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concrete floor in barn

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denwood
Join Date: Jul 2004
Posts: 542 Quarryville PA
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2004-11-03          99774


Any civil engineers or such out there that can tell me the hard facts on concrete. I am looking to put in the best floor possible using 2500-3500 lb concrete and want to know the down side if there is one (cost is not one)to high PSI concrete, 3000 or 3500 lb. It will be 45' x75'. I will not heat it, I will put in overhead lifts, it will be 4-5 inches thick over 2-6" of crushed stone, reinforced with welded wire mesh, and support heavy loads at times. I am not looking for opinions that I won't need high psi for this application, just facts. I want the strongest, longest lasting, possible within reason.



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beagle
Join Date: Jan 2004
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2004-11-03          99779


Sounds like what you are most interested in is shear srength from concentrated loads. Shear strength is around .45 compressive strength, which governs puncture shear. Believe it or not, the compressive strength of the subgrade is more important than the shear strength of the concrete. The crushed stone backfill will probably develop 2500 to 4000 lbs/sq ft compressive strength if properly installed over good soil. To keep the slab from experiencing bending, which you are not reinforcing for, you don't want to exceed the bearing capacity of the soil. With a 6" slab, with just temperature reinforcing, and 2500lb/sq ft subgrade, you have a load capacity on the slab of 10,000 lbs per square foot ( with a 6" slab, the bearing area is 2' x 2' at the subgrade). You would gain more from a thicker slab than by going to high stregth concrete. This is due to the 45 degree distribution of the load through the slab, which increases the bearing area on the subgrade.

Use regular concrete, have a well compacted subgrade, and thicken the slab to achieve the bearing capacity you want. The other option is to design a reinforced slab for bending to increase the bearing area at the subgrade, but that would get pretty expensive.

Hope this helps you. ....


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beagle
Join Date: Jan 2004
Posts: 1333 Michigan
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2004-11-03          99780


Just some other thoughts to assure a quality slab:

No more than 6" slump when placed.
Don't allow over troweling, it softens the top of the slab.
Saw cut at 15' intervals 2-3 days after placement.
Wet the subgrade before pouring.
Stay away from high-ealy concrete, too many shrinkage stresses.
Make sure you have a Ratwall. You'll be sorry if you don't.
Avoid cold joints. ....


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concrete floor in barn

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Woodie
Join Date: Jun 2004
Posts: 109 Michigan lower
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2004-11-03          99785


It also depends on the quality of the concrete/cement from the supplier. I had a drive done about 10yrs ago and it was specd 6bag this and limestone size xx, etc (overkill) wasn't 4 months and the top inch peeled/spalled, contractor didn't over trowel etc. long story short after independant lab tests showed the cement used by concrete co. was offspec no air ,ash, whole bunch of other stuff. Contractor and I not happy since that concrete company was always a respected firm. I used the same contractor for my barn30x60 different concrete co. 4-5 inch with a 12 wide 6" thick edges wiremesh and he recommended cuts every 10foot 1-2 days after. Floor is super, I also insulated under it ....


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grinder
Join Date: Oct 2003
Posts: 677 central Maine
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2004-11-04          99805


Site prep is everthing. What are you building on for a base? 3500 lb min. Don't let them add water at the site,give them several locations to pour from not exceeding the chute length by more than 10-12'.
I would not build on anything less than 18-24" of clean compacted gravel above the surrounding grade. 2-6" inches
of stone? Min. of 6" after compacted. 2" of foam and rebar only. The wire won't keep it moving. Only breaking up, if
you pour it inside of a 4' frost wall it can't go anywhere.IMHO insulated floor and frost wall is the ONLY way you will keep an unheated build in place.
If you putting in a lift I think you will need a substantial concrete base before the floor goes in. The lift
company should be able to give you the specs. Do your home work first it is not a easy fix later. I am going to e-mail you some pics of a 28x36 three car garage
foundation that I just poured. We are about to backfill and fill in the floor area with clean sharp sand. compacted every foot. 2" inches of foam 5" of 3500
lb. mix in the floor with rebar every 4' criss cross pattern. The walls are a min 4' below grade with 8" exposed when final grade is done. 3' apron with 2" of foam and rebar across the front in front of the doors. ....


