I'm analyzing a one way concrete slab and beam structure with moment frames in both directions, and I'm getting significantly larger design moments in RAM Concrete Column than I am calculating from the loads output from RAM frame. I have RAM Concrete set to use gravity forces from RAM Frame. This is not an issue when I use RAM Concrete analysis forces.
P-Delta is turned on in RAM Frame, slenderness is not considered in RAM Concrete.
Below is an example of the RAM Concrete Column design report, followed by the RAM Frame forces. RAM Concrete says the Major Moment is 743.13'k, while the results from RAM Frame give 573.36'k for the same load combination. What would this difference be caused by?
There are some significant differences in the analysis performed in Ram Frame vs Ram Concrete outlined here: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/6513/ram-ss---analysis-types-tn
Note, you can check the load cases forces from the Ram Concrete Analysis more easily in the Concrete Analysis mode using Report - Column Design forces, rather than looking at the final design forces on the column design output.
The issue is not with the analysis performed. The issue is with the design moments. I am using the RAM Frame Gravity Forces on Lateral Columns within the RAM Concrete Column Mode.
If all forces are coming from the RAM Frame analysis, why does the Top Major Moment for 1.2D+1.6L+0.5S in the Concrete Column mode not match what I calculate from the RAM Frame Member Forces? See my original post for the Concrete Column Design vs Frame member forces.
For example:
Concrete Column says Axial = 113.44k
Frame says 1.2*(69.56k)+1.6*(16.25k)+0.5*(7.94k) = 113.44k
These match. Meanwhile:
Concrete Column says Major M = 743.13 k-ft
Frame says 1.2*(340.44)+1.6*89.62+0.5*42.88 = 573.36 k-ft
These do not match. Why the discrepancy?
If the column dimension is large it could be controlled by the minimum moment. See this: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/25803/concrete-column-minimum-eccentric-moment
It's also possible that the moments are being magnified even though you said slenderness was not considered. If you send the model (or just the full design report) I can check.
How do I send the model?
This process works for even large files: