• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.99-104
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• 1994

Recently, nonlinear fracture mechanics was applied to analyze concrete structures more accurately, and new materials property such as fracture energy(Gf) was used for its application. The fracture energy was influenced by many parameters, especially the strength of concrete. Many researches on the relation between the strength of concrete and the fracture energy were performed. In spite of many researches on the relation between the strength of concrete and the fracture energy, there is no distinct conclusion. This research includes various the strength levels from low-strength of concrete to high-strength, and then intends to estimate relation between the strength of concrete and the fracture energy. Concrete used crushed sand is also included, which is going to be used much. In this research, the wedge splitting test method proposed by Prof. Linsbauer is adopted to investigate the fracture energy. Fracture behavior of concrete used natrual sand and crushed sand has the similar trend. In the strength range of 200~500 kg/$\textrm{cm}^2$, the fracture energy and the maximum splitting forces(F) increase as the strength of concrete increases. In the range of the higher strength, however, the maximum splitting forces(F) increases but the fracture energy decreases as the strength of concrete increases. Through this investigation the fracture energy of concrete was not proportional to the strength of concrete.

• Computers and Concrete
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• 제18권3호
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• pp.337-354
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• 2016

To study the influence on fracture properties of reinforced concrete wedge splitting test specimens by the addition of reinforcement, and the restriction of steel bars on crack propagation, 7 groups reinforced concrete specimens of different reinforcement position and 1 group plain concrete specimens with the same size factors were designed and constructed for the tests. Based on the double-K fracture criterion and tests, fracture toughness calculation model which was suitable for reinforced concrete wedge splitting tensile specimens has been obtained. The results show that: the value of initial craking load Pini and unstable fracture load Pun decreases gradually with the distance of reinforcement away from specimens's top. Compared with plain concrete specimens, addition of steel bar can reduce the value of initial fracture toughness KIini, but significantly increase the value of the critical effective crack length ac and unstable fracture toughness KIun. For tensional concrete member, the effect of anti-cracking by reinforcement was mainly acted after cracking, the best function of preventing fracture initiation was when the steel bar was placed in the middle of the crack, and when the reinforcement was across the crack and located away from crack tip, it plays the best role in inhibiting the extension of crack.

• 지질공학
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• 제31권4호
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• pp.719-730
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• 2021

본 연구는 무진동·무소음 암반 굴착을 위해 개발된 수압암반절개공법의 효율적인 굴착을 위하여 수압암반절개시스템의 패커 및 주입 시스템을 개량하였으며, 또한, 현장 실험을 수행하여 개선된 시스템의 효율성을 평가하였다. 수압파쇄균열은 누수로 인한 주입 압력의 손실로 인하여 균열확장 및 균열성장에 제한이 발생하였으나, 단일 패커의 팽창에 따른 인장응력에 의한 인장 변위는 암반 굴착을 용이하게 하였다. 현장 실험 자료를 바탕으로 수행한 수치해석결과는 현장 실험에서 형성된 균열의 발달을 모사할 수 있는 것으로 평가되었다.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.789-798
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• 2022

The stud shear connector is the main force transfer member in the steel-concrete composite member, and the mechanical behavior is very complicated in the concrete. The concrete around the stud is subjected to the pry-out local pressure concentration of the stud, which can easily produce splitting mirco-cracks. In order to solve the problem of pry-out local splitting of stud shear connector, a kind of stud shear connector with constraint measure is proposed in this paper. Through the push-out test, the interface shear behavior of the new stud shear connector between steel and concrete flange plate was studied, and the difference between the new stud shear connector and the traditional stud connector was compared. The results show that the stud shear connector with constraint measure can effectively avoid the adverse effect of local pressure splitting by relying on its own constraint measure. The shear stiffness of the interface between steel and concrete flange plates is greatly improved, which provides a theoretical basis for the design of strong connection coefficient of steel-concrete composite structures.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2001년도 추계학술발표회 논문집
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• pp.89-94
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• 2001

In this study we focus on variable selection in decision tree growing structure. Some of the splitting rules and variable selection algorithms are discussed. We propose a competitive variable selection method based on Kruskal-Wallis test, which is a nonparametric version of ANOVA F-test. Through a Monte Carlo study we note that CART has serious bias in variable selection towards categorical variables having many values, and also QUEST using F-test is not so powerful to select informative variables under heavy tailed distributions.

