Forgot your password?
typodupeerror
Transportation

What Happened To the Bay Bridge? 407

Posted by kdawson
from the span-in-the-works dept.
farnsworth writes "Tony Alfrey has put together a fascinating page with some history, analysis, and possible explanations for what ultimately went wrong with the recent emergency repair of the San Francisco-Oakland Bay Bridge. The bridge has been closed for days and is not scheduled to open for days to come, hugely inconveniencing more than 250,000 people a day. His analysis touches on possibly poor welding, a possibly flawed temporary fix, and the absence of a long-term fix or adequate follow-up by Caltrans, the agency responsible for the bridge. Slashdot is a great engineering community; what other insights do you have on the bridge situation?"
This discussion has been archived. No new comments can be posted.

What Happened To the Bay Bridge?

Comments Filter:
  • still dead! (Score:4, Funny)

    by MickyTheIdiot (1032226) on Saturday October 31, 2009 @02:40PM (#29936061) Homepage Journal

    For several work mornings the headline on "the new" CNN.com has been "Bay Bridge still closed."

    In my head I hear it in the voice of Chevy Chase.

    "General Francisco Franco is still dead!"

  • by Anonymous Coward on Saturday October 31, 2009 @02:43PM (#29936077)

    Four years ago I bought that bridge along with a package of subprime mortgages to highly qualified homeowners.

  • by ttimes (534696) on Saturday October 31, 2009 @02:47PM (#29936113)
    McSweeny's has a great article on this, broad reaching in its investigation of the many problems at hand. One thing that troubles me: I have seen many times in the California University and Transportation groups, failure to use earthquake retro-fit funds - they simply use them elsewhere. Its only when a problem like this arises that we learn they have not been used.
    • Re: (Score:3, Insightful)

      by Renraku (518261)

      Where did they go? Elsewhere.

      Children have been pulling this scam since money existed and they were given money. Give them some lunch money and watch them go and spend it on something non-lunch related, then come back and cry to their parents saying they don't have lunch money. So you can be a heartless parent and make them go hungry and get laughed at by their friends but learn their lesson, or you can give them some more money so that their behavior is reinforced.

      Obviously a child being hungry for one

    • Don't worry, they're using those earthquake retro-fit funds, in fact before this happened, they were already projected to go way over-budget by the time the new bridge was finished.
    • by theshowmecanuck (703852) on Saturday October 31, 2009 @06:11PM (#29937413) Journal
      I noticed that on the bay bridge dot org web site they had a bunch of high production value movies, animations, etc. presenting the bridge as well as the construction efforts. These aren't cheap to produce. I wonder how much money is wasted making beautiful 'feel good' presentations that could help reduce costs... maybe this is where some of the funds go. I suspect there are a ton of projects that California runs where they have spent several hundred thousand or even millions on 'feel good' movies and web sites. I'm not saying keeping the public informed is not important. But it kind of looks like they think because they have Hollywood they need to make the audiovisual aspect Hollywood grade. Or maybe it is a way to employ all the film school graduates and keep them off the street. It just seemed a tad much to explain that they are building a bridge.
  • by Anonymous Coward on Saturday October 31, 2009 @02:48PM (#29936119)

    They should have used duct-tape!

  • Rushed (Score:2, Insightful)

    by XPeter (1429763) *
    Things like this can't be rushed, plain and simple. Carefully executed planning is what's needed to take on these types of projects.

    Sure the commuters will have to wait a little bit longer while repairs are done, but it sure beats the mess they're in now.
    • Re:Rushed (Score:4, Informative)

      by Nefarious Wheel (628136) on Saturday October 31, 2009 @05:30PM (#29937195) Journal

      Things like this can't be rushed, plain and simple. Carefully executed planning is what's needed to take on these types of projects.

      What XPeter said.

