Suspended Concrete Floors?

[gpflepsen]

When I put a raised concrete floor in my previous 18x24 shop, I built the floor from I-joist and decked w/ 3/4" plywood. The concrete was not structural, just a 1 1/2" topping on the decking. The floor was built for the dead weight of the concrete in addition to the live loads of floor tools. It was only slightly more expensive that a typical wood floor and gave the characteristics I was looking for, i.e. thermal mass and wear surface.

What loads are you looking at? If you don't intend to drive or otherwise heavily load it, a similar approach may be applicable for you. You really are not spanning that great of a distance.

 

[MikeD74T]

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.

Is this the voice of actual experience or best guess? During my construction years as a steel erector and concrete finisher I've placed both steel & concrete in the acres, if not square miles, range. Mostly commercial work but some residential.

• An engineer will only be needed if an inspecting authority demands one. The specs for this slab are easily obtained from architectual /engineering text books which are available from most libraries. I did one slab for a friend that the building inspector insisted on an engineering evaluation. My friend believed in my design ( taken directly from "Architectual Graphic Standards") & we proceeded. When the eval came back it was capable of supporting 125 lbs/ft2 when the minimum spec was 40 lbs/ft2. That was a 14' x 18' perimeter supported slab 6" thick with a single mat of #5 rebar on 12" centers 2" from the bottom.
• Galvalume, plywood, and other materials need only remain in place until the concrete cures. Anything that holds the concrete for that duration is acceptable. I've used concrete decking (the corregated galvanized tin that is purpose made), ribbed composite roof decking, & wood all with the same result. When possible, and cost effective, the form material can be removed after the cure.
• Hiring professionals & over specing the job can make it expensive but unecessarily so. MikeD74T

 

[Cat_Driver]

There are techniques more making concrete lighter. They actually made a boat from concrete and floated it.

You can add I think they are glass beads

UNLV Students Work To Build Concrete Canoe

In order to get concrete with the exact properties they wanted, the students had to experiment with the ratios of rock, water, cement and 殿dmixtures, which are chemicals that do specific things to the concrete. The density of the mix had to be about the density of water so that the canoe would be lighter than water and resistant to sinking.

"Materials such as Styrofoam and glass beads are lighter than water, so it enabled us to build a concrete-based canoe that is still strong but will also float better in the water, Galvan said.

Structural Engineering Students Pin Hopes on 300-Pound Concrete Canoe Named ‘Dow Jones’


I played with this stuff nad talked to the professor it impressed me. I even ordered some of the glass beads.


1. A method for producing a lightweight concrete composition comprising:mixing Portland cement and sand to form a dry cementations composition;combining water and an acrylic co-polymer into the dry composition to form a mix having a desired consistency;adding at least two different sizes of foamed glass beads into the mix as a filler; and adding loose glass fibers into the mix.

2. The method of claim 1 and including replacing at least some of the sand with vermiculite.

3. The method of claim 1 and including replacing all of the sand with vermiculite.

4. The method of claim 1 wherein the foamed glass beads comprise equal volumes of 1-2 mm and 2-4 mm beads.

5. The method of claim 1 and including adding polystyrofoam particles into the mix.

6. The method of claim 1 and including replacing the glass beads with polystyrofoam particles.

7. The method of claim 6 and including pouring of the mix into a flat mold to form a cement panel.

8. The method of claim 6 wherein the ratio of foam to cement is about 5.6:1 by volume.

9. The method of claim 8 wherein the sand in the mix is about 1.5 gallon by volume.

10. The method of claim 9 wherein the foam replaces all of the fiber.

 

[Egon]

Ferro cement boats been around for years.

 

[MikeD74T]

Cat Driver, Ferro cement boats go back to the late 1800's. They are not lighter than water, they just displace more water than they weigh - just like steel boats. Ferrocement is so named for the ratio of reinforcing steel to cement. During WWII troop ships were constructed of ferro cement. However make no mistake, regardless of size,when filled with water they sink like the rock that they are.

Isn't amazing that college students & professors can repeatedly reinvent the wheel without improving it !! MikeD74T

 

[mjncad]

Is this the voice of actual experience or best guess? During my construction years as a steel erector and concrete finisher I've placed both steel & concrete in the acres, if not square miles, range. Mostly commercial work but some residential.

• An engineer will only be needed if an inspecting authority demands one. The specs for this slab are easily obtained from architectual /engineering text books which are available from most libraries. I did one slab for a friend that the building inspector insisted on an engineering evaluation. My friend believed in my design ( taken directly from "Architectual Graphic Standards") & we proceeded. When the eval came back it was capable of supporting 125 lbs/ft2 when the minimum spec was 40 lbs/ft2. That was a 14' x 18' perimeter supported slab 6" thick with a single mat of #5 rebar on 12" centers 2" from the bottom.
• Galvalume, plywood, and other materials need only remain in place until the concrete cures. Anything that holds the concrete for that duration is acceptable. I've used concrete decking (the corregated galvanized tin that is purpose made), ribbed composite roof decking, & wood all with the same result. When possible, and cost effective, the form material can be removed after the cure.
• Hiring professionals & over specing the job can make it expensive but unecessarily so. MikeD74T

Mike:

I'm basing my comments on force of habit from working near structural engineers when I was a piping & mechanical designer. Yes, I'm guilty of over-engineering something due to the industrial and commercial aspects of my work experiences. I always have to remind myself and be reminded that residential construction can get by on less engineering.

