A questionnaire survey was conducted to makers of seismic isolators, the construction companies and design companies, aiming to grasp the situation of research of aged deterioration of seismic isolators. The seismic isolator under study is 3 types, lead rubber bearings, high damping rubber bearings and natural rubber bearings. According to the answers of the questionnaire, all of them admit the importance of the research, but they indicate that there are some improvements on carrying out it.

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Base-isolation system is designed to lengthen the period of the building. However, this can also increase wind-induced responses of the structure since wind forces have long duration and predominant energy on long periods. Furthermore, the mean component in the along-wind direction also causes certain base-isolation components, such as sliding bearings to become prone to creep phenomenon. Despite of this, evaluation methods of wind-induced response considering creep property on high-rise base-isolated buildings with sliding bearings has not yet been fully investigated. Therefore, this paper examines the evaluation method on those buildings and clarifies the effect of creep property using time-history analysis.

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Performance of laminated natural rubber bearing used for 30 years in seismic isolation building was evaluated. Horizontal stiffness increased by 14.6% and vertical stiffness increased by 5.9% for 30 years. It was confirmed from rubber physical property tests that change in physical properties with age remained within a limited range from the surface of the laminated rubber bearing. Moreover, these results were compared with other research results, and the validity of the rate of change in performance of laminated rubber bearing was verified.

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 1. Introduction
 Although the performance of seismic isolation devices such as rubber bearings or dampers have been tested and evaluated through unidirectional input, in fact these devices are subjected to seismic ground motions in two direction. Recently the performance of high-damping rubber bearings under bidirectional input is found to be different from that under unidirectional input, and bidirectional tests for various isolation devices are being carried out. In this paper, bidirectional shaking table tests for SSB (Spherical Sliding Bearing / Friction Pendulum Bearing: FPB) are conducted, and the difference of their response against unidirectional response are investigated. Bidirectional effects are discussed using analytical model taking these testing results into account, followed by the studies on the effects on the response of supported superstructures.

 2. Bidirectional shaking table tests for a single SSB
 Bidirectional shaking table tests for a single SSB are carried out. A mass gives dead load 24.3 N/mm² pressure on a sliding bearing surface of the SSB, expected friction coefficient is calculated as 0.056, and natural period after slipping is 4.5 sec. As a result, the maximum response displacement of the SSB under bidirectional input is larger than that under unidirectional input, and acceleration is same level between both inputs. These differences are considered to be caused by the bidirectional effects of friction force vector.

 3. Response of multistory frames supported by SSB under bidirectional input
 The response obtained by the shaking table tests is compared with numerical analytical results with a friction pendulum model (FP model) which taking account of pendulum action and bidirectional effects of friction force vector proposed by the authors. The FP model well explains the difference of response under bidirectional vs. unidirectional input. The response of multistory frames supported by the SSB is also studied, and excitation in the displacement response and reduction in the acceleration response are observed.

 4. The effects of hysteretic models on the bidirectional response
 In this chapter, the bidirectional response effects of the FP model and ordinary MSS model (Multiple Shear Spring) which does not simulate pendulum action and has different bidirectional effects of friction force vector are discussed. As a result, the bidirectional effects of friction force vector are significant during the post-sliding frictional stiffness decreasing. Also the effects of normal reaction forces are remarkable, which are not caused by the overturning response of the superstructure, but mostly by the pendulum actions.

 5. Conclusions
 1) The maximum displacement response under bidirectional input generally becomes larger than that under unidirectional input, while acceleration response generally keeps independency between unidirectional and bidirectional input. These bidirectional response characteristics of the SSB are well explained with the FP model.
 2) In multistory frames supported by the SSB, displacement response increases in each story while acceleration response in the upper story decreases by additional bidirectional input compared with unidirectional input.
 3) Using a SSB with large spherical radius, the response by the MSS model differs from that by FP model. That is mainly because MSS model has different bidirectional effects of frictional force vector. On the other hand, the effects of nominal reaction forces become remarkable in the case of using SSB with small spherical radius, which is mainly caused by pendulum action.
 4) The proposed FP model including the pendulum action is considered to be more suitable for evaluate the response characteristics of SSB discussed above than MSS model.

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A seismic isolation system composed of a thick rubber bearing and an oil damper has been developed for Sodium-Cooled Fast Reactor. One of the advantages of the isolation system is the use of thick rubber bearings to ensure the longer vertical natural period of a plant, thereby mitigating seismic loads to mechanical components. Characteristics of thick rubber bearings have been confirmed through a series of tests. This paper focused on the aging properties of thick rubber bearings, such as basic mechanical properties and ultimate strength. An aging test of thick rubber bearings was conducted using 1/2-scale (800 mm diameter) and 1/8-scale (200 mm diameter) rubber bearings. Aging of the rubber bearings was reproduced using thermal degradation based on Arrhenius law, in which the target of aging periods was 60 years, plant life time. The hysteresis loops of the thick rubber bearings after aging were obtained through horizontal and vertical static loading tests, and the effects of aging were evaluated by comparison with the initial mechanical properties. In addition, for the purpose of further research, the effect of scale by aging was clarified to compare the mechanical properties between the 1/2-scale and 1/8-scale rubber bearings.

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