The best design source for slabs on grade is PCA. Get their publication "Concrete Floors on Ground". They have a web site. Good luck!
<p>David Allee, Architect<br><a href=mailto:darct@tfb.com>darct@tfb.com</a><br><a href= > </a><br>Professional affiliations include International Conference of Building Officials and Light Gauge Steel Engineers Association.
The best reference I know for US practice is "Designing Floor Slabs on Grade,2nd Ed, 1995, by Boyd Ringo and Robert Anderson. It is published by the Aberdeen Group and is probably available from PCA as well as any from good technical bookstore.
Bussh is right: go buy Ringo & Anderson. We have this book and it is great. It covers many methods, including PCA, WRI, Army COE, etc. I didn't know others knew about this gem.