Composite Steel-Concrete Construction & Slab Saw Cut / Control Joints
Composite Steel-Concrete Construction & Slab Saw Cut / Control Joints
(OP)
I would like some feedback on controlling shrinkage cracks in an elevated concrete slab when the structural framing system is a composite design using steel beams, shear studs, and composite floor deck. Over the years I have heard many opinions concerning the need for saw cut joints. These opinions range from the use of control joints would defeat the composite action to the joints being required at such a tight spacing that it is cost prohibitive. The other question is to what depth and spacing these joints should be cut if they are used.
Thank you for your time and assistance.
Mark
Thank you for your time and assistance.
Mark






RE: Composite Steel-Concrete Construction & Slab Saw Cut / Control Joints
a. at the beams (I am not convinced that this has any effect on the composite action, since the primary composite action is planar)
b. approximately every 15 to 18 feet perpendicular to the longitudinal flutes
c. approximately every 12 to 15 feet parallel to the longitudinal flutes
The joints should be cut to a depth of 20 percent of the cover over the rebar, but not less than 3/4 inch. Sawcuts should be made very early, even more so than slabs on grade, because of the greater restraint concentrations and because of the top and bottom cure/drying conditions. Using Sofcut or wet cutting with diamond saw will allow quicker sawcutting without raveling.
RE: Composite Steel-Concrete Construction & Slab Saw Cut / Control Joints
I did specify them once on a slab that was going to remain exposed to view, but I don't know if it made any difference.
I recently saw a 3" form deck (9/16") slab that had cracks everywhere. I don't usually specifiy those types of slabs, so I don't know if that is normal or not. In any event it's not a structural problem.
I don't think saw joints would compromise the composite action, as long as they were located on the column lines, then they would be parallel with the beam and therefore parallel with the direction of compressive stress.
markdaski@aol.com