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I'm okay. Mom just called to find out, and Brian called on my cell phone seconds later to find out as well and tell me about this thread. It's not on my way home, but it's less than two miles from my house and I use it regularly.
Thanks for your concern. It looks so far like there might not be many casualties, I certainly hope that's the case. I can't imagine how a bridge could just collapse like that. Wow.
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Traveler and Ryuko are both in St Paul, but neither post often. Zal moved here recently, I believe. Who else?
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That bridge is always packed, by the way, and it's starting to thunder. I hope they get everyone to safety before the rain hits.
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They're still gonna play baseball tonight. Resons being stated is that if they postpone the game and send people home, it'll make it a traffic headache.
ElJay and Eni:
I am thankful that you are allright and many thanks for posting.
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Okay. I just thought you might be local, since this prompted you to register. Ah, welcome to Hatrack.
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Here's a Google Maps close up of the "before" view of the bridge, for the morbidly curious. Um, like me.
The smaller bridge to the right of the main one is Cedar Avenue, and is the bridge people are standing on looking towards the collapsed one in the news footage.
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I had to re-register after I could not remember my my password. I just changed the spelling of my nickname. Thanks, though.
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Do you see him being punished, JTK? Have you checked your forehead for a scar?
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Glad everyone who has checked in is safe. I hope no one has lost loved ones. My prayers are with the injured, dead, and terrified, and their families.
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I'm from the area, though I moved to VA a year ago for grad school. Lots of friends in MN still, which is how I found out about it. I don't think anyone I know was around the bridge when it happened, but I still have to check in to make sure everyone is okay. Massive odds against anyone I know being hurt, thankfully.
Posts: 326 | Registered: Apr 2005
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Seven fatalities so far, and there are a lot more cars in the water that they weren't able to get to. Here's a local news station that's just putting up bulletins as they become available. There's information on the bridge, the rescue efforts, and eyewitness accounts.
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I'm okay. My commute is along the west side of downtown Minneapolis.
The rain (and lightening) came through heavy up here in the NW suburbs, but luckily the storm did break up mostly before it reached the disaster site.
I'd like to encourage everyone to go give blood (especially if you don't live in Minnesota -- there'll probably be a bit of a rush of blood donors here over the next weeks). Blood supplies tend to get low during the summer months as people go on vacation.
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Liza and Brian were the first two I thought of when I heard about this, and came here as soon as I could because I figured there would be a thread/update.
I didn't realize so many other people from here were in that area!
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quote:Somewhere, an engineer is having a very bad day.
Do you see him being punished, JTK?
Don' know if'n ya know many construction people, but the good ones know they could be making a lot more money doing a lot less work in another field. They're in construction for the same reason that a writer writes, a sculptor sculpts. What you see as a highway or a building or a suburb, those good construction workers see as their personal work of art. Something like a bridge, a skyscraper, a concert hall.....a child of their labor.....it's s'poseta last until long after they're dead. Even if no one had been physically injured by the bridge collapse, there'd still be a lot of good people having a very bad day; especially amongst the project engineers. Knowing people were hurt just makes it that much worse.
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I'm glad to know our Minneapolis jatraqueros are okay. How scary, how awful.
Beyond the disrupted lives of the accident victims and their families, I imagine the city itself will be upset for a while to come--I don't know Minneapolis, but from the stories it looks like that bridge is a major traffic artery.
I wish I could donate blood. Posts: 3149 | Registered: Jul 2005
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I've been watching the online videos of the scene all morning. My -- that is just unbelievable!
Someone was talking on morning radio about all the wonderful people who started jumping into the water to save others -- and wondering if all of us would react that way. I would have to say I WOULDN'T - because I don't know how to swim at all. But I would hope if I had been there I would have given "ground support" and first aid as they came to shore..
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The Minnesota Twins have cancelled the game that had been scheduled for tonight, giving the bridge collapse as the reason.
Authorities say they found no evidence of sabotage, but then contradictorily say the scene has been declared a crime scene. Maybe they figure it could be engineering incompetence or sub-standard parts or materials. There was some construction going on--basically maintenance and repair.
