Follow Slashdot blog updates by subscribing to our blog RSS feed

 


Forgot your password?
Close
typodupeerror
×

The Future is Plastic ... Bridges 72

Posted by timothy from the good-enough-for-gaston-glock dept.
ches_grin writes "BusinessWeek reports on the latest in bridge-building technology, where new materials and techniques are allowing bridges to be built in places that were previously thought impossible. New plastics are allowing bridges to be lighter and stronger than concrete, and 'using cables and new suspension techniques, these bridges traverse bodies of water that were once too deep, too soft-floored, or too earthquake-prone for conventional methods.' The article also includes a slideshow of some of the most innovative bridges, some still under construction."
This discussion has been archived. No new comments can be posted.

The Future is Plastic ... Bridges More

The Future is Plastic ... Bridges

Comments Filter:
  • I'd love to have my own Plastic... Bridgesq.

    • Plastic? Sort of... (Score:5, Informative)

      by iamlucky13 ( 795185 ) on Thursday August 03, 2006 @01:57PM (#15841207)
      FRP - Fiber Reinforced Polymer really means composites. In this case, probably some type of fiberglass or carbon fiber composites. To merely call it plastic is a little misleading, especially since not all polymers used in composites are plastics. Technically, even concrete is a composite, but obviously of a different nature than we're discussing here.

      Also, this is only relatively new. This is one of those repeat stories that comes up from time to time when some editor thinks he's stumbled upon something incredible. I think I saw an article about "glass" bridges in Popular Mechanics 7-8 years ago (meaning fiberglass, actually, but that didn't stop the PM artists from drawing pictures of transparent bridges). For several years, a largely composite cable stayed bridge has been in planning stages as a replacement for an old span on Interstate 5 in California.

      More currently, I interned with a company that assisted with a fiberglass reinforcement of a small concrete and steel bridge near Mt. Hood in Oregon. The city of Portland and Martin Marietta Materials recently replaced the slippery-when-wet steel deck on the Broadway Bridge in downtown Portland with a composite deck that performs comparably to concrete for traction and longevity, but is light enough not to interfere with raising the drawspan. Two more bridges in Portland are slated for similar modifications.

  • Recycling (Score:3, Insightful)

    by Detritus ( 11846 ) on Thursday August 03, 2006 @09:37AM (#15839108) Homepage
    Have they thought about the long term environmental impact of these bridges? Concrete and steel can be recycled.

    I was watching a television show on airplane junkyards, and they mentioned that they can't do much with the plastic and carbon-fiber composite parts that are common in newer airplanes.

    • Re:Recycling (Score:4, Informative)

      by mrxak ( 727974 ) on Thursday August 03, 2006 @09:40AM (#15839114)
      Any plastics (I'm assuming these are thermoform) that can't be recycled can be converted into raw energy in Mr. Fusion. It's not like recycling is even all that good, the energy cost is higher than producing new plastic, and the quality of the recycled plastic is not as good.

      • Re:Recycling (Score:5, Informative)

        by Anonymous Coward on Thursday August 03, 2006 @10:36AM (#15839584)
        As someone who works in this field ("I am a polymer chemist" blah blah blah), you hit it right on the head regarding recyclability.

        The main problem regarding the recycling of most plastics is that it's currently a heckuva lot cheaper to make new plastic from raw materials than it is to recycle existing materials. For example, soda bottles consist of several layers, each engineered to be slightly different: One layer prevents oxygen from entering the bottle, one prevents carbon dioxide from leaving the bottle, one layer has an antibacterial component to keep microscopic bugs from feasting on the sugars inside, etc. These layers have to be separated during the recycling process, and added complexity increases the cost.

        Most plastic raw materials are byproducts of oil refining, and as the price of oil rises, so does the price of plastics -- we'll probably see more of a push to recycle in a few years.

        Even thermoset (or thermoformed) plastics can be recycled to a small extent. While they cannot be repolymerized into new materials, they can be shredded and used in things like new plastic composites, rubbers and asphalts. Not to mention that there's a push in R&D to design new alternatives to thermosets that have comparable strength, but can be chemically degraded and reused.

        -- The other Dr. Phil
        • Oops! I meant thermoset, not thermoform. I was thinking "not thermoplastic", and typed the wrong thing. Anyway, thanks for adding some detail. But seriously, who would want to recycle a bridge anyway?

