2022 Volume 22 Issue 5 Pages 5_60-5_78
Most of the current seismic structural health monitoring technology depends on the acceleration records observed by the accelerometers installed in buildings. Recently, however, the Internet of things (IoT) has evolved, and more digital image data are utilized for various purposes than before. Since the image data during and after the earthquakes include various information including various types of damage, it is expected that it enables a new way of monitoring building damage to facilitate an agile and reasonable judgment on continuous use of a building after an earthquake. The building damage to be used for the judgement include the damage of structural and non-structural elements. This paper proposes, as a first step, a practical method of identifying parameters to estimate structural damage by using the building motion during an earthquake recorded as a single moving image. From a single moving image of seismic response of building, the inter-story drift angle and velocity of each floor are estimated by calculating the optical flow representing the velocity of each floor in the image coordinate system using the image processing methods. The structural parameters such as story stiffness, natural period and damping ratio are estimated using the recursive subspace state-space system identification method (recursive 4SID) based identification algorithm. The proposed method was verified using the results of a shaking table experiment to have the same accuracy as the conventional method using the records from accelerometer and displacement meter.
The results of this study are summarized as follows:
1) By applying the optical flow calculation method proposed in this study, a more stable and precise inter-story drift was obtained compared with those by the conventional optical flow method.
2) The inter-story drift angles, including the residual drift, obtained by the proposed method agreed well with the measurement results.
3) The results of system identification by the proposed method had almost the same accuracy as the results by the accelerometer in terms of the change of the natural period and story stiffness of a building due to nonlinear building response.
4) The proposed method successfully identifies the change of the relationships between the story shear force and the inter-story drift during earthquake excitation. The tendency of the story stiffness to decrease immediately after the inter-story drift angle increased was observed.
