few feet from the left end.

neilc

yeah,
and from the shadows I'm guessing that's the north end,
were the crackings were noted

SlamDunk

@Gordy: “I'll blame computer design programs also, and the ones that place complete confidence in their reliability“

There are two kinds of engineers these days...The kind that designs on a computer and the kind that has no drafting skills and sketches crap on a napkin and asks, can you make this?

The problem with the first is the ability to cut and paste from other jobs...mistakes and all.

The problem with the second is when you finally figure out how to make what he wants, he takes all the credit. Unless it fails.

Gordy

@Vinny have seen it. Adds to the smoking gun the post tensioning of the structure.

Either cables were not large enough diameter by design, improperly tensioned, or the dogs for the cables in the pockets failed.

Which ever they failed all at once. Not from one side to the other which would have caused the structure to move laterally on the way down.

Another thought is the upper deck could have been under designed for the compressive strength needed, or the cable tensioning on the bottom not tight enough to relieve some compression to the top deck.

Gordy

Also if you look closely at the crane, and where the hooks are. There was something being landed, or hoisted off the upper deck. Deffinetly not hooked to something on the structure, otherwise the back of the crane would have lifted, or the boom buckled. If you look closely you can see the worker falling. However the worker must have tried to hang on to what ever was on the hooks momentarily as the person doesn't fall with the structure, but slightly latter. Then the load comes lose from the hooks after.

EBEBRATT-Ed

@Vinny , thanks for posting. That bridge came down with no hesitation at all. I wonder if the crane bumped it with the boom. Doubt it.

BobC

The Zakim bridge in Boston is similar in design and the same firms were involved in this collapsed span. In Boston they discovered voids in the concrete because some rebar was so tightly packed concrete did not flow as they thought it would. They ended up having to jackhammer these ares and force concrete into these voids, I have my doubts about the longevity of this "fix" - see article posted below.

Things like this happen when the project is not under the DIRECT supervision of the designer. Materials and techniques get substituted in the never ending quest to keep on schedule and to control costs AND this is done without design approval.

I don't drive over the Zakim and I'd advise others to think about why I don't.

Bob


Big Dig officials acknowledge structure flaw in Zakim Bridge
By Associated Press

Posted Jul 28, 2001 at 2:00 AM Updated Dec 16, 2010 at 9:55 AM

BOSTON -- Big Dig officials for two years ignored a design flaw on the Leonard P. Zakim Bunker Hill Bridge, a key piece of the Big Dig, after the architect tried to draw attention to construction problems.
Project managers acknowledged on Friday that tests revealed the very problem that Swiss architect Christian Menn pointed out in 1999: that steel rods placed too close together within the structure wouldn’t allow poured concrete to entirely fill slabs in the span.
The resulting gaps within the nearly completed structure could shorten the life of the $100 million bridge, and must be fixed, Big Dig officials acknowledged.
″I wrote many letters about that. I discovered it two years ago. They didn’t recognize it,″ Menn said in an interview with The Boston Globe.
The bridge, now 98 percent complete, will connect the new Central Artery to Interstate 93. It is scheduled to open in November 2002, but Bid Dig officials planned to showcase the bridge to the public at an Aug. 26 open house.
Initially, officials of the $14.4 billion Big Dig, known formally as the Central Artery/Tunnel Project, performed testing that did not reveal the problem that Menn described, said Vijay Chandra, a Big Dig engineer.
But Chandra now admits that new tests using a ″borescope,″ a camera inserted into a drilled hole, and sound waves revealed that there were an unknown number of ″voids″ within the concrete slabs of the bridge.
″We found a lot of voids,″ said Chandra. ″We were concerned.″
Atkinson/Kiewit, the contractor building the bridge, halted work on the bridge on July 5 to avoid any damage resulting from the problem. After 15 days, work resumed away from the problem area on the southern part of the bridge.

The problem originated in 1999, when builders began pouring a concrete box beam atop two columns that extend into bedrock under the Charles River.
The construction required concrete to be poured around reinforcing steel rods, called rebars, that overlap for strength.
But Menn suspected that the rebars were laid to close together for the poured concrete to entirely fill the space under the bars. He informed project managers about his suspicions, but no one else working on the bridge the design firm, the contractors, the project consultant, or any inspectors ever detected the problem he outlined.
The question now is how to fix the problem. Big Dig officials are leaning toward ripping out the rebar and replacing the steel. They did not estimate the cost of that repair.
Menn is advocating another approach. He suggests that a new girder be built underneath, then connected to the existing one, a process that he said would cost $50,000 to $100,000.
Project director Michael P. Lewis said that fault lies with the staff of the designer company HNTB Corp., the contractor or management consultants.
″This is a cost that has to be absorbed among those three parties,″ Lewis said.

