Bucyrus wrote:It is interesting that the NTSB said in effect that they did not intend to point fingers of blame for the collapse, and then proceeded to point the finger of blame at the designers. But apparently, if the designer no longer exists, there is no finger of blame.Here is an interesting article that seems to be going against the popular orthodoxy that the question of what caused the collapse is settled.http://www.twincities.com/ci_7992046?source=rss&nclick_check=1It mentions that there was considerable corrosion on the very plates that were made too thin by the flawed design. The corrosion made them even thinner. Here is a quote from the article: Jim Schwebel, a lawyer who represents the surviving relatives of three victims, said those issues are worthy of follow-up. "If investigators have any of (the gusset plates) that were compromised by corrosion, you've got to put that into the computer model," Schwebel said. "Do they have a right to make that assumption (that corrosion wasn't a factor) if they see that the plates are undersized? And if they don't see that, are they blind?"
It is interesting that the NTSB said in effect that they did not intend to point fingers of blame for the collapse, and then proceeded to point the finger of blame at the designers. But apparently, if the designer no longer exists, there is no finger of blame.
Here is an interesting article that seems to be going against the popular orthodoxy that the question of what caused the collapse is settled.
http://www.twincities.com/ci_7992046?source=rss&nclick_check=1
It mentions that there was considerable corrosion on the very plates that were made too thin by the flawed design. The corrosion made them even thinner. Here is a quote from the article:
Jim Schwebel, a lawyer who represents the surviving relatives of three victims, said those issues are worthy of follow-up.
"If investigators have any of (the gusset plates) that were compromised by corrosion, you've got to put that into the computer model," Schwebel said. "Do they have a right to make that assumption (that corrosion wasn't a factor) if they see that the plates are undersized? And if they don't see that, are they blind?"
Corrosion over the design lifespan of the bridge is usually a factor used in the design of engineering components. The thicker the piece is, the longer it will last against corrosion. That is probably the reason they claim it is a design flaw.
I guess I just don't see where the lawyer is going with this one. Since he is representing victims, I assume that he esentially is looking for ultimate blame to be placed.
The quote I find interesting is this:
"But Rosenker said the NTSB investigation has found no evidence that cracking, corrosion or other wear “played any role in the collapse of the bridge.” "
I just cannot fathom this statement from an engineering standpoint. Surely the load on this bridge was not high enough to meet the yield stress of the original design, since that is pretty much the only way for the bridge to fail if no wear played a role.
squeeze wrote:The sad part is that there are 547 bridges that are similar to this bridge across America. I'll bet each state is scrambling to find out how there's are constructed. Here in Pa. we have 54 that are of the same build. Kinda makes you wonder.
The problem with that I-35W bridge was that if you've seen the pre-collapse pictures, the bridge sported a very spindly structure with lots of exposed structural steel and only four relatively small concrete pillars to hold up the bridge--it was a disaster just waiting to happen. The new bridge now under construction is built from reinforced concrete designed with withstand the considerable temperature changes of weather in Minnesota.
Krazykat112079 wrote: Bucyrus wrote:Do bridge designers just get to make mistakes without any consequences?The answer is no. There is almost guaranteed a Professional Engineer's seal affixed to the plans for that bridge who is accountable for design errors. But, there really needs to be a thorough investigation. It is entirely possible that the wrong pieces were installed in places that no one caught. People tend to assume that the proper thickness widget or length whatcha-ma-callit was supplied and installed. It could be a design error, supplier error, contractor error, or even inspector error.
Bucyrus wrote:Do bridge designers just get to make mistakes without any consequences?
The answer is no. There is almost guaranteed a Professional Engineer's seal affixed to the plans for that bridge who is accountable for design errors. But, there really needs to be a thorough investigation. It is entirely possible that the wrong pieces were installed in places that no one caught. People tend to assume that the proper thickness widget or length whatcha-ma-callit was supplied and installed. It could be a design error, supplier error, contractor error, or even inspector error.