I just get concerned when I hear good ideas being bandied back & forth without some decent calculations behind them, especially when heavy objects are involved. There are certain things I don't mind winging it on and others I'll defer to people with more knowledge than me.

Actually I had considered a raised concrete garage floor for the house I was designing for my wife and me before the decession put those plans on indefinite hold. The reason I was thinking about this kind of floor is that Colorado's Front Range is notorious for heaving soils causing flatwork failures, and it would be nice to have a decent garage floor to work on when need be.

 

[cdhd2001]

Just some things to add and some clarifications.

The "open" spans are 6 ft on center (vertical steel pipe pier in concrete).

I am using "C" shaped steel c-purlins for the structure (no wood).

My floor joists will be on 24'' centers and either 6'' or 8'' c-purlins.

As for the 26 gauge galvalume, from my internet research there are several suspended concrete floor systems that use decking that closely matches the specs of the galvalume R-panel.

I did a cost estimate of different flooring options. Underlying steel structure will be the same for all.

3/4" treated plywood = $315

2"x6" treated wood decking = $318

1/8" steel diamond plate = $675

4" thick slab made with Quickrete = $467

The concrete is more expensive than wood, but cheaper than steel.

I am leaning toward the concrete because it would be a smooth non flamable surface.

 

[MikeD74T]

mjncad, Fair enough, I'm not discrediting you or engineers in general. Many engineers simply reference published charts that are available to everyone that knows they exist. The good engineers will save you money by not over engineering a project. MikeD74t

 

[gpflepsen]

Just some things to add and some clarifications.

The "open" spans are 6 ft on center (vertical steel pipe pier in concrete).

I am using "C" shaped steel c-purlins for the structure (no wood).

My floor joists will be on 24'' centers and either 6'' or 8'' c-purlins.

As for the 26 gauge galvalume, from my internet research there are several suspended concrete floor systems that use decking that closely matches the specs of the galvalume R-panel.

I did a cost estimate of different flooring options. Underlying steel structure will be the same for all.

3/4" treated plywood = $315

2"x6" treated wood decking = $318

1/8" steel diamond plate = $675

4" thick slab made with Quickrete = $467

The concrete is more expensive than wood, but cheaper than steel.

I am leaning toward the concrete because it would be a smooth non flamable surface.

What's the highest load you plan on putting on the floor, e.g. driving a tractor? That will dictate how to build.

 

[Builder]

Has anyone built a suspended concrete floor for a workshop before?

I am prepping for a 12 ft x 24 ft tool shed. Because of the creek and floodplain, the floor will need to be about 3 ft above the ground. My original thoughts were to build a wood floor. But, since I do alot of welding I decided I don't want a combustible floor.

The building will be all steel pole building style with 3'' pipe and C-purlin construction. The floor would be supported by vertical 3'' pipe on 6 ft centers and floor joists of 8'' purlin on 24'' centers. If I do a concrete floor, my thoughts are to install 26 guage R-panel galvalume to the top of the 8'' purlins and ring it with 4'' purlins. This would allow for a 4'' thick concrete slab with #3 rebar at 18'' centers. I am also thinking of dividing the floor with additional 4'' perlins at 3 ft centers (divide the concrete into four 3 ft x 12 ft sections). The extra 4'' purlin would give me additional attachment points for equipment.

Any thoughts or suggestions?

I'm not sure if I understand everything you're describing here, but what I've done in the past in these situations is:

Install compacted fill up to height required before stone bed and concrete slab are installed (let's say 3') Use a rammax compactor and compact the fill in 8-12" lifts. Buy recycled concrete-it's cheap compared to gravel. You'll have to make your compacted slab considerably bigger than your 12x24 concrete footprint. I would add 3' to each side, so the compacted fill area would be 18'x30'

Dig 16" sonotube holes about 4' deep in your compacted fill. Set your ~4' sonotube forms in these holes so they sit up to the bottom of your proposed concrete slab. These sonotubes will serve as "legs" for your slab. You'll have to figure out how many sonotube footings you'll need along the edges and in the middle of the slab, but I'd guess every 4-6' apart. Install 3 rebar rods vertically in each tube to reinforce them. Let the rebar stick up 1' past the top of the tubes.

Pour 3000lb concrete in tubes and let dry. Bend the 1' extra rebar sticking up 90* until parallel with the floor.

lay your plastic foam, floor heat, rebar, etc. Tie all your rebar with wire ties. Install your wood edge forms. While concrete is drying, install anchor bolts for your walls if needed.

Pour your concrete slab. When it's dry, even if the fill settles a little, the 16" sonotube "legs" will support the slab.

Might be better if you just built perimeter block walls with 8" block and fill with compacted crushed concrete around both sides (like a garage is built). Then just build your metal framing and walls on the top course of solid block with anchor bolts. Then when the roof is on, open the shop doors and pour your floor.