Investigation on Failure Behavior of Two-Elbow Piping System Models Made of the Simulation Material Under Excessive Seismic Loads

2020 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Failure Modes ◽  
Shaking Table ◽  
System Model ◽  
Failure Behavior ◽  
Piping System ◽  
Seismic Loads ◽  
Sinusoidal Wave ◽  
Additional Mass ◽  
System Models ◽  
Piping Systems

Abstract To investigate the failure behavior of piping systems under excessive seismic loads, shaking table tests on piping system models made of a simulation material have been executed. The simulation material adopted in the experiment was lead-antimony (Pb-Sb) alloy. The piping system model was composed of two elbows made of Pb-Sb alloy, one additional mass, and two fixed anchors. Input motions were sinusoidal wave. The failure modes of the piping system were examined by varying the additional mass and frequency of the input sinusoidal wave. Through the excitation tests, the failure mode which was named as “ratchet and subsequent collapse” was obtained successfully. The result which was classified as “no failure after 500 cycles” was also obtained. It was found that the occurrence of the failure depended on the ratio of the input frequency to the specimen’s natural frequency, and the ratio of additional mass weight to the limit mass weight. Though the effect of higher modes on the failure behavior was necessary to be more investigated, it seemed that the tendency of dominant failure behavior was similar to that of the single-elbow specimen investigated in the previous study. Moreover, it was confirmed that the experimental approach to use a simulation material was applicable for piping system model with multiple elbows.

Discussion On Failure Behavior of Piping Systems Under Extremely Large Seismic Loads in BDBE

2021 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Static Loading ◽  
Failure Modes ◽  
Shaking Table ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Shaking Table Tests ◽  
Additional Mass ◽  
Pure Lead ◽  
Piping Systems ◽  
Loading Tests

Abstract To investigate the failure behavior of piping systems under severe seismic loads considering beyond design basis event (BDBE), an experimental approach to use pipes made of simulation materials was applied. "Simulation material" means the substitute material for steel to realize the structural experiment by the existing testing facilities. The simulation materials adopted in this study were pure lead (Pb) or lead-antimony (Pb-Sb) alloy. Using pipe elbows made of simulation materials, static loading tests on elbows and shaking table tests on simple piping system models composed of one or two elbows and an additional mass were conducted. From the static loading tests, the load-deflection relationship of an elbow under monotonic loading was obtained as well as the fatigue failure modes under cyclic loading depending on the several cyclic displacement levels. From the shaking table tests, several failure modes were obtained, namely, "Collapse by self-weight", "Collapse by a few cycles of input", "Ratchet and subsequent collapse", "Overall deformation", and "No failure". It was considered that the occurrence of these failure modes was affected by the ratio of the input frequency to the specimen's natural frequency, the ratio of additional mass weight to the limit mass weight, the configuration of the specimen, and the input acceleration level. The experimental results indicated that it was crucial to understand the structure's ultimate behavior when treating BDBE, and that the research approach using simulation material is effective to investigate the ultimate behavior of piping systems.

Experimental studies of a typical sprinkler piping system in hospitals

2016 ◽  
Vol 49 (1) ◽  
pp. 1-12
Author(s):  
Zhen-Yu Lin ◽  
Fan-Ru Lin ◽  
Juin-Fu Chai ◽  
Kuo-Chun Chang
Keyword(s):  
Failure Modes ◽  
Experimental Studies ◽  
Hysteresis Loops ◽  
Research Programme ◽  
Shaking Table ◽  
Piping System ◽  
Improvement Strategy ◽  
Flexible Pipes ◽  
Piping Systems ◽  
Cyclic Loading Tests

Based on the issue of life safety and immediate needs of emergency medical services provided by hospitals after strong earthquakes, this paper aims to introduce a research programme on assessment and improvement strategies for a typical configuration of sprinkler piping systems in hospitals. The study involved component tests and subsystem tests. Cyclic loading tests were conducted to investigate the inelastic behaviour of components including concrete anchorages, screwed fittings of small-bore pipes and couplings. Parts of a horizontal piping system of a seismic damaged sprinkler piping system were tested using shaking table tests. Furthermore, horizontal piping subsystems with seismic resistant devices such as braces, flexible pipes and couplings were also tested. The test results showed that the main cause of damage was the poor capacity of a screwed fitting of the small-bore tee branch. The optimum improvement strategy to achieve a higher nonstructural performance level for the horizontal piping subsystem is to strengthen the main pipe with braces and decrease moment demands on the tee branch by the use of flexible pipes. The hysteresis loops and failure modes of components were further discussed and will be used to conduct numerical analysis of sprinkler piping systems in future studies.