If they do figure out what caused this collapse, I hope they do not publicize it in too great detail, to avoid educating terrorists on how to take down a bridge.
Posts: 3742 | Registered: Dec 2001
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I'm not sure jumping in to help those in the water is universaly the correct response. A person in panic can easily kill you and themselves once you reach them.
Knowing that if I did not have an object for which to pull people out, I'd probably jump in anyway to help, I just know I could not stand there and watch somebody drown.
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I'm really fascinated by this. Given the sorry state of our infrastructure, most of which was built in the 50s and 60s, it's not at all surprising that something has happened. This particular bridge had an extra long span, and showed signs of fatigue and stress cracking in recent inspections but was judged safe. Obviously the inspection and assessment routines will have to be more frequent and stringent in the future.
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Our country's infrastructure is in terrible shape. Maintenance isn't sexy, so elected officials don't want to spend any money on it, so the condition of our bridges, dams, levees, etc. continues to deteriorate.
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Pixie and Dragon have both left for the summer. Their campus isn't particularly near there, either, if they were around, but that wouldn't mean they couldn't be involved, of course.
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Okay, thanks! I didn't even know Dragon was there. I knew Pixie was in Mexico this summer but I wasn't sure for how long, or if she might be back.
ElJay, how was traffic in the city today? Is it total gridlock without that bridge?
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It wasn't bad when I went in, but that was around 8:30. My commute was maybe 5 minutes longer than normal, and there was a very specific section where the slow-down was obviously due to people choosing an alternate route to get to the U of M because the normal route was closed. (It wouldn't have been over the 35 W bridge, but the 122 bridge shares the same approach for awhile and the road was closed before they split to allow plenty of room for emergency vehicles and the like.)
It was probably worse earlier, but it still wouldn't have approached gridlock. There are a lot of ways into and out of downtown, including two other major freeways. The estimate I read was that about 25% of the traffic going into Minneapolis takes that bridge, which sounds about right. So between the freeways and the surface roads, it redistributed pretty well. I'm sure some specific people's commutes are going to be a lot longer going forward, but it won't mess up the whole city. You've also got to remember that we have two downtown areas, Minneapolis and St Paul, that are about 7 miles apart from each other. So it's not like everyone going to work "downtown" is going to Minneapolis, either, although it is the larger of the two.
Also, there are 7 other bridges across the Mississippi within two miles on either side of the 35W one, although only one of those is a freeway. So while this was most certainly a tragedy for those involved, it's not going to be a huge deal for commuters.
I do think it's great that Metro Transit added an extra 25 buses from their park & ride lots in the northern suburbs today. . . I hope people take them and get so used to/happy with using public transit that they keep it up after traffic is back to normal.
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I was watching the footage today and I will tell you this, all of those that put their lives on the line to rescue others, are heros.
I was very touched at hearing the story about the rescue from the school bus. Wow what a story!
The story that makes me cry is the one I heard about the first responders that were there to act as messengers passing along farewells and what not to survivors. It had to be really hard to know that you can't save everyone.
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Thanks for the traffic update ElJay - I'd been wondering what they were going to do about rerouting all the commuters. Especially since one of the news blurbs I read said it might be two years before they've got a new bridge up.
And yes, I've been in NH all summer, but I'll be back in St. Paul in September. Pixie will be studying abroad in the fall though, so she won't be back until February.
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They're recommending that people coming from the North get off 35W on 280 and take it to 94, then take that West. It's only 4 lanes, so it can't move as many cars as fast, but it's not too far out of the way.
I have to go to NorthEast Minneapolis Tuesday morning, and I'm not sure exactly where I'm going, so I'll probably poke around over the weekend and find the best route.
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quote: I would have to say I WOULDN'T - because I don't know how to swim at all. But I would hope if I had been there I would have given "ground support" and first aid as they came to shore..
As well as people jumping in, there were also numerous reports of people carrying the injured to safety, climbing down treacherously low on the bridge to help others get out, and assisting those with children or other needs. I'm with you, I am not a strong enough swimmer to be any use in the water-- I could just about save myself if I went in the right way, no way I could jump in and pull someone out, I'd end up making more work for rescue personnel. But I have had enough "emergency situations" in my life to be hopeful that I would respond appropriately and be able to help in another way, perhaps even bravely putting myself in danger to help another. Just not in the water.
