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.
The people of Minnesota want a practical new bridge at the lowest cost. The political class empowers themselves by spending our money, so naturally they want the most expensive bridge. To make an expensive bridge, you design it with a lot of bells and whistles. A good way to make bells and whistles expensive is to make them intangible and hard to measure. And then when the three bids come in, you award the highest bidder because their price includes the best meeting of your intangible bells and whistles.
But, apparently nobody told two of the lower bidders how this works, and they were actually trying to bid low so they could win. However, the winning formula was to bid high and then sell your bid for intangible bells and whistles to the state with an intangible sales pitch.
I live in a suburb of Minneapolis and I was watching it on the news about 30 minutes after it happened. I believe the bridge overpassed a BN line. My old man and I biked down a month after (to the day) and saw the devastation. There is still a portopotty standing on the slanted deck leaning on the barrier. The construction was minor resurfacing and supposedly had no influence on the collapse. Thank god there was only 4 lanes of traffic instead of the 8 that are usually open due to the construction. But man the piers on the north side had been partially lifted out of the water and it was a mess. The one hopper had been crushed like a pop can. Hope I cleared some of the confusion,
Robbie.
Most trucks do not gross out at 80000. I have not seen any mention of the deicer they use on the roads and bridges. This stuff will rot steel in no time. I'm talking about the liquid deicer not the rock salt. Some bridges in the Twin Cities have this sprayed any time the weather looks bad. Could dip down and rot the bridge.
Bucyrus wrote:I too have wondered about the structural effect of removing the concrete deck, which was underway at the time of the collapse. I would assume that the structural performance of the bridge would be rated and stipulated completely independently from the deck, but I wonder about that. If the concrete deck were cast in a way that it became one with the top chord of the truss structure, it would have added compression strength to the top chord, which would stiffen it against downward buckling of the truss. If this were the case, removing the deck would reduce strength. It would also remove loading, so it is hard to say how a reduction of strength and a reduction of load would tally up.
I too have wondered about the structural effect of removing the concrete deck, which was underway at the time of the collapse. I would assume that the structural performance of the bridge would be rated and stipulated completely independently from the deck, but I wonder about that. If the concrete deck were cast in a way that it became one with the top chord of the truss structure, it would have added compression strength to the top chord, which would stiffen it against downward buckling of the truss. If this were the case, removing the deck would reduce strength. It would also remove loading, so it is hard to say how a reduction of strength and a reduction of load would tally up.
The U of Minn study on the bridge specifically mentioned the strengthening effect of the concrete deck - probably should try looking it up and posting the URL. You're right in that the concrete would be under compression and adding to the strength - heaven help us if it was under tension...
I'm looking forward to reading what Henry Petroski has to say about the collapse - though it might be a couple of years before enough data comes out of the failure analysis to paint a coherent picture.
- Erik
erikem,
I think your assessment is fairly accurate. As you point out, the bridge design was relatively unique, pushing the envelop on the efficient use of materials, but thus lacking prudent reserve or redundancy. I speculate that, for this design to be viable, it must be perfectly inspected and maintained, which did not happen. So it appears that the design may have been structurally viable, but impractical, given the high probability of inadequate maintenance.
I can see this possible scenario: The deck removal would reduce the load, partially offsetting a weakening effect, but leaving a net weakening of some amount. That amount would be considered acceptable because it was not necessary to the bridge design capacity and its proper safety factor. However, the bridge had already been weakened by a lack of maintenance, and had lost its safety factor or worse. So the amount of weakening caused by removal of the deck made the difference between holding and failing. In other words the strength added by the deck was not an essential part of the design, but became essential as the design failed over time due to structural decay.
From what I've read, there are likely three factors that lead to the collapse. My speculation is based on the UofM report done a few years ago and reading Henry Petroski's commentaries on previous structural collapses.
First was lack of redundancy (a Design failing). There were many structural elements whose failure could lead to failure of the whole structure - sound engineering practice is to never design a structure where failure of a single element could lead to total structural failure (possible exception - a large margin of safety in the design of that element). Note that the bridge was completed about the same time as the Silver bridge collapsed in Ohio - which became a textbook example of why you design structures with redundancy - and note that the I-35 bridge design was never repeated.
Second was inadequate inspection. My understanding was that inspection did not go beyond a visual look-over, no ultrasound or other NDE was performed.
