• Corrosion Science and Technology
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• v.22 no.1
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• pp.44-54
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• 2023

The rupture disk corrosion test (RDCT) method was recently developed to evaluate stress corrosion cracking (SCC) and was found to have great potential for the real-time detection of SCC initiation in a high temperature and pressure environment, simulating the primary water coolant of pressurized water reactors. However, it is difficult to directly measure the stress applied to a disk specimen, which is an essential factor in SCC initiation. In this work, finite element analysis (FEA) was performed using ABAQUS^TM to calculate the stress and deformation of a disk specimen. To determine the best mesh design for a thin disk specimen, hexahedron, hex-dominated, and tetrahedron models were used in FEA. All models revealed similar dome-shaped deformation behavior of the disk specimen. However, there was a considerable difference in stress distribution in the disk specimens. In the hex-dominated model, the applied stress was calculated to be the maximum at the dome center, whereas the stress was calculated to be the maximum at the dome edge in the hexahedron and tetrahedron models. From a comparison of the FEA results with deformation behavior and SCC location on the disk specimen after RDCT, the most proper FE model was found to be the tetrahedron model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.1-13
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• 2008

The web of a horizontally curved plate girder bridge is, in general, subject to not only longitudinal flexural in-plane stress but also out-of-plane bending stress. Therefore, the induced stresses in the fillet welded joints at the intersection of the web and flange plates in the curved plate girder bridge can be considerably high, and the welded joints of gusset plates connecting the main girder to the floor beams or sway bracings can be subject to much more severe situation than those in the ordinary straight plate girder bridge. In order to investigate the cause of fatigue crack occurred in a curved girder bridge that has been served in about 23 years, in this study, field load tests have been performed to obtain the stress characteristics at the welded joint under the real traffic flow. Using the test results, we have investigated the causes of the occurrence of various fatigue cracks and have estimated the fatigue lives for the cracks. In addition, the characteristics of structural behavior at welded joint of the curved girder bridge have been examined by comparing the FE analysis and the field test result.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.1
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• pp.47-57
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• 2024

Recently, in newly constructed apartment buildings, the exterior wall structures have been characterized by thinness, having various openings, and a significantly low reinforcement ratio. In this study, a nonlinear finite element analysis was performed to investigate the crack damage characteristics of the exterior wall structure. The limited analysis models for a 10-story exterior wall were constructed based on the prototype apartment building, and nonlinear static analysis (push-over analysis) was performed. Based on the finite element (FE) analysis model, the parametric study was conducted to investigate the effects of various design parameters on the strength and crack width of the exterior walls. As the parameters, the vertical reinforcement ratio and horizontal reinforcement ratio of the wall, as well as the uniformly distributed longitudinal reinforcement ratio and shear reinforcement ratio of the connection beam, were addressed. The analysis results showed that the strength and deformation capacity of the prototype exterior walls were limited by the failure of the connection beam prior to the flexural yielding of the walls. Thus, the increase of wall reinforcement limitedly affected the failure modes, peak strengths, and crack damages. On the other hand, when the reinforcement ratio of the connection beams was increased, the peak strength was increased due to the increase in the load-carrying capacity of the connection beams. Further, the crack damage index decreased as the reinforcement ratio of the connection beam increased. In particular, it was more effective to increase the uniformly distributed longitudinal reinforcement ratio in the connection beams to decrease the crack damage of the coupling beams, regardless of the type of the prototype exterior walls.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1698-1702
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• 2009