      On the gripping hand, they should see if there's anything left of the civil engineering group from the old Hydro-Electric Commission in Tasmania. The collapse of the bridge over the Derwent River when the ore ship Lake Illawara collided with it was repaired by them when the department of roads weren't up to the task. The old Hydro took their sweet time to fix it, but fix it they did and it's better than new (ship-repelling caissons were added). The size and type of that bridge and the treachery of the waters within which they worked make them similar cases.

  • small (Score:5, Insightful)

    by anonieuweling (536832) on Saturday October 31, 2009 @02:49PM (#29936133)
    The USA is small. Think bigger than just the 250k people. The whole infrastructure in the USA is lagging in maintenance, care, repairs and/or replacements. The USA needs trillions to fix this problem but other shenanigans of course have higher priorities. P
    • Re:small (Score:5, Funny)

      by neoform (551705) <djneoform@gmail.com> on Saturday October 31, 2009 @03:26PM (#29936333) Homepage
      The US spends $1.15 trillion a year on 'Defense', only bleeding heart liberals would want to waste any of that money on silly things like infrastructure.
      • Or heaven forbid, paying down the national debt.

        • Re:small (Score:5, Interesting)

          by hey! (33014) on Saturday October 31, 2009 @05:59PM (#29937345) Homepage Journal

          Depends on the rate of return you can get on other investments.

          True story. I had a guy working for me who applied for a loan on a sailboat. This was a non-profit, so there were a lot of rich kids doing the noblesse oblige thing. Anyhow the bank calls, and afterward the guys says, "they turned me down".

          "Why?" I asked.

          "They screwed up. They said I didn't qualify because my income was only 40K."

          "I don't pay you that much," I said.

          "Actually 40K is my bi-weekly income, but I wanted to get a loan because my investments are returning higher than the loan interest rate."

          What you want is the net value of the United States to increase as much as possible. You want the debt to go down relative to that figure. No major corporation *ever* tries to pay down all its debt. It would be insane, because they'd be paying opportunity costs. Just like my young friend, they don't worry about just one side of the ledger. They maximize their net worthy subject to whatever limitations liquidity puts on them. Naturally, this is not an option most of us ordinary mortals have.

          What you really need to worry about isn't debt alone, but what you are using the liquidity the debt gets you to do. In other words, spending the money wisely. Spending on maintaining critical infrastructure *should* be a no-brainer. You don't say, "we're going to stop painting this very important bridge because we want to reduce our debt." That would be moronic. Likewise, even if you didn't have a nickel of debt, spending money on something that doesn't return anything is just as moronic.

      • by khallow (566160)
        The irony of this statement is that bridge building is probably part of that $1.15 trillion spent on "Defense". There's probably a lot of other infrastructure in that huge price tag. Things like federal law enforcement, infrastructure in Iraq and Afghanistan, air flight, etc.
      • Infrastructure is primarily paid for by the individual states, not the federal government. What the US federal government does or does not spend is largely irrelevant; it is not as though the individual states have 'defense' as major line items.

    • Re: (Score:3, Insightful)

      by peragrin (659227)

      well your off in a lot of ways.

      he USA is 300 million people in a land area the size of Europe who has a population of 700 million plus.

      So not only are you off to start with you are making random assumptions. Sure there is a lot of engineering work that the USA needs to update. however since we have a fraction of the population that most land areas have we have to do more with less.

      Besides having been through europe. The american system is at least 3 centuries more advanced than some of the roads, and bri

      • Re:small (Score:5, Insightful)

        by moosesocks (264553) on Saturday October 31, 2009 @06:12PM (#29937415) Homepage

        That's only if you count Alaska, which is disingenuous at best, given that it's huge, and almost completely unoccupied. Continental Europe occupies 3.9 million square miles, while the 48 contiguous US states occupy 2.9 million square miles. However, the population density of Europe is indeed approximately double that of the "lower 48" (181 people/mi^2 in Europe vs. 94.5 people/mi^2 in the US)

        If we're only talking about the coastal regions, you'll find that the US East coast is almost continuously urban from Boston all the way down to Richmond. Europe has nothing that can compare to that sort of density.