EBEBRATT-Ed

Some things never change.

The thing is, when they design these things they work on paper. Do they put enough safety factor in their calculations?? Safety factor cost $$$$ we all know that. This thing was supposed to withstand a hurricane........it couldn't support itself.


Everybody who ever worked on a construction site knows things get swept under the rug. Weather conditions, heat, cold, rain etc always have an effect on the construction and the inspections.

How many of us have installed roof top units or other equipment on a roof that needed mechanical or electrical inspections? Did the inspectors in your area go on the roof? Around here they do not.

Are Bridges any different?

hot_rod

Ever seen the film of "galloping Gertie" the Tacoma narrows bridge failure.
https://www.youtube.com/watch?v=j-zczJXSxnw

Gordy

Here's an actual cable stayed design in Columbia. One tower worked the other did not.

https://youtu.be/QSU8GozlAKc.

GBart

To build the support tower and cables AFTER the bridge is built is not logical - Spock

GBart

The final bridge, which was expected to open in 2019, would have added a tower and cable stays as the main support for the structure.

WOULD HAVE???

who is(are) the moron(s) that planned this?

https://www.nytimes.com/interactive/2018/03/16/us/florida-bridge-construction.html?action=click&contentCollection=U.S.&module=RelatedCoverage&region=EndOfArticle&pgtype=article

Zman

This is completely mind boggling, even by Florida standards. I thought it was just the residential contractors that were completely incompetent.

This is the sequence that would make sense anywhere else on the planet:
1. Construct support tower along with stay cables and stay cable anchors.
2. Construct supporting columns.
3. Construct bridge alongside road.
4. Move bridge into position, be sure to leave center support in place until stay cables are attached, tensioned and tested.
5. Remove center support.
6. Construct staircases and other supporting elements.

From the looks of things, the construction team started at the bottom of the list.

My guess is that some engineer let a software program convince him that a bridge with a self weight of over 950 tons would not need the critical support cables until it was time to open it to the public and allow 1,000 people (100 tons) or so to walk across it.

SeymourCates

@Zman

Agreed.

Well said.

GBart

This is what happens when you focus on profit instead of quality and safety.

There is a right way to do everything and it has nothing to do with profit, some people cry about govt regulations, this is why we ended up with them and need them, because left to do what they want people cut corners and innocent people get hurt, poisoned, ripped off and killed.

Steamhead

GBart said:

This is what happens when you focus on profit instead of quality and safety.

There is a right way to do everything and it has nothing to do with profit, some people cry about govt regulations, this is why we ended up with them and need them, because left to do what they want people cut corners and innocent people get hurt, poisoned, ripped off and killed.

In other words- Codes are written in blood.

(don't know where I first heard this, but you can't deny it...........)

ChrisJ

> @hot rod said:
> Ever seen the film of "galloping Gertie" the Tacoma narrows bridge failure.

I was thinking about that bridge.

Pretty amazing how these things are engineered.

EBEBRATT-Ed

At least if you were on the Tacoma Narrows you had a chance. Maybe a very slim chance but a chance.

The Florida bridge just pancaked.

This is why I am so pissed. Nobody had a chance to get away from it

This is something you would expect to happen in a third world
country

1. Put 950 tons with KNOWN cracks over a highway.
2. let the traffic run under it.
3. Do the stress testing during mid day
4. Don't put the cables and support towers in place before setting the bridge.
5. Don't have intermediate supports until the cables and support towers are in place.

Someone hit the wrong button on their "bridge calculation program"

And no one with a brain saw this coming?

Canucker

https://en.m.wikipedia.org/wiki/De_la_Concorde_overpass_collapse
I remember reading about this when it happened. Similar thought process by the engineering group that led to this? Bad calculations and lack of a way to properly inspect it during it's lifetime, it would appear

ChrisJ

> @EBEBRATT-Ed said:
> At least if you were on the Tacoma Narrows you had a chance. Maybe a very slim chance but a chance.
>
> The Florida bridge just pancaked.
>
> This is why I am so pissed. Nobody had a chance to get away from it
>
> This is something you would expect to happen in a third world
> country
>
> 1. Put 950 tons with KNOWN cracks over a highway.
> 2. let the traffic run under it.
> 3. Do the stress testing during mid day
> 4. Don't put the cables and support towers in place before setting the bridge.
> 5. Don't have intermediate supports until the cables and support towers are in place.
>
> Someone hit the wrong button on their "bridge calculation program"
>
> And no one with a brain saw this coming?

