The responses obtained from the Response Spectrum analysis are absolute unsigned quantities. One can not determine the nature of the forces as they are absolute in nature. It is not suggested to use direct Response Spectrum load case in design. You need to create factored load combination of a Response Spectrum load case with dead load and imposed loads. These load combinations are to be used in design.
There has been an immerging concept of using Signed Response results. In buildings, use of the sign of responses from the dominant mode (where the % of mass participation is the highest) is a popular method. You may refer to the following literature.
Please refer to attached model where DOMINANT 0 command is used to instigate the sign of responses from the dominant mode.
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