Effect of Local Wall Thinning on the Dynamic Behavior of Piping Systems

2005 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Dynamic Behavior ◽  
Failure Behavior ◽  
Piping System ◽  
Test Model ◽  
System Models ◽  
Wall Thinning ◽  
Piping Systems ◽  
Out Of Plane ◽  
Plane Bending ◽  
Local Wall Thinning

In order to investigate the influence of degradation on dynamic behavior and the failure mode of piping systems with local wall thinning, shake table tests using 3-D piping system models were conducted. The degradation considered in this study was wall thinning, which would be caused in piping systems due to the effects of aging. The degradation condition induced in the piping system model was 50% full circumferential wall thinning at an elbow. The test model was designed to cause out-of-plane bending moment to the thinned-wall elbow by excitation tests. The model without wall thinning was also used in the excitation test to compare the behavior of the piping system models. These models were excited under same input acceleration until fatigue cracks penetrated or an excessive deformation occurred to the models. Through these tests, the vibration characteristic and the process to failure of degraded piping models were obtained for the out-of-plane bending model. This paper describes the dynamic response and failure behavior of piping systems with wall thinning based on the test results.

Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2015 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Safety Management ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Energy Agency ◽  
Piping Systems ◽  
Input Acceleration

After the accident at Fukushima Dai-ichi Nuclear Power Plant in the 2011 Great East Japan Earthquake, the International Atomic Energy Agency (IAEA) requires to consider the design extension conditions (DEC) for the safety management of nuclear power plants (NPPs). In considering DEC, it is necessary to clarify the possible failure modes of the structures and their mechanism under the extreme loadings. Because piping systems are one of the representative components of NPP, and there is a possibility to failure at seismic events, the authors conducted an experimental investigation on failure modes and their mechanisms of piping systems under excessive seismic loads. The experiments are categorized into the fundamental plate tests and pipe component tests. In this paper, the results of the pipe component tests would be described. In the pipe component tests, the authors used piping specimens constituted with one steel elbow and a weight. Though the input acceleration level was much over the allowable level to prevent collapse failure by the seismic design, the failure mode obtained by the excitation tests were mainly the fatigue failure. The reduction of the dominant frequency and the increase of the hysteresis damping were clearly observed in the high-level input acceleration due to the plastic deformation, and they affected the specimens’ vibration response greatly.

Research Plan and Progress to Realize Fracture Control of Nuclear Components

2019 ◽  
Author(s):  
Naoto Kasahara ◽  
Takashi Wakai ◽  
Izumi Nakamura ◽  
Takuya Sato
Keyword(s):  
Plastic Deformation ◽  
High Temperature ◽  
Large Scale ◽  
Failure Modes ◽  
Failure Behavior ◽  
Piping System ◽  
Piping Systems ◽  
Research Plan ◽  
Fracture Control ◽  
Accident Consequence

Abstract For safety improvement after Fukushima daiichi nuclear power plant accident, mitigation of accident consequence for Beyond Design Basis Events (BDBE) has become important. Authors propose application of fracture control concept for mitigation of accident consequence of nuclear plants as follows. In the case of reactor vessels under high temperature and pressure conditions, small cracks from local failure will release internal pressure and can avoid a large scale ductile fracture of general portions. For piping under excessive earthquake, repeated elastic-plastic deformation and ratchet deformation dissipate vibration energy and reduce input energy from floor. They can prevent collapse of piping systems or break of pipe wall. Strength of pipe supports can be designed lower than pipe itself. Controlling the failure of supports would lead to plastic deformation without the break. The ratio of the frequency of seismic loading to the natural frequency of the piping system would also affect the failure behavior of piping systems. This paper describes research plan and progress to realize fracture control of nuclear components. The first step is clarification of actual failure modes and their mechanisms. Next step is development of relative strength evaluation method among failure modes. The third step is proposals of failure control methods. One of example is a vessel under high pressure and high temperature loadings. Another example is pipe under excessive earthquake.

Introduction of a Research Activity on the Seismic Safety Evaluation of Nuclear Piping Systems Taking the Effect of Elastic-Plastic Behavior Into Account

2015 ◽  
Author(s):  
Izumi Nakamura ◽  
Masaki Shiratori ◽  
Akihito Otani ◽  
Masaki Morishita ◽  
Tadahiro Shibutani ◽  
...  
Keyword(s):  
Seismic Load ◽  
Failure Behavior ◽  
Plastic Behavior ◽  
Piping System ◽  
Seismic Loads ◽  
Research Activity ◽  
Standard Analysis ◽  
Seismic Safety ◽  
Elastic Plastic ◽  
Piping Systems

