By now most of you have seen the news. I thought I would try to put it in context.
Interstate 35 runs from Laredo, Texas to Duluth, Minnesota. Along the way, it goes through San Antonio, Dallas/Fort Worth, Oklahoma City, Wichita, Kansas City, Des Moines, and the last major metro area it goes through before ending in Duluth is the Twin Cities of Minneapolis/St. Paul, Minnesota.
In two places, Dallas/Fort Worth, and Minneapolis/St. Paul, the road splits, with one half going through each city. In both places, the designers made a decision- rather than call it I35 in one city and I235 (or I435, I635, or I835 which would have been the standard designation), they would call the eastern split I35E and the western split I35W. This decision was probably political, in both cases to avoid marking one city as the "main" city and the other as the "secondary" city. Both halves go basically north-south. Here, I35W goes through downtown Minneapolis and I35E through downtown St Paul. In Texas, I35W goes through Ft. Worth and I35E through Dallas.
At 6:05 PM Central Time today, a section of I35W over 1/4 mile (400 meters) long collapsed and fell about 65 feet into the Mississippi river. Witnesses said the center main section collapsed firat, then the end spans. The rush hour was mostly over, but traffic would still have been heavy. This section of highway served downtown Minneapolis, and was a total of eight travel lanes (four each way). About 150,000 vehicles used this bridge each day. This is approximately equal to half the population of Minneapolis. It runs close to (I think within sight of) the Metrodome, where the Minnesota Twins and Minnesota Vikings play. The main downtown area is to the west of the bridge.
The bridge was about 40 years old. The main span was a steel archway under the bridge. It had been inspected in 2004 and 2006, and no defects were found. A stress test performed in 2001 showed some signs of stress but no cracks.
The deck of the bridge was under construction. The roadway was down to two lanes in sections, with construction equipment and crews on the bridge. There has been one unconfirmed report that a construction foreman ordered his crew off the bridge just before the collapse. This may just be a rumor and may not be true. Because it was 6:05 PM, he may have just let the shift go home for the day and it was misinterpreted as something else.
Reports are that about 50 vehicles were on the bridge when it collapsed; as of 10:00 PM Central Time local stations were reporting 6 confirmed fatalities and 38 injuries, including 6 critical. One construction worker is unaccounted for.
A school bus full of children were just entering the bridge as it collapsed. I have heard that ten chidren were brought to local hospitals, but I don't know if they were on the bus or in other vehicles. The school bus did not go into the river. PJay tells me now that the reports are that all of the children on the bus are OK.
The collapsed bridge landed on at least one surface road, West River Parkway, which runs parallel to the Mississippi on the western bank. Two other roads, Bluff Street on the western bank and SE Second Street on the eastern bank may also have been affected.
The bridge also landed on a couple freight cars of a freight train. No hazardous materials were on the train. There is a freight yard under part of the bridge; I don't know if operations there will be drastically affected; they certanly will be partly affected.
There is a local road that crosses the river very near that point, the Cedar Avenue bridge. I have not heard officially, but I don't believe the collapse has damaged that bridge. As of 9:00 PM Central Time, that bridge was still closed.
I have crossed the 35W bridge dozens, if not a hundred times or more; PJay must have crossed it 300 times as part of her commute when she worked a contract in that area. Our Son-in-law has only crossed it a handful of times, but he just started his duty at Fort Snelling last week; he would have crossed it at least at least 50 and parhaps 100 times before they closed on their house in St. Paul. I spoke this evening with people who crossed it less than 20 minutes before the collapse.
The entire support structure was under the bridge. If you didn't look to the sides, you would not realize you were crossing the Mississippi. For those of you familiar with the Big Muddy, the mile-wide Mississippi is only about 300-400 feet (95-125 meters) wide at that point.
One good thing to come out of the monumental 9/11 disaster is that plans are set up and practiced in order to deal with catastrophic events like this. The number of injuries and fatalities and how they were handled by emergency workers was called "almost routine" by hospital staff.
This will become a monumental traffic nightmare. All of the traffic that used that bridge will have to find another route. The Cedar avenue bridge is nearby ad runs parallel, but is already at capacity. In addition, it is only a four-lane, local bridge; it can't replace the 8 lanes lost. From the north, some traffic will be able to switch to I-94, which runs parallel to I35W on the other side of the river a few miles to the west. Those travelling through the city have a few more options, but at least one of those, I35E through St. Paul, is already jammed because of major construction at it's junction with I-694.
I am not as familiar with the problems this will cause on the south side of the city, but they will be just as bad.
