• International Journal of Oral Biology
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• 제32권4호
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• pp.143-151
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• 2007

This study was conducted to investigate the preventing effects of OPB (Rehmannia glutinosa Libosch and Eleutherococcus senticosus Max extracts) and combined OPB/Calcium therapy on bone loss in ovariectomized rats. Sixty Sprague Dawley rats of 12-week-old were divided into eight groups: OVX (ovariectomized), OPBL (OPB 50 mg/kg), OPBM (OPB100 mg/kg), OPBH (OPB 200 mg/kg), OPBL/CAL(OPBL+CAL), OPBM/CAL (OPBM+CAL), OPBH/CAL (OPBH+CAL) and CAL (Calcium citrate 88.33 mg/kg+1$\alpha$, 25-dihydroxy-vitamin $D_3$ 33.33 IU/kg). Bone mineral density (BMD), bone mineral content (BMC), bone strength indices and cortical thickness were analyzed by peripheral quantitative computerized tomography (pQCT). pQCT scanning showed that OVX induced a significant decrease in trabecular bone mineral density and bone mineral content in the proximal tibia $(-36.4\pm2.4%,\;-21.8\pm12.7%)$. These decreases were significantly prevented by the administration of OPBM and OPBM/CAL. Cortical BMD and BMC of tibia were slightly enhanced by OPB and OPB/CAL. However there was no significant difference between OVX and OPB, OPB/CAL treated group. Bone strength indices and cortical thickness were not significantly different. Our results suggest that OPB and combined OPB/Calcium therapy are effective in preventing the development of bone loss induced by ovariectomy in rats.

• 한국강구조학회 논문집
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• 제13권2호
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• pp.177-189
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• 2001

현대 건축물들의 고층화 추세에 따라 등장한 구조물의 공사비 절감을 위한 한 방법으로 H형강보의 웨브 부분에 설비용 덕트와 배관류 등을 관통시키기 위하여 개구부를 두는 유공보를 자주 사용하고 있다. 본 연구에서는 현재 유공보의 설계에 사용되고 있는 기존의 강도식들의 문제점을 살펴보고 소성 붕괴 매커니즘에 기초를 둔 보다 합리적인 강도식을 제안하고자 한다. 제안식은 기존의 강도식들과 비교하여 볼 때 단순하며 이해하기 쉽다. 제안식의 검증은 과거에 이루어진 연구 결과들을 사용하여 평가되어 졌다. 이들 연구결과들을 근거로 제안식의 극한 강도를 비교해 볼 때 현재 실무에서 사용되어 지고있는 강도식들보다 합리적인 결과 값을 기대할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.373-376
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• 2005

The discharge of fly ash that is produced by coal-fired electric power plants is rapidly increasing in Korea. The utilization of fly ash in the raw materials would contribute to the elimination of an environmental problem and to the development of new high-performance materials. Fly ash consists of a glass phase. As it is produced from high temperature, it is a chemically stable material. Fly ash mostly consists of $SiO_{2}$ and $Al_{2}O_{3}$, and it assumes the form of an oxide in the inside of fly ash. Because this reaction has not broken out by itself, it is need to supply it with additional $OH^{-}$ through alkali activators. We used alkali activators for supplying it with additional $OH^{-}$. This paper concentrated on the strength development according to the kind of chemical activators, the curing temperature, the heat curing time.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.321-324
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• 2004

The discharge of fly ash that is produced by coal-fired electric power plants is rapidly increasing in Korea. The utilization of fly ash in the raw materials would contribute to the elimination of an environmental problem and to the development of new high-performance materials. So it is needed to study the binder obtained by chemically activation of pozzolanic materials by means of a substitute for the exiting cement. This paper concentrated on the strength development according to the kind of chemical activators, the curing temperature, the heat curing time. Also Scanning electron microscopy and X-Ray diffraction analysis show what the reaction products of the alkali activated fly ash are.

• Geomechanics and Engineering
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• 제20권6호
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• pp.505-516
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• 2020

In recent years, Nano-technology significantly invaded the field of Geotechnical engineering, particularly in soil stabilisation techniques. Stabilisation of weak soil is envisioned to modify various soil characteristics by the addition of natural or synthetic materials into the virgin soil. In the present study, laboratory experiments were executed to investigate the influence of nano-silica particles in the consistency limits, compressive strength of the soft clay blended with cement. The results revealed that the high compressibility behaviour of soft clay modified to medium-stiff condition with fewer dosages of cement and nano-silica. The mechanism behind the strength development is verified with the previous researches as well as from Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction test (XRD) and Scanning Electron Microscopy (SEM) analysis. Based on the results, the presence of nano-silica in soft clay blended with cement has a positive effect on the behaviour of soil. This technique proves to be very economical and less detrimental to the environment.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2006년도 PAN PACIFIC CONFERENCE vol.2
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• pp.433-440
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• 2006

