Concrete Slab for a Metal Building

[MickeyDBC]

Getting ready to build a 40x80x16 foot metal building at our place. It will be used for equipment and as a shop now and eventually for pecan processing in five to ten years. The soil where I want to put the building is a loam/clay/sand mix - it moves some between rainy and dry but the house slab 150 feet away has survived with minimal movement for 50 plus years and it seems to be farmer built rather than professionally poured and engineered. Bedrock is over 100" feet down so doing pilings that deep is not in the budget. I am planning on gutters and overhangs on the building to help keep water away from it.

I have talked to a several builders who have said we need to do everything from digging down 3 feet and back filling with road base with a 4" slab to doing a quick level job, use 3/8" rebar on 12" centers and pouring a 5" thick flat slab on plastic sheet. I am leaning towards 24" x 12" perimeter beams along with a center beam and cross beams at 20' and using 5/8" rebar in the beams and 1/2" rebar on 12" spacing with a 6" thick slab with a moisture barrier. This would use about 80 yards of concrete and 6500 plus pounds of rebar. Anyone have any thoughts on this? I have thought about calling in a soil engineer but after having dealt with them in the past, they seem to practice more CYA design after blowing the budget drilling test holes everywhere. Any thoughts or past experience on this?

 

[rmk700]

I’m getting a 40 X 50 metal building. Had to go with footings 3’ deep with spread footing where peers go. Had to be that deep for frost.
For the slab I went with 3 to 4” of 1”rock and a 5” slab with rebar. No way I’d go less. Planning on putting large hay bales and parking equipment and stuff in it.

 

[Tractor Seabee]

Just make sure you put a grade beam with re-bar tied to the outer footing at each building frame location. That big a building you should cast the anchor bolts into the grade beam area and bolts tied to the re-bar. Set the posts on nuts to level then grout under them. Arm chair designer, Ron

 

[MickeyDBC]

Just make sure you put a grade beam with re-bar tied to the outer footing at each building frame location. That big a building you should cast the anchor bolts into the grade beam area and bolts tied to the re-bar. Set the posts on nuts to level then grout under them. Arm chair designer, Ron

That is a good idea about putting the posts on nuts and then grouting them in when it is level. I was planning on using J bolts tied into the rebar and six pieces of 5/8" or 3/4" in the piers to help with uneven movement. I am also going to talk to a neighbor who did a 1200 foot shop behind his house and see what he did and if he would do anything differently (besides make it bigger). After reading what people have to do to deal with frost, clay looks nice compared to it.

 

[RoyKing]

What psi are going to use

 

[MickeyDBC]

What psi are going to use

I am planning on using 4000 psi.

 

[Redlands Okie]

Plans sounds ok as long as your getting down to frost level.

 

[RoyKing]

I would bump that to 6000psi and don't put any fiber in it, and three expansion joints. I just used sand about 12/14 inches watered it for week and waited 30 days before the pour. Also structural eng friend said just make a rectangle with 2 rings of rebar about two feet in from the edges inside of each area defined by the expansion joints overlap the corners and tie it on stands with plastic over lap seems by 8 feet. After the pour and it flashed the next day I put sprinklers out and watered it for 6 days. 25 years and no cracks. It is so hard it rings like bell, right after the flash I hand sprayed it with a sealer that etched the surface so it wouldn't be slippery as they used a machine finisher

 

[plowhog]

Add reinforcement in certain areas of the slab if you need it. In my garage the whole area where the motor home is parked was thicker. And I had footings poured for the four posts of my car lift.

 

[3Ts]

First, soils in different parts of the country vary significantly in their ability to support loads, frost levels, rainfall amounts, etc., so be careful about the advise you receive here.

I assume you'll be using a steel frame building, if so, the weld plates for the steel columns will replace the nuts mentioned. Be sure the weld plates have the j-bolts welded to them instead of the hex head bolts.

- With a clear span barn, all the loads will be on the exterior foot or so of the slab so the 12 x 24 beam should be sufficient.
- And that plastic vapor barrier is also a good idea.
- I'd use plastic rebar chairs at the rebar intersections and be sure they're tied to the rebar.
- Where ever you have an exterior door for equipment I'd have a slope of about 1-1/2" so any rain will drain out and equipment can roll in and out on casters. The depression for the door should include the track that the door rolls in.