Study On Accurate Modes Identification Of A Typical Structure And Its Damage Detection

Structural modal parameters include natural frequencies, modal shapesand damping ratios. The physical meanings of modal parameters are clear invibration theory. However, when the damping ratio is large modal shapescoupling each other is inevitable, how about the precision of the modalparameters at this time? Structural damage detection based on modalparameters identification is a powerful method in structural engineering. Thispaper will also present such results on shell structures.The main content of this paper is as follows:1.Three story shear-type steel frame was designed in this paper.Thetheoretical mode of the frame was analyzed firstly. And then three commonmodal identification methods(Pulsating method, displacement relievingmethod, sine wave excitation method) were used to test every mode withdamping ratio increasing from low to high.2. A silicon oil damper matching modal structure well was self-designedin this paper, which can regulate damping ratio from0.2%to5%and evenhigher.3.This test used the logarithmic decrement method, the resonancemethod and the auto-power spectrum method to test the damping ratio underdifferent conditions. The three and other common methods of testing thedamping ratio were summarized. And their practicability, merits and demeritswere compared in the meantime. The results about the accuracy of everymodal testing under conditions of different damping ratio proved that thetesting accuracy for pulsating method, initial displacement releasing methodand excitation method are gradually higher. And the accuracy of high-ordermodal testing can reach above97%.4. We make two sets of steel shell models and provide the modalmeasurement of shell without damage and shells with radial damage andcircumferential damage. We can get the time domain data,transfer functionsand auto power spectrum of these shells through these experiments andIllustrate the spectrum characteristics of intact and radial damage shellstructures. According to the characteristics of steel shell model and musicaltone criteria,this paper put forward two kind of damage identificationstandard based on effective peak and line spacing of the transfer functionspectrum.The identified results demonstrate that musical tone criteria hasgood performance in Identification of the radial damage. Broadly speaking,musical tone criteria has good effect on identifying key injuries whichchange the stiffness and force transfer mode of the structures.