Ram Concrete Slenderness calculation (nonsway)

Question

I am running a model in the Ram SS Concrete module and getting a few errors with the moment magnification factor exceeding 1.4. When I attempt to back-calculate the results the program is getting, I am not getting the same numbers. So my question here is two-fold: 
 1. Why aren't the results more transparent with its calculations of Cm, delta, beta, and Pc? 
 2. Why do my hand-calculated results not match the program results? Cm seems slightly off, and even if I use the program-calculated Cm to calculate delta, I don't get the same delta value. Is there a different equation being used than what ACI lists?

Seth Guthrie · Accepted Answer

I see the problem with the Cm factor in this case. The program is incorrectly using the ratio of the major axis moments not the minor axis moments in the calculation of Cm associated with M1 and M2 minor. It's a reported defect already fixed for our next release (Re: Defect 813994: Cm factor and end moments calc for minor axis columns)

Seth Guthrie · Answer

My results in 17.03.01.50 are a little different, but I think I can still answer. 
 First note that you can get a warning for "Magnification factor, delta, exceeds 1.4", but not see that in the report because the delta value we report is for the governing data point, i.e. the specific load combination and pattern that yields the highest Ld/Cap ratio. There is an enhancement request to update the report to include the slenderness calculations for the critical delta factor in addition to the critical data point, we just have to find a way to do this concisely. (Enhancement 877094: Slenderness section in concrete column report). See also: https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/224441/column-magnification-factor-warning-with-non-slender-column 
 Second there is the issue of the minimum eccentric moment controlling in this case since the moments from the analysis are small. See: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/25803/concrete-column-minimum-eccentric-moment 
 As for the reported value of Pn, yes it always equals Pu (when Pu is below the plateau of the PMM curve), because we are calculating a Ld/Cap ratio of the (demand moment/capacity moment) at the given axial value and angle. 
 As for the delta calculation, I'm still working on my hand verification of this, my initial results are slightly off (like yours).

Ram Concrete Slenderness calculation (nonsway)

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