Yes, in the "BOEF.xls" workbook if you read the comment boxes off to the right side those comments and the resulting calculations will give you some guidance in selecting the effective strip width for a slab on grade to resist concentrated loads. For a thin slab I would stay on the conservative side with the effective width.

For slab on grade analysis/design, you could and probably should use my "GRDSLAB.xls" workbook. I use the "BOEF.xls" workbook mainly for analyzing combined footings and strips of mat foundations.

Alex

ok thanks!

Soils appear to have ability for soils to be in tension. Would not compression only springs be more accurate? or is there an explanation for soil tension springs? Thanks very much for your time and efforts with the spreadsheet.

andiamo,
This spreadsheet is based on the well known and reputed Roark reference, as cited in the "DOC" worksheet. Depending on the degree of flexiblity of the beam or slab/mat strip, as well as the nature of the applied loads, the solution for bearing pressures may show tension (uplift) at the ends. While we all know that soil cannot resist tension, what this does represent is that your situation is too flexible to distribute out the loads. This spreadsheet is not intended to be a replacement for a finite element model (FEM) analysis, and the solution/formulas do not directly involve the use of "springs". However, sometimes we either don't have the time or it may not be worth the extra effort involved to do an FEM analysis. This spreadsheet, when used and interpreted properly, can be a very quick and powerful tool for helping the engineer determine just how flexible or rigid a particular beam or slab/mat strip really is (or needs to be), and thus how much load distribution is actually occurring. Engineers often blatantly assume "rigidity" in their analyses. This spreadsheet can help either prove or disprove those assumptions.
Hope this helps.
Alex