• Journal of the Korean GEO-environmental Society
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• v.13 no.1
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• pp.21-29
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• 2012

Ground failure by liquefaction can occur not only during shaking but also as the result of the post-liquefaction process after an earthquake. During the process of ground deformation and failure, excess pore water pressure in soil is redistributed, which can then lead to changes in the effective stress of soils. Therefore, in order to provide a further understanding of the phenomenon, we have to estimate the properties of effective stress during the recompression process in post-liquefaction as well, not only the total amount of pore water drained. The primary objectives of this study are to determine and compare the recompression properties in the post-liquefaction process in terms of the relationship between volumetric strains and mean effective stresses under the various conditions of relative density and shear stress history. In all experimental cases, the volumetric strains increase greatly in the low effective stress level, almost to the zero zone, and granite soil, which has fine grains, undergoes gradual changes in the relationship between volumetric strains and mean effective stresses compared with fine sand. And, we can also find that recompression properties in the post-liquefaction process by cyclic loading depend highly on the dissipation energy and maximum shear strain, and this fact can be obtained in all cases regardless of the existence of fine content, relative density, and loading history. Especially, granite soil having fine grains can be defined uniformly in the relationship between dissipation energy and maximum volumetric strain, while fine sand cannot be so uniformly defined.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.5 s.39
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• pp.55-64
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• 2004

In this paper, the preliminary design procedure of magnetorheological (MR) dampers is developed for controlling the building response induced by seismic excitation. The dynamic characteristics and control effects of the modeling methods of MR dampers such as Bingham, biviscous, hysteretic biviscous, simple Bouc?Wen, Bouc?Wen with mass element, and phenomenological models are investigated. Of these models, hysteretic biviscous model which is simple and capable describing the hysteretic characteristics, is used for numerical studies. The capacity of MR damper is determined as a portion of not the building weight but the lateral restoring force. A method is proposed for optimal placement and number of MR dampers, and its effectiveness is verified by comparing it with the simplified sequential search algorithm. Numerical results indicate that the capacity, number and the placement can be reasonably determined using the proposed design procedure.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.360-363
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• 2000

Deformation in the hysteresis loop of $Pb(Zr,Ti)O_3$ (PZT) thin films with various Zr/Ti ratios has been studied by varying the top electrode preparation method and the annealing temperature. Pt/PZT/Pt capacitors was found to be positively poled due to dc plasma potential generated during reactive ion etch (RIE) of Rt. Internal field is formed by space charges trapped at domain boundaries. Aging phenomenon such as constriction in the middle of the hysteresis loop was observed in the PZT film with top electrode deposited by sputtering. Top electrode annealing restores the hysteresis loop by removing the space charges. As Zr/Ti ratio decrease, voltage shift increases and an-nealing temperature at which internal field disappears also increases.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.87-87
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• 1999

본 연구에서는 Pulsed Laser Deposition(이하 PDL)방법을 이용하여 Si기판에 (Ba,Sr)TiO3(이하 BST)박막을 MFS-FET(Metal-Ferroelectric-Semiconductor Field-effect Transistor)구조로 제조하였으며 BST박막의 강유전성이 BST 박막에 유도되는 응력에 어떤 영향을 받는지 살펴보았다. 본 연구에서는 완충막을 사용함으로써 BST박막과 완충막간의 격자부정합을 이용하여 BST박막에 강유전성을 유도하려고 하였다. 또한 MFS-FET구조의 BST박막에 유도되는 응력조절을 위하여 BST박막과 완충막의 두께를 변화하였으며 XRD를 통한 구조 분석 및 C-V test를 통한 전기적 특성을 관찰을 하였다. PLD법을 통해서 epitaxial 성장된 BST 박막에서는 Si에 epitaxial 성장된 완충막과의 격자부정합에 의한 BST박막내의 자발분극의 발생이 예상된다. 따라서, 본 연구는 강유전체의 자발분극에 의하여 발생되는 C-V 이력현상이 BST박막과 완충막과의 격자부정합에 의한 응력에 의해 발생될 것으로 예상하여, BST 박막에 유도되는 응력과 C-V 이력현상의 관계를 통하여 상온에서 상유전성을 갖는 BST가 응력에 의하여 어느 정도의 강유전성을 나타내는지를 밝히기 위해 진행되었다. 본 연구에서 사용된 완충막은 YSZ(Yttria Stabilized Zirconia)박막으로 0.4mTorrO2 분위기 하에서 600~80$0^{\circ}C$의 온도에서 증착하여 상형성을 살펴보았고 $700^{\circ}C$에서 epitaxial 성장을 확인하였으며 두께는 30~$\AA$으로 변화하였다. 또한 BST박막은 완충막과의 전압분배를 고려해 300~2000$\AA$으로 두께를 변화를 시키며 증착하였다. MFS 구조에서 Al 전극을 사용하여 완충막과 BST박막간의 두께 변화에 따른 Capacitance - Voltage(C-V) 측정을 하였으며 이를 통하여 강유전상의 특성인 C-V 이력현상을 관찰하였다. 그 결과 YSZ 박막에서는 C-V 이력현상이 나타나지 않았으며 BST 박막에서는 약 1.2V의 C-V이력현상이 보였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.189-196
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• 2000