        • Re:Recycling (Score:3, Interesting)

          by Abcd1234 ( 188840 )
          These layers have to be separated during the recycling process, and added complexity increases the cost.

          Correct me if I'm wrong, but couldn't you just use thermal depolymerization [wikipedia.org] to convert the plastics back into short-chain hydrocarbons? I presume you can then use the output as raw materials for the production of new plastics. Heck, you could even use part of the output as an energy source for producing the new plastics... yes, you'd end up with less plastic than you started with, but you wouldn't have

      • It's not like recycling is even all that good, the energy cost is higher than producing new plastic, and the quality of the recycled plastic is not as good.

        Do you have evidence that supports your contention that energy costs are higher with recycled plastics that virgin plastics? While I may not agree with this I do agree about the quality of recycled not being as good as virgin plastics. Though I've asked before I haven't seen any life cycle analysis comparisons of the two.

        Falcon

        • Not that I pretend that it's the best source, but Penn & Teller Bullshit did azn episode on this and found that plastic was better trashed than recycled in almost all cases.
          -nB
    • Well, you could build bridges and airplanes out of biodegradable plastics. . . But if you did, please tell me so I can avoid using them.

      Could you please explain for the class why you would be concerned with recyclable bridges?

      BTW, it is a myth that plastics do not biodegrade.

      • I'm thinking about what we do with all that material when the bridge has outlived its usefulness. Concrete and steel are easy to recycle. What do you do with thousands of tons of plastic?

        • Re:Recycling (Score:4, Interesting)

          by glass_window ( 207262 ) on Thursday August 03, 2006 @11:59AM (#15840226)
          I'm thinking about what we do with all that material when the bridge has outlived its usefulness. Concrete and steel are easy to recycle. What do you do with thousands of tons of plastic?


          Options:
          • Donate it to a third-world country.
            We no longer need our bridge, so we are donating it to Zwataharia, who has many rivers of which people must wade through should they wish to cross.
          • Make a new park out of it.
            Welcome to the Golden Gate Bridge State Park. The Golden Gate State Bridge was bought by Ohio in 2085—airlifted here by a team of helicopters to the location you see today. . . .
          • Do what they've always done with bridges that they don't feel like destroying.
            Bobby, I'm sure glad they didn't just destroy this entire bridge, the fish sure are biting out here today!
        • Artificial reefs? [washingtonpost.com] (I'm not sure how well plastic would work for that though.)

        •   I'm thinking about what we do with all that material when the bridge has outlived its usefulness. Concrete and steel are easy to recycle. What do you do with thousands of tons of plastic?

          Write on the side of it, in huge letters: "I am Ozymandias, king of kings! Look upon my works, ye mighty, and despair!"
      • recyclable != biodegradable

    • Re:Recycling (Score:5, Insightful)

      by RoffleTheWaffle ( 916980 ) on Thursday August 03, 2006 @11:05AM (#15839813) Journal
      Presumably, one of these plastic bridges is going to stick around for a very, very long time. The only time we'd have to worry about recycling or disposing of a plastic bridge is if it completely fails and collapses. Depending on what the bridge is made of, the materials from the bridge may or may not be recycled - I'm sure there's a way, though. In the very least, it can be ground up into tiny bits and used for insulation or something.

      That said, I don't think anyone is wondering what we're going to do with the Golden Gate Bridge once we're done with it. Structures like these are made to last, not to be thrown away.
      • "Structures like these are made to last, not to be thrown away."

        Actually, they just completed a new Carcinas bridge, and on the radio, the newsperson said the new span was designed to last 70 years.

        I was stunned, frankly. I, too thought bridges were permanent fixtures, meant to last centuries. I guess they're not.
        • I can't speak to that exact bridge, but I certainly would expect some parts to need to be replaced in less than 70 years - and the surface probably more often than that. Possibly a major replacement is needed in 70 years, but replacing that part might only cost a fraction of the entire bridge.

          (For instance, all the underwater foundations can be quite involved and expensive, too.)

    • Plastics and other random hydrocarbons can now be recycled into light crude oil [mindfully.org], then cracked in a refinery to make gasoline, heating oil, diesel, and more plastic. GM is looking to do this with the thousands of tons of automotive plastics rotting in junkyards all over great lakes region.

    • Have they thought about the long term environmental impact of these bridges? Concrete and steel can be recycled.

