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-   -   How much weight can an entry arch support? (http://www.fornobravo.com/forum/f28/how-much-weight-can-entry-arch-10625.html)

kebwi 01-27-2010 10:40 AM

How much weight can an entry arch support?
 
I am quite torn on chimney design. I had purchased what I thought was an 8" interior (10" exterior) double-walled pipe (Duratech I assume) in two two foot sections locked and caulked together into a four foot pipe. My intention had been to take it apart and use one section. Upon cleaning the caulk I determined that it is a single four foot pipe, which will look absolutely ridiculous on my current design and will represent a significant wind-hazard without proper support.

I am also considering building my chimney out of flue tiles or out of fire brick...which leads to my question. If I build a chimney out of full bricks, about four bricks per layer, edge-on (4.5" high), then I need about six layers to get a two foot chimney, or about 24 bricks, which is around 175 lbs. Would an entry arch with a big hole in the top (the vent) support that kind of weight? I'm trying to picture myself standing on my vent (I'm about 160) and standing there forever, not just a minute. I don't know if my entry arch would support that kind of weight for years...or maybe it would, I don't know.

Related question, if I built a chimney out of splits on edge (4.5" tall but only 1.25" thick) would that stand up six layers without being at risk of collapse? It seems like a rather thin wall for such a height. How might that be accomplished, or are thick walls necessary a two foot tower?

Finally, on a related topic, although unspecified in the thread subject, if I go with flue tiles, I could build a brick facade around it with much lighter bricks, but only if nonfire bricks could be used in such an application. Since the clay flue is totally uninsulated, a lot of heat will hit the facade bricks, even after I leave a 1/2" gap for expansion and general adaptiveness...so the question here is: COULD nonfirebricks be used to facade clay flue liners at all, or must it be fire bricks to bear the heat?

To sum up:
  • Will a Pompeii-style (or see the arch pics in my build thread) vent-and-arch support 175 lbs (call it 200 once a cap is in place)?
  • Can a clay-clue chimney be facaded with nonfirebricks considering the heat that will certainly transmit through the clay and the gap to the facade?

Sorry for the long post.

kebwi 01-27-2010 10:42 AM

Re: How much weight can an entry arch support?
 
1 Attachment(s)
Here's a picture of my arch. Would that bear 200 lbs? It's a hard thing to promise I understand.

dmun 01-27-2010 12:29 PM

Re: How much weight can an entry arch support?
 
Quote:

Here's a picture of my arch. Would that bear 200 lbs?
I think yes. The stresses seem to be fairly well distributed to the outside of the arch, and I think the round arch is stronger than the shallow arch on top of side walls.

The duravent would make a fine chimney liner, as long as you have it already. (I wouldn't suggest buying it for that purpose.) You could brick it up with standard bricks just like you would a tile lined one. I'd keep the same air space you would with a flue tile.

kebwi 01-27-2010 12:35 PM

Re: How much weight can an entry arch support?
 
Here's the rub: My vent footprint is 12" deep, about 14" wide. Place a 10" pipe on that and I have 1" to spare front and back. I don't how to brick around that, especially with a gap.

Tscarborough 01-27-2010 12:53 PM

Re: How much weight can an entry arch support?
 
If the arch fails, it will because because the legs kick out. Can you add more mass to the bottom of the arch?

You can use regular brick to surround either the metal pipe of the clay, but leave a slight airspace for the clay flue.

kebwi 01-27-2010 12:57 PM

Re: How much weight can an entry arch support?
 
So, if I may paraphrase to make sure I understand, Tscarborough doesn't think there is much risk of the ceiling of the arch collapsing inward (downward), but rather from the sides of the arch "exploding" outward, such that a thicker "buttress" wall wrapped up the sides might offer support? Is that correct?

I do realize that the structural issue with a hemispherical arch is that (relative to a catenary) the sides are two "wide" and are prone to being pushed outward.

Just verifying. You don't think my ceiling will collapse? It's admittedly a little thin...three inches where many FB ovens have thicker arches.

I can certainly add a layer of brick wrapped up the sides of the arch.

Tscarborough 01-27-2010 01:00 PM

Re: How much weight can an entry arch support?
 
That is correct. 3" of masonry is plenty strong for the weight, the question is if the arch can support the load, and it probably can already, but why push it?.

Tscarborough 01-27-2010 01:05 PM

Re: How much weight can an entry arch support?
 
1 Attachment(s)
This is why I notched in the arch on mine, as well as laid 2 courses of full size firebrick on my timbrel arch.

kebwi 01-27-2010 01:08 PM

Re: How much weight can an entry arch support?
 
Hmmm, so, I believe it is important to insulate the arch and vent, either to get better draw or to prevent general heat loss (or both). If I add brick on the outside of the arch for additional strength, it stands to reason that I must do so before (below) the soft insulation layer (InsWool). Are there no issues there? For example.

Must all brick that is "inside" the insulation be firebrick?

Will making the thermal mass of the arch extremely wide (thick) have any other implications? Heat-up time? Quantity of wood required per session? Anything weird like that?

kebwi 01-27-2010 01:10 PM

Re: How much weight can an entry arch support?
 
Man, you command a mean vocabulary. Your posts always send me to google to see what your latest term means. :)


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