|
|
re: octet trusses for houses?
7 nov 1997
mark gooley ? [returned mail: user unknown] wrote:
>i'd like to build my own house using pressure-treated poles, and
>i wonder whether i could use that packed tetrahedron and
>octahedron space frame that buckminster fuller called the
>"octet truss" to hold up the floors and the roof.
sounds pretty complicated, vs the normal way to build a house.
and perhaps a waste of vertical space, unless you want to run pipes
and wires through the floor, or use it as an air plenum. it might
also be fire prone, with all those little pieces of wood. how about
a tensigrity tower house? :-)
>i'm thinking that i could made these out of 2 by 2 or at worst
>4 by 4 dimension lumber lag-bolted to two-piece steel hubs.
>each hub would be a flat plate with six sets of holes, bolted
>to a bent plate, a triangle with each corner and the adjacent
>area bent to 120 degrees, one set of holes in each bent area..
i'm building a poly film covered geodesic cesspool cover now, out of
25 8' 2x3s. i cut a 1.5" long x 2.5" deep x 1/8" wide slot in each end
of each one and slid a 29 cent kant sag mending plate into the slot, and
carefully put 3 2" deck screws through the wooden fork and holes in
the plate. the galvanized metal plates are 0.040" thick x 1.8" wide
x 5" long, so this leaves a 2.5" tab sticking out of each end of each 2x3.
i drilled 3/8" holes in the middle of the tabs, and bolted 6 tabs together
with a 1/4" bolt 3/4" long. just 11 bolts for the 25 2x3s :-) so far,
i've only finished the roof, but it feels fairly solid. (i'm planning
to tie the bottom 5 2x3s to some used tires filled with gravel for a
foundation inside the structure, and let the plastic film drape over
the outside and berm that with a little more gravel.) the plates bend
enough to make up for the imprecise dimensions of the components. maybe
you could make truss plates this way. i'd like to find some inexpensive
connectors to make one of these things with 25 12' 2x4s, and cover it
with 12' wide greenhouse film. it might have another convex curved piece
of wood sprung into the inside of each panel, to keep the plastic from
flapping too much in the wind. or two layers of plastic with something
to make a vacuum when the wind blows.
>the individual members could be 2 to 3 feet long, and of
>straight-grained wood free of defects (added strength).
doesn't sound worth the cost, in a forgiving structure like that.
>the problem is that i have no idea of how to calculate the
>strength, resistance to bending, etc. of these "octet trusses."
you could test it, eg build a 4x8' section and put it up on bricks at
the support points and load it up with sandbags or containers of water
or drive a car over it. that might convince a building inspector.
>any suggestions? i doubt that these space frames would
>be practical for commercial house-building, but for a
>diy type the advantages are many: no big pieces of wood
>to handle...
i can relate to that :-) although those engineered plywood trusses
seem inexpensive and lightweight.
nick
|
|
