I believe that in order to check for soft-storey symptoms the user should investigate whether or not plastic hinges may form in the columns of the same storey. This would have to do with the resistance of all members framing to the column in question and their potential overstrength. I do not think that story shear would indicate such issues. In fact I think that in order to verify the design against such issues in ETABS you need to perform a pushover analysis so as to enable frame elements to yield and hence reveal the collapse mechanism of the structure.
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