• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
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• pp.67-72
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• 1992

The heat of hydration of cement causes the internal temperature rise at early age, particulary in massive concrete structures such as a footing of nuclear reactor building or a dam. As the result of the temperature rise and restraint of foundation, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, 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 study is composed of two items. The first, it is to develop a finite element program which is capable of simulating the temperature history in mass concrete. The second, when the thermal stress of mass concrete structures considering creep is calculated by using the modified elastic modulus due to the inner temperature change. It is shown that the analytical results of this study is in comparably good agreement with JCI's analytical results.

• 한국도로학회논문집
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• 제17권3호
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• pp.85-95
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• 2015

PURPOSES : Recently, bonded concrete overlay has been used as an alternative solution in concrete pavement rehabilitation since its material properties are similar to those of the existing concrete pavements. Deteriorated concrete pavements need rapid rehabilitation in order to prevent traffic jams on Korean expressways. Moreover, speedy and effective repair methods are required. Therefore, the use of bonded concrete overlay with ultra-rapid hardening cement has increased in an effort to reopen promptly the expressways in Korea. However, mobile mixer is required for ultra-rapid hardening cement concrete mixing in the construction site. The use of mobile mixer causes various disadvantages aforementioned such as limitation of the construction supply, open-air storage of mixing materials, increase in construction cost, and etc. In this study, therefore, hydration accelerator in-situ mixing on polymer modified concrete produced in concrete plant is attempted in order to avoid the disadvantages of existing bonded concrete overlay method using ultra-rapid hardening cement. METHODS : Bonded concrete overlay materials using ultra-rapid hardening cement should be meet all the requirements including structural characteristics, compatibility, durability for field application. Therefore, This study aimed to evaluate the application of hydration accelerator in-situ mixing on polymer modified concrete by evaluating structural characteristics, compatibility, durability and economic efficiency for bonded concrete overlay. RESULTS : Test results of structural characteristics showed that the compressive, flexural strength and bond strength were exceed 21MPa, 3.15MPa and 1.4MPa, respectively, which are the target strengths of four hours age for the purpose of prompt traffic reopening. In addition, tests of compatibility, such as drying shrinkage, coefficient of thermal expansion and modulus of elasticity, and durability (chloride ions penetration resistance, freezing-thawing resistance, scaling resistance, abrasion resistance and crack resistance), showed that the hydration accelerator in-situ mixing on polymer modified concrete were satisfied the required criteria. CONCLUSIONS : It was known that the hydration accelerator in-situ mixing on polymer modified concrete overlay method was applicable for bonded concrete overlay and was a good alternative method to substitute the existing bonded concrete overlay method since structural characteristics, compatibility, durability were satisfied the criteria and its economic efficiency was excellent compare to the existing bonded concrete overlay methods.

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.511-521
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• 2015

건물외피 발생하는 열교현상은 건물의 단열성능 및 외피의 내구성에 영향을 미치며, 국내의 일반적인 주거형식인 공동주택의 발코니에 있어서 이러한 열교현상은 중요하게 고려되고 있다. 이와 같이 내 외부 발코니 슬래브 사이에서 발생하는 열교현상을 최소화하기 위한 목적으로 열교차단장치가 개발되었으며 다수의 건설현장에서 적용되고 있다. 철근콘크리트 슬래브 벽-슬래브 접합부에 열교차단장치를 적용함으로써 건물의 단열성능을 향상될 수 있으나 풍하중과 같은 양방향의 하중에 의해 열교차단장치 삽입부위가 적합한 구조성능을 확보하고 있는지에 대한 검증이 요구된다. 따라서 본 연구에서는 철근콘크리트 슬래브에 적용된 열교차단장치의 구조성능을 확인하기 위해 변위제어 방식으로 30 싸이클의 반복하중을 가력하였다. 열교차단장치가 삽입된 접합부는 요구되는 구조성능을 확보하며, 최대 모멘트강도, 에너지소산능력, 연성비가 기존의 철근콘크리트 슬래브와 비교하여 향상되는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제37권5호
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• pp.459-473
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• 2011

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.

• Structural Engineering and Mechanics
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• 제47권5호
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• pp.623-641
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• 2013

The fiber-reinforced polymer (FRP) composite panel, with the benefits of light weight, high strength, good corrosion resistance, and long-term durability, has been considered as one of the prosperous alternatives for structural retrofits and replacements. Although with these advantages, a further application of FRPs in bridge engineering may be restricted, and that is partly due to some unsatisfied thermal performance observed in recent studies. In this regard, Kansas Department of Transportation (DOT) conducted a field monitoring program on a bridge with glass FRP (GFRP) honeycomb hollow section sandwich panels. The temperatures of the panel surfaces and ambient air were measured from December 2002 to July 2004. In this paper, the temperature distributing behaviors of the panels are firstly demonstrated and discussed based on the field measurements. Then, a numerical modeling procedure of temperature fields is developed and verified. This model is capable of predicting the temperature distributions with the local environmental conditions and material's thermal properties. Finally, a parametric study is employed to examine the sensitivities of several temperature influencing factors, including the hollow section configurations, environmental conditions, and material properties.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 C
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• pp.1117-1119
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• 1995

Fluoroplastics have been used widely for chemical or electrical facility materials and lubricable engineering structural materials because they have the superior characteristics such as thermal stability, chemical stability, solid lubricity, arc resistance, wearable durability and good sealing property. In this study, PTFE composite materials for the insolation parts of high voltage and current breaker were investigated and estimated.

