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Journal Articles

Numerical analyses on perforation damage using test results of reinforced concrete panel subjected to oblique impact

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Transactions of 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

Most studies conducted till now on local damage of reinforced concrete (RC) slab structures subjected to projectile impact are about normal impact, while few research related to oblique impact can be found. The objective of this study is to carry out impact tests under different impact conditions including oblique impacts, to confirm the different impact behaviors of the RC slab structure, to develop an analysis method by investigating the test results and analytical conditions, and to validate the analysis method through comparison with the test results. This study focuses on the scabbing damage which is one of the local damage modes of RC slab. Based on oblique impact test results due to soft projectile with hemispherical nose shape, we investigate the relationship between the criterion related to the concrete fracture and the occurrence of scabbing damage.

Journal Articles

Damage status definition of piping system in industrial plants for mitigation of natech risk due to closure on elbows

Takito, Kiyotaka; Okuda, Yukihiko; Nakamura, Izumi*; Furuya, Osamu*

Transactions of 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

no abstracts in English

Journal Articles

Validation of numerical analyses on scabbing of reinforced concrete panels subjected to projectile impact

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Transactions of 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

The outer walls of nuclear facility buildings consist of reinforced concrete (RC) panels. When a projectile collides with a nuclear facility building, local damages such as penetration, scabbing, and perforation can occur in the RC panels. Numerical simulation using finite element analysis (FEA) is generally employed to assess these damage conditions. However, the impact analysis by FEA modelled with continuum elements is difficult to address phenomena such as scattering fragments of concrete because the elements deletion method for large deformation is used to prevent interruption of numerical calculations. Recently, a numerical method known as Smooth Particles Hydrodynamics (SPH), one of the particle methods, has been employed to address discontinuous phenomena. In this paper, we focus on the scabbing damages to RC panels and report on the findings obtained through the validation of the numerical analysis using the SPH method.

Journal Articles

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure

Okuda, Yukihiko; Takito, Kiyotaka; Nishida, Akemi; Li, Y.

Mechanical Engineering Journal (Internet), 12 Pages, 2024/00

After the Great East Japan earthquake and the accident at the TEPCO's Fukushima Daiichi Nuclear Power Stations in March 2011, the regulation for nuclear power plants (NPPs) has been enhanced to take countermeasures against beyond-design-basis events. To improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion, the importance of seismic probabilistic risk assessment (PRA) has drawn much attention. It is essential to evaluate the realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA. In particular, since piping systems have plant-specific complex route geometries, it is known that the arrangement and stiffness of piping support structures have a significant impact on seismic response characteristics of the entire piping system. To construct a realistic seismic response analysis method for excessive input ground motion exceeding the elastic response, it is desired to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems including pipe support structures. In this study, the applicability of the method is confirmed by the simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. Moreover, based on the good correlation between the ductility factor and the damage status obtained from the test results and simulation analysis results, it is shown that the ductility factor is effective as a damage evaluation index for piping support structures.

Journal Articles

Upgrade of seismic design procedure for piping systems based on elastic-plastic response analysis

Nakamura, Izumi*; Otani, Akihito*; Okuda, Yukihiko; Watakabe, Tomoyoshi; Takito, Kiyotaka; Okuda, Takahiro; Shimazu, Ryuya*; Sakai, Michiya*; Shibutani, Tadahiro*; Shiratori, Masaki*

Dai-10-Kai Kozobutsu No Anzensei, Shinraisei Ni Kansuru Kokunai Shimpojiumu (JCOSSAR2023) Koen Rombunshu (Internet), p.143 - 149, 2023/10

In 2019, the JSME Code Case for seismic design of nuclear power plant piping systems was published. The Code Case provides the strain-based fatigue criteria and detailed inelastic response analysis procedure as an alternative design rule to the current seismic design, which is based on the stress evaluation by elastic response analysis. In 2022, it was approved to revise the Code Case with improving the cycle counting method for fatigue evaluation to the Rain flow method. In addition, the discussion to incorporate the elastic-plastic behavior of support structures is now in progress for the next revision of the Code Case. This paper discusses the contents and background of the 2022 revision, the progress of the next revision, and future tasks.

Journal Articles

Development of seismic response analysis method of piping system; Proposal of the nonlinear spring model for piping support structures

Takito, Kiyotaka; Okuda, Yukihiko; Nishida, Akemi; Li, Y.

Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 10 Pages, 2023/07

In probabilistic risk assessment against earthquakes (seismic PRA) for nuclear power plants, the development of a realistic response analysis method for the fragility assessment of piping systems considering input seismic motions exceeding design assumptions is one of the important issues. Usually, piping systems exhibit complex three-dimensional shapes. The arrangement and stiffness of the piping support structures significantly affect the response characteristics of the entire piping system. Therefore, it is necessary to develop a realistic response analysis method of piping systems including piping support structures. In this study, a method for modeling the elasto-plastic hysteresis characteristics of piping support structures is developed to establish a seismic response analysis method of piping systems including piping support structures. First, we formulate an elatsto-plastic spring model that can express the elasto-plastic hysteresis characteristics of a piping support structure. Subsequently, we perform a simulation analysis for the loading test of a piping support structure using this model. As the analysis results and test results were in good agreement, we confirmed the effectiveness of the formulation of the model. The main contents, such as the formulation of the elasto-plastic spring model, the simulation analysis of the loading test, and the comparison between the analysis results and the test results, and the results of this study are reported in this paper.

Journal Articles

Experimental study on scabbing limit of local damage to reinforced concrete panels subjected to oblique impact by projectile with semispherical nose

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Mechanical Engineering Journal (Internet), 10(3), p.22-00370_1 - 22-00370_12, 2023/06

Many experimental studies have been reported on the impact resistance of reinforced concrete (RC) structures. However, most formulas were derived from impact tests based on normal impact to target structures using rigid projectiles that do not deform during impact. Therefore, this study develops a local damage evaluation method considering the rigidity of projectiles and oblique impacts that should be considered in realistic projectile impact phenomena. Specifically, we focused on scabbing, defined as the peeling off the back face of the target opposite the impact face, and conducted impact tests on RC panels to clarify the scabbing limit by changing the impact velocity in an oblique impact. The effects of the projectile rigidity and oblique impact on the scabbing limit were investigated based on the test results. This work presents the test conditions, equipment, results, and the scabbing limit on the local damage to RC panels subjected to oblique impacts.

Journal Articles

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure

Okuda, Yukihiko; Takito, Kiyotaka; Nishida, Akemi; Li, Y.

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05

After the Great East Japan earthquake and the accident at the TEPCO's Fukushima Daiichi Nuclear Power Stations in March 2011, the regulation for nuclear power plants (NPPs) has been enhanced to take countermeasures against beyond-design-basis events. To improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion, the importance of seismic probabilistic risk assessment (PRA) has drawn much attention. It is essential to evaluate the realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA. In particular, since piping systems have plant-specific complex route geometries, it is known that the arrangement and stiffness of piping support structures have a significant impact on seismic response characteristics of the entire piping system. In contrast, the current seismic design procedure adopts an evaluation method assuming an elastic response. To construct a realistic seismic response analysis method for excessive input ground motion exceeding the elastic response, it is desired to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems including pipe support structures. In this study, the applicability of the method is confirmed by the simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. Moreover, based on the good correlation between the ductility factor and the damage status obtained from the test results and simulation analysis results, it is shown that the ductility factor is effective as a damage evaluation index for piping support structures.

Journal Articles

Investigation on local damage of reinforced concrete panel impacted by hemispherical soft projectile

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05

Most studies conducted till now on local damage of reinforced concrete (RC) slab structures subjected to projectile impact are about normal impact, while few research related to oblique impact can be found. The objective of this study is to carry out impact tests under different impact conditions including oblique impacts, to confirm the different impact behaviors of the RC slab structure, to develop an analysis method by investigating the test results and analytical conditions, and to validate the analysis method through comparison with the test results. This study focuses on the scabbing damage which is one of the local damage modes of RC slab. Based on oblique impact test results due to soft projectile with hemispherical nose shape, we investigate the relationship between the criterion related to the concrete fracture and the occurrence of scabbing damage.

Journal Articles

Experimental study on local damage to reinforced concrete panels subjected to oblique impact by projectiles

Okuda, Yukihiko; Nishida, Akemi; Kang, Z.; Tsubota, Haruji; Li, Y.

Journal of Nuclear Engineering and Radiation Science, 9(2), p.021801_1 - 021801_12, 2023/04

Most empirical formulas were proposed to evaluate the local damage to reinforced concrete (RC) structures based on impact tests conducted with a rigid projectile at an impact angle normal to the target structure. Only a few impact tests were performed involving a soft projectile. Therefore, in this study, we conducted a series of impact tests to evaluate the local damage to RC panels subjected to normal and oblique impacts by rigid and soft projectiles. This paper presents the test conditions, test equipment, test results, and obtained knowledge on local damage to RC panels subjected to normal and oblique impacts.

Journal Articles

Local damage to reinforced concrete panels subjected to oblique impact by projectiles; Numerical analysis on test results

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 9 Pages, 2022/08

Most of the empirical formulas that have been proposed seeking to quantitatively investigate local damage to reinforced concrete (RC) structures caused by a rigid projectile impact. These formulas have been derived based on impact tests performed normal to the target structure, while only a few impact tests involving soft projectile to the target structure have been studied. The purpose of this study is to develop a local damage evaluation method that takes into account the oblique impact due to soft projectile, which should be considered in realistic impact conditions. In this paper, we compare the test results with the analytical results to examine and validate the parameter setting of analytical method for evaluating local damage in RC panel. The obtained knowledge is presented.

