Suspended Concrete Floors?

[patrick_g]

If you really want a suspended floor then consider how you will support it. If piers continued above grade is workable then you might consider a design on the order of the attached sketch or a waffle pattern but that is probably unneeded complication to go waffle (your decision.) The floor, as sketched, is not of uniform thickness but has integral beams cast monolithic to the slab. This gives you a considerable increase in the vertical moment.

My basement ceiling/great room floor is done line this and has some pretty large spans. My forms were a horizontal analog of ICF (styrofoam wall forms) but conventional forming will work fine. (Panel Deck was the product.)

There are two mats of rebar located in the slab part of the structure, one running N-S and the other E-W. There is large rebar near the bottom of the inverted truncated "peaks." The greatest vertial thickness of concrete in mine is (I think) 14 inches and the thinest (unreinforced slab portions) are about 3 1/2 or 4 inches.

I have shown the thickening running only one way. The waffle pattern would have two sets of thickening beams at right angles to one another.

This makes for a very strong structure for the amount of concrete used. Much more efficient than just making a huge slab and it is not challenged by its own weight.

If you wanted you could join the rebar in the piers to the rebar in the floor assy and pour the whole thing in one monolithic pour.

If you need a little help with the engineering just get some info on the Panel Deck product or similar and use their basic proportions. The Styrofoam in their approach adds virtually no strength.

The arrows in the sketch show where rebar would be running at right angles to that shown "on end."

In my floor there are two rebars at the bottom of each beam and each is 1 inch in diameter. This might be reduced for your application if you consult the engineering info for PanelDeck.

If for any reason you heat and bend the large rebar using a torch make sure not to bend the rebar into or away from the ridges running lengthwise on the rebar but at right angles to that. Otherwise you will just ruin the rebar. Voice of experience here.

Pat

 

[Wood_Butcher_Dav]

I just compleated the task of pouring a concrete roof for my breezeway/storm room this past weekend. The conveyer truck what what made this a DYI project.

Dave

 

[Egon]

What were the design parameters of the Roof?

 

[Wood_Butcher_Dav]

The first parameter was to make the wife feel safe during severe weather and not wake me up.

The basic design was copied from the U of Iowa plans. Theirs was an 8x8 mine is 12x12 with 4.5 inch slab roof.

I used 2x8 joists (16"ctr)for the bottom forms but will leave in place so there is room for insulation.

Dave

 

[Egon]

Thanks Dave.

 

[jbos333]

How about a plate steel floor? If the building is only 12' width you could cover the floor in steel diamond tread pieces 8x12 or 4x8 which are common sizes. Of course your 12' dimension is prob outside in which case you would have to get it sheared down to size.

 

[cdhd2001]

These are some great ideas guys! All worth considering.

 

[patrick_g]

As the dimensions of a safe room are increased above the original designed size the thickness requirements and stiffening requirements grow pretty fast.

When I built a ground level safe room for my mom I used 12 inch thick concrete "knock out" (bond beam?) blocks for forms and grouted 100% ending up with 12 inch thick steel reinforced walls (rebar in EVERY CELL, i.e. every 8 inches horizontally had a vertical rebar.) Every 8 inches of vertical extent has horizontal rebar on 8 inch centers too. The ceiling is 16 inches thick with two rebar mats almost a foot apart. (I built this after seeing "Twister" the movie with a flying 18 wheeler. All rebar is continuously spliced/lapped so the floor rebar runs up the walls to the ceiling rebar. ( I had got a good deal on a pallet load of prebent 5/8 rebar 2x2 ft corners.) It is basically a steel cage with close set bars covered in concrete. I drilled piers which are monolithic to the rest of the structure to anchor it to the ground and drilled and doweled into the garage foundation with horizontal rebar to tie the room to the garage foundation/slab.

Pat

 

[aggiehortguy91]

With a raised floor above grade only 3', I would fill with compacted dirt and pour a slab on grade floor. It would probably be much chaepr than putting in an engineed structural concrete floor. 3'x12'x24' is only 32 yards of fill, or about 4 truck loads.

This is the way I would go, but I would consider pea gravel or sand if it is not too expensive in your area. Pea gravel doesn't compact so you don't have to worry about settling as much.

 

[mjncad]

If you are seriously considering a raised concrete floor, find a good structural engineer to design it for you.

Forget the galvalume panels and get actual steel floor deck made for the purpose of containing the concrete. This is the same stuff used in high-rise office buildings.

Unfortunately any raised concrete floor is not going to be cheap.