#41  
Old 07-09-2011, 01:41 PM
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Default Re: My Modified Barrel Vault in Texas

If the flue is inside the oven chamber you need a damper, or like many kilns, simply a cap on top of the chimney. Without such an arrangement every time the door is opened all the heat from the oven goes up the fue.
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Old 07-09-2011, 02:23 PM
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Default Re: My Modified Barrel Vault in Texas

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Originally Posted by luca View Post
Also, wouldn't it have been even more structurally sound to offset/ alternate the bricks in each vault ( or is this unnecessary)?
You have to bond the bricks to achieve optimum strength, this makes the arch as one rather than a series of single arches, and less likely to fail
See here.

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Finally, does having the flue in the vault itself--as opposed to a separate chamber--have any negative issues associated with it (e.g. starting problems, heating issues/cold spots etc.)?
My flue is inside my oven and operates way better than I had hoped it would, lighting the oven is an absolute breeze, as for loosing the heat at shut down you just need a damper in the flue.

Chimney.

Flue Damper.
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  #43  
Old 07-09-2011, 02:56 PM
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Default Re: My Modified Barrel Vault in Texas

In kiln construction the end walls on a barrel vault should be inside the arch. If outside the arch steel bracing is used to prevent the end walls from tending to fall out. A large diameter arc exerts considerable lateral force at its base, a semicircle much less so and a catenery arch the best, although only if its base is about the same as its height. We are not building kilns so the temp extremes are not as destructive but the principles are the same.
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Old 07-10-2011, 02:27 PM
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Default Re: My Modified Barrel Vault in Texas

Your welcome. Angus was my constant if not particularly helpful assistant throughout the months of construction. I calculated the bevel on the bricks to allow for a specific number, in this case fourteen, bricks laid edge to edge to create a 9" wide by 2.5" thick vault. In this case, I wanted a semicircular vault with an 18" height so using all of my highschool geometry figured that meant a 36" inside diameter circle, roughly 39" outside diameter. 36" times Pi equaled a number divided by 28 yielded yet another number which when divided into the 360 degrees of the circle yielded yet another number which when divided by 2 (the bevels on each side of the brick) gave me 7 or so degrees. That is what I shaved off the long side of each brick using a 14" diamond blade in a chop saw. I cut a couple of wooden wedges at 7 degrees, propped the brick on them, then trimmed the brick. A running bond does not a stronger arch make. Each brick in any arch is bonded on every side to another brick or two. What a running bond provides is a greater number of individual or different bricks- 6 instead of 4- for any given brick to be attached to. Look at any brick in a wall and count the number of bricks it has contact with and you'll see what I mean. A running bond simply makes the failure of any individual joint less catastrophic. Finally, as I said before, the flue in the vault was a mistake, but one Im glad I made. My damper consists of a 3/8" thick steel plate backed with a thick pad of fiberglas which pivots at one end on a 3/8" steel rod running through a steel tube running through the masonry and out the front of the oven. When I turn the handle, the plate pivots up and the flue is open. Back and the damper is closed. Without the damper, my oven would have been a fireplace. I can start my fire without accelerants while the damper is open, and when the large logs are burning merrily, I can close the damper and heat the oven. We were baking pizza two hours after I lit the oven last night.
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Old 07-10-2011, 03:36 PM
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Default Re: My Modified Barrel Vault in Texas

Thanks, that's very helpful! (And now I'll need to dust off my geometry skills so I can use your formula to calculate the angle I'll need to cut...finally, someone has answered the age-old highschooler's question of "WHY do I need to learn this stuff??!!) As you'll see above, most of my questions have been (thankfully!) answered on this forum, but the BIG question that no one has responded to yet, is whether the bevels that you cut on your bricks didn't in fact increase each of your arches' strength as found in the classic arch design (i.e. since your bricks are now angled/trapezoidal rather than rectangular, isn't the force from the top of the arch transferred through each brick to its lower neighbor and thence to the floor of the oven, hence minimizing the likelihood of collapse?) If i can get a cogent answer to this question, then I'll know whether I'll need to construct a double layered vault rather than a single one, as you did (and I'm certainly leaning heavily towards the single layer). Any other comments out there on this issue??!!
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Old 07-10-2011, 04:00 PM
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Default Re: My Modified Barrel Vault in Texas

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Originally Posted by david s View Post
In kiln construction the end walls on a barrel vault should be inside the arch. If outside the arch steel bracing is used to prevent the end walls from tending to fall out. A large diameter arc exerts considerable lateral force at its base, a semicircle much less so and a catenery arch the best, although only if its base is about the same as its height. We are not building kilns so the temp extremes are not as destructive but the principles are the same.
If the barrel vault is a semi circle the lateral force at the base is very small, i don't think you have a problem. Where it can be a problem is when it is an arc of a larger diameter sitting on top of walls. Whether you cut bevels or rely on mortar to fill the gaps will not alter the forces on the arch. However if the mortar falls out (unlikely) then you lose the strength of the arch form.

Last edited by david s; 07-10-2011 at 05:25 PM.
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Old 07-10-2011, 05:01 PM
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Default Re: My Modified Barrel Vault in Texas

Yeah, that was my original premise. Soldier courses are an accommodation to a flatter, catenary vault to raise the vault ceiling. A semicircular arch doesn't need any more height. Using heatstop refractory cement as a glue- 1/8 to 3/16 joints- makes the joined bricks virtually monolithic.
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Old 07-11-2011, 05:38 AM
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Default Re: My Modified Barrel Vault in Texas

"A running bond does not a stronger arch make. Each brick in any arch is bonded on every side to another brick or two. What a running bond provides is a greater number of individual or different bricks- 6 instead of 4- for any given brick to be attached to. Look at any brick in a wall and count the number of bricks it has contact with and you'll see what I mean. A running bond simply makes the failure of any individual joint less catastrophic."

I apologize to all for the foregoing drivel. Don't know what I was thinking. After I posted it, I got to thinking about my carpentry and realized that a running bond is the masonry analog to the finger joint in carpentry which, when compared to the butt joint, is stronger by orders of magnitude. Sorry for the nonsense. A running bond is preferable to a stacked bond (or whatever the thing is called).
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Old 07-12-2011, 12:43 PM
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Default Re: My Modified Barrel Vault in Texas

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Originally Posted by wotavidone View Post
Had to look catenary arch up on wiki today. There was a complicated mathematical formula to explain that it is the curve formed when you hang a length of chain between two points. too hard for me
Here is more about why arches work and fail, its easy to understand.

Auroville Earth Institute


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Old 07-12-2011, 02:13 PM
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Default Re: My Modified Barrel Vault in Texas

The Pantheon in Rome apart from being breathtaking internally is incredibly ingenious. To make the dome lighter in weight as it rose towards the top a lightweight aggregate was used progressively for the concrete mix. They used pumice, a volcanic rock, and had it carted from Pompeii to Rome, hundreds of kilometers away (lucky they had slaves). These ancient Romans knew their stuff, about architecture and labour management.
http://www.aviewoncities.com/rome/pantheon.htm
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