I commute from the north, and this is a north-south highway. I didn't normally take I-35W, but that is just beacuse it was a little easier for me to use I-94, which also runs north-south on the north side of the city. When I ride with PJay (3-1/2 to 4 days a week), we drive in on I-94; on the other days, I use a park-and-ride and take the bus (which also uses I-94). The busses are allowed to use the shoulder, which is a significant time savings in heavy traffic. I am expecting the bus to be standing room only tomorrow, and possibly leave people at the curb. A number of bus routes, including some that used to run every few minutes, used to use that bridge.
The city's only rapid transit line rins basically from downtown Minneapolis to the Moall Of America and does not cross the Mississippi, where the bottleneck is.
Grab your wallets, taxpayers. Because this is an Interstate highway, most of the hundreds of millions of dollars it will cost to replace it will come out of your pockets.
Here is a link to a Google Maps view (http://maps.google.com/?ie=UTF8&t=h&om=1&ll=44.9789,-93.244894&spn=0.005024,0.010772&z=16) of the section that collapsed; the one that is no more is the largest one with the 35W mark on it.
Local news links:
http://wcco.com/ (includes images and video of collapsed bridge)
Austin
What in the name of heaven could cause such a thing to happen? Is anyone suggesting a terrorist act?
-Speak
Quote from: SpeakEasyWhat in the name of heaven could cause such a thing to happen? Is anyone suggesting a terrorist act?
-Speak
No evidence of terrorism. Eyewitnesses said no explosions were heard nor did anyone see anything else out of the ordinary.
The bridge was desinged in the late 1950's or early 1960s. It was completed in 1964 and was meant to last 80 years, but was designed for projected 1970's traffic levels. It has been handling three or four times the designed traffic levels, and truck weight limits have risen significantly since then.
I have heard since last night's post that a 2006 Federal inspection showed evidence of cracking, and had recommended replacement of the bridge by 2010 (or maybe 2012), but it was currently being resurfaced so I don't think anyone was thinking of actually replacing it by then.
My guess would be a combination of factors was involved. We know more about metal fateague today. We avoid building long span bridges like this (nearby bridges have many sets of pylons instead of a single long span). And the bridge was under-engineered for from today's standards. In other words, it had too much traffic, was overloaded, was too old, too weak, and just gave up.
Wikipedia's list of
bridge disasters lists nine major bridge colapses in the U.S. (The list is incomplete, but gives us some ideas.) Of those, four bridges were struck by something, three had structural failures, one was washed out, and one was improperly engineered.
There is no evidence anything in the river or on the roads under the bridge struck the bridge.
It is doubtful that the construction had an impact; the road surface has very little bearing on the structural integrity of any bridge. Even the vibration of jackhammers for a few months of construction is nothing compared to the constant pounding of big trucks day after day after day.
The most recent interstate bridge collapse (that wasn't struck by something) I am aware of was the I-90 bridge over the Schohare Creek in New York (don't let the word "creek" fool you; it was a major bridge) in 1988. Because of rain and dark of night, a number of people drove off that bridge to their deaths after the collapse. That bridge collapsed primarily because soil under footings was washed away, but also because of poor and inadequate inspections and maintenance. After this disaster, all of the interstate bridges in New York State were reviewed, and many were replaced.
In 1983, an interstate bridge in Connecticut collapsed. The reports were that the pidgeons who roosted there in large numbers had abandoned the bridge a few weeks before the collapse. In any case, that failure resulted in an inspection of all bridges in Connecticut with many being upgraded or replaced. I remember remarking to PJay at the time that we could still be confident in interstate bridges because it was such a rare event, and because this would force everyone to make sure their bridges were safe. But five years later, the Schohare Creek bridge I mentioned above went down; that was a bridge we used several times a year.
It's been 20 years since the Schohare Creek bridge, but this bridge is one we use often; our son-in-law crossed it twice yeasterday; PJay can almost see it from her building.
I may be wrong, but I believe the NTSB (National Transportation Safety Board) will head up the investigation on this. They are the people who investigate airline crashes. They are very thorough, and they will find the cause of this collapse.
My first contract in Minnesota was for MN/DOT, the Minnesota Department of Transportation. I was introduced to one of the directors, and he asked how thought transportation compared to Massachusetts. I said "You don't know how good you have it." There are roads everywhere. Then I said "You don't know how bad it is." Becasue there are few other options.
I'm glad I'm not at MN/DOT today; their lives are changed forever.
Austin
Austin, thanks for the report. You went to a lot of work putting it together.
Russ
Video of the actual collapse from a security camera:
http://www.wcco.com/video/?id=29690@wcco.dayport.com
The video immediately following shows before and after shots of significant rust on the bridge struts. If this ends up being the primary cause of the collapse, heads are ging to roll over this one.