A fiber processing method, which might be an alternative for conventional refining process, was introduced. The method consists of repetitive, gentle, mechanical impacts on fiber, and ensued fiber uncurling process. This method was very effective for OCC and BCTMP for increasing WRVs (water retention value) while keeping fiber lengths from shortening. For OCC and BCTMP, gentle mechanical impacts on fibers using Hobart mixer increased breaking lengths and tear strengths simultaneously at fast drainage level, and straightening fibers using kady mill increased those strength properties further. For SwBKP and HwBKP, only mechanical impacts using the mixer were effective on increasing tensile and tear strength at fast drainage, but not kady mill treatment. The strength increases of BCTMP by this alternative fiber processing method were exceptionally high. An extensive engineering development should be followed to actualize this fiber processing mechanism in an energy-effect way.

• 펄프종이기술
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• 제43권5호
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• pp.34-42
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• 2011

A fiber processing method, which might be an alternative for conventional refining process, was introduced. The method consists of repetitive, gentle, mechanical impacts on fibers, followed by fiber uncurling process. This method was very effective for OCC and BCTMP for increasing WRVs (water retention value) while keeping fiber lengths from shortening. For OCC and BCTMP, gentle mechanical impacts on fibers using Hobart mixer increased breaking lengths and tear strengths simultaneously at fast drainage level, and straightening fibers using kady mill increased those strength properties further. For SwBKP and HwBKP, only mechanical impacts using the Hobart mixer were effective on increasing tensile and tear strength at fast drainage, but there were no further increase by kady mill treatment. The strength increases of BCTMP by this alternative fiber processing method were exceptionally high. An extensive engineering development should be followed to actualize this fiber processing mechanism in an energy-effect way.

• 한국지반공학회논문집
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• 제20권6호
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• pp.119-126
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• 2004

본 논문에서는 현장계측을 통해 관측된 소일네일링 벽체의 거동을 분석하였다. 연구의 주요내용으로는 인발시험을 통해 산정한 네일과 지반의 경계면에서 전단강도의 발생, 지반의 수평변위, 네일에 발생하는 인장력의 분포 및 경계면에서의 전단강도의 발현 등이다. 특히, 경계면에서의 전단응력 발생 과정 및 전단강도 발현에 대한 심도있는 분석을 실시하였다. 본 연구에서 분석된 자료는 국내 소일네일링의 예비설계 단계시 참고 자료로 활용될 수 있을 것으로 기대된다.

• 한국항공우주학회지
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• 제41권8호
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• pp.625-631
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• 2013

핀풀러의 신뢰도를 몬테카를로 시뮬레이션을 통해서 예측하였다. 예측방법은 응력-강도 간섭 모델에 근거한다. 이 모델은 강도가 응력보다 작을 경우를 고장으로 간주한다. 본 연구에서 강도는 핀을 예정된 거리까지 후퇴시키는데 필요한 에너지로, 응력은 이 핀의 운동을 방해하는데 소요되는 에너지로 간주하였다. 전자는 주로 화약량에 의해 결정되고 후자는 여러 가지 마찰력과 반발방지장치에서 소모되는 에너지에 의존한다. 응력과 강도 변수들은 해석적 성능 모델로부터 계산하였다. 본 연구에서 제시된 방법은 많은 시료가 필요하지 않기 때문에 유사한 종류의 파이로 장치 신뢰도 계산에도 적용될 수 있다.

• Computers and Concrete
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• 제22권4호
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• pp.395-405
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• 2018

In this paper, the performance of post-installed adhesive bonded anchor embedded in concrete is assessed using numerical simulations. This study aims at studying the influence of parameters on the performance of a chemically bonded anchorage system. Non-linear finite element modelling and simulations are carried out by properly using the material properties and phenomenon. Materials parameters such as characteristic length, fracture energy, damage criteria, tension retention and crack width of concrete and interface characteristics are carefully assigned so as to obtain a most realistic behaviour of the chemical anchor system. The peak strength of two different anchor systems obtained from present numerical studies is validated against experimental results. Furthermore, validated numerical models are used to study the load transferring mechanism and damage progression characteristics of various anchors systems where strength of concrete, strength of epoxy, and geometry and disposition of anchors are the parameters. The process of development of strain in concrete adjacent to the anchor and energy dissipated during the course of damage progression are analysed. Results show that the performance of the considered anchorage system is, though a combined effect of material and geometric parameters, but a clear distinction could be made on the parameters to achieve a desired performance based on strength, slip, strain development or dissipated energy. Inspite the increase in anchor capacity with increase in concrete strength, it brings some undesirable performance as well. Furthermore, the pullout capacity of the chemical anchor system increases with a decrease in disparity among the strength of concrete and epoxy.