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The Science of Bridge Collapse Prevention
toddatcw writes "In the wake of the Minneapolis Interstate 35W bridge collapse this week, Computerworld investigates ongoing research which could someday help to prevent future disasters. Acoustic emissions detection systems, which listen for the sounds of metal snapping on structures, are already sold and fitted. Likewise, a new generation of detector systems that monitor for tilting of bridge columns and piers are being designed, prototyped, and researched. 'Sound waves move more efficiently through solid objects than through air, making any sounds easier to listen out for, Tamutus said. "It's not amazing. It's simple. Doctors use stethoscopes all the time. If you put your ear on a train track, you can hear a train approaching from far away... The Sensor Highway II systems, which are portable and can be moved from bridge to bridge as needed, usually cost between $20,000 to several hundred thousand dollars each. Typically, evaluations take between one day and a week.'"
Would this system also have a feature to alert the local road authority, or in a worst case scenario close the bridge?
If your neighbours roof is flying past your window, you know it's cyclone season.
instead of steel, harness the power of Cory Doctorow's ego.
Is it not the easiest just to elect people who take care of things?
At least from what I heared there are a lot of bridges in similar shape, but there's not much done about it.
-- Stephan
http://stephan.sugarmotor.org
It was known well before the collapse that the bridge was in need of repairs. It seems that no public employee, elected or not, understands that prevention is better than reaction. New techniques to detect a heightened probability of failure are useful only if someone acts on the information once it is available.
The Schwartz space ain't from Spaceballs.
Put some wireless sensor nodes across the bridge and sense for unusual vibrations between the intersections. That's what Wireless Sensor Networks is all about. When there is a crack the vibrations will cause a signal to be sent out.
Step 1: Stop nation building OTHER COUNTRIES
Step 2: Start nation bulding OUR COUNTRY
Step 3: No step 3. It doesn't have to be so complicated.
We need congress to step in and criminalize gravity.
Possibly a war on gravity may be needed.
P.S. This is not a money problem. We are shipping shiploads of cash to faraway lands and paying millionare trust fund babies not to farm. Maybe we can put those funds someplace more useful.
I'm a Twin Cities resident (local name for Minneapolis/St. Paul), and have taken this bridge hundreds of times, as well as biked along trails on the riverbanks below it. It was never an attractive bridge, but certainly showed no obvious signs of problems. I was shocked to learn that a good friend of mine was told by a structural engineer two weeks ago that he "always avoids driving on that bridge during rush hour" - apparently the engineer had already read/heard something that we're just finding out.
This smacks of criminal negligence - complete catastrophic failure in 4 seconds could not have been an undetectable condition.
Any sufficiently advanced technology is indistinguishable from a rigged demo. -- James Klass
http://en.wikipedia.org/wiki/Nondestructive_testin g
We still don't know why the bridge in question came down. The structure was non-redundant. That means that if any part of the structure fails, the whole thing fails. In that light, the sudden failure of a structural member would bring the bridge down quickly and there wouldn't be sufficient warning to save lives. For example, an off-center load might overload an otherwise safe member.
None of this is to say that bridges shouldn't be instrumented. Such instrumentation would show ongoing changes in the condition of bridges and could lead to corrective maintenance. Until now, most inspections have been visual and that has been mostly successful. The collapse of a bridge/overpass in Quebec last year came about because the builder didn't do his job properly and the inspectors weren't properly trained. Even with the most rigorous testing, cheap lazy politicians will still put off spending on maintenane items because they don't get many votes. The best way to insure the safety of our crumbling infrastructure is to hold the decision makers personally liable for their decisions.
As the old phrase goes, an ounce of prevention is worth a pound of cure. The technology's nice and all, but I'd saw the trick is getting people to look into this sort of thing, and take action, beforehand. I say this because in my area there was an old bridge that many people used regularly, however, it was a well known fact that it was deteriorating. The city, however, didn't want to spend the money to fix it, and it was years before anything was done (despite the fancy new road nobody wanted or needed that was built just minutes away). That bridge could have possibly collapsed, and everyone knew it. This new technology might make detection easier, but as long as the almighty buck is king, no amount of technology can compensate for human nature.
Acoustic emissions detection systems, which listen for the sounds of metal snapping on structures, are already are being sold and fitted.
Ever hear of "collapse of the infrastructure"? How graphic.
