Arch Top Bell- how flat can it be?

Hello Folks,

I have never laid up an arch before in brick, So if  you look at the line drawing with measurements, you will see this has a 6" high arch, Only the side brick, and the two key stone brick will require a bit more cutting. (not much)   All will be thick fire brick (2.5")

As you will notice, these will always be in compression on the mortar joints, (worked for the Romans) and pizza ovens, but I have not seen this flat.

This is for a single bell, no deviations, from general sizing specs, fire brick used from top of the batch box riser, to the top of the bell, including the key stones (see that there are two flat laid key stones, not one large one. everything below this, is full size clay brick (actually a larger than standard clay brick that I have over 1000 of)  

I building what WORKS, on the batch box, no size dimension changes.  

MY ONLY question is,      <CAN I get by, with this flat of an arch, and feel comfortable that it will last 20 years. ?>

thank you in advance.

Hi Scott;
I love the look of a brick arch!
I have not yet built one (but I will)  so my answer has no backing of experience.
A taller arch would produce more downward pressure than a low arch.
A low arch might want to push outwards.
Hopefully, a more experienced masonry person will chime in and give us the answer.

Myself, I would build it.
Then just keep a watch that it is not spreading your wall's apart.
If it starts moving then build a frame for it.

We have built 15 arches and false arches. in our house, barn, gate. Segmental, three-centered, pointed, horseshoe, pointed horseshoe.
Abutment (the walls on the sides of the arch) should be at least 1/4 thickness of the span of the arch. In your case it does not exist. Also, the arch should be loaded from above unless it is considered a flying arch (it has to have sufficient weight in this case). Arch without a top load may develop cracks in the joints - I'm seeing it in my 3 centered arch for the barn gate. It's still waiting for concrete bond beam that will load the arch.

Arch without abutment will crack a lot especially with the help of heating/cooling cycles of the heater.
I was thinking about such a solution a lot - because as you can see I love masonry structural arches. The heater walls are rather too delicate to sustain the arch load. Even if the wall is built from bricks laid on shiners it still makes the walls too thin and also the joints are made of weak clay mortar.
Also the flatter the arch - the greater force acts on the abutment. I saw one build in France with a semicircular arch used as the roof of the batchbox but I suspect it to be not the best solution unless substantial abutment walls were added.

The round/semi-circular arch will have the most equal distribution of forces. The pointed/gothic arch is the strongest for the given thickness and the parabollic one is even better in this regard (used a lot by Antonio Gaudi). Flat arches have issues even in buildings with massive abutment walls - I saw many examples.

In my opinion the best solution for the ceiling of the bell is the Peter van den Berg's Mallorca build (bricks on shiners on T-bars) or bricks on headers suspended on steel rods going through the holes in them.

Cristobal Cristo wrote:
Abutment (the walls on the sides of the arch) should be at least 1/4 thickness of the span of the arch. In your case it does not exist.
SW- So, if I am reading this correctly, A frame to resist bowing out the walls, would be in order.

Also, the arch should be loaded from above unless it is considered a flying arch (it has to have sufficient weight in this case).
SW So the weight of the fire brick is NOT considered enough weight? to put the arch in compression?

Arch without a top load may develop cracks in the joints - I'm seeing it in my 3 centered arch for the barn gate. It's still waiting for concrete bond beam that will load the arch.
SW- I don't know if this part pertains to my build or not, if I was to build, and need more weight, simply adding more to the arch will certainly supply more weight? That was/is my purpose for asking.

Arch without abutment will crack a lot especially with the help of heating/cooling cycles of the heater.
SW- Adbutment? Are you meaning the sides may move in and out, thus allowing cracks to form, if so, a frame can be done.

. The heater walls are rather too delicate to sustain the arch load. Even if the wall is built from bricks laid on shiners
SW- what does the word "shiner"in this case mean?  My walls are almost 5.5" thick

it still makes the walls too thin and also the joints are made of weak clay mortar.
SW- no weak clay mortor used on this, Brick mortor on all brick joints, Fire brick motor on all fire brick.

