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  #221  
Old 01-24-2014, 08:28 PM
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Default Re: OctoForno

Quote:
Originally Posted by Campmaki View Post
I guess I just figured that one out!!!!


Abutments
An arch abutment can be a column, wall or combination of wall and shelf angle. Failure of an abutment occurs
from excessive lateral movement of the abutment or exceeding the flexural, compressive or shear strength of the
abutment. Lateral movement of the abutment is due to the horizontal thrust of the arch. Thrust develops in all
arches and the thrust force is greater for flatter arches. The thrust should be resisted so that lateral movement of
the abutment does not cause failure in the arch. If the abutment is formed by a combination of brickwork and a
non-masonry structural member, rigidity of the non-masonry structural member and rigidity of the ties are very
important. Adjustable ties or single or double wire ties are recommended. Corrugated ties should not be used in
this application because they do not provide adequate axial stiffness. Consult Technical Notes 31A for further
discussion of abutment and tie stiffness requirements.
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  #222  
Old 01-24-2014, 08:30 PM
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Default Re: OctoForno

[QUOTE=Campmaki;168640]Abutments
An arch abutment can be a column, wall or combination of wall and shelf angle. Failure of an abutment occurs
from excessive lateral movement of the abutment or exceeding the flexural, compressive or shear strength of the
abutment. Lateral movement of the abutment is due to the horizontal thrust of the arch. Thrust develops in all
arches and the thrust force is greater for flatter arches. The thrust should be resisted so that lateral movement of
the abutment does not cause failure in the arch. If the abutment is formed by a combination of brickwork and a
non-masonry structural member, rigidity of the non-masonry structural member and rigidity of the ties are very
important. Adjustable ties or single or double wire ties are recommended. Corrugated ties should not be used in
this application because they do not provide adequate axial stiffness. Consult Technical Notes 31A for further
discussion of abutment and tie stiffness requirements.[
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  #223  
Old 01-25-2014, 02:26 AM
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Location: Australia
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Default Re: OctoForno

there seems to be an echo

Like the information I too built the same type of arch as John. We discussed this a bit a hemispherical arch is much stronger for those reasons you have highlighted.
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  #224  
Old 01-25-2014, 04:31 AM
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Default Re: OctoForno

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Originally Posted by oasiscdm View Post
there seems to be an echo

Like the information I too built the same type of arch as John. We discussed this a bit a hemispherical arch is much stronger for those reasons you have highlighted.
You mean a semicircular arch, Colin

The height of the pier which a segmental arch springs from is the real point of weakness. Most of the segmental arches built on here have sufficient thickness/ height ratio in the pier to worry about hinge failure, because the don't support that much load weight. A lot of builds here have buttressed the pier, creating and abutment, removing any possibility of overloading the arch.
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  #225  
Old 01-25-2014, 05:52 AM
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Default Re: OctoForno

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Originally Posted by stonecutter View Post
You mean a semicircular arch, Colin

The height of the pier which a segmental arch springs from is the real point of weakness. Most of the segmental arches built on here have sufficient thickness/ height ratio in the pier to worry about hinge failure, because the don't support that much load weight. A lot of builds here have buttressed the pier, creating and abutment, removing any possibility of overloading the arch.
I guess I was not giving my full thought on this issue. I think the shorter side walls need to backed up with at least a 4 inch block. there might not be an issue when using a metal chimney, but what about a clay flue liner. This adds some extra weight and downward pressure to the arch.
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  #226  
Old 01-25-2014, 07:20 AM
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Default Re: OctoForno

Quote:
Originally Posted by Campmaki View Post
I guess I was not giving my full thought on this issue. I think the shorter side walls need to backed up with at least a 4 inch block. there might not be an issue when using a metal chimney, but what about a clay flue liner. This adds some extra weight and downward pressure to the arch.
If the spans were greater than 24", had tall piers, and have 12" flues maybe, but the outer arch you are concerned about doesn't carry 100% of the load anyway. With the oven opening arch as part of the system, strength is further gained by the vent being constructed in a way so that it functions like a vault, even though it technically isn't one. It provides plenty of structural mass to support itself, and a few flues.

BTW, I was talking about loading the arch with several clay flues, not metal ones.

