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Bridge Collapse in MN 29

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Unfortunately "deck" gets used in two different senses. One is what the cars drive on. The other is the relationship between the main girders or trusses and the load-carrying roadway. With deck spans the roadway (or railway) is supported on top of the steelwork.

Where the roadway goes between trusses or girders we call it a through bridge.
 
Regarding civilperson's libertarian rant...

It is the bottom-line motivation of the private sector that leads to corner-cutting and shoddy construction such as the problems found with the Big Dig. And every weird unbuildable bridge design I come across has come from a private consultant, not a state-employed designer.

Capitalism is not the One True Answer.

Hg

Eng-Tips policies: faq731-376
 
There's a lot of truth to what HgTX says. Where I work, the company's list of qualifications needed to be a project manager (and we have various levels of PM's) does not make any mention of engineering or scientific skills.

The management thinks that being a PM boils down to watching budgets, meeting revenue targets, and keeping your staff entertained. Unfortunately, with all the corporate bureacracy we have to deal there's not enough time to deal with the engineering. Then they wonder why the company wide turnover rate exceeded 20% again.
 
The problems with a capitalistically organized economy can be considered, so much so as to raise question about whether the beneficial aspects still outweigh the negatives.

Winston Churchill suggested that democracy is the worst form of political system--except for all the rest.

He might well have suggested the same for capitalism as a form of economic organization.

Capitalism may be the "least worst" of the alternatives available to societies.
 
One lesson that may come out of this investigation for engineers is to stand your ground and don't be talked out of a correct technical decision by political pressure.
 
I work in the bridge industry, first as a designer and now as a shop fabrication inspector/QA manager. I am a licensed PE, a CWI and have passed the NBIS Bridge Inspection training.

I don't know what happened.

I have some theories as to what could have happened but I don't have access to the information necessary to figure it out. I suspect it will take some time for the NTSB to find the critical initiation point.

I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge.

This causes me to believe there was a particular failure in the first span. The collapse of the middle and final spans was very possibly caused as a chain reaction to the collapse of the first span.

I don't have the time to discuss all the mis-information I am hearing. This is a technical subject, not unlike medicine or the law, which requires an individual to have a particular vocabulary. However, for some reason, everyone thinks that engineering is earthy enough that everyone should understand what it is about, I guess because they can put their hand on the problem. Any misunderstanding regarding engineering issues is frequently attributed to the engineer's inability to communicate. I believe it is most often the lack of knowledge on the part of the audience that causes them to think they understand what they just do not.

I recommend we all just sit back and let the NTSB and the Minnesota bridge community figure out what initiated the failure. The information will get to the proper authorities in due course. - Dinosaur
 
We probably shouldn't discuss politics on this forum. I think it will only hurt this valuable resource IMHO.

J
 
Interesting that one would make the statement "I don't have the time to discuss all the mis-information I am hearing." and then proceed to state mis-information.

The statement "I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge." is incorrect.

Suggest that you red flag your post.

The collapse originated in the middle span and the collapse of the middle span triggered collapses in adjacent spans.
 
Dinosaur: There are a bunch of very experienced engineers here on this forum topic. That's all I have to say.
 
I don't think it's been definitively established that the main span (river span) went first.

The original drawings are now available from MN DOT. The south end could be the problem; the framing is a bit unusual.

Spans 3 through 5 are made up of continuous curved girders; the roadway is superelevated west to east (east being the high side.)

At the north end of Span 5 the girders frame into an end floorbeam at the beginning of the truss (Span 6). (At first glance the connection of the FB to truss (Sheet 19 of 94) is unusual. I have to look for more details) The roadway on Span 6 is also superelevated, transitioning to a normal crown at Pier 6/beginning of Span 7 (River Span).

All curved girder superstructure experiences uplift; the inner girders are the ones most affected.

enough said for now.




 
jechols,

Maybe this forum is not the place to discuss politics, but if we had some engineers in politics rather than nothing but lawyers, I think our infrastructure would not be in such sad shape.
 
"Minneapolis — NTSB Chairman Mark Rosenker put it plainly.

"We don't believe the southern portion of the bridge is where the accident began," he said Saturday afternoon."



"The south end of the bridge fell to the ground during the accident, but investigators have already determined that the stresses that caused the bridge collapse did not begin on the south end. The focus shifted over the weekend to the north and center bridge sections."


"Meanwhile, federal investigators trying to determine where the collapse began said that after closer examination, they had decided to shift their focus away from the south end of the bridge. That section shifted 81 feet during the collapse, but investigators now say they found no indications that was where the failure began."

 
Politics is involved in everything where a microphne is involved.

The dead giveaway is the phrase: "I wish to thank......".
 
bimr - I saw that quote about shifting focus to the north end - but the video clearly showed the south end falling first...unless the video was pointing south and not north.

Other witnesses stated that they saw the south end go first.

The only way I can see the north end initiating the collapse is if it failed away from the central span somehow, pulling the south end off its support and causing it (the south end) to FALL first.

 
JAE,

Agree with you. It seems that the collapse started in the vicinity of the Contractor's bulk cement semi-truck trailer close to the south end of the middle span. Once the middle span had fallen, the north and south spans then collapsed.

I was just responding to some of the recent posts above that have incorrect information and are outdated.

 
bimr,

I don't know how a statement saying, "I don't know ..." followed by "... it appeared to me ..." is mis-information. Are you saying it didn't appear to me that way?

darkwing88,

Several posters early in the thread stated they wanted to hear from someone with the right training/background what was really going on there. For this reason I provided some of my credentials, not to inmply I know more than anyone else. Then I followed with the statement that I don't know what exactly happened to initiate the failure. This was intended to illustrate my view that unless you are on the ground you don't have access to the information to know exactly what happened, and I don't think the NTSB will have the information for some time to come.

I can't fathom how you two were offended by my post.
 
Dinosaur:

Here is your statement;

"I don't recall where, but I thought I saw a video of the bridge collapsing where it appeard the first span collapsed, then the middle span, and then the final span of the three span continuous steel deck truss bridge."

The Corp of Engineers security camera video that was playing on CNN only shows the middle span and the north end span. It is impossible to see the south end span on the video because of the camera angle.

Unless you have another video, how could you possibly see something (the south end span collapsing) that is not on the video?

 
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