Research and Development of Rubber Bearings for Sodium-Cooled Fast Reactor: Ultimate Properties of Half-Scale Thick Rubber Bearings Based on Breaking Tests

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Tomohiko Yamamoto ◽  
Nobuchika Kawasaki ◽  
Tsutomu Hirotani ◽  
...  
Keyword(s):  
Fast Reactor ◽  
Static Loading ◽  
Restoring Force ◽  
Natural Period ◽  
Safety Margins ◽  
Ultimate Properties ◽  
Loading Tests ◽  
Rubber Bearings ◽  
Breaking Points ◽  
Force Characteristics

This paper describes the results of static loading tests using a half-scale thick rubber bearing to investigate ultimate properties application for a sodium-cooled-fast-reactor (SFR). Thick rubber bearings which have a rubber layer that is roughly two times thicker in comparison with existing rubber bearings have been developed by the authors to ensure seismic safety margins for components installed in the reactor building, and to reduce the seismic response in the vertical direction as well as the horizontal direction. The thick rubber bearings, 1600 mm in diameter at the full scale, have been designed to provide a rated load of about 10,000 kN, at the compressive stress of 5.0 MPa, with a horizontal natural period of 3.4 s and a vertical natural period of about 0.133 s. The restoring-force characteristics, including variations, and breaking points, for the thick rubber bearings have not been cleared yet. These validations are essential from the point of view of probabilistic risk assessment (PRA) for a base-isolated nuclear plant as well as a verification of the structural integrity of the thick rubber bearings. The purpose of this paper is to indicate the variation of the stiffness and damping ratios for restoring force characteristics, and the breaking strain or stress, as ultimate properties through static loading tests using half-scale thick rubber bearings. In addition, an analytical model for the thick rubber bearings which is able to express the nonlinear restoring force, including the breaking points, is presented.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 3 — Ultimate Properties of a Half Scale Thick Rubber Bearings Based on Breaking Test

2016 ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Tomohiko Yamamoto ◽  
Nobuchika Kawasaki ◽  
Tsutomu Hirotani ◽  
...  
Keyword(s):  
Fast Reactor ◽  
Static Loading ◽  
Restoring Force ◽  
Natural Period ◽  
Rubber Bearing ◽  
Safety Margins ◽  
Ultimate Properties ◽  
Loading Tests ◽  
Rubber Bearings ◽  
Force Characteristics

This paper describes the results of static loading tests using a half-scale thick rubber bearing to investigate ultimate properties application for a Sodium-cooled-Fast-Reactor (SFR). The thick rubber bearing, which has a rubber layer roughly three times thicker in comparison with conventional rubber bearings, has been developed by the authors to ensure seismic safety margins for components installed in the reactor building, and to reduce seismic response in the vertical direction as well as horizontal direction. The thick rubber bearings, 1600 mm in diameter at full scale, have been designed to provide a rated load of about 10000 kN with a horizontal natural period of 3.4 s and a vertical natural period of about 0.133 s. The fundamental restoring-force characteristics of the thick rubber bearings has been already cleared through the static loading tests using a half-scale thick rubber bearing, 800 mm in diameter. However, variations of the restoring force characteristics and ultimate properties have not been obtained yet. These validations are essential from the point of view of Probabilistic Risk Assessment (PRA) for a base isolated nuclear plant as well as to verify the structural integrity of the thick rubber bearing. The purpose of this paper is to indicate the variation of the stiffness and damping ratio concerning restoring force characteristics and the breaking strain or stress as ultimate properties through static loading tests using the half-scale thick rubber bearings.

Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 2 — Details of Characteristics for Disc Springs and Oil Dampers on Basis of Full-Scale Loading Tests

2018 ◽  
Author(s):  
Takahiro Somaki ◽  
Tsuyoshi Fukasawa ◽  
Takayuki Miyagawa ◽  
Tomohiko Yamamoto ◽  
Yoshifumi Hibako ◽  
...  
Keyword(s):  
Seismic Response ◽  
Analytical Model ◽  
Fast Reactor ◽  
Three Dimensional ◽  
Damping Capacity ◽  
Restoring Force ◽  
Isolation System ◽  
Loading Tests ◽  
Rubber Bearings ◽  
Force Characteristics

