Study On Modal Parameters Of Building Structure By Time-frequency Analysis

In recent years,the health monitoring of engineering structures attracts more and more attention.How to accurately identify the modal parameters such as natural vibration frequency and damping ratio is the core issue in the health monitoring,control,and condition assessment of engineering structures.Therefore,modal parameter identification technology and its theoretical basis have become research hot spot in the civil engineering field.Affected by the size of the engineering structure,bind condition and other factors,it is too difficult to exert artificial excitation and efficiently measure excitation signals on engineering structures.Therefore,traditional modal parameter identification methods with testing input and output signals have been seldom used in practical applications.In comparison,modal parameter identification methods under ambient excitation are more convenient,safer,cheaper and more in line with the actual situation.Therefore,these methods have been widely used in the engineering field.However,the existing modal parameter identification methods often need to consider the excitation signal as white noise or stationary signal,which is not consistent with the non-stationary characteristics of the ambient excitation itself.As a result,the suitability of these methods is insufficient.Meanwhile,the existing modal parameter identification methods have many shortcomings regarding the accuracy,noise resistance,etc.In response to existing problems in the current research,methods of structure modal parameter identification under ambient excitation are studied in this paper,the main contents are as follows:Chapter 2 presented the theories of two new time-frequency analysis methods,namely synchrosqueezed wavelet transforms(SST)and empirical wavelet transform based on multiple signal classification algorithm(MUSIC-EWT)as well as the theories of some traditional signal processing methods.Combining the two time-frequency analysis methods and the traditional signal processing methods,two methods were developed for structural modal parameter identification under ambient excitation,which are called SST+NExT and MUSIC-EWT+NExT,respectively.In addition,since the high-rise building is the structure with closely spaced modes,mode mixing phenomenon often occur in the process of analyzing the measured response data.Meanwhile,there is often plenty of noise in the measured response data,which will also affects the result of parameter identification.Therefore,the difference spectrum of singular value was introduced into the parameter identification process of SST+NExT and MUSIC-EWT+NExT to restrain the influence of noise and mode mixing.Based on this,two improved methods were developed,namely SST+SVD and MUSIC-EWT+SVD,respectively.In Chapter 3,a numerical simulation of a four-story frame structure was employed to discuss the performance of the several methods developed in this paper.SST+NExT and MUSIC-EWT+NExT were used to analyze the response data under the impulsive load and non-stationary excitation for parameter identification.The accuracy,stability and noise immunity of these methods are evaluated.Meanwhile,the superiority of SST+NExT and MUSIC-EWT+NExT were verified by comparing the identified result with the value estimated by CEEMD.In addition,SST+SVD and MUSIC-EWT+SVD were used to analyze the response data of the structure under50% noise intensity,which verified the denoising ability of the difference spectrum of singular value and the superiority of these improved methods.CITIC Plaza as well as its health monitoring system was introduced in Chapter 4.Based on the project background,the measured acceleration responses of CITIC Plaza during Typhoon Damrey were analyzed by using SST+NExT and MUSIC-EWT+NExT.The practical application values of these methods was further verified by comparing the identified results with the values estimated by CEEMD.Meanwhile,SST+SVD and MUSIC-EWT +SVD were also used to identify modal parameters of the building,and the practical application value of difference spectrum of singular value was verified by comparing the identified results with the values estimated by SST+NExT and MUSIC-EWT+NExT.Taipei 101 Tower and its health monitoring system were introduced in Chapter 5.Based on the project,SST+SVD and MUSIC-EWT+SVD were used to analyze the measured response of the structure under the far-field earthquake(Wenchuan Earthquake,May 12,2008),and the first three translational modal parameters of the structure were identified which were compared with the values estimated by Finite Element Analysis and Frequency Domain Decomposition(FDD).Finally,a developed method for solving instantaneous frequency is studied based on Taipei 101.