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new concrete layer on top of brick vault ceiling

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greznik91

greznik91

Structural
Feb 14, 2017
186
SI
Hi,

I'm dealing with a very old buidling (stone walls) with RC slab on top. There is a room with brick vault ceiling that was added later (similar to attached photo bellow). There are vertical cracks between old and added part on both sides of the wall(there is no dilatation between). Investor wants to add RC slab on top of existing brick ceiling (there is nothing but self weight on top right now). This will connect both parts and it is a good move in case of seismic forces but I'm wondering about extra weight (concrete on top of brick vault ceiling) since there are already vertical cracks between older and newer part of structure. I think this is due diferental settlements (I have no data about the foundations). Investors said cracks are the same for 50 years now and are not getting larger. What would you suggest in this situation since I have very little data of existing structures? I think there are 2 options - to make aprox. 50 mm thick concrete layer on top of existing brick ceilnig that is connected to existing RC slab (in this case existing ceiling is loaded more) or to make a thicker reinforced slab that will have load bearing function so - I'm wondering how can this be done - How can you support brick ceiling like that before concrete took over?

Sorry for bad language.

Thank you.


r1_fz4s5o.png


R2_mnzkix.png



a3_gjhj8o.jpg
 
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Why concrete? You only need to provide wood/steel ties between the two walls to keep the entire things stable. The cracks looks likely due to shrinkage from moisture changes.
 
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greznik91 said:
Investors said cracks are the same for 50 years now and are not getting larger.
Click to expand...
Unless they took very detailed measurements, digital pictures etc, I would place virtually no weight on that comment. Some defects such as this change so slowly, they never look any different day to day. But across years they add up. I told one person that I see they had lost 14" of soil due to erosion down the side of their house to which they responded "No Way, it is the same as when I bought the house 15 years ago'. That comes to 1" a year, or 1/12" per month to 1/360" per day. I doubt anyone can detect these amounts on a daily basis.

Do you have any real knowledge of the brick vault design?
Can you add the concrete without using the vault for support?
To me, pushing down on an old brick vault is risky.
 
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Agree with Ron247, a vaulted roof is just a 3D version of an arch. As load is applied to either of these, the walls supporting a vault/arch tend to "blow out" sideways. That's why medieval cathedral builders had to add "flying buttresses" to resist horizontal load on walls:

Flying_Butress_bwuxxs.jpg


Suggest watching this video, or at least the part that begins at 22 minutes: "Building the Great Cathedrals"
The video also shows how historic vaults/arches were shored when they were constructed.

[idea]
 
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This should do. Leave a space between the wood/metal ties and the vault ceiling.

image_yzi0oy.png
 
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Thank you for replies.
I agree that adding loads / pushing down on an old brick vault is risky (especially since there is nothing already on top of it, just self weight).
Id like to make RC slab but I dont see how.
Is there a way to support vault ceiling until concrete is hard?

How about adding steel tension tie? Is that doable?

TIE_qvsanf.png
 
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A tie can make up for outward movement due to the thrust but does it change the increased moment on the brick vault?

I assume you are dealing with unreinforced brick and old brick. Hoe old is the original building and the addition?
 
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Did you look at the top of the vault for cracks also?
 
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