Study on Three-Dimensional Seismic Isolation System for Next Generation Nuclear Power Plant: Independent Cable Reinforced Rolling-Seal Air Spring

In Japan, the development of the next generation NPP has been conducted in recent years. In the equipment/piping design of the plant, seismic condition has been required much more mitigate than before. So, the three-dimensional (abbreviation to 3D) seismic isolation system development has also been conducted since 2000. The superlative 3D base isolation system for the entire building was proposed. The system is composed of cable reinforced air springs, rocking arresters and viscous dampers. Dimensions of the air spring applied to the actual power plant are 8 meters in the outer-diameter and 3.5 meters in height. The allowable half strokes are 1.0 meters in horizontal and 0.5 meters in vertical respectively. The maximum supporting weight for a single device is 70 MN. The inner design air pressure is about 1.8MPa. This air spring has a distinguishing feature, which realizes 3D base isolation with a single device, whose natural periods are about 4 seconds in horizontal and about 3 seconds in vertical. In order to verify the 3D performance of this system, several feasibility tests were conducted. Firstly, 3D shaking table tests were conducted. The test specimen is scaled 1/4 of the actual device. The outer diameter and inner air pressure of air spring is 2 meters and 0.164 MPa. Next, a pressure resistant test for the sub cable, textile sheet and rubber sheet, which composed air spring, were conducted as a full scale model test. Then, air permeation test for the rubber sheet was also conducted. As a result, the proposed system was verified that it could be applied to the actual nuclear power plants.

Failure Behavior of Elbows With Local Wall Thinning Under Cyclic Load

Pressurized piping systems used in nuclear power plants are supposed to be degraded by the effects of aging. Local wall thinning is one of the defects considered to be caused in piping systems due to the effects of aging, but the failure behavior of thinned wall pipes under seismic load is still not clear. Therefore an experimental and analytical study to clarify the failure behavior of thinned wall pipes is being conducted. In this paper, the experimental results of locally thinned wall elbows under cyclic bending load are described. Displacement-controlled cyclic bending tests were conducted on elbows with local wall thinning. The test models were pressurized to 10MPa with room temperature water and were subjected to in-plane or/and out-of-plane cyclic bending load until their failures. From the tests, the failure modes of the thinned wall elbows were found to be fatigue failure at the flank of the elbow, or fatigue and buckling failure accompanied with ratchet deformation. It was also found that the life of the thinned wall elbow subjected to out-of-plane bending were extremely lower than that of the elbow without wall thinning. The failure modes and fatigue lives of elbows seemed to be affected by a ratchet phenomenon.

An Assessment of Simplified vs. Detailed Methodologies for SSI Analyses of Deeply Embedded Structures

Sponsored by the US Nuclear Regulatory Commission (NRC), Brookhaven National Laboratory (BNL) is carrying out a research program to develop a technical basis to support the safety evaluation of deeply embedded and/or buried (DEB) structures as proposed for advanced reactor designs. In this program, the methods and computer programs established for the assessment of soil-structure interaction (SSI) effects for the current generation of light water reactors are evaluated to determine their applicability and adequacy in capturing the seismic behavior of DEB structures. This paper presents an assessment of the simplified vs. detailed methodologies for seismic analyses of DEB structures. In this assessment, a lump-mass beam model is used for the simplified approach and a finite element representation is employed for the detailed method. A typical containment structure embedded in a soil profile representative of a typical nuclear power plant site was utilized, considering various embedment depths from shallow to full burial. BNL used the CARES program for the simplified model and the SASSI2000 program for the detailed analyses. The calculated response spectra at the key locations of the DEB structure are used for the performance assessment of the applied methods for different depths of burial. Included in the paper are: 1) the description of both the simplified and detailed models for the SSI analyses of the DEB structure, 2) the comparison of the analysis results for the different depths of burial between the two methods, and 3) the performance assessment of the analysis methodologies for SSI analyses of DEB structures. The resulting assessment from this study has indicated that simplified methods may be capable of capturing the seismic response for much deeper embedded structures than would be normally allowed by the standard practice.

Detection and Identification of Bridges Considering Soil Effect

Unexpected collapses and near collapse of bridges during the 1999 Chi-Chi earthquake underline the need for effective structural monitoring. Periodic structural condition monitoring of bridge structures is necessary to ensure that they provide a continued and safe service. A systematic study of typical bridges is needed, focusing on identifying elastic analytical models that will incorporate the existing state of bridge. To establish dynamic monitoring as a routine bridge inspection method, the soil-structure model of these two bridges are established and compared theoretically and experimentally.

