What kind of SNIP is this? It is unclearly, why static vertical load should be taken regardless of horizontal seismic?
Otherwise, take the elevation (for instance overlapping) you are interested in and which will be checked. Calculate load on fragment from columns of upper storey (in general, even from stairs flight) in interfacing nodes with considered elevation. Calculate DCL both with seismic and without it. Open standard table of loads on fragment for nodes from DCL without seismic (firstly one combination, then each one separately), then transfer it to EXCEL and summarize column with vertical loads. It will be static vertical load from certain DCL (it could be few DCL). Do it in the same manner, but for DCL with seismic. While, in Excel, first count separately the sum for x and y columns. After you have obtained total x and y, find their resultant. This will be the shear force. Again, if you have few DCL tables with seismic, then do it for each separately.
Something like that, theoretically.