Study on Structural Health Monitoring Method By Recursive Subspace Identification Based on Shaking Table Tests of Wooden Structure

Abstract eng:
In Japan, many buildings and structures suffered damages during the 2011 Tohoku Earthquake that occurred off the Pacific Coast. Since then, structural health monitoring (SHM) methods have attracted attention. Numerous studies have investigated the seismic safety of structures based on the system identification approach in time domain. The subspace state space system identification (4SID) approach has been used as the one of the SHM methods. This method enables us to evaluate the seismic response characteristics, such as natural frequency, damping ratio, and story stiffness of a structure. If a building suffered damages during an earthquake, it shows nonlinear behavior. Therefore, the seismic response characteristics of a building change with time. Hence, the time variation of the characteristics during an earthquake relates the damages of a structure. One of the objectives of SHM is to grasp the change in the characteristics. In the 4SID approach, structures are modeled as linear systems. However, structures that suffered damages due to an earthquake show nonlinear behavior. Hence, there might be discrepancies between the identified characteristics and the real phenomenon. However, the identification accuracy of the 4SID approach has not been investigated sufficiently. Thus, the system identification accuracy must be validated. Therefore, this study investigates the system identification accuracy of recursive and nonrecursive 4SID approaches. Both these approaches are applied to the acceleration data obtained during full-scaled shaking table tests conducted on wooden post and beam structures. The temporal variation of natural frequencies, damping ratio, and story stiffness of the specimens were evaluated through each approach. Next, the identified story stiffnesses were compared with the hysteresis loops of the specimens. Thus, it was clarified that the recursive 4SID approach is suitable for SHM when a structure shows strongly nonlinear behavior during an earthquake.

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