Study on the Actual Responses of Seismically Isolated Structures in the Hualien TzuChi Medical Center

Study on the Actual Responses of Seismically Isolated Structures in the Hualien TzuChi Medical Center

The HeXin Building, which is one of the hospital buildings in the TzuChi Medical Center located in Hualien City, is designed as a seismically base-isolated building. This structure was completed in February 2005 and is installed with real-time monitoring systems to measure its structural responses. Four representative and significant earthquakes that struck the HeXin Building on April 30th, 2005, December 19th, 2009, October 31st, 2013, and February 6th, 2018, are measured and discussed in this study. Owing to a mere 2 km distance from the Milun Fault, most of earthquakes measured near the HeXin Building feature the near-fault phenomenon. The reconnaissance and monitoring results are first exhibited in this study, and then a numerical model is established according to the system identification results from the measurement data of the 2009 earthquake. The accuracy of this model is verified through dynamic time history analysis of the other earthquakes mentioned above. Then, the displacement responses of the isolation system are compared through numerical analysis to two identical design-response-spectrum-compatible ground motions that originated from earthquake records with and without near fault phenomenon. The results show that even though these two input ground motions possess similar response spectra, the near-fault phenomenon still caused an isolation displacement of 64% more than one without the phenomenon. Therefore, it is noteworthy for designers to consider any earthquake record with near-fault phenomenon near the site to ensure a conservative design.