Structural Modal Parameters Identification And Application Based On Earthquake Response Data

The structural earthquake response observation is the foundation of theearthquake engineering. The structural response and damage process underearthquake excitation are mainly be understood by this kind of observation. Theseismic design theories and methods of structures are also be examined by thestructural earthquake response observation. In recent years, all the governmentsof the world and earthquake engineering field have paid more and more attentionsto the structural earthquake response observation, which has been made quitegreat progress. In China, with the development of the digital strong earthquakeobservation, more and more high-rise and important buildings will be installedstrong earthquake response observation array. Once the observation systemobtained strong earthquake response records, the records can be used to structuralmodal parameter identification and engineering seismic research, and the resultscan be considered as fundamental data for structural health diagnosis and seismicsafety evaluation after earthquake. The structural modal parameters identificationand damage detection are always the concerned problems in the field ofearthquake engineering. The paper has made some researches of structural modalparameter identification and its applications under the excitation of earthquakesystematically and deeply. The main works of the paper are summarized asbelow:1. HHT Analysis of Structural Earthquake Response RecordsA new non-linear and non-stationary signal processing method-HHT(Hilbert-Huang Transform) with its meaning and arithmetic was introduceddetailedly in the paper. According to the arithmetic, a toolbox of HHT wasproduced and developed in the paper. Then a 7-storey steel concrete building andit earthquake response records and damage in several earthquakes wereintroduced. The HHT was used to deal with 3 main and representativeearthquakes response data and the amplitude-frequency-time distributions ofstructural earthquake response data were obtained. The HHT marginal spectrawere also given and compared with Fourier spectra and some significativeconclusions were made.2. System Identification of Structure under Excitation of EarthquakePresent the modal parameter system identification methods for structureunder excitation of small and severe earthquakes. If a structure were not intotime-varying response stage and the whole response were in linear elastic range,the modal parameters can be identified by using the whole earthquake responsetime-history. If the structure were surely into the time-varying response stage, thewhole earthquake response time-history was compartmentalized into threesegments. The first and the third segments were treated as time-invariant stage,and modal parameters identified from first and third segment were considered asthe intact and damaged cases of the structure respectively. For the secondsegment, the recursive identification method was used to identify the modalparameters and obtained the time-varying modal parameters from which thevariety property and law of the structural modal parameters could be found outduring the earthquake excitation. Also, the starting and end time point of thedamage could be observed clearly. According the method and thoughts of thepaper, a 7-storey RC building which had suffered 4 earthquakes and obtainedresponse data was used for the analysis. The modal parameters under theexcitation of small and severe earthquakes were identified and the time-varyingmodal parameters were also given in the paper. It is shown that the method of thepaper is very available and the results are accurate and reasonable.3. Statistical Analysis for Fundamental Periods of StructuresPresent experimental formulas for the fundamental periods of two types ofbuildings based on earthquake response data. A total of 40 RC frame-shear wallstructures and 36 moment resisting steel frame structures were used for thestatistical analysis. All the buildings had obtained earthquake response recordsduring one or more earthquakes. The fundamental periods of all the building inintact case were firstly identified, and then, the experimental formulas of the twotypes structures were given by non-linear regression method. The simpleexperimental formulas proposed in the paper can be used to for the code revision and structural earthquake-resistant design researches.4. Torsion Modal Parameter Identification using Earthquake DataPresent a method to decouple the lateral-torsional coupling earthquakeresponse and identify the torsion modal parameters. The torsional response time-history of structure under excitation of earthquake was decoupled from the lateralearthquake response data, and then the torsion modal parameters were identifiedfrom the torsional response data. The time-invariant and time-varying torsionmodal parameters were identified in the paper. A 7-storey RC building with itsearthquake response records was used for the analysis and some significativeconclusions were made.5. Damage Identification of Structure under Earthquake ExcitationBase on the structural simulation results of finite element model, the changesof structural modal parameters under different damage level were studied in thepaper. The relationship between the damage index and the change of modalfrequency was established, as well as the change of mode shape. Some empiricalequations between the damage index and modal frequency variety and modeshape variety were given by non-linear regression method. The equations can beused to predict the damage state once some building records the earthquakeresponse data. The modal parameters of intact structure need not to be knownprior to the earthquake, because the modal parameters before and after damagecan be identified simultaneously only using one-earthquake response records bythe methods of the paper.