Like building structural redundancy into the bridge to begin with?
what's ironic is that modern technology has therefore made bridges less safe, by empowering those from the middle of the last century who wished to save money by losing less materials, at the expense of safety by sacrificing redundancy. just read what he says, saying it better than me:
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
Usually "The Science of Bridge Collapse Prevention" is called "The Science of Bridge Construction"
don't cut it off www.mgmbill.org
that last 2000 years or more?
Little maintenance.
No sensors.
No inspections.
No reports.
By the time you can hear the little beams cracking, isn't it too late? Isn't the roadway in a free fall within an instant?
It's a hard question, so I think I'll just ignore it, in light of the sad truth that a month from now, no one (who doesn't have a personal connection to the tragedy) will care. To hell with "doomed to repeat it."
The Schwartz space ain't from Spaceballs.
I have a method of Minnesota infrastructure maintenance that can assure sound bridges. My technique involves billing the Twins owner for the $392 million of government revenue (collected via a sale tax hike) being used to fund the new $522 million baseball stadium. My technique also involves continuing to dash the hopes of Minnesota football fans for a new government funded $0.5 billion football stadium. Instead, let the team owners rely on sports geek revenue to fund their stadiums, and misappropriate the tax revenue into infrastructure.
On the other hand, perhaps it isn't necessary to piss off all the Minnesota sports geeks (read: voters) and instead utilize the $2 billion dollar state surplus to deal with the states bridges. But alas, there are voters to buy with that money.
This is about the priorities of the citizens of a staggeringly wealthy nation being focused on everything but the infrastructure.
Lurking at the bottom of the gravity well, getting old
What a joke. We've been building bridges for the whole of recorded history, and some of them have stood for much of that time. We have the capability and have had it for centuries if not millenia to build a bridge that doesn't fall. We just have to pay attention and maintain what we build. It's not THAT hard.
Maybe if we stop worrying about falsely exaggerated threats like terrorism and manufactured problems like the war on in Iraq, we'll have more than adequate resources to build a really damn good infrastructure, and then things like the bridge collapse in Minneapolis and the steam main explosion in NYC wouldn't ever happen.
You see? You see? Your stupid minds! Stupid! Stupid!
Stop building goddamn sports stadiums and zoo exhibits and concentrate on what's important.
What is the difference between an American freeway bridge and a lasagna?
Nothing.
Maybe we should go back to stone and mortar bridges. Today's bridges in America don't last very long and they never meet the roadway without a bump or a dip. Many are obsolete or too small by the time they are even completed. Modern engineering doesn't stand a chance to the builders of yesterday.
Take a look at the famed Rialto Bridge in Venice, Italy. This bridge was built almost 500 years ago and still stands even after numerous earthquakes in the region.
Then there is the stone bridge in the Czech Republic, the Charles Bridge that is a short 650 years old. Listed in the "Most Beautiful Bridges of the World", it was built in 1357 to replace an earlier bridge that was destroyed. It's still functioning fine.
Lets trek on over to Aberdeen, Scotland and their Brig o Balgownie bridge dating from 1286 and still in use today.
Even in the United States, we have 165 year old High Bridge in New York and Steel Bridge in Oregon that are both in use and good condition today. Although not stone bridges, they were built to last.
Now, we have a 40 year old bridge collapsing yesterday and a 35 year old bridge being completely replaced here. The Woodman bridge has a huge bump in it that will almost certainly remove your air-dam if you go the posted 40 MPH speed limit. A small bridge in Denver had to be replaced about 10 years ago and it was only about 10 years old. It seems that we are no longer capable of building a bridge that will last.
One must ask why with all the advances in science and engineering during the past 5 centuries why we can't build a decent bridge today? Why can't we have a street and bridge meet so the pavement is the same level? Why don't we build bridges like they used to? Even aquaducts built 15 centuries ago are still supplying water to Istanbul.
Obviously, when it's cheaper to build a bridge like the one in Minneapolis-St. Paul that only lasts 40 years and only kills a few people during its lifetime, but will cost hundreds of millions of dollars to cleanup, law suits and to replace, one must ask where are the priorities? Why not build a bridge to last centuries instead of decades? Wouldn't it be cheaper in the long run?
We just don't make them like we used to. Somewhere along the line, the need to have something last has been lost. Are our bridges disposable commodities like the cars we drive across them? It does make one wonder.
Banjo - The more I know about Windoze, the more I love *nix
+ this if you can
Because Soul Coughing is fundamentally beautiful.