Well that would be my take on it too. But as I listen to all the local news, I detect virtually zero curiosity about the accountability for the design flaw. The general thrust seems to be that the bridge fell down, and it is nobody's fault because the design occurred so long ago. It makes you wonder how many other Minnesota bridges have lost all accountability for their designs because their designers went out of business, sold out, retired, or died.
I wonder why the NTSB, after lecturing us all fall about not jumping to conclusions, would come out now, nine months before their final report, and tell us they stongly suspect that a design flaw was at fault, but they are not sure.
Kind of makes you wonder, though, when engineers (all kinds) make mistakes, lots of people may die, but athletes and other entertainers get paid the big money.
Wonder things like what? If the bridge your driving across could suddonly fall out from under you leaving you suspended in midair with sign reading "Help!"
http://www.designnews.com/article/CA6466909.html
Here is an interesting article from last fall that discusses the rust-frozen roller expansion bearings, which impeded expansion / contraction movement of the truss. It says that prohibition of this movement caused the truss to deflect out of plane, and speculates as to the amount of extra stress this loading caused, and whether it pushed the bridge past its design limit. At one point, last fall, I heard that this condition of locked expansion bearings had caused the force of expansion / contraction to tip one of the piers out of plumb. However, that is not confirmed by this article. The following is from the article:
Seventeen years ago, the federal government first said the bridge was structurally deficient, citing significant corrosion in its bearings. Seven years later, significant out-of-plane distortion was noted in the main trusses connected to cross girders due to resistance to motion at the connection cross bearings, according to a report released by the University of Minnesota civil engineering department. The cracks in the girders were drilled to prevent further propagation. Support struts were also added to the cross girder.
Bridge bearings, such as the multiple roller bearings used in the I-35W bridge, are used to transfer loads from the deck to the superstructure as weight burdens vary or weather conditions change. Their primary purpose is to redistribute major longitudinal shifts in load.
Just to clarify, I did hear the NTSB say they had not concluded that the design flaw caused the collapse. However, most if not all of the news during the last 24 hours unequivocally declared that the design flaw was the cause of the collapse. Even listening to the NTSB press conference, one would have to work hard parsing words in order to conclude that the NTSB was not announcing that the design flaw was the cause of the collapse.
And they certainly did rule out the possibility of the collapse being caused by a lack of inspection and/or maintenance. I don't understand how a potential cause can be ruled out while the actual cause is still unknown.
Stepping way out on a limb... (or was that thin ice?) My background is in EE not CE, so take what I write with a large grain of salt.
From what I have read so far, this looks like a case of ordinary negligence for the bridge designers and builders, after all the bridge did stay up for 40 years. What looks to me as the critical design flaw was a lack of redundancy in the structure - that is failure of a single component could lead to failure of the whole structure. This point was driven home by the failure of the Silver Bridge in Ohio/WV in December 1967, also about 40 years after construction. If I recall correctly, design work was already underway on the I-35W bridge before the collapse of the Silver Bridge. Incidentally, FAA regs on large aircraft design require the airframe to have enough structural redundancy to survive failure of a major member, e.g. a wing spar.
As for the crowd responsible for maintaining the bridge, it remains to be seen if the point of failure was something that could be detected by inspection.
There's some leaping to conclusions and conspiracy theory here.
The NTSB has not determined a cause for the collapse. All that it said today is that 8 of 112 gusset plates of the main trusses were significantly undersized for the load the design called for them to carry. The gussets have not been determined to be a cause of the collapse or even a contributor to the collapse; all is known is that one of the gussets (identified as U10) appears to have failed early in the collapse event.
The NTSB released this preliminary finding in order to alert owners of similar bridges to a risk factor. This is normal and conservative.
Quote: "The Safety Board has issued this recommendation, at this time, to ensure that the original design calculations for other bridges of this type have been made correctly, before any planned modification or operational changes are accomplished affecting such bridges and before any additional stresses are placed on them," said NTSB Chairman Mark V. Rosenker.
