The gravity column design interaction equation H1-1a in RAM SS does not account for the Mux/(0.9Mnx) in the unity equation. Why is that ?
What design code year are you using, AISC 360 - 2016? What version of Ram Steel? There have been changes to this approach over the years.
Seth I'm currently using AISC 360-2010 LRFD, and the RAM version is 16.00.01.06 CL
Here's what the 2010 code says (note 2016 is slightly revised)
I believe you are in the rare case where the moment is primarily about the major axis, and the minor axis moments are small enough that you qualify for the use of H1.3 yet the minor axis moments end up controlling. To confirm you can adjust the eccentricity to see at what point the Mry is more than 5% of Mcy and the program will go back to using H1.1a.
Or you can send your file over and I can confirm. I was not able to build a test case that produced this output so far.
Yes, it is controlled by H1.3 but still the H1-1a equation is used to determine the limit state of in-plane instability but I couldn't see ratio of Mux/ Mcx being considered in the equation, it just considers the Muy/Mcy (which it can ignore). I can send the file over please let me know how can I upload? Thanks
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Make sure you go to the next page of the report, it's actually Eq H1-2 that controls here.
If you reduce your report margins you can get it all on one sheet.
As a further test I set the minor axis eccentricity for column 3B at L12 to 19" and then the program reports H1-1a controls (and the column fails).
I still have to check into why the alternate condition of using Mrx/Mcx vs. Mry/Mcy is not reported here.
Thank you Seth yes I saw that earlier the column was controlled by Eqn H1-2 and it gave a DCR of 0.902. But that happened because Eqn H1-1a did not consider Mrx/Mcx (which comes to around 0.15) in the equation and if added to 0.819 (Pr/Pc) it would give a higher DCR. Please let me know if otherwise.