| The ancient masonry tower has a long history in China,which is an outstanding representative of ancient high-rise buildings.Affected by the natural environment and human factors,the tower structure will be damaged to varying degrees,and the earthquake is one of the main factors causing the damage of the ancient masonry tower structure.China is a country with frequent earthquakes.It is very common that ancient masonry towers are damaged by earthquakes.Especially under the action of near-fault impulse ground motion,there are many cases of masonry tower collapse.In order to study the seismic performance of ancient masonry tower under the action of near-fault ground motion,this paper takes Longhu Relic Tower in Deyang,Sichuan Province as the research object,and studies the response characteristics,damage mechanism,and vulnerability of the ancient masonry tower under the action of near-fault impulse ground motion by numerical simulation method,in order to provide the basis for evaluating the seismic risk of ancient masonry towers.The main contents are as follows1.The numerical model of ancient masonry tower is established.Based on ABAQUS finite element program,the integral modeling method is used to establish the numerical model of the Longhu Relic Tower considering the elastic-plastic characteristics of masonry materials.The modal analysis of the structural numerical model is carried out,the comparison of the dynamic characteristics of the numerical model with the measured and the results of empirical model is performed,so as to test the rationality of the structural numerical model.2.In this paper,the characteristics of seismic response of the tower under impulse and non impulse ground motions are studied.Pushover and dynamic elastic-plastic analysis methods are used to study the seismic response characteristics of the ancient tower under impulse and non impulse ground motions.The results show that the distribution characteristics of maximum inter story displacement angle with height obtained by the two methods are similar,and the maximum top displacement of the structure has a high correlation,and the correlation coefficient can reach 0.88.Compared with the non impulse ground motion,the mean value and standard deviation of the seismic response of the ancient pagoda under the impulse ground motion are larger,in which the maximum peak displacement,the maximum interlayer displacement angle,the peak acceleration at the top and the shear stress amplitude at the bottom exceed 40.0%,39.3%,56.4%and 38.2%respectively.3.The earthquake damage mechanism and evolution process of the tower are studied.The results show that under the action of large earthquake,the flexural capacity of the structure is insufficient,the interlaminar shear force is plastic with the change of interlaminar displacement,and the interlaminar stiffness degradation is significant,especially under the action of impulse ground motion.The main reason is that the material strength is too low and the hole weakens.The seismic damage of the ancient tower is characterized by shear diagonal cracks at the openings of each floor,which are connected vertically,and then form vertical through cracks,accompanied by local horizontal bending cracks and tower eaves damage.The simulated damage is consistent with the real damage4.In this paper,the seismic vulnerability of the Longhu Relic Tower under impulse ground motion is studied.Combined with incremental dynamic analysis and correlation analysis method,the seismic intensity measure IM suitable for ancient tower structure is determined.The results show that the dual parameter index composed of PGA and Ia can reduce the discreteness of structural demand.The results of vulnerability analysis show that when PGA is 0.1g,the main damage of the ancient tower is below the medium level;When PGA is larger than 0.2g,the ancient tower is mainly damaged and collapsed,especially when PGA is larger than 0.4g,the possibility of collapse is very high. |
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