• Journal of the Korean Wood Science and Technology
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• v.37 no.4
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• pp.330-339
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• 2009

The material properties of Cedar (Cryptomeria japonica) were evaluated according to heat treatment conditions. The special focus was made on the color control of cedar wood by heat treatment. The difference of color between sapwood and heartwood could be reduced by heat treatment at a temperature above $170^{\circ}C$. Long heating time was more effective in reducing the difference. The Equilibrium Moisture Content (EMC) of heat-treated wood was as low as 50 percent. The result obviously indicates that heat-treated wood is more dimensionally stable in the change of moisture condition than the control. The heat-treated wood was also effective in increasing the durability against wood rotting fungi. However, more study is required to develop heat treatment as an environmentally-friendly technology for wood preservation without chemical. The mechanical properties of heat-treated wood showed relatively higher performance than the control in general. Meanwhile the dramatic decrease in impact bending stress due to the loss of ductility may limit uses of heat-treated wood in certain cases. There were no significant changes in microscopic structure which may cause changes in mechanical properties. Further study on the chemical analysis of heat-treated wood is needed to scrutinize the causes of changes of material properties.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.109-117
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• 2022

There has been an increasing number of studies on photovoltaic energy generation system in an offshore site with the largest energy generation efficiency, as increasing the researches and developments of renewable energies for use of offshore space and resources to replace existing fossil fuels and resolve environmental challenges. For installation and operation of floating photovoltaic systems in an offshore site with harsher environmental conditions, a stiffness of structural members comprising the total system must be reinforced to inland water spaces as dams, reservoirs etc., which have relatively weak condition. However, there are various limitations for the reinforcement of structural stiffness of the system, including producible size, total mass of the system, economic efficiency, etc. Thus, in this study, a floating breakwater is considered for reducing wave loads on the system and minimizing the reinforcement of the structural members. Wave reduction performances of floating breakwaters are evaluated, considering size and distance to the system. The wave loads on the system are evaluated using the higher-order boundary element method (HOBEM), considering the multi-body effect of buoys. Stresses on structural members are assessed by coupled analyses using the finite element method (FEM), considering the wave loads and hydrodynamic characteristics. As the maximum stresses on each of the cases are reviewed and compared, the effect of floating breakwater for floating photovoltaic system is checked, and it is confirmed that the size of breakwater has a significant effect on structural responses of the system.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.273-280
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• 2015

Equivalent Single-Degree-of-Freedom(SDOF) analysis, most used for blast-resistant design, does not consider the effects of gravity load on the performance evaluation of blast resistance of structural members. However, since there exists gravity load on columns and walls of structures, the blast resistance of structural members should be evaluated considering gravity load on them. In this paper, an approach to reflect the gravity load effects on the equivalent SDOF analysis for dynamic blast response of structural members is proposed. For this purpose, the parametric studies using finite element analysis were performed by varying maximum blast load, blast load duration, and gravity load with constant the resistance and natural period of a structural member. The finite element analysis results were compared with the equivalent SDOF analysis results and the blast response of the structure member was estimated by conducting finite element analyses for various gravity loads. Finally, a graphical solution for ductility of a structural member with the variables of blast load, gravity load and structural member properties was developed. The blast response of structural members under gravity load could be estimated reasonably and easily by using this graphical solution.

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.63-74
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• 2006

During the construction of circular underground pipe, the non-proper compaction along the pipe and the decrease of compaction efficiency have been the main problems to induce the failure of underground pipe or facility. The use of CLSM (controlled low strength materials) should be one of the possible applications to overcome those problems. In this research, the full-scaled field test and the numeric analysis using PENTAGON-3D FEM program were carried out for three different cases on the change of backfill materials, including the common sand, the soil from construction site, and the CLSM. From the full-scaled test in field, the use of in-situ CLSM as backfill materials reduced the vertical and lateral deformation of the pipe, as well as the deformation of the ground surface. The main reason for reducing the deformation would be the characteristics of the CLSM, especially self-leveling and self-hardening properties. The measured earth pressure at the surround of the corrugated pipe using the CLSM backfills was the smaller than the other cases, and the absolute value was almost zero. Judging from the full-scaled field test and FEM analysis, the use of CLSM as backfill materials should be one of the best choices reducing the failure of the underground pipes.