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denwood
Join Date: Jul 2004
Posts: 542 Quarryville PA
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2004-11-04          99845


Thanks for the replies, just wanted to add more details so reccomendations may be more accurate for my situation. I had to cut and fill to get level ground I was shooting for a 40 x 60 building but when the excavator was done, we realized a 45 x75 would fit so that is what I ordered. All top soil was stripped and sub-soil was used for pad. Soil was loamy with mica , not a lot of clay or sand or rock. Compaction was done with 955 cat with narrow tracks as it was filled. Site sat for a year to settle and then I layed fabric and 3/4" crushed stone about 4" deep. The building is all steel I-beam type. When the building came, we cut holes in the fabric and excavated (8) 4'x4' pits for the uprights and poured 12" of concrete with rebar frames coming out the center, then 2'x 18" forms up to finished floor grade with the anchor bolts. The reason I now have 2-6" of stone is the concrete trucks pumped the muck under the fabric as they drove over. We had a very wets pring. The building has been up for about 1.5 years and the dirt is very hard under the fabric. I tried my jumping jack and it wouldn't budge, just pulverized the fabric. The tin on the sides sets 1.5 inches below finished floor grade. I planned on bracing it on the outside with wood and putting plactic sheets on the inside and pouring right to the wall to fill the corrugation pattern of the tin. A purlin is 12" above floor grade. At the very least I wanted to put plactic down under the concrete, possibly double bubble foil/plastic insulation or 1" foam sheets. I worry about the foam because of the tight tolerance to finished grade and getting enough concrete in. I may heat part later but not on a regular basis. What is a rat wall and why would I want one? Never heard one mentioned in this area by any builders/ masons. We are zone 6 near the edge of 7. rarely gets to 0 F and pipes only go 36" deep to insure no freeze Most frost I have seen is 12-18" ....


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grinder
Join Date: Oct 2003
Posts: 677 central Maine
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2004-11-05          99910


Not sure about the rat wall term,perhaps a 4' frost wall?
Kinda late for that. Sounds like a decent footing under your posts, have they moved? I would go with the 1" foam
and lots of rebar(it's cheap)with 5" of 3500 lb min. I have used the 1" here in maine without a problem. We generally have a 4' frost or more. I have gone to two inch for insurance and no call backs. You might consider a two foot wide strip of foam around the exterior laying flat, butted up to the building. covered with stone
12-18 " of frost is more than enough to heave a floor. ....


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beagle
Join Date: Jan 2004
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2004-11-05          99913


Rat wall and frost wall are essentially the same thing. Sometimes called rat wall because not only does it help control movement of the slab edge, it keeps critters from habitating under the slab. The exposed edge of the slab from the outside is a perfect place for rodents and small mammals to dig under the slab for a home. The "rat wall" prevents that. Also keep in mind that if you aren't heating the building, the subgrade will freeze everywhere under the slab. The best way to prevent frost heave is to keep water drained away from the building, and have good drained soil under the slab. The frost wall won't help keep the interior of the slab from heaving if you don't have drainage.

Insulating the comcrete in an un-heated barn isn't necessary. If you plan to heat it in the future, you probably want to consider it now, along with a good vapor barrier. If you use a compressable insulation, you will greatly reduce the bearing capacity of the slab. The location for rebar placement in the slab cross section, and the total area of steel in the cross section are critical if you are trying to increase the bearing capacity of the slab through bending. If temperature stability is what you are after, you need to consider that steel and concrete have very different coefficients of expansion, meaning that too much steel can be worse than not enough. It is recommended that for temperature reinforcement, steel should be about 1.5% of the cross section. As the concrete cures, it shrinks, developing compressive stresses in the steel reinforcing, with the subsequent tensile stresses in the concrete. Temperature changes add to these effects in cold weather as the slab shrinks further. If you have too much reinf steel, the tensile stresses in the concrete will lead to cracking.
The balance between the two materials is inportant. ....


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grinder
Join Date: Oct 2003
Posts: 677 central Maine
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2004-11-06          99935


Beagle
You said insulating an unheated slab isn't needed? Don't you
think that it would keep the frost from penetrating the soil under the slab? ....


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Woodie
Join Date: Jun 2004
Posts: 109 Michigan lower
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2004-11-07          99996


my insulation came with visqueen attached. even for unheated barn as mine it keeps excess moisture from being pulled up thru floor, also when weather changes Real quick ,(cool than hot humid or vs vers) the floor doesn't get as damp ....


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beagle
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2004-11-07          100016


Vapor barriers can be usefull, but it is the warm air that causes moisture to travel. If you don't have any heat in the barn, there really isn't anything to cause the moisture to move. The temperature inside the barn is going to be whatever the outside temperature is if you don't heat it. Insulation is only useful to stop heat transfer. If you don't have heat, there isn't anything to insulate. All the insulation is iseful for is to help keep the barn floor warm if you heat it. The ground under the floor will freeze if the barn isn't heated continuously, insulated or not.

Compressable insulation will reduce the bearing capacity of the slab. The best thing you can have under your floor is a well compacted granular fill, with plenty of drainage.
I don't have insulation or a plastic vapor barrier under my floor. I heat it only when I use it in the winter. I have a couple feet of compacted sand and gravel under the slab, and have no moisture problems. With a well draining fill, there isn't any moisture to move.

Most modern industrial plant floors are fiber-reinforced comcrete over 12"-18" of engineered fill. ....


