• Computational Structural Engineering
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• v.3 no.3
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• pp.53-54
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• 1990

응력 변형율의 관계가 시간에 대한 미분의 형태로 나타나는 비선형 탄소성 혹은 점탄소성 재질을 갖는 구조물이나 지만의 거동 문제를 유한요소법 등의 방법을 이용하여 해결하려고 하는 경우 주어진 외력에 의한 새로운 응력이나 응력 강화 현상을 표현하는 여러 재료 상수값들을 구하기 위해서는 적분을 요하게 되며 일반적으로 수치해석적 방법에 의해 수행된다. 이러한 수치해석적 적분방법은 보다 정확한 결과를 얻기 위하여 알고리즘 자체의 정확성과 안정성이 요구된다. 정확성은 수치해석적 적분방법이 적용될 수 있는 step size에 관계없이 거의 동일한 결과치를 얻을 수 있느냐 하는 것을 말하고 안정성은 큰 step size에서도 수렴된 결과치를 얻을 수 있느냐 하는 것을 의미한다. 그 뿐만 아니라 비교적 복잡하고도 그 대상영역이 큰 문제를 해석하고자 할 때는 수렴속도 또한 빠른 해석방법이 바람직하게 된다. 따라서 본 기사에서는 여러가지 가능한 수치해석 적분 방법을 소개하고 그들의 장단점을 논하고자 한다.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.143-148
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• 2003

This paper provides two types of engineering J estimation equations for cylinders with finite internal axial surface cracks under internal pressure. The first type is the so-called GE/EPRI type J estimation equation based on Ramberg-Osgood materials. Based on detailed 3-D FE results the GE/EPRI-type J estimation equation along the crack front is proposed and validated for Ramberg-Osgood materials. For more general application, the developed GE/EPRI-type solutions are then re-formulated based on the reference stress concept. The proposed reference stress based J estimation equation has good agreement between the FE results and the proposed reference stress based J estimation provides confidence in the use of the proposed method for elastic-plastic fracture mechanics of pressurised piping

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2001.11a
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• pp.169-174
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• 2001

원자력발전소 배관계통에 존재하는 균열을 해석하는 방법으로, 이제까지는 균열을 고려하지 않은 상태에서 지진하중을 고려한 탄성 배관해석을 수행하여, 배관에 작용하는 하중을 구한 후, 다음 단계에서 파괴해석 방법으로 균열을 가정한 탄소성 균열해석을 수행하는 2단계의 해석을 통해 균열안정성을 평가해 왔다. 이러한 방법은 전체 배관의 거동과 배관 내에 존재하는 균열의 거동을 서로 독립적인 것으로 고려하고 있으며 재료물성치로는 설계값을 사용하는 등의 보수적인 가정들을 포함하고 있어 배관에 작용하는 하중 또는 응력을 과도하게 계산하는 결과를 초래하고 있다 특히, 지진하중과 같은 반복적인 외부 동적하중이 작용하는 경우, 배관에 국부적인 소성변형이 발생함에도 이를 단지 탄성거동으로 간주하게 되는 것이다. 이러한 몇몇 보수적 가정들을 포함하고 있는 기존의 해석방법은 지나친 보수성을 가질 뿐만 아니라, 균열에 의한 실제 배관의 파단하중과 계산에 의한 파단하중의 비교로서 배관의 안전여유도를 예측하는 방법으로는 적절하지 못하다.(중략)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.1
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• pp.1-14
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• 1999

선형탄성이론을 기초로 한 구조해석의 경우 사용하중상태에서의 변형과 응력은 만족할 만한 결과를 나타내지만, 항복후의 처짐과 파괴시의 극한하중 산정의 정확한 해석이 불가능하다. 평판의 극한해석시, 상한계 이론을 바탕으로 한 항복선 이론이 널리 사용되고 있으나 이론적으로 평판의 강도를 과대평가하게 된다. 그러므로, 임의의 하중조건과 경계조건에 대한 비선형 거동과 극한내하력을 산정할 수 있는 해석기법이 필요하다. 평판의 정확한 극한하중을 위해 p-Version 유한요소법을 제안하며, p-Version의 해석치를 범용 구조해석 프로그램인 ADINA의 결과와 문헌의 이론치와 비교하였다.

• Journal of the KSME
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• v.31 no.4
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• pp.380-388
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• 1991

고에너지 속도 가공법 중에서 주요한 것을 발췌하여 그 개요와 금후의 전개에 대하여 기술하 였다. 폭발압착과 같이 실제로 활용되고 있는 기술로부터, 폭약 또는 전자기력에 의한 분말압축 성형과 같은 개발도상의 기술까지 고에너지 속도가공법의 범주에 속하는 기술분야는 광범위하다. 관용의 가공법에 비하면 역사도 짧고, 실용화에 있어서 해결하여야 할 문제도 많이 남아있다. 현재 실용화를 위한 연구도 착실히 성과를 얻고 있으며, 고에너지 속도 가공법의 앞날은 밝다고 할 수 있다. 고에너지 속도가공의 진보와 발전을 위하여는 가공기술에 관한 연구와 함께, 재료가 고속변형을 받을 때의 거동과 특성에 관한 연구를 함께 진행할 필요가 있다. 여기서는 후자의 연구에 관하여 언급하지 않았으나, 고속재료 시험법과 그 평가법, 소성도 전파 해석, 계측법 등 많은 연구 성과가 매년 보고되고 있다.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.6
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• pp.1-12
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• 2008

