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Journal Articles

Method for detecting optimal seismic intensity index utilized for ground motion generation in seismic PRA

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Ugata, Takeshi*; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*

Transactions of 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08

For the purpose of improving the precision of probabilistic seismic PRA for NPPs, the authors developed the methodology for generating hazard-consistent ground motions based on stochastic fault models which include seismic-source uncertainties by Monte Carlo Simulation. The PRA with HCGMs would require a lot of computer power. The optimization of ground-motions generations is one of the most important subjects for practical application of the PRA method. For optimizing the ground-motions generations, seismic sources for the generations should be selected effectively, and this can be conducted by utilizing optimal seismic index in the hazard analysis. In this study, the method for detecting the optimal seismic intensity index which corresponds with damage probabilities of the target equipment system was developed, and the validity of the proposed method was confirmed for some equipment systems, which has different weak equipment with each other.

Journal Articles

Hazard-consistent ground motions generated with a stochastic fault-rupture model

Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Uchiyama, Yasuo*; Yamamoto, Yu*; Muramatsu, Ken*; Takada, Tsuyoshi*

Nuclear Engineering and Design, 295, p.875 - 886, 2015/12

 Times Cited Count:2 Percentile:17.75(Nuclear Science & Technology)

Most probabilistic risk assessments (PRA) of structures involve the use of probabilistic schemes such as the scheme using probabilistic seismic hazard and fragility curves. Even when earthquake ground motions are required in Monte Carlo Simulations (MCS), they are generated to fit the specified response spectra, such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with corresponding seismic source characteristics. In this paper, the authors propose a methodology based on MCS to reproduce a set of input ground motions to develop an advanced PRA scheme that can explain the exceedance probability and sequence of functional loss in a nuclear power plant. These generated motions are consistent with the seismic hazard for the target site and their seismic source characteristics can be recognized in detail.

Journal Articles

Seismic response analysis of reactor building and equipment using a 3D-FE model for reliability enhancement of seismic risk assessment of NPP

Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Muramatsu, Ken; Takada, Tsuyoshi*

Dai-8-Kai Kozobutsu No Anzensei, Shinraisei Ni Kansuru Kokunai Shimpojiumu (JCOSSAR 2015) Koen Rombunshu (CD-ROM), p.108 - 113, 2015/10

Research and development on next-generation seismic probabilistic risk assessment by using 3D vibration simulators is ongoing to evaluate the seismic safety performance of nuclear plants with high reliability. Most structural PRA uses probabilistic schemes such as the scheme that uses probabilistic seismic hazard and fragility curves. Even when earthquake ground motions are required in Monte Carlo Simulations (MCS), they are generated to fit the specified response spectra, such as uniform hazard spectra at a specified exceedance probability. However, these ground motions are not directly linked with their corresponding seismic source characteristics. In this context, the authors propose a methodology based on MCS to reproduce a set of input ground motions to develop an advanced PRA scheme. This paper describes the methodology to reproduce a set of input ground motions briefly and the analytical results of a nuclear plant building and equipment using the set of input ground motions.

Journal Articles

Study on building function loss evaluated by hazard-consistent ground motions

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

Dai-8-Kai Kozobutsu No Anzensei, Shinraisei Ni Kansuru Kokunai Shimpojiumu (JCOSSAR 2015) Koen Rombunshu (CD-ROM), p.535 - 541, 2015/10

In this study, building function loss induced by hazard-consistent ground motions (HCGMs), which are consistent with seismic hazard of the reference site and are associated with seismic source characteristics, was evaluated in order to confirm the influence by the variance and/or inter-period correlation of response spectra of ground motions on the resulted damage probabilities of equipment system. Firstly, the statistics values of the response spectra of HCGMs were evaluated, and 3 cases of simulated ground-motions sets are generated so that they fit to the median response spectra of HCGMs. The authors conducted structural response analysis with these ground motions set, and calculated annual damage frequency of equipment system. As a result, it was found that the variance of response spectra was more important factor on damage probability evaluation of systems than inter-period correlation.

