Idestatic performance analysis is for reinforced concrete buildings. The building you mentioned has the characteristics of a masonry building rather than reinforced concrete. Building a masonry building on this type of reinforced concrete building is already against the regulations, but if you want to give an account to the municipality. First, load this floor's loads on a lower floor. Then treat this floor as a separate masonry building and you have to do the performance analysis manually as stated in section 7.7.5 of the Earthquake code. An additional note: If your project is not very urgent, it is useful to wait for version 6.403 for performance analysis in reinforced concrete structure. Performance analysis has been greatly improved in this version. Suat