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ShinYoung Kwag; Seunghyun Eem; Eujeong Choi; Jeong Gon Ha; Daegi Hahm. Suggestions for Enhancing Sampling-Based Approach of Seismic Probabilistic Risk Assessment. Journal of the Computational Structural Engineering Institute of Korea 2021, 34, 77 -84.
AMA StyleShinYoung Kwag, Seunghyun Eem, Eujeong Choi, Jeong Gon Ha, Daegi Hahm. Suggestions for Enhancing Sampling-Based Approach of Seismic Probabilistic Risk Assessment. Journal of the Computational Structural Engineering Institute of Korea. 2021; 34 (2):77-84.
Chicago/Turabian StyleShinYoung Kwag; Seunghyun Eem; Eujeong Choi; Jeong Gon Ha; Daegi Hahm. 2021. "Suggestions for Enhancing Sampling-Based Approach of Seismic Probabilistic Risk Assessment." Journal of the Computational Structural Engineering Institute of Korea 34, no. 2: 77-84.
The probabilistic safety assessment (PSA) of a nuclear power plant (NPP) under single and multiple hazards is one of the most important tasks for disaster risk management of nuclear facilities. To date, various approaches—including the direct quantification of the fault tree using the Monte Carlo simulation (DQFM) method—have been employed to quantify single- and multi-hazard risks to nuclear facilities. The major advantage of the DQFM method is its applicability to a partially correlated system. Other methods can represent only an independent or a fully correlated system, but DQFM can quantify the risk of partially correlated system components by the sampling process. However, as a sampling-based approach, DQFM involves computational costs which increase as the size of the system and the number of hazards increase. Therefore, to improve the computational efficiency of the conventional DQFM, a two-stage DQFM method is proposed in this paper. By assigning enough samples to each hazard point according to its contribution to the final risk, the proposed two-stage DQFM can effectively reduce computational costs for both single- and multi-hazard risk quantification. Using examples of single- and multi-hazard threats to nuclear facilities, the effectiveness of the proposed two-stage DQFM is successfully demonstrated. Especially, two-stage DQFM saves computation time of conventional DQFM up to 72% for multi-hazard example.
Eujeong Choi; ShinYoung Kwag; Jeong-Gon Ha; Daegi Hahm. Development of a Two-Stage DQFM to Improve Efficiency of Single- and Multi-Hazard Risk Quantification for Nuclear Facilities. Energies 2021, 14, 1017 .
AMA StyleEujeong Choi, ShinYoung Kwag, Jeong-Gon Ha, Daegi Hahm. Development of a Two-Stage DQFM to Improve Efficiency of Single- and Multi-Hazard Risk Quantification for Nuclear Facilities. Energies. 2021; 14 (4):1017.
Chicago/Turabian StyleEujeong Choi; ShinYoung Kwag; Jeong-Gon Ha; Daegi Hahm. 2021. "Development of a Two-Stage DQFM to Improve Efficiency of Single- and Multi-Hazard Risk Quantification for Nuclear Facilities." Energies 14, no. 4: 1017.
As part of the LEAP-UCD-2017 and the LEAP-ASIA-2019 exercises, dynamic centrifuge model tests were conducted at KAIST on a submerged 5° sloped medium-dense and dense model grounds of Ottawa F-65 sand. In this paper, the experimental procedure along with the testing results are presented. It was found that liquefaction occurred in the medium-dense model indicated by large lateral surface displacements and pore pressure buildup, while soil layers only partially liquefied in the dense models. The frequency characteristics of liquefied and partially liquefied models were observed using Fast Fourier Transform (FFT), ratio of response spectra (RRS) and time-frequency analysis of recorded accelerations. A shift in the fundamental frequency of the model grounds to lower frequencies due to softening associated with excess pore pressure buildup was seen in the FFT analysis. From the RRS, it was found that high-frequency amplification in accelerations due to soil dilatancy was similar within the liquefied zone in the medium-dense model regardless of confining pressure, while in the partially liquefied dense models, the high-frequency amplification was different according to the soil depth. Moreover, using time-frequency analysis, a shift in mean frequency of base motion (1 Hz) to lower frequencies was evident after liquefaction but not after partial liquefaction. Hence, by observing the frequency characteristics of liquefied and partially liquefied soil layers, the occurrence and depth of liquefaction can be ascertained. This provides an independent check for liquefaction in dynamic centrifuge testing using acceleration data.
Satish Manandhar; Seong-Nam Kim; Jeong-Gon Ha; Kil-Wan Ko; Moon-Gyo Lee; Dong-Soo Kim. Liquefaction evaluation using frequency characteristics of acceleration records in KAIST centrifuge tests for LEAP. Soil Dynamics and Earthquake Engineering 2020, 140, 106332 .
AMA StyleSatish Manandhar, Seong-Nam Kim, Jeong-Gon Ha, Kil-Wan Ko, Moon-Gyo Lee, Dong-Soo Kim. Liquefaction evaluation using frequency characteristics of acceleration records in KAIST centrifuge tests for LEAP. Soil Dynamics and Earthquake Engineering. 2020; 140 ():106332.
