The site class is determined by the user.
Design Response Spectrum parameters are determined automatically using equations specified in Codes.
International Design Codes
ASCE 7-16 : 11.4.4 Site Coefficients
TSC 2018 : Site Class and Site Coefficients
Notation in ACSE
Fa = Short-Period Site Coefficient
Fv = Long-Period Site Coefficient for a period of 1.0 seconds
SMS = Short-period design spectral response acceleration parameter [dimensionless]
SM1 = Design spectral response acceleration parameter for a period of 1.0 seconds [dimensionless]
SS = the mapped MCER spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.2,
S1 = the mapped MCER spectral response acceleration parameter at a period of 1 s as determined in accordance with Section 11.4.2
SD1 = Design spectral response acceleration parameter for a period of 1.0 seconds
SDS = Design earthquake spectral response acceleration parameters at short periods
Site Class, a classification assigned to a site based on the types of soils present and their engineering properties. Based on the site soil properties, the site is classified in various names. By determining the site class, the site coefficients are determined for design response spectrum curve. Site class and site coefficient are defined in Seismic Design Codes.