Poor design led to I-35W bridge collapse?

Dear Anders Lager=E5s:
The key word is "expected". This makes the persons that: * estimates usage of this bridge over the expected life, and * updates usage (number of lanes) and refurbishment as responsible as the original designer. Do they have the same qualifications? Do they get called into court? No. From their armchair, everyone blames the engineer.
And fatigued parts also.
Untrue. You may have an unusal (but not uncommon) definition of "well designed". Any material (except steel and carbon-epoxy composite) has a finite fatigue life, for finite applied load. So what has to be done, is to estimate the load, design the various joints to deliver that service, apply a factor of safety, and pray that the people that allow loads on it, and maintain it, and (apparently) inspect it all do their jobs.
When these things are not done, especially the loading *estimation*, fatigue-to-failure can be the result.
.=2E.
Lets hope so.
At least one person would not have died had this "lane reduction" happened. One of them only ever took this bridge based on traffic, and this would both have extended the life of the span (but not the mode of failure), and kept that person off this bridge.
Why? Because bearings suffer fatigue and corrosion.
I agree with you. I am just not naive enough to believe there is no fatigue allowed in real structures.
This has not been shown to be the case. This bridge is similar to thousands of others that have not failed, and do not have "structurally deficient" reports on them... presumably because someone maintained them.
Given that ASHTOO may cover this, and be stated on the design drawings, an additional statement may not be any more necessary than the number of lanes the bridge is to carry, the design loading, the tons of black top added, teh number of strikes by speeding snow plows, and the numbers of strikes by (ships and) ice navigating the Mississippi.
But there would be no chance for fatigue. Are you saying that what is known to work should be a basis for future designs now? Because what works, are designs exactly like this now-failed bridge, only with maintenance.
Untrue. Cite the relevant paragraphs that require this ad hoc addition of yours.
Untrue. If you don't build it only from cast iron embedded in bedrock, it will both corrode and suffer fatigue.
You say that like it is a dirty word.
A bridge is like building a car. The engineer and contractor build the car, but it is up to the owner to carry it through its 100 year mission. It is not like a firing a howitzer, where all the brainwork and muscle power occur at the time of launch.
I understand you will disagree with some of this. Your words can be the last.
David A. Smith
Reply to
dlzc
Loading thread data ...
Yes, it does, they often need to have better qualifications than the original designer. At least here in Sweden it works like that. And they would have to appear in court.
The bridges around here at least are designed in that way, and people do their job most of the time. The oldest ones still around are usually railroad bridges, since the load has not increased that much, steamengines were quit heavy. Some loose rivets have to be replaced, but that is about it. =20
But they do not have a design lifetime as long as that of the bridge.
Fatigue it self is unavoidable but it must not be allowed to cause any problems during the expected lifetime of the bridge. A structure and its details can be more or less fatigue prone, less is to prefer for a bridge.
And maybe did more that that.
We will see what caused this collapse.
It does not need to last forever only the design lifetime.
I like maintenance! But I usually think of maintenance as the work that is know from the start to have to be carried out during the expected lifetime. Replacement of parts, reinforcements or other improvements needed as a result of problem with the design, heavier traffic than expected or what ever is something else, even if necessary, but not maintenance of the bridge.
Yes but it can be more or less difficult to take care of.
I would not like to have a car that needs a new engine every now an then because it gets fatigued. That the manufacturer did not take fatigue in to account, even though it has been know how to deal with it for 200 years, would I see as a problem.
But you would not mind I guess! Not ever after the third engine replacement the same month would you complain, it is only maintenance!
--=20 Mvh Anders Lager=E5s
Reply to
Anders Lagerås
Dear Anders Lager=E5s:
.=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
Reply to
dlzc
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:
formatting link
formatting link
Reply to
juanes
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 money was no object the best approach would probably be to have massive gravity structures such as the Roman arch bridges. The use of tension and flexion to resist loads makes for much more economical structures, but they are also more vulnerable to the passage of time. It's a matter of choosing to put all the money up front, or spend it piecemeal. To satisfy the commuters' (and journalists') demands of ever more links the choice is obvious from a political perspective. But then there is always a need to streamline the maintenance schedule too. And if it can be postponed 4 or 5 years more, that's to the good.
Anders Lagerås wrote:
Reply to
juanes
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
formatting link
Quoting from there:
"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
Reply to
Mike Beaty
: 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.
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.
formatting link
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.
Reply to
Androcles
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
Reply to
jmfbahciv
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
Reply to
jmfbahciv
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
Reply to
jmfbahciv
After one or two bridge lessons, hard earned, I'm afraid.
Brian W
Reply to
Brian Whatcott
...
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
Reply to
Brian Whatcott
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
Reply to
N:dlzc D:aol T:com (dlzc)
...
...
A useful point perhaps. Minnesota is by no means a finance impoverished state.
formatting link
Running under a biennium MN has a 08-09 budget fund of 55.393 billion USD. 38.4% of that (21.2 billion USD) to Heath and Human Services, 27.4% of that (15.1 billion USD) to K-12 Education, and 8.7% (3 billion USD) for Transportation (Roadways and public transit).
The Minnesota Department of Transportation (MNDOT) is responsible for 30,194 lane miles of roadway, 5009 lane miles within the Twin City Metro Area.
formatting link
In Minnesota, MNDOT is funded through earmarked funds including various licensing fees, and a State fuel tax.
formatting link
And yes, Minnesota use deicing chemicals in the winter, more recently moving away from Salt as a deicing product, but certainly for a majority of the bridges life it was salt.
Reply to
Mike H
...
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
Reply to
Brian Whatcott
: : >
formatting link
> : >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? :-)
formatting link

Reply to
Androcles
The UofM study pointed out this design's lack of redundancy.
Reply to
Richard Henry
Four months from opening to collapse.
Reply to
Richard Henry
Depends on the failure mode, analysis will tell.
It would not even have to be a continuous measurement. They can take 3D "holographic" measurements of a bridge in a short period of time (good to fractions of an inch). They could look for signs of shifting in key members between successive "snapshots".
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
Reply to
dlzc
Does that mean that this bridge is in immenent danger of collapse?
formatting link
It meets all your requirements of a "poor design". Plus a 976 foot span, a tad longer than the I35W bridge's 458 foot span.
formatting link
formatting link
Reply to
Matthew Beasley

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.