      That was something I was wondering about too. And though plastic can be made from plants, vegetation, much plastic is made from petroleum today. I'd like to see a life cycle analysis of Fiber-reinforced polymers versus concrete and steel, as well as other methods.

      Falcon
    • Concrete and steel can be recycled

      Can they? Please give me an example.

      As far as I'm aware, the only way of reusing a steel-reinforced concrete structure is as hardcore in the footings of another building. There's no reason why plastic wouldn't be just as good - if all you're after is a load of rubble to pack down hard, big chunks of plastic would be just as good. The steel is so tightly bound with the concrete that extracting it for reuse is significantly more expensive than mining and processing some mo
      • I could see that extracting rebar from concrete might be more trouble than it's worth, but what about all the structural steel?
    • you can't do a great deal with concrete either, you can crush it and use it as rubble for foundations but thats about all you can do with it.

  • The future (Score:5, Funny)

    by liak12345 ( 967676 ) on Thursday August 03, 2006 @09:39AM (#15839111)
    The future is Spell.... Checkersq.

  • long bridgeq (Score:5, Funny)

    by gEvil (beta) ( 945888 ) on Thursday August 03, 2006 @09:43AM (#15839136)
    I went to look at the slideshowq. From the first slideq: "From Shanghai to Sicily." That's one hell of a bridgeq!
    • i don't get these q jokes

      can anyone enlighten me
      i've scavenged through the Article but can't seem to find why you guys are doing this!


      Anyway My regards

  • Finally! (Score:2, Funny)

    by Alicat1194 ( 970019 )
    A use for all that spare Lego I have hanging around!

    • Re:Finally! (Score:2, Funny)

      by eam ( 192101 )
      There's no such thing as "spare" Lego. Just bricks awaiting their next adventure.

      After all, if something is "spare", you don't really need it.

  • Gibraltar Bridge (Score:4, Interesting)

    by Mab_Mass ( 903149 ) on Thursday August 03, 2006 @10:17AM (#15839409) Journal

    I'm personally waiting for the Gibraltar Bridge [union.edu]. (scroll down for photos)

  • If an airplane's 'black box' is indestructible... (Score:5, Interesting)

    by ExE122 ( 954104 ) * on Thursday August 03, 2006 @10:18AM (#15839419) Homepage Journal
    Carbon, glass, and aramid fiber reinforced polymer rebars have been in use in combination with concrete structures for a while now. They are non-corrosive and have a high tensile strength, making them a better choice for steel. They are especially good for pre-stressed structures, such as concrete tubes which have the rebars stretched by a hydraulic machine and spun around as the concrete is poured so that it will cure under centripetal force (I think Modern Marvels on the History Channel did something about this).

    Yet I still find it surprising that they are willing to build the entire bridge out of it. Despite all the hype about how much stronger FRP is than steel, I'm wondering how it will hold up in extreme conditions.

    A couple months ago, I got into a discussion about the WTC collapse. One thing that was mentioned is that a large part of the collapse was due to the extreme temperatures of burning jet fuel weakening the elastic modulus of the steel-framed structure. I'm wondering if an FRP structure would've held out any better.

    My guess is that while FRP is stronger than steel in ideal conditions, temperature has a more drastic effect on its properties. I suppose there less of a risk of this with a bridge, but I'm sure the decision to make buildings out of this material won't be far off. I think it would be most unfortunate if support beams started bending like straws should a fire break out.

    I'm also wondering about the cost argument. Sure it may be cheaper material-wise... but how many construction crews are experts at extremely large scale plastic construction? How many are even willing to undertake such an endeavor? I'm sure they're going to need to spend a lot of money on experts and engineers, and hopfeully there won't be any serious oversights due to inexperience and human error.

    And I won't even get started on the environmental impact. I agree with the previous posts covering that concern.

    ---
    "A man is asked if he is wise or not. He replies that he is otherwise" ~Mao Zedong

    • Re:If an airplane's 'black box' is indestructible. (Score:4, Insightful)

      by multimediavt ( 965608 ) on Thursday August 03, 2006 @11:03AM (#15839800)
      I would also like to know how long-term UV exposure affects the structural properties of this material. Most plastics and polymers break down over time with prolonged UV exposure. Of course, it is being built in England, not known for its overly sunny climate.