Journal Articles

Seismic damage probability by ground motions consistent with seismic hazard

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Uchiyama, Yasuo*; Yamamoto, Yu*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

Transactions of 23rd International Conference on Structural Mechanics in Reactor Technology (SMiRT-23) (USB Flash Drive), 10 Pages, 2015/08

In the preceding study, the methodology to generate ground-motion time histories for advanced PRA of NPPs was proposed by Nishida et al.. They are consistent with seismic hazard at reference site, and incorporate uncertainties of seismic-source characteristics. The ground motions utilized in conventional PRA are generated to fit to specified spectra such as UHS, and they are often generated without considering the variation of spectra. Even if it is considered, their inter-period correlations are generally assumed to be 1.0. In this paper, the authors prepared some cases of ground-motions sets. Ground motions are generated to fit to the response spectra calculated from hazard-consistent ground motions. While the target response spectra have the same median for all case, they have different variation and inter-period correlation. The response analyses of general RC structure and PWR building are conducted and the damage frequencies of simplified equipment system are compared.

Journal Articles

Structural response by ground motions from sources with stochastic characteristics

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 10 Pages, 2015/05

In the preceding study, the ground-motion time histories consistent with seismic hazard were generated by Nishida et al.. In this study, structural response analyses of general RC structure are conducted with the 2,736 waves of ground motions which were generated from one seismic source, minami-kanto earthquakes. These ground motions incorporate the differences of their seismic-source characteristics. The multi-regression analyses are also conducted with the results of response analysis. As a result, the seismic moment, stress drop and Q-value coefficient showed clear positive correlation with seismic intensities and maximum structural responses. This can be expressed by the relationship between the Fourier spectra of seismic source and seismic-source characteristics. On the other hand, asperity location showed negative correlation with seismic intensities and maximum structural responses. The trend can be expressed by the relationship of location between reference site and faults.

Journal Articles

Characteristics of simulated ground motions consistent with seismic hazard

Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Uchiyama, Yasuo*; Yamamoto, Yu*; Muramatsu, Ken*; Takada, Tsuyoshi*

Transactions of 22nd International Conference on Structural Mechanics in Reactor Technology (SMiRT-22) (CD-ROM), 10 Pages, 2013/08

Most probabilistic risk assessments (PRA) of structures involve the use of probabilistic schemes such as the scheme using probabilistic seismic hazard and fragility curves. Even when earthquake ground motions are required in Monte Carlo Simulations (MCS), they are generated to fit the specified response spectra, such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with corresponding seismic source characteristics. In this context, the authors propose a methodology based on MCS to reproduce a set of input ground motions to develop an advanced PRA scheme that can explain the exceedance probability and sequence of functional loss in a nuclear power plant. These generated motions are consistent with the seismic hazard for the target site and their seismic source characteristics can be recognized in detail.

Oral presentation

Ground motion generation method for advanced seismic hazard analysis

Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Muramatsu, Ken; Takada, Tsuyoshi*

no journal, , 

In a probabilistic safety assessment of structures, probabilistic schemes are applied in general, e.g. probabilistic seismic hazard and fragility curves. Even in cases where earthquake ground motions are used in the Monte Carlo Simulation, ground motions are generated so that they fit to the specified response spectra such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with each seismic source characteristics. In this context, the authors propose a methodology to generate a set of ground motions that can fit to the seismic hazard to take into consideration of source characteristic difference for developing an advanced PSA scheme based on MCS.

Oral presentation

Reproductions of ground motions consistent with seismic hazard, 1; The Outline of the method for ground motions reproduction

Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Muramatsu, Ken*; Takada, Tsuyoshi*

no journal, , 

Most probabilistic risk assessments (PRA) of structures involve the use of probabilistic schemes such as the scheme using probabilistic seismic hazard and fragility curves. Even when earthquake ground motions are required in Monte Carlo Simulations (MCS), they are generated to fit the specified response spectra, such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with corresponding seismic source characteristics. In this context, the authors propose a methodology based on MCS to reproduce a set of input ground motions to develop an advanced PRA scheme that can explain the exceedance probability and sequence of functional loss in a nuclear power plant. In this report, the outline of the methodology to reproduce a set of input ground motions is shown.

Oral presentation

Reproductions of ground motions consistent with seismic hazard, 2; The Characteristics of reproduced ground motions

Igarashi, Sayaka*; Nishida, Akemi; Sakamoto, Shigehiro*; Muramatsu, Ken*; Takada, Tsuyoshi*

no journal, , 

Most probabilistic risk assessments (PRA) of structures involve the use of probabilistic schemes such as the scheme using probabilistic seismic hazard and fragility curves. Even when earthquake ground motions are required in Monte Carlo Simulations (MCS), they are generated to fit the specified response spectra, such as uniform hazard spectra at a specified exceedance probability. These ground motions, however, are not directly linked with corresponding seismic source characteristics. In this context, the authors propose a methodology based on MCS to reproduce a set of input ground motions to develop an advanced PRA scheme that can explain the exceedance probability and sequence of functional loss in a nuclear power plant. In this report, the analytical results of seismic source characteristics of 200 ground motions consistent with seismic hazard are shown.

