How to build da Vinci's self-supporting bridge

May 16, 2006 10:10 AM

Need help building da Vinci's self-supporting bridge.

The first project on the machine collection page of a da Vinci site shows a self-supporting bridge made of logs. The site will sell you a CD that includes a toy kit to make the bridge.

I want to make one of these. Does anyone know of a resource that explains the process? I'll order the kit as a last resort.

posted by F Mackenzie to Science & Nature (21 answers total)

Most self supporting structures need support during the construction process. The easiest way to build it from a technical standpoint is to use some easily removable support like sand. Not sure if you want a step by step guide of how they would interlock? It seems relatively obvious.
posted by JJ86 at 10:26 AM on May 16, 2006

Response by poster: JJ, a small image on the linked page shows the bridge in various stages of completion, and it does not appear that sand or other supporting material is used outside of the logs themselves. On the CD order page, some of the logs are notched. I'm not an engineers, so it does not seem relatively obvious to me.
posted by F Mackenzie at 10:44 AM on May 16, 2006

Do you plan on actually building this over something? Then it becomes signifcantly more complicated. The easiest way is probably to lift the "key" log into place and then build down from it.
posted by ChasFile at 10:51 AM on May 16, 2006

The notches may not be wholly necessary but may make it easier to remain together on a smaller scale where gravity isn't much of a factor. It appears that all of the logs are of the same length.

Even though the pictures show no support, that doesn't mean that none is required for easiest construction. A full sized construction would definitely require formwork. Brick vaulting requires formwork. Use whatever is most easily available like sand, thicker curved paper or even a small box.

Image 1

Image 2
posted by JJ86 at 11:04 AM on May 16, 2006

I assume you are going to build a scale model like the kit and not a life sized structure?
posted by JJ86 at 11:05 AM on May 16, 2006

I wonder if lincoln logs would be a good substitue for the sticks in the kit?
posted by boo_radley at 11:11 AM on May 16, 2006

If you want to build one yourself, all you need are parts of equal size, like in this picture. Wood works better than plastic, for example, because there's going to be less friction.

Supposedly, you can build (a small) one alone, but I imagine it's easier if you've got someone to help you. Start building on one end (this drawing may help to see how it's done) and continue until the bridge is wide enough for your purpose. I don't think you'll need a support during building the bridge.

I don't know if you want to build one in "real-size", but I would recommend building a model one first. Maybe you can use the little wooden sticks from popsicles?
posted by amf at 11:12 AM on May 16, 2006

As for why there's no supports in the illustrations, it might be to increase visibility of the structure in the manual or instructions. The little bridge shown would definitely require some support while being built.
posted by boo_radley at 11:14 AM on May 16, 2006

That Bridge has been built as a real life model in china. There is a discovery documentary about it. It seems such a bridge existed in china long time ago and they re-built it in that documentary. The Special thing about this bridge is the usage of Logs, while logs do not form good bridges to support distributed loads, arches do a much better job doing that. Hence the purpose of the usage of short logs in a certain weave to create an overall Arch like structure.

The support points on the edges of the bridge also work the same way you would build an arch, so you need lateral support on the sides, because the forces are transferred from the top to the sides and the ends, almost in a 45 degree angle, and not like a log span bridge, 90 degrees angle to the ground.

Hope that helps, I do not remember the name of the documentary though.
posted by convex at 11:19 AM on May 16, 2006

Response by poster: I assume you are going to build a scale model like the kit and not a life sized structure?

IF there were a method of construction that didn't require formwork, I was considering building this out of small cedar logs left over from clearing a hillside behind my house. I've got a tractor, loader, and chains to assist.

Seems like a fun project if doable. This is the staged-construction image that intrigues me. I wonder if I can build the middle, then just keep raising the ends one at a time.

Thanks for the comments thus far.
posted by F Mackenzie at 11:24 AM on May 16, 2006

The way to go about building it, is not start from the ends, but build one frame, and then interweave the second frame , in other words, decide what frame you want to start with, build it on the ground on the side, raise both, introduce horizontal members, then add the 2nd interweaved logs to strengthen the structure and finally, add more horizontal members on top to create the surface. And as I mentioned before, make sure you add the suitable kind of support at the ends, you will need vertical support wall like, to support the ends, horizontal support will not be enough.
posted by convex at 11:33 AM on May 16, 2006

oh, man. I can't make out squat in that image.
posted by boo_radley at 11:34 AM on May 16, 2006

Most self supporting structures need support during the construction process.

For a BRILLIANT illustration of this concept see David MacAulay's BRILLIANT Cathedral and watch groin vaults being built.
posted by Shane at 12:50 PM on May 16, 2006

My thought is to precut all the notches, then work from one end to the other like so:

side view(bmp file)

and repeat... The capital-I shaped things are temporary supports to jack up the end. (Sorry, all I have here at the moment is Windows Paint, so that's why its a bmp and looks like crap.) I haven't tested this, but it looks to me like it would work. Of course, it wouldn't work if you're trying to build it across a bottomless ravine.
posted by teg at 1:35 PM on May 16, 2006

That Bridge has been built as a real life model in china. There is a discovery documentary about it.

I remember seeing that documentary too, and it was the first thing I thought of when I read this question. FWIW, it wasn't a discovery channel doc*, but a Nova episode. Here's a link to the "teacher's guide" for it: http://www.pbs.org/wgbh/nova/lostempires/china/.

IIRC, they had a *crapload* of trouble getting the thing built, and this was with a bunch of manpower AND swarms of bright engineers. If you're planning on building one of these over the creek by your house you might just look into knocking over some trees or inviting the beavers by or something.

* thank god. is it only i who thinks that both the discovery channel and the history channel put out the most half-assed info-tainment shows ever? "After the break we'll show you the same stock footage we've been replaying for the last fifteen minutes, and have our lame-ass narrator rephrase exactly what he is saying now"
posted by fishfucker at 1:39 PM on May 16, 2006

I just tried building it with 15 pencils and a box as a central support. Pencils aren't the best thing to use because they have too little friction but even still there are difficulties with maintaining balance. Ideally in a real full size application, the easiest way to do it would be to make a dirt mound and use that as your form. Logs placed on the mound would not shift during the assembly.

This low tech method was supposedly a way in which Stonehenge may have been created. It has been around for tens of thousands of years. When all the pieces are finally in place, then the dirt is excavated. This method requires the simplest of tools and needs nothing more than basic manpower. Unfortunately it isn't too realistic when trying to build a bridge over a river :(
posted by JJ86 at 2:10 PM on May 16, 2006

teg I am with you. I seems to me you could proceed as you outline, jacking up either end of existing structure enough to get the next pair of logs in. I don't see any reason for any support other than the structure itself and whatever needed to jack up the working end.
posted by pointilist at 6:21 PM on May 16, 2006

Response by poster: I'm going to try several versions suggested here using 2" diameter cedar poles as a test. I'll post a link to pictures and findings early next week!
posted by F Mackenzie at 6:56 PM on May 16, 2006

OK, here's my improved, complete diagram:



The grey arrows are temporary supports, jacks, or very strong people. I haven't tested this and IANAE (I am not an engineer).
posted by teg at 9:20 PM on May 16, 2006

I'm not an engineer, and this is probably the stupidest answer in the thread, but could you not build it on its side and tip it upright when done?

How you would do this over something, I have no idea, short of building on one bank and then using a crane to hoist it into the air and drop it into place.
posted by Ritchie at 9:34 PM on May 16, 2006

Did you ever take pictures of your test F Mackenzie?
posted by Mitheral at 6:39 PM on May 1, 2007