The Minneapolis Star Tribute (http://www.startribune.com/) (where PJay is working as a contractor) is now reporting 4 dead and 79 injured with 20 still missing. At midnight last night, they were reporting 9 dead...
Austin
Austin,
You and your family were the first ones I thought of when I heard the news last night. Thanks for the insight and information first hand. That particular bridge was 40 years old we (as you know) have bridges here that are older than that in Massachusetts. I think this will change things all around for bridge inspections, to bad it had to come to that.
Keep updating us first hand, I'm interested.
Quote from: HargusAustin,
You and your family were the first ones I thought of when I heard the news last night. Thanks for the insight and information first hand. That particular bridge was 40 years old we (as you know) have bridges here that are older than that in Massachusetts. I think this will change things all around for bridge inspections, to bad it had to come to that.
Keep updating us first hand, I'm interested.
There are several others here on PUT from the Twin Cities area. As far as I know, PJay and I are the only ones who commute into Minneapolis from the north. Kelly (
click here for profile) and her children live north of St Paul (about 15-20 miles east of us). I don't think she commutes into Minneapolis, but I could be mistaken.
The rest escape me now. Most Twin Cities pop-uppers seem to hang around on PUX.
Austin
Here is an alert for everyone...the U.S. Department of Transportation rated this bridge as "structurally deficient" starting two years ago. I don't know how the DOT defines "structurally deficient," but it probably means politically that "this is something we will do when we get to it." The bridge was being considered for work about 5 years in the future.
Here is the important thing...this DOT database lists hundreds of bridges as "structurally deficient" around the country. It may be time for all of us to find out what our state, county, and local governments are doing to correct "structurally deficient" bridges. They will tell you everything is fine, that you are not in the same boat as Minnesota. It's a lie. That's what they would have told us here on Tuesday. It's what they would be telling us today if the collapse had happened in any other state.
Austin
I've been seeing a lot of pictures of the underside of that bridge, prior to the disaster. The rust in the pictures in inexcusable (in my mind).
I attended General Motors Institute. My degree is in Dealership Management but I also took several courses in engineering. Anyone that takes engineering classes starts out with the dynamics of "Bridge" construction and physics.
That type of bridge depends totally on the steel fasteners that hold it together. As we well know, Minnesota salts it's roads in the winter and we also know what a toll all that salt takes on steel members and particularly steel fasteners that really can't be inspected without removal.
Seeing those pictures, I was appalled at the amount of rust that was evident. It just appears that little has been done for many years to manage the rust on that bridge.
The other thing that seems a bit suspicious is the fact that both ends of the bridge failed simultaneously. That just seems extremely odd and lends itself to the suspicion of tampering.
I guess time will tell but I don't have a lot of confidence in the truth ever coming out in this disaster.
Quote from: waveryI've been seeing a lot of pictures of the underside of that bridge, prior to the disaster. The rust in the pictures in inexcusable (in my mind).
Rusty bridges are standard fare all over the north, as are spalling concrete bridge abutments. Of course, that doesn't make it excusable. That would certanly fit my definition of "structurally deficient."
QuoteI attended General Motors Institute. My degree is in Dealership Management but I also took several courses in engineering. Anyone that takes engineering classes starts out with the dynamics of "Bridge" construction and physics. That type of bridge depends totally on the steel fasteners that hold it together.
I helped my daughter build a bridge out of toothpicks, so I understand this. The toothpicks are not usually what fails, it's the glued joints.
QuoteAs we well know, Minnesota salts it's roads in the winter and we also know what a toll all that salt takes on steel members and particularly steel fasteners that really can't be inspected without removal.
Check out the Wikipedia article...they used quite a coctail of chemicals to try to prevent "black ice" on that bridge, and dispensed them automatically via an embedded system.
http://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridgemagnesium chloride
liquid potassium acetate
other unnamed chemicals (corn by-products? Huh?)
QuoteSeeing those pictures, I was appalled at the amount of rust that was evident. It just appears that little has been done for many years to manage the rust on that bridge.
Who knows. I contracted for MN/DOT (in the group that was responsible for required archaeologial and historic surveys on new construction). Everyone I met was professional, highly compentent, and overworked. Knowing what was being put on the bridge, it's possible the joints were being painted every fall, and the paint stripped every winter by the road chemicals.
While the amount of rust does seem excessive, I have seen other bridges that bad. If I had a chance, I know I could find coastal bridges in California that are as bad or worse. Whether I could find a span that long or even an interstate highway bridge is subject to debate.
QuoteThe other thing that seems a bit suspicious is the fact that both ends of the bridge failed simultaneously. That just seems extremely odd and lends itself to the suspicion of tampering.
