Isolation Performance of Intelligent Seismic Isolation System Using Air Bearing

This paper describes three-dimensional isolation performance of seismic isolation system using air bearings. Long period seismic waves having predominant period of from a few seconds to a few ten seconds have recently been observed in various earthquakes. Also resonances of high-rise buildings and sloshing of petroleum tanks in consequence of long period seismic waves have been reported. Therefore the isolation systems having very long natural period or no natural period are required. In a previous paper [1], we proposed an isolation system having no natural period by using air bearings. Additionally we have already reported an introduction of the system, and have investigated horizontal motion during earthquake in the previous paper. It was confirmed by horizontal vibration experiment and simulation in the previous paper that the proposed system had good performance of isolation. However vertical motion should be investigated, because vertical motion varies horizontal frictional force. Therefore this paper describes investigation regarding vertical motion of the proposed system by experiment. At first, a vertical excitation test of the system is carried out so as to investigate vertical dynamic property. Then a three-dimensional vibration test using seismic waves is carried out so as to investigate performance of isolation against three-dimensional seismic waves.

Evaluation Method of U-Bolt Energy Absorption

At domestic PWR plants in Japan, one of the major key issues is earthquake-proof safety [1–3]. Recently, a design procedure using energy absorption, not conventional rigid design, was authorized according to revised review guidelines for aseismic design (JEAC4601). Therefore, we focused on the design technique that utilizes energy absorption effects to reduce the seismic responses of the piping system with U-Bolt, by the static and dynamic tests of simplified piping model supported by U-Bolt. The force-displacement characteristics and a fatigue diagram were obtained by the tests.

Multiple Yield and Bounding Surfaces Model for Analysis of Multiple Friction Pendulum System

In order to systematically investigate the mechanical characteristic of a multiple friction pendulum system with more than two concave sliding interfaces and one articulated slider located between these concave sliding interfaces, on the basis of the plasticity theory, a plasticity model called the multiple yield and bounding surfaces model is proposed in addition to analytical formulations derived from the proposed concept of subsystems in this study. The proposed model has two separate groups of multiple yield and bounding surfaces. The first group is adopted to describe the mechanical behavior of the subsystem including the concave sliding interfaces above the articulated slider and the second group is used for modeling the sliding characteristic of the subsystem representing the concave sliding interfaces below the articulated slider. The connection of these two subsystems in series forms the mechanical characteristic of the entire MFPS isolation system. By virtue of the proposed model, the phenomena of the sliding motions of the MFPS isolator with multiple concave sliding interfaces under cyclical loadings can be clearly understood. Analytical results infer that the natural frequency and damping effect of the MFPS isolator with multiple concave sliding interfaces change continually during earthquakes and are controllable through appropriate designs.

Research and Development of Damping Device for Light Weight Mechanical Structure Using Damping Effect Caused by Eddy Current

A base-isolation and vibration control technique has been applied positively to architectural and civil structures after Kobe earthquake, and now the techniques are adopted as general vibration reduction technique for many structures. In such situation, an application of the vibration attenuation device to the small-scale structure has been carried out actively in recent years. Especially, in the important institution of the cities such as a refuge place, a hospital, a school, an information and a communication institution where function maintenance is needed, it is important to maintain its performance of the machinery and equipment in the facility with an upgrade of structural seismic safety. Moreover, in the future, upgrading of seismic safety of the particular equipments is urgent business. This study has been examined a low cost and compact damping device for base-isolation system of light weight mechanical structures like a computer server rack. In this paper, the experimental and analytical results on the basic performances of the damping device using damping effect by Eddy-Current.

Energy Dissipation Behavior of an Autonomous Controller for Semi-Active Control Device

In this research, autonomous controller is developed to provide the function of “Sensing-Computing-Transferring” for improving of energy dissipation capability of semi-active control device. This proposed controller has qualifications of detecting structural response under the excitation of earthquake; it depends on the control law to produce control order to adjust and control the action of semi-active control damper. The principle of this controller is: 1.) autonomous controller and damper-added stiffness element are parallel connection; 2.) the direction of pressure force and velocity moving direction of structure are changed simultaneously by this controller; 3.) the action of switching direction of damper has been finished when the tiny displacement of structure is happened by reverse process of moving direction of structure. Practically, this controller was simulated by connecting soft springs, damper and actuator in serial. The experimental results indicate that the function and energy-dissipating behavior of this proposed controller is similar to traditional semi-active controller except that this controller can switch the damper status at the right moment. This proposed controller can replace the detector, central control computer and damping controller included in original semi-active control system. The advantages of this developed autonomous controller are: 1.) low manufacturing cost; 2.) low requirement of system maintenance; 3) high reliability of control system.

