Research On Damage Spectrum Of Soft Ground Main-aftershock And Near Field Pulsed Main-aftershock

After the main shock has occurred,a large number of aftershocks will occur in a short period of time,thus forming a sequence earthquake.The structure often breaks down under the action of the main shock,and the action of the strong aftershock will increase the damage of the structure,produce the accumulative damage effect,and even destroy the damaged structure.But the reality is that the seismic design code of China and the world are only considering a single earthquake,did not mention the influence of the structure of the aftershocks,which significantly underestimated the ability to destroy the ground motion sequence.The frequency of ground motion of soft soil site is rich,and the amplification of structure acceleration is especially obvious in every period of structure;The near-field pulse type seismic source is near and the velocity history contains obvious velocity pulses,especially the damage to the structure.Therefore,the study of the failure ability of soft soil and near field main-aftershock ground motion is very important for considering the aftershock action in structural seismic design.The damage spectrum considers the contribution of structural displacement and hysteretic energy dissipation to the ultimate damage of structures.It can effectively reflect the damage effects of ground motion on structures and the cumulative damage effects of multiple earthquakes.Therefore,it has important research value.But so far,the study of ground motion damage spectrum of soft soil and near-field pulse type main-aftershock is still blank.Therefore,this paper will systematically study the damage spectrum of soft ground and near-field pulse type main-aftershock.The main research contents are as follows:(1)Firstly,the magnitude relation between the main shock and aftershock is calculated according to historical earthquake data.Based on the prediction formula of aftershock earthquake motion,a method for generating ground motion of soft soil main aftershock and impulsive main-aftershock is proposed.soft soil main aftershock and impulsive main aftershock are generated by the selected ground motion.(2)The reaction characteristics of inelastic single degree of freedom structure under the main aftershock of soft soil are studied.The influence of aftershock on different reaction indexes is analyzed and compared.The characteristics of damage spectrum are analyzed statistically by using the structure of the main-aftershock of the soft soil,and the influence of aftershock on the damage spectrum is studied,and the prediction formula of the earthquake damage spectrum of the soft soil main-aftershock is put forward.The results show that the damage index can reflectthe cumulative damage of the structure under the main-aftershock.The influence of aftershock on the damage spectrum of EPP model can reach 30%,which has more influence on the damage spectrum of the degenerated model.(3)The damage spectrum characteristics of near field pulse type main-aftershock ground motion are studied.The influence of factors such as cycle,strength reduction factor,hysteretic model and aftershock strength on the damage spectrum is quantitatively analyzed.A prediction formula of seismic damage spectrum of near field pulse type main-aftershock is proposed.The results show that the near-field pulse ground motion is more harmful to the shorter periodic structure than the non pulse;the damage to the longer periodic structure is smaller than that of the non pulse;and the influence of the three near-field pulse type aftershocks on the damage spectrum can exceed 20%.