When Bridges Collape : Understanding Before Blame

My heart goes out to those affected by the tragic collapse of the I35W bridge in Minneapolis. And, for all of the rest of us, this is a scary thing. I remember the 1989 California Earthquake, when the Cyprus Structure collapsed. This was also close to the time of Rush Hour— which may have been a bit early as people were going home to watch the World Series game. Quite a number of people were killed there as the upper deck of the two-deck section of freeway collapsed on the lower deck. I know that visions of that haunted me for years; I'd been on the upper deck of that freeway that very morning, driving back down to college at the end of a fall break. (Ironically, I wasn't supposed to be; my sister and I cluelessly drove on the wrong freeway, and had to correct for it later.) It was only the next day when I realized that my Dad was in fact on that freeway heading north, and was just before the Cyprus Structure when it collapsed. His main workplace was in another direction, but he had been south of Oakland at a jobsite. He got off of the freeway to pick up a bottle of wine, and was there when the earthquake hit. (I related this to people in West Dorm, the famous party dorm, and they said, "See! It's good to drink, saves your life!")

My sincere hope is that rescue efforts in Minnesota will proceed as efficiently and as effectively as possible, that those who are missing will be found alive, and that the families of those who were injured or killed will find comfort.

When we're past that stage, I hope that we place a much greater emphasis on understanding what went wrong than we do on finding somebody to blame. When something like this happens, we all feel fear and shock and anger. It's so tempting to want to find a target of that anger— to find somebody whose fault it was. I suspect that in this case the fault will not be so obvious. And, in any event, understanding what went wrong is more important, so that hopefully we can figure out if there's anything we can do to stop similar things from happening in the future. One of the classic things we always talk about in introductory Physics classes is the Tacoma Narrows Bridge, which catastrophically collapsed in 1940. Because of that accident, we learned something about the various resonant modes that one must take into account when designing a bridge. Who knows if there will be anything as relatively straightforward as that with this collapse— but once the disaster recovery is over, I sure hope that we are able to place more emphasis on figuring out what happened, than deciding whom or what to blame.


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My limited understanding is that the understanding what went wrong part is already starting to become clear: the bridge was aging and deteriorating, well behind schedule for repairs, and was being worked on when the accident happened. The likely culprits, as far as I have heard, are severe lack of maintenance over the course of more than a decade, and/or a construction accident. I am sure the investigation will tell how much the construction had to do with the collapse...

There's no way that all of that's fully set right now. My point is that we should do the investigation and figure out what went wrong before jumping to say that (favorite group we don't like) was responsible.


The papers over here has "experts" claiming that these types of boxed bridges are seldom used here, because they aren't sturdy and robust - easier to move and easier to collapse. And that in a country without hurricanes, large tornadoes (far north) or large earth quakes (old plate).

Don't know if it is to reassure or if it is a reality behind. But if it's true maybe bad construction codes, more than bad maintenance, is the basic cause.

By Torbjörn Larsson, OM (not verified) on 02 Aug 2007 #permalink

I suspect the situation here will probably be much more straightforward than the Tacoma Narrows bridge. That one is a fun physics/engineering example because it is so dramatic, and complicated in an interesting way. But it is complicated, enough so that I would hesitate to discuss it in an intro physics class -- students would be sure to remember the images but I doubt they'd remember the explanation. The better students will probably remember it as an example of resonance as in the forced pendulum, which it really wasn't.

Shocking, and we hear that there are tens of thousands of bridges of a similar kind. Kinda makes one worry about them... but then that also means that tens of thousands of such bridges have not collapsed, for decades. So I'm guessing that nothing's perfect, and that one in tens of thousands, over decades, is actually pretty safe. So regarding reasons, maybe that one bridge was just unlucky?

So regarding reasons, maybe that one bridge was just unlucky?

Perhaps -- but if it turns out that there's some correctable flaw, even if a very minor one, it's worth correcting.