Posts: 21182 | Registered: Sep 2004
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I've watched that footage of the bridge falling over and over to try and understand what happened first. It's weird cause it almost seems like the main span let go on both ends at once. And it stayed so level as it fell, for the most part. It's as though whatever happened happened symmetrically on both sides of the bridge at once (widthwise), on both columns.
quote: Bridge 9340 consists of a deck truss and steel multi-girder approach spans built in 1967. The deck truss has a center span of 139 meters, north and south spans of 80.8 meters, and cantilever spans of 11.6 meters. The bridge was designed using the 1961 AASHO standard specifications. At that time, unconservative fatigue design provisions were used. AASHTO fatigue design rules were substantially improved as a result of research... in the 1970s.
The approach spans have exhibited several fatigue problems; primarily due to unanticipated out-of-plane distortion of the girders. Although fatigue cracking has not occurred in the deck truss, it has many poor fatigue details on the main truss and floor truss systems.
Stress ranges calculated using the lane load as live load are greater than fatigue thresholds for many of the details. The poor fatigue details in the deck truss include intermittent fillet welds, welded longitudinal stiffeners and welded attachments at diaphragms inside tension members. These details are classified as Category D and E with threshold stress ranges 48 and 31 MPa, respectively.
The design analysis using the AASHTO lane load in all lanes, shows design-live-load stress ranges in the truss members much higher than these thresholds. Design-live-load stress ranges were greatest, up to 138 MPa, in members that experience load reversal as trucks pass from the outside spans onto the center span. The predicted average life at that stress range is between 20,000 and 40,000 cycles. With 15,000 trucks per day crossing the bridge in each direction, these details should have cracked soon after opening if the stress ranges were really this high.
It seems like they're coming rather close to arguing that since it hasn't failed yet, it must actually be okay despite the fact that analysis shows it should have fallen a long time ago.
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Realize that this isn't my specialty at all. I'm totally an amateur here. Anyone who is a civil engineer, or anyone who actually designs bridges, or works with actual legacy bridge designs like this one, please weigh in with your opinion which will perforce be much more informed than mine.
Bob Scopatz, you're a traffic safety guru. What think ye of this event?
Posts: 6246 | Registered: Aug 2004
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Oh, okay. In the meantime I'm still investigating. I can't let this go. When I read these parts of this civil engineering report, I'm just chilled. The thing is, engineers are asked to research and give opinions on things all the time, and of course we aren't perfect. But there IS a systematic bias toward telling whomever is paying the engineer to study something whatever it is they want to hear. We're trying hard not to let that happen all the time. That's what our professional ethics are about. But it's very hard not to let it creep in a little, subconsciously, because so many things are so very open to interpretation, and the client just could (and sometimes does) fire the engineer and get another one, if the engineer tells them too many things they don't want to hear. There are responsibilities going in the other direction too. The client should listen to what the engineer says and actually base their decisions on it, instead of brushing it off or pretending they didn't hear or understand it, or firing that firm and hiring someone else who gives them an answer they like better.
But I wonder if we don't need a different system altogether somehow. I wonder if we should change how things are done. Here's what the engineers said about that bridge a few years ago (2001), in the executive summary of their report (i.e. the only part decision-makers are going to read).
quote: Bridge 9340 is a deck truss with steel multi-girder approach spans built in 1967 across the Mississippi River just east of downtown Minneapolis. The approach spans have exhibited several fatigue problems; primarily due to unanticipated out-of-plane distortion of the girders. Although fatigue cracking has not occurred in the deck truss, it has many poor fatigue details on the main truss and floor truss systems. Concern about fatigue cracking in the deck truss is heightened by a lack of redundancy in the main truss system. The detailed fatigue assessment in this report shows that fatigue cracking of the deck truss is not likely. Therefore, replacement of this bridge, and the associated very high cost, may be deferred.
