Tuesday, February 24, 2009

What is it?

Last week I posted this photo and asked what is it? Most people were fooled into thinking that is was something with spokes, or something that spins. Tim did notice the unique way that the tubes were connected to the hub, but was not sure what it was for.

The object is actually a connector for a Triodetic building foundation system.

In most of the rest of the world you dig down to stable soil or bedrock and pour a concrete foundation for your building. This technique does not work well here in the arctic with permafrost and other unstable soils. Building in these conditions presents many interesting challenges. You must make sure that the permafrost does not thaw out and you need to spread the weight of the building over a large area. The usual solution is to build the structure several feet off the ground with a foundation that contacts the ground in many spread out locations.

The Triodetic system is made just for these applications. It consists of these aluminum connectors with galvanized steel tubes between them. The ends of the tube slide into the slots in the connectors. All of the pieces can be assembled by hand without any special tools or equipment. Each connector has threaded rod in the center of it to adjust for uneven ground and settling. When assembled the system of connectors and tubes makes a solid base for the building to sit on.



Soren said...

I wondered why there were only a few tubes stuck into that piece. This was a good one, I didn't get it even though I've seen the houses up there with this system.


Tim Sullivan said...


Of course, the follow-up question would be: what footing designs does one use for these supports in perma-frost?


Rudstroms said...

This system is a footing design for permafrost.

To prepare a building site here in permafrost conditions you typically roll out a geotextile fabric on top of the original ground. This is then covered with several feet of gravel. The fabric prevents the gravel from sifting down through the organic material. If time allows it is best to let this all settle for a year. The organic material and the several feet of gravel act as a layer of insulation to insure that the underlying permafrost stays frozen. If the permafrost is frozen it is very stable. A good building site would also allow for proper drainage to keep the gravel layer dry and prevent any seasonal changes in that layer.

That is all there is too it. The building foundation (in this case it's a Triodetic, sometimes a system of pads and beams is used) sits right on top of the gravel.


Anonymous said...

Rudstrom family. Thanks for your post.
Anyone who is interested in learning more can find it on www.multipoint-foundations.com