    • Re:If an airplane's 'black box' is indestructible. (Score:5, Interesting)

      by oneiros27 ( 46144 ) on Thursday August 03, 2006 @11:10AM (#15839853) Homepage

      Some of the advantages of composite materials is that you have have a protective coating around a material that might have problems. (eg, the concrete around steel columns helps provide a degree of insulation)

      You also have to look at more than just absolute strength (even at a range of temperatures), and look at how it fails at different temperatures. For instance -- steel at 'room temperatures' typically fails through plastic deformation -- it stretches, and we get a chance to notice that something's wrong before it explosively fails. However, it becomes brittle at cold temperatures, and a sudden impact can break it. (one of the theories of the Titanic disaster is that this is what happened).

      Today's engineers don't just try to make the building strong, but to make sure that it fails in predicable ways. (eg, steel reinforced concrete is supposed to make sure the steel fails before the concrete ... so you see sagging before the concrete explodes in a shower of chunks).

      Another thing to remember is that the building codes list a set of conditions that the design has to be able to take -- it's not that a structure will never exceed those given loads, but that the probability of exceeding those conditions is low enough. (after all, we can't be 100% sure that the concrete was poured correctly, and that we'll get the exact properties that they got in lab conditions). The codes will list the stresses that it has to take, and the safety factors to use -- they often vary by area. (eg, in colder climates, you expect more total snow load, but don't have to design for as much variability).

      I'm not going to pretend to be an expert on these matters -- I have a bachelor's in civil engineering, but I'm not a practicing engineer. But I do trust that the majority of PEs (Professional Engineers) are going to look at these sorts of things ahead of time -- who wants to be known as 'the guy who built the $2billion bridge that fell down in 3 weeks and killed 2k people'. I also trust most safety inspectors are actually going to inspect the work as they're required to do. I'm going to assume that that unless something has completely broken down in the processes that these materials have been tested past the expected operating ranges they're expected to be used in, and the structures will be built to take more load and ecentricity than is expected.

    • Actually, instead of saying "And I won't even get started on the environmental impact. I agree with the previous posts covering that concern.", I wish you would go into your thoughts on the environmental impacts. If we design the bridge correctly, we shouldn't need to replace it, provided a study on the UV / evironmental degredation proves that it's a viable option. If it's cheaper, stronger, lasts longer, why wouldn't we use it? Wouldn't it be prudent to make the bridge out of a hydrophobic material, so
    • >A couple months ago, I got into a discussion about the WTC collapse. One thing that was mentioned is that a large part of the collapse was due to the extreme temperatures of burning jet fuel weakening the elastic modulus of the steel-framed structure.

      Doesn't sound like a good discussion then. Most of the jet fuel exploded outside the building. A half-hour later, there were people [the7thfire.com] standing in the impact zones. Chief Palmer reached the 78th floor and reported that they could "knock it down with two lin [wtc7.net]
    • Here's a listing of the degradation temperatures and melting temperatures (for those that do melt) of some high-performance plastics and components of plastic composites:

      Nomex: Melts at 285 C, degrades at 371 C
      Kevlar: Doesn't melt, degrades at 400 C
      Spectra: Melts at 144 C, and I can't remember or find a degradation temperature
      Fiberglass: Doesn't melt, degrades at 2000 C Carbon Fiber: Doesn't melt, degrades at 3000 C

      I don't know the corresponding temperatures for concrete, asphalt, or the various grades of

    • When someone says fiber reinforced polymer (FRP), the mean a composite like fiberglass or carbon fiber. Reporters generally don't understand this and like the sound of FRP better anyway. The material is nothing new.

      They're not talking about building an entire bridge out of it. The article doesn't say what, although I could probably find it with a thorough google search. Most likely the road deck (the city of Portland has one drawbridge that was recently retrofitted with composite decks for weight savings
    • Put essentially all of the structural support outside of the living areas, like an exoskeleton.

      This keeps fuel from sitting on the support structure. A few floors get burned, and perhaps collapse, but the structure remains sound.

      With the right density of verticals, an airplane could be pretty well broken up. This causes the bulk of the fuel to go up in a quick fireball, which will dissipate most of the heat via a great big fireball.