Lets just lay the blame on the knucklehead that got us into this disaster of depleted local resources and the rest of his gang of cronies. His little war has cost devastated the resources and personnel needed to deal with this. this is symptomatic of Katrina and the Iraq War. They were too busy with their wet dreams to pay attention to wet people and cities.
The Dems may be effective but nobody can match a Republican for Naked Greed.
See Delay, Stevens, Foley, Rupert Murdoch, Ad nauseam
Sorry about the writing. Robot fingers, you know? Cliff Steele in DOOM PATROL #23
A massive bridge collapsing underneath you is terrifying, e.g. a source of terror. We could close the thousands of bridges in the US that, like the 35W bridge, are rated "structurally deficient", in the name of preventing "another 8-1". This might help expedite funding to rehab these bridges, and fighting the "terror" of unsafe bridges would fit with our current national priorities.
www.cgstock.com
What do they have about the _SOCIAL_ science of politicians who say, "Well, it probably won't fall down on _my_ watch so I'm going to be a 'tax-cutter'"?
Yes, a little testy. From the Cities and watched it from first rumor until dark on the MythTV box. Burned a DVD of the lot. Used to work at U of M and commuted from near South Minneapolis. Remember the bridge well.
Dumb bitch of the Transportation Commissioner was on the news 10 minutes ago. I just looooved her line about, "Don't any of you accuse me of wanting this bridge to collapse!" Hey, babe. I'd never accuse her of that. That would take THINKING and intention. I'm accusing her of knee-jerk dumber-than-crap Republican sucking of all money out of infrastructure for tax cuts to the rich. And, yes, I can imagine she sincerely _didn't_ want the bridge to collapse because she was "_HOPING_" ("praying"?) it wouldn't so she wouldn't get caught with her pants down where everyone could see how WORTHLESS her Neocon "management" was.
I'm just waiting to see whether they sell off the right to the Saudis to build a toll bridge over the river now that a convenient and handsome business opportunity has "presented itself". GOD, I HATE REPUBLICANS THIS WEEK.
A similar thing happened in California wrt the 1971 Sylmar earthquake. Several bridges of the newly completed I-5 came down, the cause was found to be lack of hoop strength in the re-bar inside the column. Columns built after that used helically wound rebar to keep the column intact under seismic loading. The need for retrofitting was driven home during the 1989 Loma Prieta quake and was further sped up after the 1994 Northridge quake when the reinforced bridges survived and the ones waiting for reinforcement collapsed.
A Shadeless room is a brighter room.
If you put your ear on a train track, you can hear a train approaching from far away
Has anyone done this before? The bumper sticker on a train reads If you can hear me, your head will be cut off.
Feel a rail on a track. Long after a train has passed, the track is still hot. I put my ear to the track, but could not hear the train through the rail. This was a rail that has its segments bolted for high speed trains. However, I did hear the train in the air, ear not on rail. The train was a high speed train with a loud diesel. As a wheel passes over the gap between two segments of track, there is a click that is loud enough to be a thunk, but the train would have to be too close before that sound is transmitted through the rail loud enough to be heard over the engine, which is audible when the train is over 2000 metres away and out of sight.
Trying to listen for the snap, crackle, pop of a bridge may be futile. A traffic bridge would have all kinds of noise from vehicles and surrounding industry. The bridge in Minneapolis crosses a river and a railway. Not a quiet scene.
Know your pads. One time pad: good for cryptography. Two timing pad: where to take your mistress.
Minneapolis? Heck bridges have been falling down like dominos in Montreal. Why do you think we drive so fast? We want to get by the overpass as quickly as possible!
This is a parking garage story.
About five years ago, a chunk of cement about the size of a football fell on a buddy's car in the parking garage. At that time, the garage was a few years old.
Engineers were called in and placed acoustic monitors all over the place on many of the beams. Then drove vehicles over them on a couple of weekends.
Evidently acoustics found anomalies. They determined that the interior cabling was insufficient.
After a couple of different fix attempts engineers decided on the following.
Added two reinforcing high tension cables to the outside of each approximately 60 foot beam in that huge parking garage. This involved drilling two six inch holes at the ends of each beam. A heavy wall pipe was put into each hole. Them flanges were welded to the ends of each pipe. Then cabling was strung on each side of the beam. The beams were curved so at the apex of the curve were placed hangers that the cabling went over. This way the cabling did not go directly to the other side but roughly followed the beam's curve.
