I have a question regarding the calculated parameters for controlling combined column loads. I am validating the design for a column supporting a transfer girder. The girder delivers a factored load of around 325k and frames into the strong axis of the column. The eccentricities are set to the default of the (column depth/2) + 2.5". The report below shows the correct eccentricities listed, but I don't follow how the moments are being calculated. I expected to see Mx = 325 kip * (9.9in/12) = 268 kip-ft. The column is an edge column with girders framing into both sides of the weak axis and the transfer girder framing into the strong axis on one side. Any help would be greatly appreciated.
Thanks!
Does the column continue up? If so, half the unbalanced moment goes up, half goes down into the column you are reporting. See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/2055/ram-steel-columns-faq
Yes, the column continues up and I read through the moment split explanation, but wasn't sure I was reading the output properly. If I understand it correctly, the forces should be applied concentrically from the column above and then the moment from the eccentricity is generated at each level from the beam reactions - does that sound accurate? In other words, the moment is created only from the eccentric beam reaction at each level (or skip loading) and also the distribution from any columns above or below?
So, to back-check the values, it would be easiest to validate this moment by pulling the beam reactions and applying those at the column eccentricity?
One final question somewhat related - and I haven't found it spelled out in the documentation (please point me to it if it is there and I missed it) - can you please clarify the convention used by RAM? Is the local x-axis parallel to the strong axis of the member? Switching between programs frequently, I often get confused on the convention being used. Is Mx the moment about the x-axis or the moment in the x-direction (bending about the y-axis)?
Thanks, Seth.
The manual, section 3.4.1 Unbalanced Moments explains better than I can. I think the easiest way to hand check the program is to chop off the upper stories so the column in question is the top. The link I added before gets into column orientation and sign convention. Mx is the Major moment, the moment that causes the column flanges to go into tension/compression. My is minor axis.