• 한국지반공학회논문집
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• 제29권11호
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• pp.73-84
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• 2013

사면 내 토사가 붕괴되거나 토석류가 발생하는 경우 파괴면에 작용하는 전단강도는 0에 가깝게 되면서 토사가 비점성 액체와 같이 유동한다. 점성토는 함수비 증가에 따라 그 연경도가 달라지며 액체상태로 바뀌는 액성한계에서 도 약간의 전단강도를 가진다. 본 연구에서는 점성토의 전단강도가 0이 되어 흐름을 유발하는 함수비를 찾고자 하였 다. 카올리나이트, 벤토나이트, 그리고 카올리나이트(50%)+벤토나이트(50%)와 같은 세 종류의 점토에 혼합수로 증류 수, 해수, 또는 미생물용액을 혼합하여 액성한계 상태로 만든 다음 함수비를 단계적으로 증가시키면서 토베인 시험기 를 이용하여 비배수전단강도를 측정하였다. 액성한계와 소성한계에서 비배수전단강도의 범위는 각각 3.6-9.2kPa와 24-45kPa 정도이었다. 한편 측정 결과로부터 비배수전단강도가 급격하게 변화하는 값에 해당하는 함수비를 흐름함수 비(Flow Water content)로 정의하였으며, 비배수전단강도가 0이 될 때의 함수비를 흐름한계(Flow Limit)로 정의하였다. 그리고 흐름한계와 액성한계의 상관관계를 살펴보기 위하여 흐름한계와 액성한계의 차이를 점성지수(Cohesive Index) 로 정의하였다. 또한 흐름한계와 소성한계의 차이를 새로운 소성지수(New Plasticity Index)로 정의하였으며, 흐름한계를 이용하여 새로운 액성지수(New Liquidity Index)도 정의하였다. 흐름한계(Flow Limit)는 액성한계보다 1.5-2배 정도 높은 값을 보였으며, 새로운 소성지수는 기존 소성지수보다 2-5.5배 정도 높았다.

• Structural Engineering and Mechanics
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• 제50권2호
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• pp.201-214
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• 2014

Due to the confinement effects, Steel-Straps Tensioning Technique (SSTT) can significantly enhance the strength and ductility of high-strength concrete (HSC) members (Moghaddam et al. 2008). However, the enhancement especially in strength may result in slender member and more susceptible to instability (Jiang and Teng 2012a). This instability is particularly significant in HSC member as it inherent the brittle nature of the material (Galano et al. 2008). The current slenderness limit expression used in the design is mainly derived from the experiment and analysis results based on Normal strength concrete (NSC) column and therefore the direct application of these slenderness limit expressions to the HSC column is being questioned. Besides, a particular slenderness limit for the SSTT-confined HSC column which incorporated the pre-tensioned force and multilayers effects is not yet available. Hence, an analytical study was carried out in the view of developing a simple equation in order to determine the slenderness limit for HSC column confined with SSTT. Based on the analytical results, it was concluded that the existing slenderness limit expressions used in the design are appropriate for neither HSC columns nor SSTT-confined HSC columns. In this paper, a slenderness limit expression which has incorporated the SSTT-confinement effects is proposed. The proposed expression can also be applied to unconfined HSC columns.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.271-282
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• 2019

The span record of cable-stayed bridges has exceeded 1,000 m, which makes research on the maximum possible span length of cable-stayed bridges an important topic in the engineering community. In this paper, span limit is discussed from two perspectives: the theoretical span limit determined by the strength-to-density ratio of the cable and girder, and the engineering span limit, which depends not only on the strength-to-density ratio of materials but also on the actual loading conditions. Closed form equations of both theoretical and engineering span limits of cable-stayed bridges determined by the cable and girder are derived and a detailed parametric analysis is conducted to assess the engineering span limit under current technical conditions. The results show that the engineering span limit of cable-stayed bridges is about 2,200 m based on materials used available today. The girder is the critical member restricting further increase in the span length; its compressive stress is the limiting factor. Approaches to increasing the engineering span limit are also presented based on the analysis results.

• 한국구조물진단유지관리공학회 논문집
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• 제11권1호
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• pp.171-180
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• 2007

처짐, 응력 및 휨강도 한계상태에 대한 PSSC(prestressed steel and concrete)거더의 신뢰도해석을 수행한다. PSSC 거더는 시공비용과 형하공간의 확보 면에서 지간 40m이상인 교량에 적용하는데 커다란 장점을 가지고 있는 형식이다. 이 논문에서는 다양한 지간, 단면 및 설계 응력수준을 가지는 PSSC 거더를 설계하여 중앙점 처짐, 응력 및 단면 휨모멘트 해석을 수행하고, 각각에 대한 한계상태를 가정한 후, Monte-Carlo 시뮬레이션과 Rackwitz-Fiessler 방법을 이용하여 신뢰도지수를 구한다. 결과를 분석하면 PSSC 거더에 대한 처짐한계상태는 응력한계상태보다 적절하게 큰 신뢰도지수 값을 보이며, 휨강도에 대한 신뢰도지수가 매우 큼을 알 수 있다.