Oral presentation

Seismic response analysis of structural analysis applying ground motions consistent with seismic hazard

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*

no journal, , 

In this R&D, the authors proposed a methodology based on Monte Carlo Simulations (MCS) to reproduce a set of input ground motions to develop an advanced PRA scheme that can explain the exceedance probability and sequence of functional loss in a nuclear power plant. The ground motions consistent with seismic hazard consist of 200 seismic waves whose PGAs are between 700 gal to 1100 gal on the free rock surface. In this report, the analytical results about the influence of uncertainties of ground motion characteristics to structural responses obtained by using the 200 ground motions as input are shown

Oral presentation

Seismic response analysis of structure incorporated uncertainties of seismic source characteristics

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

no journal, , 

Recently, probabilistic risk assessment, which is incorporated various uncertainties related to seismic source characteristics, structural characteristics and damage of structure or equipment, is applied as efficient method for evaluating seismic safety performance of atomic power plant facility. Authors propose next-generation PRA method, which is used a lot of ground motions reproduced by Monte Carlo Simulation. These ground motions are incorporated seismic source uncertainties and difference of seismic source region. In this paper, the relationship between seismic source characteristics and structural response are shown. Also, the most appropriate seismic intensity for evaluating fragility of structure is considered.

Oral presentation

Comparison with ground motions generated by different methods considering source uncertainties

Takada, Tsuyoshi*; Nishida, Akemi; Igarashi, Sayaka*; Sakamoto, Shigehiro*; Muramatsu, Ken*

no journal, , 

For next-generation probabilistic risk assessment for nuclear power plant, the authors proposed a methodology where hazard-consistent ground motions generated by Monte Carlo simulation were used for response analysis of NPP structure. As ground motions for next-generation PRA of nuclear facilities at Oarai, the two sets of hazard-consistent ground motions, case A and case B, were generated. The ground motions of case A consider aleatory uncertainties in microscopic source characteristics. On the other hand, the ground motions of case B consider not only aleatory uncertainties but also epistemic uncertainties in macroscopic source characteristics. In this context, the detailed characteristics of case B ground motions are shown, by comparing them with those of case A ground motions. It was found that the composition of seismic sources and the shapes of response spectra of two sets of ground motions have different tendencies each other.

Oral presentation

Dynamic analysis of structures with hazard consistent ground motions, 1; Ground motion intensity and structural fragility evaluation

Sakamoto, Shigehiro*; Igarashi, Sayaka*; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*

no journal, , 

In the preceding study, the ground motions consistent with seismic hazard, which incorporate seismic-source characteristics, were generated. In this context, the seismic intensity indices, PGA, PGV and cumulative absolute velocity (CAV), of 1600 ground motions generated from a seismic source were calculated to reveal the relationships between seismic-source characteristics and seismic intensity indices. Also, the response analysis of multi-mass system supposing a RC structure was conducted to examine which seismic intensity indices are appropriate for evaluating fragility of structure. As a result, it was found that stress drop and high-frequency cut filter, which are stochastic source characteristics, have higher correlations with PGA and PGV than those of other source characteristics. As for stress drop, high correlations were also observed with structural response. Furthermore, it was found that CAV was not appropriate as the index for evaluating fragility than PGA and PGV.

Oral presentation

Dynamic analysis of structures with hazard consistent ground motions, 2; Varieties of structural response by structural characteristics and/or ground motion characteristics

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Takada, Tsuyoshi*; Nishida, Akemi; Muramatsu, Ken*

no journal, , 

For next-generation probabilistic risk assessment of nuclear plant, the authors proposed a methodology where hazard-consistent ground motions generated by Monte Carlo simulation were used for response analysis. In the preceding study, 200 ground motions were generated in the PGA range of 700 to 1,100 cm/s$$^{2}$$. In this context, the response analysis of multi-mass system supposing a RC structure was conducted to reveal the relationship between seismic-source characteristics and seismic intensity as well as the relationship between seismic-source characteristics and structural response. It was found that stress drop and high-frequency cut filter have high correlation with peak ground acceleration. On the other hand, the stress drop has high correlation with structural response, while high-frequency cut filter has low correlation with structural response. The reason of these results was explained from the point of seismic source acceleration spectra.

