• 콘크리트학회논문집
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• 제25권6호
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• pp.683-691
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• 2013

깊은 보의 파괴거동은 전단경간과 유효깊이의 비(a/d)에 따라 크게 변한다. $a/d{\leq}1.0$의 깊은 보는 복부의 쪼갬현상과 하중점과 재하점 부근에서의 콘크리트의 연화현상을 동반하는 파괴모드가 지배적인 파괴모드가 되는 것과 복부에 배치된 전단철근은 보의 파괴모드를 변화시키는 역할을 하고, 이러한 목적으로 복부철근을 배근할 때에는 반드시 연직 및 수평철근을 동시에 사용하거나 또는 사인장균열에 직각을 이루도록 철근을 배치하여야 한다. 한편, 1.0${\leq}2.5$의 깊은 보의 경우, 전단파괴시 주인장철근이 항복상태에 도달하지 않도록 충분히 배치되어져 있다면 복부에 배치된 수평철근으로 인한 전단강도 증가는 거의 기대하기 어렵다. 하지만 연직전단철근은 1.0${\leq}2.5$의 깊은 보가 일찍 타이드아치기구로 전이되는 현상을 방지함으로서 전단강도를 증대시키는 역할을 한다. 본 연구에서는 깊은 보에 대한 기존의 실험연구로부터 얻어진 파괴거동과 그것에 영향을 미치는 주요 인자들에 대해 정성적으로 분석하고, 소성이론을 적용하여 파괴강도를 구하는데 기초가 되는 역학모델을 정의하였다. 또한 정의된 역학모델을 근거로 소성이론의 상계정리(upper bound theorem)를 적용하여 a/d가 1이하의 깊은 보에 대한 전단강도식을 이론적으로 유도하였다. 이 연구에서 제안된 전단강도 산정식은 $a/d{\leq}1.0$의 깊은 보의 전단강도를 정확하게 예측하였다.

• 전기학회논문지
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• 제56권6호
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• pp.1031-1034
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• 2007

Electric transmission lines pass through a variety of area. Foundation supporting the conductors and tower are selected properly in accordance with external load, for example dead load, wind load, snow load, construction load etc, and topography and geology condition. Typical types of foundation are as follows: pad foundation for small load and hard soil or rock in mountainous area, pile foundation for medium or large load and soft soil in plain field area. This paper introduced cylindrical foundation design & construction for large load and mountainous area. This foundation failure mode against pulling-out show splitting failure by tensile force toward circumferential direction.

• Steel and Composite Structures
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• 제17권6호
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• pp.791-801
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• 2014

The effects of anchor on fractured specimens in splitting test are simulated by DDARF method, the results of which are compared with laboratory test results. They agree well with each other. The paper contents also use the laboratory model test. The main research objects are three kinds of specimens, namely intact specimens, jointed specimens and anchored-jointed specimens. The results showed that with the joint angle increased, the weakening effects of jointed rock mass are more obvious. At these points, the rock bolts' strengthening effects on the specimens have become more significant. There is a significant impact on the failure modes of rock mass by the joint and the anchorage.

• 한국임상수의학회지
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• 제19권1호
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• pp.110-113
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• 2002

An atrial septal defect (ASD) is a congenital hole in the atrial septum that allows flow between the two atria. Small ASDs are usually well-tolerated defects and do not result in significant clinical abnormalities. In large ASDs or in the presence of other cardiac defects, clinically significancy is increased. Atrial septal defects in 2 Dogs with cardiac and respiratory signs were diagnosed at seoul animal medical center. In ascultation, systolic murmur and the splitting of second heart sound were heard at pulmonary or tricuspid valve region. In radiograph, right-sided cardiomegaly, pulmonary artery dilation, increased pulmonary vasculature makings, and pleural effusion or pulmonary edema signs were observed. In echocardiography, the region, location and size of septal defect was identified. Also, the direction and degree of shunt was measured. These dogs were treated with medicine for cardiac failure. One dog is well-tolerated, the other dog died.