• 한국생산제조학회지
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• 제4권4호
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• pp.42-49
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• 1995

It is not clearly known how defects or inclusions of a low carbon steel affect a fatigue strength. We study this issue using SM15C materials. The investigation is carried out by a quantitative evaluation, and experimental findings are: (1) a fatigue limit of A series smooth specimen is 205MPa, and that of B, C, D series is 245MPa, 304MPa and 245MPa, respectively. (2) the fatigue limit varies with respects to the stress distribution I the vicinity of a defects and crack. (3) the micro hole creates a half-circular shape crack, while the hole depth is not critical to the fatigue strength, (4) considering the fatigue strength, the hole diameter is more significant than the hole depth, and (5) Fatigue limit of artificially defected specimen is lower than that of a flawless one (5-10%), however, there exist allowance size and depth of defect which don't get to influence at fatigue limit.

• 한국안전학회지
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• 제29권5호
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• pp.97-103
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• 2014

To ensure durability and light weight of bridges, high-strength concrete is required for long-span deck slabs. Such a technology eventually extends the life of bridges and improves the economic efficiency. The results of this study suggests a formula for calculating the minimum thickness of long-span deck slabs built with high strength concrete. The minimum thickness is proposed based on the limit states indicated in the CEB-FIP Model Code and the Korean Highway Bridge Design Code(limit state design). The design compressive strength of concrete used for the study is 80MPa. Moreover, the required thickness for satisfying the flexural capacity and limiting deflection is estimated considering the limit state load combination. The formula for minimum thickness of deck slabs is proposed considering the ultimate limit state(ULS) and the serviceability limit state(SLS) of bridges, and by comparing the Korean Highway Bridge Design Code and similar previous studies. According to the research finding, the minimum thickness of long-span deck slab is more influenced by deflection limit than flexural capacity.

• 대한기계학회논문집A
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• 제32권5호
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• pp.411-418
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• 2008

In this work, the effect of strength mismatch on plastic limit loads is quantified for similar metal weld plates with cracks under tension load, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate geometry and crack length are systematically varied, in addition to the weld width. An important finding is that mis-match limit loads can be uniquely quantified through strength mis-match ratio and one geometry-related parameter. Based on the proposed limit load solutions, reference stress based J-integral estimates is also investigated. When the reference stress is defined by the mis-match limit load, predicted J-integral values agree overall well with FE results.

• 한국강구조학회 논문집
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• 제17권5호통권78호
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• pp.605-615
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• 2005

수평하중을 받는 콘크리트충전 각형강관 기둥의 축력과 변형능력의 관계를 조사하기 위하여 실험 및 해석적 연구를 수행하였다. 36개 기둥으로 구성된 실험 시리즈는 일정 축하중과 수평하중 하에서 반복실험을 실시하였다. 반복 수평하중을 받는 기둥이 저항할 수 있는 축하중을 보증내력 한계축력이라고 규정하였으며, 해석 모델은 수평하중을 받는 캔틸레버 기둥을 모델화하였다. 반복 횡하중을 받는 기둥의 축하중을 누적보증내력 한계축력이라고 정의하였다. 본 연구의 목적은 주어진 동일부재각에 부합하는 축력과 수평하중을 받는 콘크리트 충전강관 기둥의 보증내력 한계축력을 연구하기 위한 것이며, 두 번째는 콘크리트 충전강관 기둥의 누적보증내력 한계축력과 보증내력 한계축력의 비교가 본 연구의 목적이다.

• 한국구조물진단유지관리공학회 논문집
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• 제10권5호
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• pp.115-121
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• 2006

본 논문에서는 다양한 형태의 케이블 요소들의 거동이 강사장교의 극한강도에 미치는 영향을 검토하였다. 연화소성힌지 모델을 사용한 극한강도 평가 시 보-기둥 부재의 기하학적 비선형은 안정함수를 사용하여 고려하였고 재료적 비선형성을 반영하기 위하여 CRC 접선계수와 포물선 함수를 사용하였다. 케이블 부재는 새그의 영향이 고려되었다. 연구 결과 등가탄성계수가 반영된 등가트러스 요소를 사용한 경우 강사장교의 극한강도가 케이블 요소 또는 현수선 요소를 사용하여 평가한 극한강도 보다 안전측으로 평가되었다.

• Interaction and multiscale mechanics
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• 제1권2호
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• pp.231-250
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• 2008

The statistical two-order and two-scale method is developed for predicting the mechanics parameters, such as stiffness and strength of core-shell particle-filled polymer composites. The representation and simulation on meso-configuration of random particle-filled polymers are stated. And the major statistical two-order and two-scale analysis formulation is briefly given. The two-order and two-scale expressions for the strains and stresses of conventionally strength experimental components, including the tensional or compressive column, the twist bar and the bending beam, are developed by means of their classical solutions with orthogonal-anisotropic coefficients. Then a new effective mesh generation algorithm is presented. The mechanics parameters of core-shell particle-filled polymer composites, including the expected stiffness parameters, minimum stiffness parameters, and the expected elasticity limit strength and the minimum elasticity limit strength, are defined by means of the stiffness coefficients and elasticity strength criterions for core, shell and matrix. Finally, the numerical results for predicting both stiffness and elasticity limit strength parameters are compared with the experimental data.