Soldier- beveled or no?

[BeanAnimal]

Re: Soldier- beveled or no?

I don't disagree at all cheese... If my explanation implied differently then it was due to poor wording on my part

[lwood]

Re: Soldier- beveled or no?

Nice example Cheese. Agreed, it's primarily academic. We can use my 60" low-dome as a test case. No buttressing, red clay fire-brick and a solider course extending 2" above the hearth, covered with 4 inches of 5-1 unexpanded perlite.

My feeling is that the red clay fire-brick would fail long before the aluminized fire-brick. so mine should be the worst case. This discussion has gotten me nervous about my dome, especially anyone climbing on it. I don't worry, so much, about the static forces. It's any sudden loads may be a problem. No cracks so far, so good. I need to add another layer of vermiculite before finishing. So am going to be careful. It did support one small Filipino mason during the insulation layer installation.

I think the insulation layer itself also provides some structural support.

Overall, I think the idea of buttressing is a good idea over say 42" dia. But less than that it's a bit over-kill.

[Cheesesteak]

Re: Soldier- beveled or no?

It may help for those having trouble with the physics to take a simple cross section of the dome, through its peak. You end up with an arch. The dome is (for the most part) an arch rotatated around an axis and the forces act in the same manner with regard to the legs and base. The strenght of the vertical legs must be sufficient to prevent the arch from spreading or toppling the legs. Any joint in the arch or legs should be at an angle (or of sufficient strength if not) that resists the forces acting upon them.

When the leg and/or joint is of sufficient strength to be static, then the force is counteracted and the load (mass) is transfered to the bearing surface. The difference between the truncated dome and the perfect half sphere are somewhat ambiguos in this case, as the entire dome is made of stacked chains of brick. The angled joint atop the soldier course does help to counteract the outward thurst of the arch, so long as the soldier course is held in place and prevent from sliding outward.

In any case, I don't see many failed domes, so the entire subject would appear to be more academic than important to our projects

I agree with most of what you have here - except that the loads are transferred vertically. The arch load pushes down and out. See here for a basic illustration: Arch Loading

If the arch simply pushed "down," there would be no need to mortar the "soldier" course in place. The reason it needs to be mortared to to provide some resistance against the outward force caused by the arch. The bigger (higher, heavier) the arch - the more buttressing needed.

Buttressing . . .

[BeanAnimal]

Re: Soldier- beveled or no?

In the past, we used to go to Gobblers Knob and watch Phil while drinking beer. Much has changed with the event over the years and it, for lack of better words, is just not much fun anymore

I hope to start the foundadtion this coming week if the weather holds. Due to the heavy clay, I need to be able to dig the footers, pour, stack and backfill without rain or my excavation will fill with water and NEVER drain unless I pump it out

[azatty]

Re: Soldier- beveled or no?

I did a half soldier course for the first chain. Though not a perfect arch, it "felt" better to me, and I think my thrust is still within acceptable limits. My entry arch is a different matter. I'm buttressing that thing.

Brickie trivia: a brick is called a "soldier" when it stands upright with narrow side ("stretcher") facing out. It is called a "sailor" when it stands upright with the wide side facing out. That's why it's called the "soldier course.". I'm amazed at all the masonry lingo and trivia I've picked up working on this project.

[lwood]

Re: Soldier- beveled or no?

Bean, good discussion on this subject, thanks for bringing it up. Did Phil see his shadow this year, you should be starting soon...

[BeanAnimal]

Re: Soldier- beveled or no?

I think I would agree that the need for lateral support on a 30" dome is much less of an issue. These are not "sprung" structures and instead the forces at play are a simple function of mass. Larger structures have more arched mass and therefore concentrate more force at their moorings.

I would also fully agree that the ideal situation is preventing the first chain (soldier course) from sliding or tiping instead of trying to anchor a flat course above it and relying on a mortar joint to hold. As you indicate, the larger the dome, the more important this point becomes.

All of this talk of domes and am I still yet to break ground. Soon my friends... soon...

[lwood]

Re: Soldier- beveled or no?

If the soldier course is beveled, then the course above it will tend to want to tilt it outward, or force it to slide if it can. The bevel locks the second chain in place, transfering all of the force to the soldier course. Reinforcing he soldier course locks everything into place.

The only benefits I see of having a full 9" (or close too) height on the first chain is to create more floor space, especially on a low dome that narrows quickly, especially on a dome that is built AROUND the floor instead of on it.

Agreed, I believe the soldier course locks the dome into place and reinforcement around the soldier course is the safest method. Primarily because with the lateral forces pushing on brick as apposed the mortar joint, I think the solid brick would win a shear test. The lateral forces are the same no mater the configuration, so yes the soldier course has a tendency to be pushed out. Thus the need for abutment at the soldier course.

Because of my experience with my 60" oven I don't really think you start needing abutment until you get over 30" dia. I have gotten away with no reinforcement so far. But now that I know better, I wouldn't recommend it to anyone.

[tmarsala]

Re: Soldier- beveled or no?

I used 1/2 bricks for my soldier course. Not much movement one year later and I slam my oven regularly with 1400-1600 degree firings at the max. The only movement so far was along one side of the dome where my 1/2 bricks weren't overlapping well-only about an 1/8 inch gap or so. I didn't even consider NOT using a soldier course.

