Defining Time history ground accelerations in orthogonal directions

I need to define ground acceleration using time history loading in orthogonal directions. How can I do that in STAAD.Pro ?

An example file is attached (Please visit the site to view this file)

Please note that in STAAD.Pro, one cannot have multiple time history load cases in the same file but one is allowed to define multiple time history loads as part of the same load case. So one is allowed to define ground accelerations in the form of acceleration time histories in two orthogonal directions as long as these are specified as part of the same load case.