RAPID: Performance of the Base-Isolated Christchurch Women's Hospital during the Sequence of Strong Earthquakes and Aftershocks in New Zealand from September 2010 through 2011

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The objective of this Rapid Research Response (RAPID) award is to collect perishable data on the seismic response of the base-isolated Christchurch Women's Hospital during the sequence of strong earthquakes and aftershocks in Canterbury, New Zealand from September 2010 through 2011. The relatively high probability of additional strong aftershocks in 2011 presents a unique opportunity to capture high-fidelity data on the performance of a modern seismically-isolated structure. This project involves collaboration among researchers at Duke University and the University of Canterbury. The project team will travel to Christchurch to temporarily instrument the isolation galley and the top level of the Christchurch Women's Hospital with accelerometers, displacement transducers, and data recorders loaned from the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) facility at the University of California, Los Angeles. This instrumentation is capable of enabling near real-time observation of the building response measurements. Aftershock responses will be recorded automatically over a period of months and ambient vibrations will be recorded periodically. These records will be used to assess the behavior and to develop mathematical models of this seismically-isolated structure, including soil-foundation-structure interaction effects and the effects of inter-structural coupling. Understanding soil-foundation-structure interactions and coupled-structure interactions in base-isolated buildings is needed for advancing knowledge and future implementation of this method of seismic hazard mitigation. Visual inspection of the seismic isolators following the New Zealand earthquakes of 4 September 2010 and 22 February 2011, and the first-person accounts of motions felt within the hospital during these events, indicate that the isolation system deformed less than may have been expected given local ground motion records. High-fidelity response measurements of this structure to strong aftershocks will provide the basic quantitative information required to assess the mechanisms at play in this and many similar base-isolated structures. Future implementation of base isolation as a seismic mitigation strategy will therefore benefit from the knowledge gained from examining the performance of a modern base-isolated facility responding to strong ground motions. Collaboration among researchers in the United States and New Zealand in this project will advance the development of seismic isolation internationally. Knowledge generated from this project will be used to illustrate soil-foundation-structure interaction effects in an interactive web-based educational tool, and will provide opportunities for undergraduate research.