前川 晃

Abstract This paper proposes an improved contactless measurement method for vibration stress of piping systems, by which the measurement time is shorter and the measuring works are more simple. The proposed method includes two processes, in which the bending mode shape of piping vibration is identified by a transmission-type light emitting diode (LED) displacement sensor and the vibration stress is calculated based on beam theory using the approximated curve of the bending mode shape. The proposed method uses one advanced LED displacement sensor to measure the vibration stress in contrast to multiple conventional LED sensors, which must be used in the previous method developed by the authors. Therefore, the measuring system could be reduced in size and a light-weight and portable measurement instrument was developed. The measurement accuracy and reliability of the new method were validated by the vibration experiment using a mockup piping system.

The purpose of this study is to verify the applicability of the proposed noncontact measurement method of vibration stress using multiple laser displacement sensors. In order to demonstrate its applicability, the factors that influence the measurement accuracy were investigated. Since the proposed method has a simple measurement theory and few restrictions on measurement conditions, it can be applied to vibration measurement of various beam-shaped structures such as pipes. However, in actual vibration measurement, it is expected that an inherent error will occur due to the basic principle of the proposed method. Identification and quantitative evaluation of the influential factors that cause the error are important basic findings for determining the practical application of the proposed method. First, based on the basic principle of the proposed method, the influential factors that can occur due to the use of the laser displacement sensor were clarified. Second, the errors caused by the identified influential factors were quantitatively evaluated. Third, a vibration test was performed to verify the identified influential factors and the errors caused by those factors. Finally, from the obtained results, the applicability of the proposed method was demonstrated, and measures for further improving the accuracy were suggested.

This study presents the response mitigation effect of piping systems by inelastic seismic design based on elastic-plastic property of steel pipe supports. The inelastic seismic design to control vibration by absorbing energy using elastic-plastic properties of materials can be one of useful ideas. The design idea to use the elastic-plastic behavior of pipe supports is addressed in Technical Code for Seismic Design of Nuclear Power Plants (JEAC4601) published by the Japan Electric Association in Japan. Here, the component named an elastic-plastic pipe support is proposed as an energy-absorbing element. However, in order to put the inelastic seismic design using the elastic-plastic pipe supports into practical use, it is necessary to accumulate more findings related to the seismic response and the application range. This study aims to investigate the applicability of the inelastic seismic design taking the elastic-plastic pipe supports in the piping systems and to increase the basic findings. In this study, the seismic response analysis using three-dimensional piping system with an elastic-plastic pipe support was conducted. As a result, it was found that the elastic-plastic pipe support affected the seismic response largely. Additionally, the vibration characteristics, the response acceleration, and the load generated in the piping system were discussed relating to the plastic deformation and the plasticity rate of the elastic-plastic pipe support.

This study describes inelastic seismic design of piping systems considering the damping effect caused by elastic-plastic property of a pipe support which is called an elastic-plastic support. Though the elastic-plastic support is proposed as inelastic seismic design framework in the Japan Electric Association code for the seismic design of nuclear power plants (JEAC4601), the seismic responses of the various piping systems with the support are unclear. In this study, the damping coefficient of a piping system is focused on, and the relation between seismic response of the piping system and elastic-plastic behavior of the elastic-plastic support was investigated using nonlinear time history analysis and complex eigenvalue analysis. The analysis results showed that the maximum seismic response acceleration of the piping system decreased largely in the area surrounded by pipe elbows including the elastic-plastic support which allowed plastic deformation. The modal damping coefficient increased a maximum of about sevenfold. Furthermore, the amount of the initial stiffness of the elastic-plastic support made a difference in the increasing tendency of the modal damping coefficient. From the viewpoint of the support model in the inelastic seismic design, the reduction behavior for the seismic response of the piping system was little affected by the 10% variation of the secondary stiffness. These results demonstrated the elastic-plastic support is a useful inelastic seismic design of piping systems on the conditions where the design seismic load is exceeded extremely.