Seismic Performance Analysis And Damage Assessment Of Ancient Masonry Tower

Ancient masonry towers are the important vehicles of China’s 5000-year civilization,widely distributed in the nationwide and are an outstanding high-rise building in ancient China.However,the ancient masonry towers are tall and built with dense masonry materials,which makes them more sensitive to earthquakes than other types of ancient buildings,earthquakes are the main reason for the destruction and even collapse of most ancient masonry towers in China.On the other hand,the damage of the ancient masonry towers caused by different levels of seismic loads is different,the damage assessment of the ancient masonry towers after the earthquakes lacks reasonable evaluation criteria.Therefore,analyze the seismic performance and propose seismic damage assessment methods of ancient masonry towers have important implications.A 1/8-scale masonry tower model representative of Xi’an Xiaoyan tower was built by the sticky rice lime mortar and old bricks,and then tested by shaking table,the seismic performance of tower model and damaged tower model are both studied;At the same time,the numerical analysis of the ancient masonry towers is carried out based on the cohesive friction contact model,and the suitable earthquake damage assessment model for the ancient masonry tower is also explored based on the analysis results;Finally,according to the disaster characteristics,the shaking table testing results and numerical analysis,the performance levels of the ancient masonry tower are divided,the seismic damage indexes corresponding to the performance levels is also quantified,and the seismic damage assessment method of the masonry ancient tower is given.The main researches are listed as follows:(1)According to the related research and the seismic survey results of ancient masonry towers in different regions of China,the structural characteristics of the ancient masonry towers are summarized,the main features of the damage are tilt of the tower,cracks in the tower body,and collapse of the top and Tasha of the tower,its typical damage characteristics and the corresponding causes are analyzed qualitatively,which provides a reference for the subsequent exploration of the seismic performance of the ancient masonry towers.(2)The initial and damaged ancient masonry tower model is tested successively by shaking table to better understand the seismic performance of the ancient masonry tower and provide data support for the subsequent research of numerical ancient tower model.The failure mode,dynamic characteristics and dynamic response of the initial and damaged ancient masonry tower model under different earthquake actions are compared and analyzed.The comparative analysis shows that the eccentricity effect caused by the inclination and the overturning bending moment caused by earthquake and gravity may aggravate the seismic response of the damaged towers.(3)Based on the cohesive friction contact model,the numerical analysis of the ancient masonry towers was carried out,the correctness of the contact criterion is verified.At the same time,considering the importance of the deformation performance of masonry under cyclic loading and the correlation between cumulative hysteretic energy consumption and damage,the numerical analysis of the masonry ancient tower wall is further carried out to illustrate the rationality of the contact theory in the structural application,and also lay the foundation for the establishment of a refined numerical model of the ancient masonry tower.(4)After verifying the correctness of the numerical model of masonry ancient tower wall,further research on the parameters of the walls were carried out.Based on the 16 wall numerical models with different parameters,the effects of different vertical compressive stresses,different height width ratios and different hole sizes on the damage modes,ultimate loads,stiffness degradation of ancient tower masonry walls are analyzed.Finally,based on different damage assessment models,the damage evolution process of the ancient tower wall is analyzed,the differences among the damage assessment models are compared and analyzed,and the seismic damage assessment model suitable for masonry towers is determined.(5)Based on the cohesive friction contact model introduced in the previous paper,the refined numerical model of ancient masonry towers is established using the bodyshell combination model,and the relevant parameters involved in the model analysis are discussed.The numerical results are compared with the relevant test results of the shaking table tests,and the damage process and characteristics of the tower are analyzed,which verifies the effectiveness of the numerical analysis model.To establish a refined numerical model of ancient masonry towers that can reflect the crack development and damage patterns more comprehensively,the numerical model of the damaged ancient tower is established by considering the initial cracks and inclination factors,the interface of the damaged area is individually divided to make the corresponding attenuation according to the degree of damage,based on the Design Expert analysis software,the interface parameters of the damaged model are determined through Box Behnken inversion calculation.It provides new ideas for the method of determining the parameters that are not easily measured in the numerical model of ancient towers.(6)On the basis of the numerical model of the ancient masonry tower,the damage index of the tower walls is obtained,the floor damage index and then the overall damage index of the ancient tower are calculated based on different weighted combinations.According to the test and numerical results,the performance levers of the ancient masonry tower is proposed and the damage indexes of the ancient tower structure under various performance levels are quantified.It provides a reference for damage assessment of ancient masonry towers after earthquakes.