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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 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!
Sheesh.
"Trolls they were, but filled with the evil will of their master: a fell race..." -- J.R.R. Tolkien on Olog-hai
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.
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"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.
Maybe the moderators were trying for +5 funny moderations on their moderations.
Editor Emeritus and Senior Writer, TeleRead.org
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.
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.
>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.
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
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.