Chicago/Turabian StyleSatish Manandhar; Seong-Nam Kim; Jeong-Gon Ha; Kil-Wan Ko; Moon-Gyo Lee; Dong-Soo Kim. 2020. "Liquefaction evaluation using frequency characteristics of acceleration records in KAIST centrifuge tests for LEAP." Soil Dynamics and Earthquake Engineering 140, no. : 106332.
The effect of inertial interaction of a superstructure with the soil must be understood to evaluate soil–foundation–structure interaction (SFSI) problems. Inertial interaction causes period lengthening and damping increasing and affects the foundation behavior, rocking and swaying motions. This effect is also significant in systems that induce foundation-yielding behaviors during earthquakes, such as rocking foundation. This study evaluates the structural inertial interaction effects on the foundation behavior through an analytical calculation to obtain the natural frequencies of the foundation's rocking and swaying motions. Dynamic centrifuge tests were also conducted to evaluate the variations in natural frequencies of an SFSI system on the rocking foundation. Test results demonstrate that the natural frequency of foundation motion is close to that of structural motion as far as foundation yielding behaviors are concerned. From strong seismic data, with free-field motion as the input motion, a reasonable natural period of the structure is identified. However, the structural natural period is considered abnormal when the foundation motion is used as the input motion. This phenomenon should be considered in future SFSI studies.
Kil-Wan Ko; Jeong-Gon Ha; Dong-Soo Kim. Structural inertial interaction effects on foundation behavior. Soil Dynamics and Earthquake Engineering 2020, 136, 106238 .
AMA StyleKil-Wan Ko, Jeong-Gon Ha, Dong-Soo Kim. Structural inertial interaction effects on foundation behavior. Soil Dynamics and Earthquake Engineering. 2020; 136 ():106238.
Chicago/Turabian StyleKil-Wan Ko; Jeong-Gon Ha; Dong-Soo Kim. 2020. "Structural inertial interaction effects on foundation behavior." Soil Dynamics and Earthquake Engineering 136, no. : 106238.
A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs has focused on the load transfer mechanism, foundation and soil settlement, bearing capacity, load distribution, and bending moment of the piles. DPR piles can act to increase the bearing capacity of the ground, and DPRs can reduce settlement while securing the bearing capacity. In this study, centrifuge model tests are performed to simulate the static behavior of DPRs under actual stress conditions. The behaviors of the DPR foundation for axial load, axial load distribution among the piles, and bending moment are compared to those of the connected piled raft foundation to understand the complex behaviors of DPRs. The centrifuge test results show that DPRs help reduce the pile axial load and bending moment during vertical loading. In addition, DPRs show smaller vertical settlement than shallow foundations. Therefore, we confirm that DPRs can be applied in foundation design as settlement reducers.
Heon-Joon Park; Kil-Wan Ko; Young-Hun Song; Myung-Jun Song; Seokwoo Jin; Jeong-Gon Ha; Dong-Soo Kim. Centrifuge modeling of disconnected piled raft using vertical pushover tests. Acta Geotechnica 2020, 15, 2637 -2648.
AMA StyleHeon-Joon Park, Kil-Wan Ko, Young-Hun Song, Myung-Jun Song, Seokwoo Jin, Jeong-Gon Ha, Dong-Soo Kim. Centrifuge modeling of disconnected piled raft using vertical pushover tests. Acta Geotechnica. 2020; 15 (9):2637-2648.
Chicago/Turabian StyleHeon-Joon Park; Kil-Wan Ko; Young-Hun Song; Myung-Jun Song; Seokwoo Jin; Jeong-Gon Ha; Dong-Soo Kim. 2020. "Centrifuge modeling of disconnected piled raft using vertical pushover tests." Acta Geotechnica 15, no. 9: 2637-2648.
Probabilistic safety assessment (PSA) of nuclear facilities on external multi-hazards has become a major issue after the Fukushima accident in 2011. However, the existing external hazard PSA methodology is for single hazard events and cannot cover the impact of multi-hazards. Therefore, this study proposes a methodology for quantifying multi-hazard risks for nuclear energy plants. Specifically, we developed an efficient multi-hazard PSA methodology based on the probability distribution-based Boolean algebraic approach and sampling-based method, which are currently single-hazard PSA methodologies. The limitations of the probability distribution-based Boolean algebraic approach not being able to handle partial dependencies between the components are solved through this sampling-based method. In addition, we devised an algorithm that was more efficient than the existing algorithm for improving the limits of the current sampling-based method, as it required a significant computational time. The proposed methodology was applied from simple examples to single- and multi-hazard PSA examples of actual nuclear power plants. The results showed that the proposed methodology was verified in terms of accuracy and efficiency perspectives. Regarding the sampling-based method, it was confirmed that the proposed algorithm yielded fragility and risk results that have similar degrees of accuracy, even though it extracted a smaller number of samples than the existing algorithm.
ShinYoung Kwag; Jeong Gon Ha; Min Kyu Kim; Jung Han Kim. Development of Efficient External Multi-Hazard Risk Quantification Methodology for Nuclear Facilities. Energies 2019, 12, 3925 .
