US Bridge Collapse

godtabh

Link

Any ideas what happened?

Good man yourself kearnsr, I was thinking of starting this exact thread!

The bbc had in their 'in pictures' section a before and after set of pics, but they seem to have updated them for pictures of the scene. I'll try and find the exact pics. Seems quite odd to have collapsed given it was checked in 2005 & 2006.

Edit: the 'before' pic is this one from wikipedia:



And from wiki:

Cause

The cause of the collapse remains unknown. A 2001 Mn/DOT report indicated weakness at the joints of the steel that held the concrete deck above the river, due to "unanticipated out of plane distortion" of the steel girders. The report also noted a concern about lack of redundancy in the main truss system.[38] Being a non-redundant structure, the bridge had a greater risk of collapse in the event of a structural failure of any joint or member ocuring.

Linked from the above is a document entitled 'Fatigue Evaluation of the Deck Truss of Bridge 9340', which is here (PDF, 11MB).

godtabh

Not knowing much about bridges the near side pier looks very small and possible easily damage due to scour

Another thing to note is the way it failed. Ie it just failed. No warning.

It also wasnt fully loaded (a couple of lanes closed down).

Yeah, just saw the video of it collapsing on youtube:

https://www.youtube.com/watch?v=OA23jQcEGvQ

You can see the sections closest to the camera hit the water first.

godtabh

Myth wrote:

Yeah, just saw the video of it collapsing on youtube:


You can see the sections closest to the camera hit the water first.

It looks like the connections went and that brought the bridge down.

Thats a very bad failure

tak

But wasn't there a report on the news of a 2002 inspection that showed significant fatigue crack development ? (It would be interesting to know the location of the cracks, as this would give clues as to where the highest local stresses were being taken as well as their likely cause.)
That being so, it defies belief why effective repair and/or crack monitoring procedures were not put in train.

tak

tak wrote:

But wasn't there a report on the news of a 2002 inspection that showed significant fatigue crack development ? (It would be interesting to know the location of the cracks, as this would give clues as to where the highest local stresses were being taken as well as their likely cause.)
That being so, it defies belief why effective repair and/or crack monitoring procedures were not put in train.

I assume that it was the report I linked to a few posts down. It did mention about fatigue but also said how it was also possible that the structure would not collapse if one member was severed.

What's interesting is the rush to examine the other bridges similar to the one which collapsed.

tak

Yes, Myth.
http://abcnews.go.com/US/story?id=3441034

It'll be interesting to read what the stress monitoring system was reading during construction and after opening. Such monitoring would be normal for 1967 bridges surely, not least with a low redundancy framework.

godtabh

I thought I read some where or some one told me that very little redundancy was built into the bridge.

kearnsr

kearnsr wrote:

I thought I read some where or some one told me that very little redundancy was built into the bridge.

Yeah, in fact it was a non-redundant bridge entirely, but again if a collapse happened they weren't sure if the loads would be transferred accordingly or if it would collapse.

godtabh

Myth wrote:

Yeah, in fact it was a non-redundant bridge entirely, but again if a collapse happened they weren't sure if the loads would be transferred accordingly or if it would collapse.

The way it failed suggested that bridge had two modes. Working or in the river