ABSTRACT
A survey of previous applications of frequency content indicators suggests that the utilization of these indicators has been applied mainly to SDOF systems or to MDOF systems but using the predominant period as the indicator. This parameter is known to have significant scatter in data and hence not recommended for use as an indicator of frequency content (Rathje et al., 2004). In this study, the mean period of the ground motion (Tm) is adopted due to its accurate representation of acceleration time history and also since a large portion of the frequency range of a record is used in its calculation. Additionally, this parameter is stable and reliable, and has the ability to reflect the variation in shapes of response spectra; it holds a linear variation with distance and nonlinear variation with magnitude (Rathje et al., 2004). Tm represents the mean of the periods of the Fourier Amplitude Spectrum (FAS) in the specified frequency ranges, where the weights are assigned based on the Fourier amplitudes and calculated using following expression.
