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.

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.

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 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.

Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 4 — Proposal of Optimal Combination Method for Disc Spring Units and Newly Friction Model for Sliding Elements

2019 ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Takahiro Somaki ◽  
Takayuki Miyagawa ◽  
Masato Uchita ◽  
...  
Keyword(s):  
Seismic Response ◽  
Friction Force ◽  
Three Dimensional ◽  
Friction Model ◽  
Optimal Combination ◽  
Combination Method ◽  
Restoring Force ◽  
Optimal Method ◽  
Isolation System ◽  
Disc Spring

Abstract The authors proposed a newly three-dimensional isolation system, consisting of a rubber bearing, vertical oil dampers and disc spring units, to reduce the seismic response in the vertical direction as well as horizontal direction. This isolation system is employed with a number of disc spring units to provide the vertical restoring force to the superstructure. The disc spring units are combined by three disc springs in parallels and they are are stacked in six serials. The vertical restoring force has susceptible to the variation forces for the individual disc springs because the disc spring units are combined in the six serials. The The purpose of this paper is to present two kinds of proposal to improve the quality control of our isolation system and the prediction accuracy of seismic response. The first is to create the the optimal combination method for the disc spring units using the meta-heuristic algorithm to minimize the variation of vertical vertical restoring force. The proposed optimal method was verified through the result of static loading tests using the 72 disc springs which have the half dimensions to full scale. The second is to create a newly analytical model for the friction force caused by polymeric materials. The proposed analytical model was verified by comparing the loading test results. Moreover, the seismic isolation performances were clarified by the seismic response analysis that consider the vertical restoring force of the disc spring units which were combined using the optimal method and the friction force of sliding elements which were modeled by the proposed friction model. This analytical result revealed that our isolation system can reduce the seismic response not only for the high frequency components but also the low frequency ones.

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.

Reduction of Seismic Response of Mechanical System by Base Isolation System With Friction Bearing

2007 ◽  
Author(s):  
Shigeru Aoki ◽  
Yuji Nakanishi ◽  
Kazutoshi Tominaga ◽  
Takeshi Otaka ◽  
Tadashi Nishimura ◽  
...  
Keyword(s):  
Mechanical System ◽  
Seismic Response ◽  
Base Isolation ◽  
Low Frequency ◽  
Simulation Method ◽  
Shaking Table ◽  
Restoring Force ◽  
Isolation System ◽  
Friction Bearing ◽  
Base Isolation System

Reduction of seismic response of mechanical system is important problem for aseismic design. Some types of base isolation systems are developed and used in actual base of buildings and floors in buildings for reduction of seismic response of mechanincal system. In this paper, a base isolation system utilizing bearing with friction and restoring force of bearing is proposed. Friction bearing consists of two plates having spherical concaves and oval type metal or spherical metal with rubber. First, effectiveness of the base isolation system is examined experimentally. Using artificial time histories, the isolated table is shaken on the shaking table. The maximum value of response is reduced and sum of squares of response is significantly reduced. Power spectrum is significantly reduced in almost of all frequency regions, except for very low frequency region. Next, in order to examine reduction of seismic response of actual mechanical system, a console rack is set on the isolated plate. Seismic response is also significantly reduced. Finally, obtained results of experiment are examined by simulation method. An analytical model considering friction and restoring force is used. From simulation method, effectiveness of the proposed base isolation system is demonstrated.

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 6 — Proposal of New Type of Hysteresis Model for Ultimate Behavior

2017 ◽  
Author(s):  
Tsuyoshi Fukasawa ◽  
Shigeki Okamura ◽  
Tomohiko Yamamoto ◽  
Tomoyoshi Watakabe
Keyword(s):  
Seismic Response ◽  
Hysteresis Loops ◽  
Response Analysis ◽  
Hysteresis Model ◽  
Seismic Response Analysis ◽  
Restoring Force ◽  
Proposed Model ◽  
New Type ◽  
Rubber Bearings ◽  
Hysteresis Characteristics

This paper describes a new type of hysteresis model applied for seismic response analysis, which provides restoring force characteristics containing various types of hysteresis loops generated by calculating differential equations, based on static breaking tests regarding thick rubber bearings. In order to reduce residual risk, there is increasing necessity to accurately predict seismic response against both design-basis ground motion and ground motion exceeding design-basis. This process of seismic response prediction is called seismic Probabilistic Risk Assessment (PRA). In general, a restoring force of rubber bearing under large deformation due to a major earthquake has strong non-linear characteristics containing the hysteresis loops. To improve the accuracy of seismic response predictions up to the ultimate behavior in PRA, a new hysteresis model to be applicable up to the breaking point in horizontal and vertical directions is proposed by the authors. The features of the proposed hysteresis model are as follows: (1) The hysteresis characteristics obtained by the proposed model have smooth curves as substantive hysteresis loops measured in breaking tests. (2) The various types of hysteresis characteristics can be captured efficiently as initial value problems since the proposed model, consisting of differential equations, directly allows the skeleton function, and unaffected by hysteresis law such as Masing law. This paper indicates applicability of the proposed hysteresis model to seismic response analysis through comparison of results of the static breaking test with results of analytical, and also describes the breaking mode obtained by the seismic response analysis.

Study on Analytical Model of Nonlinear Vibration for Elastic Plates With Gaps Under Random Waves

2004 ◽  
Vol 126 (4) ◽  
pp. 504-509 ◽  
Author(s):  
Masanori Shintani ◽  
Manabu Hamai
Keyword(s):  
Nonlinear Vibration ◽  
Analytical Model ◽  
Force Characteristic ◽  
Solid Model ◽  
Random Waves ◽  
Elastic Plates ◽  
Analysis Model ◽  
Restoring Force ◽  
Elasto Plasticity ◽  
Force Characteristics

In this paper, an analytical model for the nonlinear elastic-plastic vibration for long plates with gaps subjected to random vibrations is considered. The nonlinear vibration is caused by the collision phenomena between a mass through a gap and plates with thickness of 0.5, 0.6, and 0.8 mm. An elastic perfectly plastic solid material is assumed in some cases, which adds another aspect to the nonlinear behavior of the system. The material characteristic of the steel is assumed to be an elasto-plasticity solid model. A restoring force characteristic is obtained as the nonlinear vibration of a cubic equation for 0.5, 0.6, and 0.8 mm, the thickness of the plates by experiments. Now the analytical model is proposed by the elasto-plasticity solid model. The relation between the displacement and the force is described by a complicated equation. The curve from the analytical model is called a deflection curve. The results by the analytical model are compared with the results by the experimental model. The restoring force characteristics by the analysis agree with those of the experiment. The restoring force characteristics of the analysis are described using cubic equations. The simple analysis model for evaluation of the vibration characteristic of the nonlinear vibration system, which performs collision vibration with gaps, is proposed by elasto-plasticity solid model in this paper. The results of this proposed analytical model agree with the experimental results better than the results of the minimum of error of square.

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