Journal Articles

Experimental study on local damage to reinforced concrete panels subjected to oblique impact by projectiles; Analysis of experimental results

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Transactions of 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 8 Pages, 2022/07

So far, studies on local damage to reinforced concrete (RC) panels subjected to projectile impact have mainly focused on collisions that occur at an angle normal to the structure, while research on oblique impact is scarce. In this research, we conducted a series of impact tests to confirm validity of the analytical method based on the investigation on local damage behavior of RC panel due to projectile impact under various impact conditions covering impact angles, projectile types (rigid and soft) and RC panel's thickness. In part 2, we concentrate on the investigation to the penetration damage and scabbing damage of RC panels subjected to normal and oblique impact by rigid and soft projectiles. Based on the analysis of experimental results, the obtained knowledge will be presented.

Journal Articles

Study on influence evaluation of internal equipment installed in structure subjected to projectile impact

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Transactions of 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 10 Pages, 2022/07

When a projectile collides with a nuclear building, stress waves are generated at the impacted area and propagate to the interior of the building through the building structure. Assessing the influence of dynamic responses generated by the projectile impact on internal equipment is important, because stress waves are likely to excite high-frequency vibrations of the internal equipment and may influence the functionality of the internal equipment. Therefore, we performed a projectile impact test on a reinforced concrete (RC) structure that models a nuclear building with internal equipment. This paper presents the results of the investigation of the impact response characteristics of the RC structure subjected to projectile impact.

Journal Articles

Analytical study on dynamic response of reinforced concrete structure with internal equipment subjected to projectile impact

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Doboku Gakkai Dai-13-Kai Kozobutsu No Shogeki Mondai Ni Kansuru Shinpojiumu Rombunshu (Internet), 8 Pages, 2022/01

In case missiles crash into reactor buildings of nuclear power plants, stress waves due to the missile impacts propagate from the impacted wall to the interior of the structure. Stress waves are likely to excite high-frequency vibrations of internal equipment in the reactor building, so it is an important issue to assess the damage against missile impact for safety related internal equipment. The OECD/NEA launched the IRIS benchmark project in order to assess the response for nuclear facility by projectile impact and the third phase of IRIS (IRIS 3) contributes to the investigation on the dynamic response of reinforced concrete (RC) structure with internal equipment. We participated in the IRIS3 and have conducted the calibration analysis for projectile impact test of the structure which models a reactor building and internal equipment. This paper presents simulation and test results from dynamic response of the RC structure with internal equipment.

Journal Articles

Experimental and analytical investigation on local damage to reinforced concrete panels subjected to projectile impact, 1; Penetration damage mode due to normal impact

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 28th International Conference on Nuclear Engineering (ICONE 28) (Internet), 10 Pages, 2021/08

Most empirical formulas have been proposed to quantitatively evaluate local damage to reinforced concrete (RC) structures caused by a rigid projectile impact. These formulas have been derived from impact tests performed to the target structure with a normal angle, while only a few impact tests involving soft projectile to the target structure have been studied. Recently, we conducted a series of impact tests to evaluate local damage to RC panels subjected to normal and oblique impact due to rigid and soft projectiles. The final goal of our study is to establish a new formula for evaluating local damage to RC structures caused by soft projectile with oblique angle based on experimental and analytical investigation. This paper summarizes the results of experimental and analytical investigation on penetration damage mode to RC panels subjected to normal projectile impact. Through the comparison between experimental and analytical results, the validity of the analytical method is confirmed.

Journal Articles

Hybrid dynamic response test focusing on the support structure of piping systems

Okuda, Yukihiko; Nishida, Akemi; Sakai, Michiya*; Shiogama, Yuzo*; Li, Y.

Proceedings of 28th International Conference on Nuclear Engineering (ICONE 28) (Internet), 6 Pages, 2021/08

To develop a more realistic seismic evaluation method of nuclear power plants, it is necessary to evaluate the seismic behavior considering the joints of each component that are treated as independent models during design evaluation, such as buildings, equipment, and piping systems. Particularly, the piping support structure, which is the joint between the building and piping, is important in the seismic evaluation of the piping system. While the current seismic evaluation of piping support structures is performed within the elastic range, it is important to consider the realistic elastic-plastic response of piping support structures for fragility assessment in seismic probabilistic risk assessment. However, the seismic evaluation method that considers the elastic-plastic response of piping support structures has not yet been established, and there is a need to improve seismic evaluation methods. In this study, a hybrid dynamic response test for simulating the seismic behavior of the piping support structure, including the elastic-plastic response, has been conducted. Specifically, static cyclic loading tests and hybrid dynamic response tests were conducted using four types of piping support structures to understand the basic mechanical behavior. This report presents the details of the tests and test results.

