new concrete slab on top of existing arch ceiling 1

[mats12]

I am designing a new concrete slab on top of existing arch ceiling - steel beams are 1,50 m apart, masonry arches between. Spans are not that large but what I am strugling with is how to achieve that the new slab wont transfer any load to existing ceiling? Before concrete pouring I was thinking about supporting every steel beam along the length. But after the concrete hardens and supports are removed there will be a load transfer on to the existing ceiling?
Suggestions?

EXAMPLE OF EXISTING CEILING:

 

[jayrod12]

Where are you intending on supporting the slab? If the steel beams, you need to somehow detail that out so that you can load the steel beams without loading the ceiling. Then I would have sacrificial formwork installed that provides a gap between underside of concrete slab and top of masonry ceiling.

 

[mats12]

The new slab will be supported on the bearing walls and steel beams. I was thinking about something like that. Thank you for reply.

 

[jayrod12]

There are going to be people, specifically the contractors, that will say this is way more expensive than just pouring the slab directly on the ceiling. They'd be correct. But if there's no faith that the ceiling is strong enough to support the weight of the concrete slab, then I don't see another option.

Why a 200 thick slab if only spanning 1.5m? Seems overkill?

 

[mats12]

yup, there's no faith that the ceiling is strong enough to support the weight of the concrete slab

 

[r13]

The flat slab will draw variety of loads to the existing roof, if you are uncertain about its strength now, how can you be confident later? Alternatively, if proper bearing can be provided, 1) design separate steel framing/joist system to support the slab, 2) use precast panels/hollow core slab.

 

[jayrod12]

Retired makes a good point. The spans are not outside the realm of standard 200 thick hollow-core plank to span the entire way to the outside walls. Probably easier than bastardizing a suitable stable connection to the steel beams.

 

[KootK]

Is this a roof or a floor?

What's the motivation for the upgrade?

Will the clay arches be left exposed in the finished structure? They do look pretty sexy.

The clay tile arches actually look to be in pretty good shape to me. And those can be pretty robust when working as intended. I also agree with jayrod's assertion that somebody probably will want this done in a way that they feel is cheaper and/or more practical. To that end, I wonder if one might:

1) Shore the beams appropriately;

2) Remove everything currently above the clay tile.

3) Cast in new concrete to a level 3" above the existing top of arch elevation and but rebar in the topping slab.

Once the concrete dries:

4) The concrete will behave like wonderful little compression arch bridges (consider end span implications).

5) The clay tile will likely be less likely to fall out than it is now because the weight of the concrete will kind of pre-stress the arches.

 

[KootK]

If you can just get this thing to the finished state somehow, what you'd have left would be quite robust.

 

[r13]

I'll do KtooK's design with foam material to separate the vault ceiling and the new concrete. The ceiling tile should be supported until the concrete has reached full strength. And, if the new concrete rib can be reinforced as support beam, for the slab, spanning from wall to wall will be great.