• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.331-334
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• 2005

The nature of bond of untensioned prestressed strand in concrete differs from that of plain or deformed reinforcing bar as well as tensioned prestressed strand. There is a very limited amount of published research information regarding bonding of this type reinforcing. In order to use and design untensioned strand as reinforcing, relationships defining the load transfer characteristics of the strand are necessary. A program based upon pullout tests was designed to develop data relating the critical parameters for determining load transfer behavior of the untensioned strand. The purpose of this study is to investigate the characteristics of bond and development length between untensioned strand and concrete. The test variables include diameter of strands (9.3mm, 12.7mm) and development lengths. The maximum bond stress at the 9.3mm and 12.7mm strands decreases with the increase of the rate of development length. The untensioned prestressed strands displayed bond performance when secure development length more than 80$\%$ according to the development of deformed bars equation.

• Earthquakes and Structures
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• 제7권5호
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• pp.843-859
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• 2014

In the present study, the seismic performance of structural walls with boundary elements confined by conventional tie hoops and steel fiber concrete (SFC) was investigated. Cyclic lateral loading tests on four wall specimens under constant axial load were performed. The primary test parameters considered were the spacing of boundary element transverse reinforcement and the use of steel fiber concrete. Test results showed that the wall specimen with boundary elements complying with ACI 318-11 21.9.6 failed at a high drift ratio of 4.5% due to concrete crushing and re-bar buckling. For the specimens where SFC was selectively used in the plastic hinge region, the spalling and crushing of concrete were substantially alleviated. However, sliding shear failure occurred at the interface of SFC and plain concrete at a moderate drift ratio of 3.0% as tensile plastic strains of longitudinal bars were accumulated during cyclic loading. The behaviors of wall specimens were examined through nonlinear section analysis adopting the stress-strain relationships of confined concrete and SFC.

• Steel and Composite Structures
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• 제27권2호
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• pp.243-253
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• 2018

In recent years, concrete-filled box or tubular columns have been commonly used in high-rise buildings. However, a number of fire test results show that there are significant differences between high strength concrete (HSC) and normal strength concrete (NSC) after being subjected to high temperatures. Therefore, this paper presents an investigation on the fire resistance of HSC filled steel tubular columns (CFTCs) under combined temperature and loading. Two groups of full-size specimens were fabricated to consider the effect of type of concrete infilling (plain and reinforced) and the load level on the fire resistance of CFTCs. Prior to fire test, a constant compressive load (i.e., load level for fire design) was applied to the column specimens. Thermal load was then applied on the column specimens in form of ISO 834 standard fire curve in a large-scale laboratory furnace until the set experiment termination condition was reached. The results demonstrate that the higher the axial load level, the worse the fire resistance. Moreover, in the bar-reinforced concrete-filled steel tubular columns, the presence of rebars not only decreased the spread of cracks and the sudden loss of strength, but also contributed to the load-carrying capacity of the concrete core.

• KCI Concrete Journal
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• 제12권1호
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• pp.91-99
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• 2000

A new type of retrof=t anchor bolt that uses deformed reinforcing bars and a commercial adhesive was developed and then an experimental study was carried out to determine the behavior of the anchors in direct shear. The steel-to-concl몫ete interface was tested. Plain concrete slabs with about 20-MPa compressive strength were used for 23 direct shear tests performed Test variables were anchor diameters (D16, D22. and D29) and edge effect. Three different shear tests were completed: simple shear, edge shear where anchors were pulled against the concrete core, and edge shear where anchors were pushed against the concrete cover In the simple and the edge shear tests where the anchors were pulled against the core, the theoretical dowel strength determined by (equation omitted) was achieved but with relatively large displacements. The shear resistances increased with the increasing displacements. In the edge shear test where the anchors were pushrd against the cover, the peak shear strengths signif=cantly lower than the theoretical dowel strength were determined due to cracks developed in concrete when the edge distance was 80 mm. The peak strengths were about 50% of the dowel strength for Dl6 bar. and about 25% or less of the dowel strength for D22 and D29 bars. Test results revealed that the edge shear where the anchor was pushed against the cover controled.

• 대한한방내과학회지
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• 제32권3호
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• pp.345-360
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• 2011

Objectives : This study was examined to investigate the effects of Cheonmagudeng-um gagam (CGG) extract on spontaneous hypertension. Methods : For the study of CGG, we divided rats into three groups. The normal group was Wister Kyoto rats (WKY). The control group was spontaneously hypertensive rats (SHR). The treatment group was SHR which were administered CGG extract (SHR-CGG). SHR-CGG were orally administered CGG extract that was diluted in distilled water at the various concentrations for 4 weeks (234.5 mg/kg) and SHR were orally administered the same dosage of plain distilled water as SHR-CGG. Then we measured anti-oxygen effects, ACE inhibitory activity, weight of heart and kidney, blood pressure, heart rate, plasma aldosterone, electrolyte, creatinine, uric acid, BUN, and observed the cortex of the cardiac muscle, kidney, and adrenal gland. Results : CGG increased DPPH scavenging activity and SOD similar activity depending on the concentration. CGG significantly decreased ROS, TNF-${\alpha}$, IL-6, IL-$1{\beta}$, heart weight, blood pressure, heart rate, aldosterone, and BUN in SHR. CGG increased ACE inhibition activity depending on the concentration. CGG inhibited the heart, kidney and adrenal gland tissue injury that is caused by hypertension. Conclusions : These results suggest that CGG is effective in treatment and prevention of hypertension.

• 한국농공학회지
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• 제20권2호
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• pp.4645-4687
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• 1978

This study was attempted to investigate the mechanical properties of concrete and crack control effects of reinforced concrete with steel and glass fiber. The experimental program includes tests on the properties of fresh concrete containing fibers, compressive strength, tensile strength, flexural strength, Young's modulus, Shrinkage and deformation of steel or glass fiber reinforced concrete. Also this study was carried out to investigate the effect of steel or glass fiber to retard the development in reinforced concrete subject to uniaxial tension and thus facilitate the use of steels of higher strength. The major conclusions that can be drawn from the studies are as follows: 1. The effect of the fibers in various mixes on fresh concrete confirmed that fibers do have a significant effect on the properties of fresh concrete, bringing much more stable and exhibiting a signiflcant reduction in surface bleeding, and that the cohesion is greatly improved and the internal resistance increases with fiber concentration. But the addition of an excess contents and length of fibers brings about the reduction of workability. 2. With the addition of steel fibers(1.5% Vol.) to concrete, the compressive strength as compared with plain concrete showed a very slight increase, but excess addition, over 1.5% Vol. of steel and glass fiber reduced its strength. 3. Splitting tensile strength of fiber reinforced concrete showed a significant increase tendency, as compared with plain concrete. In case of containing steel fiber (2.5%, 30mm), it showed that the maximum increase rate of 1.48 times as much rate, and in case of containing glass fiber (2.5%, 30mm), the increase rate of strength was 1.25 times as much rate. 4. Flexural strength of fiber reinforced concrete showed a significant tendency, as compared with plain concrete. Containing steel fiber (2.5%, 30mm) showed the maximum increase rate of 1.64 times as much rate and containing glass fiber (2.5%, 30mm) showed the increase rate of strength of 1.32 times as much rate, and in general, the 30mm length brougth the best results. 5. The strength ratio ($\sigma$b/$\sigma$c and $\sigma$t/$\sigma$c) increased, when steel fiber's average spacing was up to 3.05mm, but decreased when beyond 3.05mm, and it was confirmed that tensile or flexural strengths of steel fiber reinforced concrete are apparently governed by fiber's average spacing. 6. The compressive strain of fiber reinforced concrete showed a significant increasing tendency as the fiber was added, but Young's modulus. with the addition of steel and glass fibers, showed a slight decrease tendency. And according to the increase of flexural strength, a considerable increase was seen in toughness. 7. With the addition of fiber's the shrinkage of concrete was significantly decreased, in both case of adding steel fibers 12.5%, 30mm, and showed a significant decrease ratio, in average 30.4% and 36.7%, as compared with plain concrete. 8. With the increase of fiber volume fraction and length, the gained stress in reinforcing bar in concrete specimens increased in all crack widths, but at different rates, with the decrease of fiber diameter, the stress showed a considerable increasing tendency. And the duoform steel fibers showed the greatest improvement, as compared with the other types tested. 9. The influence of fiber dimensions in order of significanse on the machanical properties of concrete and the crack control of reinforced concrete was explained as follows: content, length, aspect ratio and dimeter.

• 패션비즈니스
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• 제2권4호
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• pp.93-101
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• 1998

Knit products which had been limited only to underwear, recently became popularized, fashionized and highly classified covering even outer garments such as sportswear like golfwear, woman's dress, and man' s suit. As fashion cycle is getting shorter and the more a nation advanced prefers knit to woven fabrics knit industry has a very bright prospect, particularly woman's knit which is sensitive to fashion can be said as a fashion product with high value added. This study is to grasp the physical properties of stitch which are fundamental to the development of knit products. For this purpose, 2/20s of 100% wool were woven by the author of this study to basic plain stitch, rib stitch, varied transfer stitch, and float stitch on a SEMASEIKI cross knitter 7G to test the physical properties, and the result was as follows; 1. As for the relation between knit stitch and rate of extension recovery, rate of extension recovery was higher in the course direction than in the wale direction of three stitches except transfer stitch; rib stitch showed the highest rate of extension recovery in the course direction while float stitch showed the highest rate of extension recovery in the wale direction. 2. As for the relation between knit stitch and bursting strength elastic rib stitch showed higher bursting strength to indicate elasticity is an important factor of bursting strength and float stitch showed higher bursting strength too to indicate that the floating yarn on the surface plays a role of support. 3. As for the relation between knit stitch and air permeability perforated transfer stitch showed the lowest air permeability to prove that the size of perforation affects on the air permeability a great deal. 4. As for the relation between knit stitch and warmth retaining rib stitch through two lined needle bar showed the highest degree. The reason the warmth of perforated transfer stitch didn't decrease much was because the perforation wasn't big enough and content of air increased from the unevenness of the perforated parts through stitch variation. Based upon this result, each stitch can be characteristically summarized as follows; plain stitch showed a stable condition of knit cloth in four kinds of physical property test. And rib stitch is proper to tighten the edge of sleeve or clothe making use of its excellent extension recovery and to make socks for the highest bursting strength and warmth retaining. In the case of transfer stitch, seasonable designs can be taken by controlling the size of loop. Considering the pleasantness, underwear should be made of stitches with good air permeability float stitch was revealed to have color and pattern effects and a great bursting strength. This study has limitations in the aspect that it dealed with a small part of various knit stitches and the items of physical property test were not enough. The author of this study hopes that further studies would make deeper understandings about knit stitch based on more varied stitches and physical property tests ultimately to contribute to the development of fashionable designs proper to maximize the usage, function and originality.

