i believe i staved off what could have been truly catastrophic today...
i mentioned in a previous thread about how my arch header above my oven opening had creeped forward as everything settled into place. today i came out to the oven and noticed that one of the top two pieces of my header (the keystones, essentially) had wiggled loose, and when i touched it, it dropped an inch! it's tapered, so it couldn't fall all of the way out, but somehow, the pressure had obviously shifted off of what should have been a very load-bearing brick.
bear in mind that the entire weight of the front of the dome rests on this header. somehow, i managed to slip my arch form (good thing i still have it!) back in, and remove the brick. i slathered it up really good with mortar and slipped it back into place. after pointing mortar into every remaining gap as well as possible, i removed the form and it is standing strong (i hope) again.
the moral, i believe, is that if anyone else uses an arch design for their doorway in the future, they should make sure to adequately compensate for lateral thrust of the top of the dome against it. i will bolster mine up, and hopefully my dome won't crumble....
...please dome, don't crumble!!!!
another lesson to learn from this, would be to perhaps make more of a curved arch, rather than the sharp-cornered version i made, which is similar in shape to to the angle iron header. this would transfer the load down more quickly, alleviating the lateral load on the top part of the arch.
Near Catastrophe and angle iron profile
(M) Paul, you wrote:
"another lesson to learn from this, would be to perhaps make more of a curved arch, rather than the sharp-cornered version i made, which is similar in shape to to the angle iron header. this would transfer the load down more quickly, alleviating the lateral load on the top part of the arch."
(M) I was with you until you mentioned a version 'which is similar in shape to the angle iron header'. I visualized your igloo throat arch as something like |*| with the asterisk representing the arc of a circle. I understood that you would have changed that to more like ^ so that the stresses would have been more vertical rather than strongly horizontal. What I did not get was how the shape of the angle iron relates to that. Can you clarify?
the shape of my header is similar to the rectangularish version made by using angle iron to span the top of the opening. i was doing this to ensure proper venting and accessibility, but now that i have seen it venting plenty, i think it could be more of a ^ shape. it vents wonderfully as is, with a clearly visible draw-in and vent-out. this stated, i really like my opening. i just need to make sure it is secure in it's position.
if you read this, what is your take as a trained engineer? if i remember right, i believe you mentioned before that you concurred with my theory that the arch was too flat on top...
BTW, I'm ready to start, I just am delayed by the need to pour a few more retaining walls around the oven mainly because I'm afraid of a mistake causing damage to the oven if I build the oven before I pour the walls.
take a look at some of your old cathedrals - You will find that when the domes and/or walls started to bulge out, the builders would add buttresses to stop them from falling down. Later on they figured out that they did not need to add to the materail to the walls/domes materail so that it looked like an earth dam but that the load had direction and that is when flying buttresses came into use. Now a flying buttress on the oven might be a bit of minature overkill. Possibly adding a load wall up to the arch will help in transferring the load.
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