Bridge Collapse in MN 29

[unclesyd]

The bridge is already modeled.

http://www.memagazine.org/Story.html?story_id=109037912&category=Engineering&ID=asme

Look down at the reference to the 2001 inspection statement.

http://www.memagazine.org/Story.html?story_id=109037779&category=Engineering&ID=asme

Sidelight:

Hoan Bridge in Minneapolis

http://www.memagazine.org/Story.html?story_id=109029308&category=Engineering&ID=asme

 

[darkwing888]

GUTLESS BUREAUCRATS, NO BRIDGE REHABILITATION "SUPERFUND," INADEQUATE INSPECTION AND EVALUATION PROCEDURES, DESIGNING TO A "NAT'S ASS."

GUTLESS BUREAUCRATS: They see engineering recommendations as optional!

NO BRIDGE REHABILITATION "SUPERFUND:" Money and politics should not be a roadblock when it comes to life safety.

INADEQUATE INSPECTION AND EVALUATION PROCEDURES: Bridge engineers should reevaluate their fatigue analysis procedures. They should replace stress range approaches to damage tolerant crack growth procedures.

DESIGNING TO A "NAT'S ASS:" The bridge designer should be using significantly lower allowable stresses for fracture critical details.

 

[Qshake]

Maui - The last thing we need to encourage is speculation by bridge engineers not familiar with this specific bridge. There are many different bridges and 99% of bridge engineers today are only familiar with the typical slab and girder overpasses. It would not speak well of them (or others) to offer opinions on this collapse.

Unclesyd - The Hoan bridge is in Milwaukee!

As I read the posts from the beginning I can't beleive some of the writings actually belong to engineers. It's true that infrastructure is aging and needs to be dealt with but some of the rants and raves posted here are no better than lay people, media Zealots or meteorologists.

As for Architects - they should also refrain from commenting, shop drawing review or not as should the folks I've listed above. Experience with steel design especially with buildings be they large, deep plate girders acting as transfer girders doesn't play into this since there is virtually no fatigue cycling in that environment. Fatigue and Fracture Mechanics is a specialty area of engnieering and those who've had a course in it (as I have) will tell you that it is far from exact science and requires dedicated study.

As for the history of the bridge, we scour what we can from teh web, but has it occurred to anyone that we're barely scratching teh surface? This bridge could have been retrofitted or rehabbed for other purposes and we have no idea what or how it could have been modified or how those modificatinos affected the original behavior.

So please let's not act like the very people we curse upon hearing mis-information.

Regards,
Qshake

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

 

[unclesyd]

Sorry about the problem with locations. It a problem when you get old and try to do two things at once, type and listen to the news.

Qshake,
You and I have been around and about enough to see the same refrain form the bureaucrats when they come out with explanations and hyperbole, along with dancing, around any event such as this. I know that most bridge engineers and professors can't speak out about things like this if they want to keep their job or get grants.

I think it about time more people, maybe not the best informed, get concerned and rant a little until the next bridge fails.

 

[Maui]

Qshake, there is a great deal of speculation that has already been offered in this thread by individuals who have made it clear that they are NOT experts in the structural engineering of bridges. If anyone is to offer potential explanations for this particular collapse, I would prefer that it come from an expert who is trained and experienced in this specific discipline. So far, I have not not read any replies from individuals who have made it clear that they are. That is the reason why I posted the question above.

I asked for

...experience-based insight into the likely reasons for this particular collapse?

I would not expect someone who is unfamiliar with this type of bridge design to reply to my question, nor would I want them to. But if someone is experienced, trained, and qualified to provide the requested information, and they are inclined to do so, then it does not speak ill of them (or others) to formulate an appropriate reply. Each case is different, and a failure analysis must be performed to determine the specific reasons for the collapse. But if we followed the same line of reasoning that you provided in response to my question, very few engineering questions would ever receive replies on this website.


Maui

 

[darkwing888]

Maui,

With all due respect, at this point all there can be is speculation even from experienced bridge designers until the forensic report is published.

I have some fatigue and fracture analysis experience for other structures. What I don't understand is how bridge engineers can determine the life of a cracked structure using stress range approach. Once you have a significant crack, the stress range approach is meaningless and fracture mechanics is necessary to determine an estimate of remaining life to failure.

David N Watson, P.E.
Drummond Company, Inc.

http://www.drummondco.com

 

[SteelMover]

Evaluation of this bridge collapse should include bridge experts, the inspection team, as well as material experts, fatigue experts, those with knowledge of long-span truss design, geotech & foundations. A diverse team such as that can avoid tunnel vision you get when you have a very specialized group who have seen the same details over and over and may not recognize possible faults.

Some of what is said above is useful, or at least insightful because it comes from a different point of view. Notice how nearly all of the structurals zero in on the steel, while the civil guys seem to focus on the foundations. Besides isn't the point of this thread a collaboration of thoughts & evidence from engineers of all disciplines. Offer up some helpful thoughts for the discussion.

 

[Qshake]

darkwing - that is what i had hoped to point out among other things - it is too early for any sort of accurate speculation.