        The west coast is a bit more sparse, although California follows population patterns very similar to what you'd see in a typical European country.

  • whoa (Score:4, Funny)

    by nimbius (983462) on Saturday October 31, 2009 @02:52PM (#29936159) Homepage
    I knew people had been talking about the state falling apart due to budget problems, but i didnt think they meant it literally
  • Lets see here... (Score:4, Insightful)

    by Darkness404 (1287218) on Saturday October 31, 2009 @02:53PM (#29936167)
    Lets see, when you have a pretty much bankrupt state (California), a bridge that is too necessary to fully replace without inconveniencing many people, the fact that it isn't exactly in a stable environment, with wind, rain and corrosion everywhere is it any surprise that a bridge that has been up for over 70 years needs some emergency repairs?
    • Re:Lets see here... (Score:5, Informative)

      by glsunder (241984) on Saturday October 31, 2009 @03:36PM (#29936417)

      "In 2003, Californians sent $50 billion more to Washington in federal taxes than the state received in federal expenditures. Representing a slight increase from levels that have held steady for three preceding years, the Golden State’s imbalance set a new record for any state, surpassing the previous mark (set also by California, in 2000 and 2001) of $48 billion."

      http://www.calinst.org/pubs/balance2003.htm [calinst.org]

      Maybe if that weren't the case, California wouldn't be so broke right now.

      • Re:Lets see here... (Score:4, Informative)

        by caladine (1290184) on Saturday October 31, 2009 @06:39PM (#29937557)
        Looking at that report, there are quite a few other states that see a significantly smaller "ROI" for federal funds than California (Check out NJ's 0.5, compared to Cali's 0.79). It's nothing but pure sensationalism when people talk in absolute numbers. Besides, one should look at how much money California takes in every year as a percentage of it's gross "domestic" product. Maybe if they weren't spending so much on social programs and padding their votes, they might have something left from that amazingly large take for infrastructure. Not that this is a problem unique to California or anything...
    • by FudRucker (866063)
      not to mention California is earthquake prone, and there is a good possibility earthquakes rattle and shake lots of infrastructure over the years without causing visible damage but still weakening them.
  • by Noose For A Neck (610324) on Saturday October 31, 2009 @02:53PM (#29936169)
    Slashdot is a great engineering community; what other insights do you have on the bridge situation?

    No, Slashdot is mostly made up of computer janitors; the greatest insight you'll get out of most of the posters here is, "hurrr durr, the bridge must've been running Windoze! LOL!", with maybe a little "omg the twin towers were collapsed by EXPLOSIVES!!!!"-style conspiracy theory and "THE GOVERNMENT IS BAD!!!" braindead libertarianism thrown in for color.

    • by Stele (9443)

      I accidentally picked the wrong moderator item, so I'm responding here to back out.

      I would have picked Insightful.

    • I think your name, speaks for it's self in regards to your post.
    • by Animats (122034) on Saturday October 31, 2009 @03:56PM (#29936577) Homepage

      No, Slashdot is mostly made up of computer janitors.

      I do get that feeling now and then.

      Many years ago, I went to a serious engineering school. There, the final exam in a course in structural engineering was this:

      At the final exam, each student had to design a link to attach two pins some distance apart. There were obstacles between the pins and the link had to go around then. The design was to be for a specified grade of aluminum and had to support a specified load. Students knew in advance what the exam would be, except for where the obstacles would be. For the exam, you sat at a drafting table, and turned in a drawing.

      The link you designed was then machined out of aluminum by a machinist. It was put in a testing machine and placed under the specified load. If the link broke, you failed the course.

      If the link didn't break, it was weighed. Lower weights yielded higher grades for the course.

      This is how good structural engineers are trained. (I'm not one. I was in EE/CS, and we had a different make-or-break exam.)

