Improvement And Application Of Modal Identification And Damage Diagnosis For Frame Structure

Modal parameter identification and damage diagnosis of engineering structures isthe core technology and theoretical basis of structural health monitoring. Structuralseismic damage can be estimated by changes of the physical parameter and dynamicproperties of the structure, thus structural seismic damage can be assessed by means ofmodal parameter identification method. Structural seismic damage assessment providestheoretical basis for the safety assessment and structural reinforcement and restorationafter the earthquake, having an important engineering practical value. In this paper, firstthe structural modal parameter identification and damage diagnosis methods areproposed, and then structural seismic damage is assessed, the main works of the paperare summarized as below:①The research background and significance was briefly introduced, the researchstatus of structural modal parameter identification, structural damage diagnosis andseismic damage assessment method were described.②In view of the shortcomings of empirical mode decomposition, ARMA method,SRCE method and STD method were improved on the basis of the combination ofdigital filter and empirical mode decomposition. Modal parameter identification of afour-story steel frame test model, BHM Benchmark test model and simulation modelwas conducted. The results indicate that the proposed methods can separate intensivemode effectively, avoiding modal aliasing problem that may arise by the use ofempirical mode decomposition alone, avoiding the problem of modal orderdetermination of ARMA method, SRCE method and STD method. The modal parameteridentification results of stochastic subspace identification method was further compared.③Propose a new two-stage damage diagnosis method on the combination of theadvantages of change rate of modal strain energy and direct analyzing method, in thefirst stage, change rate of modal strain energy was used to identify the damage location,and in the second stage the direct analytical method was used to quantify the damage.The numerical simulation indicates that the proposed method not only reduces thenumber of damage parameters of direct analyzing method greatly, but also greatlyreduces the number of required modes for damage identification, damage diagnosis canbe conducted accurately only with the lower mode, thus it is more closer to practicalengineering theoretically. ④By calculating the change of structural modal parameters before and after theearthquake, the relationship between this change and structural damage state parameterwas established, providing a practical structural seismic damage assessment method.The seismic response of a five-story reinforced concrete frame structure was analyzedby IDARC to compartmentalize the seismic response using the story damage indextime-history curve, then the structural modal parameters of good and damage state wasidentified by stochastic subspace identification method. Modal parameters of differentdamage degree was obtained by changing the input peak ground acceleration, thus therelationship between the overall structural damage index and changes of modalparameter was established, the empirical formula was also fitted.Thus the overallstructural damage index obtained through changes of modal parameter can be used toassess the seismic damage state of structures.