      A wider structure also spreads out the load-bearing structure. The width of
    • You've hit several points here, but most importantly engineering is not purely about strength. It's about the right properties to perform for the least cost. FRP (I'm assuming carbon fibre, fibreglass etc) is expensive, difficult to recycle (sustainability is a major driver in todays' world) and - from an engineering point - it fails unpredictably. Steel/concrete fails predictably - it sags/stretches/cracks well befor the entire thing fold in half and kills people. You can monitor it. Fibre reinforced compo

  • umm... (Score:1, Interesting)

    by Anonymous Coward
    Correct me if I'm wrong, but I always thought that oil is involved somewhere in the process of manufacturing plastic. So, how is this going to be the 'bridge technology of the future' when oil supply is on the verge of drying up? (yes I know it's in tens of years... but it's already a future near enough to be worried about it)
    • Plastics are usually made from petroleum products, but they don't have to be. There's a growing number of plastics that are made from corn [wikipedia.org]. I'm not sure of the characteristics of these new bioplastics, but I'd guess that they come in as wide a range of types as the petroleum-based plastics.
    • oil is nowhere near drying up, but we have hit the end of the easy oil. From here on out, less will flow out of the ground. Sadly, burning up the oil for energy is a waste of of it. But oil is not the only way to get plastics. It is just that it has been one of the cheapest ways to get pre-built hydrocarbon chains.
    • plastics are mostly made from hydrocarbons, currently the cheapest way to derive theese is generally from oil but there are many other sources possible.

      also oil won't "run out" as such, it will just reach the point where it is not viable as a source of energy (e.g. where you need more energy to extract the oil than you get from burning it).

      sooner or later the world is going to have to bite the bullet and get serious about nuclear again with modern efficiant breeder reactors and hopefully eventually fusion.
  • Best dept. ever! *brandishes his G22*

    Ontopic, I think this sounds like a great idea, so long as adequate stressor testing is done and the structure is reinforced with steel and probably anchored with steel and concrete. Remember, while a lot of carbon fiber rods being used in construction nowadays have great tensile strength, they have poor compression strengths and terrible resistance to breakage along the lateral axis (*forgets the name of that type of force, just now... axial? transaxial?*). Polymers h
  • Is anybody worried about Static Electricity? Remember what it was like to go down a plastic slide as a kid? Now do it on a Gigantic Bridge, wow, now that's a lot of hair on end.
  • Seeing that plastic is going to get incredibly expensive once the petroleum is all gone [princeton.edu] (2025 by the most realiable non-industry estimates) I don't think we want to be using plastic. Personally I think the future lies in ceramics. Of course that doesn't help the bridge builders out since it's heavy and probably not stable enough for bridges.

    • Re:Yes... Plastic... There's a "Good Idea" (Score:1, Insightful)

      by Anonymous Coward
      The princeton source you link to only takes into account current methods and sources. Basically, he looks at the rate at which new sites are discovered and notices that it is dwindling. Hopefully he takes into account the length a field is useable, too, but he doesn't mention if he does. He definitely does not take into account oil already known to be located in shale deposits and tar sands, which are more expensive to retrieve but theoretically triple the available extractable oil.

      Also, as others have n

  • if they could only keep politicians out of this... (Score:4, Interesting)

    by Palal ( 836081 ) on Thursday August 03, 2006 @01:19PM (#15840888) Homepage
    http://www.newbaybridge.org/ [newbaybridge.org] This is being built to replace the existing bridge built in 1936. The eastern span was damaged in the Loma Prieta quake and is now seismically unsafe. While the design is relatively simple compared to anything mentioned in TFA politics has played a major role in stalling construction. 1. Cost overruns are discovered 2. Arnie (Terminator) desides to 'simplify' the project, stalls it, later it's found that existing design will be cheaper. 8 months down the drain 3. Steel workers pissed off at their union/coworkers say rebar welds are unsafe. FBI goes in to investigate and finds that "these welds should be used in the classroom to show HOW TO WELD." 4. Caltrans takes the longest time selecting a contractor to build the cable-stayed "self-suspension" span. 5. It's recently discovered that a lower quality concrete was used on another project on the same bridge (replacement of all approaches to the bridge from the western end which date back to 1936). All of this stuff is/(is influenced by) politics which has crept into construction in the U.S. We won't be seing too many marvels any time soon. BTW. I got a chance to take a tour of the construction site last year. Pix are here: http://palal.net/baybridge.html [palal.net]

Slashdot Top Deals

Remember to say hello to your bank teller.

Close