Average Normalized Time-Frequency Response Spectrum for Different Types of Sites

The normalized time-frequency response spectrum is a three-dimensional spectrum that includes the three essential components of seismic motion: amplitude, frequency spectrum, and duration. It can effectively compensate for the shortcomings of traditional response spectrum theory and elastoplastic time history analysis. To better study the structural damage mechanism and predict the potential destructiveness of seismic motion, the structural damage curve must be combined with the normalized time-frequency response spectrum. According to four site categories, 10 seismic records were selected from the Pacific Earthquake Engineering Research Center earthquake motion database. The site categories in the US are classified based on the equivalent shear wave velocity Vs30 of the surface soil layer thickness up to 30m. Sites with a shear wave velocity Vs30 above 510 m/s correspond to Category I sites in Chinese standards; Vs30 between 510 m/s and 260 m/s correspond to Category II sites; Vs30 between 260 m/s and 150 m/s correspond to Category III sites; and Vs30 below 150 m/s correspond to Category IV sites in Chinese standards. Through statistical analysis, the normalized time-frequency response spectrum for each site category was calculated and then averaged, resulting in what is referred to as the average normalized time-frequency response spectrum for each site category. This provides a reference basis for subsequent structural seismic verification, seismic design of buildings, and the revision of seismic regulations.