Also the flatter the arch - the greater force acts on the abutment.
SW- back to my original question, "How flat is to flat? With double the arch height, and same basic compression, my loads go down almost strait down (or so I was thinking)


The round/semi-circular arch will have the most equal distribution of forces. The pointed/gothic arch is the strongest for the given thickness and the parabollic one is even better in this regard (used a lot by Antonio Gaudi). Flat arches have issues even in buildings with massive abutment walls - I saw many examples.
SW- all good things to think about, if I had unlimited space, which I do not, thus I inquired about how flat was to flat.

In my opinion the best solution for the ceiling of the bell is the Peter van den Berg's Mallorca build (bricks on shiners on T-bars) or bricks on headers suspended on steel rods going through the holes in them.

I will have to wait to understand the term "shiners"  The T bars I understand, but is this 1/4" angle back to back to get the T-bars or thicker yet,  And can we wrap these good enough to avoid the destruction from heat?    So you can see, I have learned just enough to know,  that I don't know.  ;-)

On shiners - means that they are laid flat.
Actually wrapping them may be counter effective. You want the heat from the T-bars to go to the bricks positioned above - they work as heat sink. T-bars 1.5x1.5" should be sufficient. Thickness min 4.5mm (3/16"). Regular steel works. I'm going to use either 316 or RA330 - I like things that last.

Hi,

Not a Structural Engineer and no experience with arches, but:

Both arches will put the same amount of vertical load into the base. The flatter arch will carry more put more outward lateral ('thrust') load into the base. You may want to reinforce the sides ('abutments') to react the additional thrust. How much? I could help with this, or there may be tables online.

Think of it this way: Arches are effective because they carry load in hoop compression (which is efficient) rather than bending (which is inefficient and produces tension - bad for brick). Depending on how rigid the structure is, as the arch gets flatter it will either generate more thrust or start to behave like a beam in bending (bad).

Let me know if you would like more help!

Daniel Vogel wrote:Hi,

Not a Structural Engineer and no experience with arches, but:

Both arches will put the same amount of vertical load into the base. The flatter arch will carry more put more outward lateral ('thrust') load into the base. You may want to reinforce the sides ('abutments') to react the additional thrust. How much? I could help with this, or there may be tables online.

Think of it this way: Arches are effective because they carry load in hoop compression (which is efficient) rather than bending (which is inefficient and produces tension - bad for brick). Depending on how rigid the structure is, as the arch gets flatter it will either generate more thrust or start to behave like a beam in bending (bad).

Let me know if you would like more help!

Thanks Dan,  here is my plan
AS most have seen, I can draw up just about anything (view) to calculate the needs. That way I can verify it can be built. (most of the time) Then onto the calculations for loads and so on.   If I can make the suggested T-bars work, that would be the simplest, but because of the size of this stove bell, I was in great hopes, someone has done and used extensively over the course of a full season or more.  As of yet, I have not found this to be true for a single bell, 7" size.

So in the mean time, I will keep laying up the bell and batch stove, as I know and trust the specs for both of those.

cheers
Scott

Scott,

What is the black rectangular structure below the arch on your drawing?

Cristobal Cristo wrote:Scott,

What is the black rectangular structure below the arch on your drawing?

It was suggested that I use fire brick from the top of the riser, to the top of the bell,  This is 2.5" on edge, vs the lower brick (brick look) of standard brick, thus the grey (black) look from the point up to the arch.

I thought it was some thick black steel frame that in theory could hold a quite flat arch.
In case of upper part of bell laid on stretchers it would have even less abutment. Now I can also see that it's a standard bell over 7" batchbox. Blowing hot exhaust on the bottom of the arch with almost no abutment and not built from arch bricks (tapering) with uneven joint thickness is not something that would last 20 years or even one. Also the arch is part of the hot part of the bell and in theory even if abutment was erected in the form of the outer layer of the bell it would be probably separated with insulative material that would not be able to transfer the load to the abutment.  The only way I see it possible to work would be to build the walls 1 brick wide (9" thick) and they would resist the spreading force - like in commercial bread ovens with 9" walls for heat storage, 8" of insulation and then outer wall. It would make the masonry heater way too unresponsive and too heavy.

