Wave Theory Based Structure Damage Detection

In recent years,earthquakes occur frequently all over the world,which has posed a heavy threaten on people's life and property.After an earthquake,monitoring the integrity of a building and assessing potential collapse risk timely may significantly reduce loss of life and injuries.Surely,it also can help avoiding some needless evacuation after earthquake,which is very important for quake relief.Since 1990 s,structure damage detection under earthquake has already become an important research topic in civil engineering.However,most researchers focused on analyzing modal information of structure,there is less study about damage detection based on wave theory.In this paper,research was started from the wave solution of structure under earthquake,and concentrated on the identification of shear wave speed which can be used to detect the change of structure.The main work and conclusion include:(1)From the view of wave propagation,the relationship between structure dynamic responses in different floors is analyzed;the solution of wave equation for shear beam and Timoshenko beam is deduced;the definition of impulse response functions and transform functions is presented,and the numerical formula of impulse response functions for shear beam is proposed.(2)The problem of damage detection is turned into the identification of shear wave velocity of structures.Two methods,which are respectively based on cross correlation function and impulse response function,are proposed to identify shear velocity of structures.In first method,time delays between responses in different floors are acquired by cross-correlation analysis based on K-Y formula.In second method,time delays are acquired by analyzing peak offset in impulse response function based on numerical formula of impulse response functions for shear beam.Time delays can be used to computer structure shear wave speed if transmit length is known.These two method are validated by using three real structure and results show that they both can identify the change of shear wave speeds if wave transform time in structure is long enough.Finally,the effect of data sampling rate on identification results is investigated and it's found that the increase of sampling rate can help reduce identification errors in some degree.(3)Numerical method is used to identify shear wave velocity of structures.Shear beam model and Timoshenko beam model are used to simulate structure dynamic response and the wave velocity of structure is equal to the one of model when the discrepancy of impulse response function between model and real structure is minimized.The methods are validated by three real structures and results show that they both can identify the change of shear wave speeds.Besides,identification results based on different methods are compared and the application ranges of different method are analyzed.Finally,some improvements,including multi-step identification strategy and model parameters reduction,are made for damage detection method based on Timoshenko beam model.The innovation of this paper includes:(1)Based on wave propagation theory,a new structure damage detection method is proposed by taking shear wave speed as index and analyzing structure dynamic response directly.(2)Two beam models are used to simulate structure dynamic response and structure shear wave velocity is identified by minimizing the discrepancy between real and simulated response.The change of structure shear wave speed can be used as damage index.(3)Some improvement for damage detection method based on Timoshenko beam model is made,which includes proposing multi-step identification strategy and reducing model parameters.