How do you plan to connect the hollow core to the light gage walls? I am not sure if this is part of your question.
As others have mentioned, you can place rebar in the cut end cores and grout. You might consider a continuous angle with headed studs welded to the top track. The grout will...
I totally agree with StructuralEIT on the RamAdvanse and RamSS comments.
I use them both in a similar fashion.
I tried STAAD after I already used RamAdvanse, and it did not take long for me to give up based on the poor user interface.
I understand your question. However, you should think of the flexible diaphragm in terms of force distribution based on tributary widths to the frame/shearwall.
It would be conservative to take the worst case from your simple/continuous beams models, but if you feel better using this than go...