• 콘크리트학회논문집
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• 제27권3호
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• pp.253-263
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• 2015

최근 RPC를 활용한 초고강도 콘크리트가 개발되면서 100 MPa 이상의 높은 압축강도를 보유한 콘크리트가 취성적 파괴의 방지 목적과 인장강도 증진을 위해 강섬유를 혼입하여 사용되고 있다. 따라서 인장강도의 결정이 중요하나, 현재 초고강도 콘크리트 영역에서의 인장강도 추정을 위한 연구결과가 산발적으로만 이루어지고 있는 상황이다. 따라서 본 연구에서는 80~200 MPa의 압축강도를 보유한 RPC의 재료 시험을 수행하여 압축강도와 인장강도의 상관관계를 검토하였다. 시험 결과 100 MPa 이상의 압축강도를 보유할 경우에도 보통강도 또는 고강도 콘크리트 영역에서의 변화 경향이 유지되고 있는 것을 확인할 수 있었다. 이에 기존 연구로부터 수집된, 쪼갬인장강도 원주형 공시체 시험 결과 284개와 265개의 파괴계수 시험 결과를 활용하여 기존의 추정식들을 평가하였다. 평가 결과 100 MPa 이상의 초고강도 콘크리트에서는 기존 추정식을 안전하게 사용하기 어려운 것을 확인하였으며, 100 MPa 이상의 초고강도 콘크리트에도 적용 가능한 회기식을 도출하였다.

• 지질공학
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• 제32권4호
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• pp.725-733
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• 2022

본 연구에서는 기존 패커를 개량한 하이브리드패커를 장착한 수압암반절개시스템을 벤치컷 공법에 적용하였다. 하이브리드패커는 주입압을 이용하여 수압파쇄균열을 생성시키고 고무패커를 팽창시켜 수압파쇄균열을 확장하고 연장시키는 두 가지 기능을 하나의 패커에 접목시킨 패커시스템으로, 무소음·무진동 수압암반절개에 효율적으로 적용할 수 있도록 설계되었다. 본 연구에서는 벤치컷 굴착을 위해 사면 최상단에 설치된 실험공과 자유면으로부터의 이격거리와 주입설정 등 실험조건을 조정하면서 현장실험을 수행하여 주입 조건에 따른 암반 굴착 효율성을 비교하였다. 5 m의 이격거리를 지닌 조건에서는 굴착이 이루어지지 않은 부분이 발생하였으나 1 m의 이격거리에서는 굴착되지 않은 부분이 발생하지 않았다. 주입압에 의해 생성된 수압파쇄균열은 대체적으로 자유면과 평행하게 발달하여 고무팽창에 의해 확장 및 연장되어 벤치컷 굴착이 용이하게 이루어졌다. 벤치컷 암반 굴착에 수압암반절개공법을 체계적으로 적용하기 위해서는 다양한 암반 상태에 대하여 실험조건을 변화하면서 현장실험 결과를 축적하여야 할 것으로 판단된다.

• Computers and Concrete
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• 제18권1호
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• pp.113-137
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• 2016

Extensive experimental studies on remarkable mechanical properties Polypropylene Fibre Reinforced Self-compacting Concrete (PFRSCC) have been executed, including different fibre volume fractions of Polypropylene fibers (0.25%, 0.5%, 0.75%, and 1%) and different water to cement ratios (0.21, 0.34, 0.38, and 0.41). The experimental program was carried out by using two hundred and sixteen specimens to obtain the impact resistance and mechanical properties of PFRSCC materials, considering compressive strength, splitting tensile strength, and flexural strength. Statistical and analytical studies have been mainly focused on experimental data to correlate of mechanical properties of PFRSCC materials. Statistical results revealed that compressive, splitting tensile, and flexural strengths as well as impact resistance follow the normal distribution. Moreover, to correlate mechanical properties based on acquired test results, linear and nonlinear equations were developed among mechanical properties and impact resistance of PFRSCC materials.

• KIEAE Journal
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• 제4권2호
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• pp.37-40
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• 2004

New visible photocatalyst(Nanovis$^{(R)}$) has been synthesized to overcome the barrier of limitation of UV light utilization of current $TiO_2$ photocatalyst. It was found that red shift of absorption spectrum to 550nm was achieved. Its physical properties were characterized by XRD, BET and TEM. It is also observed that Nanovis$^{(R)}$ has a photocatalytic activity for photodegradation of Trichloroethylene under visible light irradiation. V,VII group doped into substitutional sites of $TiO_2$ has proven to be indispensable for band-gap narrowing and photocatalytic activity. These test results lead us to conclude that Nanovis$^{(R)}$ can be used for IAQ improvemen and for photocatalytic water splitting to hydrogen.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.873-878
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• 2000

Tension stiffening effects of reinforced concrete member with large diameter bar, mainly used at reactor building of nuclear power plant, are studied by uniaxial structural tests. Bond length and stress of steel bar, size of steel bar, and compressive strength of concrete are evaluated to tension stiffening by uniaxial tests. Problems and solution during the uniaxial test are suggested. The prevent splitting cracks, concrete cover-to-bar diameter ratio $c/d_{b}$ is kept 2.6~2.8. Because the bond length is increased as the size of steel bar, the specimen length of the D35 steel bar is required at least 2.0 m. The specimen length must be decided with bond length as well as concrete cover-to-bar diameter ratio to prevent splitting crack.