Third was a lack of appreciation of how much the concrete deck aided the structural rigidity of the bridge. The UofM report discussed developing a model of the bridge that agreed with measurements of controlled truck traffic - the model was only close when the stiffening action of the concrete deck was taken into account.
As for comments about the relative impact (pun somewhat intended) of car versus truck traffic - consider that 80,000 pounds of cars will be generating a lot less impact than one 80,000 pound truck - a couple of reasons: the impact of the cars will be relatively incoherent while the impact of the truck will be coherent; the springs on cars are typically a lot softer than springs on a truck.
Yes the collapse was just the opening act of this fiasco. Multiple investigations of the cause are underway. I would be surprised if they all reached the same conclusion, considering the complexity of the collapse event. My prediction is that the cause will be unsettled in the minds of a majority of observers indefinitely. The cause of the collapse poses a potential threat to some of the organizations that are investigating it. A sure refuge for them is to keep the investigation going a long, long time under the excuse of diligence.
And if there were not already enough controversy surrounding the probable government negligence that caused the collapse, a new heap has been added by the act of MNDOT awarding the rebuild contract to the highest bidder with the longest delivery time. There are many elements to this latest chapter of the bid that are just beginning to emerge. The news coverage of the winning bid has been very uneven and difficult to absorb. More will be learned as soon as all the contestants assume their positions for this battle.
....From all of that, it seems we'll be hearing more about that bridge situation. Might even become a campaign issue if it delays the start of rebuild....And....also saps money from other projects.
I thought emergency money was going to be made available for that rebuild....
Quentin
Thanks, Quentin- yeah, things are progressing quickly on the clean-up, but the construction of a new bridge promises to be a different matter altogether. There was alot of concern in the news that other state highway projects might have to be postponed in order to get this one done, because the federal money hasn't been officially approved yet (it's part of the latest bill that President Bush is threatening to veto). Not only that, but bids have already been accepted and a contractor chosen, but the one chosen was one of the higher bids, and I guess the lower-bid contractors are considering suing over the deal...
That lock I believe is the last lock going north on the river, and as such doesn't get alot of use- it only handles one or two barges at a time by the looks of it.
Brian (IA) http://blhanel.rrpicturearchives.net.
....Brian: Those are good photos. Appears lots of demolition and clean up work all ready accomplished. I wonder if it has been decided what type of bridge will replace the destroyed one. And if the authorities are ready to start right in to construct the "new" one. That is pretty harsh climate up there that we're going into now a few months hence.
In looking over the scene, I see the falling bridge was close to some of the river lock structures. If it had broken some of that, that certainly would have added to the woes....Don't have any idea what kind of river traffic moves thru those locks that far north.
I didn't really see or hear any speculation while I was up there, other than from my Dad (former MnDOT bridge inspector until he retired 20 years ago). He doesn't talk much about it, but when asked by one of my siblings, he said he felt it was heat stress.
Perhaps some of the members here who live in the area have heard or read more about it?
Made it up to the Twin Cities this weekend- while the ladies held a bridal shower for my daughter, I, my father, and my future son-in-law made a trek downtown to check out progress on the clean-up. Here's one of the shots I got- looks like those poor covered hoppers are finally about to be freed.
Pushing over a concrete support...
A couple of large sections left to remove yet...
jeaton wrote: Bucyrus wrote: Unless this collapse turns out to be an act of God, the cause will be negligence. The I35W bridge was rated structurally deficient; and it did fall down. However it is not true that all bridges rated structurally deficient have achieved that status through negligence and are in danger of collapse. Yet that was the blatantly dishonest theme of the "Aging Infrastructure" pieces last night on ABC, CBS, and NBC. That was complete and utter political propaganda put forth by those who want to expand the role of government and their willing accomplices in the media. They even broke down the price tag so we would know how much it would cost us individually. In order to drive home their lie that structurally deficient bridges are dangerous, they presented an old concrete bridge with holes through the deck and rebar hanging out of crumbling concrete. The bridge was closed, blocked, and obviously out of service. But all that mattered was that it was in the group of bridges rated structurally deficient, and it could therefore serve as an example to reinforce the bald face lie that all bridges rated structurally deficient are dangerous. I'm confused here. I know that a very few public highways, toll roads actually, and their bridges have been sold to private parties. The Chicago Sky Way and the Indiana Toll Road come to mind. However, hasn't it always been role of government to build and maintain highway bridges along with the rest of the public highway system? Where on earth did you get the idea that there is some sort of conspiracy on the part of the media and the government to "expand" their roll? How would that even be possible, given the fact that that is their roll."Negligence" means not paying attention. In fact, the Minnesota Highway Department and the Federal Highway Administration have been paying attention to the I-35W Bridge and every other bridge in Minnesota. The same is true in every other state. The reason that bridges are deficient is a shortage of funds. Unless you have another idea for getting the money to do the repairs or replacements, I am afraid it is going to come from taxes.I agree with you that not every bridge that is considered deficient is dangerous, but the simple truth is that we are not keeping up with repairs, rebuilds or replacement of either our bridges or highways-let alone building more to meet growing demand. One doesn't need to read government studies to get that. Just go for a drive. If we don't start to catch up, eventually deficient bridges will become dangerous. I guess if we don't want to spend the money we could just close them down. Yeaah! That's the ticket!
