Take a look at the attached footing module design. It is subject to uplift and shear on the concrete pedestal. If I decrease the thickness of the footing my overturning factor of safety and bearing pressure goes down significantly. If I increase the thickness of the footing my FS overturning goes down and bearing pressure increases? Why is this? Can anyone help me understand how the footing module treats the soil load and concrete dead load?
For some reason I cannot upload a .ftd file, so here is a link:
https://dl.dropboxusercontent.com/u/65240332/RAM%20Footing%20Design.ftd
Take a look at this post that has some details on how uplift and overturning are dealt with in Ram Foundation. communities.bentley.com/.../spread-footing-overturning-and-uplift-checks-in-ram-foundation.aspx
If you have a combination where there is some significant overturning concurrent with small net downward load, those are the cases that can show unexpected overturning results, so I recommend always considering the self weight of the footing when checking soil stress in the design criteria.