• Magazine of the Korea Concrete Institute
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• v.1 no.2
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• pp.23-30
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• 1989

• 레미콘
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• no.6 s.12
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• pp.11-20
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• 1987

• Korean Journal of Agricultural Science
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• v.22 no.1
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• pp.1-10
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• 1995

All agricultural crops and products should be cultured, harvested, handled and processed by the proper mechanical methods in the mechanized farming systems. Agricultural crops might be injured or deformed through various working stages due to static or dynamic forces of machines. Mechanical forces had to be applied with proper degrees to the agricultural crops in incoincidence with properties of crops without any damage of crops so as to increase the work efficiency qualitatively. Knowledges of mechanical properties of agricultural materials are essential to prevent of agricultural crops in relation with mechanical farming system. This study was carried out to examine and analyze the creep behavior of the rice stalk on growing and harvesting periods by mechanical model with computer measurement system in radial directional compressive force and bending force. The creep behavior of the rice stalk could be predicted precisely and its results approached closely to the measured values. The creep behaviors were increased greatly with increase of compressive force, namely, the steady state creep behavior occurred at the force less then 25N and the logarithmic creep behavior at the force bigger than 30N. The instantaneous elastic modulus $E_o$ and the retardation time ${\tau}_K$ were increased together with increase of applied forces, meanwhile the retarded elastic modulus $E_r$ and viscosity ${\eta}_v$ were decreased with increase of applied forces in mechanical model being expected the creep behavior in relation with the level of applied forces, which was well explained that the rice stalk might be visvo-elastic material. In the creep test along the stalk portion with compressive force and bending force, the intermediate portion showed greatest values and also the lower portion showed the least values, which implied that the intermediate portions of rice stalk were very weak. The steady state creep behavior occured at the intermediate portion and the upper portion in the rice stalk at the compressive force larger than 25.0N, which showed the possibility of injury due to external forces.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.4
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• pp.143-148
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• 1983

A general numerical procedure for the time dependent analysis of concrete structures due to the effects of creep, shrinkage, aging of concrete and temperature variations is presented. Creep is represented by a superposition integral, and is considered as dependent on concrete age and temperature. An efficient numerical formulation of creep is possible through the use of a special exponential form of specific creep function which forms the kernel function of the superposition integral. The accuracy of this method is demonstrated by a numerical example.

• Journal of Biosystems Engineering
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• v.20 no.2
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• pp.133-140
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• 1995

The model of Poisson's ratio of the fruits was developed on the basis that the cylindrical fruits specimen became the barrel shape when it was being compressed. The model of the corrected creep compliance of the fruits was developed under considering the developed model of Poisson's ratio. Both of the Poisson's ratio and the corrected creep compliance of the samples showed the nonlinear viscoelastic behavior. Those models were a similar form, but their coefficients of the model were different, and these behaviors of the samples were well described by the nonlinear model as a function of the initial stress and time. Effects of storage condition and period on the Poisson's ratio of the samples were investigated, and comparisons between the corrected and the uncorrected creep compliance of the samples were made.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.981-986
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• 1995

