Development of soil amplification factor by considering the dependency of Chinese site classes and natural vibration period

The fifth generation of the Chinese seismic hazard map (CSHM5) in terms of the return period value of the annual maximum peak ground acceleration (PGA) was adopted as the basis for seismic design. The PGA value is used as a scaling factor together with the seismic design coefficient curve (i.e., standardized response spectrum) to obtain the seismic design spectrum. CSHM5 also recommended the soil amplification factor, F _a , based on the PGA value alone to account for different site classes, although such a suggested value is not adopted by the code, and the soil amplification of the response spectrum depends on the fundamental natural vibration period of the structure, T _n . In the present study, we calibrate the T _n -dependent soil amplification factor by considering the Chinese site classification and the seismic hazard mapping results over the Chinese mainland. For the calibration, we used the seismicity model employed to develop CSHM5 and a set of newly projected ground motion models for different seismic regions over the Chinese mainland. Our results indicate that the soil amplification is insensitive to the earthquake magnitude and distance, and seismic regions in China. It was found that our calibrated factor is smaller than that suggested by CSHM5 for site Classes I₀ and I₁, and this is reversed for site Classes IV. For practical applications, based on the calibrated values, we developed new empirical predictive equations for the soil amplification factor for each site class stipulated in the Chinese seismic design code.