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grinder
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2004-11-08          100036


Beagle
I would agree with that on a perfect site prep. but most
are not done under an engineers eye.
Just for fun take a piece of 2" foam 4'x4' and lay it on the ground before freeze up. Lift it up in the middle of the winter and try a spade. I will bet you that you can dig down . I have built many Lakefront decks in places you can't
prepare the site properly(enviromental rules) can't disturb the soil near lake. We always lay foam down under our pads
that the posts will sit on.Seems to work? We use a high density foam board made
for ground contact. ....


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concrete floor in barn

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beagle
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2004-11-08          100040


Thanks, I am going to try it. I have another shed planned for next year that I would love to have options to use on the floor. Any organic material in the soil does create heat as it decays. I've though about adding organics to the soil under a floor to create heat during the winter, but have never tried it.

Sometimes being an engineer can be a handicap if you don't listen to practical solutions. I'm not too to old (yet) to listen. Just don't tell my wife. She thinks I'm just a brick headed Italian who happens to be an engineer. ....


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grinder
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2004-11-09          100089


We can all learn something from anyone, My understanding on the matter is that the foam will maintain the grounds natural temp. and not allow the frost to penetrate. If you look at my pics of my house, my shed roof off of the garage
is on 18" x6" round concrete pads with 2" of foam under them.
Seems to stay alright with Maine temps?
I think that if you can keep the water away from them it helps. ....


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grinder
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2004-11-13          100289


Beagle-Denwood
Here is a web page on foundation insulation you might find interesting.
They also cover many other subjects when it comes to building. ....


Link:   

Click Here


 

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2004-11-18          100511


We tend to go with 10' spacing on the control joints whether tooled or saw cut. We get a lot of requests--and some are adamant--that they want 6x6 wire mesh. Some building inspectors don't allow it for many reasons: doesn't do any good as the concrete is going to crack anyway, and when it does crack the joint allows water to rust the wire then the wire breaks. Also, some concrete recyclers are refusing to accept wire-containing concrete as it tears up their equipment. I charge 50%-100% more for removal if I find wire in concrete. ....


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beagle
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2004-11-18          100517


Thanks for the article grinder. Interesting stuff for home building. I think it's important to note that the article discusses heated structures. The introduction of heat to the system changes the design requirements, and how you want and need the structure to act. ....


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grinder
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2004-11-19          100536


Good point! I'm not sure if that web page discusses unheated building science, but I am going to look.

....


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hardwood
Join Date: Dec 2002
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2004-11-19          100540


First off I'm not an engineer, so this is just something I did about 25 yrs ago and it seems to have worked out fine so far. I added section on an existing building that I wanted to heat without any open flame. It's a stud frame structure with steel siding 6 in. roll insulation and sheetrock. the ceiling has about a foot of blown in insulation. I had investigated different types of non flame heat, what looked best were radiant cove heaters placed on the wall about a foot down from the ceiling. The manufacturer of the heaters recommended that the concreet floor be on top of 3 inch foam board insulation and this would give the concreet floor itself the ability to act as heat sink storing heat from the radiant heaters. This system has worked out real well, in fact I installed three heater units and found that no more than two were ever needed so I took one down and used it in another installation. Far as floor strength, it was just standard strength mix (6 in. thick) with re-bar. It's had some mighty heavy machines on it for all those years and I don't see any signs of stress cracking so far, plus it's been an amazingly economical building to heat. I do realize that in theory my floor should have bent, broken and had to have been replaced by now because of the lack of firm support by the foam, but in the real world it's just as good today as 25 yrs. ago. Just my experience. Frank. ....


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grinder
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2004-11-20          100624


Frank
I'm curious,do you keep the building constantly heated ?
I don't believe the foam will compress any more than it
did after you poured the floor.
grinder ....


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hardwood
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2004-11-20          100645


Grinder; Yes this building is kept heated 24/7 at about 55 degrees. It has allways been used as an assembly room for furniture. 90% of our glue work is done with yellow glue and most of the rest with hide glue, both seem to set up fine but just somewhat slower than in the summer. We seem to allways be going from the heated to the unheated parts of the shop, so around 55 seems to be a comfortable temp for a light jacket and the same jacket being adequate for short periods on the cold side. We also use cove heaters in our finish room built basicly the same as the assembly room only it has a insulated wood floor, only we go a couple steps farther with it. it is also humidity controlled and heated to about 75 degrees but only when doing actual finish work. Between jobs we back the heat off to just above freezing, it also has a filtered air exchange system that changes the total volume of the air in the building about two and a half times a minute. This may sound like some flashy high tech operation, but 90 percent of these heat and air exchange systems are home made, but they've worked fine for years. As for the floor, I seem to remember that we put about twice as much re-bar in as was called for, so maybe that's why it held up. Thanks for your intrest. Frank. ....


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