Use the RF-/DYNAM Pro - Natural Vibrations add-on module for RFEM 5 / RSTAB 8 to easily determine natural frequencies and mode shapes.
Furthermore, the RF-/DYNAM Pro - Equivalent Loads module extension generates equivalent seismic loads using the multimodal response spectrum analysis. The Mexican standard CFE Sismo 08 has already been implemented for you.
RF-/DYNAM Pro - Natural Vibrations Add-on Module for RFEM 5/RSTAB 8 RF-/DYNAM Pro - Equivalent Loads Add-on Module for RFEM 5/RSTAB 8