• 대한금속재료학회지
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• 제49권6호
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• pp.468-473
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• 2011

Determining the residual stress during casting processes is important for evaluating the mechanical properties and strength of materials and to optimize manufacturing conditions. In this study, we propose a field data interface procedure between FDM and FEM in a 3-dimensional space for analyzing the casting process and structural analysis. The casting process was analyzed using FDM and the data of the temperature distribution were converted into a format suitable for FEM analysis to calculate the thermal stress and safety factor by tightening force. The results of the coupled analysis between FDM and FEM showed that casting residual stress is an important factor in predicting life time and evaluating durability.

• 한국도로학회논문집
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• 제15권1호
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• pp.1-9
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• 2013

PURPOSES: The purpose of this study is to evaluate physical properties, durability, fatigue resistance, and long-term performance of poly-urethane concrete (PU) which can be possible application of thin layer on long-span orthotropic steel bridge and to check structural stability of bridge structure. METHODS : Various tests of physical properties, such as flexural strength, tensile strength, bond strength and coefficient of thermal expansion tests were conducted for physical property evaluation using two types of poly urethane concrete which have different curing time. Freezing and thawing test, accelerated weathering test and chloride ion penetration test were performed to evaluate the effect of exposed to marine environment. Beam fatigue test and small scale accelerated pavement test were performed to assess the resistance of PU against fatigue damage and long-term performance. Structural analysis were conducted to figure out structural stability of bridge structure and thin bridge deck pavement system. RESULTS: The property tests results showed that similar results were observed overall however the flexural strength of PUa was higher than those of PUb. It was also found that PU materials showed durability at marine environment. Beam fatigue test results showed that the resistances of the PUa against fatigue damage were two times higher than those of the PUb. It was found form small scale accelerated pavement test to evaluate long-term performance that there is no distress observed after 800,000 load applications. Structural analysis to figure out structural stability of bridge structure and thin bridge deck pavement system indicated that bridge structures were needed to increase thickness of steel deck plate or to improve longitudinal rib shape. CONCLUSIONS: It has been known that the use of PU can be positively considered to thin layer on long-span orthotropic steel bridge in terms of properties considered marine environment, resistance of fatigue damage and long-term performance.

• 한국건설순환자원학회논문집
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• 제2권4호
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• pp.297-306
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• 2014

Recently nano-materials are gaining more importance in the construction industry due to its enhanced energy efficiency, durability, economy, and sustainability. Nano-silica addition to cement based materials can control the degradation of the fundamental calcium-silicate-hydrate reaction of concrete caused by calcium leaching in water as well as block water penetration and therefore lead to improvements in durability. In this paper, the influence of synthesized nano silica from locally available rice husk on the mechanical properties and corrosion resistant properties of OPC (Ordinary Portland Cement) has been studied by conducting various experimental investigations. Micro structural properties have been assessed by conducting Scanning Electron Microscopy, Thermo gravimetry and Differential Thermal Analysis, X-Ray Diffraction analysis, and FTIR studies. The experimental results revealed that NS reacted with calcium hydroxide crystals in the cement paste and produces Calcium Silicate Hydrate gel which enhanced the strength and acts as a filler which filled the nano pores present in concrete. Hence the strength and corrosion resistant properties were enhanced than the control.

• 한국구조물진단유지관리공학회 논문집
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• 제17권3호
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• pp.108-117
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• 2013

석탄화력 발전의 부산물 중에서 플라이애쉬는 콘크리트 혼화재료로서 많은 공학적 장점을 가지고 있으므로 다양하게 활용되고 있다. 그러나 바텀 애쉬를 포함한 나머지 부산물 등은 주로 매립되어 공학적 활용성이 떨어진다. 본 연구에서는 매립된 부산물인 매립회 (PA: Pond Ash)를 이용하여 시멘트 모르타르를 제조하였으며, 매립회 시멘트 모르타르의 공학적 특성을 평가하였다. 이를 위해 두 매립지로부터 유연탄 및 무연탄 매립회를 채취하였으며, 2가지 물-시멘트 비 (0.385, 0.485)와 3가지 잔골재 치환률 (0%, 30%, 60%)을 고려하여 시공성, 역학성능, 내구성능을 평가하였다. 흡수율이 높은 무연탄 매립회의 경우, 적절한 시공성, 우수한 강도발현과 내구성능을 확보하였는데, 매끈한 표면과 내부의 풍부한 자유수로 인해 조직구조가 치밀한 시멘트 모르타르가 제조되었기 때문이다. 매립회 중에서도 우수한 성능을 가진 무연탄 매립회의 경우 일반 잔골재의 성능을 확보하고 있으므로, 자원의 재활용이 가능하리라 판단된다.