• Geotechnical Engineering
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• v.12 no.6
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• pp.185-198
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• 1996

EPS is increasingly used as a filling material in soft ground. The beneficial effects of the use of EPS derive from minimizing the stress increment, which, in turn, increases the bearing capacity and reduces the settlement. EPS can also be used as a backfill material for retaining walls and abutments to reduce the horizontal earth pressure. However, there is no rational application for the selection of the EPS fill which is essential to the selection of the filling configuration and the settlement calculation. In this paper, therefore, the nonlinear numerical model developed from the results of triaxial compression tests is applied to the construction of EPS and verified through the comparison between the prediction and in-situ measurements.

• Geotechnical Engineering
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• v.12 no.6
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• pp.163-184
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• 1996

In this study, physical and geotechnical properties of the light weight mixed soil( weathered granite soil mixed with small pieces of waste EPS) were analyzed by laboratory experiments to examine its suitability for backfill materials of the reinforced-earth walls. Friction characteristics of geogrid-light weight sized soil were also investigated by performing the pullout tests for two types of geogrids having different flexural rigidity. Also a procedure was proposed to evaluate friction strength between geogrid and light weight miffed soil by using a stress-strain relationship of the orthotropic composite material subjected to both longitudinal and vertical loadings. By the procedure proposed in this study, values of the calibration coefficients ul and uf applicable for the evaluation of friction strengths between two types of geogrids and light weight mixed soils were further presented.

• Journal of the KSME
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• v.16 no.4
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• pp.41-48
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• 1976

재료의 피로문제에 대해서는 꽤 오래 전부터 많은 연구가 이루어져왔고, 피로의 현상파악에서부 터 피로이론의 구명, 나아가서는 실제문제로서의 피로설계, 피로수명예측 등에 기여한 업적은 아 주 크다 하겠다. 그러나 종래의 피로문제연구의 방향이, S-N 곡선에서 얻어지는 피로한계강도 (더 정확한 표현으론 피로파괴한계강동)에 바탕을 두고, 정력확적인 설계관례인 안전계수의 도입 을 빌려, 피로강도를 실용화할려는 선에서 이루어져 왔다고 보겠다. 재료의 피로한계강도란, 그 정의로 미루어, 다분히 정적으로는 극한강도 또는 피로강도의 개념에 견주어 질 수 있는 공칭응 력으로써 탄성학적으로 해석될 수도 없고, 다만 탄역성이론의 개념을 바탕으로 근사해석례만이 허용되고 있을 뿐이다. 재료에는 소위 평활재이건 절결재이건 간에 또 검출여부에 관계없이, 내외 부에 대소각종의 결함이나 역학적 불연속부가 잠재해있음은 이미 공지의 사실이며, 이들 결합, 불 연속부등이 외하중하에서 응분의 응력집중원이 되어 재료를 전반적인 파괴로 몰고 갈 수 있다 함 도, 또한 이러한 역학적거동이 피로파괴에 까지 확장해석될 수 있을 것이란 것도 이미 잘 알려져 있는 터이라 하겠다. 재료내외부의 제결합을 응력집중이 극대인 crack로 대체해서 외하중하에서 의 응력장거동을 해석한 선형탄성파괴역학(LEFM)은, 바로 이러한 실제재료의 강도설계에 보다 큰 정확성을 부여한 방법론적 학문이라 하겠고, 나아가서는 재료의 파괴기구를 파헤치는데 진일 보적인 역학적인 수법이라 하겠다. 취성파괴, 연성파괴에 바탕을 둔 파괴역학(LEFM)을 피로파괴 에 적용시키는 데는 상당한 문제점들을 수반할 것임은 충분히 인지되나, 제한된 경계조건하에서 의 적용 예는 종래의 어떤 방법에 의한 것 보다도 피로강도설계, 안전사용 피로수명예측 등에 획기적인 진전을 보여주고 있다. 파괴역학은 crack 재의 강도학이고, 더 구체적으로 음력학대계수 (stress intensity factor) K 또는 이와 연연되는 parameter 인 strain energy release rate(G), crack-tip plactic zone size r$_{p}$,.rho., crack-tip opening displacement .phi., strain intensity 등을 쓰는 재료강도학이기 때문에, 이 수법을 피로파괴에 적용시킴은, 종래의 공칭응력으로 피로 문제를 다루던 방법과는 판이하다 하겠다. 본고에선 파괴역학의 관점에서 피로구열의 안정성장을 논하고, 과거 10여년간의 피로 crack문제에 대한 연구방법, 실험방법 등을 소개하는 방향으로 고 를 진행시켜 나가겠다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.117-124
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• 2015

