• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.689-692
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• 2006

The crack of concrete induced by the heat of hydration is a serious problem, particularly in massive concrete structures. In order to control the temperature crack of massive concrete, the selection of appropriate materials like low heat cement, mixture materials, etc. is essential. In tills study, mix proportion using low heat portland cement and lime stone powder was designed and the best mix proportion, B-1, was selected. When bottom slab of the #219 LNG tank in Incheon was constructed, concrete temperature was measured. And thermal stress was analyzed about bottom slab of the LNG tank. As results of the thermal analysis, crack index was 1.60 in bottom slab and satisfied with construction specifications(over 1.0).

• Computers and Concrete
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• 제21권3호
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• pp.279-289
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• 2018

Hydration heat and thermal induced cracking have always been a fatal problem for massive concrete structures. In order to study a massive reinforced concrete wall of a storage tank for liquefied natural gas (LNG) during its construction, two mock-ups of $0.8m{\times}0.8m{\times}0.8m$ without and with metal corrugated pipes were designed based on the actual wall construction plan. Temperature distribution and strain development of both mock-ups were measured and compared inside and on the surface of them. Meanwhile, time-dependent thermal and mechanical properties of the concrete were tested standardly and introduced into the finite-element (FE) software with a proposed hydration degree model. According to the comparison results, the FE simulation of temperature field agreed well with the measured data. Besides, the maximum temperature rise was slightly higher and the shrinkage was generally larger in the mock-up without pipes, indicating that corrugated pipes could reduce concrete temperature and decrease shrinkage of surrounding concrete. In addition, the cooling rate decreased approximately linearly with the reduction of heat transfer coefficient h, implying that a target cooling curve can be achieved by calculating a desired coefficient h. Moreover, the maximum cooling rate did not necessarily decrease with the extension of demoulding time. It is better to remove the formwork at least after 116 hours after concrete casting, which promises lower risk of thermal cracking of early-age concrete.

• 콘크리트학회지
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• 제15권2호
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• pp.108-112
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• 2003

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1205-1210
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• 2004

Cracks in the underground structures are mainly observed due to internal ununiformity of thermal stresses or restraint of structural movement in associate with rapid temperature gradient. Especially, thermal cracks are known to occur easily in a massive structure, but possibility of these depend on the amount of cement applied and ratio of span to height of the structure even though the thickness is less than specification‘s. Thus, this study aims at how to control thermal cracks in a massive subway structure and figures out an optimized construction method and procedure. As results of parametric study for length, height and outer temperature for concrete placement, it is found that hydration heats were not affected by both length and height of concrete placement but thermal stresses were greatly dependent. Most effective ways of controling thermal cracks were to fit a proper ratio of length to height of concrete placement and to decrease temperature of concrete placement as much as possible.

• 한국방재학회 논문집
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• 제6권2호
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• pp.1-7
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• 2006

콘크리트 댐, 원자력발전소 및 항만구조물등의 대형구조물을 시공하기 위해서는 짧은 기간에 막대한 양의 콘크리트를 타설하게 된다. 매스콘크리트 구조물을 시공하는 단계에서 발생되는 수화열은 심각한 온도균열을 발생시켜 본래의 기능수행능력과 사용수명에 있어서 심각한 저하를 초래할 수 있다. 본 연구에서는 매스콘크리트 구조물의 대표적인 예라고 할 수 있는 교대구조물에 대하여 수화열 및 온도응력을 사전해석하고 그 결과를 바탕으로 구조물 성능확보를 위한 온도균열제어대책을 제시하였으며, 제시된 대책을 바탕으로 이루어진 시공현장에서 교대기초부 및 본체부에서의 온도분포와 응력을 계측하고 온도균열 발생양상을 관찰하여 제시된 대책의 타당성을 단계별로 확인하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2004년도 학술.기술논문발표회
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• pp.21-25
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence, to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete (800kgf/$\textrm{cm}^2$) especially for CFT through the data from the real size mock-up.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.458-461
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence. to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete $(800kg/cm^2)$ especially for CFT through the data from the real size mock-up.

• 한국컴퓨터산업학회논문지
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• 제9권3호
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• pp.99-104
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• 2008

매스콘크리트에서 수화열에 의한 응력은 외기온도와 콘크리트의 타설온도에 따라 변하므로 이들의 영향을 고려한 해석이 필요하다. 본 연구에서는 교각의 코핑부를 대상으로 해석을 수행하여 분석하였다. 최대 인장응력은 타설 후 2.75일을 전후하여 표면 모서리부에서 발생하며 균열지수는 계속 증가하여 균열 발생 가능성은 거의 없는 것으로 나타났다. 그리고 계절에 관계없이 콘크리트의 타설온도를 낮추면 수화열에 의한 균열 발생 가능성을 줄일 수 있는 것으로 나타났다. 따라서 콘크리트를 타설하기 전에 타설온도를 낮추기 위한 여러 가지 방안을 강구하면 수화열에 의한 균열을 최소화할 수 있다.

• 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.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 봄 학술발표회 논문집
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• pp.194-200
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• 1993

The objective of this study is to clarify analytically the pullout behavior of axial bars from a footing. The bond stress-slip model obtained from the results by the finite element method as well as the pullout tests in massive concrete was used in order to evaluate the slip of bars from the footing. Also, the process of bond mechanism was taken into consideration on order to express the deterioration of bond stress along bars, The shape and magnitude of bond stress distribution depends upon each loading steps. Using equilibrium equation of axial force, $\tau$-S relationship and $\sigma$s-$\varepsilon$s relationship, the differential equations of each loading steps are derived. Applying both boundary and equilibrium conditions to the equations, the amount of slip could be determined. Calculated values on the basis of proposed method evaluation of the slip of bars have a good agreement with the experimental results.