This was at headquarters of a national clothing retailer JCP.
Thanks,
Jim
Coupled with my government's incompetence, bigotry and history of wasting money (read Iraq), it will surely be a wonder if this setup ever works. God help us!
Jesus people, I guess it's time to waste a billion dollars making sure all of our bridges our safe, or the terrorists have won. Honestly though, it is sad that innocent people died, but come on, what is the death toll, like 5-20. Everyones attention, money, and time would be much better spent fighting more important problems, like cancer and heart disease. Anything more than having a few engineers look into some old bridges they built is overkill. Are there not laws requiring continual safety reviews of major public structures already?
Metal snapping? Why not just listen for motorists screaming? I assume these actually listen for some kind of metal stress sound, rather than actual failure? No, I didn't read TFA, so feel free to ignore me.
For more info, see today's Minneapolis Star Tribune article.
In 2010 we'll have flying cars and those skateboards from BTTF Part 2 so we'll just fly over these places that need bridges.
Perhaps if this accident killed hundreds of people, and resulted in a settlement of tens of billion of dollars, then the landscape might shift. Or, if like automobile manufacturers of past, we find that the accountants are making fundamental compromises of safety merely because the cost of a human life is less than the cost of implementing the features.
About the only thing that does not fall under this risk analysis is the military. This is why they can get away with spending 100 billion dollars a year with only a discrediting italian letter to substantiate the claim, a letter not even endorsed by the US government, but by the british. Otherwise we have to use the imperfect system of where to spend our money and where not to. I don't suppose that we are going to see an increase in taxes, or the removal of the new corporate welfare incorporated a few years ago, or a reduction in say in money spent on standardized test for kids. i think we can have anything we want if it is really worth sacrificing.
"She's a scientist and a lesbian. She's not going to let it slide." Orphan Black
1. Engineer tells politician bridge needs fixed.
2. Politician tells engineer "Ok, fix it".
Sadly, the more common scenario is...
1. Engineer tells politician bridge needs fixed.
2. Politician is too busy bragging about his "low tax government" to listen.
3. Bridge falls over.
4. Politician calls an official enquiry, staffed by his cronies, which blames the engineer.
Quidquid Latine dictum sit, altum videtur (anything said in Latin sounds important)
I had the opportunity to take a course on U.S. Intelligence and National Security from a gentleman who had worked on the Senate Intelligence Committee as a staffer for 10 years during the Cold War, specifically during the Carter and Reagan administrations.
Discussing the politics of funding, he pointed out that it was easy - very, very easy - to get funding for new photo and signals intelligence sattelites, listening equipment, spy planes, and toys. He noted that, yes, some lobbying went on for these projects, but the lobbying isn't what swayed Congress - it was the new and shiny. They could all go home and say to themselves "wow, I put up a massive spy sattelite that can photograph buttons on Russian officers!"
However, when it came to support for this equipment - analysts to look at the data they gathered, technicians to keep them running, maintenance facilities, etc. - they always came up short. In some instances, multi-million dollar pieces of equipment were purchased and deployed only to have the data they gathered analyzed only long after it was too old to be useful, assuming it was ever analyzed at all.
I realize that this post is a bit off topic, but the problem of not supporting what is already there exists all through government. In the case of this bridge, shutting it down would have met with massive protest from all involved. Projects would have caused inconvenience, just as increased personnel staffing creates great cost for the government in many areas. People do the same thing all the time - buy new cars and toys, but never spend the money on maintenance, it all went to the toy. But if we build it or buy it we better be able to keep it in good shape.
Though I don't people anyone died, the flood in Dubai is also interesting news today along with this.
...I think of Computer World!
It's not a zero-sum game. We're a superpower for Christ sake! There's no reason for us to not do both. And both, my I remind you, are of national interests. The idea that we can do only one or the other is short sighted.
Second point. The bridge problem was first spotted in 1990. That's 17 years ago. Also, (like New Orleans) the public infrastructure funding falls squarely at the state level, NOT federal.
Life is not for the lazy.
