• Nuclear Engineering and Technology
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• 제53권9호
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• pp.3112-3121
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• 2021

One of the major factors affecting the life span of a Reactor Pressure Vessel (RPV) is the Pressurised Thermal Shock (PTS). PTS is a thermo-mechanical load on the RPV wall due to steep temperature gradients and structural load created by internal pressure of the fluid within the RPV. Safe operating life of a nuclear power plant is ensured by carrying out fracture analysis of the RPV against thermal shock. Carrying out fracture tests on RPV/large scale components is not always feasible. Hence, studies on laboratory level specimens are necessary to validate and supplement the prototype results. This paper aims to study the fracture behaviour of standard Compact Tension [C(T)] specimens, made of RPV steel 20MnMoNi55, subjected to thermal shock through experimental and numerical investigations. Fracture tests have been carried out on the C(T) specimens subjected to thermal transient load and tensile load to quantify the effect of thermal shock. Crack resistance curves are obtained from the fracture tests as per ASTM E1820 and compared with those obtained numerically using XFEM and a good agreement was found. A quantitative study on the crack tip plastic zone, computed using cohesive segment approach, from the numerical analyses justified the experimental crack initiation toughness.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.455-465
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• 2008

In this study, the load distribution and deformation of rock-socketed drilled shafts subjected to axial load are investigated based on small scale model tests. In order to analyze the effects of major influencing factors of end bearing capacity, Hoek-cell triaxial tests were performed. From the test results, it was found that the initial slope of end bearing load transfer (q-w) curve was highly dependent on rock mass modulus and pile diameter, while the ultimate unit toe resistance ($q_{max}$) was influenced by rock mass modulus and the spacing of discontinuities. End bearing load transfer function of drilled shafts socketed in rock was proposed based on the Hoek-cell triaxial test results and the field loading tests which were performed on granite and gneiss in South Korea. Through the comparison with pile load tests, it is found that the load-transfer curve by the present study is in good agreement with the general trend observed by field loading tests, and thus represents a significant improvement in the prediction of load transfer of drilled shaft.

• 대한토목학회논문집
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• 제7권4호
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• pp.1-12
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• 1987

LRFD 설계형식의 개별안전계수를 확률이론에 의하여 구할 때 주로 AFOSM 방법이 이용되어 왔다. 그러나 이 방법에 의해 구한 하중 및 저항계수를 사용하면 결과적인 신뢰성지수는 목표 신뢰성지수와 다를 수 있다. 최근 Ayyub 등이 제안한 Reliability-Conditioned(RC) 방법은 목표 신뢰성지수에 부합하지만 계산의 신속성 및 일관적 체계를 유지할 수 없다. 본 연구에서 제안한 RC/AFOSM 조합방법을 이용하면 계산의 체계가 일관적이고, 다양한 설계조건에 대하여 거의 일정한 개별안전계수를 결정할 수 있으며 이로부터 결과되는 신뢰성지수도 목표 신뢰성지수에 매우 근접하다.

• 한국지반공학회논문집
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• 제31권10호
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• pp.5-16
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• 2015

본 연구에서는 국가건설기준이 한계상태설계법으로 전환됨에 따라 현재 연구기반이 미약한 쏘일네일링의 LRFD 설계법 개발의 일환으로 인발저항에 대한 저항편향계수를 분석하였다. 쏘일네일링의 설계 및 시공 기술수준 등 지역적 특성을 반영하기 위하여 국내 비탈면과 굴착공사에서 수행된 인발시험 자료를 수집하고, 지반특성, 쏘일네일의 제원, 인발시험 결과 등으로 구성된 데이터베이스를 구축하였다. 쏘일네일링의 인발저항에 대한 저항계수를 보정하기 위하여 국내에서 가장 많이 이용되며 비교적 자료수가 충분한 중력식과 가압식 그라우팅공법의 인발저항에 대한 저항편향계수를 산정하였다. 저항편향계수는 1.144~1.325으로 실제 극한인발저항력을 비교적 보수적으로 예측하고 있으며 미국의 연구사례(NCHRP Report)보다 안전측으로 설계가 이루어지고 있으나, 인발저항력에 대한 불확실성은 $COV_R$=0.27~0.43으로 비교적 큰 것으로 나타났다. 또한 가압식 그라우팅공법은 중력식 그라우팅공법에 비해 내재된 안전여유가 많으며, 실제 발휘되는 극한인발저항력의 불확실성이 낮은 것으로 분석되었다.

• Steel and Composite Structures
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• 제51권2호
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• pp.203-223
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• 2024

This study shows functionally graded material structural topology optimization under buckling constraints. The SIMP (Solid Isotropic Material with Penalization) material model is used and a method of moving asymptotes is also employed to update topology design variables. In this study, the quadrilateral element is applied to compute buckling load factors. Instead of artificial density properties, functionally graded materials are newly assigned to distribute optimal topology materials depending on the buckling load factors in a given design domain. Buckling load factor formulations are derived and confirmed by the resistance of functionally graded material properties. However, buckling constraints for functionally graded material topology optimization have not been dealt with in single material. Therefore, this study aims to find the minimum compliance topology optimization and the buckling load factor in designing the structures under buckling constraints and generate the functionally graded material distribution with asymmetric stiffness properties that minimize the compliance. Numerical examples verify the superiority and reliability of the present method.

