Field Testing of Full-scale Seismically Isolated Bridge Considering the Characteristics of Low-to Moderate Setismicity

To verify the validity of optimal design technique of seismically isolated bridge, field testing of full-scale bridge system has been conducted. The optimum design of seismically isolated bridge primarily focuses on minimizing the life-cycle cost (LCC) of the bridge, which makes it possible to simultaneously guarantee both seismic safety and cost efficiency in consideration of the seismic characteristics of Korea, that is, low-to-moderate seismicity. Test bridge was selected as one to be representative of expressway bridges in Korea and, accordingly, seismic isolation bearings are optimally designed. In addition, quick release devices, or hydraulic jacks with quick release valves, have been developed to perform the free vibration test of the seismically isolated bridge. Through the test, the nonlinearity of hysteretic behavior and dynamic properties of the seismic isolation system were identified and compared with the design values. Due to the in-situ low temperature condition (-10) during the test, identified hysteretic behavior of the isolation bearings showed a little difference with the design value. Even though the time history of the nonlinear response of the isolated bridge occurring at the early stage of the test could not be captured exactly due to the hindrance of the hydraulic jacks to the recovery motion of the bridge deck, the frequency response of the numerical analysis model showed a good agreement with that of the experimental result. The results of this study may thus provide realistic data to improve design technology of seismically isolated bridges in low-to-moderate seismic region.