Tom

[BeanAnimal]

Re: Soldier- beveled or no?

It may help for those having trouble with the physics to take a simple cross section of the dome, through its peak. You end up with an arch. The dome is (for the most part) an arch rotatated around an axis and the forces act in the same manner with regard to the legs and base. The strenght of the vertical legs must be sufficient to prevent the arch from spreading or toppling the legs. Any joint in the arch or legs should be at an angle (or of sufficient strength if not) that resists the forces acting upon them.

When the leg and/or joint is of sufficient strength to be static, then the force is counteracted and the load (mass) is transfered to the bearing surface. The difference between the truncated dome and the perfect half sphere are somewhat ambiguos in this case, as the entire dome is made of stacked chains of brick. The angled joint atop the soldier course does help to counteract the outward thurst of the arch, so long as the soldier course is held in place and prevent from sliding outward.

In any case, I don't see many failed domes, so the entire subject would appear to be more academic than important to our projects

[RTflorida]

Re: Soldier- beveled or no?

I have no clue if what I did was good, bad, or indifferent to my dome structure but it worked for acheiving the dimensions I was shooting for.
I did a shortened soldier course with bevel. Not sure of the exact dimensions, but I believe the inner edge was around 5 3/4" and the outer around 6 1/2". At the time, a soldier course was the norm, in the plans, and nearly everyone was doing it. I remember reading a thread or two about using a bevel for the exact reason I chose - achieve a specific height and keep the outer mortar joints to a minimum.
Based on my dimensional goals of 36" int. diameter, 18" interior height, the odd dimensions of my firebricks (roughly 2 1/4 x 3 7/8 x 8 3/4), and no horizontal exterior mortar joints greater than 1/4", I came up with the 5 3/4 x 6 1/2" (again, my memory may not be exact) bevel. No advanced geometry, no CAD programs; I simply spent about an hour laying out bricks on my garage floor until I had the dimensions I wanted.
In the end, my diameter was exactly 36", no mortar joints were over 1/4", but I was off by 1/8" at the very top center height...came in at 18 1/8". As for structure, never had any interior cracking and on the exterior only a recurring arch crack, which I eliminated last year when I completely refinished the exterior.

RT

[dmun]

Re: Soldier- beveled or no?

the weight of the dome is tranferred directly downward through the soldiers, eliminating the side thrust

I'm not convinced of this. I think the forces exist in a given dome shape pretty much independent of the brick arrangement. I think the problem with a full-height soldier course is the "corner" not whether the bricks are laid flat or upright.

Time for the auroville earth institute dome force tutorial again...

[GianniFocaccia]

Re: Soldier- beveled or no?

So the "soldier course" if not beveled, with a truncated sphere resting on it will transfer the weight down towards the floor

This point is quite interesting. I recently saw some photos of an Italian Pompeii-style oven manufacturer who used a hoist to lower a separately-built truncated dome onto soldier-like oven walls. My assumtion is that with this configuration, the weight of the dome is tranferred directly downward through the soldiers, eliminating the side thrust and transferring stresses directly to the upper dome portion itself.

John

[BeanAnimal]

Re: Soldier- beveled or no?

The "soldier course" is just another name for the first chain. Just becuase the bricks have narrow faces and stand a bit taller does not change the physics of the dome significantly. I suspect we call it a soldier course simply due to the way it looks.

In theory, any truncated dome (one that is not a complete half sphere) will have lateral forces at the acting on the chain at the floor interface. Any complete half sphere (again in theory) would have no lateral forces at the floor interface.

So the "soldier course" if not beveled, with a truncated sphere resting on it will transfer the weight down towards the floor. The chain above it will want to spread outward. The strength of the bond may or may not put lateral force on the soldier course. Adding reinforcement to the soldier course may, or may not prevent movement depnding on the bond strength to the chain above it.

If the soldier course is beveled, then the course above it will tend to want to tilt it outward, or force it to slide if it can. The bevel locks the second chain in place, transfering all of the force to the soldier course. Reinforcing he soldier course locks everything into place.

The only benefits I see of having a full 9" (or close too) height on the first chain is to create more floor space, especially on a low dome that narrows quickly, especially on a dome that is built AROUND the floor instead of on it.

[lwood]

Re: Soldier- beveled or no?

The larger the oven dia the more importance of having reinforcement. Especially for low-dome ovens. I believe that is why Ferera does it. There is a big lateral force pushing out and it's concentrated at the floor or the seam you create with a solder course. I am frankly surprised my oven hasn't collapsed yet. My oven is a Low-dome 60" dia with red-clay fire-brick, no abutment reinforcement and unexpanded perlite 5-1 mix insulation. It works great but I fully expect it to collapse some day. Then I get to build it back correctly. This oven was basically a proof of concept and using what ever materials I could get at the time. Non the less.....it works great.

Personally I think there is an argument for a soldier course with a bevel. It eliminates the horizontal seam created at floor level. If the dome has any slight inflection point, which it will, the lateral force is allowed to slide on the seam resulting in a crack. With a soldier course, the lateral force is transfered through the fire-brick to the floor....rather than the seam. the dome sits securely on the soldier course bevel. I'm not suggesting that no abutment is required but that the soldier-course configuration is more stable. IMHO