• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.433-440
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• 2002

A branched crack in a semi-infinite plate under uniform tension and bending moment is considered in this study By using the superposition, the stress and moment intensity factors for the branched crack subjected to uniform tension and bending moment we evaluated. The stress intensity factors we obtained by using the finite element method and the J-based mutual integral. The moment intensity factors are calculated by extrapolating the values of the moment new the crack tip. Numerical results lot the normalized stress and moment Intensity factors we shown as functions of the ratio of branched crack length to main crack length and the branching angle.

• Magazine of the Korea Concrete Institute
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• v.3 no.1
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• pp.79-85
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• 1991

This paper aims at experimentally investigating the relationship between tensile load and average strain in the tension zone of SFRC beam. Also, it is attempted to find post cracking tension behavior of SFRC under tensile loading condition. The tension stiffening test is conducted on the long prizm of SFRC which embeds reinforcing bar in both ends of member. From this study, an empirical equation which represents the tension stiffening effect(i.e.effect of increasing tensile-~3trengthening contnbuted by SFRC when the reinforcing bar embeded in the SFRC member is under tensile loading condition) as a function of the average strain is presented .

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.726-732
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• 1998

가압 경수로형 원전에 사용되는 Alloy 600 증기발생기 전열관재료의 입계응력부식균열 거동에 미치는 냉간변형의 영향을 1차 냉각수 모사조건에서 정속인장시험방법으로 조사하였다. 인장 냉간변형은 응력부식균열을 크게 가속화 시키지는 않았으며 변형량이 25%이상인 경우에는 응력부식균열이 발생하지 않았다. 이 현상은 냉간 변형량 및 형태에 따른 미소변형 및 응력의 불균질성에 영향을 받는 것으로 사려되며 응력의 크기는 직접적인 영향을 주지 않는 것으로 보인다. 국부적인 큰 응력구배가 존재하는 경우 균열의생성 및 성장이 현저히 가속화되었는데 이는 원전 1차측 응력부식균열 기구가 응력구배에 의존하는 과정과 연관되어 있다는 증거이다. Hump 시편을 이용한 정속인장시험방법은 짧은 실험기간내에 원전 1차측 응력부식균열 특성을 평가할 수 있는 방법이었다.

• Journal of Korean Society of Forest Science
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• v.105 no.4
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• pp.435-440
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• 2016

This study was carried out to examine of soil physical property and crack shape by collapse process on landslide area (by land creeping) in Hadong, Gyeongnam. We investigated morphological characteristics (length, depth, cut slope) between main crack and local crack, soil physical properties change between undisturbed section and disturbed section. As a result, morphological characteristics of crack showed no significant difference main crack between local crack. In case of soil physical property variation, soil liquid phase was significantly higher at 31-40 cm of soil depth in disturbed section. And this result is likely to be due to site factors.

• Explosives and Blasting
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• v.23 no.2
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• pp.45-56
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• 2005

In this study, fracture formation and fracture volume by blasting demolition of model reinforced concrete pillars were compared with various vertical load and influence of reinforced steel bar. The more vertical load increased, the more tensile cracks and vertical direction cracks produced. In vertical load of 2.0ton, tensile cracks on vertical direction were predominantly produced. Generally, the more vertical load increased, the more bending deformation of concrete steel bar decreased. As a result, vertical load was influenced fracture formation of concrete and bending deformation of reinforced steel bar. Reinforced steel bar was influenced fracture volume of concrete. According to vertical load and influence of reinforce steel bar by blasting demolition of reinforced concrete pillars, drilling and blasting pattern may be modified.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.1
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• pp.46-54
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• 2013

Two different UHPCCs having different fiber lengths and volume fractions are considered to be applied to bridge decks. The objective of this study is to estimate cracking resistance of the two UHPCCs. The notched beam tests were performed with the UHPCCs, and the relationships between load and CMOD(Crack Mouth Opening Displacement) were obtained from the tests. The tensile stress and crack opening relationships optimally fitting the measured load-CMOD curves were found through the inverse analyses. The UHPCC with 2% volume fraction of 13 mm long fiber has lower fracture energy than the UHPCC with 0.5% and 1.0% volume fractions of 16.3 mm and 19.5 mm long fibers, respectively. It indicates that the latter UHPCC is more effective in uniformly distributing crack formation and reducing crack width.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.745-754
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• 2007

This paper presents a unified modeling technique for tension stiffening effect in structural concrete members. The model is mathematically derived from the bond stress-slip relationships which account for splitting crack. The relationships in CEB-FIP Model Code 1990 and Eurocode 2 are employed together with the assumptions of a linear slip distribution along the interface and the uniform condition of concrete tensile contribution for the mid section of cracked member at the stabilized cracking stage. With these assumptions, a model of tension stiffening effect is proposed by accounting for the force equilibrium and strain compatibility condition associated to the steel strain and concrete contribution by bond stress. The model is applied to the test results available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.305-310
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• 1995

토목 및 건축재료로서 폴리프로필렌 섬유 모르타르 및 콘크리트의 사용은 미국, 영 국 등지에서 개발되기 시작하여 많은 연구가 진행되어 왔는데, 가격이 저렴하고, 화학적인 안정성과 내구성이 우수하여 그 사용이 점차 증대되고 있는 실정이다. 이러한 폴리프로필렌 섬유의 사용은 모르타르 및 콘크리트가 건조나 냉각에 의해 수축될 때 구속에 의해 발생하 는 인장응력 및 균연을 제어하고, 인성의 증가와 충격, 마모, 피로에 대한 저항성, 내구성을 증대시키는 등의 장점을 가지는 것으로 보고되고 있다. 본 연구에서는 이러한 폴리프로필렌 섬유 모르타르 및 콘크리트의 역학적 거동특성인 압축강도, 인장강도, 인성, 유동성과 균열 특성을 실험적으로 규명하고자 하였다. 실험결과 폴리프로필렌의 혼입량이 증가할수록 압축 강도, 인장강도, 인성의 증가를 보였으나, 혼입향 0.2%를 초과할 경우 유동성, 강도 모두 감 소하는 것을 볼 수 있었다. 그리고 단섬유형 보다는 메쉬 형태의 폴리프로필렌 섬유가 역학 적 특성면에서 우수한 것으로 관찰되었으며, Kraai 방법에 의한 소성수축균열제어 특성 실 험에서 약 45% 이상으 균열감소 (0.1%혼입) 효과를 볼 수 있었다.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.205-214
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• 2012

Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.67-75
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit panicle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20$^{\circ}$~40$^{\circ}$. In condition that the loading angle is 20$^{\circ}$, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than I mm and loading rate less than 0.01 mm/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.