The NTSB report is found here: http://www.ntsb.gov/Pressrel/2008/080115.html as is a link to an FHWA interim report. If you want to skip the math just read the introduction and look at figures 5-6-7-8, then read the Interpretation of Results. That's depressing enough, I think.
Weights of materials:
Plain reinforced concrete, 150 lb./cf
Asphalt paving, 120-140 lb./cf
The deck supported by the bridge main truss was 1,064 feet long x 104' wide curb face to curb face. I have no idea of the dimensions of the curbs, center divider, etc., which are important.
A question is posed about liability. That would depend upon applicable law, which might only be the State of Minnesota. Generally ordinary negligence in professional services is a civil matter and can result in payment of damages, civil fines, and loss of professional license for the Engineer of Record, assuming no intervening Statute of Limitations. Gross negligence -- a willful and reckless disregard of safety -- can result in criminal penalty or punitive damages, depending upon applicable law. Given that the bridge was designed more than 40 years ago, the parties to the design are likely deceased.
RWM
spokyone wrote:Here is article about press conference.http://www.startribune.com/local/13796646.html
On the 2nd page of this link, they talk about center barrier, higher outside walls and 2" thicker paving. Can anyone guess how much extra weight that would be? They also mentiontioned 300 tons of equipment. But that would only be 8 loaded semi trucks.
Mr_Ash wrote: I think the real blame should fall on Gravity, ofcorse gravity cant be fired or sued so who ever designed the bridge should get introuble because if they didnt build it then it wouldnt have fallen so its gotta be there fault
I think the real blame should fall on Gravity, ofcorse gravity cant be fired or sued so who ever designed the bridge should get introuble because if they didnt build it then it wouldnt have fallen so its gotta be there fault
Gravity is probably an explanation that most Minnesotans would accept.
Modelcar wrote: ...Has maintenance been eliminated as an issue....?
...Has maintenance been eliminated as an issue....?
I think that is the official burning desire.
....And I believe they are indicating many other bridges scattered over the country have the same type gussets....If they are the culprit, I wonder if it is a straight forward matter of doubling the thickness of them by adding another layer on the original...If so they better get busy. But how can they be sure that was the only problem. Has maintenance been eliminated as an issue....?
Quentin
eastside wrote: Today the NTSB is scheduled to give a news conference to announce its results concerning the Interstate 35W bridge collapse in Minneapolis. StoryEarly in the investigation of the Minneapolis case, the safety board identified the plate, called a gusset plate, as a possible cause.
Today the NTSB is scheduled to give a news conference to announce its results concerning the Interstate 35W bridge collapse in Minneapolis.
Story
Early in the investigation of the Minneapolis case, the safety board identified the plate, called a gusset plate, as a possible cause.
Semper Vaporo wrote: If you will remember, some comedian said:"Remember: Interstate bridges are built by the lowest bidder."This alluding to the fact that they MIGHT not be safe.Now, one has collapsed, adding credence to the quip.Could the Authorities have awarded the bid to the lowest bidder this time, without public recrimination for doing so?Would it be prudent for the news media to begin some journalistic investigation as to why it was not awarded to the lowest bidder? What kind of headline would this be:"The old bridge fell down, why aren't we building a cheaper one!"
If you will remember, some comedian said:
"Remember: Interstate bridges are built by the lowest bidder."
This alluding to the fact that they MIGHT not be safe.
Now, one has collapsed, adding credence to the quip.
Could the Authorities have awarded the bid to the lowest bidder this time, without public recrimination for doing so?
Would it be prudent for the news media to begin some journalistic investigation as to why it was not awarded to the lowest bidder? What kind of headline would this be:
"The old bridge fell down, why aren't we building a cheaper one!"
I know the joke about getting something you want to be safe built by the lowest bidder. However, it seems to me that there should not be any connection between the bid price and the safety or quality of the bridge. There would definitely be a correlation between the quality, strength, and durability of the bridge as those characteristics are embodied in the design. If you design an inferior bridge, its performance will reflect that, but the performance should not be affected by the construction. If the contract is properly enforced, you get the same bridge, no matter whether the bid is high or low.