효과적인 저수지 수질관리를 위해서는 신뢰도 높은 수리 및 수질모델이 필요하며, 이러한 모델의 성능은 다양한 수문사상에 대하여 적용함으로써 검증할 수 있다. CE-QUAL-W2 모델(이후 W2)은 횡방향 평균 2차원 수리 수질 해석 모델로써 수체의 길이에 비해 폭이 상대적으로 좁고 수심이 깊은 우리나라 대부분의 저수지 지형에 적합한 모델이다. 본 연구의 목적은 기존 연구에서 가뭄년인 2001년과 평수년인 2004년 수문사상에 대하여 보정한 대청호 W2 부영양화모델을 최근 평수년인 2006년과 가뭄년인 2008년을 대상으로 검증하는데 있다. 모델의 검증은 물수지, 수온성층 구조 변화, 부영양화 해석에 중점을 두었으며, 실측자료와 모의결과의 적합성 비교 평가는 결정계수값$(R^2)$, AME(absolute mean error)와 RMSE(root mean square error)를 이용하였다. 저수지 물수지의 적합성을 검증하기 위하여 모의수위와 실측수위를 비교한 결과, $R^2$값이 2006년과 2008년에 각각 0.9945, 0.9972로 나타나 신뢰도가 높은 것으로 확인되었다. 계절별 성층구조 변화 모의 성능을 검증하기 위해 회남수역과 댐 앞 지점에서 수심별 수온의 모의값과 실측값을 비교하였다. 2006년의 경우 모델은 홍수기 동안 안정적으로 수온 성층현상을 모의하였으나, 댐 앞 지점에서 수온 약층이 형성된 구간에서 실측값과 다소 편차를 보였으며, 오차크기는 AME가 $0.561\sim2.088^{\circ}C$, RMSE는 $0.797\sim2.762^{\circ}C$범위였다. 반면, 가뭄년인 2008년에는 전 기간에 걸쳐 모두 안정적으로 저수지 수온 성층현상을 모의하였으며, 오차크기는 AME $0.413\sim1.162^{\circ}C$, RMSE $0.546\sim1.415^{\circ}C$ 범위였다. 조류의 생산성이 높은 표층에서 T-N, T-P 및 Chl-a 농도 모의결과를 장계교, 대정리, 회남대교, 댐 앞, 추동취수탑 및 문의취수탑에서 시계열로 실측값과 비교 검증한 결과, T-N과 T-P는 2006년과 2008년 모두 모든 비교 지점에서 모의값과 실측값의 시계열 변동이 매우 잘 일치하였으며, 홍수기 이외 기간에는 큰 변동 폭을 보이지 않았다. 그러나 기존 연구에서 확인된 바와 같이 7월 이후부터 T-P 모의값이 실측값을 과대 산정하는 경향을 보였는데, 그 원인은 산소 결핍상태에서 저니층에서 용출되는 철(Fe) 또는 망간(Mn)과 같은 이온 성분이 인과 흡착하여 침전되는 기작이 모의과정에 적절히 반영되지 않은 것이 원인으로 판단된다. 조류(Chl-a)농도의 경우, 2006년과 2008년에 모든 지점에서 모델은 조류의 발생과 시계열 변화를 적절히 모의하였으나, 2008년 1월부터 8월까지 댐 앞과 추동 및 문의취수탑에서는 모의값이 실측값을 과대 산정하는 경향을 보였다. 이는 해마다 그리고 계절별로 우점하는 조류 종이 상이한 반면, 모델에서는 이에 대한 매개변수를 적절히 고려하지 못한 것이 원인으로 판단된다.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.581-586
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• 1997

중대사고시 노심의 손상에 의한 노심용융물이 원자로 용기 하부 반구로 재배치될 때 고온의 노심용융물에 의한 열적 부하로 원자로 용기의 파손을 일으키게 된다. 원자로 용기하부 반구 내에서의 노심용융물의 열적 거동 및 하부 반구에 대한 열적 부하에 대한 분석은 용융물의 성분 및 재배치 과정의 복잡성 등으로 인한 실험적 모사의 한계성 및 현상 분석의 난이함에도 불구하고 기존 원자로의 중대사고에 대한 안전 여유도의 제고와 이에 따른 노내외 사고 관리 전략의 수립을 위하여 연구의 필요성이 제기된다. 본 연구에서는 노심용융물 냉각연구(SONATA-IV)의 예비 실험으로 노심용융물의 상사물로 $Al_2$O$_3$/Fe Thermite 용융물을 이용하여 실제 원자로 용기 하부 반구를 1/8 로 선형 축소한 반구형 실험 용기로 주입하는 실험을 수행하였다. 아울러 원자로 용기 하부 반구로 재배치된 노심용융물에 의한 열적, 기계적 부하에 대한 분석을 수행하기 개발된 유한 요소 프로그램인 CALF (Computer Analysis for Lower Head Failure ) 코드를 이용한 하부 반구의 열적 거동에 대한 해석 결과를 정리하였다. 용융물 주입 실험 결과 용융물 주입과 동시에 하부 반구에 직경 5cm 크기의 하부 반구 파손이 발생하였다. 이는 고온 용융물에 의한 제트류(Jet Impingement)의 효과로 생각된다 동일한 조건에서 CALF 코드로 하부 반구의 열적 거동을 분석하였는데, 실험과는 달리 하부 반구의 파손이 발생하지 않았다 이같은 해석 결과는 용융물의 제트류 효과가 존재하지 않는다면 고온의 용융물이 하부 반구 내로 재배치되더라도 하부 반구의 파손이 발생하지 않는다는 것을 보여준다.>$_3$ 흡착제 제조시 TiO$_2$ 함량에 따른 Co$^{2＋}$ 흡착량과 25$0^{\circ}C$의 고온에서 ZrO$_2$와 $Al_2$O$_3$의 표면에 생성된 코발트 화합물을 XPS와 EPMA로 부터 확인하였다.인을 명시적으로 설명할 수 있다. 둘째, 오류의 시발점을 정확히 포착하여 동기가 분명한 수정대책을 강구할 수 있다. 셋째, 음운 과 정의 분석 모델은 새로운 언어 학습시에 관련된 언어 상호간의 구조적 마찰을 설명해 줄 수 있다. 넷째, 불규칙적이며 종잡기 힘들고 단편적인 것으로만 보이던 중간언어도 일정한 체계 속에서 변화한다는 사실을 알 수 있다. 다섯째, 종전의 오류 분석에서는 지나치게 모국어의 영향만 강조하고 다른 요인들에 대해서는 다분히 추상적인 언급으로 끝났지만 이 분석을 통 해서 배경어, 목표어, 특히 중간규칙의 역할이 괄목할 만한 것임을 가시적으로 관찰할 수 있 다. 이와 같은 오류분석 방법은 학습자의 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minim