Perhaps, and I'm going out on a limb here, but stay with me here... maybe if we wouldn't elect people who are fucktarded to positions of power and maybe if we didn't stand for it when they appoint their fucktarded and inexperienced cronies to tell them what they want to hear instead of what's actually going on, maybe we wouldn't have problems like this. Now I admit, the fucktarded person is appealing. He's promising that if you elect him he'll crap flowers and fairies and all sorts of other shit that could not possibly be funded in the current situation. But you know all he's going to do is loot the state and leave all the citizens holding the bag. So for God's sake just use some common sense and try to vote for the guy who sounds like he will, too.
Blah. You know no one will be held responsible for this, and I'm willing to bet that there's a single person who said "You know what, that bridge will hold up for another year..." when they were redirecting those highway funds to some other pet project.
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
Or at least, that's what recent evidence suggests.
A huge cost in almost anything is simple maintenance. Simply keeping what is currently in use functioning, it is also the easiest to cut spending on because usually the effects won't be immidiate.
It doesn't matter wether it is something huge like defence spending or seemingly trivial like road sweeping. If you don't keep spending the needed money on it sooner or later you are going to find that all of sudden you have an army with equipment that is falling apart and roads that are filthy.
Exactly what is happening right now in holland, the dutch army finds itself involved in the afghan conflict (right wrong, does not matter for this discussion) and that all the years of defence cuts have resulted in the equipment just not being up to the task. It is a good thing in some ways that it is being found out in afghanistan and NOT in a conflict that directly treathens dutch security.
The dutch also used to be known for their clean streets, recently the dutch themselves voted their own country as one of the filthiest in europe.
You can see the same thing in holland (and england and the US) with the rail system, years of neglect resulted in the american rail system being a joke, some massive accidents in england and the dutch system is slowly falling apart with increasing outages and even accidents (dutch railways used to be extremely safe)
But hey, as you say, anybody who would try to raise the money (taxes) to combat this and make sure that what we come to rely upon remains in a fit condition would not just get voted out of office, they would never get a change to get into office in the first place.
Don't worry, before the last bodies have been buried in this latest avoidable disaster, some politician will have promised to reduce taxes (offcourse never by cutting their own salaries) and the people will vote for it the first change they get.
Back when I worked for a government office, we were housed in a building that was collapsing. One corner was over a foot lower than the other three and sinking. Huge chunks of bricks were falling off the building. There was a lawsuit over some renovations that were done to the building that allegedly caused the instability. A "feasibility study" was done to determine whether they should spend money to move us all to emergency facilities until a new building was erected, or just take a chance at the building collapsing and having to pay out wrongful death lawsuits. It was determined that "chances are" the building will last and it was financially better to take the chance of hundreds of deaths. (Luckily, the lawsuit was settled pretty quickly and we were moved out within a year and the building was demolished.) I can't help but wonder if the same kind of "feasibility studies" are done on our nations bridges and infrastructure. "Money over lives" is chosen far too often by the powers that be, both governmental and corporate. These new testing methods are just a way to make money off tragedy. We already know what the problem is, we just need to decide that it's "feasible" to fix it.
At univ. i wrote a program to simulate sound propagating through any material, bridges and other constructions in mind.
I used fancy algorithms to make the simulation time independent, so it's not really a simulation, more like a gigantic formula for pressure at a vertice with time as variable.
For a programmer this was really interesting, but for real life, i've find it's nearly useless. the sound waves are all ready there....damn!
Sounds like a recipe for generating candidates for the Darwin Award...
www.osmos-group.com This French company already has fiber optic remote real-time monitoring on 550 structures around the world. There is no reason to wait for something else to be invented. It's been installed in the Eiffel Tower, the Leuvre, the Manhattan Bridge, 3rd Ave Bridge, a NYC subway tunnel, damns, tall buildings (that are a bit tilted), etc
Will arrive by mail on Monday. Please do not remove it as Cheney's evil MC waves will penetrate your brain and cause you to post more imbecilic posts like the one you just did.
It's simple, really. Politicians spend your money to build new roads, bridges, etc. so that they can put their names on them. Free re-election ads permanently posted on every route into the city, that's what we're talking about! How much publicity is there in replacing the rusted out girders and adding earthquake retrofits?
> He says look at the WTC, it collapsed because
> of the lack of redundancy.
>
> What?
>
> Seriously, the building was hit by 150,000 lb
> aircraft carrying 20,000 gallons of flammable
> liquid. It was obviously never designed to
> withstand that kind of structural complication.
