Study On Synthesis Of Ground Motion And Design Spectrum Considering The Characteristics Of Near-Fault Pulse-like Ground Motion

Near-fault pulse-like ground motion usually has some special characteristics,such as,large amplitude,long period and high concentrated energy.Recently,these characteristics draw more and more attentions of researchers all over the world.Since the energy spectrum or the seismic design spectrum cannot reflect the pulse characteristics of ground motion,either of the two approaches for design of engineering structures in near-fault areas would lead to safety issues.Therefore,research on the effects of pulse-like ground motions on the energy spectrum and seismic design spectrum is necessary,and it will provide references for structural design on near-fault sites.On the other hand,the time-history analysis of structures is always limited since rare of the pulse-like ground motion.Therefore,research on the synthesis of such kind of ground motion is necessary.This study focuses on the identification method,extraction of parameters of pulses,and synthesis of near-fault pulse-like ground motions.Further,the correction of the energy spectrum and design spectrum including the near-fault effects were conducted.In this work,near-fault pulse-like ground motion is studied systematically to provide a scientific foundation and theoretical support for seismic design.The main contributions of this study are as follows.(1)Because the methods proposed for identification of pulse-like ground motion are usually complicated and low efficiency,a relative energy zero rate method(REZR)is proposed to identify the pulse slices of a record.Based on REZR,the trend of increase or decrease of the short-time energy curve and the short-time zero crossing rate is opposite in pulse and non-pulse interval.Further a comparison study is carried out.The proposed algorithm does not need to approximate the original seismic record with any predefined waveform function,and discontinuous pulses in one record can be identified at the same time.(2)Based on the identification of near-fault pulse-like ground motion,the cumulative peak point method is proposed to improve the precisionof current methods when extracting thepulses from a recrod.The correlation between pulse parameters and seismological parameters is analyzed,and the regression models of peak velocity and pulse period are established.Furthermore,near-fault pulse-like ground motion is synthesized according to the stochastic model of low-frequency pulse model,which is used in the nonlinear time history anslysis of structures.As the quantitative knowledge about near-fault effects are more and more,this study provides design recommendations and more consistent safety guarantee for structures located in near-fault regions.(3)The influence of long-period components cannot be ignored for structures subjected to long periods of ground motion.The values of the spectrum in the existing design code are magnified for the specific range of frequency of ground motions and site conditions.In this paper,a modified method is proposed to analyze the frequency of the design spectra in the range of 5Tg to 6s,based on the seismic input spectra of energy reflecting pulse characteristics.The proposed method is evaluated by selecting real records of ground motions with long-period components that possess the characteristic of velocity pulse,and the modified acceleration spectrum is obtained.The pseudo-velocity spectrum and the displacement spectrum associated with the acceleration spectrum are obtained.The proposed method accurately reflects the characteristics of the seismic input spectra for the total and instantaneous input energies.(4)Many studies found it is difficult to represent the response of a structure under real pulse-like ground motion by analytical expression.In this study,four types of simplified pulse-like waveforms are used to derive the relationship between the ground motion parameters and response spectrum.It is suggested that the two-parameter representation should be used instead of only one parameter.The influence of pulse shape on the design response spectrum of four typical pulses are discussed under the condition with the same PGA and same PGV values.Based on the analytical results,the seismic design spectrum is suggested for near-fault areas.This study also provides some suggestions for selecting a pulse model in seismic hazard analysis.