Cristobal Cristo wrote:I thought it was some thick black steel frame that in theory could hold a quite flat arch.
In case of upper part of bell laid on stretchers it would have even less abutment. Now I can also see that it's a standard bell over 7" batchbox. Blowing hot exhaust on the bottom of the arch with almost no abutment and not built from arch bricks (tapering) with uneven joint thickness is not something that would last 20 years or even one. Also the arch is part of the hot part of the bell and in theory even if abutment was erected in the form of the outer layer of the bell it would be probably separated with insulative material that would not be able to transfer the load to the abutment.  The only way I see it possible to work would be to build the walls 1 brick wide (9" thick) and they would resist the spreading force - like in commercial bread ovens with 9" walls for heat storage, 8" of insulation and then outer wall. It would make the masonry heater way too unresponsive and too heavy.

Cristo, thank you for your reply, and that makes a lot of sense. I am glad I asked.  I have not built up to this level (height) yet, so no problems have been built in.

thanks again.
Scott

Scott Weinberg wrote:

Daniel Vogel wrote:Hi,

Not a Structural Engineer and no experience with arches, but:

Both arches will put the same amount of vertical load into the base. The flatter arch will carry more put more outward lateral ('thrust') load into the base. You may want to reinforce the sides ('abutments') to react the additional thrust. How much? I could help with this, or there may be tables online.

Think of it this way: Arches are effective because they carry load in hoop compression (which is efficient) rather than bending (which is inefficient and produces tension - bad for brick). Depending on how rigid the structure is, as the arch gets flatter it will either generate more thrust or start to behave like a beam in bending (bad).

Let me know if you would like more help!

Thanks Dan,  here is my plan
AS most have seen, I can draw up just about anything (view) to calculate the needs. That way I can verify it can be built. (most of the time) Then onto the calculations for loads and so on.   If I can make the suggested T-bars work, that would be the simplest, but because of the size of this stove bell, I was in great hopes, someone has done and used extensively over the course of a full season or more.  As of yet, I have not found this to be true for a single bell, 7" size.

So in the mean time, I will keep laying up the bell and batch stove, as I know and trust the specs for both of those.

cheers
Scott

I attached two images.

In the first one I indicate in blue a few likely points of potential failure.

In the second I calculate the lateral thrust load as a function of the applied load, FY, the arch height, h, and arch span, c.

Daniel Vogel wrote:

Scott Weinberg wrote:

Daniel Vogel wrote:Hi,

Not a Structural Engineer and no experience with arches, but:

Both arches will put the same amount of vertical load into the base. The flatter arch will carry more put more outward lateral ('thrust') load into the base. You may want to reinforce the sides ('abutments') to react the additional thrust. How much? I could help with this, or there may be tables online.

Think of it this way: Arches are effective because they carry load in hoop compression (which is efficient) rather than bending (which is inefficient and produces tension - bad for brick). Depending on how rigid the structure is, as the arch gets flatter it will either generate more thrust or start to behave like a beam in bending (bad).

Let me know if you would like more help!

Thanks Dan,  here is my plan
AS most have seen, I can draw up just about anything (view) to calculate the needs. That way I can verify it can be built. (most of the time) Then onto the calculations for loads and so on.   If I can make the suggested T-bars work, that would be the simplest, but because of the size of this stove bell, I was in great hopes, someone has done and used extensively over the course of a full season or more.  As of yet, I have not found this to be true for a single bell, 7" size.

So in the mean time, I will keep laying up the bell and batch stove, as I know and trust the specs for both of those.

cheers
Scott

I attached two images.

In the first one I indicate in blue a few likely points of potential failure.

In the second I calculate the lateral thrust load as a function of the applied load, FY, the arch height, h, and arch span, c.

This certainly puts the science into the "rocket science" part of the stove.  Thank you.