Totally incorrect. The WTC was designed to withstand being hit by an airliner. I recall this from the various documentaries post-9/11; a web reference describing this is:
http://911research.wtc7.net/wtc/analysis/design.ht ml
which contains the quote (with citation):
Engineers who participated in the design of the World Trade Center have stated, since the attack, that the Towers were designed to withstand jetliner collisions. For example, Leslie Robertson, who is featured on many documentaries about the attack, said he "designed it for a (Boeing) 707 to hit it." Statements and documents predating the attack indicate that engineers considered the effects of not only of jetliner impacts, but also of ensuing fires.
In the future, please use Google searches to verify claims you make in public posts. It's to no one's benefit to have discussions based on speculation and bullshit.
"Whatever happened to fair use?"
-- Duff-Man
I live in Minneapolis, quite close to the I-35W bridge that collapsed. I was there Wednesday evening before many of the professionals were and helped with crowd control when the area I was in became an impromptu staging facility. I've driven over the bridge quite literally thousands of times. Like most people, I feel quite vested in my community and its infrastructure. I was completely unaware (as I am sure most people were) that the bridge had any problems at all. If I had to pick the least likely bridge to fall, it is quite likely I would have picked that one. It was quite frequently maintained and from all outward appearances looked to be in good shape.
I have had some time to think about it now and have come to the conclusion that we have not been good stewards of the infrastructure that our parents and grandparents worked so hard to give us. Instead of using the tsxes that we all pay to maintain our interstate system, dikes, levees and other items of commerce we have been off playing policeman for the world. We are like the nosey neighbor who complains about everything everyone else is doing while they let their own house and yard waste away. Only we do it on a global scale.
When I compare this disaster to the other recent disasters in the US, I think it compares not to 9/11 or the San Francisco earthquake but more to hurricane Katrina in New Orleans. I think this because what happened in New Orleans was not a "natural disaster" but rather a failure of infrastructure. If the levees and dikes had held like they were intended to, not much would have happened in New Orleans, the natural disaster would have been a memorable big storm that caused damage, not the disaster it was.
In the past twenty or thirty years we have not kept pace with the growth of infrastructure that we saw in the fifties and sixties when almost the entire system of interstate highways were built. With the disasters that we have seen I believe that there is enough evidence to show that we have not been good stewards of the gifts that our predicessors left us. We have failed. It really is that simple.
It is time to learn our lesson and time to reinvest in America. We may need to stop dropping bombs and bring our serviemen and servicewomen home so that we can afford to do this. We may need to cut back on pork-barrel politics and instead concentrate on commerce. We may need to scale back on missions to mars and the moon. Hell, we may even need to raise taxes!
Most importantly, and I do not know how to do this, we need to elect people who will do the job we need them to do in Washington and the state capitols.
Finally, although this is off-topic, I want to say that the emergency crews that responded to this disaster did an amazing job. These people are civil-service workers and voulinteers. They deserve special recognition for their heroic efforts. In less than an hour responders from across the state were there and had already put together a structured and effective rescue plan.
..given that such a thing does not exist. ;)
After reading the references to economics with regard to the bridge construction I'm reminded of the poem: The Deacon's Masterpiece.
You see - the Deacon built the shay perfectly. Each piece was perfectly designed and beautifully crafted. This is why it lasted 100 years.
The Deacon eliminated all un-needed redundancy. His shay never needed to be fixed. It worked perfect until its last moment. Then all parts failed simultaneously.
If we could perfect engineering then we could build modern structures and machines this way. Why have components fail after the machine or structure no longer serves any useful purpose? Its a waste right?
Maybe the shay the Deacon built wasn't nearly as perfect as his engineering skills and his ability to optimize. Perhaps our accountants, efficiency experts, and engineers are merely striving to reach the standards set by the Deacon.
Maybe we've been misinterpreting the poem all along.
Pieces of paper impress me a lot.
I realize we have to wait for the NTSB's findings, but as someone who drove over this bridge every workday, twice a day for years, I have to say the repairs seemed more than a minor resurfacing. They were jackhammering down below the re-bar to pour the new concrete. They had just finished two lanes in either direction (the traffic was traveling over the new pavement), and they were getting ready to pour more concrete.
I suspect the repairs accelerated the structural damage, but I agree that it was probably just a matter of time before it collapsed.
<sigh> Sad, sad thing to have happened. And, of course, we Minneapolitans are reminded about it every day by big, amber signs: Road closed at I94; Road closed at TH280. It's going to be like this for a long time. </sigh>
Sig goes here.