Base isolation is an innovative design strategy that provides a practical alternative for the seismic design and retrofit of structures. The role of base isolators under seismic loading is to isolate the structure from the horizontal components of the earthquake ground movement, while the vertical components are transmitted through to the structure relatively unchanged. Base isolators, mainly employed to isolate large structures under earthquake ground excitations and rehabilitate structures damaged by past earthquakes, deflect and absorb the seismic input energy horizontally transmitted to the structures. Design methods of base isolation systems have been improved, and experimental studies on the base isolators have been performed by many investigators. When the inelastic properties of base isolators are defined, it is usual to model the base isolators by simple models, such as a bilinear model, in numerical analysis procedures. However, it would be desirable to conduct experimental studies on the structural systems with base isolators, since the inelastic behavior of the base isolation system sometimes becomes very complex to be represented by a simple numerical model. Hence, extensive experiments are very much needed to study the nonlinear behavior and to provide data for analysis and design of the base-isolated structure. Various experimental methods are available for this purpose, such as quasi-static tests, forced-vibration tests, shaking table tests, and the pseudodynamic tests. Shaking table test is the most reliable experimental method for evaluating the inelastic seismic performance of structures, though the size, weight and stiffness properties of the test structure are significantly limited by the capacity of available shaking table. During the last two decades, the pseudodynamic test method particularly the one incorporating a substructuring technique, has become a very powerful tool to test the inelastic earthquake responses of structures. The pseudodynamic test can be conducted on the full-scale or large-scaled specimens by using the same basic equipment as in the conventional quasi-static test. Another advantage of the pseudodynamic test method is that it is not necessary to apply the real-time dynamic loading, to simulate the earthquake response of the test model. Therefore, it can provide better controlled experimental conditions for large and heavy structures than the shaking table test.
This study demonstrates that base isolation systems offer effective performance for the building and bridge during severe seismic loading through shaking table and pseudodynamic tests. For building, a series of experiments were conducted on a 1/4 scaled three-story structure base-isolated by laminated rubber bearings through shaking table and pseudodynamic tests. The objectives are evaluation of the effectiveness of the base-isolation systems for low-rise structures during severe seismic loads through shaking table tests, verification of the substructuring pseudodynamic test method for base-isolated structures by comparison with the shaking table test results, and development of an analytical model for predicting the earthquake response of base-isolated structures. From the study, it has been found that the pseudodynamic test which requires conventional basic test equipments is very effective for predicting the dynamic response of the base isolated structure. The responses by the pseudodynamic tests are very well compared with those by the shaking table tests. It has been also that the numerical analysis by employing an approximate bi-linear hysteretic model can reasonably simulate the earthquake responses of the base isolation system compared with two test methods. For bridge, various base isolation systems such as laminated rubber bearing and lead rubber bearing with and without fluid dampers were tested. The shaking table test results strongly show that the deck acceleration and pier shear force of the bridge isolated by all base isolation system are significantly reduced. The application of the fluid dampers as parts of seismic energy dissipation systems for bridge has been experimentally studied. Experimental results demonstrate that fluid dampers enhanced the system's ability to dissipate energy resulting in substantial reduction of relative displacement between deck and pier.