      • by QuoteMstr (55051) <dan.colascione@gmail.com> on Saturday October 31, 2009 @06:06PM (#29937389)

        I do get that feeling now and then.

        As do I, but the occasional insightful posts make the whole exercise worthwhile.

        What school has that exam, by the way?

      • by DerekLyons (302214) <(moc.liamg) (ta) (retawriaf)> on Saturday October 31, 2009 @10:00PM (#29938689) Homepage

        The link you designed was then machined out of aluminum by a machinist. It was put in a testing machine and placed under the specified load. If the link broke, you failed the course.

        Took a school like that in the Navy, six weeks on the mechanics of a disk drive. (The size of a footlocker, with hydraulic, mechanical, electromagnetic, and optical components. It held an amazing 10meg (not shabby for a 1964 era drive) and was built like a friggin' tank.) For the final exam you walked in and the whole damn thing was dismantled and spread out on 3-4 tables...
         
        You had two days to put it back together and perform all the alignments - then it was plugged into it's electronics and the 'self test' button was pushed. If it passed, you did. If it didn't, you didn't - and got to repeat the entire school.
         
        Don't even ask about the school on the drive electronics. Nearly a quarter of a century later I still have nightmares about that school.

    • by syousef (465911)

      No, Slashdot is mostly made up of computer janitors

      Well janitors aren't usually asked to solve problems - they do boring repedative manual work, which is why they aren't paid so well.

      he greatest insight you'll get out of most of the posters here is, "hurrr durr, the bridge must've been running Windoze! LOL!"

      What I find particularly sad is that you've clearly just abused the community and they think you're kidding.

      ith maybe a little "omg the twin towers were collapsed by EXPLOSIVES!!!!"-style conspiracy theo

    • Re: (Score:3, Interesting)

      by fm6 (162816)

      Your comment is painfully accurate. Thing is, Slashdotters were a lot smarter when I signed up 8 years ago. There have always been Linux obsessives, conspiracy wingnuts, and kneejerk libertarians, but even they had something worth contributing now and then. There was a lot of stupid noise, but every once in a while you could have a really interesting and informative conversation with some random stranger. Now it's all just flames, rants, and temper tantrums.

      I blame changes in the moderation system. Original

      • Re: (Score:3, Insightful)

        by IntlHarvester (11985)

        More likely, you just personally have gotten smarter and wiser.

        Slashdot has always been filled with bogosity passing as "insight", it's always had karma-whoring (since moderation started), and it's always had trolls having a nice laugh at everyone's expense. If you were to criticize Slashdot for anything, it's not that it's gotten worse, but that its is going into middle-age without getting any better. It is stuck in that same mid-1990s adolescent "Windows drools, Linux rools, Gimmie warez" state forever an

  • A private one would have been more Ron Paul

  • by barfy (256323) on Saturday October 31, 2009 @03:01PM (#29936205)

    People use other bridges and the bart.

    To say there isn't redundancy, is simply silly.

  • Caltrans Says (Score:5, Informative)

    by tlord (703093) on Saturday October 31, 2009 @03:02PM (#29936211)

    The engineering authority in charge of the bridge and repairs already gave their answer to this on the morning news (yesterday, I think):

    They found the crack. They designed the "band-aid": the saddle, T-bar, rods, etc. They had it fabricated and installed.

    In subsequent days, they went back up to look at how it was doing. They found that it was vibrating more than they thought it should: it wasn't as rigid as it was designed to be. They recognized that this would lead to fatigue and failure.

    They began designing the improved "band-aid" and planned to install it sometime in coming weeks.

    To their surprise, *perhaps* related to unusually high winds, the system failed sooner than they thought it could.

    The completed their improved design and are now installing it. (And they are counting their blessings that nobody was killed: they got lucky, that way.)