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.433-452
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• 2018

The shield tunneling method can minimize surface settlements by preventing the deformation of tunnel face and tunnel intrados due to tunnel excavation. For this purpose, it is very important to control the operating conditions of shield TBM. The face pressure and backfill pressure for tail void grouting should be the most important and immediate measure not only to restrain surface settlement, but also to influence the effective stress and pore water pressure around the circumstance of tunnel during excavation. The reaction of the ground to the application of face pressure and backfill pressure relies on the stiffness and permeability of ground. Especially, the reaction of saturated clayey ground formations, which shows the time-dependent deformation, is different from the permeable ground. Hence, in this paper it was investigated how the TBM operating conditions, ground stiffness, and permeability impact on the surface settlement of saturated clayey ground. For this purpose, a series of parametric studies were carried out by means of the stress-pore water pressure coupled FE analysis. The results show that the settlement of soft clayey ground is divided into the immediate settlement and consolidation settlement. Especially, the consolidation settlement depends on the ground stiffness and permeability. In addition, the existence of critical face pressure and backfill pressure was identified. The face pressure and backfill pressure above the critical value may cause an unexpected increase in the ground settlement.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.769-777
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• 2003

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Because carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of enhancing bond of CFM. Therefore if bond strength is sufficient, it will be expect to enhance reinforcement effect. Unless sufficient, expect not to enhance reinforcement effect, because of occuring bond failure between concrete and CFM. In this study, the bond strength and load-displacement response of CFM to the concrete by the direct pull-out test(the tensile-shear test method) were investigated using the experiment and the finite element method analysis with ABAQUS. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.163-172
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• 2011

The CFTA girder developed is a concrete filled steel tubular system with arched shape and external post-tensioning (PT) tendons which control the initial camber and the bending stress of the girder. In the present study the effects of the PT tendons on the dynamic behavior of the girder subjected to a moving vehicle load are numerically investigated. Various levels for the tendon quantity and the tendon forces are considered, using the existing FE model of the girder. The vehicle considered is a DB-24 truck and is modeled with two tracks-three axles. Equivalent-load pulse time histories are applied to each node to simulate the moving vehicle, depending on the time of arrival and the discretization. The vehicle speeds are varied from 40 km/hr to 100 km/hr with increment of 20 km/hr. The analysis results show that the tendon forces do not produce any influences on the dynamic responses of the girder. However the dymamic deflection of the girder increases when a smaller amount of tendons is used. The Dynamic Amplification Factors (DAF) are evaluated based on the static and dynamic responses. Much lower values of the DAF are obtained, even no tendons applied, than those provided by the design criteria of the AASHTO LRFD and the Korea Highway Standard Specification.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.445-453
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• 2007

The purposes of this study lie on understanding characteristic water-rock interaction mechanisms of groundwater in the Geochang, Hapcheon, and Changryeong areas and establishing correlation between geological factors and groundwater chemistry by statistical tools. Based on the statistical results from the relationship between rock types and groundwater chemistry, fluorine is correlated with Fe and Al in the diorite area, whereas it is correlated with Cl and $NO_3-N$ in the andesite area. Hardness, total solids, and $SO_4$ show that they are closely related to each other in all rock types, especially with highest relationship in sedimentary rocks. Although it is generally acknowledged that TDS increases with depths of aquifer due to the long term water-rock interaction, no remarkable relationship between well depth and water chemistry is found in this study. It appears that hydrogeological system in the study area may be complex or the path of water-rock interaction is inconsistent with well depth.

• Journal of the Korean Geotechnical Society
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• v.33 no.10
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• pp.33-47
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• 2017

A self-supported temporary excavation method called IER is normally applicable to excavation depth ranging from 6.0 m to 7.0 m though the method depends on ground condition and overburden load. Combining IER with another method is required in deeper excavation depth in order to maintain the structural stability of the IER. In this study, we performed model tests and 3D FE analysis to check the stability of the IER adopting soil nailing method, and to propose its effective installation method. The lateral displacement of the IER using soil nailing decreased by 92% of that of IER without soil nailing. Optimum design is possible for both economic feasibility and stability when interval spacing and length of soil nails is $1.5m(S_h){\times}0.75m(S_v)$ and 86% of excavation depth, respectively. Excavation depth using IER increases 1.71 times by adopting soil nailing in increment of lateral displacement of IER right before the last excavation stage.