written by Rene K. Mueller, Copyright (c) 2006, last updated Thu, May 17, 2007
Since I'm moving to a new place with my yurt, see my Yurt Diary, I have to postpone further developments on the dome, and continue as soon as possible - either having a working yurt (without thermal insulation) or otherwise a facility to work on the dome.
I made two bows composed by three 3.05m 1/2 bamboo splits, when I began to bend the two bows they started to split at the narrow ends of each part, and splitted 2 to 3 times. In other words 1/2 splits are not suitable as guessed.
Conclusion: at least 1/4 or 1/6 are suitable, this implies larger and more expensive bamboo poles.
I checked again the bamboo option, I can use large diameter bamboo (e.g. 10cm), split 4 to 6 times as the original StarDome Building Instructions suggests, or use smaller ones and split only once and risk the bending will increase probability of having splits split again lengthwise due the surface tension when I bend the bamboo split.
Here some calculation examples (regarding length and pricing), 17 x 10m bows (170m total):
- 6m long 100/120mm diameter (1 piece CHF 71), with 6 splits I get 6 x 6m (100 &pi / 6 = 52mm)
- 2x 6m = 12m, probably cutting away 2m from each bow as otherwise the dome gets too big (dome 7.6m diameter, 3.8m height),
- total cost of all bamboo (5 poles = 5 x 6 x 6 = 180m) CHF 355 per dome
- 5.20m long 50/55mm diameter, (1 piece CHF 20), with 4 splits I get 4 x 5.20m (50 &pi / 4 = 39mm)
- 2x 5.20m = 10.40m, ideal with 40cm long junction
- total cost of all bamboo (10 poles = 10 x 5.20 x 4 = 208m, which lasts for 1 dome with 38m leftover), CHF 200 per dome
3.66m long 28/30mm diameter, (50 poles CHF 87), with 2 splits I get 2 x 3.66m (28 π / 2 = 43mm, 14mm wide).
- 3x 3.66m = 10.98m, very good, using 45cm twice for two junctions
- total cost of all bamboo (50 poles = 50 x 3.66 x 2 = 366m, which lasts for 2 domes) CHF 43.50 per dome
3m long 22/24mm diameter (100 poles CHF 87), with 2 splits I get 2 x 3m (22 π / 2 = 34mm, 11mm wide)
- 3x 3m = 9m, too short
- 4x 3m = 12m a bit too long, given I use 30cm overlapping, total length 12-0.9 = 11.1m apprx.
- total cost of all bamboo (100 poles = 100 x 3 x 2 = 600m, which lasts for 3 domes), CHF 29.00 per dome
I will summarize the results in the first page of this diary.
As found out later, the 1/2 splits are not suitable, that's why these options are not longer an option.
I started to contact various companies who manufacture synthetic pipes:
Jansen (Switzerland), 2006/8/21: the head engineer told me during an extensive phone call, that he could not recommend me any material for the usage I described (10m in length, and bent to form 6.4m half bow), and suggested to combine two materials, such as PE with extended UV resistance, plus strength of another material, e.g. bamboo. He also suggested a mix of carbonfiber or fiberglass supported plastic. Yet, the problem of mix of PE or PP with bamboo is that a micro-climate with humidity within the synthetic pipe with bamboo, which could open another challenging issue.
(Switzerland), 2006/8/25: Visited them and spent apprx. 2 hours with sales manager showing me at least a dozen of different kind of synthetics, providing me later also the E-Modul (E) or Young's Modulus (elasticity value) for the most suitable ones for me (as listed below). For now I consider 20 - 32mm diameter, long-livity of 10-15 years. The cost are rather high for low volume or prototype production, and I thought to try with pressure suitable PVC (higher quality PVC) for the prototype for now. The material which otherwise seems considerable (linking german Wikipedia, for other languages follow link and switch language then):
- PVC (Poly-Venyl-Chlorid) with Cold-Support: 2400 N/mm2
- POM (Poly-Oxy-Methylen)
- ABS (Acrylnitril-Butadien-Styrol)
- PC (Polycarbonat)
- ASA (Acryl-Styrol-Acrylester)
Durolaminat (Switzerland): no feedback so far
Geberit (Switzerland): I approached them a few weeks ago already, but they don't sell direct so I had to find a reseller and reviewed the PE 32mm pipe, which was too soft, but for sake of completion: 5m PE 32mm CHF 17.55, for 170m: CHF 603 per dome
Drawing some of the details about how to make the pipe part junctions (4 pipe parts making one bow). As well detail drawing on how the roof bows connect the base bows, either with a tie or another fixation. The holes in the roof bow as well in the base bow/pipe, together with an angle allows any bow to be used at any position for the Star Dome.
So far I researched following materials:
Polyethylen (PE): black 32mm pipe, 5m long the pipe, and bends nicely, not too stiff, not too weak, costs CHF 17.80 (CHF 3.55/m), € 11 or US$ 14 per 5m pipe, whereas I need 34 pipes (17 bows a 10m)
Unfortunatly I haven't found any white colored pipes in PE, which I try to find since I saw that heat radiation of the sun passes through semi-transparent layers and those pipe will get get very warm, if not hot when they are black. Another option is the paint them, which I also have to check.
So, the cost of skeleton with PE pipe is about CHF 610 (€ 381, US$ 488)
(End of Article)