I occasionally design outdoor slabs on grade for vehicular traffic, such as semis and single-unit trucks (usually assuming AASHTO standard design vehicles), telehandler fork lifts, etc. My primary design guide is by the American Concrete Institute: "ACI 360R-10, Guide to Design of Slabs-on-Ground" (April 2010).
For secondary references, I use the Portland Cement Association document, "Slab Thickness Design for Industrial Concrete Floors on Grade" (1996), and the US Army and Air Force technical manual, "Army TM 5-809-12/Air Force AFM 88-36, Chapter 15, Concrete Floor Slabs on Grade Subject to Heavy Loads."
In addition to slabs handling traffic, these design guides also deal with heavy fixed loads such as warehouse shelving.
============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill