• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.267-281
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• 2015

Six full-scale prestressed concrete (PC) I-beams with steel fibers were tested to failure in this work. Beams were cast without any traditional transverse steel reinforcement. The main objective of the study was to determine the effects of two variables-the shear-span-to-depth ratio and steel fiber dosage, on the web-shear and flexural-shear modes of beam failure. The beams were subjected to concentrated vertical loads up to their maximum shear or moment capacity using four hydraulic actuators in load and displacement control mode. During the load tests, vertical deflections and displacements at several critical points on the web in the end zone of the beams were measured. From the load tests, it was observed that the shear capacities of the beams increased significantly due to the addition of steel fibers in concrete. Complete replacement of traditional shear reinforcement with steel fibers also increased the ductility and energy dissipation capacity of the PC I-beams.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.206-210
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• 2003

Machining of deep holes with conventional boring bars frequently induce chatter vibration because of their low dynamic stiffness which is defined as the product of static stiffness and damping of conventional boring bar materials. In addition, the specific stiffness ($E/{\rho}g$) of boring bars is more important than the static stiffness to increase the fundamental natural frequency of boring bars in high speed machining. Therefore, boring bar materials should have high static stiffness and high damping as well as high specific stiffness. The best way to meet requirements is to employ fiber reinforced composite materials for high speed boring bars because composite materials have high static stiffness, high damping and high specific stiffness compared to conventional boring bar materials. In this study, the dynamic characteristics of carbon fiber epoxy composite boring bars were investigated. From the metal cutting test, it was found that the chatter was not initiated up to the ratio of length to diameter of 10.7 at the rotating speed of 2,500 rpm.

• Korean Membrane Journal
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• 제1권1호
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• pp.100-105
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• 1999

A novel system to thicken the concentrated colloidal solution from membrane water treat-ment processes was developed. A hollow-fiber microfilter(hydrophilic polyethylene nominal pore size 0.1 ${\mu}$m total surface area 0.42 m2) was installed in an acrylic housing that has an aeration port 5 cm below the membrane and a clarifier in the bottom. The concentrate was uniformly supplied from the top of the housing. Bacuum filtration caused downward flow of concentrate and as a result thickening interface. The addition of poly-aluminum chloride (PAC) resulted in rapid increase of trans-membrane pressure (TMP) and in no improvement of the filtered water turbidity and thickening process. Two types of con-centrate and concentrate turbidity had little effect on the increase of TMP and concentrate thickening. It was observed that for the same height of membrane housing membrane surface area to housing volume (A/V) ratio had significant effect on the increase of TMP. When the housing volume was increased ten times the increasing rate of TMP was three times faster as compared to the original housing. A hydraulic model successfully simulated the formation and sedimentation of thickening interface.

• Fibers and Polymers
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• 제5권3호
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• pp.230-233
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• 2004

The optimum conditions for durable press treatment of cotton fabrics using glyoxal as a nonformaldehyde crosslinking agent were investigated. Crosslinking reaction was conducted in the presence of different catalysts such as aluminum sulfate, magnesium chloride, or magnesium chloride-citric acid mixture at various mole ratios of catalyst to glyoxal. Aluminum sulfate was proven the most effective one among those used. Glycol addition into a glyoxal padding bath increased the wrinkle recovery angle(WRA) and whiteness of treated fabrics. The optimum mole ratio of glycol to glyoxal was 1:1. Diethylene glycol addition produced better overall performance to the glyoxal-crosslinked fabric compared to ethylene glycol addition.

• Steel and Composite Structures
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• 제10권4호
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• pp.361-371
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• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• Computers and Concrete
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• 제24권1호
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• pp.37-49
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• 2019

In this study, the shear behaviour of reinforced concrete (RC) beams that were retrofitted using precast panels of ultra-high performance fiber reinforced concrete (UHPFRC) is presented. The precast UHPFRC panels were glued to the side surfaces of RC beams using epoxy adhesive in two different configurations: (i) retrofitting two sides, and (ii) retrofitting three sides. Experimental tests on the adhesive bond were conducted to estimate the bond capacity between the UHPFRC and normal concrete. All the specimens were tested in shear under varying levels of shear span-to-depth ratio (a/d=1.0; 1.5). For both types of configuration, the retrofitted specimens exhibited a significant improvement in terms of stiffness, load carrying capacity and failure mode. In addition, the UHPFRC retrofitting panels glued in three-sides shifted the failure from brittle shear to a more ductile flexural failure with enhancing the shear capacity up to 70%. This was more noticeable in beams that were tested with a/d=1.5. An approach for the approximation of the failure capacity of the retrofitted RC beams was evolved using a multi-level regression of the data obtained from the experimental work. The predicted values of strength have been validated by comparing them with the available test data. In addition, a 3-D finite element model (FEM) was developed to estimate the failure load and overall behaviour of the retrofitted beams. The FEM of the retrofitted beams was conducted using the non-linear finite element software ABAQUS.

• 콘크리트학회논문집
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• 제22권4호
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• pp.575-583
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• 2010

이 연구는 비틀림 강섬유(T- 섬유) 의 비틀림 횟수가 인발거동과 T- 섬유를 사용한 고성능 섬유보강 시멘트 복합재료의 인장거동에 미치는 영향을 조사하였다. T- 섬유의 여러 인자와 비틀림 횟수가 섬유의 인발거동에 미치는 영향을 해석적으로 조사하고, 최대의 인발에너지를 생성할 수 있는 비틀림 횟수를 조사하였다. 이와 더불어 T- 섬유의 인발시험과 인장시험을 수행하여, 비틀림 횟수가 고인성 섬유보강 시멘트 복합재료의 인장거동에 미치는 영향을 조사하였다. 비틀림 횟수가 6ribs/30 mm인 T(L)- 섬유와 비틀림 횟수가 18ribs/30 mm인 T(H)- 섬유를 사용하였다. T(H)- 섬유는 인발시험시 섬유의 파단되어, T(L)- 섬유보다 높은 인발응력을 유발했음에도 불구하고 낮은 총 인발에너지를 생성하였다. 이러한 인발 시험서의 결과는 인장 거동에도 분명하게 반영되었다. T(L)- 섬유를 사용한 고인성 섬유보강 시멘트 복합재료의 경우, T(H)- 섬유의 사용시보다, 우수한 변형능력과 에너지 흡수능력, 그리고 미세균열 거동을 보였다.

• 콘크리트학회논문집
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• 제26권3호
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• pp.307-313
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• 2014

섬유보강 콘크리트의 균열 후 인장 거동을 예측하기 위해서는 균열면에 걸쳐 있는 섬유의 개수를 산정하는 섬유분포계수를 합리적으로 예측하는 것이 필요하다. 이 논문에서는 원형단면에서의 섬유분포계수를 분석하기 위해, 콘크리트 압축강도, 단면 크기, 섬유 종류 및 섬유혼입률 등을 변수로 강섬유보강 콘크리트 공시체를 제작하였으며, 제작한 공시체들을 타설 방향에 수직인 방향으로 절단한 후, 절단된 원형 단면에서의 섬유 개수로부터 섬유분포계수를 측정하였다. 측정 결과, 섬유가 타설면에 평행하게 분포할 확률이 증가함에 따라 실제 원형단면에서의 섬유분포계수가 일반적으로 알려진 0.5보다 작은 것으로 나타났다. 또한, 단위 면적 당 섬유 개수가 증가할수록 섬유분포계수가 감소하는 것으로 나타났다. 이 논문에서는 원형단면에서의 섬유분포계수를 합리적으로 예측하기 위해 섬유가 분포할 수 있는 각을 기하학적으로 분석하고, 이로부터 상세 모델과 단순화한 식을 유도하였다. 제안된 모델과 실험에서 측정된 섬유분포계수를 비교한 결과, 제안된 모델이 실제 원형단면에서의 섬유분포계수를 잘 예측하는 것으로 나타났다. 이 연구로부터 확보된 실험 결과 및 제안 모델은 향후 원형단면을 지닌 섬유보강 콘크리트 기둥 부재 등의 구조적 거동 연구에 매우 유용할 것으로 사료된다.

• 한국잠사곤충학회지
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• 제34권2호
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• pp.52-57
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• 1992

견의 저온염색용 조제(K-1)를 사용하여 염료 농도, 염욕의 pH, 염색시간에 따른 염색속도를 구하여 이 저온염색용가 염색에 미치는 영향을 분석한 결과를 다음과 같이 요약한다. 1. pH 7에서 K-1의 농도가 증가할수록 무첨가구에 비해 흡진율은 증가 하였으며, K-1의 농도가 3% o.w.f. 이상에서는 증가의 경향이 둔화되었다. 2. pH 5에서도 무첨가보다 K-1의 첨가구에서 높은 흡진율을 보였으며, pH 7의 5$0^{\circ}C$ 첨가구가 pH 5, 5$0^{\circ}C$의 무첨가구보다 확산성은 높게 나타났다. 3. 염료 농도별로 볼 때 pH 7과 pH 5에서 모두 K-l 첨가구에서는 무첨가구보다 흡진율이 클 뿐만 아니라 염료 농도에 따른 흡진율 감소가 적게 일어났다.

• 펄프종이기술
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• 제42권5호
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• pp.37-46
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• 2010

This study was carried out to develop new application field and obtain the basic data of mixed paper with wood pulp and chitosan fiber for producing functional paper. Two types of wood pulp, such as SwBKP and HwBKP, were mixed with chitosan fiber. Physical and optical properties, water vapor absorption, air permeability, antibacterial activity and ash were measured. And the surface morphology of manufactured paper was observed using SEM. The results are as follows. It was revealed that density, breaking length, burst index, tear index, folding endurance and brightness were reduced but water vapor absorption and air permeability were on the rise in the structural view of SwBKP according to increasing the chitosan fiber ratio. Those HwBKP added chitosan fiber were great not only in the strength but also water vapor absorption and air permeability except for brightness. The water vapor absorption was lower and the air permeability was higher in the HwBKP added various chitosan fiber ratios than those with no chitosan fiber. It is estimated that these properties were related with various mixed rate of chitosan fiber. Particularly, air permeability was strongly dependent on the mixed rate of chitosan fiber. The chitosan fiber has superior antibacterial property, comparing with wood fiber. Adding chitosan fiber to the wood pulp was found to have an excellent antibacterial activity, more than 90%. The ashes were determined within 0.5%. Special bonds between chitosan fiber and wood pulp was observed by SEM and it means that the chitosan fiber were combined equally in the interior of wood pulp. In conclusion, mixing wood pulp with chitosan fiber can not only improves the quality of paper but also extend the usage of paper as a functional paper by using inherent property of chitosan. After all, production of functional paper added chitosan fiber is expected for new valuable industry of paper.