What program or software does everyone keep talking about?


As far as seeming like something that would happen in a third world country, ever research what took place at Three Mile Island?

EBEBRATT-Ed

@ChrisJ ,

"the bridge calculation program" probably doesn't exist, but who knows??

With the advent of computers the engineers workload has changed. Changed for the better? Changed for the worse? I have no clue.

But now instead of calculating all they do is push buttons.

I don't know nothing about bridges........but ALL the HVAC jobs I see in the commercial world are copy and paste jobs, it's the name of the game. Get it done cheapest, fastest.

Don't forget PUBLIC MONEY. Consulting engineers have to bid on their services against other designers.....just like us contractors do!

They certainly took the low bid.

This time it didn't work out so well.

Solid_Fuel_Man

Are we all still guessing, or has there been any published data of what actually happened? Poor design, poor/inadequate materials, poor workmanship, or improper procedures of bridge placement.

All these things should have checks and balances, but obviously something was missed. It's so tragic that whoever missed it killed people. It's a sobering thing of what CAN happen, and what we take for granted.

Fred

@Solid_Fuel_Man , it's the standard answer. "It's going to take months to figure out what went wrong. We are trying to salvage as much of the evidence as possible to allow for an appropriate investigation."
Always much harder to piece things back together, after the fact. Probably more money will go into the forensics than went into the design/Engineering.

Gordy

Let’s get some things straight about “federally funded” projects.

Materials

Materials must meet requirements for any project, and be manufactured in the USA.

Material suppliers must be on an approved list. If not must meet approval requirements.

Is there cheaper materials through different approved suppliers? Sure, but they must meet the standard requirements for the material. Examples are Reinforcing steel, steel girders, precast concrete beams, epoxy to name a few.

Concrete

Concrete can be purchased cheaper between batch plants. Most times in comes down to who is the closest for haul time. Yet all batch plant aggregate stock piles must meet state approval on a yearly bases. Scales, sieves for aggregate sizes etc. must be calibrated yearly, and inspected for accuracy. Portland, and flyash, any additives such as water reducer, retarder, plasticizers etc. must all be approved materials, and suppliers to use by the state.

There are specs for rebar placement, clearances, how often it is tied etc.
There are specs for batched concrete. Entrained air, slump, temperature, the right mix design for the application, meeting strength requirements etc.

This is just a little. Bottom line is the cheap materials argument doesn’t hold water.

A contractor choosing to ignore the standards, and specs will not be paid for anything out of spec. Not only not be paid, but will have to tear it out, and replace it. So it doesn’t even pay to do it. Everything has to have the proper paper work to prove its authenticity adhereing to the standards, and specs before being paid.

Workmanship has to follow standards also. You just can’t put rebar where ever you want, form it to what dimension works for you with your eyes closed, or pour concrete, and not vibrate it. You won’t be paid period.

Labor is the single highest cost to a job period.

In this case, I do believe the contractor was following the recommended procedure to set that span according to the direction of the designers. In other words they didn’t just install the span when it called for shoring in the center, or some other method of temporary support, but decided they were not going to do it, and proceeded. Ain’t going to happen, and that would have been the end of this story that day if they tried. Someone would have pointed that out in an instant after the failure.

I do believe the cracking was a precursor to the catastrophe. Quite possibly it may have worsened after the initial observation, and phone call to FDOT. FDOT didn’t respond. So it could be possible the adjustments made, were with out direction from a reliable entity in a panicked attempt to correct the problem.
No one wants to make that call to 911, or FDOT to say the bridge is going to fall we need to detour 6 lanes of traffic right now.
Quite frankly they probably never believed it was going to fail until it was to late. They also probably didn’t think the adjustments would end up causing those consequences.


If you have ever seen a yield test on a prestressed, or post tensioned beam that is properly tensioned the failure is not an abrupt failure. There is a very noticeable amount of deflection before the strands, or tendons fail then it comes down.

So noticeable the workers, engineer, and whom ever else were up top observing would have been off the bridge, clearing the area, stopping traffic on their own, and making calls.