The Minneapolis Bridge Collapse

I lived for a number of years less than a mile from the freeway bridge that collapsed catastrophically and without apparent reason yesterday in Minneapolis. Because it was my own neighborhood, I almost never drove across that bridge–the traffic was terrible and the location extremely close to both the University and downtown, such that I tried to walk most of the time. I did walk underneath the 35W bridge quite often, on my frequent river ramblings and to escape freeway noise above me. And I used to both walk and drive across the Mighty Mississippi on the intact bridge that parallels the collapsed one about a block away, as shown nicely on the photo on BBC.

I did not check my email or the online news before bed last night, after having left the office at just past 7, and so I woke up this morning to the screaming headlines about my old neighborhood. It’s bizarre, as a Minnesota girl living in England, normally no one would know where that was or have heard of it (except for the Mall of America). Today it’s the top story on the BBC (as well as Yahoo and everywhere else). What will be interesting is to see if any of my colleagues pick up on the fact that I might have a stronger-than-typical interest in this particular news story (especially given the focus on “US” bridge and not “Minneapolis” or “Minnesota” in the local headlines–although the BBC does have a lovely city map of my old neighborhood).

The story itself is a huge question-mark right now. It sounds as though the thing just gave way. It had been regularly inspected and was not particularly a concern in terms of age or use. The AP says:

“There were two lanes of traffic, bumper to bumper, at the point of the collapse. Those cars did go into the river,” said Minneapolis Police Lt. Amelia Huffman. “At this point there is nothing to suggest that this was anything other than a structural collapse.”

I’m just waking up and sort of in shock, so I’m fuzzy on all of it. I’m sure I have some photographs of the bridge in my digital archives; it was not the prettiest or the most interesting of the bridges in that stretch of town, but I actually really like structural architecture in general, and bridges especially, so I’m sure I took some photos of it and I’ll see what I can find later today.

If you’re interested, for local news I’d suggest the Kare11 website (the local NBC affiliate and one place I regularly check the news back in MN from a long distance). The death toll is due to rise dramatically today (20 still missing) and I’m sure there will be much more news. For those keeping track, I fly to Minneapolis three weeks from today and should get an interesting view once there. The Strib website has a gallery of photos and it appears they may be relaxing their ridiculous registration requirements as I was able to look at the photos.

Update: for the structural or engineering minded among us, a new article here is quite interesting. For the best pictures I’ve seen yet of what actually happened, go here (on the Pioneer press website)

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9 responses to “The Minneapolis Bridge Collapse

  1. The Star Tribune posted a 2001 MNDOT report on “Fatigue Evaluation of the Deck Truss” of the bridge on their website here:

    http://media.startribune.com/smedia/2007/08/01/21/bridges200110.source.prod_affiliate.2.pdf

    From pages 3-4 of the report :

    Concerns about fatigue cracking in the deck truss is heightened by a lack of redundancy in the main truss system. Only two planes of the main trusses support 8 lanes of traffic. The truss is determinate and the joints theoretically pinned. Therefore, if one member were severed by a fatigue crack, the plane of the main truss would, theoretically, collapse.

    I’m not an engineer and it’s too early to make determinations, but it sure looks to me like the plane of the main truss collapsed. If so, and if this is the cause, somebody has some ‘splainin to do.

  2. notfromaroundhere

    I actually am an engineer by training and that is quite a damning piece of information about the bridge design. Basic statics of truss structures is essentially second year undergraduate engineering–about the first thing we are taught regardless of discipline. It is quite surprising that it would not have been flagged up for replacement, although I saw some comments about the “exorbitant costs of bridge replacement” in today’s news in this context. It’s also perhaps somewhat surprising that a bridge built so recently would have so little redundancy. Normally factor of safety type engineering calculations would require worst case scenarios. While admittedly 1967 was prior to the modern era in terms of computer models and calculations, the fact that the thing collapsed so completely without warning or any sort of predecessor event (pier being hit by a boat, etc.) really does indicate a fundamental design flaw. You can bet that this truss structure will now be studied by generations of civil engineering and architecture students. And perhaps also students of Materials Engineering. Minnesota weather is really extreme and the thermal loading due to regular and more than 100 degree F temperature swings every year might be a loading that was not considered by bridge designers in their fatigue calculations.

    A book recommendation on this subject:
    Why Buildings Fall Down: How Structures Fail by M. Levy, M. Salvadori,
    http://www.amazon.com/Why-Buildings-Fall-Down-Structures/dp/039331152X

  3. Hi Lady! All safe here for the Cole clan, thought I should check-in. More later.

  4. notfromaroundhere

    Glad to hear from you… seeing as we were practically neighbors and this was our part of town. How strange does this feel? I can’t seem to get away from the mental images of the twisted metal in the Mississippi, and I’m 4000 miles away. It’s remarkably haunting.

  5. Some of my friends still live in the area and here are some pictures from around the neighborhood

    ttp://senthil.homelinux.com/2007/08/02/minneapolis-i-35w-mississippi-bridge-collapse-pictures/

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