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-   -   1/3 vs 1/2 brick thick dome (http://www.fornobravo.com/forum/f8/1-3-vs-1-2-brick-17374.html)

fcifone 02-12-2012 10:57 AM

1/3 vs 1/2 brick thick dome
 
Has anyone used bricks cut in thirds, +/- 2 3/4" thick for the dome. My main concern is minimum weight while maintaining enough mass for good cooking. Are'nt most floors only 2 3/8" thick?

I know looks (1/3 of the bricks will have a cut end showing) may be an issue.

Amac 02-14-2012 12:30 PM

Re: 1/3 vs 1/2 brick thick dome
 
Quote:

Has anyone used bricks cut in thirds,
I would say it probably depends on your floor size. If you are doing something smaller than say 30" then it probably makes sense. I don't think the cut ends showing will be ny kind of issue. Again that depends on how you are cutting - but even using an angle grinder - as I am - I would be happy enough showing 90% of the cut ends - but so far the inside cut of the entry arch is the only cut which I am showing.
Is it a portable oven?
Aidan

stoveup 02-14-2012 12:56 PM

Re: 1/3 vs 1/2 brick thick dome
 
The dome's structural stability is directly related to the thickness of the shell. Since a hemisphere is not the ideal shape for an arch, as the shell gets thinner you have an increasing risk of the thrust from the weight of the bricks moving outside the curvature of the bricks. If the thrust line exits the bricks to the outside of the dome, the dome will collapse outwardly. If the thrust line exits the bricks to the inside of the dome, the dome will collapse inwardly. Either way is a recipe for disaster. Thicker dome walls are more likely to contain the thrust line within the bricks.

Think twice about building a thinner dome. If you decide to anyway, think again!:D

turkey 02-14-2012 02:13 PM

Re: 1/3 vs 1/2 brick thick dome
 
I thought a dome is the perfect self supporting structure, the arch transition might be harder but nothing a metal support cannot assist ?

stoveup 02-14-2012 02:31 PM

Re: 1/3 vs 1/2 brick thick dome
 
That's a very common misconception. The most stable shape for an arch is a catenary. Check out this website: Auroville Earth Institute.

The thrust of the dome's weight will always follow a catenary shape. Ideally, an arch that is a different shape will be thick enough for the thrust catenary to stay within the walls. The Auroville web site explains this much better than I can.

Amac 02-15-2012 04:20 AM

Re: 1/3 vs 1/2 brick thick dome
 
Check out Dmuns geodesic - I think that has a pretty thin shell 36" - some pics here - you could ask him about it's heat retention etc

http://www.fornobravo.com/forum/8/dm...ven-765-2.html

Amac 02-15-2012 11:56 AM

Re: 1/3 vs 1/2 brick thick dome
 
Here is the thickness of Dmuns geodesic:1
Quote:

.. what I'm not doing is adding a layer of refractory material to the outside of the dome to add mass. Remember that my dome is only 2 1/4 thick,
I haven't heard that it collapsed!

Amac 02-15-2012 01:50 PM

Re: 1/3 vs 1/2 brick thick dome
 
rereading dmuns thread and this is comment from after his build:
Quote:

I am currently discouraging anyone from building as thin a dome as I did. Four inches seems to be the minimal thermal mass to assure strength and longevity. There is nothing wrong with the geodesic system per se, but a two and a quarter inch dome is just too thin. I used proper refractory mortar, and I have major structural cracking in my dome.

If for any reason you need a dome that thin, you need to get a modular oven.
so maybe there is your answer


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