By using the parameters determined in Table 12.2-1 and 11.5.1, the Reduced Design Spectral acceleration, Sa is determined automatically according to Section 12.9.1.2.
Symbols
Cd = Deflection amplification factor
Ie= Seismic importance factor
R = Response modification coefficient
The reduced design spectral acceleration Sa, which is the ordinate of the reduced design acceleration spectrum for a given natural vibration period T, used to determine the reduced seismic loads in the horizontal direction, is that of Sa Horizontal Elastic Design Spectrum (ASCE 7-16), is obtained by dividing the R, Reduced Design Acceleration Spectrum for Modal Analysis and multiply with Ie.
On the Analysis ASCE 7-16 Wizard - Design Spectra tab, the spectral acceleration coefficients obtained from USGB based on the coordinates and the horizontal elastic design spectrum Sa is calculated according to the formula below . Horizontal Elastic Design Spectrum (ASCE 7-16), it is represented by a total of 4 functions, different in each region, and shown with the graph below.
According to the structural system type, using the R, Cd and Ωo coefficients obtained from Table 12.2-1, R/Ie and the reduced design spectral acceleration are calculated automatically.