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Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Ito, Masaharu; Li, Y.
Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 9 Pages, 2024/08
Most studies conducted till now on local damage of reinforced concrete (RC) slab structures subjected to missile 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 effect of the stiffness of the supports for oblique impact on the reaction forces of RC slab. Until now, static loading tests were conducted to confirm the stiffnesses of the supporting parts that supported the RC specimen during oblique impact tests. Based on the obtained load-displacement relationships, and so on, the stiffnesses of the supporting parts are estimated.
Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 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.
Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 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.
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.
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.
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.
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.
Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 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.
Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 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.
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.
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.
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.
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.
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.
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.
Kang, Z.; Nishida, Akemi; Okuda, Yukihiko; Tsubota, Haruji; Li, Y.
Mechanical Engineering Journal (Internet), 7(3), p.19-00566_1 - 19-00566_20, 2020/06
Most impact research has been presented on the basis of impact tests and numerical analysis performed by rigid projectile impact perpendicular to the target structure. On the other hand, there are only few reports on impacts at an oblique angle. To evaluate more realistic conditions regarding issues related to oblique impacts to reinforced concrete (RC) structures, we have proposed an analytical method to estimate the local damage to RC structures by an oblique impact and have validated the evaluation approach by comparison with experimental results. At present, we have finalized simulation analyses of oblique impact assessments on RC panels using rigid/soft projectiles with a flat nose shape utilizing the validated approach. Furthermore, in this study, we focus on impacts caused by rigid/soft projectiles with a hemispherical nose shape. The same analytical method is applied to simulate the structural damage caused by an RC panel due to a rigid/soft projectile with a hemispherical nose shape. Results on the penetration depth of the RC structure and the energy-contribution ratio are presented. By comparing the results of local damage to an RC structure caused by projectiles with flat and hemispherical nose shapes, the influence of the nose shape of the projectile on local damage of the RC panel has been investigated.
Nishida, Akemi; Kang, Z.; Nagai, Minoru*; Tsubota, Haruji; Li, Y.
Nuclear Engineering and Design, 350, p.116 - 127, 2019/08
Times Cited Count:8 Percentile:65.31(Nuclear Science & Technology)Many empirical formulas have been proposed for evaluating local damage to reinforced concrete structures caused by impacts of rigid missiles. Most of these formulas have been derived based on tests involving impact normal to target structures. Thus far, few tests with oblique impact onto target structures have been carried out. As a final goal of this research, we aim to propose a new formula for evaluating the local damage caused by oblique impact based on previous experimental and simulation results. In this study, we perform simulation analyses for evaluating the local damage to reinforced concrete panels subjected to oblique impacts with various angle by soft missiles under various impact velocities using a simulation method that was validated using the results of previous impact experiments. In this paper, the investigated results and obtained knowledges from them are shown.
Kang, Z.; Nagai, Minoru*; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08
Many empirical formulae have been proposed for evaluating the local damage to reinforced concrete (RC) structures caused by rigid projectile impact. The majority of these formulae aim at impact tests perpendicular to target structures, while few impact tests oblique to the target structure 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 past experimental and simulation results. Up to now, we validated the analytical method by comparison with the experimental results and conduct the simulation analysis of impact assessment on RC panel by rigid/soft projectile with flat nose shape using the validated approach. In the part 1 of this paper, the same analytical method is used to simulate the local damage to RC panels caused by oblique impact of rigid/soft projectile with hemispherical nose shape. The results associated with penetration depth of RC structure, energy contribution ratio, etc. are presented.
Kang, Z.; Nagai, Minoru*; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 9 Pages, 2019/05
Many empirical formulae have been proposed for evaluating the local damage to reinforced concrete (RC) structures caused by rigid projectile impact. The majority of these formulae aim at impact tests perpendicular to target structures, while few impact tests oblique to the target structure 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 past experimental and simulation results. The finite element code LS-DYNA R7.1.2 is used to perform the numerical analysis by adopting Lagrangian finite elements and explicit time integration. So far, we validated the analytical method by comparison with the experimental results and conduct the simulation analysis of impact assessment on RC panel by rigid/soft projectile with flat nose shape using the validated approach. Results of reduction coefficient with respect to rigid/soft projectile and impact angle were obtained. Therefore, in this study, we focus on the impact problems caused by rigid projectile with hemispherical nose shape. The same analytical method is used to simulate the local damage to RC panels caused by oblique impact of rigid projectile with hemispherical nose shape. The results associated with penetration depth of RC structure, energy contribution ratio, etc. are presented. According to the comparison analysis of results of local damage to RC structure by rigid projectiles with flat and hemispherical nose shape, the influence of different nose shapes of rigid projectile on the local damage of RC panels caused by oblique impact is investigated.
Nagai, Minoru*; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05
In this study, the final purpose is to propose a new formula for evaluating the local damage caused by oblique impact based on past experimental results and previous research achievements. Up to now, we validated the analytical method by comparison with the experimental results and conducted simulation analysis associated with impact assessment on RC panel by soft/rigid projectile with flat nose shape using the validated approach. In the part 1 of this study, the same procedure of our previous work is followed to investigate the local damage to RC panel caused by rigid projectile with flat and hemispherical nose shape. In the part 2, we focus on the comparison analysis of simulation results of local damage to RC panel subjected to oblique impact by soft missile with flat and hemispherical nose shape. The structural damage of RC panel and projectiles, energy contribution ratio, etc. is studied for each case. The results indicate the difference of nose shape of projectile is of great importance to influence the penetration depth generated by oblique impact of soft projectile.