Research on Streamlining Seismic Safety Evaluation of Underground Reinforced Concrete Duct-Type Structures in Nuclear Power Stations - Part-1. Scope, Objectives and Major Results of the Research

Content Provider	Semantic Scholar
Author	Aoyagi, Yukio Kanazu, Tsutomu Endoh, Tatsumi Okaichi, Akihiro
Copyright Year	2001
Abstract	In Japan an extensive review has been made on the earthquake safety evaluation of civil engineering structures since the Great Kobe Earthquake occurred in January 1995. Also, underground important reinforced concrete structures in nuclear power plants are critically scrutinized in line with the streamlining the seismic design. Electric power industry has been jointly conducting research project on this specific type of nuclear power related RC structures since 1987, dividing the research into two phases, the first from 1987 through 1991 and the second from 1997 through 2001. The paper introduces the historical background and the achievements of the research and the concept of seismic safety assessment guideline to be concluded within 2001. The paper serves as an introductory briefing on the series of papers, which follows as Part-2 through Part-6. INTRODUCTION Despite the world trend of diminishing nuclear energy, in Asia, especially in East Asian countries including Japan, Korea and China, nuclear power development is still gaining momentum in the supply of electric power. In those earthquake prone countries, availability of convincing seismic design for nuclear plants is of prime importance in gaining public acceptance. On the other hand, streamlining the earthquake resistant design is another crucial factor to keep the nuclear energy competitive with other energy sources. This series of papers deals with the research on interactive dynamic behaviors of soil and embedded reinforced concrete (RC) duct-type structures with a view to streamlining the seismic design and structural safety evaluation of such structures. The research has been supported and participated by all the major electric power companies in Japan since 1987. BACKGROUND OF THE RESEARCH In Japan the first design specification of RC structural members based on limit states was officially announced in October 1986 by JSCE (Japan Society of Civil Engineers), which allowed us to apply limit states concept in place of allowable design utilized up to that time. The new limit states design, which basically consisted of partial safety factors, was considered to be effective also in rationalizing and economizing the design of nuclear power plant related RC structures. To materialize the design method applicable to what we call civil engineering RC structures in nuclear power stations, a working study committee was organized, being participated by professors and design engineers specializing in this field. The research started as a common project across the electric power industry in Japan as early as 1987. The committee is headed by Prof. Okamura, then Professor of Civil Engineering at University of Tokyo. After five years' strenuous experimental as well as analytical works, in September 1992 a safety assessment guide" Safety Evaluation Manual for Earthquake Resistant Design of Important Civil Engineering Structures in Nuclear Power Plants"[ 1 ] was published. The target structures were RC underground ducts for accommodation of emergency cooling water pipes, intake water pits, emergency cooling water channels etc, (Fig.1). The basic philosophy of seismic design was that two levels of design earthquakes (S 1 and $2) were considered in the safety check-up, in which the structural ultimate capacity of the section checked shall be satisfied against $2, while the section shall remain within elastic limit or the stress in steel shall not exceed yield stress against S 1. The economical advantage of applying this limit states design was that we could reduce the section depth and in some cases the area of reinforcement by taking into account the reduction in section stiffness caused by cracking and/or yielding in steel. In the meantime in January 1995 Great Kobe Earthquake occurred leaving devastating damages and claiming thousands of human lives. But what shocked us most was the collapse of center pillars in a metro station in Kobe (Fig.-2). We had to face the fact that possibility of collapse in underground RC hollow structures could not be ruled out. The opening eyes event motivated us to restart the second phase of the research in line with the review and revision of earthquake resistant design of civil engineering structures attempted as an urgent task by JSCE. The focal point of the second phase was clarification of dynamic interactive behaviors of soil and RC structures embedded. Also, the development of analytical method achieved during the past ten years should also be incorporated. Large scale laminar shear box tests were conducted in this phase, which are discussed in the papers to be followed in the series. In the framework of JSCE, concept of seismic design has been shifting from that of limit states design to that of performance based design. The structural safety performance must be checked in the light of two or three levels of design earthquakes maintaining the functions demanded depending on importance of the structure. The second phase of our research, which will be completed in March 2002, aims at drafting a seismic safety assessment guideline for important underground RC structures in nuclear power plants, considering the performances required during their expected life spans.
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