Its my first time to post an inquiry, I think I was bewildered on putting the same post in the files area. My interest was on how to properly model the soil spring support of a semi-buried cylindrical concrete tank (around 15m diameter) with conical base slab. I had tried to utilize the plate mat command like as specified below (i defined my plates into groups also), but i have second thoughts about the output, as i getting quite small base slab stresses. Was there a some special notes to consider on inclined bases like this model? I could send the std file but dont know how. Any help would be highly appreciated.
SUPPORTS
_MATSLAB PLATE MAT DIRECT Y SUBGRADE 40000 PRINT COMPRESSION
Based on your support command that I see, this is what STAAD.Pro will do. It will calculate the area of influence for each node of the plate mat considering the appropriate area of the plates attached to the node. It will multiply the area calculated at each node by the value of the subgrade modulus to calculate the spring stiffness at each node and then apply the spring in the vertical ( global Y ) direction. If that is what you intended to do, you are fine. However if your intention was to apply springs normal to the inclined surface, you need to use inclined support. You can find details on inclined supports at section 5.27.2 of the Technical Reference Manual.
The following wiki has details on how to upload files to Bentley Communities Forum
http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/28129.how-can-i-upload-files-in-the-bentley-communities-forum