Precompression Failure

Question

Hello, 
 
 I am seeing a precompression failure for my two-way slab with opening infill beams (Layers > Deign Status > Status Plan). When I go to use the Auditor tool, I do not see much information about the precompression failure (i.e., the needed precompression for the design strip). 
 
 I created a new precompression plan following this page: Creating a new precompression plan (bentley.com) . 
 I found that I needed 122 psi precompression for a section. Is there a breakdown of this calculation done by the program? Also, how would I remediate this for cantilevers in the program? 
 
 Thank you, 
 Skylar Calhoun

Seth Guthrie · Answer

I assume your issue is with too little precompression, though it could also be too much. 
 You can plot the Service Design - Gross Centroid stress plot next to (or on top of) the Design Status to help see where the issues are. Note, if you plot the capacity limit plot lines here, those are the code limits in tension and compression, not the user specified limits. 
 Those limits are set in the design strip properties, for example: 
 
 The ACI code stipulates a min of 125 psi, but for years we were not strictly checking this. There are several reasons for this, but I won't get into that here. Suffice to say, I would use a small cushion. 
 For cantilevers, I suppose it depends on the span. Checking deflection and extreme fiber stress, might be good enough. Very short cantilevers might not even need to have strips at all. Like any span, you can enter a range of acceptable stress values and then the program will check those. 
 Here's what the audit looks like for my test case with centroid stress barely beyond my (arbitrary) limit of 300 psi: 
 
 Ultimately, if you want to affect the precompression, then we are taking about changes in the tendons (number or elevation), or changes in the strips (width or trimming). 
 See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/52277/ram-concept-connect-edition-v8-update-2-release-notes