SYSTEM IDENTIFICATION AND DAMAGE ASSESSMENT OF EXISTING STRUCTURES

It is desirable to assess structural damage by means of several rational damage indicators which are related to the physical deterioration of existing structures. In this thesis, two indicators namely maximum plastic deformation and natural frequency, are discussed. An approach for damage assessment of existing structures by utilizing system identification techniques is emphasized. Therefore, changes of identified parameters such as natural frequencies and damping ratios during an earthquake are studied for the correlation with the physical structural damage. The application of simple methods of system identification to existing structures from observations of responses to earthquake inputs is elucidated. Numerical examples of two existing buildings and two test structural models with various damage levels are given to demonstrate the effectiveness of these new methods. The significance of changes in structural characteristics with respect to time is discussed. Results which are improved by imposing various conditions to remove undesirable data points along with the treatment of measurement noise and error are also presented. Finally, available data are summarized and plotted to show the relationship between damage ratio and change in natural frequency of structures. Recommendations and extensions are also made to improve this approach