That fooled me at first too. But a careful examination of the video shows the near end hitting the water while the far end was still at least 20 feet in the air. Keep the perspective in mind - you are looking lengthwise along 1,000 feet of bridge that fell 64 feet. The falling vehicles are moving forward at 50 or more MPH. But they do not appear to move at all because of the perspective. It is more than possible that the bridge, as it started falling, moved towards or away from the camera (much more likely towards, IMHO), by 10 or 15 feet without being visible in the video. A movement of two feet could be enough to cause the other end to fail.
QuoteI guess time will tell but I don't have a lot of confidence in the truth ever coming out in this disaster.
I do. I have seen the way the NTSB works. Right now, they are collecting video from at least a half dozen other security cameras, some of which we may never see. They will be examined frame by frame, and when I say examined, I don't mean watched. Known points will be measured and timed to determine speed and direction. Eyewitnesses will be interviewed. They will review every bolt, every rivet, and every document. They will interview every contractor and every sub-contractor who ever did work on the bridge. They don't give a rip about Minnesota politics. They don't work for those whose heads will roll. We will know. The question is will we do anything about it. I am sure we will here in Minnesota, as they did in New York after the 1988 bridge collapse.
What will be done about "structurally deficient" bridges in other states is what everyone should be concerned about. They exist in your state.
Austin
That collapse is horrific. I hope all from MN and their families are ok.
We have 3 bridges here in MI of that same design, the DOT is re - inspecting
each of them.
Quote from: AustinBostonThere are several others here on PUT from the Twin Cities area. As far as I know, PJay and I are the only ones who commute into Minneapolis from the north. Kelly (click here for profile) and her children live north of St Paul (about 15-20 miles east of us). I don't think she commutes into Minneapolis, but I could be mistaken.
The rest escape me now. Most Twin Cities pop-uppers seem to hang around on PUX.
Austin
I don't commute into Minneapolis, AB. I take an exit right before 35W off Hwy 36. I have driven that stretch of 35W many many many times, though.
The only other Twin Citian that I can think at PUT right now is PLJ and I think they are in the southern part of the metro area.
I think that it is rather remarkable how many Gvm't Officials have made the statement, "Just because a bridge is rated, 'structurally deficient' doesn't mean that it isn't safe"..............................OMG people......that bridge was NOT safe....IT COLLAPSED. If you listen to these people, not one single person has said, "That bridge was not safe......"..........I say, "Get a grip". A lot of people are dead and injured.......to hell with the money. It is evident that one of four things are true. 1. Either someone screwed up big time on an inspection or 2. The rating system has some "acceptable risk" :eyecrazy: factor built in that just cost lives or 3. the earth moved or 4. there was foul play . Bridges just don't have catastrophic failures for no reason.
As far as trusting the NTSB is concerned........I don't trust ANY GMT agency that has the power to not fully disclose all findings to the public.
If they are going to grade these bridges (which they do) they should be required to post that grade ON the bridge so that people can make a decision whether to use it or not. In California, we grade all of our restaurants and the grade is posted. I will NOT eat in any restaurant that is not graded "A" and you better believe that I would not drive on a bridge that is graded "Structurally deficient".
BTW,
Both sides of that bridge started falling at exactly the same time. The fall was nearly horizontal at first. That is very puzzling. The other thing is......the cars were not going at ah speed. They were traveling at 0-10MPH according to eye witness accounts, including drivers that were on the bridge.
My mother is burried about 2 miles from that bridge (Hillside Cemetery) and I have been across it many times also.
We spent Wednesday night near Philadelphia (camped in a driveway) at the home of a couple who had lived in Minneapolis for many years and crossed that bridge thousands of times. They have a son and daughter still living there, both of whom work at the Metrodome (hope that's the name of the stadium there). A Twins game was about to begin, they were both at the stadium and had both driven over the bridge moments before the collapse. We were informed of the collapse moments after it happened by their son calling. I have never seen two people more distraught and relieved at the same time.
QuoteWikipedia's list of bridge disasters lists nine major bridge colapses in the U.S. (The list is incomplete, but gives us some ideas.) Of those, four bridges were struck by something, three had structural failures, one was washed out, and one was improperly engineered.
This bridge crossed the river in the town that I work. Silver Bridge (http://en.wikipedia.org/wiki/Silver_Bridge)
QuoteIf they are going to grade these bridges (which they do) they should be required to post that grade ON the bridge so that people can make a decision whether to use it or not. In California, we grade all of our restaurants and the grade is posted. I will NOT eat in any restaurant that is not graded "A" and you better believe that I would not drive on a bridge that is graded "Structurally deficient".
I posted earlier that the DOT (this is national) rated hundreds of bridges as "structurally deficient." That was based on somethign someone told me. When I found documentation, it's more like 70,000 bridges rated "structurally deficient". There is a good chance you drive on one or more every day.