Journal Articles

Analytical study of perforation damage in reinforced concrete slabs subjected to oblique impact by projectiles with different nose shapes

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Mechanical Engineering Journal (Internet), 8(1), p.20-00331_1 - 20-00331_16, 2021/02

Considerable research has been carried out to establish a rational assessment method for nuclear power plants against local damage caused by an accidental projectile impact. Most of the empirical formulas that have been proposed seek to quantitatively investigate local damage to reinforced concrete (RC) structures caused by a rigid projectile impact. These formulas have been derived based on impact tests performed normal to the target structure, while only a few impact tests oblique to the target structure have been studied. This study aims to propose a new formula for evaluating local damage to RC structures caused by oblique impact based on experimental and simulation results. At present, we have validated an analytical method via comparison with experimental results and have conducted simulation analyses of oblique impact assessments on RC slabs using projectile with flat nose shape. In this study, the same analytical method will be used to investigate perforation damage to RC slabs subjected to oblique impact by projectiles with hemispherical nose shapes. In this paper, the effects of projectiles' nose shapes on perforation damage to RC slabs, the residual velocity of projectiles and the time history of energy transmission will be discussed.

Journal Articles

Analytical study of perforation damage to reinforced concrete slabs subjected to oblique impact by projectiles with different nose shapes

Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 7 Pages, 2020/08

Plenty of researches have been carried out to establish a rational assessment method for nuclear power plants against local damage caused by accidental projectile impact. Most of the empirical formulas have been proposed for quantitatively investigating the local damage to reinforced concrete (RC) structures caused by rigid projectile impact. These formulas have been derived on the basis of impact tests performed perpendicular to the target structure, while few impact tests oblique to the target structures have been studied. The final objective of this study is to propose a new formula for evaluating the local damage to RC structures caused by oblique impact based on experimental and simulation results. At present, we have validated an analytical method via comparison with experimental results and have conducted simulation analyses of oblique impact assessments on RC slab using various projectiles with flat nose shape by this method. In this study, the same analytical method will be applied to investigate the perforation damage to RC slab subjected to oblique impact by projectiles with hemispherical nose shape. In this paper, the effects of projectile's nose shape on the local damage of RC slab, the residual velocity of projectile and the time history of energy transmission will be discussed.

Journal Articles

Analytical study on dynamic response of reinforced concrete structure with internal equipment subjected to projectile impact

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 10 Pages, 2020/08

In case of projectile impact to reactor building of nuclear power plants, stress waves due to the projectile impact propagate from the impacted wall to the interior of the structure. It is an important issue to assess the dynamic response generated with projectile impact for safety related internal equipment because stress waves are likely to excite high-frequency vibrations of internal equipment in the reactor building. The OECD (Organization for Economic Co-operation and Development) / NEA (Nuclear Energy Agency) launched the IRIS (Improving Robustness Assessment Methodologies for Structures Impacted by Projectiles) benchmark project in order to assess the dynamic response for nuclear facility by projectile impact and the third phase of IRIS (IRIS 3) contributes to the investigation on the dynamic response of reinforced concrete (RC) structure with internal equipment. We have participated in the IRIS 3 and have performed the calibration analysis for projectile impact test on the structure which models a reactor building and internal equipment. Specially, we have developed and validated a numerical approach to investigate impact response of the RC structure with internal equipment through the calibration correction. This paper presents partial simulation results from dynamic response of the RC structure with internal equipment and discusses the effect of supporting condition of the internal equipment and stress wave propagation.

Journal Articles

Local damage to reinforced concrete panels subjected to oblique impact by projectiles; Outline of impact test

Nishida, Akemi; Kang, Z.; Okuda, Yukihiko; Tsubota, Haruji; Li, Y.

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 5 Pages, 2020/08

Studies on the local damage to reinforced concrete (RC) panels subjected to projectile impact have mainly focused on collisions that occur at an angle normal to the structure; thus, research on oblique impact is scarce. Therefore, we conducted research focusing on oblique impact to enable more realistic impact assessment of projectile collisions. To date, the validity of the analytical method has been confirmed by comparing the results with those of previous tests, and the local damage of RC panels that have collided with projectiles has been analytically investigated focusing on the impact angle. Therefore, this study aims to confirm the validity of the analysis method by conducting impact tests under various conditions including the impact angle, and obtaining data for validation. This paper outlines the test for the local damage of RC panels subjected to normal and oblique impact.

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