Investigation On The Dynamic Performance Of Base-isolated Frame Structure Without Infill Walls Based On Dynamic Test

Dynamic characteristics analysis of engineering structures based on dynamic test has significant meaning in both engineering field and academic field. It is an active research issue in structural engineering area. The precise identification of the dynamic characteristics is the precondition and basis for the study of some important problem, such as structural seismic analysis and damage diagnosis. For many years, a lot of new methods of dynamic identification were created and developed in succession. However, there are some shortcoming and disadvantage for certain traditional identification technology, so the more precise method of dynamic characteristics identification need further research and discussion, and then making them to adopted well in real engineering. Given the case above described, a base isolated structure was viewed as a study object, and the modal parameters were identified using the time-domain method and frequency-domain method respectively. Finally, dynamic characteristics of the base isolated structure were investigated further based on the identification results.In this thesis, the identification methods of structural parameters under ambient excitation were summarized. The theories of SSI, STD and RFP methods were introduced detailed, and the main problems relative to the identification process were also discussed.The three methods adopted by this thesis have big advantage in the aspects of signal processing and precise identification for dynamic parameters. Stochastic subspace identification is a comparatively advanced time domain method for modal identification under ambient excitation. Its mathematical model is created using the state space equation, the input is assumed to be white noise. The modal parameters of system are obtained by solving the system matrix and output matrix of the state space equation. The impulse response or free-decay response is used in STD, the response matrix is created by time-delay and virtual test technique, and Hessenberg matrix is created directly, this avoid the QR decomposition for eigenvalue matrix and the error can be identified and avoided, then the parameters for user select is decreased and then increase identification precision. RFP method start from the characteristic of rational fraction polynomial of transfer function or frequency response function, the dynamic characteristics are identified by fitting ordinary power polynomials coefficients of numerator and denominator of transfer function or frequency response function. In this thesis, dynamic test was conducted for a four-storey base isolated structure without infill-walls, the structure is located on Lanzhou. The finite element model was created and the modal parameters was identified using three method above mentioned, the comparative result showed that the three methods all had high precision and the result of every two methods had well correlation. Given actual horizontal stiffness of isolated layer under ambient excitation different from the corresponding value in design, horizontal effective stiffness of the isolated layer under ambient excitation was identified using the multi-objective optimization method. The result showed that the stiffness value was very larger than that in the case of frequently occurred earthquake level, and damping characteristics and dynamic performance of the base isolated system were analyzed.