• 한국항공우주학회지
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• 제42권2호
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• pp.119-126
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• 2014

본 연구에서는 연료가 비등점 이상의 고온으로 가열된 경우 오리피스 인젝터를 통해 분사되는 특성을 실험한 결과를 정리하였다. 크기가 다른 오리피스 인젝터 3종을 이용하여 3, 5, 10 bar의 분사압력을 가할 때 온도범위 $50{\sim}270^{\circ}C$에서 유량계수(${\alpha}$)를 측정하였다. 측정된 유량계수는 연료온도가 $180^{\circ}C$ 이하 영역에서는 점진적으로 감소하였으나 비등점인 $187^{\circ}C$를 넘어가면서 급격히 감소하였다. 비등점보다 높은 연료온도에서의 유량계수 감소 기울기는 분사압력에 따라 다른데, 특히 분사압력이 낮을수록 비등의 영향이 크게 작용하므로 더 급격한 특성을 보였다. 또한, 직경이 큰 인젝터의 유량계수가 더 크고, 낮은 연료온도 영역에서 난류-층류 천이현상으로 보이는 유량계수의 점프현상이 관찰되었다. 유량계수를 캐비테이션 수($K_c$)에 대하여 도시한 결과 인젝터의 크기가 작을 때는 연료 비등으로 인한 분사특성이 분사압력과 무관한 일정한 값을 가지는 것을 확인하였다.

• 생태와환경
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• 제36권1호통권102호
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• pp.74-82
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• 2003

본 연구는 자연형 하천공법을 적용한 서울시 양재천의 과천, 서초 및 학여울 등 3개구간에서 공법 적용 이후에 나타난 조류상의 변화를 파악하고, 향후 하천을 복원할 경우 알맞은 조류 서식지조성에 대한 의견을 제시하고자 수행하였다. 각 구간별로 자연형 하천 공법적용이후 과천구간에서는 조류의 종수와 개체수가 모두 감소하는 경향을 보였다. 서초구간에서의 조류의 종수는 거의 변화가 없었지만 개체수는 증가하였으며, 특히 수면성 오리류(Dabbling Ducks)가 많이 증가하였다. 학여울구간에서도 종수와 개체수 모두 증가하는 경향을 보였으며, 백로류(Herons)와 수면성 오리류의 개체수는 증가하였지만 할미새류 (Wagtails)는 급격히 감소하였다. 과천구간을 제외한 두 지역에서 자연형 하천공법을 적용한 이후 조류의 종수와 개체수는 증가하는 경향을 보였다. 특히 하천의 사행화 (곡선화)로 인하여 발생한 모래톱, 저수호안의 식생복원과 둔치에 만든 인공연못은 조류의 서식에 많은 도움을 주었다. 하지만, 둔치 가장자리를 따라 만들어진 자전거도로는 조류의 서식에 부정적인 영향을 미친 것으로 사료된다.

• 콘크리트학회지
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• 제11권2호
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• pp.251-259
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• 1999

최근 다양한 침해환경에 건설되는 구조물이 증가함에 따라 철근 및 강재의 부식위험성이 높아지면서, 철근 콘크리트 구조물의 내구성 저하문제가 큰 관심으로 떠오르고 있다. 특히 해양 환경하에 건설된 철근 콘크리트 구조물의 경우 구조물 외부로부터 침투되는 염분의 영향으로 인한 철근부식이 발생 및 진행되어 콘크리트 구조물에 균열, 박리 등의 손상을 받게된다. 그러므로 해양콘크리트 구조물은 염해에 대해 내구성 및 신뢰성 확보가 중요시되고 있다. 따라서, 본 연구에서는 철근의 부착강도를 크게 감소시키지 않게 하는 방법으로서 시멘트 계통의 방청시멘트를 철근에 도막한 후 내부식성능과 부착강도특성을 실험적으로 연구하였다. 본 연구결과, 방청시멘트 도막철근은 소요의 내부식성능을 갖고 있으면서도 부착강도특성도 일반철근과 유사하였으며, 앞으로 실구조물의 내구성증진을 위해 효율적으로 사용될 수 있는 토대가 될 것으로 사료된다.