The site class is chosen by the user.

According to ASCE 7-16 Section 20.3. 1, site response analysis must be performed for F site classes.

Spectrum parameters are determined automatically using Equation 11.4-3 and 11.4-4.


SYMBOLS

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 Coefficients 

According to ASCE 7-16 Table 20.3-1, the soil class is determined according to the top 100 ft (30 m) of the soil profile. It has been defined as six classes, from A to F according to Table 20.3-1.

Depending on the site classes defined in ASCE 7-16 11.4-1, site coefficients Fa and Fv are given in Table 11.4-1 and Table 11.4-2. Straight - line interpolation is performed for intermediate values ​​of site coefficients in the tables.