On 1/11/2013 11:48 AM, Warren Smith wrote:
re earlier discussion about optimal domes, and also earlier discussion re "quadrangulations" etc... an interesting -- and it seems highly economical -- way to make a dome is the "cable dome."
This has cables going round the "lines of latitude" of a dome, carrying pure-tensile stress, and struts going up the "meridians" of the dome and fastened to the cables where they cross. The struts carry pure compressive stress.
In effect this is what a yurt approximates, the 'meridians' are broken lines consisting of a vertical part and a part that is a radial on a cone; and there is only one cable around the circumference, at the top of the vertical walls. Brent
The struts and cables can be made from different materials. It also is possible to make the struts not be along meridians, but instead between each two adjacent parallel cable-rings, a zigzag of struts could be employed thus partitioning said annular region into triangles instead of quadrilaterals.
The whole thing seems cheap, light, and easy to erect. You can roof it with membranes, e.g. a greenhouse. Such cable-dome structures were built for use as Olympic stadia in Korea and then later in Atlanta Georgia.
The triangulated method clearly produces a rigid dome. But it is more expensive than the quadrangulated scheme (more beams).
One might naively imagine the quadrangulated dome would be nonrigid and "floppy". I think that is true but I also think it nevertheless will have (if designed right) the property that the desired geometry is an energy-minimum, so it will stably self-restore after any distortion.
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