Modal Parameter Identification And Finite Element Model Updating For Adjacent Structures With Separation Joints Based On Ambient Vibration

Adjacent structures separated by a separation joint are usually taken as independent ones by engineers at the design stage.Technical solutions for sealing and covering separation joints may induce dynamic interactions between as-built adjacent structures.Dynamic characteristics of the adjacent structures may be changed due to the separation joints.Therefore,ambient vibration tests were conducted in three cases of multi-story adjacent structures.In addition,in order to consider the quantitative uncertainties of the prediction error due to tests and modeling,a probabilistic method is used to identify the modal parameters.The effects of the separation joints on the dynamic characteristics of the adjacent structures are analyzed.Modeling methods for adjacent structures are proposed considering the separation joints.In order to account for the discrepancy between the design assumption and actual technical solutions,and the quantitative uncertainties of the residual between vibration tests and modeling so as to get a more precise finite element model,model updating should be carry out based on the identified results and probability theory.The main contents and conclusions of the thesis are as follows:(1)Ambient vibration tests were conducted in three cases of reinforced concrete adjacent multi-story structures,respectively.With the measured acceleration response,the fast Bayesian FFT method was employed to identify the most probable values and associated quantitative uncertainties of the modal parameters of the adjacent structures.The identification results show that the continuous false ceilings and floor paving bricks across the expansion joint may lead to the dynamic characteristics of adjacent structure are exactly the same.It indicates that there is a strong link between the adjacent structures.The two structures connected via the joint in the floor slab behave as one structural system.In the case of the stiff infill in the joint,the torsional mode appears before the longitudinal translational mode.It shows that median level of link exists between the adjacent structures.If the seismic joints were constructed in accordance with the design code strictly,the joints seems to provide weak link to the adjacent structures.In this case,some natural frequencies of the higher structure have been found shown as peaks in the spectrum of its adjacent lower or same height structure.(2)A finite element model updating method based on the Bayesian theory and application programming interface technology between commercial software was proposed.In this method,the uncertainty of the test error and modeling error is considered quantitatively.The finite element model parameters are updated directly.The proposed method was verified by a numerical example.Updated model parameters obtained by two Bayesian objective functions are compared.(3)Finite element modeling methods for adjacent structures considering the separation joints were proposed.To simulate the strong link between the adjacent structures,a floor slab across the expansion joint was used to connect the floors of the adjacent structures.To simulate the median level of link between the adjacent structures,stiffness in the longitudinal direction was increased in each floor across the joint.Independent models were used to simulate the weak link between the adjacent structures.The modal analysis results of the finite element models of the three cases of adjacent structures agree with the identification results.The proposed model updating method and modal parameter identification results were used for the model updating of adjacent structures.The natural frequencies and mode shapes obtained from the updated finite element models and the ones identified from the field vibration tests are found to be in good agreement.