Just so I'm clear, I am not saying a segmental arch is as strong as a semicircular one. Only that building an abutment ( or buttressing as referred to on the forum) is not necessary in most cases and is over building. It's not a design flaw to omit it, but it is good insurance, and there is nothing wrong with that.
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Last edited by stonecutter; 01-25-2014 at 08:19 AM.
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  #227  
Old 01-25-2014, 08:34 PM
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Default Re: OctoForno

Quote:
John, I have been wondering about an issue I see with some of the builds on here. Being a mason by trade, what I see that concerns me is the construction of the entries on some builds. I believe the stronger entry is the type you built, where the arch starts right at the floor. I see some where a short height side wall is built then a shallow arch connects the two short height walls. My thinking is that this could over time collapse. These brick side walls are not tied back into the dome structure itself
Interestingly, I had this same concern and abandoned my original plan which included the conventional 5.5" soldier course in the dome and a four-deep vertical-walled entryway. This was based on my readings of Forces Acting in Arches and Vaults, which can be found here:

Auroville Earth Institute

However, after my I completed the masonry portion of my oven, I totally agree with Stonecutter, and that a number of these forces are not significant, at least in the scale that our ovens occupy.

With zero prior building experience, I tried to apply to my build every sound principle I could learn, including lines of thrust, not only in the dome, but also in the archway design which is also semi-circular. Because of the heatbreak, my entryway is essentially it's own separate, smaller vault, which has no additional buttressing to support the weight of its flue (unlike the oven arch that is tied into the oven itself).

I applaud your interest in applying sound principles in overcoming gravity and predictably, heat transfer. I too, was critical of every element (I could think of) I observed in previous FB builds and tried to envision a better approach. I think this kind of scrutiny is what makes for the evolution of WFO's and with the collective's contributions, result in viable improvements.
SCChris likes this.

Last edited by GianniFocaccia; 01-25-2014 at 08:36 PM.
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  #228  
Old 01-26-2014, 11:24 AM
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Default Re: OctoForno

Quote:
Originally Posted by GianniFocaccia View Post
Interestingly, I had this same concern and abandoned my original plan which included the conventional 5.5" soldier course in the dome and a four-deep vertical-walled entryway. This was based on my readings of Forces Acting in Arches and Vaults, which can be found here:

Auroville Earth Institute

However, after my I completed the masonry portion of my oven, I totally agree with Stonecutter, and that a number of these forces are not significant, at least in the scale that our ovens occupy.

With zero prior building experience, I tried to apply to my build every sound principle I could learn, including lines of thrust, not only in the dome, but also in the archway design which is also semi-circular. Because of the heatbreak, my entryway is essentially it's own separate, smaller vault, which has no additional buttressing to support the weight of its flue (unlike the oven arch that is tied into the oven itself).

I applaud your interest in applying sound principles in overcoming gravity and predictably, heat transfer. I too, was critical of every element (I could think of) I observed in previous FB builds and tried to envision a better approach. I think this kind of scrutiny is what makes for the evolution of WFO's and with the collective's contributions, result in viable improvements.
Thanks to the two of you for your input on the "thrust" issue. I just do not want a failure to occur. I have built plenty of arches during my career as a bricklayer, whether it be stone, brick or even cmu. From veneers on buildings to fireplaces, it seems we always had some sort of "buttressing". In my mind I would go that little extra to support the sidewalls , just to be on the safe side. Just an added note to this subject, On projects with arches, such as a brick veneer, you have brick laid above the arch which adds more support .
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  #229  
Old 01-26-2014, 01:10 PM
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Default Re: OctoForno

Quote:
Originally Posted by Campmaki View Post
On projects with arches..... you have brick laid above the arch which adds more support .
This is not a correction, but a clarification for anybody following this or have an interest in arch physics...


The weight of the masonry around an arch does not act in support. It contains load thrust, while the weight above the arch and the thrust line stabilizes the abutment.

The blah,blah,blah aside, from a strictly aesthetic point of view, I like a semi better than a segmental arch any day.
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  #230  
Old 01-26-2014, 05:27 PM
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Default Re: OctoForno

Quote:
The weight of the masonry around an arch does not act in support. It contains load thrust, while the weight above the arch and the thrust line stabilizes the abutment.
Kind of like this? From what I've read, I believe the forces of water pressure on the arc of the dam actually cause it to compress, making it stronger.

Quote:
from a strictly aesthetic point of view, I like a semi better than a segmental arch any day
Me too!
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