MOST slabs on grade are plain concrete. While welded wire fabric is placed in them for "crack control", this does nothing for design tensile reinforcement.
Slabs on grade may be designed with a variety of approaches, the most common being Westergaard's procedures or some variant thereof. Elastic layer analysis is also used and finite element/difference procedures may be used as well.
The PCA and AASHTO both use the Westergaard approach for pavement design, as this is the most common application of design whether it is a roadway pavement or a warehouse slab serving as a pavement with forklift or other traffic.
I use the Westergaard approach and elastic layer analysis (ELA). ELA is quick and easy and gives me a cross-check on the PCA or AASHTO methods.
When faced with high static contact stresses, such as point load of shelving legs or similar, then a shear or bending design approach is more applicable, usually with shear being the primary controlling factor. In this analysis, code requirements for max. shear and bending should be used.
The performance of slabs on grade depends on several primary factors, including: proper thickness design for the anticipated loads, proper durability design in the concrete mix design (usually a minimum of 4000 psi concrete is necessary for durability requirements in pavement slabs or warehouse slabs subjected to traffic), proper placement techniques and thickness control, and proper joint design and placement.