Study On Extraction Of The Velocity Pulse And Effects Of Inclusion On Ground Motion

There are a large number of pulse records in the near fault ground motion,and the velocity pulse has a significant influence on the long period structure.Therefore,the velocity pulse has attracted the attention of seismologists and engineers.The ground motion would be amplified or shielded at different frequencies by the complex site,such as the inclusion and the interlayer,so the complex site would be taken into the consideration seriously by the location and seismic fortification of the building.On the basis of previous studies,we establishes a mathematical model to fit the pulse amplitude,pulse period,half pulse number and phase of pulse record,and studies preliminarily how the inclusion and interlayer affect the ground motion and pulse-like characteristic of the typical velocity pulse under vertical three-dimensional wave incidence.The main conclusions are as the following:1.Combined with the previous research on the method of velocity pulse extraction,we establishes a new mathematical expression of the pulse model,which can fit different shapes of velocity pulses,and gives the velocity pulse discrimination index appropriate to it.Using the pulse records of NGA,We nchuan earthquake and Ludian earthquake,the results obtained in this paper are compared with the Baker wavelet method.The results show that the fitting results of the mathematical expression of the pulse model presented in this paper can reflect the pulse characteristics of the original velocity record,and the residual energy ratio(Energy ratio)can be a pulse type ground motion discrimination index.2.By using three dimensional finite element method and transfer function,the influence of the inclusion size,impedance ratio,depth and the distance between two inclusions on the ground motion is studied.Research shows that,under the same frequency,the point affected most by inclusion is located in a straight line parallel to the vibration direction o f incident wave and through the centroid.Below the frequency of initiation of shielding effect,the point affected most by soft inclusions is located on the sides of the inclusion;when higher than the frequency,the one is the centroid..The long axis of the amplification effect region at a certain frequency is the wavelength corresponding to the frequency.With increase of the inclusion size,the distance from the point affected most to centroid increases;in the soft inclusion,the degree of growth of transfer function of the centroid is the most;in the hard inclusion,the degree of decrease of transfer function of the centroid is the most;the initial frequencies of amplification effect and shielding effect of soft inclusion and shielding effect of hard inclusion are all reduced;the rang from the initial frequency of amplification effect to the one of shielding effect is reduced.With the increase of the impedance ratio,the initial frequencies of amplification effect and shielding effect of the soft inclusion increase;the initial frequency of the shielding effect of the hard inclusion is reduced;the rang from the initial frequency of amplification effect to the one of shielding effect increases.With the increase of depth,the initial frequencies of a mplification effect of the soft inclusion and shielding effect of the hard inclusion all increase;the long axis of the safe region of hard inclusion increases;the long axis of the dangerous region of soft inclusion is reduced;in the soft inclusion,the degree of decrease of transfer function of the centroid is the least.in hard inclusion,the shielding effect is dominant,the amplification effect of area far from inclusion can be ignored.When the wavelength is smaller than the spacing between the two inclusions,there is on effect on each other.The area affected most is located between the two inclusion,and the degree of amplification effect or shielding effect,decreases with the increase of spacing.With the decrease of the spacing,the initial freq uencies of the amplification effect of soft inclusion and shielding effect of hard inclusion decrease,and the initial frequency of shielding effect soft inclusion is unchanged.3.The effect of three dimensional single inclusion and the actual complex interlayer on the velocity pulse shows that,with the inclusion size variation,the change of PGV and pulse amplitude is also increasing,and when the inclusion size is large enough to be considered as an interlayer,the change of PGV and the pulse amplitude is very obvious,but the pulse period is almost constant.