Slashdot Mirror
The Future is Plastic ... Bridges
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."
I'd love to have my own Plastic... Bridgesq.
-mrxak
Onions Will Kill You
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.
Mea navis aericumbens anguillis abundat
The future is Spell.... Checkersq.
I went to look at the slideshowq. From the first slideq: "From Shanghai to Sicily." That's one hell of a bridgeq!
This guy's the limit!
This looks good in principle, but I wonder about the chemical safety concerns of certain plastics. What happens when a fire breaks out on the bridge? Will we have toxic fumes along the lines of the DEHP that makes vinyl siding your house a public safety risk?
Slashdot Burying Stories About Slashdot Media Owned
A use for all that spare Lego I have hanging around!
You can learn a lot about a person if you just take the time to inject them with sodium pentathol
I'm personally waiting for the Gibraltar Bridge. (scroll down for photos)
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
Capitalism: When it uses the carrot, it's called democracy. When it uses the stick, it's called fascism.
Here are some links about dihydrogen monoxide:
Stroller.
I think all the countries in the Middle East should have these. Israel can bomb the bridges out, they can unbox a new bridge when the dust settles.
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)
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.
"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."
Well no. A large part was the inadequacy of the fireproofing that was on the beams. e.g. blown off easily. Now one characteristic of plastic (some) is that they char. Char can be an adequate protection against heat (with it being mostly carbon).
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.
Build it, and they will come^Hplain.
http://cache.lego.com/images/shop/prod/3351-0000-X X-13-1.jpg
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 that the environmental impact of rain and such is reduced?
just an analog boy living in a digital age.
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 have a little less of this issue, but also have generally weaker than stuff like steel thanks to polymer chain alignment being only kinda good most of the time where as you can make some fabulous steel grain patterns. Luckily, advances in polymers lately (I use lately loosely here) have improved their strengths greatly.
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.
future near enough to be worried about it?!
,canada's oil sands etc . enough oil to last hundreds and hundreds of years
.. it never happens
there are tons of more sources for oil . shale
they are always saying we will be running out of oil in 10 years . they have been saying that for long as we have been using oil
Seeing that plastic is going to get incredibly expensive once the petroleum is all gone (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.
-"...bad old ideas look confusingly fresh when they are packaged as technology" - Jaron Lanier (Digital Maoism on Edge.o
>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 standing in the impact zones. Chief Palmer reached the 78th floor and reported that they could "knock it down with two lines."
The WTC collapses may be a tricky structural subject, but extreme temperatures is probably the biggest, most easily proved flaw in the argument.
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 steel, let alone the grade used in the WTC.
Hopefully someone else here does.
As for environmental impact, plastics generally take much less energy to produce than their traditional counterparts. Also, they take much less energy to ship, because they weigh less. I touched on recyclability earlier (as AC).
I do share your concern about needing speciallized engineers to properly utilize these new materials. We don't need more accidents like the recent one at the Big Dig in Boston.
-- The other Dr. Phil
http://www.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
Note to self: select "Plain text formatting" next time or add some br tags
-Palal
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.
That's better than anything else I got on my resume.
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, with two more planned/in progress) and possibly some of the girders and cables. Most of the mass of the bridge will undoubtably still be concrete and steel.
Composite materials (including FRP's) typically begin to break down at a few hundred degrees, although that is highly dependent upon the type of matrix material (usually an epoxy) that is used. The matrix will generally fail well before the fiber does. Also a minor correction, but the WTC collapse was due to a phenomena known as creep, where metals at elevated temperatures slowly deform despite being well below their yield stress. In this case, they deformed to the point where some members buckled, and collapse proceded rapidly from that point.
Cost of building processes is taken into account when planning for a major project. This includes developing repeatable processes that can be conducted in a construction environments and training the workers. In this case, many of the members will actually be prefabricated and installed whole using more traditional methods of assembly. Most likely in this case, one of the bidding companies has some particular expertise working with composites.
I believe most environmental impact filings on civil projects also require end-of-life plans. Fiberglass is quite capable of being disposed of safely.
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 noted, oil is not the only way to make plastics.
Also, as I've been trying to point out to others, THIS ISN'T PLASTIC! It's composites, which may contain plastics, but the journalist who wrote the article really has no clue.
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 an airplane then impacts a smaller proportion of the total.
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 composities usually fail catastrophically, i.e. when the reach their failure load they just break apart, buckle, collapse completely. There is no stretch (elastic/plastic strain) or warning, just a failed structure.
For bridges there are other things to consider as well - how does the material handle dynamic loads (cars/trucks/trains driving over it)? Wind loads (major loading in civil applications)? What about harmonic oscillation modes (ever seen the movie of the concrete bridge behaving like a piece of paper in the wind)? can you make it in large enough sections? Do you need experts to lay FRP? How reliable are the material properties from section to section? etc etc etc It's a very rare engineering application that is all about strength.
Finally, how much does it cost for it to do the job? If steel/conrete can do the job you can pretty much bet it's going to be cheaper.
"Because it's there." - George Mallory, when asked why he wanted to climb Mt Everest, March 18, 1923 (New York Times)
the trick with plastics and UV is to add a pigment (carbon is often used at least with outdoor electical cables) that absorbs a lot of UV light and therefore prevents the bulk of the plastic from being effected by it.
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
from being effected by it
"affected".