While the bidders on the I35W bridge apparently were given latitude on the design and style of the structure, it is ultimately up to the state to design a bridge that won't fall down. Ideally, they would then get multiple bids on that specific bridge, then consider price, delivery, and competence, and then select the best-suited bidder on that basis.
Selecting a high or low bid would have no effect on the strength, durability, or longevity of the bridge, because those characteristics would be established by the design and specifications. It would be up to the state to guarantee that the specifications have been met.
Many politicians blamed the collapse on a lack of funds for proper maintenance, but of course this is nonsense. A lack of funds cannot possibly be the reason for the collapse. This is axiomatic because the state has a responsibility to know the bridge's condition, and maintain it in safe condition. If they cannot perform either one of these tasks for any reason, they must close the bridge. Letting the bridge collapse for lack of funding would be criminal. Even MNDOT officials ran for the hills when they heard the reckless politicians blaming the collapse on Minnesotans not paying enough taxes.
Semper Vaporo
Pkgs.
Convicted One wrote: Bucyrus wrote:. But as a taxpayer, it would be nice to know the workings of MNDOT's so-called technical score that justified their awarding the contract to the contractor that bid $57 million higher than the next highest bidder. I share COMPLETELY your sentiment there. So the following should not be taken as an argument against your position, just stating facts.At one time I was heavily involved in contract work with the General Services Administration. Where EVERYTHING is supposed to be bid competitively. Anyone who is qualified to bid the various projects (supposedly) being welcome to do so. Often the contracting officers know before the original solicitation for offers is even made public, exactly who it is they intend to have do the work. The bidding process is (often) a mere formality to maintain a charade of protecting the public interest.In such instances there are unlimited opportunities to make the prefered contractor somehow appear to be 'uniquely qualified' in order to steer the work towrds the intended awardee'. It feels great when you know you are the contractor that they prefer to use anyway, and EXTREMELY frustrating in the instances where you figure out that they have a prefered source OTHER than you. Making you feel like you are beating your head against a wall even writing the bid.Sometimes the rationale in determining a 'prefered' awardee is semi legitimate, maybe a contractor has an extensive track record of completeing the type project at hand in an expedient and trouble free (to the contracting officer/government) manner.And sometimes the motives are LESS than honorable. Hard telling which is which in the example at hand.Funny that the government does not feel the need to be more forthright in explaning the conditions you mention. Usually when the government is at a loss for words, that runs up a red flag, fwiw
Bucyrus wrote:. But as a taxpayer, it would be nice to know the workings of MNDOT's so-called technical score that justified their awarding the contract to the contractor that bid $57 million higher than the next highest bidder.
I share COMPLETELY your sentiment there. So the following should not be taken as an argument against your position, just stating facts.
At one time I was heavily involved in contract work with the General Services Administration. Where EVERYTHING is supposed to be bid competitively. Anyone who is qualified to bid the various projects (supposedly) being welcome to do so. Often the contracting officers know before the original solicitation for offers is even made public, exactly who it is they intend to have do the work. The bidding process is (often) a mere formality to maintain a charade of protecting the public interest.
In such instances there are unlimited opportunities to make the prefered contractor somehow appear to be 'uniquely qualified' in order to steer the work towrds the intended awardee'.
It feels great when you know you are the contractor that they prefer to use anyway, and EXTREMELY frustrating in the instances where you figure out that they have a prefered source OTHER than you. Making you feel like you are beating your head against a wall even writing the bid.
Sometimes the rationale in determining a 'prefered' awardee is semi legitimate, maybe a contractor has an extensive track record of completeing the type project at hand in an expedient and trouble free (to the contracting officer/government) manner.
And sometimes the motives are LESS than honorable. Hard telling which is which in the example at hand.
Funny that the government does not feel the need to be more forthright in explaning the conditions you mention. Usually when the government is at a loss for words, that runs up a red flag, fwiw
That sure sounds like what this I35W bid looks like. There was a little hubub in the news right as the story revealed that the highest bidder won, but it quickly faded. I can understand the state not stepping forth to expose the process behind the technical scoring. It was challenged by the other two bidders, but apparently that has gone nowhere. They claimed that they did not know that the bridge project included public outreach. What is most disconcerting is the complete lack of curiousity on the part of the local press and TV news.
