On Near-fault Ground Motion Refined Characteristics Based On Decomposed Method

Recent years, researches show that, due to the impact of the fault rupture forward directivity effect, ground motion lacated in near-fault region usually behaves high velocity amplitude, short duration and long-period characteristic, which has spectial destructive effect to long-period engineering structures. Containing ample low-frequency components is one of the major characteristics that for near-fault ground motion different from the ordinary record, meanwhile which is the major reason that cause serious damage to long-period structure. In traditional study, pulse characteristic always is the major content, but scarce scientific analysis on the long-period characteristic of near-fault ground motion has been made. The traditional seismic design spectrum is obtained by the statistical averageing and smoothing by a large number of ground motion response spectra. But this approach has failed to consider the effect of near-fault ground motion. For futher study the engineering speciality of near-fault ground motion and try to propose a near-fault response spectrum which is suitable for structure seismic design in fault zone, near-fault ground motion is decomposed based on multi-scale method, and then the produce reason for many features of near-fault ground motion is revealed from the aspect of ground motion component, and used for seismic design. The main research content includes the following several aspects:(1)Multi-scale analysis is introduced in the dispose process of near-fault ground motion, and a reliable ground motion decomposition methos is proposed. The accuracy and effectiveness of this decomposition method is discussesed. A suite of typical near-fault ground motion is decomposed by this method, and a series of ground motion component is obtained. According to the difference of frequency range,4classes of ground motion component with different frequency content are divided.(2)The parameter characteristic (amplitude, period, etc) is systematically analysed in this paper. Pulse characteristic and the composition of low-frequency components are explored from the aspect of component. The attenuation relations of acceleration amplitude for near-fault ground motion and its component are given out in this study. (3) The analysis on normalized and bi-normalized response spectra is presented in this paper. A near-fault response spectrum which could effectively considering of near-fault ground motion direction effects is proposed based on the bi-normalized response spectra of ground motion component. The comparison between design spectra is also carried out in this paper.(4) The constant ductility displacement ratio spectra and the constant ductility strength reduction factor spectra of original ground motion and ground motion component are analysed in this paper. The reason that caused to the difference for inelastic spectrum between near-fault ground motion and ordinary ground motion is explored in this study.