Use the Modal Analysis add-on for RFEM 6 / RSTAB 9 to determine natural frequencies and mode shapes with minimum effort.
In contrast, the Response Spectrum Analysis add-on for RFEM 6 / RSTAB 9 allows you to perform seismic analyses using the multi-modal response spectrum analysis. Among others, the Indian standard IS 1893 is also implemented here.
Modal Analysis Add-on for RFEM 6 / RSTAB 9 Response Spectrum Analysis Add-on for RFEM 6 / RSTAB 9