Analysis Of The Abnormal Change Of Isolated Structure Vibration Characteristics Under Healthy Condition And Model Updating Based On Long-term Monitoring Data

Seismic isolation technology has become one of the most important methods to resist the earthquake disaster because of its excellent performance.The upper structure of base isolation is protected by isolation layer,which can greatly reduce the casualties and economic losses.A large amount of research upon the base-isolated structure have been made by domestic and foreign scholars,whereas,the existing research is based on laboratory data and numerical simulation results,while the structure actual working environment is complex and changeable,thus the analysis results are not suitable for the real working condition of the isolated structure.Furthermore,the measured response data of the isolated structure under the excitation of actual environmental factors is relatively less,and the response data under the earthquake excitation is very rare.In order to verify the isolation design and ensure the safety of the structure,In this paper,considering the characteristics of the seismic isolation structure of a middle school in Jiayuguan City,Gansu Province,then design and install a long-term health monitoring system for the isolated structure.For the purpose of analyzing the isolated structure performance by using the measured data.The main researches of this paper are as follows.(1)Drawing on the experience of the design and implementation of the existing structural health monitoring system,and according to the characteristics of the base isolation structure selected in this paper,a long-term health monitoring system is designed and installed to record the main environmental factors and structural response data.And it can provide a lot of valuable data for structure damage identification,model updating and condition assessment.(2)Based on the measured data of structural response under ambient excitation and the main environmental factors,combined with the spot investigation results,the main factors affecting the modal parameters of the isolated structure are analyzed.The result shows that the correlation between the mass change and the modal frequency or damping ratio are both relatively large.The correlation between the temperature change and the modal frequency is large,while the correlation of change and damping ratio is small.At the same time,using the finite element software to analyze the influence of human activity and temperature on the isolation performance,and proposing the improvement suggestion for the isolated structure design.(3)According to the structural response data under earthquake excitation,the isolation properties of the isolated structure under earthquake excitation is analyzed and verified,in order to inquiry the variation law of the isolated structure modal parameters during the earthquake excitation process.The result shows that the isolation layer can not work effectively under the micro seismic excitation,and the vibration characteristics of isolated structure are strongly dependent on the vibration intensity.Finally,a comparative analysis is made with response spectrum of foundation acceleration response and the top of isolation layer,it is found that the seismic waves can be filtered by the isolation layer,and the spectral characteristics would be changed.(4)Based on the monitoring data of isolated structural response,the layer quality,story stiffness,damping ratio and other structure parameters were corrected by using the genetic algorithm,which take the coincidence degree between the measured FRF and the theoretical FRF as objective function.The corrected structure model shows more exact with the actual structure,and can reflect the working state of the actual structure under the environment and the slight earthquake excitation.The research results provides reference for the research of damage identification and condition assessment of isolated structure.