Slab on Ground contraction joints through thickened slabs

[twinnell]

I have a 4000 sf office building with glulam columns forming an inner and an outer ring in the center of a square footprint. The rings are 7 feet apart. The exterior walls are wood stud framed. I have a few interior wood framed shear walls. At the request of the contractor and architect I am using a monolithic slab and footing configuration for the column footings (column reaction is 18 kips max). The interior shearwalls are located on 3 sides of the outer ring and I have a thickened slab under the shearwalls with a footing at each end (also a thickened slab).

Now to my question, with all the thickened slab areas, 12 columns in the outer ring, 8 columns in the inner ring, and pretty much 12 inch wide thickend slab under the shearwalls that are between each outer ring column on 3 sides, how do I cut contraction joints in this slab. Can I saw them through a thickend slab without increasing the depth of the cut? Instead of a 4 inch slab should I go thicker and add more reinforing at the top, cut the joints through the thickend areas and just try to limit the crack width.

Or should I completely isolate the thickened areas from the rest of the slab. Essentially pour a C shaped footing, top of footing is top of slab, construction joint that where appropriate, then pour the 4 inch slab up to that footing ring?

Or am I worrying about it too much. Slabs crack, just try to limit the width.

 

[msquared48]

You mention monolithic implying slab and footings in one pour with no construction joints. Then you mention a two pour option. If you can go to a two pour option, why not just pour your strip footings to the underside of the slab in one pour, then finish with the slab in a second pour over the footings. Cut in your construction joints at the normal depth and spacing and forget it. No worries.

Watch the tile areas though. May want to have CJ's closer here to limit the slab crack widths. Also may want to try to locate the joints at the grout lines, if possible. Fibermesh might help here.

Mike McCann
McCann Engineering