On our commute home yesterday, I pointed out visible rust on every bridge we drove under. You know what? a little paint goes a long way...
Quote from: waveryBoth sides of that bridge started falling at exactly the same time.
At less than two frames per second,
you can not know that from the video. (Watch the woman walking around after the collapse - she takes a step between frames.) A co-worker and I have repeatedly gone over that video frame by frame, and there is simply no way to tell. The best copy may have more resolution, but the versions on the web are not clear enough.
At 1/2 second, the bridge could easily fall 8 feet between the frame before and the frame after it started to fall, which is more than enough to pull the other end off it's mounting.
If the collapse started at the other end, it could have been falling for at least two frames before it would be clearly visible. At the distance of the other end of the bridge (1,000 feet), one image pixel is about 8 feet, or 1/2 second of falling.
It also assumes that the bridge wasn't shifted lengthwise before it started to fall, which is a distinct possibility. Construction workers on the bridge reported significant vibration before the collapse. That went on long enough for a foreman to order everyone off the bridge. Based on the reports, I don't think it was long enough for workers to begin complying.
And then there is the design of the bridge. It was held up at the very ends only. The bridge relied on both ends having full support at all times. If one end started going, the other was also going down - NOW. I have been told (but I have not seen images or read about this) that the main span's steel structure was on rollers in order to deal with expansion & contraction. I have seen other bridges built this way, so I know it is done. If there was lengthwise movement because of the initial failure, the other end was going down NOW.
In the end, I believe the facts will show that this bridge fell because of a combination of bad/underdesign, overweight traffic, improper maintenance, inadequate inspection, improper materials, excess vibration, government delays, and other forms of incompetence.
Austin
This video clearly shows the rust that Wayne is talking about...and clearly shows it is a point of failure (not the same as cause, but it sure looks bad). It shows before and after images of a specific joint that has clearly failed.
http://www.wcco.com/video/?id=29695@wcco.dayport.com
The other thing these images show is that significant parts of the structure are box beams. Box beams are fairly strong, but very difficult to properly inspect, and nearly impossible to properly maintain. How do you paint the inside of what is essentailly a 30 foot long tube with both ends partly blocked? How do you remove loose rust, and prevent water and salt entry?
This collapse started before it was even built.
Austin
Quote from: AustinBostonBut in the end, I believe the facts will show (whether you want to accept them or not) that this bridge fell because of a combination of underdesign, overweight traffic, improper maintenance, inadequate inspection, improper materials, excess vibration, government delays, and other forms of incompetence.
I think that's probably right. I heard this morning that the bridge may have been rated to carry a much heavier load than it should have been, when it was built.
I find it interesting that we have several city streets that have signs that say "No Trucks".....over a certain weight. There are bridges with similar signs. I think that they should not allow trucks over a certain weight to cross bridges that are rated "structurally deficient". It just seems like a no brainer but it's all about politics and $$.
In California, we have arranged a "Shake test" :yikes: every year or so for our bridges :p .
Quote from: waveryI think that's probably right. I heard this morning that the bridge may have been rated to carry a much heavier load than it should have been, when it was built.
I find it interesting that we have several city streets that have signs that say "No Trucks".....over a certain weight. There are bridges with similar signs. I think that they should not allow trucks over a certain weight to cross bridges that are rated "structurally deficient". It just seems like a no brainer but it's all about politics and $$.
In California, we have arranged a "Shake test" :yikes: every year or so for our bridges :p .
Did you arrange the shake test, or did someone of a somewhat higher authority? :p
We do "stress tests" of our bridges. It consists of watching and/or measuring stress at key points while the stress (weight) is applied and removed. The stress...three fully loaded tractor trailers are driven over an empty bridge at the same time. Hello???? This is an eight lane bridge...how about driving eight tractor trailers (with tandems) at the same time?
I write software that undergoes stress testing. Stress testing for us (in part) consists of appplying between two and ten times the expected load...and lives don't depend on my software.
Austin
There are many factors involved including how much total weight was on the bridge and how much of that was stationary or near stationary. On the Del Mem Bridge that I drive ever day, they tend to monitor for excessive truck traffic on days where there are backups. If needed they stop traffic coming onto the bridge to reduce the load.
Understand also, as someone that sells steel, even prime steel can have "bad spots" which sometimes are called inclusions which if in the right spot can undermine the best engineering. Furthermore, some forms are steel, namely A871 weathering steel are designed to rust initially. Rust alone is not a sign of bad material.
Utimately, it was a great loss of life and hopefully they will learn from and correct future mistakes out of this.