    -t

    • Re:Caltrans Says (Score:4, Interesting)

      by ctmurray (1475885) on Saturday October 31, 2009 @03:33PM (#29936383) Journal
      At least when they found the flaw they recognized the danger and attempted to fix before the bridge fell down. [wikipedia.org]. The I35 bridge gusset plates were seen years earlier to be warping and this clue was missed.
    • Re: (Score:3, Interesting)

      by hey! (33014)

      This is what you call a rock-and-a-hard-place scenario.

      Stuff suspended over people is the thing that gives the civil engineers I know nightmares. Closing a bridge like that gives traffic planners nightmares.

      You put the two together, and there's a lot of pressure to do a little wishful thinking. That the emergency field repairs on the single most important piece of infrastructure in a major city are acting in an unexpected way is the kind of news nobody wants to hear. And so it's so easy to say, "well, w

  • by Anonymous Coward on Saturday October 31, 2009 @03:03PM (#29936217)

    If their goal was to improve the safety of the bridge, then they totally succeeded.

  • It is old, 73 years, and may take a few days to identify and repair especially after first attempt failed.

    Who says anything is wrong?

    This all seems perfectly normal.

    (I like the fact that many people here would rather their be multi-billion dollar solutions, rather than this is simply how it is).

  • by SethJohnson (112166) on Saturday October 31, 2009 @03:19PM (#29936305) Homepage Journal
    As a hobbyist welder, and someone who has worked with welders in an industrial setting, I strongly doubt that the welding is the culprit. "Faulty welding" doesn't happen on something of the scale of a bridge. If it's one welder working, maybe. But this bridge repair would have had dozens of welders working. No one person's welding could have broken a bridge. Sure, they were under a time crunch, but that doesn't result in shoddy welds. It means more welders are put on task. Those guys are trained and certified and their work is defined by specs that they follow and then is inspected by city or state engineers. If the welding is the problem, it means the original spec was faulty.

    Seth
    • by phantomfive (622387) on Saturday October 31, 2009 @03:41PM (#29936467) Journal
      It wasn't the whole bridge that failed, it was a little support brace that was added to fix an earlier crack in the bridge. It wasn't a huge piece and very well could have been the work of a single worker.
    • welds, even properly done welds, tend to be significantly weaker and more brittle than a typical solid piece of unwelded material. The subsequent temporary fixes that they tried failed before they were designed to which suggests that they may not have built in enough redundancy on the structure as they should have. It could just be a case where they over-estimated the strength of these welds and decided to cut a few corners on the design its self.

    • by Snowblindeye (1085701) on Saturday October 31, 2009 @03:55PM (#29936571)

      I strongly doubt that the welding is the culprit. "Faulty welding" doesn't happen on something of the scale of a bridge.

      You're right on. If the author of the article would have watched any of the Caltrans news conferences, they would have answered some of his theories.

      The weld that he claims failed was clearly described as only being tacked, not structurally welded. That weld wasn't supposed to hold the structure together, the tie rods were, which failed. One of the improvements they are making now is to replace the tacking with a structural weld, so that even if something broke, these pieces won't come apart. The other improvements center around reducing vibration, especially in the tie rods

      Who wrote that article anyway? Some guy on the internet who looks at some pictures of the repair and thinks he knows what a bunch of engineers working on the problem didn't know?

    • by BitZtream (692029)

      My understanding is the welding isn't being blamed, but I'll be the first to admin I've not bothered to read more than this article about ... however ...

      In the perfect world, more welders would always be added to speed up the process. But we do not live in a perfect world. You may live in a dream world, but thats not the one we live in.

      I see, on a regular basis, 'trained and certified professionals' take shortcuts and break the rules. I know state road inspectors that will pass things that really are que

  • What happened indeed (Score:5, Informative)

    by hardihoot (1044510) on Saturday October 31, 2009 @03:21PM (#29936313)
    Perhaps if the state of California hadn't diverted transportation funds and had actually used the money to maintain its infrastructure (similar to New Orleans not using its allocated money to maintain the levee system) this probably would not have happened.

