Bridge Collapse in MN 29

[NS4U]

http://www.cnn.com/2007/US/08/01/bridge.collapse/index.html

It happened around 7pm ET today

 

[concretemasonry]

I went over it about 2 hours before. It is a good thing it happened after rush hour and not all lanes were not open. I think there might be as many as 8 lanes total in some areas if ramps/acceleration lanes were included.

Built in 1967. Steel main span over the river with simple spans north and south. The entire section of freeway (several miles) was undergoing surface and other repairs. Some lanes on the bridges were closed and some construction equiment was deployed on portions of the other unused lanes that were under repair.

The collapse apparently started on the south end and progressed northward. Somce sections went quickly and other much slower as people had already stopped. At some expansion joints one side went up and the other went down. The intersting thing was that there was a lateral movement or twisting of some of the spans instead of just vertical.

It will take a good independent professional study to determine the real cause because it was obviously not subjected to classic highway loading conditions.

 

[JAE]

Someone on the Fox news interviews stated they drove over it right before it fell and they saw the construction workers had punched a large hole through the deck. Did you see that? They said there was expansion joint repairs going on but the hole in the deck "didn't look right".

 

[JAE]

Here's a photo of what the bridge used to look like:

 

[SWComposites]

More photos are on the NYTimes web site.

 

[cap4000]

Sounds like the jackhammering vibrations of the deck slab for two months may of caused the sudden failure of a bridge.

 

[WillisV]

Apparently this bridge was studied fairly extensively in 2001. See below for a link to a report done by the University of Minnesota. The report details extensive fatigue analysis studies including SAP 2000 analysis and field testing comparisions under both controlled and open traffic conditions.

One of the conclusions being "Since the measured and calculated stress ranges were less than the fatigue threshold, it is concluded that fatigue cracking is not expected in the deck truss of this bridge."

http://www.lrrb.gen.mn.us/PDF/200110.pdf

I'm sure this will get pulled soon....

 

[MichSt]

Star Tribune in Minneapolis released some info on the bridge inspection report. The bridge was rated structurally deficient. Sounds like there were some poor fatigue details on these trusses.

http://www.startribune.com/10204/story/1338970.html

 

[NS4U]

http://www.cnn.com/2007/US/08/02/bridge.collapse/index.html#cnnSTCVideo

A security camera caught the collapse

 

[unclesyd]

WillisV,
Is this the same report that CNN was quoting that determined that there was no redundancy in two planes of the structure and that fatigue would be problem?

CNN also had a professor of civil engineering that went over the design, steel-arch, of this bridge in detail. He summed up his discussion with the statement that in this particular design it only took the failure of one member the truss to cause complete failure.

 

[SteelMover]

I was down there yesterday just after it happened and it was surreal to see that there was just no bridge there where there used to be one. Unfortunately someone with our knowledge couldn't help much as it was a complete collapse. From watching the video I see an almost perfectly symmetrical, and instantaneous, collapse of the main span.

My own 2 cents freom what I saw (and I know there will be a lot of this)

You just don't see failures initiate and progress perfecly symmetrical within a span like that, leading me to believe that the collapse must have begun on the backspan. It is almost certain that the main span needed the moment contribution from the back spans. Two plausible scenarios are a local deck failure that dropped and the falling mass energy took out an important backspan truss member on the south side, or a failure within the truss at that location, leading to progrsssive collapse on the south side of the south pier, and a complete failure of the main span as a result of unforseen moment deficiency.

 

[SteelMover]

Additionally, the visible failure or the north side of the main span seems to progress as shear failure at the within the truss at the north abutment, but the south side seems to already be moving, and ahead of the north side. It is plausble that the failure mode seen at the visible abutment had already occurred at the one just out of the picture.

 

[archeng59]

great thread.

Is anyone else having problems reading the right end of everyone's posts? Or is it just me?

 

[cedent]

I can read the page fine. Have you tried viewing some other web pages?

 

[archeng59]

cedent, yes. It's just this thread for some reason. Usually, there is a scroll bar at the top or bottom of a page that won't fit within the window, but not this time. Odd.

 

[bridgebuster]

SteelMover - I'm looking at a birdseye view in Local LIve. Are the backspans (anchor spans) cantilevered to support the approaches?

 

[lkjh345]

archeng59.

I'm having the same problem.

 

[csd72]

I think its the big picture - it has blown the browsers.

csd

 

[SteelMover]

See below

http://en.wikipedia.org/wiki/I-35W_Bridge

It doesn't look like a true cantilevered back span, though I'm not a brige guy

 

[RARWOOD]

I did not see the CNN report, however, based on a discussion with a co-worker, I believe the person they interviewed was Retired Professor Ted Galambos. Professor Galambos was a long time member of the University of Minnesota Engineering Faculty.