Study On Parameter Characteristics And Damage Spectra For Mainshock Aftershock Ground Motions

Past earthquakes have shown that the mainshock is always followed by lots of aftershocks. Aftershock will increase the damage of structure which has been damaged by the corresponding mainshock. Because of the short time interval existed between the mainshock and aftershock, it is impossible for the mainshock-damaged structure to be repaired before the subsequent aftershocks. Thus it is necessary to incorporate the aftershock into the seismic design. However, the current seismic design codes are based on the mainshock or single earthquake, while ignoring the danger of aftershock. In this case, the structure designed by these codes may experience unexpected damage in the mainshock aftershock enviroment, and then cause the unacceptable human injury and economic loss.In the field of earthquake engineering, the study of ground motion characteristics and inelastic response spectra play an important role in the seismic design. The damage spectra can comprehensively consider the contribution of deformation and hysteretic energy to the damage of structure, thus it can provide a more accurate evaluation on the damage of the structure under the ground motion. In order to consider the danger of aftershock in the seismic design, this dissertation studies the mainshock aftershock ground motion characteristics and damage spectra. The main contents are as followings:(1) The relation of intensity measure between the aftershock ground motion and mainshock ground motion is studied. Based on the analysis, the conditional prediction equation of aftershock ground motion is proposed, and the results of this study are compared with other prediction equations. It should be noted that the aftershock ground motion prediction equation proposed here depends on the mainshock.(2) The influences of aftershock on ductility demand, residual displacement ratio, normalized hysteretic energy and damage index are studied. The ability of these response indicators to characterize the additional damage of structure is compared. The results indicate that the hysteretic energy and damage index are more effective than the ductility demand to reflect the additional damage of the structure. In the post earthquake environment, the residual capacity of the structure evaluated with residual displacement may provide the un-conservative results.(3) The damage potential of aftershock ground motion is analyzed by the correlation between the relative intensity of aftershock ground motion and relative damage index of structure. The effects of period of vibration, strength reduction factor, hysteretic models are studied. Based on the weighted mean correlation coefficient, the final intensity measures are selected to represent the damage potential of aftershock ground motion for the entire period range. The results indicate that spectral acceleration can better characterize the damage potential of aftershock.(4) The effects of ground motion scaling on the structural damage are based on the correlation analysis. The efficiency of the scaling measure is analyzed by comparing the correlation between the scaling measure and structural response before and after scaling. The results indicate that the scaling has greater influences on the aftershock ground motions, and efficiency of scaling measure for aftershock ground motion is more random when the scaling factor increases. Spectral acceleration generally has higher efficiency than other scaling measures.(5) With the modified Park-Ang damage index, 4 hysteretic models and lots of mainshock aftershock ground motions, the damage spectra for the mainshock aftershock ground motions are investigated. The aftershock ground motions are scaled by spectral acceleration to different intensity levels to simulate the aftershocks with different intensities. The influences of period of vibration, strength reduction factor, site condition, aftershock intensity, damping, hysteretic model, and the parameters in the definition of damage index on the damage spectra are studied. The prediction equation of damage spectra is proposed to facilitate the application in the seismic performance evaluation.