    Raids of Public Transportation Funds [transformca.org]

    Ruling on a case started in 2007 by the California Transit Association, the California Appeals Court found that the gimmicks used to reroute public transit funding to other programs were not consistent with voters' intent for the funds to be spent on public transportation

    nearly $2.5 billion was diverted away from transportation programs [transportationca.com]

  • Meanwhile, in Segovia (Spain), the Roman aqueduct is still up & running :
    http://en.wikipedia.org/wiki/Aqueduct_of_Segovia [wikipedia.org]

    Without mortar, with just granite blocks on top of each other, it is more than 2000 years old.
    I can't help but wonder when mankind began to suck at building anything that should last more than a few years....

    • by WCguru42 (1268530) on Saturday October 31, 2009 @03:49PM (#29936523)
      Not to take anything away from the impressive feat of engineering that the Roman aqueducts are but there is a big difference between carrying water and carrying 250,000 vehicles ranging between 1 and 50+ tons. Also, the Romans didn't really have to worry about costs seeing as the aqueducts were more than likely built by slave labor.
      • by QuoteMstr (55051) <dan.colascione@gmail.com> on Saturday October 31, 2009 @04:00PM (#29936605)

        You have no clue what you're taking about. Roman legionaries (who were paid) and paid laborers were used to build Roman infrastructure.

      • by smoker2 (750216)
        I don't think all 250,000 vehicles are on the bridge at once. Considering a cubic metre of water weighs a tonne, any aqueduct [wikipedia.org] with a water channel 1 metre wide, 1 metre deep and longer than 100 metres is carrying at least 100 tonnes at any moment, constantly. And your last comment is derisable, considering a dead slave is worth nothing so at the least they must be fed.
    • Re: (Score:3, Insightful)

      by phantomfive (622387)
      When we decided that building out of concrete and steal is cheaper and easier than chiseling out huge granite chunks of rock. We still could build things that last like that aqueduct, if we were willing to pay for it, we just find it is cheaper to use easier materials and then pay maintenance costs.

      The Segovia aqueduct needs maintenance too, unfortunately.
    • Re: (Score:2, Informative)

      Roman Aqueducts were made of stone. The bridges in San Francisco were made of steel.

      Stone erodes. This takes a long time. The erosion can be seen on the original stones in the aqueduct you mentionned. It is happening, slowly but surely, and eventually, if not properly maintained, the aqueduct will collapse. (parts of it have already collapsed, and been repaired... it's in the Wiki you linked, even.)

      Steel corrodes. Unlike erosion, corrosion happens relatively quickly. Again, with proper maintenance, it can b

    • Meanwhile, in Segovia (Spain), the Roman aqueduct is still up & running : http://en.wikipedia.org/wiki/Aqueduct_of_Segovia [wikipedia.org]

      Without mortar, with just granite blocks on top of each other, it is more than 2000 years old. I can't help but wonder when mankind began to suck at building anything that should last more than a few years....

      You have something of a point, sort of, but in addition to the problems pointed out by the other responses, you forgot to scroll down in that Wikipedia article and notice that the Aqueduct of Segovia has been reconstructed multiple times. Also note that we think of it as special because it's still there, whereas most other aqueducts collapsed 100-1600 years ago.

    • by photonic (584757) on Saturday October 31, 2009 @05:55PM (#29937325)
      Note that there is a large selection bias in the example you cite. The Romans were great engineers, but I am pretty sure they also built a lot of shitty bridges and aqueducts. It is a sort of natural selection, the ones that are still standing today happen to be the good ones.
  • by nick_davison (217681) on Saturday October 31, 2009 @03:37PM (#29936435)

    It took me a while to figure out but then I realized: CALTRANS only actually employes three guys.

    Driving the 15 in San Diego, I wondered why there were all these construction sites with absolutely no one working. Eventually I pieced it together... CALTRANS only employs three guys and one of those has to hold the sign.