Quote from: dademtUnderstand also, as someone that sells steel, even prime steel can have "bad spots" which sometimes are called inclusions which if in the right spot can undermine the best engineering.
I believe the kinds of defects you mention are unavoidable. That is the reason redundancy is so important in large structures. The concept is that there might be (or might develop) a defect in a critical part. If the odds of a defect are 1 in 10,000, that's the best you can do. If the structure uses 1,000 of those parts, then there is a 1 in 10 chance of the structure containing a defective one. But in a redundant structure, that changes dramatically. Now you need two defective parts in the same place. The odds of two together being defective is 1 in (10,000 x 10,000), or 1 in 100,000,000. Because there are twice as many parts, the odds of having a defective one go up, so that it would now be 2 in 10 (or 1 in 5), but the odds of two defective parts together would be very small, about 1 in 100,000. Now you have a bridge that is (in theory) ten times safer for twice the price. It also simplifies maintenance, because any one part can be removed and replaced without compromising the whole structure.
Of course, there is a limit to this. Improper maintenance can adversely affect all of the parts, putting the whole redundancy scheme in jeopardy. Two parts can rust through as easily as one.
This bridge had a number of potential single points of failure.
aw738 mentioned the Silver Bridge over the Ohio river. This bridge collapsed in 1967 in a large part because of a lack of redundancy. Even though the "eyebars" were significantly over-engineered, if one failed, the nearby "eyebars" would not be able to take the added weight and would fail. A defect of one tenth of an inch in one eyebar brought the whole thing down at rush hour, killing 46 people.
Another example where redundancy worked (for a time) was in the World Trade Center. If redundancy had not been designed and built in to the buildings, they both would have come down immediately, instead of standing for long enough for most occupants to be able to evacuate.
QuoteFurthermore, some forms are steel, namely A871 weathering steel are designed to rust initially. Rust alone is not a sign of bad material.
Absolutely not! But, in most cases, excess rust is a sign of inadequate maintenance, and rust can become a cause of failure if allowed to continue too long.
I can remember seeing some new oil storage tanks in Boston. The tank pieces were put in place and carefully welded. Then the completed tanks sat there and rusted for some time - I think about 6 months, but it could have been much longer or shorter - in the Massachusetts salt air. Eventually a co-worker asked why, if the existing tanks were all painted in the company colors, weren't the new tanks being painted?
Apparently, the question had been asked many times, because the receptionist had a sheet for him that explained it. The way the tank sections were manufactured, they ended up with thin layers of steel on the surface that could easily peel off. If they were painted when new, the paint would just peel off in places. By allowing the tanks to rust, this microscopically thin layer would be removed (where it existed). In addition, the microscopic pits formed by the rusting formed a much better bonding surface for the new paint. The rust was a deliberate part of the design.
QuoteUtimately, it was a great loss of life and hopefully they will learn from and correct future mistakes out of this.
While I would not have considered this bridge to be a diamond (more like a piece of quartz), I think what one former member of the NTSB said about airline crashes is appropriate. He said "Diamonds reveal their hidden flaws when broken." What he meant was that we learn things from failures (even things that did not cause the failure) that can make other airliners safer. That really ought to apply to bridges as well.
One other thing - if they were starting from scratch today, I suspect that bridge (specifically the long span that crossed the river) would be built in 3-6 spans, not one. There was no operational need for a single span, and several other bridges in the area are set on multiple pylons (as many as 15). With shorter spans, even if one fails - hopefully not, but always a possibility - it can be replaced with a temporary structure in days or weeks. This thing is going to take years to replace.
Austin
Quote from: AustinBostonI believe the kinds of defects you mention are unavoidable. That is the reason redundancy is so important in large structures. The concept is that there might be (or might develop) a defect in a critical part. If the odds of a defect are 1 in 10,000, that's the best you can do. If the structure uses 1,000 of those parts, then there is a 1 in 10 chance of the structure containing a defective one. But in a redundant structure, that changes dramatically. Now you need two defective parts in the same place. The odds of two together being defective is 1 in (10,000 x 10,000), or 1 in 100,000,000. Because there are twice as many parts, the odds of having a defective one go up, so that it would now be 2 in 10 (or 1 in 5), but the odds of two defective parts together would be very small, about 1 in 100,000. Now you have a bridge that is (in theory) ten times safer for twice the price. It also simplifies maintenance, because any one part can be removed and replaced without compromising the whole structure.
Redundancy does not have to be the answer. Where $ is concerned, like oil pipe lines or aerospace, every single piece of metal that goes into these structures are x-rayed for cracks and material defects. It is an expensive procedure but it can't be any more expensive than building a bridge with 100% redundancy (which is what it would take).