Okay, so obviously whatever warnings are contained in here should have (in retrospect) been very much more strongly worded, at the very least. What indications do we actually see in this report that their conclusions are not fully supported by the observations? They let a failure of the bridge to do what it was designed to do count as a GOOD thing instead of bad. Because the bearings were corroded and the supports weren't free to slide, the members were under less stress than the model predicted, and so they concluded we're SAFER. Instead, a failure should count as a failure! The bearings aren't moving so some member somewhere is under a lot higher compression than it was designed to take. Red flags should have been going up.
They did this same meta-idea with the Challenger O-rings, too. They took a failure (the O-Rings were burned through 1/3 of the way) and bizarrely reinterpreted it as having a safety factor of three. I'm not an expert in this field, and so I could be wrong, yet that seems wrongheaded to me, to credit a failure in the bridge to function as designed, as though it were a good thing instead of bad, as though it made us safer instead of throwing us into totally unknown and unanticipated territory.
This whole thing makes me really, really upset. Engineers have a sacred duty to protect people, so that they never have to think about crossing bridges or flying in planes or crossing the ocean depths in ships or whatever it may be. We have been tasked with the divine responsibility of making it as safe for people to do these things as though they were sitting beside the well in the cool of the evening. If we're going to fulfill this sacred charge, we have to develop and maintain systems of checks and balances, of reviews and counter-reviews, that will translate physical reality into models we use to decide how to act, where to spend money, what projects to undertake and which to defer. If we collectively let our wishes be the determining factor, instead of hard reality, then we are doomed to fail.
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -Richard P. Feynman, Challenger accident report.
quote:The detailed fatigue assessment in this report shows that fatigue cracking of the deck truss is not likely.
That's a risk assessment: they believed the likelihood of failure was low enough that replacement was not immediately required. The fact that it did fail doesn't necessarily imply that they were wrong in their conclusion that it was unlikely to do so.
I agree with your broader point that the principal obligation of an engineer is to protect people, but at this point based on extremely limited information and a situation that is well outside my spheres of expertise I'm not willing to conclude that the engineers who assessed the bridge and compiled the report were biased, subconsicously or otherwise. I think that's premature.
This made me curious about the engineering code of ethics here in Ontario, though, so I went and read a bit more about it. Here's a summary:
quote:The Code of Ethics is a basic guide to professional conduct and imposes duties on the practising professional engineer, with respect to:
society; employers; clients; colleagues, including employees and subordinates; the engineering profession; and himself/herself.
Section 77 of Regulation 941 states that "it is the duty of a practitioner to the public, to the practitioner's employer, to the practitioner's clients, to other licensed engineers of the practitioner's profession, and to the practitioner to act at all times with,
i. fairness and loyalty to the practitioner's associates, employers, clients, subordinates and employees, ii. fidelity to public needs, iii. devotion to high ideals of personal honour and professional integrity, iv. knowledge of developments in the area of professional engineering relevant to any services that are undertaken, and v. competence in the performance of any professional engineering services that are undertaken."
Through the Code of Ethics, professional engineers have a clearly defined duty to society, which is to regard the duty to public welfare as paramount, above their duties to clients or employers. Their duty to employers involves acting as faithful agents or trustees, regarding client information as confidential and avoiding or disclosing conflicts of interest. Their duty to clients means that professional engineers have to disclose immediately any direct or indirect interest that might prejudice (or appear to prejudice) their professional judgement.
quote:This whole thing makes me really really angry. Engineers have a sacred duty to protect people, so that they never have to think about crossing bridges or flying in planes or crossing the ocean depths in ships or whatever it may be. We have been tasked with the divine responsibility of making it as safe for people to do these things as if they were sitting beside the well in the cool of the evening. If we are going to fulfill our sacred charge, we have to develop and maintain systems of checks and balances, of reviews and counter-reviews, that will translate physical reality into our models that we use to decide how to act, where to spend money, what projects to undertake and which to defer.
I agree that engineers have a responsibility to whomever uses their creations, but I wouldn't say it's sacred or divine.
It's also too early, in my opinion, to say whether this collapse was the fault of an engineer or a politician, or neither.