According to investigations of several nuclear power plants (NPPs) hit by actual seismic events and a number of experimental researches on the failure behavior of piping systems under seismic loads, it is recognized that piping systems used in NPPs include a large seismic safety margin until boundary failure and the current code design allowable stresses are very conservative. Since the stress assessment based on the elastic analysis does not reflect actual response of piping systems including plastic region, rational procedures to estimate the elastic-plastic behavior of piping systems under a large seismic load are expected to be developed for piping seismic design applications. With the aim of establishing a procedure that takes into account the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, a research activity has been planned. Through the activity, the authors intend to establish two kinds of guidelines; 1) a guideline of a standard analysis procedure to evaluate elastic-plastic behavior of piping systems under extreme seismic loads with rational and conservative margins, and 2) a guideline that provide criteria for the seismic safety assessment of piping systems by the standard analysis to evaluate elastic-plastic behavior established by the above guideline. As the first step of making out the analysis guideline, benchmark analyses are conducted for a pipe element test and a piping system test. In this paper, the outline of the research activity and the preliminary results of benchmark analyses for a pipe element test are described.

Experimental Study on Seismic Behavior of a Typical Sprinkler Piping System in Hospitals

2014 ◽  
Author(s):  
Fan-Ru Lin ◽  
Kuo-Chun Chang ◽  
Juin-Fu Chai ◽  
Zhen-Yu Lin ◽  
Wen-I Liao ◽  
...  
Keyword(s):  
Failure Modes ◽  
Hysteresis Loops ◽  
Shear Capacity ◽  
Shaking Table ◽  
Piping System ◽  
Inelastic Behavior ◽  
Improvement Strategy ◽  
Flexible Pipes ◽  
Piping Systems ◽  
Cyclic Loading Tests

Based on the immediate needs of emergency medical services provided by hospitals after strong earthquakes, this paper is to introduce a research program on assessment and improvement strategies for typical configuration of sprinkler piping systems in hospitals. The study involved component tests and subsystem tests. Cyclic loading tests were conducted to investigate inelastic behavior of components including concrete anchorage, screwed fittings of small bore piping and mechanical couplings. Parts of horizontal piping systems of the aforementioned seismic damaged sprinkler piping system were tested using shaking table tests. Furthermore, the horizontal piping subsystems with seismic resistant devices such as braces, flexible pipes and mechanical couplings were tested. The test results show that the main cause of the damaged case is the poor shear capacity of the screwed fitting of the small-bore tee branch. The optimum improvement strategy to achieve higher nonstructural performance level for the horizontal piping subsystem is to strengthen the main pipe with braces and to decrease shear demands on the tee branch by flexible pipes. The hysteresis loops and failure modes of components were further discussed and will be used to conduct numerical analysis of sprinkler piping systems in future studies.

Investigation of the Seismic Safety Capacity of Aged Piping System: Shake Table Test on Piping Systems With Wall Thinning by E-Defense

2011 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Yuji Sato ◽  
Hajime Takada ◽  
Koji Takahashi ◽  
...  
Keyword(s):  
System Model ◽  
Seismic Load ◽  
Piping System ◽  
Shake Table ◽  
Shake Table Tests ◽  
Seismic Safety ◽  
System Models ◽  
Primary Stress ◽  
Wall Thinning ◽  
Piping Systems

In order to investigate the seismic safety capacity of the piping system with local wall thinning, shake table tests on 3-D piping system models were conducted using E-Defense. Two piping system models which were the same in appearance and different in degradation condition were arranged on the shake table of E-Defense. One of the models was put into degradation condition of about 50% wall thinning at four elbows and one tee. Modified seismic motions were applied to these models at the same time. As a result, the piping system model with wall thinning did not fail for the primary stress limit level of sound piping system model, though a ratchet deformation was observed on the thinned wall tee. The model with wall thinning finally failed at the thinned wall tee by over five times larger excitation than the limit level. From the experiment, it was found that the life of the piping system with wall thinning would be reduced compared with that of the piping system without wall thinning, but it was also found that the degraded piping system still had a certain seismic margin until the piping system failed by the seismic load.

Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Failure Modes ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Experimental Stress ◽  
Safe Management ◽  
Piping Systems ◽  
Input Acceleration ◽  
High Level

The accident at the Fukushima Dai-ichi Nuclear Power Plant (NPP) resulting from the 2011 Great East Japan Earthquake raised awareness as to the importance of considering Beyond Design Basis Events (BDBE) when planning for safe management of NPPs. In considering BDBE, it is necessary to clarify the possible failure modes of structures under extreme loading. Because piping systems are one of the representative components of NPPs, an experimental investigation was conducted on the failure of a pipe assembly under simulated excessive seismic loads. The failure mode obtained by excitation tests was mainly fatigue failure. The reduction of the dominant frequency and the increase of hysteresis damping were clearly observed in high-level input acceleration due to plastic deformation, and they greatly affected the specimens’ vibration response. Based on the experimental results, a procedure is proposed for calculating experimental stress intensities based on excitation test so that they can be compared with design limitations.

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