Tests And Identification For Dynamic Characteristics Of Storage Cabinet Structures For Cultural Relics And Finite Element Model Updating

Movable cultural relics in museums are very abundant in China.It is important to establish an anti-seismic system that contains the museum,the storage cabinets(or showcases),and the cultural relics.Museums as public buildings need to satisfy the requirements of code for seismic design of buildings.The storage cabinet is used as the structure for setting cultural relics.It is also a secondary structure of the museum.It is important for determining the real dynamic characteristics of the storage cabinet for the purpose of assure the anti-seismic security of the cultural relics.In order to obtain the actual dynamic characteristics of the storage cabinet structure,the field ambient vibration tests were conducted for a storage cabinet in a famous museum in this paper.Considering the test error and model error,the Bayesian method is used to identify the modal parameters and stiffness parameters.The finite element modeling method of the storage cabinet structure is proposed with reference to building structures.The finite element model of the storage cabinet structure is updated by a Bayesian method.The main research contents are as follows:(1)Ambient vibration tests of storage cabinet structures of four-storied and six-storied were conducted.The modal parameters were identified by the fast Bayesian FFT method.The effects of different story and different boundary conditions(floating and fixed)on the dynamic characteristics of the structure are compared.The uncertainties of the identification results of classical probability and Bayesian probability are compared.The results show that the dynamic characteristic of the storage cabinet structure is similar to that of the reinforced concrete structure.The identification accuracy of the natural frequency obtained by the fast Bayesian FFT method is much higher than that of the damping ratio.Given the test data,the identification accuracy of the mode shape is high.The first two natural frequencies of the six-storied storage cabinet structure are larger than those of the four-storied storage cabinet structure,respectively.The mode shapes of the first two modes of the two storage cabinet structures are similar,respectively.In the elastic stage,the storage cabinet structure floating or fixed on the floor has no influence on its dynamic characteristics.The statistical uncertainty of identification results in multiple tests is larger than the remaining uncertainty of the identification result in a single test by the Bayesian method.(2)Based on the modal parameter identification results of the four-storied and six-storied storage cabinet structures,the story stiffness of the storage cabinet structure is identified using the deterministic method and the Bayesian model parameter identification method.A multiple degree of freedom system model for the storage cabinet structure is established.The results show that the story stiffness obtained by the deterministic method is between the most probable value minus triple standard deviations and the most probable value plus triple standard deviations of the story stiffness identified by the Bayesian method.The stiffness along the short axis of the cabinet structure is greater than that along the long axis.(3)The members of the storage cabinet structure are defined.The connections between the structural members are assumed.The finite element modeling method of the storage cabinet structure is proposed with reference to the frame structure.The finite element modal analysis results of the four-storied and six-storied structures are close to the test results by adjusting the stiffness of the connecting elements that is neither fixed nor pinned.(4)A model updating method combined the numerical optimization Bayesian method with the sampling Bayesian method is proposed in this paper.Local optimal solutions can be avoided in this method.The model parameters are updated directly making the physical meaning of the model updating more clearly.Using the proposed method,the initial finite element models of the four-storied and six-storied storage cabinet structures are updated.The results show that the model parameters obtained by the proposed method are global optimal solutions.The coefficients of variation of the model parameters can also be obtained.The finite element models of the four-storied and six-storied storage cabinet structures with higher accuracy are obtained.