Oral presentation

Seismic response evaluation of structure incorporated uncertainties of seismic source characteristics

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Takada, Tsuyoshi*; Nishida, Akemi; Muramatsu, Ken

no journal, , 

In the probabilistic risk assessment for nuclear power plant, methods based on Monte Carlo Simulation of response analyses with variously simulated ground motion time histories have been conducted. In the preceding study by Nishida et al. (2013), the ground motion time histories, which are consistent with the seismic hazard and are associated with seismic-source characteristics, were generated. In this context, the authors conducted response analyses of structures with generated ground motions from a seismic source contained seismic-source characteristics uncertainties. The response analyses were conducted for a simple multi-mass system supposing a RC structure. The relationships between seismic-source characteristics and ground-motion intensities as well as the relationships between seismic-source characteristics and structural responses were examined.

Oral presentation

Effect of seismic-source characteristics uncertainties on seismic intensity and structural response

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

no journal, , 

In the preceding study, the ground-motion time histories, which are consistent with seismic hazard and incorporate the uncertainties of seismic-source characteristics, were generated for advanced seismic PRA utilizing structural response analyses. However, the relationships between seismic-source characteristics, seismic intensities and structural responses have not been clarified. In this study, total 2,736 ground motions are generated for one seismic source of "Southern-Kanto earthquakes" where the magnitude is 7.1 and the fault distances are 45-65 km. These ground motions also incorporate the uncertainties of seismic-source characteristics. Moreover, the structural response analyses of simple RC structure are conducted with these time histories. The influence of seismic-source characteristics on the seismic intensities and structural response are examined.

Oral presentation

Building function loss evaluated with hazard consistent ground motions, 1; Correlation of structural response

Nishida, Akemi; Sakamoto, Shigehiro*; Igarashi, Sayaka*; Muramatsu, Ken; Takada, Tsuyoshi*

no journal, , 

In the preceding study, the ground-motion time histories, which are consistent with seismic hazard and incorporate the uncertainties of seismic-source characteristics, were generated for advanced seismic PRA utilizing structural response analyses. In this paper, results of structural analyses with generated ground motions, 250 ground motions with peak accelerations of 5-10 m/s$$^{2}$$, are presented. In the response spectra of ground motions on the rock surface, correlation gap range was found around the period of 0.1-0.2 s, which could be found in the input ground motions and in the structural responses. While ductility factors of the structural response were high, their influences on the correlations were not large.

Oral presentation

Building function loss evaluated with hazard consistent ground motions, 2; Influence of correlation on damage

Sakamoto, Shigehiro*; Igarashi, Sayaka*; Nishida, Akemi; Muramatsu, Ken; Takada, Tsuyoshi*

no journal, , 

This paper is intended to clarify the difference of building function loss possibilities which depend on the realization way of the variation and/or inter-period correlation in the response spectra of ground motions. The authors prepared some cases of GMs sets shown in following. The response analyses of a simple RC structure were conducted for each cases and the damage frequencies of equipment system were compared. case(n): simulated GMs which have no variation in response spectra. case(p): simulated GMs which have the same variation in response spectra with case(r), while the inter-period correlation coefficient is 1.0.. case(c): simulated GMs which the same variation with case(r) and the modeled inter-period correlation of case(r) in the response spectra. where, case(r) is the set of original ground motions.

Oral presentation

Application of an efficient evaluation method for predicting building function loss using ground motions with fault models

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Ugata, Takeshi*; Nishida, Akemi; Takada, Tsuyoshi*

no journal, , 

The authors have investigated an efficient method for generating ground motions based on fault models detecting the optimal seismic intensity index which has good correlation with the seismic risk of the building. This method is based on the examination of the errors of generated ground-motions which are ordered by the damage probabilities of the system or by their seismic intensity indices. In this study, the errors were evaluated for some cases of an equipment system which has different weak equipment components in order to validate the method. As a result, the smallest error was obtained to the expected seismic intensity index of each system, and the validity of the proposed method was confirmed. The authors also indicated the workflow to conduct the seismic risk assessment for arbitrary building utilized the ground motions based on fault models.

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