Failure modes for piping elbows under beyond design basis seismic loads

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

Haikan Gijutsu, 68(2), p.1 - 7, 2026/02

no abstracts in English

Vibration tests for failure mode analysis of piping system toward Natech risk assessment

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

Proceedings of the ASME 2025 Pressure Vessels & Piping Conference (PVP2025) (Internet), 10 Pages, 2025/07

Natech stands for Natural Hazard Triggered Technological Accidents. The assessment of Natech and the implementation of appropriate measures have been highlighted by the accidents at the Fukushima Daiichi Nuclear Power Plant (NPP), and the gas tank fire caused by the earthquake in Japan. However, the data related to the structural failure with the system function is not sufficient to carry out the assessment of Natech in industrial plants, not only at NPPs. Therefore, the authors have investigated piping failure modes under seismic input to refer to the relationship between piping failure modes and assurance of piping function. Moreover, the authors have already performed the elbow and tee loading tests, the shaking table tests on a simple piping system to observe the referred failure modes of small-bore carbon steel piping. As a result, the authors have shown two of the referred modes are an elbow collapse and the axial crack growth of an elbow. In addition, it observed bifurcating into collapse mode and low cycle fatigue mode due to the relation between the dead load and input acceleration level. Consequently, to observe the failure modes under more realistic configurations, the authors fabricated a three-dimensional pipe specimen with multiple elbows and performed vibration tests using the vibration table in this study. The test specimen was designed to observe an elbow collapse or the axial crack growth on an elbow and under shaking table test. From the above, this paper reports the overview of this study and the results of the vibration tests. Especially, it shows the observed two different failure modes, axial plus circumferential crack and not just an elbow collapse but the overall fall including deformation of multiple elements under the shaking table tests.

Proposal of a nonlinear spring model on piping support structures for an elastoplastic response analysis method

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

Journal of Pressure Vessel Technology, 146(6), p.061301_1 - 061301_12, 2024/12

https://doi.org/10.1115/1.4066278

Effects on a bending pipe behaviour via simple pre-loading for considering functional limitations of piping in industrial facilities

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

Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 8 Pages, 2024/11

https://doi.org/10.1115/ICONE31-133764

Benchmark analysis on pipe support structures for establishing inelastic seismic design

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

Proceedings of the ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 9 Pages, 2024/07

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), 11(2), p.23-00405_1 - 23-00405_12, 2024/04

https://doi.org/10.1299/mej.23-00405

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.

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 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.

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

https://doi.org/10.60316/jcossar.10.0_143

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.

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

https://doi.org/10.1299/mej.22-00370

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.

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.