Poor design led to I-35W bridge collapse?

Dear Anders Lager=E5s:

On Aug 6, 1:16 pm, Anders Lager=E5s wrote: .=2E.

So you obviously have a Rolls-Royce, with a sealed hood. I notice that they do not offer this anymore, and they sold few of these types of cars.

"40 years" does not correlate to "100 years", as "1.33 weeks" correlates to "5 year, 50000 miles".

Please explain to the class how you never change your oil, check lubricants, or coolants; and wait to failure, and claim "design problem" if the front universal joint shatters when your transmission locks up, and drives the drive shaft through one of your co- occupants. That makes about as much sense in this context... if you want to butcher an analogy.

David A. Smith

People keep coming back to design, but the thing DID stand up for 40 years. In my book that makes the design adequate. But civil engineering design makes no provision for deterioration over time beyond the safety factors used. As far as I know, there is no systematic approach to recommend the timeschale for maintenance work to be performed without compromising the structural integrity. But you can be fairly certain that the peak loads were reached sometime during the 40 years, and that there were many occasions of assymetric failure.

After 40 years, I believe the only thing that can be said is that better tools are needed to determine when structural components may not be able to carry their initial design loads. But those same 40 years of loading and unloading tend to show that the design itself was not at fault. I am not familiar with that area, but I believe that Minneapolis suffers cold winters does it not? If so, and if salt is commonly used as a defrosting agent, then maintenance is even more of a concern. Steel is not known for liking salty weather.

Probably instrumenting structures and monitoring them throughout the life cycle would enable municipal engineers to evaluate the relative changes in capacity of the structural elements. I am not aware of such endeavours, or the costs that would be associated to them. But if the cost is significantly smaller than undertaking significant structural changes at arbitrarily short periods of time, it should definitely be worthwhile.

Robert Clark wrote:

Last year, a concrete span bridge (30 years old) collapsed in Montréal. Although theoretically concrete being a basic material protects steel against corrosion, the heavy use of salt as a deicing agent in winter turns the pH of concrete from basic to acidic. As a result the steel reinforcement weakens, and bulges weakening the concrete also. Ironically a number of people were saying back then how concrete shouldn't be used and such structures should be made of steel. I suspect the steel and concrete lobbies may encourage either rumor.

The only real protection is to ensure that the strength of the component members are sufficient for the design loads at each phase of the life cycle of the structure. The tendency is to minimize cost during construction, and as a consequence maintenance becomes more important.

Of cuourse, if m> >> i dont ahve much information about thespecific case

I suspect that you are referring to the AASHTO (American Association of State Highway and Transportation Officials) and their "Standard Specifications for Highway Bridges", correct?

Now in the 17th Edition and available from

"The structural design standards used by state bridge engineers, engineering colleges and universities, and practicing engineers worldwide. Now features separate tables of contents for figures and tables. Updates provided on bridge web site for download and printing. For the first time, includes easy-to-use CD-ROM with the following functions:

Easy access to specific sections; Hyperlinks from table of contents and within text to sections/articles, commentary, figures, tables, and equations; Search by section, subject, table/figure, article number, equation, or ASTM reference; Extensive index; and Detailed tutorial and help menu. Customary U.S. units. Replaces the 16th edition and its interims (1997-2003)."

Of course, the 1961 version wouldn't have been available in any media version but print :-). Mike

Begin painting one end. Keep going to the other end. Return to start. Begin painting one end. Keep going to the other end. Return to start. Begin painting one end. Keep going to the other end. Return to start. Begin painting one end. Keep going to the other end. Return to start. Begin painting one end. Keep going to the other end. Return to start.

Are you forgetting that the bridge was built decades ago? The kind of instrumentation you think should have been put into the bridge while under construction hadn't been developed. Most of us hadn't even envisioned a computer that could carried in a human hand.

I don't know about Minnesota politics, but the politics in my state dropped most of its maintenance responsibilities.

/BAH

This is a foolish "if". Take a look at the project known as the Big Dig in Boston. Billions were spent and pieces of the project were broken before the project was finished.

Play a pretend game... YOu are a politician who has been elected and will need to be elected in the next election. You are about to vote on the state budget. Do you spend tax monies on schools and the so-called social programs or maintenance of infrastructure? Do you choose capital expenditure projects that are paid by the state or the ones that will bring in oodles of money from the Federal government? If you are a Congressman, do you allocate monies for mainteance of the infrastucture or dump more money into social programs?

/BAH

I don't understand what you are measuring. Breakage of the wire? Don't you think that would be too late? In addition, are you assuming that all single point failures are known? If they were, the bridge would not have fallen.

Now multiply it by at least a million.

There is no infrastructure finance impoverished. Half of the monies spent on these projects is graft, pure unadulterated graft.

A state highway board hires a contractor to do X. The bills the contractor sends to the state has doubled the amount of each line item.

/BAH

After one or two bridge lessons, hard earned, I'm afraid.

Brian W

...

This thread made me ask: what could you do to instrument single point of failure critical bridges? Here's one suggestion, off the top.

Take a long reel of fine weather-proof insulated copper wire. String it across every joint and single point failure path. Glue it to structure each side of a joint.

Monitor path resistance. Add a bell or an autodial capability.

This approach would cost, no doubt - perhaps as much as seven thousand per bridge? And most alarms would not be joint failure related. But this might work for the infrastructure finance impoverished.

Brian Whatcott Altus OK

Dear jmfbahciv:

I think he was imagining a "poor boy's strain gauge".

Brian, the failure of the bridge would be seconds away when the strain gauge had a non-secular change in resistance. You go from plastic yeild to brittle failure in a very short period of time.

Wouldn't help anyway. Need better non-destructive test methods. Or simply assume all load bearing members are fuses... to be replaced every few years. (Fuses also suffer fatigue failure, just like MOVs.)

If they are that impoverished, then they cannot afford the coming lawsuits for first degree murder, right? They knew that the bridge would fail, and they knew it would be under load when it did. Premeditated, unless they had foreknowledge that only unmanned vehicles would be on this bridge over the next few years.

David A. Smith

On Aug 7, 7:06 am, Brian Whatcott wrote: ...

...

A useful point perhaps. Minnesota is by no means a finance impoverished state.

The Minnesota Department of Transportation (MNDOT) is responsible for

...

Unfortunately, failure is usually NOT seconds away with a fatigue break. Even visible breaks exist for years - and people grow complacent. Knowing about every extra joint's relative motion would be helpful, I suspect.

Brian Whatcott Altus OK

: >Over salt water. Formally completed on 4 March 1890 . : >Still in use today. In my book that makes the design adequate. : >40 years? Huh! Your book is worthless. : : : After one or two bridge lessons, hard earned, I'm afraid. : : Brian W

How long did this one last? :-)

The UofM study pointed out this design's lack of redundancy.

Four months from opening to collapse.

Depends on the failure mode, analysis will tell.

It would not even have to be a continuous measurement. They can take

And I agree with that. The bridge does not "fail to breaking axles, and popping tires", it only fails to the river bottom.

But it was state-of-the-art in the 60's, "probably" all the government required (and was willing to pay for), and adequate (the lawsuits will tell, of course) to the task defined at the time. With required maintenance, or controlled loading.

David A. Smith

Does that mean that this bridge is in immenent danger of collapse?

Oh, and to add: It's 72 years old with a rating of 48.7%