Seismic Qualification by Testing for Electrical and Active Mechanical Equipment to be Installed in Hard-Rock High Frequency Sites

All electric and active mechanical equipment important to safety must be seismically qualified by either analysis, testing, or a combination of both. The general requirements for seismic qualification of electric and active mechanical equipment in nuclear power plants are delineated in Appendix S to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), item 52.47(20) of 10 CFR 52.47, and Appendix A to 10 CFR Part 100. The staff at the US Nuclear Regulatory Commission (NRC) has recognized that the Certified Design Ground Motion may be exceeded by the site-specific ground motion. The exceedances are generally in the high-frequency range for the Central and Eastern US sites. For equipment seismic qualification consideration, the exceedances must be addressed at both the ground level and the floor level where the equipment is located. Thus, the in-structure response spectra at some locations may exceed those in-structure response spectra generated by the certified seismic design response spectra. The U.S. nuclear industry and the NRC have initiated activities to address this issue. Two scenarios that revealed themselves during the review activities of the design certification and combined license applications for new reactors will be expounded upon in the paper. In Case I, equipment seismic qualification has been approved for a certified design and equipment is to be installed at a hard-rock high frequency (HRHF) site with certified seismic design response spectra (CSDRS) exceeded by the Ground Motion Response Spectra (GMRS) of the hard-rock site. In Case II, equipment seismic qualification has not been approved for a design certification and there is an application with GMRS exceeding the not-yet-approved CSDRS. In the paper, the staff will begin the discussion with the regulatory requirements for seismic qualification of electric and mechanical equipment. The focus of the paper is to identify the staff concern and illustrate the resolution between the NRC staff and an applicant on the seismic qualification of equipment by testing, in particular for equipment to be installed in hard-rock high frequency sites, to meet the regulatory requirements.

Seismic Performance of Vibration Control Device That Generates Power

In a previous paper the authors proposed a semi-active vibration control device (VCD) that generates power. The device utilizes a ball screw, and has inertial and damping forces. The damping coefficient is adjusted by altering resistance at the terminal of the power generator. A small-scale VCD was manufactured for experimental testing. Frequency responses of a small-scale spring mass structure were measured in order to confirm the effects of vibration suppression within a wide range of frequencies. In this paper, as the next step, vibration tests using a benchmark structure with an installed VCD that has a 30 kN capacity are carried out at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The benchmark structure has three stories with a 3 m height and a mass of 6 tons at each floor level for a total height and weight of 9 m and 18 tons, respectively. The VCDs are installed between adjacent floors with steel chevron braces. A simple control law that is based on a minimized Lyapunov function and employs bang-bang operation is used as a variable current controller instead of the modifying the resistance level of the VCD. Scaled earthquake motions including the Imperial Valley El Centro north-south component that is normalized to be a peak level of 0.5 m/s2, are applied to the base of the steel framed structure in the horizontal direction by a shaking table. Experimental responses of each floor for the uncontrolled and controlled cases are compared with analytical responses, and effects of vibration suppression for the large-scale model are discussed quantitatively.

Construction of the Health Monitoring System of a Machine Structure

When big power like an earthquake acts at the place that the machine is normally operating, abnormalities may occur to a machine. If the machine is operated without finding abnormally, danger may attain to mechanical fatal damage and a mechanical work pursuer. Therefore, detecting in the situation where mechanical abnormalities are operated is very important as a health monitoring system. In this research, the system that takes in the vibration wave on the rotation part of the machine currently rotated is constructed. A vibration wave is analyzed using time-frequency analysis (STFT, the Wigner distribution, wave let analysis) From the result, the system by which normal vibration and abnormal vibration are evaluated is constructed from random noise. As a result of comparing normal vibration with abnormal vibration, the peak may have occurred in the high frequency region. It turned out that the analysis result of an unsteady state has a peak 2000Hz–3000Hz of frequency domains, and 4000Hz–5000Hz also in STFT and Wigner distribution. I think that this becomes the important tool which distinguishes the stationary state and unsteady state in health monitoring.

Semi-Active Control of Civil Structures With a One-Step-Ahead Prediction of the Seismic Response

We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.

Shaking Table Tests With Large Test Specimens of Seismically Isolated FBR Plants: Part 1—Response Behavior of Test Specimen Under Design Ground Motions

The seismic isolation technology is planned to introduce to the next generation’s fast breeder reactor (FBR) plants in order to reduce seismic load subjected to components. To grasp the ultimate behavior of a seismically isolated plant under extremely strong earthquake at a level beyond the design ground motions and to establish ultimate strength design methods of seismic isolators, we made a series of shaking table test with large test specimen of seismically isolated FBR plants. The ultimate behavior test was performed using one of the world largest three-dimensional shaking tables “E-Defense” of National Research Institute for Earth Science and Disaster Prevention of Japan to obtain ultimate behavior data of a technologically-feasible large scale model. Test specimen consists of concrete blocks, reinforced concrete walls and isolation layer with six laminated rubber bearing with lead plug (LBR). The gross mass of upper structure of the test specimen is about 600ton. The diameter of the LRB is 505mm that reduced prototype dimensions to about 1/3. In this study, the following three behaviors were assumed as the ultimate behavior of the seismic isolation system; 1) loss of response reduction function of the isolation system by hardening of rubber, 2) non-linear response behavior by the cracking of the concrete wall and 3) braking of the LRB. When the input acceleration level increased, the test specimen was designed to show the ultimate behavior in the above-mentioned order. The ultimate behavior test of the seismic isolation system was carried out on the condition of two input waves by using two test specimen sets of the same dimensions. In this paper, details of the test specimen including the LRB and loading conditions are described. Response behavior of the test specimen under design ground motions is also reported. The restoring force characteristics of the LRBs were stable. The response acceleration of a horizontal direction measured at the upper structure of the specimen was reduced. Prior to the ultimate behavior tests with strong input waves, the response reduction functions of the test specimen under design ground motions were confirmed.