Convicted One wrote: I don't think that by saying the new bridge will be designed to last 100 years, they are trying to say the original was designed to last only 40. They are just pointing out that it did last ONLY 40.Surely the catastrophic failure of the original was never planned as transpired
I don't think that by saying the new bridge will be designed to last 100 years, they are trying to say the original was designed to last only 40. They are just pointing out that it did last ONLY 40.
Surely the catastrophic failure of the original was never planned as transpired
Convicted One,
I understand and agree that that is what they were saying, but there are implications in the overtone. The old bridge failed to meet its projected 50-year lifespan, which surely must have been proudly heralded when it was opened in 1967 just as the 100-year life is proclaimed about the new bridge today. I would hate to think the citizens of Minnesota could be led to believe that the reason the bridge collapsed was that they bought a cheap, low quality bridge the last time.
You may be right about the public outreach. Public outreach may be a bridge to the community. The more I read about this project, the more apparent it becomes that this is about so much more than just building a bridge. There are statements to be made about the tragedy and loss, and also about the fabric of the riverfront. But as a taxpayer, it would be nice to know the workings of MNDOT's so-called technical score that justified their awarding the contract to the contractor that bid $57 million higher than the next highest bidder.
Bucyrus wrote: It is interesting that the contractors apparently submitted their bids base on their own bridge designs. How can you compare bids when the item being bid is different with each bidder? In addition to the comparison of the actual price of each bid for the new bridge, the state used a technical score based upon criteria other than price. Here are the criteria used by the state to score the bids: Evaluation Criteria Utilized (Corresponded to Criteria Contained in the RFP)Quality (50 percent)Experience and authority of key individualsExtent of quality control/quality assuranceSafetyMeasures to evaluate performance in constructionAesthetics/Visual Quality (20 percent)Visual enhancements to the structureInvolvement of the public after lettingEnhancements (15 percent)Geometric and structural enhancementsPublic Outreach/Involvement (15 percent)Impacts to the publicApproach to communicationsNote the item called, Public Outreach weighted at 15%. I can understand how experience, quality control, and safety would be needed to build a bridge, but I do not understand why the state needs to pay the bridge builder for public outreach. Or in other words, how much public outreach does it take to screw in a light bulb?
It is interesting that the contractors apparently submitted their bids base on their own bridge designs. How can you compare bids when the item being bid is different with each bidder?
In addition to the comparison of the actual price of each bid for the new bridge, the state used a technical score based upon criteria other than price. Here are the criteria used by the state to score the bids:
Evaluation Criteria Utilized (Corresponded to Criteria Contained in the RFP)
Note the item called, Public Outreach weighted at 15%. I can understand how experience, quality control, and safety would be needed to build a bridge, but I do not understand why the state needs to pay the bridge builder for public outreach.
Or in other words, how much public outreach does it take to screw in a light bulb?
Just my opinion, but the 'outreach' comment looks like a cover for something along the lines of using minority owned contractors/sub-contractors... You know, making sure ALL the community feels involved? etc.
Bucyrus wrote: Quote from the above linked article:"Executives of the joint venture promised to erect a bridge with structural redundancies that would allow it to last 100 years, 60 more than its predecessor."That sounds like it is comparing a bridge built to last 100 years to one built to last 40 years. It is true that the old one lasted 40 years, but how long was it supposed to last according to its designers? Certainly it was not built as a bridge with an intended lifespan of only 40 years.
Quote from the above linked article:
"Executives of the joint venture promised to erect a bridge with structural redundancies that would allow it to last 100 years, 60 more than its predecessor."
That sounds like it is comparing a bridge built to last 100 years to one built to last 40 years. It is true that the old one lasted 40 years, but how long was it supposed to last according to its designers? Certainly it was not built as a bridge with an intended lifespan of only 40 years.
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