what all the above say is good advice; I can't add much more...Just some concepts to consider. A concrete slab, 4 inches thick, should not run in any linear direction to exceed 16 ft before a control joint is to be utilized. Control joints are just that; joints in the slab to relieve tensive forces that accumulate along the linear dimensions i.e. trying to control or induce cracking along the joint lines rather than in the interior field of the slab. That's not to say that this is what happens all of the time. If you park a hydraulic press, that weighs say 3 tons in the middle of a 16 ft concrete slab? Concrete has no tensile strength of its own so adjutants such as fiberglass filaments, steel rods (rebar) and welded wire mesh(WWM) are added/placed in the wet concrete to add tensile strength to the slab, as it cures.
Depending on your situation, ask a pro, in your locale,for a solution. Do expect to pay for the advice, but don't spend too much. It is advice on how to proceed, not a contract to do the work for you. Or ask the local building inspector. Building inspectors are required to know this stuff and most are fairly nice people, BUT not during construction season!