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Trapezium dome design  I’ve had some interest in the space helmet dome design and thought I would elaborate on the concept and provide a few drawings and measurements. This design is built using equilateral trapezium panels (top and bottom edges are parallel and side edges slope in towards the top) A trapezium-panelled dome integrates better with square geometry than a geodesic dome; square doors and windows will fit with less waste and compromise, also building a half dome against a building is much more straightforward than it would be using geodesic dome geometry.  There are 4 separate panels that form a segment and 16 segments making a total of 64 panels, all x measurements are equal, base angles for each trapezium are: A = 88 degs B = 84 degs C =81 degs D =79 degs (this one is a triangle) Dihedral angles are 157degs for panels joined vertically, angles for horizontally joined panels range from 158 – 161 – 167 – 176 degrees, see diagrams below:   Use the trapezium calculation tool to work out all the sizes you need to build this type of dome. |
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| [ comments 7 ] |
| posted by Russ | |
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| posted by colin | |
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| Hi Russ The eyelet method is certainly cheap and easy but anything screwed into the endgrain is not going to be that strong. The stacking height is another factor to consider, 6 eyelets made of 6mm wire will have a combined stacking height of 36mm so you`ll end up with wavey roof struts. There`s also little to prevent the strut rotating on axis either. My advice is to use a tubular hub or use steel banding/strip to make a sturdy connection. | |
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| posted by Mike Chastain | |
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| The trapezium dome has very obvious advantages for joining with non-dome architecture, uniformity of panels, mating better with doors and windows, etc. Where could I find comparisons between the load and stress characteristics of trapezium versus geodesic domes? | |
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| posted by Colin | |
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| Hi Mike From a frame only point of view a geodesic would be much stronger for an equal size structure using the same materials. Make a triangle and a trap panel frame and load them to destruction..the triangle will win. | |
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| posted by Admin | |
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| I agree with Colin that a triangle will be stronger, you could run a strut diagonally across the trapezium panel to make it stronger. Using 20mm ply as a stressed skin would also improve the strength. I would only use a trap design if the end use precluded a geodesic form for some reason. | |
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| posted by Mark Ludwig | 17/11/2008 19:04:52 |
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| This structure looks like it would be very weak with respect to torsional forces about the central axis (ie take the top and twist it). Have you done any structural analysis on these? | |
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| posted by William | 20/05/2010 08:30:47 |
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| I really like this dome design. There is a boat building technique that is called stitch and glue it allows a person to build a boat using plywood and no frame. I wonder if the same technique could be done with this. I will do some small scale experiments it should be interesting. | |
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