Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 13 Fragility Analysis Based on Structural Health Monitoring

Abstract

Abstract Thermal power plants are one of the critical infrastructure facilities that support modern society. A boiler is a main large structure in a thermal power plant, and it is suspended from its support structure not to restrict thermal expansion, thus it is easy to respond during earthquakes. Therefore, steel dampers are usually installed in boiler structures to absorb vibration energy by plastic deformation of steel. In the meantime, aftershocks of the Great East Japan Earthquake in 2011 have occurred frequently in the Tohoku region even now. For example, in February 2021 and March 2022, large earthquakes of magnitudes 7.3 and 7.4, respectively, occurred in the same epicenter area as the Great East Japan Earthquake. In addition, the long duration and long period ground motions have been focused on after the Great East Japan earthquake. Therefore steel damper has high risk of fatigue failure by earthquakes. Given these backgrounds, it is necessary to improve the seismic resistance of boiler structures, especially for steel dampers. In this study, we have proposed application of viscoelastic dampers in boiler structures instead of conventional steel dampers. Viscoelastic dampers absorb vibration energy by fluid resistance of a viscoelastic fluid. Component tests of the viscoelastic damper and seismic response analysis using a multi-mass point system and frame model have been conducted in the previous papers. As a result, it was confirmed that the viscoelastic dampers have high vibration control performance and long life. Then, many acceleration sensors have been installed on an actual boiler structure to improve the accuracy of the analytical model used in seismic response analysis, and actual seismic responses have been observed since 2021. In PVP 2023, fragility analysis using seismic response measured in actual seismic events is introduced. Fragility analysis is a powerful tool to quantitatively assess the risk of structural damage. This paper demonstrates the usefulness of structural health monitoring.