Fundamental Study of Active Mass Damper for Improving Livability of Houses Against Traffic Vibration: Substantiation Test

In Japan, there are many houses built in limited space as well as in close proximity to causeways and railroads, due mainly to concentration of population in the cities in recent years. Slender structures and especially 3-story houses are susceptible to vibration induced by external forces such as traffic. This effect often creates an uncomfortable environment for habitation. Because houses often have a complex geometry, it is difficult to establish the vibration characteristics of a structure. Furthermore, the response characteristics of a house will change with environmental conditions. A prototype Active Mass Damper (AMD) has been developed to address some of these issues. This has been tested in an exhibition house in Tokyo. It uses two AMD’s of 1,725N mass each for both X-axis and Y-axis. Both AMD’s are applied in X and Y directions and are installed at RooF level, they are controlled by Direct Displacement Feedback (DDFB). The test showed that the AMD could dramatically reduce vibration. Of particular note was reduction about 6dB to 8dB (L10) in the first mode of vibration even though the house mass is double the prototype target weight. Also, vibration was dramatically decreased by the AMD on 3rd floor of the house. Vibration level and comfort are important criteria for this kind of system.

Compressive Stiffness Verification of Stirrup Rubber Bearing

In recent years, there has been an immense amount of interest in utilizing the rubber bearing system as a practical approach to seismic-resistant design. The stirrup rubber bearing is confined and bonded by stirrup equipments so as to restrict the lateral expansion of the rubbers due to axial load and increase the compression stiffness. Based on two kinematics assumptions that the horizontal plane parallel to the stirrup equipments or rigid bounding steel plates remains plane and the vertical lines become parabolic after loading, the pressure function and compression stiffness for the stirrup rubber bearing are derived. A good agreement between experimental results by the component tests and computational results by the proposed formulae has been obtained.

Structural Analysis of High-End Server Computer Frames Under Earthquake Loading

This paper reports the mechanical design, structural analysis, and experimental correlation of bracing concepts for high-end computer servers subjected to loads simulating earthquake conditions. The development and evaluation of these stiffening alternatives follows a step-by-step process of finite element analysis coupled with parallel experimental testing. The numerical model is derived from the simplified CAD geometry of an existing server frame. An analysis of this frame model is subjected to a load environment similar to those endured under actual horizontal table vibration tests. The result of this series of analyses is a design study examining how a range of bracing designs affects the global frame rigidity. This design study builds toward the objective of constructing a verified model of the server frame and components that will lead to a guideline for implementing stiffener designs on high-end server systems.

Application of Earthquake Experience Data as Part of the Seismic Verification of Modified Main Steam Isolation Valve Leakage Pathway Piping

The Monticello Nuclear Generating Plant made modifications to the turbine island in 1998 to achieve a 5% power uprate. The radiological analysis conducted for power uprate took credit for deposition and holdup of radioactive iodine in the steam lines downstream of the Main Steam Isolation Valves (MSIV’s) and in the main condenser. The original design basis of certain main steam system piping, equipment, and components that comprise the MSIV Leakage Pathway was not in accordance with Seismic Category I requirements. As part of the original program seismic verification walkdowns were performed to demonstrate the main steam system piping, equipment, and components were seismically rugged. The walkdowns were done using the methodology suggested to seismically evaluate this pathway in the Boiling Water Reactor Owners’ Group report, entitled “BWROG Report of Increasing MSIV Leakage Rate Limits and Elimination of Leakage Control Systems”. In 2001, Monticello made significant changes to improve the performance of the plants hydrogen recombiner process. The hydrogen recombiners are part of the off gas system a portion of which was in the original MSIV Leakage Pathway. These modifications significantly redefined MSIV Leakage Pathway and required an updated assessment of the seismic ruggedness of piping and associated equipment in the MSIV Leakage Pathway. This paper describes the approach and methodology used to update and expand the seismic evaluations and seismic verification walkdowns. It also summarizes the results of these walkdowns and the steps necessary to demonstrate the seismic adequacy of the piping and equipment.

Seismic Capacity of Threaded, Brazed and Grooved Clamped Joints

A series of static and shake table tests were conducted on threaded, brazed and mechanical pipe joints, commonly used in fire protection systems, to understand their integrity under extreme lateral loads, of the type that would be expected in large earthquakes. This paper presents the measured loads and deflections of the joints up to the point of failure. It also describes the joints’ static and dynamic failure mode. This information can be used to model the joints’ flexibility under large lateral displacements, determine their ultimate capacity, and help understand their leak and rupture characteristics.

Analysis and Experiment on the Effect of Seismic Protection of Buildings by High Damping Rubber Bearings

In recent years, many studies on base isolation strategies and devices have been developed and applied in U. S. A., Europe, Japan, and New Zealand. The high damping rubber bearing belongs to one kind of the earthquake-proof ideas of base isolation technologies. The installation of high damping rubber bearings can lengthen the natural period of a building and simultaneously reduce the earthquake-induced energy trying to impart to the building. The objective of this paper is to investigate the base isolation effect of high damping rubber bearings. The uniaxial, biaxial, and triaxial shaking table tests were performed to study the seismic behavior of a 0.4-scale three-story isolated steel structure in the National Center for Research on Earthquake Engineering in Taiwan. The experimental and analytical results show that the nonlinear mechanical characteristics of the high damping rubber bearings can be reasonably simulated.