• 산업기술연구
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• 제2권
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• pp.3-11
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• 1982

Reliability analysis methods have been employed in this study to determine the safety index ${\beta}$ for flexure associated with reinforced concrete designs that are in accordance with current USD code of Korea. In reliability analysis, the mean first-order second-moment methods are employed. The following specific conclusions can be drawn from this study; 1) Levels of safety for reinforced concrete design, measured by ${\beta}$, vary from 2.8 to 3.8 in flexure depending on the limit state, the ratio of live load to dead load and the uncertainties. 2) Target reliability ${\beta}$ associated with reinforced concrete beams in flexure is assumed to be 3.5~4.0 in Korea. 3) Load factors and resistance factors in flexure associated with the current provisions contained in USD code generally seem to be too high. The writer concluded the factors as following; ${\phi}=0.8,\;{\gamma}_D=1.1\;{\gamma}_L=1.75$.

• 대한토목학회논문집
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• 제31권4A호
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• pp.323-329
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• 2011

대부분의 콘크리트구조설계기준은 구조물의 안전에 대한 여유를 확보하기 위해 하중계수 및 저항계수의 안전계수를 고려하고 있다. 이 안전계수는 하중과 저항의 통계적 불확실성을 적절하게 고려한 구조신뢰성 이론에 근거하여 결정되어야 하는데, 구조신뢰성 이론의 적용은 하중 및 저항에 대한 통계적 모델의 정립이 선행되어야 한다. 이 논문에서는 콘크리트 압축강도, 철근 항복강도 및 부재 단면치수의 통계적 변동성을 고려한 철근콘크리트 부재의 저항모델을 개발하였다. 통계모델 개발에 적용된 자료는 국내의 실험 및 시험 자료를 기초로 하였으며, 몬테칼로 시뮬레이션(Monte Carlo Simulation)기법을 적용하였다. 이 논문의 결과는 콘크리트 구조설계 기준의 검증 및 개정작업에 유용한 자료를 제공할 것으로 기대된다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.24-34
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• 2021

This paper predicts the speed-power-rpm relationship in regular head waves using various indirect methods: load variation, direct powering, resistance and thrust identity, torque and revolution, thrust and revolution, and Taylor expansion methods. The subject ship is KVLCC2. The wave conditions are the regular head waves of λ/LPP = 0.6 and 1.0 with three wave steepness ratios at three ship speeds of 13.5, 14.5 and 15.5 knots (design speed). In the case of λ/LPP = 0.6 at design speed, two more wave steepness ratios have been taken into consideration. The indirect methods have been evaluated through comparing the speed-power-rpm relationships with those obtained from the resistance and self-propulsion tests in calm water and in waves. The load variation method has been applied to predict propulsive performances in waves, and to derive overload factors (ITTC, 2018). The overload factors have been applied to obtain propulsive efficiency and propeller revolution. The thrust and revolution method (ITTC, 2014) has been modified.

• 한국강구조학회 논문집
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• 제20권1호
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• pp.183-193
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• 2008

국내 LRFD 도로교설계규정을 정립하기 위한 자료로 활용하기 위하여 단경간 및 3경간 연속 플레이트 거더 및 박스 거더 합성단면을 하중저항계수설계법으로 설계하고 설계된 단면의 휨에 대한 신뢰도해석을 수행하였다. LRFD 법에 의한 합성거더 단면 설계 시에는 최근 국내 통행차량의 특성을 분석하여 새로 제안된 활하중을 적용하였다. 신뢰도해석에서 휨저항강도는 최근 국내에서 생산된 16,000여 구조용 강재 표본의 항복강도 통계적 특성을 반영하여 재료 비선형 소성해석으로 구한 강합성단면의 휨저항강도 통계를 이용하였다. 활하중에 의한 작용모멘트의 편심계수는 1.0~1.2를 적용하였으며 강거더 자중, 콘크리트 바닥판 자중, 포장면 자중 등에 의한 고정하중 모멘트 통계 값은 A SHTO 보정자료를 사용하였다. Rackwitz-Fiessler 법으로 신뢰도해석을 수행하고 지간별, 강거더 형식별, 활하중계수별, 활하중 모멘트의 편심계수별로 신뢰도지수 계산 결과를 제시하였다.

• Smart Structures and Systems
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• 제12권6호
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• pp.661-678
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• 2013

In this paper, a wireless sensing system for structural field evaluation and rating of bridges is presented. The system uses a wireless platform integrated with traditional analogue sensors including strain gages and accelerometers along with the operating software. A wireless vehicle position indicator is developed using a tri-axial accelerometer node that is mounted on the test vehicle, and was used for identifying the moving truck position during load testing. The developed software is capable of calculating the theoretical bridge rating factors based on AASHTO Load and Resistance Factor Rating specifications, and automatically produces the field adjustment factor through load testing data. The sensing system along with its application in bridge deck rating was successfully demonstrated on the Evansville Bridge in West Virginia. A finite element model was conducted for the test bridge, and was used to calculate the load distribution factors of the bridge deck after verifying its results using field data. A confirmation field test was conducted on the same bridge and its results varied by only 3% from the first test. The proposed wireless sensing system proved to be a reliable tool that overcomes multiple drawbacks of conventional wired sensing platforms designed for structural load evaluation of bridges.