Minneapolis bridge update

From MarketWatch:

It is not yet known why or how the bridge collapsed, but Minnesota and Minneapolis officials have said the likely cause was “structural failure.”

No, you think?

I have more comments and recommended reading over at my DailyKos page. I am particularly going to watch if any of the Katrina comparisons play out. I'm also wondering if Alaska's “projects” are going to get another strong look?

I-35W bridge collapse in Minneapolis

Once again, the news intersects with our interests here at CatSynth, this time in a disastrous and tragic way. From AP:

MINNEAPOLIS – An interstate bridge jammed with rush-hour traffic suddenly broke into huge sections and collapsed into the Mississippi River Wednesday, pitching dozens of cars 60 feet into the water and killing at least seven people.

The eight-lane Interstate 35W bridge, a major Minneapolis artery, was in the midst of being repaired and two lanes in each direction were closed when the bridge buckled.

[AP Photo/The Star Tribune, Brian Peterson]

Here is what the bridge looked like for the 40 years it spanned the river:

[Todd Murray]

And here's a piece of what's left after the collapse:

[AP Photo: Adam Wolf]

Between this last photo and the first, one can see that there was a total and complete structural failure, and tragically one that happened during a busy rush hour, killing several people and injuring more. It must have been incredibly frightening to watch the bridge collapse, or be on it as the road buckeled and cracked and suddenly one ends up 50 feet down on the river. We at CatSynth extend our sympathies to those who lost friends or family is this tragedy.

Of course, people are already beginning to ask what could cause a bridge like this to completely fall apart like this? The construction on the bridge comes to mind, but apparently that was just on the roadway and “None of it would be related to the structure” [AP]. As for the structure:

Gov. Tim Pawlenty said Wednesday night that no structural deficiencies were found during bridge inspections in 2005 and 2006. The bridge deck was scheduled to be replaced in 2020 at the earliest, Pawlenty said, and legislators offered a similar assessment.

But public reports on the bridge raised questions about its safety.

In 2005, inspectors from the Minnesota Department of Transportation deemed the bridge “structurally deficient,” in data submitted to the Federal Highway Administration's National Bridge Inventory.[Pioneer Press]

I did not know there was a National Bridge Inventory. Some more detailed structural engineering (from the same Pioneer Press article):

The I-35W bridge apparently is what state transportation officials consider a “fracture critical” bridge, meaning it has at least one critical tension member whose failure would be expected to result in a collapse of the bridge…
…engineers said the fatigue cracking was a serious issue due to the lack of redundancy in the main truss system. Only two planes supported eight lanes of traffic, they wrote.

“The truss is determinate and the joints are theoretically pinned,” the report states. “Therefore, if one member were severed by a fatigue crack, the plane of the main truss would, theoretically, collapse.”

At first, the description sounded to me like the classic resonance or self-excitation collapses, as described on this site. But it sounds like all that was needed was one well-placed beam to give, and the whole thing would fall apart. We'll see what info continues to come out in the following days…

Seriousness with Highways: MacArthur Maze

I had planned to do a “fun with highways post” on the MacArthur maze, which connects highways I-80, I-580 and I-880 to the Bay Bridge in Oakland:

Well, it turns out not to be so “fun” at this time. A major tanker truck crash and explosion in the southest corner of the maze. The resulting conflagration on the elevated southbound I-880 melted the steel of the even more elevated eastboard connector from I-80 to I-580, which eventually collapsed onto the lower highway.

Please visit this article to view images. You can see a video taken by an eyewitness at the time of the fire. Watch it here instead of at the YouTube site in order to avoid the boorish and in some cases quite inappropriate comments.

This looks like it was rather intense, and scary. Indeed it was rather freaky to see the charred freeway photos last night when first logged on last night. I know that section of freeway quite well from my time in Berkeley and frequent trips to San Francisco and the East Bay since then. That section of southbound 880 had only re-opened a few years ago, having been closed and then rebuild after the infamous collapse of the 880 double-decker freeway in the 1989 earthquake.

Fortunately, the driver of the truck escaped with only moderate burns, and nobody else was hurt in either the fire or the collapse of the freeway. Presumably when you see something like that ahead of you, you opt not to keep heading into it. The area is also fairly spare industrial land, so no homes in West Oakland were threatened. Could have been a lot worse, I suppose…