SYSTEM IDENTIFICATION AND DAMAGE DETECTION OF R.C. STRUCTURE

Abstract eng:
Evaluation of system parameters of civil engineering structures using system identification techniques has attracted considerable attention in recent years. Recorded dynamic responses of the structures due to ambient or earthquake excitations are utilized for identification of system parameters of the structures. Huge amount of works have been carried out in the field of linear time invariant system identification; but the application in time varying system identification is very limited. In the present study, three numbers of numerically simulated models of 1/5th scaled bare frame two storey R.C. buildings have been considered. Nonlinear time history analyses are carried out to detect the changes of modal parameters of the deteriorating structure. Further, acceleration responses are collected from different floors during base excitation of models. Linear Deterministic-Stochastic Identification (DSI) technique (e.g. N4SID) is then used for the identification of modal parameters (natural frequency). Since, a linear DSI algorithm would not be applicable for structures excited to nonlinear range, hence modal parameters are obtained for short data time windows. These instantaneous modal parameters are found to represent the deterioration of the structure reasonably well. Further, an approach referred to as the sequential non-linear least-square estimation (SNLSE) is used to compare the identified result obtained from N4SID algorithm using short time data window. In this approach, acceleration responses and external excitations are measured, whereas the structural parameters and response state vector are estimated similar to the Extended Kalman Filter (EKF) approach. It is superior to EKF in terms of stability and convergence.

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