Design of Specific Site Response Spectrum

Abstract eng:
Parameters of response spectra must be reciprocal from physical point of view. Therefore these parameters can’t be set independently. To study the basic properties of spectra one must be normalized to level and predominant frequency. The averaged spectrum shape is more simply when double logarithmic scale is used. It is possible to approximate the spectrum slopes by straight lines. The normalized spectrum has one parameter only: S, logarithmic width of the spectrum. This parameter is defined as the difference between the logarithms of the frequencies of spectral half-maximum points (on the high- and low frequency slopes of the spectrum). Correlations between different parameters of response spectra with 5% damping were provided using 802 records of most intensive horizontal components. The processing of strong ground motion records shows that the correlation between parameters is considerable. The value of S is very stable disregard to earthquake magnitude, source mechanism, distance and ground condition. Influence of these factors is estimated. It is shown, that response spectrum for acceleration is practically symmetrical in double logarithmical scale. The mean spectrum slopes are proportional to frequency. The spectrum slopes are estimated also for different confidence levels. It is possible to estimate the media quality Q from parameters of response spectrum. The quality Q and logarithmic spectrum bandwidth are functionally connected. Thus to design the site specific one need to estimate expected level of ground acceleration and expected predominant period. The empirical relations to estimate these values are proposed.

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