Research On Near-fault Pulse-like Ground Motion Filter Processing Method

Filtering is one of the key steps of earthquake ground motion processing before its application to engineering practice,and high-pass filtering is particularly important due to rich contents of low frequency in pulse-like ground motion signals.In particular,the impulsive properties of the ground motion recorded in near-fault zones are very sensitive to the high-pass filtering,and thus selecting a reasonable filtering method becomes a critical issue that determines the reliability of the structural analysis results.This study aims to investigate the high-pass filter processing method of near-fault pulse-like ground motions.The pulse-like ground motions were processed by Butterworth acausal high-pass filter using two methods,relative cutting frequency that is dependent on the pulse frequency f_p and absolute cutting frequency,respectively.The influence of filtering on the attenuation of the elastic displacement response as well as constant ductility inelastic displacement spectra,inelastic displacement ratio spectra,strength reduction factor spectra and energy spectra were investigated from a set of pulse-like ground motions filtered with different parameters.The influence of cutting frequency on the lowest usable frequency,determination of the pulse properties and pulse period of pulse-like ground motion were also analyzed.In addition,the application and rationality of the two cutting frequency values were compared based on the response analysis of the J2 high-rise base-isolated structure.The findings obtained from the investigations can be concluded as follows:(1)The filtered response spectra results of pulse-like ground motions are significantly affected by their pulse periods.As the relative cutting frequency is 0.4times as small as the pulse frequency,the pulse characteristics including pulse properties and pulse period of before and after filtering remain the same.At this time,the ratio between cutting frequency and lowest usable frequency is nearly 0.8,similar as that obtained from general far-field ground motions.(2)Compared with the elastic spectra,inelastic spectra are more sensitive to filtering.The filtering leads to the greater amplified effect on inelastic spectra during tiny period,and thus attention should be paid to filtering.As the cutting frequency is less than 0.2f_p,there is no significant change between the inelastic spectra characteristics and the pulse properties.(3)The pulse-like ground motions are divided into two groups with 3 s as a threshold,and a cutting frequency of 0.10 Hz and 0.20 Hz were recommended for application to short-to-mid period pulse records(T_p,unpro<3 s)and mid-to-long pulse records(T_p,unpro>3 s),respectively.Under these filtering conditions,the pulse-like records still retain the pulse properties,and minor changes have been observed in their response spectra within the period range of engineering interest.(4)Based on the response of the J2 base-isolated structure,the results of pulse-like ground motions after filtering with relative cutting frequency have large dispersion.Therefore,as for high-pass filtering of pulse-like ground motion,it is recommended to adopt the method of absolute cutting frequency.(5)There is great difference between high-pass filtering of pulse-like ground motions and that of non-pulse-like ground motions.The high-rise base-isolated building is far less sensitive to filtering when subjected to non-pulse-like ground motions than pulse-like ones.For non-pulse-like records,0.10 Hz is recommended for filtering use considering that much less dispersion was observed in the results.