Modal response spectrum analysis specified in Codes is done automatically.
İnternational Design Codes
ASCE 7-16 : 12.9.1 Modal Response Spectrum Analysis
TSC 2018 : Modal Response Spectrum Analysis
Number of Modes: The natural modes of vibration for the structure is determined by structural analysis. The analysis should include a sufficient number of modes to obtain a combined modal mass participation. Modal mass participation value is given Codes.
Modal Response Parameters: The value for each force-related design parameter of story drifts, support forces, and individual member forces for each mode of response, is computed using the properties of each mode and the response spectra defined in Codes.
Combined Response Parameters: The value for each parameter calculated for the various modes is combined using the square root of the sum of the squares (SRSS) method or the complete quadratic combination (CQC) method.