I have an existing two-way slab that I am trying to analyze. At locations of negative bending, the effective depth for one way shear calculations is much smaller than I'm calculating it to be by hand.
Based on the value that the audit is showing, it looks like it is using the reinforcement at the bottom as tension reinforcement and calculating the effective depth as the distance from the bottom of the slab to the centroid of the bottom reinforcement rather than the tension reinforcement at the top face. I've set the CS shear effective depth calc to "Maximum Effective Depth", but I am still having this issue.
How can I fix this?
Thanks, Seth. I tried running it neglecting axial forces and it was still giving an error. However, when I increased the spacing of the sections it solved the issue, as the error was occurring at the inflection points.
See this for details: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3094/ram-concept-shear-reinforcement-faq
Where you have net axial forces this can cause a small, or unexpected depth to the tension reinforcement. In flat, RC slabs some users might neglect the net axial force, but I don't generally recommend that. Adding some rebar to the opposite face can sometimes help, or re-spacing the design sections if it's limited to only a few specific locations (i.e. near inflection points).
Answer Verified By: Jessica Dineen