I am designing 3-story Eccentric Brace Frames using the Seismic Provisions in RAM Frame and I am confused with the required strength value that is being determined for the axial design of the 1st story column.
The Member Code Check report for the column indicates that the required strength is being determine per AISC 341-10, Section D1.4a, which which notes that the required strength of columns shall be determined by 1) the load effects of Chapter F, and 2) the amplified seismic load per applicable building code.
From what I can tell, RAM checks the ultimate axial load considering the seismic load amplified by Omega (omega*1.0E = 2.0E), but it does not (edit) completely check for the axial load required by Chapter F.
In Section F3.3, the required strength for columns shall be determined assuming the the forces at the ends of the links correspond to the adjusted link shear strengths. In other words, the required axial strength should be the ultimate gravity axial load plus the summation of Vmh of the links in the stories above (which is exactly what is shown in the design examples provided in both the AISC Seismic Design Manual, as well as the SEAOC Seismic Design Manual).
RAM approaches this check differently. Instead, RAM determines an amplification factor per Link Capacity / Max Link Shear for the link at the given level, and amplifies the seismic axial load with that factor (in this example, it is 1.53). There is a note at the bottom of the Member Code Check Report that indicates that the axial design check assumes all links at the stories above yield at the same amplification level of seismic forces as the link at the given level. I am finding this assumption to be very unconservative, as the link cap/demand ratios for the links above can be much larger (1.84 and 2.94, in this example). This means the required axial strength is not properly considering the Vmh for the links at the stories above and is much smaller than required (for this example, Pu = 372 kips per RAM, but hand calcs show Pu = 478 kips).
Why would RAM implement an assumption that can be so dangerously unconservative? Why is there not a check that properly implements the requirements of AISC 341, Section F3.3?