The objective of this paper is to propose an analysis technique to predict the behavior of PC wall structures subjected to cyclic load. While PC wall panel is idealized by finite elements, the joints at which PC walls are connected each other are idealized by nonlinear spring elements. Axial and shear spring elements are developed for simulating shear, compression and tension behaviors of joints. The strength and stiffness of each spring elements we presented from the previous research results and incorporated into the computer program of DRAIN-2DX. The proposed analysis technique is evaluated by analyzing specimens previously tested and comparing with those. On the strength, stiffness, energy dissipation and lateral drift, analytical results show good agreements with test results. This means the proposed technique is effective to predict the response of the PC wall structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.89-95
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• 2008

Until recently lots of time-history seismic analyses were performed with the earthquake motions recorded at the soft soil surface without taking into account the effects of the soft soil amplification. However, it is important to utilize the bedrock seismic motions for the rational seismic analyses of a structure considering the site soil conditions. In this study, 26 bedrock earthquake records were selected from publicly available 1557 seismic records provided by the Pacific Earthquake Engineering Research Center (PEER) for the study, and the characteristics of them were investigated. Study results showed that it is not reasonable to estimate earthquake acceleration intensity from the magnitude of an earthquake without considering the site soil conditions and it is also hard to draw any general relationships between earthquake acceleration intensity, earthquake magnitude and epicenter distance with bedrock earthquake records in the PEER database. However, 26 bedrock earthquake records selected in this study can be utilized for the time-history seismic analyses of a structure-soil system as bedrock earthquake ones, and it is also confirmed that it is necessary to take into account acceleration intensity, magnitude, epicenter distance and site conditions simultaneously for the proper use of those selected earthquake records.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.55-64
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• 2006

Shallow failures of slopes in weathered soils are caused by infiltration caused by prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in suction induced by the water infiltration. In this paper, hysteresis on soil-water characteristic curve (SWCC) of granite and gneiss weathered soils is investigated using transient flow analysis respectively. Each case was subjected to artificial rainfall intensities and time duration depending on the laboratory-based drying and wetting processes. The results show that the unsaturated seepage on weathered slopes are very much affected by the initial suction of soils and unsaturated permeability of the soils. In addition, a granite weathered soil has a lower air-entry value, residual matric suction, and wetting front suction and less hysteresis loop than a gneiss weathered soil.

• Food Science and Preservation
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• v.30 no.3
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• pp.459-471
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• 2023

The Bayesian network (BN) model was applied to analyze the characteristic variables that affect compliance with safety inspections of farmed eel during the production stage, using the data from 30,063 cases of eel aquafarm safety inspection in the Integrated Food Safety Information Network (IFSIN) from 2012 to 2021. The dataset for establishing the BN model included 77 non-conforming cases. Relevant HACCP data, geographic information about the aquafarms, and environmental data were collected and mapped to the IFSIN data to derive explanatory variables for nonconformity. Aquafarm HACCP certification, detection history of harmful substances during the last 5 y, history of nonconformity during the last 5 y, and the suitability of the aquatic environment as determined by the levels of total coliform bacteria and total organic carbon were selected as the explanatory variables. The highest achievable eel aquafarm noncompliance rate by manipulating the derived explanatory variables was 24.5%, which was 94 times higher than the overall farmed eel noncompliance rate reported in IFSIN between 2017 and 2021. The established BN model was validated using the IFSIN eel aquafarm inspection results conducted between January and August 2022. The noncompliance rate in the validation set was 0.22% (15 nonconformances out of 6,785 cases). The precision of BN model prediction was 0.1579, which was 71.4 times higher than the non-compliance rate of the validation set.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.55-66
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• 2012

To investigate the hysteresis of the suction stress in unsaturated weathered mudstone soils (CL), matric suction and volumetric water content were measured in both drying and wetting processes using Automated Soil-Water Characteristics Curve Apparatus. The drying and wetting processes in unsaturated soils were reproduced in the test; the drying process means to load matric suction to spill pore water from the soils, and the wetting process means to unload matric suction to inject pore water into the soils. Based on the measured result, Soil Water Characteristic Curve(SWCC)s were estimated by van Genuchten model (1980). SWCCs have nonlinear relationship between effective degree of saturation and matric suction. The hysteresis in SWCCs between drying and wetting processes occurred. As a result of estimating Suction Stress Characteristic Curve(SSCC) using Lu and Likos model (2006), the suction stress rapidly increased in the low level of matric suction and then increased slightly. Also, the hysteresis in SSCCs between drying and wetting processes occurred. In order to design geo-structures and check its stability considering unsaturated soil mechanics, therefore, it is more reasonable that the SSCC of drying process should be applied in the condition of rainfall infiltration and the SSCC of wetting process in the condition of evaporation or drainage.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.101-112
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• 2002

In this study, a new methodology fur the assessment of liquefaction potential is proposed and characteristics of the proposed methodology are verified. The experimental parameter of this methodology, that is, the plastic shear strain trajectory, is compared with the dissipated energy. It is shown that this parameter can express the liquefaction behavior which is generated by excess pore water pressure. This methodology takes advantage of the shear strain time history determined from the site response analysis based on the real time history of earthquake. In this site response analysis, shock type and vibration type records of similar predominant frequency are inputted. The liquefaction safely factors based on the proposed methodology and Korean detailed assessment related to the classical method are calculated from the results of the site response analysis and laboratory dynamic tests. Through this study, it is found that the proposed methodology can not only simulate the liquefaction behavior of saturated soils hut also express the seismic characteristics reasonably : leading type, predominant frequency, maximum acceleration, duration time.