Minneapolis I-35W Bridge Collapse Failure Analysis

opinion | 8-21-2007 | jeffers

[shield]

bfl

[lesser_satan]

bump

[MichaelP]

You really oughta charge for that....Great work!

Mike

[trooprally]

ping

[SouthTexas]

Thank you very much, will read it in depth as soon as we plant this storm. ;)

[Bean Counter]

Many, many thanks for this analysis jeffers; pretty soboring stuff...

[PA Engineer]

Based on these tenative additional comculsions, I believe it most likely that the east truss U7-U6 top chord failed in tension at or near the U6 connection gusset very early in the collapse progression, quite possibly as the collapse sequence initiating event.

Have you been able to correlate this with the reported gusset corrosion (pictures) in the MDOT report? I have to head out and will check the replies later. Thanks.

[lapsus calami]

 

 

 

Whoa - you put some brain cells to serious work on this - will be interesting to see how any "official" report is going to stack up in comparison.

 

 

Thanks for the ping!

 

 

 

 

BUMP!

[rawhide]

Incredible!

[spanalot]

Awsome - isn’t that where the lower chord goes from tension to compression?

[concretebob]

Thank You..

Jeez Man, don't you have a job?
Thats some good forensic engineering...

[brityank]

Many thanks, jeffers. I have gained a little more knowledge in an area of which I know nothing, and have gained a better understanding of the forces in play — all thanks to you and FR. I’m fairly certain the knowledge base here on FR is better than most think tanks, mainly because it’s done with love and pride and not mandated by position and money.

[TXnMA]

Great work! And thanks for the ping to it!

Adopting the standard nomenclature really helps. I haven't worked my way completely through the entire analysis yet, but from what I have read, it looks like you have pretty well nailed it.

I am still interested in the much-belated action that took place on the north shore -- and I'm still looking for video source that starts before the initiation of collapse. (Even the CNN cut starts after first motion has obviously occurred.)

I'm nearly done refining the presentation of my diferential frrame analysis, but, I will say that I do notice some very early-on buckling of the main-span western lower chord -- right at the nothern pier end...

So, if you (or anyone reading this) know(s) the URL for a copy of that surveillance video that does not have the pre-collapse frames edited out I would love to have it to work with.

I probably will check back when I have had time to digest all you wrote and posted...

Again, thanks for the ping -- and for your (obviously competent and thoughtful) work!!!

[jim_trent]

Thanks for the ping. Let me look at this for a while.

[xarmydog]

I was wondering what the people on the other bridge were thinking as they parked to take pictures and otherwise rubbernecked to get a view of the bridge collapse.As I watched the news,I could not help but think,GET OFF THE BRIDGE!!You may be next!

[Hunble]

I agree with this basic analysis. This is some outstanding Freeper research, and we should all be proud of Jeffers!

[norwaypinesavage]

Great analysis. I am an engineer who has specialized in metal fatigue. I lived across the alley from the bridge while it was being built. (The houses on the alley behind me were torn down for the bridge.) I used to walk along the railroad tracks under the bridge while on a hiking route that included the upstream Old Stone Bridge when I visited the U (a little Minnesota lingo, here). So I have followed your reports with interest. Please include me on your ping list.

[jeffers]

Two corrections, one a mistake in labelling, another a mistake in identification of east truss members, neither of which affect the conclusions drawn in the discussion.

One, a typo in Image 4, the member designated “Top Chord Tension Member U8-L7” should instead be labelled “Top Chord Tension Member U8-U7.”

Two, in images 3 and 4, the member labelled “Southeast Pier 6 Kingpost” is probably, on deeper reflection, the U8-L9 Tension Diagonal. Visual inspection indicates this is a flanged H-beam member, not a built up box beam as the kingpost would be.

The kingpost is minimally visible in Image 4, very close in location to the member mis-identified as the kingpost, but very difficult to see as it rests directly behind the U8-L7 tension diagonal when viewed from this angle.

In Image 4, the visible sliver of the SE kingpost is seen immediately below the terms “sway brace” in “U8 Floor Truss Top Chord or Sway Brace Horizontal (?)”.

The lower sections of the SE kingpost identified in Images 6 and 7 are labelled correctly.

Sorry for any confusion this may have caused.

[dr_lew]

Excellent. I was thinking along these lines, but in a vague sort of way, and I was losing concentration.

I had found those two photos you have here by Noah Kunin. These were taken minutes after the collapse, before any emergency response. ( The one with the roller on the ground is falsely credited in at least one FLICKR page. ) Note the driver being helped from the maroon car in the second photo, taken from about the same spot. Kunin has an earlier photo showing the guy in the yellow bicycle helmet about to venture out onto the collapsed approach.

In the one with the roller, you can see the ladder cage that I think is on L6-U6, visible in your reconstruction diagrams. Isn’t that right? When you say “kingpost” do you mean the L8-U8 vertical element? I thought this was L6-U6, as I say.

Also, you have the top chord mislabeled as U8-L7, when it should be U8-U7 ... a typo, right? This is in the “maroon car” photo.

I was thinking that the truss above pier 6 must have rocked back to the south, analogously to the north side behavior at pier 7, and this is what “kicked” the roller bearing parts to the north, and its what caused the rotation of the roadway back and to the east.

Anyway, I think your analysis is very close to the actuality. I saw a news item about the gusset “design flaw” that singled out U6, or maybe U10, which corresponds to U6. I got the idea that this “discovery” had to do with failure to account for bending moments applied to the gusset by relaxation of the framework.

So, thanks, and great work.

[pillut48]

Wow! Way over my head, but wonderfully researched and thought out. Thanks for the ping! It will be interesting when the final official report on the bridge comes out, can’t wait to compare your work with theirs!