Bridge Collapse in MN 29

[unclesyd]

There was center support as the arch spannnd (463 ft)to not impeded the river traffic.

Checkout the post by JAE at the top of the page

 

[COEngineeer]

I dont see any center support. The supports are on both sides of the river.

Never, but never question engineer's judgement

 

[bimr]

You are correct, I had the bridge ends incorrect. Lets try again. The piers are on land and from the pictures do not look like they shifted. You can clearly see the south end piers sticking out of the debris in this picture.

The entire bridge did not fail straight down. If you look at the picture below, the bridge did not come straight down at the south end. The debris at the south end of the bridge shows that the top of the south end of the bridge fell or twisted to the east.

The north end of the bridge came straight down, following the failure at the south end.

If you look at the picture above, it looks like they were pouring concrete.

Maybe, the concrete formwork collapsed onto a lower structure member.

Does anyone know what that truck is by the concrete hauler.?

NY Times Picture:

Wikipedia Picture:

NY Times Graphic:

 

[steve1]

The MSNBC link was very informative, espically the profile view of the collapse. The illustraton shows a cantilever truss that would have been constructed from both ends simultaneously cantilevering from the end spans and meeting in the middle.

One problem with the graphic is that the location of the railroad tracks is different in the birds eye and profile views. My understanding is that the tracks are between the end piers.

 

[SteelMover]

Dr. Dexter's 2001 report summary:

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.

He discusses scary fatigue details and pigeons as identified above by concretemasonry. The report maintains that the truss has a severe lack of redundancy. South approach span initiation still looks credible.

 

[blinkd]

This might be relevant -- I haven't seen it cited yet.

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_354.pdf

Inspection and Management of Bridges with Fracture-Critical Details, Transportation Research Board, 2005

Co-author is Robert Dexter who worked on the 2001 Mn/DOT report.

 

[bimr]

The construction semi truck trailer is right in the middle of the area that collapsed. Is it possible that the bridge collapsed from being overloaded?

"Sloan said his crew was placing concrete finish on the bridge for what he called a routine resurfacing project. "It was the final item on this phase of the project. Suddenly the bridge gave way," he said."

For what purpose are the semi truck and loaders used? It looks like it was a material staging area. Is the truck for asphalt, sandblasting, or concrete deck repair?

Milwaukee Journal Picture:

Another Milwaukee Journal Picture of the truck:

Here is another of the construction trucks that look similar to the crashed one.

 

[swall]

I watched the CNN video from the security cam and heard the anchorwoman comment something to the effect, "you can see the smoke as the bridge hit the river". I am thinking, oh jeez, here we go again with the thermite conspiracy wackos.

 

[kenvlach]

The workaround for those with RHS of page truncated is to increase display sttings, e.g., from 1024x768 to 1152x864 pixels. The issue has been discussed before; as Eng-Tips controls neither linked photos or user displays, it would be impractical to resize wide images.

 

[Stratagerm]

Links to a number of photos of the north pier:

http://www.flickr.com/photos/thecurseofbrian/981843488/

http://www.flickr.com/photos/thecurseofbrian/981062289/

http://www.flickr.com/photos/thecurseofbrian/981062289/

http://www.flickr.com/photos/thecurseofbrian/981880976/

http://www.flickr.com/photos/thecurseofbrian/981831000/

http://www.flickr.com/photos/thecurseofbrian/981101517/

A flickr search with quite a number of photos:

http://www.flickr.com/search/?q=bridge+collapse+minnesota+news&m=tags&z=t&s=int

 

[unclesyd]

This photo link posted by Stratagerm clearly shows one of the supports leaning.

http://www.flickr.com/photos/thecurseofbrian/981843488/

 

[mtnengr]

It appears that some of the earlier investigtions included a fatique evaluation. Three basic members were determine critical. These evaluations were using Miner's rule. Does anyone know the material and its transition temperature of the basic truss?

I did not see any K1c evaluations, only stress range.

It would seem to me that a structure subject to -35F could have crack propagation problems that could cause accumlative fatigue that could later cause problems during the summer months.

 

[Qshake]

There is more (better) techincal reporting on ENR.com.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Stratagerm]

An even better photo of the north pier showing its lean:

http://www.flickr.com/photos/diversey/990643158/

Another photo from before the collapse:

http://www.flickr.com/photos/80651083@N00/979238541/

 

[unclesyd]

In the picture above showing the leaning support it looks like it has twisted also. if you constructed a plane through the center line of columns if would be funny looking. This maybe because the bad looking one is on the up stream side.

 

[SteelMover]

Mtnengr - For a good example of crack propagation due to material temperature see the Hoan Bridge failure in Milwaukee. It was really cold when that happened. Three girders had fatigue cracks propagate clean through. Though it didn't fall due to catenary action in the deck. It is believed temps played a role there but the 90+ degree day we had here would not support temperature embrittlement, at least not with the event that finally broke the camel's back.

 

[DaveAtkins]

I watched the CNN video repeatedly, and I noticed that there is clearly a time delay between the main span collapsing, and the approach span collapsing.

I am not sure what that means--did the collapse of the main span precipitate the collapse of the approach spans?

DaveAtkins

 

[Tomfh]

did the collapse of the main span precipitate the collapse of the approach spans?

That looks like what happened at the north end. With the main span gone the approach span could collapse. I imagine this is why the pier is pushed towards the river - the approach spun thrusted it out of the way as it progressed through its collapse.

 

[bimr]

Of course the piers on the north end are leaning.

However, if the north end piers were leaning and imitated the collapse, the collapse would have started on the north end.

But the CNN video clearly shows the collapse started on the south end. After the main spans collapses, a pause occurs before the north approach span collapses. It is logical that the collapse of the north approach span pushed the north end piers off center.

 

[wannabeSE]

Inspection reports and studies of the bridge are on the Minnesota DOT website.

http://www.dot.state.mn.us/