System identification is an inverse analysis of the dynamic system to identify system parameters and detect parameter changes based on given input and output (I/O) information, in which three basic components are input excitation, dynamic system, and output response. In structural engineering, system identification is generally applied to structural parameter identification, damage detection, and health monitoring. Stiffness and damping of the dynamic system can be identified to update or calibrate the numerical model so as to better predict structural response and build cost-effective engineering structures. Furthermore, system identification methods can potentially be developed as a useful non-destructive evaluation method
and can provide an in-service condition assessment or health monitoring of existing and retrofitted structures. In earlier days, only visual inspection by UAV or ROV and local non-destructive techniques such as ultrasound detection and acoustic emission method are available for structural health monitoring. However, visual inspection is often incomplete and local non-destructive techniques are limited to detection of individual structural components. In this regard, implementation of identification methods is able to globally and quantitatively identify the structural dynamic system as a real-time strategy. Numerous system identification methods have been developed including classical and non-classical methods and their brief introduction is given in this section.