AMA StyleShinYoung Kwag, Jeong Gon Ha, Min Kyu Kim, Jung Han Kim. Development of Efficient External Multi-Hazard Risk Quantification Methodology for Nuclear Facilities. Energies. 2019; 12 (20):3925.
Chicago/Turabian StyleShinYoung Kwag; Jeong Gon Ha; Min Kyu Kim; Jung Han Kim. 2019. "Development of Efficient External Multi-Hazard Risk Quantification Methodology for Nuclear Facilities." Energies 12, no. 20: 3925.
The Gyeongju Historic Areas, which include the millennium-old capital of the Silla Kingdom, are located in the region most frequently affected by seismic events in the Korean peninsula. Despite the numerous earthquakes documented, most of the stone architectural heritage has retained their original forms. This study systematically reviews and categorises studies dealing with the seismic risk assessment of the architectural heritage of the historic areas. It applies research methodologies, such as the evaluation of the engineering characteristics of subsoil in architectural heritage sites, site-specific analysis of the ground motions in response to earthquake scenarios, geographic information system (GIS)-based seismic microzonation according to the geotechnical engineering parameters, reliability assessment of dynamic centrifuge model testing for stone masonry structures and evaluation of seismic behaviour of architectural heritage. The M 5.8 earthquake that hit Gyeongju on September 12, 2016 is analysed from an engineering point of view and the resulting damage to the stone architectural heritage is reported. The study focuses on Cheomseongdae, an astronomical observatory in Gyeongju, whose structural engineering received considerable attention since its seismic resistance was reported after the last earthquake. Dynamic centrifuge model tests applying the Gyeongju Earthquake motions are performed to prove that it is not a coincidence that Cheomseongdae, a masonry structure composed of nearly 400 stone members, survived numerous seismic events for over 1300 years. The structural characteristics of Cheomseongdae, such as the well-compacted filler materials in its lower part, rough inside wall in contrast to the smooth exterior, intersecting stone beams and interlocking headstones are proven to contribute to its overall seismic performance, demonstrating outstanding seismic design technology.
Heon-Joon Park; Jeong-Gon Ha; Se-Hyun Kim; Sang-Sun Jo. Seismic Performance of Ancient Masonry Structures in Korea Rediscovered in 2016 M 5.8 Gyeongju Earthquake. Sustainability 2019, 11, 1565 .
AMA StyleHeon-Joon Park, Jeong-Gon Ha, Se-Hyun Kim, Sang-Sun Jo. Seismic Performance of Ancient Masonry Structures in Korea Rediscovered in 2016 M 5.8 Gyeongju Earthquake. Sustainability. 2019; 11 (6):1565.
Chicago/Turabian StyleHeon-Joon Park; Jeong-Gon Ha; Se-Hyun Kim; Sang-Sun Jo. 2019. "Seismic Performance of Ancient Masonry Structures in Korea Rediscovered in 2016 M 5.8 Gyeongju Earthquake." Sustainability 11, no. 6: 1565.
This paper proposes a dynamic centrifuge model test method for the accurate simulation of the behaviours of a liquid storage tank with different types of foundations during earthquakes. The method can be used to determine the actual stress conditions of a prototype storage‐tank structure. It was used in the present study to investigate the soil‐foundation‐structure interactions of a simplified storage tank under two different earthquake motions, which were simulated using a shaking table installed in a centrifuge basket. Three different types of foundations were considered, namely, a shallow foundation, a slab on the surface of the ground connected to piles and a slab with disconnected piles. The test results were organised to compare the ground surface and foundation motions, the slab of foundation and top of structure motions and the horizontal and vertical motions of the slab, respectively. These were used to establish the complex dynamic behaviours of tank models with different foundations. The effects of soil–foundation–structure interaction with three foundation conditions and two different earthquake motions are focused and some important factors, that should be considered for future designs are also discussed in this research. Copyright © 2017 John Wiley & Sons, Ltd.
Heon-Joon Park; Jeong-Gon Ha; Sun-Yong Kwon; Moon-Gyo Lee; Dong-Soo Kim. Investigation of the dynamic behaviour of a storage tank with different foundation types focusing on the soil-foundation-structure interactions using centrifuge model tests. Earthquake Engineering & Structural Dynamics 2017, 46, 2301 -2316.
AMA StyleHeon-Joon Park, Jeong-Gon Ha, Sun-Yong Kwon, Moon-Gyo Lee, Dong-Soo Kim. Investigation of the dynamic behaviour of a storage tank with different foundation types focusing on the soil-foundation-structure interactions using centrifuge model tests. Earthquake Engineering & Structural Dynamics. 2017; 46 (14):2301-2316.
Chicago/Turabian StyleHeon-Joon Park; Jeong-Gon Ha; Sun-Yong Kwon; Moon-Gyo Lee; Dong-Soo Kim. 2017. "Investigation of the dynamic behaviour of a storage tank with different foundation types focusing on the soil-foundation-structure interactions using centrifuge model tests." Earthquake Engineering & Structural Dynamics 46, no. 14: 2301-2316.