"bridge in a backpack"

[KENAT]

gwolf, I don't think they were using corrugated steel, it was some kind of composite. Also as for the 'fill' above corrugation, I think maybe they just used sand or compacted dirt not concrete.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[gwolf2]

Gulp! I wouldn´t drive over it!

 

[btrueblood]

"The composite will fall to bits over time leaving the circular arches unconnected to anything. These will in turn fall off sideways leaving a piece of corrugated steel dangling by hope alone to the concrete. The metal will then fall off leaving a wierd corrugated arch profile on the bridge. Water will get into the pores and inevitable voids in th corrugated profile and if there is any freeye thaw action at all the corrugations will fall off in chunks."

Guffaw. Except that our current crop of highway bridges, especially in high road-salt-usage areas, pretty much follow the "rot away to the rebar" pattern in some 30 years. While for the composite arches, the vinyl ester resin is potentially a moisture and salt barrier for the concrete, the assumption is that the barrier is not breached for some period of time (to justify their claims of 50+ year life). One bum with a campfire under the bridge...bingo, no more composite.

 

[SKIAK]

Hmm... I do have my reservations about the lifespan of the composite, but isn't this stuff used in the aerospace field as well? Seems like it should be a little more durable than you make it sound. Don't they use carbon fiber laminate to repair or reinforce existing concrete structures?

 

[btrueblood]

"isn't this stuff used in the aerospace field as well?"

Yes, and the damage susceptibility is a real problem there; it is managed to minimize problems, and costs are (sometimes) traded off against the performance advantages of the lightweight properties of the materials. But when a mechanic drops a wrench on a carbon fiber wing section, that section can quite readily develop hidden damage due to fiber breakage or delaminations. A lot of time and money are spent inspecting parts made of composite materials to ensure they aren't falling apart, or about to. They certainly don't park their expensive aircraft on roadsides.

 

[SKIAK]

Thats a good point, if I owned an airplane I don't think I would park it on the side of the road either. Although going down the road of campfires, I live in close proximity of several timber bridges. I know that large wood members can resist fire, but I can't imagine that this carbon fiber construction would be more susceptable to fire than wood... right? I guess I don't have a good grasp on carbon fibers. I wonder if they put any thought into repairing these tubes.

 

[Gymmeh]

SKIAK,

do you ski? I had carbon fiber ski poles once, when they broke you can see the carbon fibers held strong but they are held together by some epoxie media which splintered - possibly from the cold. I would guess they would just hold up well against a small fire...

how big of fires do bums normally have?

 

[SKIAK]

Heck ya I ski. Love it. Although I don't think I have had a pole break, but maybe I'll start a bonfire this weekend and throw one in... for research purposes.

 

[btrueblood]

I was being a bit facetious about bums and campfires. But weathering and impact damage would be my worries for a bridge 'round here. We have big storms that send a lot of wood debris churning down streams.

 

[SKIAK]

Sometimes its hard to tell... and I agree, I could see a problem with a large log ramming into the side of one of these.

All things considered (or at least most), I think its apparent that this type of construction has its limitations as with any. I just enjoy reading about people "thinking outside the box." Helps remind me that there is still a lot of creativity and ingenuity that goes on out there.

 

[btrueblood]

Agree with your last, Skiak. It's a cool technology, and some simple tweaks could make it robust against the types of things we are quibbling about here. Certainly the speed of construction and use of light(er) equipment make it a nice idea for emergency repairs, or road work well back in the boonies where heavier equipment might not be available or transportable over existing roads.

 

[GregLocock]

An interesting observation by JE Gordon is that there is no uniform 'best' solution for bridge structures, despite the rather obvious limitations on the general requirement. So, expanding the envelope of possibilities is a good move.




Cheers

Greg Locock

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