Seismic Performance Evaluation Of RC Frame Structures Considering Directivity And Main And Aftershock Effect

Historical data show that a single earthquake may be accompanied by aftershocks.After the main shock,the structure is damaged,its stiffness and strength change,and the stress and strain inside the component are redistributed.Under the action of aftershocks,the structural damage is often aggravated,and it is difficult to ensure the structural safety.The research shows that there is a great difference between the structural response under the action of the main shock and the main aftershock sequence type ground motion^[1].Even a small aftershock may cause great damage to the structure.Therefore,the study of the structural response under the action of the main aftershock is of great significance to the actual earthquake resistance.The ground motion has the characteristics of randomness and complexity.In the code^[2],the ground motion is applied on the two principal axes of the structure and the response combination method is used to consider the input direction of the ground motion.However,the ground motion in the actual earthquake disaster may come from any direction,and the most unfavorable direction of the structure under the earthquake action is not necessarily in the principal axis direction.Therefore,it is of theoretical and practical significance to consider the dynamic response analysis of the structure in different main and aftershock input directions.A 6-story reinforced concrete（RC）frame structure is designed according to the mainshock-aftershock design spectrum.The mainshock-aftershock sequence is incident into the structure in different directions to analyze the structural response.The structural response law of the mainshock-aftershock ground motion is summarized when the mainshock-aftershock ground motion is incident in different directions,and the response difference between the directional effect and the mainshock-aftershock effect is compared.Based on the law of the most unfavorable incident angle,the incremental dynamic analysis of RC frame structure is carried out,and the probabilistic seismic vulnerability model is established to analyze the seismic performance of the structure from the aspect of exceeding probability.The main research results are as follows:1)A 6-story RC frame structure is established by yingjianke,and the finite element model of the structure is established in Open Sees.The modal information and elastic-plastic time history analysis results in Open Sees software and SAUSAGE are compared.Taking the quasi-static collapse test data of the test frame structure as the simulation object,the structural hysteresis curve under quasi-static action is analyzed,and the finite element model is established to verify whether the model in Open Sees meets the engineering application.2)Four kinds of response parameters,including base shear,top displacement,story drift angle and improved Park-Ang damage index,are selected to analyze the sensitivity and response law of the four response indexes when the directional effect and the main aftershock effect are considered separately.The appropriate response indexes are selected to study the dynamic response characteristics of RC frame structures considering directional effect and main aftershock effect.The results show that the top displacement,base shear force and inter-story displacement angle are more sensitive to the directivity,but the three indexes are less sensitive to the main aftershock effect.The improved Park-Ang damage index maintains high sensitivity to the directivity and the main aftershock effect,which can be used to measure the damage effect of the two effects on the structure.The structural response considering both directivity and mainshock-aftershock effect is calculated,and the variation law of structural response with incident angle under mainshock-aftershock effect is analyzed.3)Based on the previous study of the most unfavorable incident angle,the appropriate ground motion intensity index and structural damage index are selected,and the different limit states of the structure are defined.The incremental dynamic analysis of the RC frame structure under different incident angles is carried out,and the structural vulnerability model is established to analyze the seismic performance of the structure from the probability.