Bucyrus wrote: Unless this collapse turns out to be an act of God, the cause will be negligence. The I35W bridge was rated structurally deficient; and it did fall down. However it is not true that all bridges rated structurally deficient have achieved that status through negligence and are in danger of collapse. Yet that was the blatantly dishonest theme of the "Aging Infrastructure" pieces last night on ABC, CBS, and NBC. That was complete and utter political propaganda put forth by those who want to expand the role of government and their willing accomplices in the media. They even broke down the price tag so we would know how much it would cost us individually. In order to drive home their lie that structurally deficient bridges are dangerous, they presented an old concrete bridge with holes through the deck and rebar hanging out of crumbling concrete. The bridge was closed, blocked, and obviously out of service. But all that mattered was that it was in the group of bridges rated structurally deficient, and it could therefore serve as an example to reinforce the bald face lie that all bridges rated structurally deficient are dangerous.
Unless this collapse turns out to be an act of God, the cause will be negligence. The I35W bridge was rated structurally deficient; and it did fall down. However it is not true that all bridges rated structurally deficient have achieved that status through negligence and are in danger of collapse. Yet that was the blatantly dishonest theme of the "Aging Infrastructure" pieces last night on ABC, CBS, and NBC. That was complete and utter political propaganda put forth by those who want to expand the role of government and their willing accomplices in the media. They even broke down the price tag so we would know how much it would cost us individually.
In order to drive home their lie that structurally deficient bridges are dangerous, they presented an old concrete bridge with holes through the deck and rebar hanging out of crumbling concrete. The bridge was closed, blocked, and obviously out of service. But all that mattered was that it was in the group of bridges rated structurally deficient, and it could therefore serve as an example to reinforce the bald face lie that all bridges rated structurally deficient are dangerous.
I'm confused here. I know that a very few public highways, toll roads actually, and their bridges have been sold to private parties. The Chicago Sky Way and the Indiana Toll Road come to mind. However, hasn't it always been role of government to build and maintain highway bridges along with the rest of the public highway system? Where on earth did you get the idea that there is some sort of conspiracy on the part of the media and the government to "expand" their roll? How would that even be possible, given the fact that that is their roll.
"Negligence" means not paying attention. In fact, the Minnesota Highway Department and the Federal Highway Administration have been paying attention to the I-35W Bridge and every other bridge in Minnesota. The same is true in every other state. The reason that bridges are deficient is a shortage of funds. Unless you have another idea for getting the money to do the repairs or replacements, I am afraid it is going to come from taxes.
I agree with you that not every bridge that is considered deficient is dangerous, but the simple truth is that we are not keeping up with repairs, rebuilds or replacement of either our bridges or highways-let alone building more to meet growing demand. One doesn't need to read government studies to get that. Just go for a drive. If we don't start to catch up, eventually deficient bridges will become dangerous. I guess if we don't want to spend the money we could just close them down. Yeaah! That's the ticket!
You are correct in that the government owns the bridges and must collect taxes to pay for them. I am not opposed to that. The government does have a roll as you say. However, I disagree that the government has no ability or motive to expand its roll beyond what it legitimately needs to be. In fact I believe it is highly motivated to expand, and if there were no resistance by the electorate, the public sector would simply expand until there was no more private sector. It is not a conspiracy. It is not a secret plan that was hatched out in the dead of the night in a secret room. It just naturally flows through the veins of the public sector.