According to newspaper accounts,the bridge was over 40 years old. Given the increase in traffic, particularly truck traffic, since it was built, it would appear that this was an accident waiting to happen. As for assessing blame, I am attaching a thread from PZs' blog. The blame lies with the politicians who trumpet the siren song read my lips, no new or increased taxes. As PZ points out, the Governor of the State of Minnesora recently vetoed in increase in the gas tax, funds from which would have gone to the maintainence of transportation facilities. Of course, the Governor is on of those Rethuglicans who warble this tune. Here in the State of Virginia, the Rethuglicans in the lower house of the state legislature have been singing the same tune in frfusing the raise the gas tax to pay for maintainence and new transportation facilities. Just as ones' automobile will eventually stop running if the oil is not changed regularly, so transportation facilities will fail if not properly maintained.


We learned about metal fatigue after these sorts of bridges were built, and know not to build more like them. Scientifically, it might just be another datapoint in fatigue and corrosion datasets. We already knew we were operating a system outside its design limits and technology. What we might be able to learn might be things like decay happens and low-probability events do have a chance of happening.

over decades, is actually pretty safe.

You describe a frog in heating water situation. What is your criteria for "safe" or "acceptable risk"?

Bridge constructions and safety limits vary. If you can't decide on the above from comparing with other traffic hazards and damage costs, you can compare such populations of bridges, compensating for different climates stresses. Perhaps some bridges are much less safer. If they are, and that is what I hear (and here again from Dave), you could start discuss if you would like to change the construction codes and also possibly reinforce some bridges.

By Torbjörn Larsson, OM (not verified) on 03 Aug 2007 #permalink

Apparently the bridge was scheduled for some reinforcements, but it wasn't deemed time critical, so the resurfacing was allowed to go ahead of the reinforcements. My guess is our inspection proceedures need to be improved, so that serious weaknesses can be found before failure.

Now, don't quote me on this as fact as it's only hearsay. My wife, during the weekend, said she heard on one news station that some of the ground around the main supports gave away. I haven't tried to verify if she heard it correctly and since I wasn't paying attention much to the news this weekend I just took her word for it. Did anyone else hear something similar?

Sorry for making you think that I was describing frogs! Seriously though, there will be lots of stuff done now that should have been done before, but what about in a few years time? The time to do most of the stuff that's being done now was a few years ago. We've had disasters before, and we still react like this! I say "most of" because you're right, it's always worth rechecking stuff after a failure. But I bet that the rechecking that's done now will be all about looking OK in the media, and I worry about what sort of scheduled stuff is going to be delayed to make way for it.

SLC -- what PZ is doing is exactly the kind of crap I'm saying is unworthy. Yes, several people here at scienceblogs.com leaped at the opportunity to justify that it's all the Republicans fault that the bridge collapsed.

I have also read Op Eds from conservative commentators who say that it's all the liberals fault because they direct government spending towards things that are highly visible and get them re-elected rather than towards infrastructure.

Both of you are completely full of hot air at this point. Not only is it premature in terms of the amount of information we have to assign blame, it's an asinine knee-jerk reaction to use this tragedy as an opportunity to place the blame for yet another thing on your favorite enemy.


Re Rob Knop

1. I can't speak to the issues in Tennessee but I can speak to the issues in Virginia. The fact of the matter is that the Rethuglicans in the Virginia House of Delegates have repeatly refused to raise the gas tax to pay for maintainence of existing transportation facilities and development of badly needed new transportation facilities.

2. As for the comments of the so-called conservative commentators, the fact of the matter is that their comments are a pile of crap as far as this state is concerned. Both houses of the state legislature are controlled by Rethuglicans so that any such government spending is their responsibility.

3. I would agree with Dr. Knop, as does PZ Myers by the way, that one can not blame the refusal of the Rethuglicans in Minnesota to raise the gas tax for the collapse of this particular bridge. I can blame the Rethuglicans in the Virginia legislature for the refusal to do anything about congestion in Northern Virginia or for the deferral of maintainence on a number of bridges throughout the state.