Being compatible with the seismic and thermal loads for the large Sodium-cooled Fast Reactor (SFR), the three-dimensional isolation system is inevitable technology. The three-dimensional isolation system consists of the thick rubber bearings, the disc springs and the oil dampers. Since the isolation performances on the rubber bearings in the horizontal direction have been revealed by the previous studies [1], the vertical isolation performance and characteristics such as restoring force and damping performance should be clarified by loading tests to build the analytical model. This paper presents these fundamental vertical isolation characteristics obtained by loading tests with full-scaled disc springs and oil dampers. The disc springs as the vertical restoring forces have 700 mm in external diameter and 34 mm in thickness. The oil dampers have the maximum damping force of 2,000 kN at the velocity of 0.25 m/s. The disc spring is one of the largest size, and the oil damper is one of the largest damping capacity in Japan. The static loading tests such as incremental cyclic loadings under the supporting load were conducted to investigate the restoring force characteristics for the disc springs. The dynamic loading using sinusoidal waves with varied input frequencies or the seismic response waves obtained by seismic response analysis were conducted to investigate the damping performance for the oil dampers. The applicability of the design method and the analytical model for disc springs and oil dampers were demonstrated by the restoring force characteristics obtained from tests. It should be noted, this paper is in series from Part 1.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 2 — Fundamental Characteristics of Half-Scale Rubber Bearings Based on Static Test

2015 ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Tomohiko Yamamoto ◽  
Nobuchika Kawasaki ◽  
Takahiro Somaki ◽  
...  
Keyword(s):  
Fast Reactor ◽  
Static Loading ◽  
Seismic Isolation ◽  
Linear Strain ◽  
Isolation System ◽  
Rubber Bearing ◽  
Strain Limit ◽  
Seismic Force ◽  
Loading Tests ◽  
Rubber Bearings

This paper described the results of the static loading tests using a half-scale thick rubber bearing to investigate the fundamental characteristics such as horizontal and vertical restoring force of a rubber bearing applied to a Sodium-cooled-Fast-Reactor (SFR). Since the SFR has thin-walled component structures, a seismic isolation system is employed to mitigate the seismic force. A rubber bearing with thick rubber layers is used for the seismic isolation system applied to the SFR, it was developed aiming for isolation of not only horizontal response acceleration, but also vertical response acceleration. The thick rubber bearing of 1600 mm in diameter full-scale was designed to provide about a 10000 kN rated load with a horizontal natural period of 3.4 s and a vertical one of 0.125 s. Moreover, a linear strain limit of the thick rubber bearing was designed to accept a horizontal displacement of 700 mm or more in order to ensure a double safety margin for response displacements against a design basis ground motion. The static loading tests were performed using a half-scale thick rubber bearing with a diameter of 800 mm to investigate the horizontal/vertical stiffness, damping ratio, a linear strain limit in horizontal direction and a tensile yield stress in the vertical direction. The fundamental characteristic of rubber bearings employed to the SFR and the validity of a design formula became clear through the static loading tests.

Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 1 — Proposal of Analytical Models Based on Loading Tests

2018 ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Takahiro Somaki ◽  
Takayuki Miyagawa ◽  
Masato Uchita ◽  
...  
Keyword(s):  
Seismic Response ◽  
Analytical Model ◽  
Three Dimensional ◽  
Analytical Models ◽  
Response Analysis ◽  
Seismic Response Analysis ◽  
Natural Period ◽  
Isolation System ◽  
Loading Tests ◽  
Rubber Bearings

This paper describes that the analytical model for the three-dimensional isolation system [1], which consists of thick rubber bearings, disc springs and oil dampers, is created through loading tests. The new-type analytical models of each element are proposed to improve the prediction accuracy of the seismic response analysis. The concept of the three-dimensional isolation system has been proposed to ensure the structural integrity for large reactor vessels. The primary specifications of the three-dimensional isolation system are a horizontal natural period of 3.4 s and a vertical natural period of 0.33 s. The investigations of horizontal isolation performances have been conducted for the various types of isolation devices, beginning with rubber bearings, whereas the previous studies focused on the vertical isolation performances are only a few. Hence, isolation characteristics, such as restoring force and damping force, should be clarified by loading tests using vertical seismic isolation elements, and analytical model to assess the seismic response should be identified on the basis of the loading test results. This paper presents a new analytical model with providing of the differential equations to improve the prediction accuracy and demonstrates the seismic performance, including beyond-design-basis ground motion, for the three-dimensional isolation system by the seismic response analysis.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 4 — Aging Properties of a Half Scale Thick Rubber Bearings Based on Breaking Test

2016 ◽  
Author(s):  
Tomoyoshi Watakabe ◽  
Tomohiko Yamamoto ◽  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Takahiro Somaki ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fast Reactor ◽  
Seismic Isolation ◽  
Hysteresis Loops ◽  
Natural Period ◽  
Isolation System ◽  
Rubber Bearing ◽  
Aging Properties ◽  
Rubber Bearings ◽  
Effects Of Aging

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. Based on many previous studies, rubber bearing technology has progressed, but test data regarding the effect of aging is not sufficient. Moreover, there is no data on the limits of linear strain and breaking behavior for thick rubber bearings after aging. 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 (800mm diameter) and 1/8-scale (200mm diameter) rubber bearings. Aging of the rubber bearings was reproduced using thermal degradation, in which the target of aging periods were 30 and 60 years. 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.

Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 3 — Characteristics for Elements on Basis of Half-Scale Loading Tests

2019 ◽  
Author(s):  
Takahiro Somaki ◽  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Takayuki Miyagawa ◽  
Masato Uchita ◽  
...  
Keyword(s):  
Fast Reactor ◽  
Seismic Isolation ◽  
Design Method ◽  
Three Dimensional ◽  
Isolation System ◽  
Rubber Bearing ◽  
In Series ◽  
Loading Tests ◽  
Rubber Bearings ◽  
Disc Spring

Abstract The authors have been developing the three-dimensional isolation system for a Sodium-cooled Fast Reactor, and reported the details of characteristics of disc springs and vertical oil dampers on the basis of full-scale loading tests [1]. To clarify the fundamental characteristics of the three-dimensional isolation system, the loading tests using a half-scale assembled specimen have been planned, which is composed of a rubber bearing, disc spring units, the horizontal supporting functions, the smoothly sliding elements, and the rotate restraint elements. This paper describes each characteristic of the rubber bearings, disc springs and sliding element before assembling a half-scale specimen of the three-dimensional seismic isolation system by the static or dynamic loading. The applicability of design method, the scaling effect in disc springs, and the dependence on the friction coefficient of the sliding elements were investigated and confirmed. Additionally, the method of minimizing the variation of force-displacement relationships between four disc spring units, each of which has the three disc springs stacked in parallel and six disc springs stacked in series, was studied. It should be noted that this paper is in series from Part 2 [1] held on 2018PVP.

Hysteretic Restoring Force Characteristics of High Damping Rubber Bearings Under High Compressive Stress

2004 ◽  
Author(s):  
Yasuhiro Kasahara ◽  
Shigenobu Suzuki ◽  
Takashi Kikuchi
Keyword(s):  
Compressive Stress ◽  
Seismic Isolation ◽  
Damping Ratio ◽  
Loading Test ◽  
Restoring Force ◽  
Scaled Model ◽  
High Damping Rubber Bearings ◽  
High Damping Rubber ◽  
Rubber Bearings ◽  
Force Characteristics

Hysteretic restoring force characteristics — shear stiffness, equivalent damping ratio, and ultimate properties — of seismic isolation bearings are significantly affected by compressive stress. In this study, dependence of shear properties of high-damping rubber bearings (HDR) on the compressive stress σ and secondary shape factor S2 was studied by dynamic loading test with scaled-model and static loading test with full-scale isolators. The results highlighted the high compressive stress dependency on restoring force characteristics of HDR with the isolator of relatively small S2. It is concluded that large S2 is desired when isolators are designed for high compressive stress. The applicability of HDR under high compressive stress was experimentally verified.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 5 — Non-Linear Analytical Models for Thick Rubber Bearing

2017 ◽  
Author(s):  
Tsutomu Hirotani ◽  
Takahiro Mori ◽  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Tomohiko Yamamoto ◽  
...  
Keyword(s):  
Vertical Direction ◽  
Analytical Models ◽  
Test Results ◽  
3D Fem ◽  
Restoring Force ◽  
Fem Model ◽  
Rubber Bearing ◽  
Non Linear ◽  
Rubber Bearings ◽  
Breaking Points

Application of seismic isolation system is essential to reduce the seismic force not only for the horizontal direction but also for vertical direction since the component installed to the Sodium-Cooled-Fast-Reactor (SFR) has thin-walled structures to reduce thermal stress. The authors have performed static loading tests using a half-scale thick rubber bearing to investigate ultimate properties include breaking, and confirmed that the thick rubber bearings have sufficient performance compared to the conventional thin rubber bearings. The present paper describes the evaluation of analytical models for the thick rubber bearing by following two approaches based on the obtained test results. a) Spring model Horizontal and vertical spring models, which are employed to the non-linear seismic response analysis, are compiled to examine applicability of conventional analytical model for thin rubber bearing. In addition, the horizontal and vertical spring models are modified, as a suitable non-linear analytical model for the thick rubber bearing. For the horizontal direction, hysteresis rules composed of multiple lines considering slip effect are modified to correspond to the hysteresis characteristics obtained test results. Hysteresis rules under vertical direction composed of multiple lines in consideration of effect on the shear strain due to horizontal seismic response is constructed. b) 3D FEM model The prediction methods of break strain for thin rubber bearings as the conventional rubber bearing have been examined, which have been proposed by the authors as 3D finite element analysis in consideration of the hyper elasticity. To improve suitable the above mentioned methods for the corresponding the restoring force characteristics for thick rubber bearing, 3D FEM model containing a higher-order elements was constructed to express the skeleton curve as restoring force characteristics up to the breaking points. The validity of the constructed 3D FEM model was investigated comparing breaking test results under horizontal and vertical direction. Consequently, the analytical results demonstrated that the skeleton curves up to the horizontal and vertical breaking points can express with constructed 3D FEM model. In addition, this paper describes the criteria with respect to the breaking strain by utilizing the analytical results.

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