Currently, Eco-friendly construction materials are widely utilized for reducing $CO_2$ emission in construction. Furthermore various engineering fibers are also added for improving a brittle behavior in concrete. In the paper, concrete specimens with 10% and 20% replacement ratio with RHA (Rice Husk Ash) are prepared, and engineering behaviors in RHA and OPC concrete are evaluated with different addition of coconut fiber from 0.125~0.375% of volume ratio. Several basic tests including compressive strength, tensile strength, flexural strength, impact resistance, and bond strength are performed, and crack width and deflections are also measured in flexural test. RHA is evaluated to be very effective in strength development and 0.125% of fiber addition leads significant improvement in tensile strength, ductility, and crack resistance. RHA and coconut fiber are effective construction material both for reutilization of limited resources and performance improvement in normal concrete.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.39-43
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• 1995

대형 상용차용 내연기관에서 방출되는 소음의 음압 레벨은 경우에 따라 140dBA 이상으로 환경소음 배출규제에 부합되는 배출 소음을 위하여는 소음기의 적절한 설계가 필요하다 하겠다. 소음기는 방출 소음을 저감시키는 기본적인 작용 이외에 엔진의 효율을 저하시키는 배압(back-pressure) 상승의 효과를 동반할 뿐만 아니라 차체에의 장착을 위하여 크기와 무게의 제약을 받는다. 따라서 소음기는 설계자의 경험과 과거에 사용되어 온 소음기에 대한 이해, 소음기를 구성하는 단위 요소에 대한 음향학적 해석이론, 제작 과정에서의 경험과 튜닝 등에 바탕을 두고 설계되어져 왔다. 본 연구에서는 대형 상용차에 장착되는 기존 소음기 구성요소의 투과 손실(Transmission Loss: TL)을 전달 행렬법으로 해석하여 음향학적 특성을 규명하고 개별 소음기 요소에 대한 기존의 연구 결과를 바탕으로 공명기와 다공 요소를 이용하여 기존 소음기를 재설계함으로써 배출 소음의 저감을 이루어 나간 과정을 소개하고 이를 적용 사례를 중심으로 살펴보고 있다. 소음기의 설계를 위하여 고려할 수 있는 음향학적 요소는 그 기능과 형태면에서 다양하나 본 연구에서는 대형 상용차용 소음기에 주로 사용 가능한 공명기와 다공관을 주된 설계요소로 생각하였다. 공명기는 공명 주파수 대역의 소음을 저감하는 역할을 하므로 일정한 엔진 회전수 하에서 엔진의 방출 소음중 폭발 성분에 의한 소음을 줄이는데 효과적으로 사용될 수 있지만 가속 주행시에는 회전수(rpm)의 변화에 따라 폭발 주기가 변화하게 되므로 공명기의 설계에 주의를 기울여야 한다. 내연 기관용 소음기에 빈번하게 쓰이는 다공 요소의 해석 방법으로는 Sullivan[1], Kim and Yoon[2] 등의 분할 접근 방법(Segmentation approach)과 Jayaraman and Yam[3], Munjal[4], Peat[5] 등의 연성 제거 방법(Decoupling Approach)등이 제시되었고 평면파 영역에 한하여 해서되어져 왔다. 본 논문에서는 분할 접근 방법(Segmentation Approach)을 이용하여 다공 요소로 이루어진 소음기를 해석하는데 적용하였다.

• Composites Research
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• v.17 no.3
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• pp.29-37
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• 2004

The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube. The outboard main blade, flexbeam and torque tube are all assumed to be an elastic beam undergoing flap bending, lead-lag bending, elastic twist and axial deflections, which are discretized into beam finite elements. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory is used for aerodynamic computation. The finite element equations of motion for beams are obtained from Hamilton's principle. The p-k method is used to determine aeroelastic stability boundary. Numerical results are presented for selected bearingless rotor configurations based on the lay-up of laminae in the flexbeam and pitch links location. A systematic study is made to identify the importance of the stiffness coupling terms on aeroelastic stability for various fiber orientation and for different configuration.