My son-in-law owns a company that builds huge x-ray machines
http://www.willick.com/index.html . He built the x-ray machine for inspecting whole component parts for the latest space shuttle assembly. They can put an entire wing in this machine at once. There is no reason why they couldn't do the same with bridge construction materials (today, not in 1967).
The part that really ticks me off is that there is a company that has been trying to sell devices to the DOT and the States for about 2 years now. This device is placed in critical areas of any structure (like a bridge) and it measures small movements and can tell of a potential failure minutes before it takes place in 90% of cases. This devise is relatively inexpensive and I will bet that every bridge in the US will have them within a year or 2 (or immediately after the next tragedy).
Absolutely not! But, in most cases, excess rust is a sign of inadequate maintenance, and rust can become a cause of failure if allowed to continue too long.
Hey Austin, with all due respect, I am right about this one. Here is the information from the ASTM spec ( abbreviated version )
ACTIVE STANDARD: ASTM A871/A871M-03 Standard Specification for High-Strength Low-Alloy Structural Steel Plate With Atmospheric Corrosion Resistance
(http://www.astm.org/IMAGES/blicense.gif) (//%22javascript:onClick=OpenLicense('LICENSE_ASTM.htm');%22)Developed by Subcommittee: A01.02 (//%22http://www.astm.org/cgi-bin/SoftCart.exe/COMMIT/SUBCOMMIT/A0102.htm?L+mystore+nuoc7742+1186206362%22)
See Related Work (//%22http://www.astm.org/cgi-bin/SoftCart.exe/COMMIT/SUBCOMMIT/A0102.htm?L+mystore+nuoc7742+1186206362%22) by this Subcommittee
Book of Standards Volume: 01.04
1. Scope
1.1 This specification covers high-strength low-alloy steel plate intended for use in tubular structures and poles or in other suitable applications. Two grades, 60 and 65, may be provided as-rolled, normalized or quenched and tempered as required to meet the specified mechanical requirements.
1.2 The atmospheric corrosion resistance of this steel in most environments is substantially better than that of carbon structural steels with or without copper addition (see Note 1). When properly exposed to the atmosphere, this steel can be used bare (unpainted) for many applications.
Note 1
Quote from: waveryRedundancy does not have to be the answer. Where $ is concerned, like oil pipe lines or aerospace, every single piece of metal that goes into these structures are x-rayed for cracks and material defects. It is an expensive procedure but it can't be any more expensive than building a bridge with 100% redundancy (which is what it would take).
While it is less expensive, it is also less effective. One of the things that was drilled into us when I worked in Quality Assurance was that "100% inspection is not 100% effective" (100%
inspection is actually only 85% effective, and we proved it repeatedly). 200% inspection is actually
worse that 100% inspection. Testing is more effective than inspection because it takes the human element out of detection, but still is not 100% effective. I have to assume the x-ray system you suggest is somewhere in between testing and inspection.
I don't know if the pieces of the alaskan oil pipeline were all X-rayed, but I know some of it was, and it has had failures.
Obviously, not everything can be made 100% redundant. Making a plane with an entire second set of wings (either of which could fly the plane) would make the plane effectively worthless. But when you have thousands of identical devices, with each one being mission critical, redundancy is the only way to go.
QuoteMy son-in-law owns a company that builds huge x-ray machines http://www.willick.com/index.html . He built the x-ray machine for inspecting whole component parts for the latest space shuttle assembly. They can put an entire wing in this machine at once. There is no reason why they couldn't do the same with bridge construction materials (today, not in 1967).
Remember, 100% inspection is only 85% effective...
QuoteThe part that really ticks me off is that there is a company that has been trying to sell devices to the DOT and the States for about 2 years now. This device is placed in critical areas of any structure (like a bridge) and it measures small movements and can tell of a potential failure minutes before it takes place in 90% of cases. This devise is relatively inexpensive and I will bet that every bridge in the US will have them within a year or 2 (or immediately after the next tragedy).
While I've pointed out flaws with this (or any) inspection system, please don't think I don't think it's a bad idea. There is NO 100% effective solution (including redundancy). It becomes a matter of risk versus cost (or risk vs. risk). For example, we could drastically reduce the risk of rust-related failure by making bridges from aluminum. The cost of the bridge would skyrocket, and the risk of metal fateague would go up.
The real solution lies in a number of areas, including:
- Designs that are not prone to single points of failure (this could be accomplished through redundancy, but there are other ways.
- Avoiding designs where failure is so catastrophic. For example, this would have been less devastating if this collapse had been contained to just the main span. But after the main span fell, additional spans fell on either side, and on one end, additional spans after that, until all spans of the bridge had failed.
