Study On Cumulative Additional Damage Of RC Frame Structures Under Main Shock-aftershork Sequence-type Ground Motions

It is showed by the large number of historical seismic data that the probability of a single earthquake is very small after an earthquake occurs,which means there are so many aftershocks accompanied by when a strong earthquake occurs.According to the statistics,about the 89% strong shallow earthquakes are often accompanied by strong aftershocks and most aftershocks tend to occur in a short period of time after the main shock.It makes the structure damaged in the main shock subjected to aftershocks before having time to be repaired and reinforced,which the damage of the structure already damaged is increased or even the structure si collapsed,the more serious casualties and the property losses are caused.However,unfortunately in the current seismic design codes of our country and most other countries of the world the only single earthquake is considered but the aftershocks that can cause cumulative additional damage of the structure are not taken into account,which makes the designed structure is tend to unsafe.Therefore,it is of great significance that the study of the cumulative additional damage of the structure caused by aftershock is carried out.Based on the previous studies,taking a five story reinforced concrete frame structure as an example,firstly the influence on the analysis results of the different time interval between the main shock and aftershocks is studied;secondly the differences between each index which are measured the cumulative additional damage of the structure caused by aftershocks is studied;thirdly the variation pattern of the cumulative additional damage of the structure caused by aftershocks is studied;lastly the effect of cumulative additional damage of the structure by the characteristic of the aftershocks and the damage degree of the structure in the main shock is studied.The main contents are showed as follows:(1)A typical five story reinforced concrete frame structure is designed by using PKPM,then the finite element analysis model of the frame is established by using the finite element performance evaluation software PERFORM-3D and the research on the above mentioned problems are carried out one by one through taking this model as an example.(2)The influence on the analysis results of the structure response of the different time interval between the main shock and aftershocks is studied when the main shockaftershock sequence is constructed.(3)The differences of different damage indexes(deformation index,energy index and composite index),which are measured the cumulative additional damage of the structure caused by aftershocks are studied,and the characteristics and the use of each damage indexes are described and some suggestions are given.(4)Using the beam and column component utilization index,the damage index DId based on the component deformation,the damage index DIE based on component energy consumption and the Park damage index DIp four damage indexes,the variation pattern of the cumulative additional damage of the structure under the action of aftershock from the component damage level is studied.(5)The effect of cumulative additional damage of the structure by characteristic of the aftershocks and the damage degree of the structure in the main shock are studied.