Posts: 5462 | Registered: Apr 2005
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Oh I totally agree that I'm not assessing blame. I'm examining the system with a particularly critical eye on the job of engineers, since I am one, and I know something about how the system works. I would expect decision-makers to do soul-searching on their part, and contractors, and so on. All of us need to re-examine our standard operating procedure, I think, in light of such disasters.
Posts: 6246 | Registered: Aug 2004
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Oh, and you quoted stuff I rephrased. Sorry about that. When I started editing there were no posts after mine, and I did think again about how to be more precise in what I'm trying to say. But I got delayed during editing. Can you fix the quote to match my edited version? I don't think I changed the meaning, I just phrased it better.
Posts: 6246 | Registered: Aug 2004
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To change tacks completely, to take off my public policy hat and simply examine and make wild guesses about the physical system itself, about what happened and how.... I have a tentative theory.
After watching the collapse over and over on video, and studying the bridge structure model shown in the civil engineering report, and looking at the pictures of the collapsed debris, my tentative theory (highly speculative) is that there was buckling in the South approach span, or the south column substructure gave way allowing the south columns to topple, or maybe the superstructure above the south columns failed. I think whatever it was that started the whole chain of events, started back at the south column or pier. Then I think the main span was pulled southwards away from the North pier, causing the main span to drop neatly into the river. A few seconds later the North approach span, because it lost the counterbalancing pull from the main span after it fell, crumpled under the load. The north pier with concrete columns stayed intact.
If you look, the roadway surface is folded over the south pier with concrete columns, laying on top of it. The north pier with its concrete columns are the ones visible in the video, and they remain standing while the steel breaks up and falls off all around them. So it looks like the initiating event happened in the south span or over the south columns.
The structure is supposed to be pinned at one of the four support points, and free to roll on bearings at the other three points, in order to accommodate thermal expansion, and the small shape adjustments that come from squashing the elastic truss members under load. However, the bearings were corroded so they weren't completely free to move, as they should have been. Instead of flagging this as a serious failure of the bridge to be working as designed, though, the engineers inexplicably take comfort in this, since it means the steel members don't have to take nearly as much stress in tension as they would if the whole thing was flexing properly, as I noted in the post above.
But surely this has to mean (if it's designed to flex and it's not able to flex) that other members are experiencing far more compression than they were designed to feel. Steel isn't the best thing to use for compression members (the way I understand it, and civil engineers please correct me.) Concrete is far better in compression than steel.
If the approach spans were showing out of plane distortion of girders, then maybe that's because they were close to buckling with the extra compression. That's what happens to a steel beam when you put it into more compression than it can take, it buckles. I'm trying to find now which support point was supposed to be fixed and which were designed to allow motion.
Again, just speculative theories, but I can't help poring over the evidence and wondering. Maybe I should go into forensic engineering. Posts: 6246 | Registered: Aug 2004
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From what the experts are saying, it seems to be the general consensus that the deck truss design for bridges is inherently inferior, because if one key point goes, the whole deck falls. There are no fallback supports to handle the weight as in more modern construction techniques. Local governments all over the country now are scrambling to see if they have any deck truss bridges in their jurisdiction, and if so, re-inspect them pronto.
Posts: 3742 | Registered: Dec 2001
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One thing that seems sure to have been a factor is that it was heavily loaded, it was rush hour, with bumper to bumper cars and trucks across the whole bridge. Of course they were doing work on the bridge, so some of the lanes might have been closed. I see traffic barrels in some of the pictures. Perhaps there was even less total load at the time than usual during rush hour. Maybe the distribution of the load was different than usual, causing particularly high stress in some members, or something.
Another factor might have been that it was a hot day. If so then thermal expansion would have been at a maximum. In fact, weather observations for the city show there was a high of 92F that day. Warm, but not the hottest day of recent weeks. It was 98 on July 7th, for instance.
Another possible contributing factor could be the unique deicing system installed on the bridge. What if the chemical they sprayed for deicing had some unintended effect on the steel? That's something that would need to be examined, since it's not a commonly used system.
What other factors could there be?
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