| After thousands of years of ups and downs,Yingxian wooden pagoda has been degraded to varying degrees by sustained environmental erosion,ageing of materials,natural disasters due to earthquakes and strong winds,and man-made damage.Its static and dynamic performance maintenance and safety limit has suffered very serious impact.The dynamic performance based on ambient vibration can not only envelop the static performance of Yingxian wooden pagoda,but also be used as the basis of seismic and wind performance evaluation.It is an effective means to solve the problem of Yingxian wooden pagoda performance maintenance and safety limit evaluation.In this paper,the dynamic characteristics of the structure with multi-mode coupling and environment effect are obtained by means of in-situ vibration test in Yingxian wooden pagoda.The Modal Participation Coefficient is analyzed and the stiffness distribution in vertical and multi-dimension of the floor plane are identified effectively.The results of the study provide a solid basis for the continuous monitoring and assessment of the Mechanical Properties of Yingxian wooden pagoda in the future.The main contents of this paper are summarized as follows:(1)This paper summarizes the research status of mechanical properties of ancient pagodas and other pavilions in Yingxian wooden pagoda through literature review,and reveals the deficiencies in the study of Yingxian wooden pagoda at present.The studies need to be conducted in this thesis on the topic of ambient vibration test in this paper is also made clear.(2)Firstly,to solve the problem of modal aliasing and low precision of damping ratio identification,this paper introduces a kind of Hilbert transform based on variational modal decomposition,and verifies its feasibility by numerical simulation.This method can improve the identification accuracy of frequency and damping ratio.(3)Secondly,in view of the difficulty of decoupling and identification of multi-mode coupling in Yingxian wooden pagoda and the change of dynamic characteristics caused by environment effect,80 test points were set up on two vertical columns of the wooden tower.Two field tests in winter and summer were carried out,and the dynamic characteristics of the structure were obtained.(4)Then,based on the results of modal identification,the calculation method of modal participation coefficient for the Yingxian wooden pagoda based on the valid value of time domain vibration is introduced.This method also verified by numerical simulation model.The parameters and coefficients of each vibration mode are identified by using the effective values of the measured vibration data.The results show that the first-order translational motion is the largest,and the first-order torsional vibration is the second,it provides a reference for further analysis of structural dynamic characteristics changes and modification of the finite element model.(5)Finally,based on the above research results,the longitudinal and storey plane stiffness distribution of the wooden tower is studied in detail.In this paper,we simplify the wooden tower to the interlaminar shear model,calculate the interlaminar stiffness of each layer,and propose a method to identify the stiffness center of each layer based on the vibration test.The research shows that in the longitudinal dimension,there is a large stiffness mutation between the light and dark layers,which leads to serious structural deformation.In the plane dimension of the floor,the eccentricity of each floor of the wooden tower in the direction of the two vertical columns is identified,and the identification result is more reliable through the comprehensive analysis of the structure and deformation of the wooden tower.55 diagram,25 charts,74references... |
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