이 논문의 목적은 축대칭 프리스트레스트 콘크리트 탱크의 시간의존성 유한요소해석법을 제안하는 것이다. 오늘날 PC구조물은 교량, 포장판, 해상구조물, 원자로 격납구조물, 대규모 액체저장용 탱크 등 여러 형태의 구조물에서 그 사용 예를 쉽게 찾아볼 수 있다. 특히 본 논문에서 고려하고자 하는 압력창기나 액체 저장용 탱크의 경우 유체압력 등의 내부압력에 의해 발생하는 균열은 프리 스트레스를 도입함으로써 매우 효과적으로 제어할 수 있기 때문에 상당히 유리한 구조형식이 된다. 그러니 이러한 구조물의 해석과 설계에 있어서 균열의 예측과 더불어 콘크리트의 크리이프, 건조수축 및 PC강재의 리락세이션 등과 같은 시간 의존성 변형으로 인한 프리스트래스의 손실, 여러 단계의 긴장력을 도입함으로써 발생하는 순간변형인 탄성단축 및 이로 인한 긴장력 감소 등을 정확히 계산하는 일은 매우 복잡하고 어려운 일이다. 본 논문에서는 크리이프, 건조수축 및 리락세이션 등과 같은 시간의존성 변형과 순차적으로 다단계의 프리스트레스 도입으로 인한 순간변형 및 탄성단축의 영향을 고려한 축대칭 PC 탱크 구조물의 시간에 따른 거동 및 긴장력의 변화를 유한요소법을 적용하여 해석할 수 있는 해법체계를 정리하고 이를 전산 프로그램화하여, 축대칭 PC탱크 구조물의 시간 의존성 거동에 대한 보다 정밀한 해석을 수행하였다.

• Journal of Biosystems Engineering
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• v.21 no.2
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• pp.191-197
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• 1996

Allowable stacking duration of the corrugated fiberboard boxes being widely used for packaging fruits and vegetables was analyzed by the creep behavior and the cumulative load correction factor for the boxes. The stacking boxes were assumed to be stored at a nearly constant temperature and relative humidity condition. When the stacking duration was short period, the stacking height determined by two methods showed a little difference between them, but almost no difference was shown as the stacking duration was longer. Allowable stacking duration was rapidly decreased with the increase of static load applied on the stacking boxes, and allowable stacking duration of Box A was estimated the longer than that of Box B. A model of allowable stacking duration for the corrugated fiberboard box was developed as a function of the stacking load and the ambient relative humidity.

• Proceedings of the Korean Fiber Society Conference
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• 1998.10a
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• pp.348-351
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• 1998

토목 및 건설용으로 사용되는 토목섬유 중 지오그리드는 경사와 위사 방향으로 10~100mm 크기의 aperture가 형성된 격자 구조를 갖는 것을 지칭하며 1980년대에 개발되어 토목공사에 적용되어 왔으며, 강도가 요구되는 방향으로 높은 인장강도를 지님으로써 도로의 기초 지반과 포장층의 보강, 제방과 사면의 보강 및 보강토 옹벽공사용 둥에 사용되고 있다. (중략)

• Journal of Biosystems Engineering
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• v.20 no.4
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• pp.323-332
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• 1995

The horizontal compression test of some selected corrugated fiberboards was performed to determine the cushioning properties of them. Creep behavior of the corrugated fiberboard boxes, which have been widely used in rural area for packaging fruits and vegetables, was tested. The flute crushing stress of the corrugated fiberboard depended upon mainly the basic weight of the corrugated medium, comparing with the combined basic weight of corrugated fiberboard. When moisture content of the corrugated fiberboards was increased about 8% (d.b.), the flute crushing stress of them was decreased at the rate of 44%~64%. The cushion factor of the sample fiberboards showed much higher value at the lower moisture content of them. These trends appeared to be more obvious at the lower applied stress levels. Also, the cushion factors of the double wall corrugated fiberboards(DW) were observed to be little higher than those of the single wall corrugated fiberboards(SW). The creep behavior of the sample boxes was found to be highly moisture and static load dependent. The creep behavior of the corrugated fiberboard boxes could be well analyzed by the asymptotic slope derived from the creep model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.771-781
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• 1994

The heat generation of cement causes the internal temperature rise and volume change at early age, particulary in massive concrete structures. As the results of the temperature rise and restraint conditions, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction in order to control the cracks developed in mass concrete. In case of young concrete, creep effect by the temperature load is larger than that of old concrete. Thus, the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This paper is concentrated on the development of a finite element program which is capable of simulating the temperature history and the thermal stress considering creep and the modified elastic modulus due to inner temperature change and maturity. The analytical results in the inner parts highest important to control cracks are in good agreement with experimental data. Therefore this study may provide available method to control the cracks.