Analysis Of The Characteristics Of Horizontal Pulse-like Ground Motion Parameters

The strong damage of engineering structures caused by pulse-like ground motions has aroused wide attention of earthquake engineering researchers.The analysis of the characteristics of pulse-like ground motions is of great value to reveal the generation mechanism of pulse and to carry out the seismic fortification of engineering structures.Previous studies have shown that the ground motion characteristics of pulse-like ground motions in the strongest pulse direction are significantly different from those in other horizontal directions,and the seismic response of the structures in the strongest pulse direction is more significant.The research on the characteristics and influencing factors of pulse period which plays an important role in the seismic analysis of near-fault structures is not comprehensive.In order to reveal the variation of the ground motion parameters of pulse-like ground motions in the strongest pulse direction with fault distance,and to explore the relationship between the pulse period and ground motion parameters,based on the pulse-like ground motion records of Taiwan Chi-Chi earthquake and other earthquakes with pulse-like ground motions in the near-fault area selected from PEER database,the spatial distribution characteristics and attenuation laws of amplitude,spectrum,duration and energy of the perpendicular and parallel to the fault strike directional components and strongest pulse directional component of Chi-Chi earthquake pulse-like ground motions were compared and analyzed.The variation of pulse period of near-fault ground motions with magnitude and the correlation between the pulse period and ground motion parameters were discussed.The main research contents and results obtained are as follows:(1)The continuous wavelet transform was used to identify the strongest pulse directional component of the selected pulse records.(2)11 kinds of ground motion parameters of the perpendicular and parallel to the fault strike directional components and strongest pulse directional component of the selected pulse records were calculated.(3)The spatial distribution characteristics of 11 kinds of ground motion parameters of the perpendicular and parallel to the fault strike directional components and strongest pulse directional component of the pulse-like ground motions of Chi-Chi earthquake were compared and analyzed.The results show that the spatial distribution of the amplitude,spectrum and energy parameters of strongest pulse directional component in the near-fault area is generally more significantly affected by the directivity effect,fling-step effect,and hanging wall effect than that of the perpendicular and parallel to the fault strike directional components.The spatial distribution characteristics of duration parameters of three horizontal components in the near-fault area are similar.(4)The non-linear least square method was used to analyze the attenuation laws of11 kinds of ground motion parameters of the horizontal recording,perpendicular and parallel to the fault strike directional components and strongest pulse directional component of pulse-like ground motions of Chi-Chi earthquake.Except for 90% energy duration,the other ground motion parameters decrease with the increasing of fault distance.The attenuation laws of various ground motion parameters have obvious directional differences.Except for the acceleration response spectrum peak,the displacement response spectrum peak and the duration parameters,the attenuation speed of the other ground motion parameters in strongest pulse direction is greater than that of the other horizontal components.(5)The near-fault pulse-like ground motion time histories which are perpendicular and parallel to the fault strike direction and the strongest pulse direction were identified,and the pulse period of each time history was determined.The variation of the pulse period of three horizontal components with magnitude was compared.The results show that the pulse period of each component increases with the increasing of magnitude.The rate of pulse period increasing with the increasing of magnitude is the fastest in the perpendicular to the fault strike direction,the slowest in the parallel to the fault strike direction,and the strongest pulse directional component is between them.In most cases,the pulse period of the bedrock site increases faster with the increasing of magnitude than that of the soil site.In bedrock site,the pulse period of the strike-slip fault ground motion increases faster with the increasing of magnitude than that of the non-strike-slip fault ground motion,but it is the opposite in soil site.(6)The correlation between the parameters and the pulse period of the components in perpendicular and parallel to the fault strike direction and the strongest pulse direction of the near-fault pulse-like ground motions was analyzed.The results show that in addition to the velocity peak and the velocity response spectrum peak of the parallel to the fault strike directional component,the other ground motion parameters of the parallel to the fault strike direction and the 11 ground motion parameters both in the perpendicular to the fault strike direction and the strongest pulse direction show that the logarithmic linear correlation with the pulse period is stronger than the linear correlation.Among the 11 kinds of ground motion parameters,the displacement peak and the displacement response spectrum peak of the three directional components show the strongest logarithmic linear correlation with the pulse period.