All splices- joints must be out of the concrete. continuous run under the concrete. as far as expansion contraction, I have seen concrete roads buckle in the hot sun . That should not be a problem inside a building out of direct sun. if you build over expansive clay soils you can have floor cracking. In a lot of areas the local building department already has area soil maps. I hit clay down at 4 ft. My engineer spec'd 3 ft sq footings with 12 in sq posts with 6 pieces of 1/2 rebar uprights with 3/8 hula hoops 6 in apart for the steel column supports. There has been no movement in the 20 post locations. The footings must be deep enough for the soil type or a grade post-beam system. 18 inch holes about 6 ft deep with rebar L'ed into the floor, and foundation walls about a foot thick floor around the edges and use lots of rebar in the floor slab. Plenty of crushed rock then poly vapor barrier, sand and foam insulation. Grade the area around the building to keep rain and snow melt water away. In my main 12 X 12 doorway I also brought out 1/2 rebar 18 inches apart to tie into the driveway slab The backhoe weighs about 10 tons. . In 9 years there has been no movement or cracking in the main doorway. . In the back door the slab has lifted about 1/2 inch, I didn't put in the rebar ties out like the front and the ground base level is 18 inches higher, not as good of drainage. I had about 100 yards of base gravel hauled for under the floor, I should have raised it more, but didn't like having to do a 3 ft in 40 ft ramp in front.
Last edited by timothale; 02-26-2011 at 07:49 AM.