The Future is Plastic ... Bridges 72
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 want one! (Score:2)
Plastic? Sort of... (Score:5, Informative)
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)
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)
Re:Recycling (Score:5, Informative)
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
Re:Recycling (Score:2)
Re:Recycling (Score:3, Interesting)
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
Re:Recycling (Score:2)
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
Re:Recycling (Score:2)
-nB
Re:Recycling (Score:1)
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.
Re:Recycling (Score:2)
Re:Recycling (Score:4, Interesting)
Options:
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.
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. . .
Bobby, I'm sure glad they didn't just destroy this entire bridge, the fish sure are biting out here today!
Re:Recycling (Score:2)
Re:Recycling (Score:2)
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!"
Re:Recycling (Score:1)
Re:Recycling (Score:5, Insightful)
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.
Re:Recycling (Score:2)
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.
Re:Recycling (Score:2)
(For instance, all the underwater foundations can be quite involved and expensive, too.)
Re:Recycling (Score:2)
Re:Recycling (Score:2)
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.
FalconRe:Recycling (Score:2)
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
Re:Recycling (Score:2)
Re:Recycling (Score:2)
The future (Score:5, Funny)
Re:The future (Score:2)
long bridgeq (Score:5, Funny)
Re:long bridgeq (Score:1)
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
Re:What sort of plastic? (Score:4, Funny)
Sheesh.
Re:What sort of plastic? (Score:2)
Wake up mods! DHMO = H2O (Score:2, Informative)
Here are some links about dihydrogen monoxide:
Stroller.
Re:Wake up mods! DHMO = H2O (Score:3, Funny)
Re:Wake up mods! DHMO = H2O (Score:2)
At any rate, I wasn't aiming for "+5 funny" -- I was aiming to make people chuckle.
I'm not concerned at all about bonuses to karma, I've plenty to burn and that's not why I post on slashdot anyway.
Re:What sort of plastic? (Score:2)
In any event it was a joke. +5 Funny if I had any points.
Re:What sort of plastic? (Score:2)
Finally! (Score:2, Funny)
Re:Finally! (Score:2, Funny)
After all, if something is "spare", you don't really need it.
Gibraltar Bridge (Score:4, Interesting)
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)
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)
Re:If an airplane's 'black box' is indestructible. (Score:2)
Re:If an airplane's 'black box' is indestructible. (Score:5, Interesting)
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.
Re:If an airplane's 'black box' is indestructible. (Score:1)
Re:If an airplane's 'black box' is indestructible. (Score:2, Informative)
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]
Re:If an airplane's 'black box' is indestructible (Score:1)
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
Re:If an airplane's 'black box' is indestructible. (Score:2)
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
WTC impacts should be survivable (Score:2)
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
Re:If an airplane's 'black box' is indestructible. (Score:2)
umm... (Score:1, Interesting)
Re:umm... (Score:2)
Re:umm... (Score:2)
Re:umm... (Score:2)
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.
Gaston (Score:1)
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
A Thought (Score:1)
Yes... Plastic... There's a "Good Idea" (Score:2)
Re:Yes... Plastic... There's a "Good Idea" (Score:1, Insightful)
Also, as others have n
if they could only keep politicians out of this... (Score:4, Interesting)
NOTE TO SELF (Score:2)