Damage Spectra Based On Main Shock-aftershock Sequence-type Ground Motions

Historical earthquakes have showed that many aftershocks often follow the occurrence of a large main shock. Structures subjected to practical seismic excitations may be subjected to one or more aftershocks within a short period following the occurrence of main shock, in such cases, aftershocks have the potential to cause collapse of a structure that has been already damaged by the preceding main shock and not yet been repaired because of the accumulation of damage. This phenomenon, which can be easily found in many earthquake field reconnaissance reports, will cause extensive property losses and injuries to building occupants. However, the most current seismic codes in the world only consider single'design earthquake'without taking into account the influence of the main shock-aftershock sequence-type ground motions. Damage spectra can measure the actual damage of structures under the earthquakes for their comprehensive consideration of first passage failure and low cycle fatigue failure; they can be used to illustrate the effect of damage accumulation of main shock-aftershock sequence-type ground motions. Up to now, only a few researchers studied the characteristic of damage spectra and most of them ignored the effect of aftershock, so there is still a long way to go to explore the characteristic of damage spectra of main shock-aftershock sequence-type ground motions. This dissertation will study the damage spectra of main shock-aftershock sequence-type ground motions, the main contents of this dissertation are as follows:(1) The NGA-based method to construct main shock-aftershock sequence-type ground motions is recommended, which is based on the utilization of the seismology statistic law and the summarization of the other methods of constructing this type ground motions.(2) The systematic analysis on response characteristic of the inelastic SDOF structures under the main shock-aftershock sequence-type ground motions are performed. A rational method to calculate the Park-Ang damage index is proposed, the damage index with this method can effectively consider the accumulation of damage. On this basis, the accumulations of damage of the inelastic SDOF systems under the main shock-aftershock sequence-type ground motions are analyzed with the damage index and the corresponding level of earthquake intensities.(3) Damage spectra of main shock-aftershock sequence-type ground motions on four different class sites are researched with a large number of constructed main shock-aftershock sequence-type ground motions. The influences of period of structures, force reduction factor, site condition, damping, and hysteretic model on the damage spectra are investigated, and the corresponding quantitative results are presented.