    Sure, they could just do one tiny little roadwork at a time. But that'd completely give away the hundreds of millions CALTRANS budget is being spent on three construction workers with the rest going to hookers and blow. Instead, they dump cones everywhere, dig holes everywhere, then quickly move on to the next site. Sure, you'll never actually see a CALTRANS guy working but it sure as hell looks like they must have a lot of people doing the work if they can dig up that much crap and have roadworks every couple of hundred yards.

    So, when judging the bridge collapse, try not to blame the three overworked guys. They're doing the best they can. Their job was to put up some cones, slap on some duct tape in the two minutes they had assigned, then get on to making somewhere else look busy. If you want to blame someone, figure out who spends the other 99.9% on those hookers and that blow. Imagine how much could be achieved if his habit went to pay for actual workers instead.

    • by TubeSteak (669689) on Saturday October 31, 2009 @04:58PM (#29937007) Journal

      Instead, they dump cones everywhere, dig holes everywhere, then quickly move on to the next site. Sure, you'll never actually see a CALTRANS guy working but it sure as hell looks like they must have a lot of people doing the work if they can dig up that much crap and have roadworks every couple of hundred yards.

      Most highway work gets done at night. Late at night.
      If you can figure it out, I have no doubt CA's dot.ca.gov website will show you where and when they're actively doing construction.

      I drive around during the day and see cones.
      I drive around at night and I see construction crews.

  • by sajuuk (1371145) on Saturday October 31, 2009 @03:38PM (#29936441)
    Consider yourself lucky Californians. Us dwellers of Northern New York have a much bigger problem than you have if we want to get to Vermont. The NY DoT let the Crown Point Bridge, one of only two bridges across Lake Champlain fall into utter disrepair and it is now closed indefinitely. The shortest 'detour' to go across the lake and into Vermont adds around 100 miles to the trip, just to get to the crossing.
    • There is a huge difference between a bridge mostly used for long distance travel and a bridge 250,000 people use to get to their jobs every morning.

  • I heard the problem was the weld between old and new steel. Temperature change caused the materials to contract or expand and, being slightly different, they changed at different rates, breaking the weld.

  • by Anonymous Coward
    The city is so nice and uncongested today. I don't own a car, so admittedly I am very biased, but I would be quite content just to leave the bridge closed. Plus it puts the focus on public transit, where a compact city like SF should be focused. For example, BART (the subway) is running 24 hour service this weekend. As strange as it may sound, despite being an urban environment we don't have 24 hour subway service normally!!!
  • by Animats (122034) on Saturday October 31, 2009 @04:30PM (#29936851) Homepage

    It's surprising that they had trouble there. That's a big, stiff truss span, with lots of cross-bracing. Those usually don't have serious wind problems. (The Tay Bridge disaster [wikipedia.org] was, of course, one involving a truss bridge. But it was badly designed and very badly fabricated.) The worst case for wind is a long, narrow, thin span. The Tacoma Narrows Bridge collapsed through that kind of failure, and the Golden Gate Bridge was vulnerable to it. In 1951, during high winds, the Golden Gate Bridge deflected enough that one side of the roadbed was 11 feet higher than the other. Stiffening trusses [flickr.com] were added under the span. (These are big trusses, each over 20' high, but the bridge is so huge that few people noticed the retrofit.)

    In the 1989 quake, the Bay Bridge had an upper deck section break at the joint between the high truss span and the lower spans. That was an impedance mismatch - the two sections oscillated in different ways, and the stress at the transition point was enough to break bolts. When the Bay Bridge was designed in the 1930s, those problems weren't well understood, and could not yet be simulated.

    The problem seems to be that the quick fix for the crack was underdesigned. That was recognized within days, and a second fix was under construction.

    The damaged eyebar could be replaced, but that requires fabricating a new eyebar and some specialized tooling to take off the load from that whole eyebar chain during repair. This span will be torn down in a few years, when the new span is finished, so that may not be worth it.

The more cordial the buyer's secretary, the greater the odds that the competition already has the order.

Working...