The goal of structural health monitoring (SHM) are effective recognition and identification of possible structural damage, estimation of the actual state of a structure, and its potential for further exploitation, and finally, assessment of the eventual need for reparation. This research attempts to describe steps and procedures for SHM in order to locate possible damages to the structural and non-structural elements of buildings due to earthquakes.
The target structure for SHM, in this study, is the Urban Disaster Prevention Research Center (UDPRC), located in Tsukuba, Japan. The SHM procedure is an addition to the regular monitoring of the UDPRC building for the purpose of detecting damage sustained since the building’s original construction.
The SHM methodology, described in this paper, consists of analyzing strong motion acceleration records from the year 1999 till 2012, and microtremor acceleration records from 2009 and 2011. Dynamical properties of the structure (natural frequencies, damping ratios, mode shapes) and parameters related to stiffness are extracted from the records by applying parametric system identification methods (ARX, ARMAX and N4SID). The changes of these parameters in time indicate the possible occurrence of damage to the building. Damage detection and localization have been performed by tracing the history of changes in the extracted dynamical parameters and storey stiffness during the observed period. The results obtained demonstrate the tendency of natural frequencies and storey stiffness to decrease, and damping ratios to increase due to aging and exposure of the structure to strong ground motion. A loss in frequency and stiffness is most evident in the year 2011, after the Great East Japan earthquake.