Ribbed concrete roof slab w/CMU infill? 1

[sTrucTureTec]

I am investigating a roof design that I have not previously seen. The roof consists of a 2.5 in. slab cast with 6"x12" RC beams spaced at 21". Between the beams are 12"x8"x16" hollow core CMU blocks. I assume the CMU was cast with the concrete and are anchored in some fashion. My question is what was the purpose of adding the CMU, resulting in a large DL on the roof? Is the CMU providing any structural contribution?

Kelly Lyons, PE
Principal

http://www.sTrucTure-Tec.com

 

[UcfSE]

It might be a variation of this type of system:

http://www.aircrete.co.uk/buildingwith/floors.htm

where the cmu turned sideways is slid into place and supports the floor. The cmu is then supported by beams at each end. I remember a web page that had a system designed for cmu but can't find it now. This is just a guess that came to mind.

 

[JAE]

If its a fairly old structure, past practice included using masonry as a form fill between joist ribs. A flat system of formwork was constructed first, with the masonry just loose-stacked in a fashion to form the continuous joist ribs. Then the joist reinforcing was added and then the concrete placed.

The masonry, having irregularities, holes, etc. would be interlocked with the concrete such that when the formwork below was removed, the masonry just stayed put. Then you'd end up with a flat surface that could be plastered without constructing a secondary ceiling support system.

 

[sTrucTureTec]

Yes, it's a structure build in the 60's. Your discription matches what I am seeing. Thank you both for your reply.

Kelly Lyons, PE
Principal

http://www.sTrucTure-Tec.com