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May 7, 2007 4:12 AM

I want to build an eight foot long arch bridge in my backyard. How should I do this?

Last night as I was going to sleep, I came up with the idea of building a arch bridge over a low area in my yard out of concrete. What I am thinking is to have it in three pieces: two half arches and a keystone in the middle. What resources (other than bridge history sites) are out there that could help me build this?

posted by buttercup to Home & Garden (6 answers total)

Do you want to do it yourself, or do you just want an arch bridge in your backyard? If it's the latter, try to get in touch with Odyssey of the Mind types, people who are trying to win the science fair or become Eagle Scouts, engineering fraternities, etc. These kinds of folks are often looking for this kind of project.
posted by box at 6:13 AM on May 7, 2007

Architecturally, it would look a bit off to have a keystone when the rest of the bridge is a pair of cantilevers. What you're probably going to want to to do is dig out either "bank" (if you consider teh low spot to be like a river), and place some plywood in an arch making the span. Lay in some wire mesh, and pour a bunch of concrete.

However, if you're not sure how to even start doing this, you might not want to be doing it. Concrete can eat the hell out of your hands, and is a pain to work with and get good finishes from if you don't really know what you're doing. Plus, it may not be even close to structurally sound.
posted by notsnot at 6:13 AM on May 7, 2007

The first thing is to decide what would work and what you want. Pore over pictures in books or the internet. A library generally has the better resources in finding home projects like this. Obviously you don't care about bridges fording 100-ft ravines.

If I were you and had no idea what I was doing, I would go to the nearest college with a structural engineering program and talk to a professor. Do this after you have a good idea of what you want. Ask if there are any students that might want to design the bridge for you.
posted by JJ86 at 6:42 AM on May 7, 2007

Any particular reason to use concrete? This is what wood was made for.

(Well, other than the "holding up leaves" thing.)
posted by dmd at 8:00 AM on May 7, 2007

With all the time you would spend cutting rebar and building concrete forms, you might as well make it out of wood. Unless you have a very large backyard and a very large house, a concrete bridge is aesthetically a large, heavy, looming stucture. Wood is a better fit in almost any environment. Here's a site that talks about how arches work- I think building a wooden arched bridge is entirely doable with the right help. Concrete too difficult and expensive (not to mention a big pain in the ass for you or anyone else to take out at a future time).
posted by oneirodynia at 9:54 AM on May 7, 2007

To follow up oneirodynia: I googled "chinese rainbow bridge" and got this (commercial) site for wooden backyard bridges (either plans or assembly kits).
posted by hangashore at 11:26 AM on May 7, 2007