• Geomechanics and Engineering
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• 제30권5호
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.343-363
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• 2017

The objective of this work was finding out the most advisable testing conditions for an effective and robust characterization of the tensile strength (TS) of concrete disks. The independent variables were the loading geometry, the angle subtended by the contact area, disk diameter and thickness, maximum aggregate size, and the sample compression strength (CS). The effect of the independent variables was studied in a three groups of experiments using a factorial design with two levels and four factors. The likeliest location where failure beginning was calculated using the equations that account for the stress-strain field developed within the disk. The theoretical outcome shows that for failure beginning at the geometric center of the sample, it is necessary for the contact angle in the loading setup to be larger than or equal to a threshold value. Nevertheless, the measured indirect tensile strength must be adjusted to get a close estimate of the uniaxial TS of the material. The correction depends on the loading geometry, and we got their mathematical expression and cross-validated them with the reported in the literature. The experimental results show that a loading geometry with a curved contact area, uniform load distribution over the contact area, loads projected parallel to one another within the disk, and a contact angle bigger of $12^{\circ}$ is the most advisable and robust setup for implementation of BT on concrete disks. This work provides a description of the BT carries on concrete disks and put forward a characterization technique to study costly samples of cement based material that have been enabled to display new and improved properties with nanomaterials.

• Composites Research
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• 제36권4호
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.9-10
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• 2010

본 연구에서는 CFRP로 보강한 2방향 콘크리트의 정하중 및 저속 충격하중에 대한 실험을 수행하였다. 압축강도 40MPa의 콘크리트 및 이와 동일한 배합에 0.75%의 강섬유를 혼입한 강섬유 보강 콘크리트로 $50{\times}350{\tims}350mm$의 부재를 제작하여 CFRP로 보강하였다. CFRP와 강섬유로 보강한 시험체는 콘크리트가 쪼개지는 파괴와 펀칭 파괴가 복합적으로 나타나고, 이 때 쪼갬 균열 수는 보강하지 않은 콘크리트에 비해 확연하게 줄어들었다. CFRP와 강섬유로 동시에 보강한 시편은 충격하중 하에서 2방향 콘크리트 시험체가 파괴되는 데에 6.8배의 에너지가 소모되었다.

• Structural Engineering and Mechanics
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• 제90권2호
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• pp.107-116
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• 2024

This study examined the changes in the mechanical properties of coral concrete under different coconut fiber admixtures. To accomplish this goal, the compressive strength, splitting tensile strength, flexural strength and elastic modulus properties of coral concrete blocks reinforced with coconut fibers were measured. The results showed that the addition of coconut fiber had little effect on the cube and axial compressive strengths. With increasing coconut fiber content, the flexural strength and splitting tensile strength of the concrete changed substantially, first by increasing and then by decreasing, with maximum increases of 36.0% and 12.8%, respectively; additionally, the addition of coconut fibers resulted in a failure type with some ductility. When the coconut fiber-reinforced coral concrete was 7 days old, it reached approximately 74% of its maximum strength. The addition of coconut fiber did not affect the early strength of the coral concrete mixed with seawater. When the amount of coconut fiber was no more than 3 kg/m3, the resulting concrete elastic modulus decreased only slightly from that of a similar concrete without coconut fiber, and the maximum decrease was 5.4%. The optimal dose of coconut fiber was 3 kg/m3 in this study.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.225-228
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• 2008

철근콘크리트 구조물을 해석하는 경우, 하중조건 및 이들 하중의 증가에 따라 나타나게 되는 상이한 거동 특성들 즉, 인장균열, 압축파괴, 다축상태일 때의 강도의 증가, 전단파괴 시의 취성적 파괴특성 등을 반드시 고려해야만 한다. 유한요소법에 의한 해석적 평가 시, 최대하중 이후에는 요소크기에 따라 상이한 구조응답을 나타내는 요소의존적인 응답결과를 보인다. 본 연구에서는 이러한 요소의존성을 극복하기 위한 연구결과들 중 하나인 적분형 비국소화 모델을 이용하여 전력구 모형 실험체의 파괴거동을 해석하였다. 실험결과와 해석결과를 비교하여 적분형 비국소 모델의 신뢰성과 타당성을 검토하는 것을 목적으로 한다.