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.

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.

Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2004 ◽  
Vol 126 (1) ◽  
pp. 85-90 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

Shaking table tests of three-dimensional piping models with degradation were conducted in order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems. The degradation condition induced in the piping models was about 50 percent full circumferential wall thinning at elbows. Four types of models were made for the shaking table tests by varying the location of wall thinning in the piping models. These models were excited under the same input acceleration until the models failed and a leak of pressurized internal water occurred. Through these tests, the change of the vibration characteristics and processes to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and the damage was concentrated on the weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2002 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Vibration Characteristic ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

In order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems, shaking table tests of 3-D piping models with degradation were conducted. The degradation condition induced in the piping models was about 50% full circumferential wall thinning at an elbow or elbows. By varying the induced parts in the piping model, 4 kinds of models were made for the shaking table tests. These models were excited under the same input acceleration until the models failed and caused leak of pressurized internal water. Through these tests, the change of the vibration characteristic and the process to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and therefore the damage concentrated to a weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Improved Model Tests to Investigate the Failure Modes of Pipes Under Beyond Design Basis Earthquakes

2018 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Failure Mode ◽  
Failure Modes ◽  
Shaking Table Test ◽  
Shaking Table ◽  
Piping System ◽  
Input Frequency ◽  
Shaking Table Tests ◽  
Pure Lead ◽  
Design Basis ◽  
Improved Model

In order to investigate the failure modes of piping systems under the beyond design basis seismic loads, the authors proposed an experimental approach to use pipes made of the simulation material instead of steel pipes in the previous study. Though the ratchet-collapse (ratchet and subsequent collapse) was successfully obtained as the failure mode through the shaking table test using the pure lead (Pb) pipes as the simulation material pipe specimens, there was concern that characteristics of pure lead was somewhat extreme considering the analogy with the stress-strain relationship of steel. In order to resolve such concern, a modified experimental procedure has been developed. In the modified procedure, lead-antimony (Pb-Sb) alloy is used as the simulation material. Through the shaking table tests on single elbow pipe specimens made of Pb-Sb alloy, it is found that the typical failure mode is the ratchet and subsequent collapse, as same as the results by the shaking table tests of the Pb pipe specimens. The results indicate that the lower input frequency than the specimen’s natural frequency is prone to cause failure to the specimen, while the higher input frequency hardly causes the failure. The tendency of the global behavior of specimens is similar each other between the Pb pipe specimens and the Pb-Sb alloy specimens, but the strength of self-weight collapse of the Pb-Sb alloy pipe specimen is much higher than that of the Pb pipe specimen. Due to such higher strength of Pb-Sb alloy pipes, a prospect to conduct an excitation test on a more complicated piping system model is obtained.

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.

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.

Trial Model Tests With Simulation Material to Obtain Failure Modes of Pipes Under Excessive Seismic Loads

2016 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Failure Mode ◽  
Failure Modes ◽  
Experimental Studies ◽  
Shaking Table ◽  
Seismic Load ◽  
Seismic Loads ◽  
Steel Pipes ◽  
Piping Systems ◽  
Collapse Failure ◽  
Input Motion

Piping systems are one of the central components of NPP; It is well known that the major failure mode under seismic loads is likely to be fatigue failure. Other failure modes, however, such as ratchet-buckling failure, have been reported to occur under particular conditions. It is necessary to clarify the conditions that cause different failure modes of piping systems under very high seismic motion, but experimental studies with steel pipes are difficult to achieve, mainly due to the limitations of testing facilities and safety concerns. In order to overcome such difficulties, we propose a new experimental approach that uses pipes made of a simulation material instead of steel. Lead (Pb) pipes were used for the simulation material, and shaking table tests were conducted on lead elbow pipe specimens. Results showed that ratchet-collapse and overall deformation of pipe specimens were possible failure modes. The ratchet-collapse failure mode appeared to be affected not only by input acceleration level but also by the direction of gravity, the primary constant stress level of its own weight, and the frequencies of the input motion. The dynamic behaviors of pipes in the high inelastic region where a nearly fully plastic section was assumed were quite different from those in the elastic region, and those of the steel pipes in previous studies. We demonstrate that the proposed test approach is effective for qualitatively clarifying various kinds of failure behaviors with large plasticity under excessive seismic load.

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.

Failure Behavior of Elbows With Local Wall Thinning Under Cyclic Load

2004 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Seismic Load ◽  
Failure Behavior ◽  
Cyclic Bending ◽  
Wall Thinning ◽  
Bending Load ◽  
Piping Systems ◽  
Out Of Plane ◽  
Effects Of Aging ◽  
Local Wall Thinning

Pressurized piping systems used in nuclear power plants are supposed to be degraded by the effects of aging. Local wall thinning is one of the defects considered to be caused in piping systems due to the effects of aging, but the failure behavior of thinned wall pipes under seismic load is still not clear. Therefore an experimental and analytical study to clarify the failure behavior of thinned wall pipes is being conducted. In this paper, the experimental results of locally thinned wall elbows under cyclic bending load are described. Displacement-controlled cyclic bending tests were conducted on elbows with local wall thinning. The test models were pressurized to 10MPa with room temperature water and were subjected to in-plane or/and out-of-plane cyclic bending load until their failures. From the tests, the failure modes of the thinned wall elbows were found to be fatigue failure at the flank of the elbow, or fatigue and buckling failure accompanied with ratchet deformation. It was also found that the life of the thinned wall elbow subjected to out-of-plane bending were extremely lower than that of the elbow without wall thinning. The failure modes and fatigue lives of elbows seemed to be affected by a ratchet phenomenon.

Sign in / Sign up

Export Citation Format

Share Document