- Using designs that lend themselves to simple inspection and maintenance. This is another area assisted by redundancy. In a fully redundant system, you can replace any part while in service without a service disruption. But even more important is avoiding construction that ends up doing things like create hidden recesses that require exotic mechanisms to inspect or maintain.
- Using appropriate means to reduce or eliminate defects in materials and workmanship. Examples would include buying high quality materials (I believe in forcing the vendor to prove to me that it's good - via x-ray, via statistical testing, via vodoo - as long as he proves it is good) and using things like X-rays to inspect welds and rivets at the site.
- Building in a sliding weight scale, so that as a bridge ages, it's weight rating automatically goes down. I believe that no matter how careful we are in design, and no matter how careful we are in inspection, there are always going to be types of fateague that we don't anticipate or don't understand and therefore potential types of failures that are totally unexpected. If the bridge is designed for a useful life of 100 years, the weight rating should meet the anticipated traffic weight in 100 years. At that point, the bridge would need to be replaced or would have to have enforced weight restrictions. If traffic weight risies faster than anticipated (which was the case with the Silver Bridge), that point comes sooner (as it should). I think the same will be found with this bridge; I believe it was never expected to be an 8-lane bridge, but a 6-lane bridge with right-side shoulders. That is a 33% increase in traffic weight with no structural improvements to the bridge!
- Diligence, diligence, diligence when it comes to inspection and maintenance. This is where my mistrust of the government comes in. The bridge was being resurfaced (probably because of complaints). But comparatively, that resurfacing was simply cosmetic. People see potholes and complain, so that's where the money goes. But the real problem was only 25 feet lower, and may have cost no more to correct. Meanwhile, MN/DOT had a report (that they commisioned) that said certain joints (I'll bet we know which ones) should be reinforced with steel plate. Instead, they decided to "fix the cracks."
All of this, of course, cost $$$. In the end, I am one who feels rail systems are far more cost effective than road systems. Here in the Twin Cities, we have far fewer passenger rail systems than comparable metro areas in the U.S. (And the U.S. is way behind most other countries.) Of course, don't ask about rail bridge maintenance... :yikes:
Austin
Quote from: dademtHey Austin, with all due respect, I am right about this one.
With all due respect, where I went to school, if you said "Rust alone is not a sign of bad material." and I said "Absolutely not!" it would be an
agreement, not a
disagreement. If there was any ambiguity, the rest of the paragraph (and the next two)
should have made my intent
obvious. Did you read them?
Austin
Quote from: AustinBostonWith all due respect, where I went to school, if you said "Rust alone is not a sign of bad material." and I said "Absolutely not!" it would be an agreement, not a disagreement. If there was any ambiguity, the rest of the paragraph (and the next two) should have made my intent obvious. Did you read them?
Austin
My appologies. I do agree with you also, people should stop doing the work with the lest effective materials to pass the current test with the attitude that it can be someone elses problem tomorrow. You don't know how many times someone has called asking for a grade of material only to hear the price and comment that they need to get the engineer to figure out if something less expensive will do. If frustrates me royally. I wish you had supervised some of the engineers in western pa when I use to deal with them.
Quote from: dademtI do agree with you also, people should stop doing the work with the lest effective materials to pass the current test with the attitude that it can be someone elses problem tomorrow. You don't know how many times someone has called asking for a grade of material only to hear the price and comment that they need to get the engineer to figure out if something less expensive will do. If frustrates me royally. I wish you had supervised some of the engineers in western pa when I use to deal with them.
Thinking a third time, I could have been clearer in my first response.
This should have been one of my bullet points, and is at the core of the problem here:
The government does business in only one of three ways: 1) Lowest bidder; 2) Highest briber; 3) Overwhelming public pressure. Don't assume because #3 exists that #1 and #2 aren't still going on.
I don't object to using a lower grade of material
if you use enough more of it to make up the difference (in both rating and risk). But as I am sure you know, that seldom actually saves money. If I use two or three of grade "B" when I could have used one of grade "A", now everything supporting that has to be upgraded for the extra weight..."Why is it so expensive? Can't we find a cheaper way?"
Austin
what an incredible journey of fabrication to get to your point of currupt government.
Quote from: AustinBostonThinking a third time, I could have been clearer in my first response.
This should have been one of my bullet points, and is at the core of the problem here:
The government does business in only one of three ways: 1) Lowest bidder; 2) Highest briber; 3) Overwhelming public pressure. Don't assume because #3 exists that #1 and #2 aren't still going on.
I don't object to using a lower grade of material if you use enough more of it to make up the difference (in both rating and risk). But as I am sure you know, that seldom actually saves money. If I use two or three of grade "B" when I could have used one of grade "A", now everything supporting that has to be upgraded for the extra weight..."Why is it so expensive? Can't we find a cheaper way?"
Austin