I agree that there is a shortage of funds for bridges and roads, but what government function is not short of funds? In my opinion, government is always short of funds because of its inherent motivation to expand its power, which it does by collecting taxes and spending money. The primary objective is to spend money and come up with reasons to spend more. So they over-spend. And unlike the private sector, government spends without any financial risk, and without much accountability. And when they collect taxes that are justified by a targeted application such as roads and bridges, they spend the money on a lot of unrelated things. Then they come back to the taxpayers and tell them they are not paying enough to cover the target application. I think it is a serious mistake to believe that government simply spends money as legitimately needed, like a responsible head of household seeking a return of value for the money spent.
But back to the bridges. It is true that bridges will fall down if not maintained, and that maintenance costs money. It is also true that many bridges are rated structurally deficient due to a shortage of funds. However it is not true that bridges fall down because of a lack of funds. That would be impossible because we have a federal bridge inspection program that monitors the condition of all bridges in great enough detail to know how close they are to the point where they would fall down, and prescribes the most cost effective maintenance necessary to get the most life out of them. If there are not enough funds to perform the maintenance, then the bridge needs to be closed. If there are not enough funds to inspect the bridge, then the bridge needs to be closed. These are not just my suggestions. They are the rules of the game.
The job of the inspectors is to go over the bridge with a fine-tooth comb to the extent that they know exactly how strong the structure is. There is no guesswork. A component of this inspection is to monitor the traffic load and keep it within the safe limit. So if a bridge falls down because of corrosion, broken members, stress cracks, missing bolts, etc., it has to be due to negligence of this inspection routine. There is no option to compromise that inspection routine because of a lack of funds. So a lack of funds cannot possibly be the cause of the I35W bridge collapse even though many Minnesota politicians and all Minnesota media are saying it is so.
On the note of construction occurring along I-35W, an initial thought when this happened was whether the construction along the highway actually saved lives. I was in the Twin Cities about a month back when they were doing construction on segments north of the bridge. As a result, we generally followed the Cedar Ave detour. I wonder if people were actually saved because they were on Cedar Ave instead of I-35W. This assumes the decking work on the bridge was not involved in the collapse. Hopefully so.
And, again, still keeping the victims in my thoughts this evening.
WIAR wrote: I was surprised to hear the speculation about the Minnesota Commercial train moving slowly underneath possibly having something to do with the collapse. I hardly think so - I'm no structural engineer but I have been down in that area before and I'd never believe the vibrations from a train moving at 8 MPH in that area could affect the highway bridge.
There was no train moving under the bridge. The tracks under the bridge is a dead end - a very small single ended storage yard, where the Minnesota Commercial keeps a few old cars.
Hadn't been an engine there for days before the accident, according to the Trains Magazine News Wire.
Whatever it was that made the bridge fall, it was not a moving train passing under the bridge at the time of the collapse.
Stein
"We have met the enemy and he is us." Pogo Possum "We have met the anemone... and he is Russ." Bucky Katt "Prediction is very difficult, especially if it's about the future." Niels Bohr, Nobel laureate in physics
Here are some photos. Miraculous that so many people came out of this alive. Thoughts and prayers to the families, friends, and others affected.
The media?
We got the bubble-headed-bleach-blonde who Comes on at five She can tell you bout the plane crash with a gleam In her eye Its interesting when people die- Give us dirty laundry
-Eagles-
http://www.conphoto.net/collapse.html
Bridges get the "structurally difficient" tag for all sorts of reasons, not safety reasons. If a bridge looks like it is going to fall, they close it. A 2 lane bridge with 3 lanes on either end is "structurally difficient" because it does not match up to the roads (the Bay Bridge in Maryland is a good example). A bridge designed to carry 150,000 cars a day is difficient when it carries 160,000. The news channels like to make it sound like they are all going to fall down tomorrow.
I just hope while people are cringing driving over the bridges and overpasses tonight that they hang up their phone and pay attention so they don't hit me or someone else.
FJ and G wrote:I heard on CNN about an hour ago that an average of one bridge collapses each week in the US. I wasn't aware of this. I thought these structures are made to last forever. How come the Romans could make stuff last and we can't?
Because if we built things the way the Romans did, with today's costs, the bridges would be so expensive that there would be very few built. Have you priced stone or stonemasons lately?
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