Maui - one would have to have 'exact' experience in order to speak expertly on this matter. I am not aware of any similar bridge collapses.

darkwing - back to fracture and fatigue mechanics in bridges. Unlike the fracture and fatigue evaluations that GE or Honeywell or the DOD or Boeing or pressure vessel manufactures might undergo to determine the remaining life of a structure or element within a structure, once a bridge member cracks and is found and noted in an inspection, the crack is usually arrested via a arrestor hole drilled in. It is further watched as are the surrounding members and or similar members.

If the crack cannot be controlled by those means, the member or part thereof is typically replaced. The bridge industry does not engage in fracture studies as I point out may occur in other industries/companies.

That said, there are numerous bridge structures still performing well today with cracks and arrestor holes.

Steelmover - there are many, many different areas that could have, in concert, acted to collapse the bridge.....I don't see the point in speculating about all of them.

Regards,
Qshake

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

 

[shin25]

Lane closures usually create congestion in
the open lanes, also, should distribute
more load to some members than they were
designed for. I like to see if this has to
do anything with the failure.

 

[Maui]

Darkwing and Qshake, I think that you may be reading more into my post than was intended. I understand that it is impossible to make a determination for the exact cause of this bridge collapse without a complete analysis of the appropriate forensic data by qualified experts. And it is simply too early in the process of the investigation for the experts who are currently working on this case to draw any conclusions themselves. I get it. So does everyone else here. But that isn't what I asked for. I requested insight into the likely reasons for the collapse, not for a detailed explanation of the specific cause of this particular failure. My objective was to get some objective feedback from a qualified, seasoned professional on the possible mechanisms of failure that could have produced this result (examples include fatigue mechanisms, corrosion, overload, etc). Based on your replies, it would appear that you feel it is not possible or appropriate to do this at this point. I did not expect to receive a definitive answer.

Maui

 

[mtnengr]

Darkwing888 is absolutely correct. If you review the 2001 report by Univ Mn., it points out that cracks had been observed in 1990. As a "fix", holes were drilled at the end of the cracks to stop their propagation. I could not examine the details of the "fix."
The questions that I had brought up earlier have not been answered. Is there a report that evaluates the state of stress with a hole at the end of the crack? A K1c calculation before and after the "fix" should have been made.

How many cracks and/or their density could exist before the margins of safety of the bridge is jepordized?

 

[JAE]

Maui,
I think that there could be numerous reasons that could be listed here by bridge engineers on this site. Just not likely reasons.

Saying "likely" implies that there is knowlege available to rate each reason's probability. I agree with Qshake that no one except those directly investigating the bridge can even come close to that "likely" position.

 

[Robertmet]

I'm a new member, retired metallurgist. Two points for this thread .Some of those photos show distinct camera lens distortion so that things seem to be tilting when actually they are not !!....Vibrations - we got a new bridge here [Delaware River] and when they took down the old one last winter they chewed away the concrete support with jack hammer on excavator and at one point the entire truss hit resonant frequency !! Amasing to watch the frequency was about 2 cycles per second.Nothing subtle the whole truss vibrated ,loud,dust and dirt coming off the truss.I doubt that the roadway replacement would have caused that resonance !!

 

[subtech]

The vibration/resonance idea is interesting. I believe it is important to remember that buildings and structures of most any shape/size can have many resonant frequencies. I once found that a rather large gymnasium had three acoustically resonant frequencies using a signal gererator, a rather large amplifier, and some voice of the theatre speakers. I'm confident that more points of resonance could have been established had the school principle not shown up and dragged me outside by the scruff of the neck...
(Its amazing how much dust you can shake from the rafters with only a couple hundred watts)

 

[bimr]

Probe to See if Construction Played Role

http://www.nytimes.com/aponline/us/AP-Bridge-Collapse-Contractor.html

 

[hokie66]

Fatigue, corrosion, resonance, footing failure, all things to consider. But all I have to go on are some photos. And the photos of the bearing and the main compressive web member show some brown staining which seem to indicate corrosion. That steel member is carrying the entire load of the bridge, just as is the concrete pier. And if reports that the bearing was locked are correct, that would bring bending of the strut into play. For those who don't like speculation, apologies, but that vertical strut is where I would look first.

 

[kenvlach]

I'm not a bridge/structural expert, but suggest that people not get carried away with resonance schemes (the Tacoma Narrows 'Galloping Gertie' ca. 1940s makes a great visual on TV but very likely not relevant), as the New York Times article (bimr's link) notes "The most recent jackhammering of deteriorating concrete had occurred the day before, and none was performed the day of the accident, he said."

As to why it fell when it did, lots of corrosion issues and fatigue cracks, but as to the 'straw that broke the camel's back,' I have a hunch that the cement truck is mentioned in the final report.

 

[Robertmet]

kenvlach, yes, there is a big difference between vibration and resonant vibration. The resonant type will tear things apart quickly....BTW the bridge here doesn't have expansion rollers .It was explained to me that the underside of the girder has a highly polished plate of stainless steel which then rests on the support which has a layer of teflon. Perhaps one of you bridge types can give details.Of the hundreds of photos I took I don't have one of that.We also have here a bridge , originally an a canal aqueduct, built by John Roebling in 1848 !!!

 

[Tomfh]

2 year old photo of roller bearings:

 

[BigInch]

Its enough with all the bolt (rivits???) holes to scare me. I don't suppose its seal welded either...? And it looks like paint is pretty expensive too.

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