As internal and external seismic experiment results, the seismic performance of RC bridge piers is largely dependent on the ratio of lap-spliced bars to all longitudinal reinforcing bars in plastic hinge regions, and confining effects of transverse reinforcements. Capacity and displacement ductility of non-seismically designed existing RC piers are reduced by lap splices in plastic hinge regions. The provision for the lap splice of longitudinal reinforcing bars was not specified in KBDS (Korean Bridge Design Specifications) before the implementation of 1992 seismic design code, but the ratio of lap-spliced bars to all longitudinal reinforcing bars in plastic hinge regions is restricted to 50% in the 2005 version of KBDS. This paper presents a seismic assessment of RC piers at lap-splicing ratios of 0%, 50%, and 100%. Through a comparison of experimental and analytic results of RC piers, we introduce an appropriate ultimate strain of confined concrete in plastic hinge regions with lap-splices, and propose a method for estimating displacement ductility ratios of non-seismically designed existing RC piers using fiber element analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.53-59
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• 2016

Ultrasonic nonlinear evaluation is generally utilized for detection of not only defects but also microdamage such as corrosion and plastic deformation. Nonlinearity is determined by the amplitude ratio of primary wave second harmonic wave, and the results of its comparison are used for evaluation. Owing to the experimental features, the experimental nonlinearity result contains system nonlinearity and material nonlinearity. System nonlinearity is that which is unwanted by the user; hence, it acts as an error and interrupts analysis. In this study, a bulk wave mixing technique is implemented in order to minimize the system nonlinearity and obtain the reliable analysis results. The biggest advantage of this technique is that experimental nonlinearity contains less system nonlinearity than that for the conventional nonlinear ultrasonic technique. Theoretical and experimental verifications are performed in this study. By comparing the results of the bulk wave mixing technique with those of the conventional technique, the strengths, weaknesses, and application validity of the bulk wave mixing technique are determined.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.529-535
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• 2011

In this study, evaluation of acoustic emission signals characteristics for the post weld heat treated (PWHT) multi-pass weldment and weldment was dealt. Charpy standard specimens were taken from the lowest, middle and highest regions of the weld block. Pre-crack was made using the repeated load. Four point bend and AE tests were conducted simultaneously. Regardless of the specimens, AE signals were absent within elastic region and produced in the process of plastic deformation. AE signals for all specimens were not emitted after the maximum load. Value of signal strength for the all PWHT specimens was lower than that of the weldment. Besides, relations of plastic deformation zone size and accumulated AE counts for the PWHT specimens were more simple compared with the weldment. In case of the PWHT specimen, particles on the fractured surface decreased prominently compared with the weldment due.to PWHT. From these results, it can be concluded that PWHT was effective in reducing the AE sources for the weldment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.81-92
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• 2013

The ultimate flexural strength of HSB I-girders, considering the effect of local bucking, was investigated through a series of nonlinear finite element analysis. The girders were selected such that the inelastic local flange buckling or the plastic yielding of compression flanges governs the flexural strength. Both homogeneous sections fabricated from HSB600 or HSB800 steel and hybrid sections with HSB800 flanges and SM570-TMC web were considered. In the FE analysis, the flanges and web were modeled using thin shell elements and initial imperfections and residual stresses were imposed on the FE model. An elasto-plastic strain hardening material was used for steels. After establishing the validity of present FE analysis by comparing FE results with test results published in the literature, the effects of initial imperfection and residual stress on the inelastic flange local buckling behavior were assessed. The ultimate flexural strengths of 60 I-girders with various compression flange slenderness were obtained by FE analysis and compared with those calculated from the KHBDC, AASHTO LRFD and Eurocode 3 provisions. Based on the comparison, the applicability of design equations in these specifications for the flexural strength of I-girder considering flange local buckling was evaluated.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.687-694
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• 2014

This study established a displacement ductility ratio model for ductile design for the boundary element of shear walls. To determine the curvature distribution along the member length and displacement at the free end of the member, the distributions of strains and internal forces along the shear wall section depth were idealized based on the Bernoulli's principle, strain compatibility condition, and equilibrium condition of forces. The confinement effect at the boundary element, provided by transverse reinforcement, was calculated using the stress-strain relationship of confined concrete proposed by Razvi and Saatcioglu. The curvatures corresponding to the initial yielding moment and 80% of the ultimate state after the peak strength were then conversed into displacement values based on the concept of equivalent hinge length. The derived displacement ductility ratio model was simplified by the regression approach using the comprehensive analytical data obtained from the parametric study. The proposed model is in good agreement with test results, indicating that the mean and standard deviation of the ratios between predictions and experiments are 1.05 and 0.19, respectively. Overall, the proposed model is expected to be available for determining the transverse reinforcement ratio at the boundary element for a targeted displacement ductility ratio.