• 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.

• 대한토목학회논문집
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• 제34권3호
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• pp.755-761
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• 2014

콘크리트의 크리프와 건조수축 변형에 대한 내적 혹은 외적 구속은 크리프 발생 응력조건을 변화시키며 이에 따라 크리프 변형의 발생은 응력변화에 종속적으로 변화한다. 시간이력 하중을 받는 크리프 거동문제로서 이해되는 이러한 크리프 거동현상의 수학적 모델링은 일반적으로 재하시의 콘크리트 재령과 물성값 및 하중이력을 기본 구성인자로 고려하여 시간적분 혹은 점증적 형태로 유도되었다. 본 논문에서는 시간이력하중을 받는 크리프 모델 가운데 단일 크리프 곡선을 사용하는 초기 크리프 모델인 평행 크리프 법의 단순성을 고려하여 이 방법이 갖는 단점과 한계성을 극복하고 성능을 개선한 평행 크리프 법을 유도하였다. 유도된 크리프 모델의 성질을 분석하고 예측 성능을 검증하기 위한 목적으로 원통형 콘크리트 공시체를 제작하고 시간이력 하중 하의 크리프 실험을 수행하였다. 끝으로, 콘크리트 공시체의 크리프 변형으로 인한 초기하중의 변화가 공시체의 재령에 따른 거동에 미치는 영향정도를 실험을 통해 분석하였으며, 크리프 시험기의 스프링계수를 측정하여 이로 인한 실험오차를 보정하였다.

• 대한치과기공학회지
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• 제42권3호
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• pp.208-212
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• 2020

Purpose: This study aimed to analyze the shrinkage and expansion strain of ultraviolet (UV)-cured resin according to the wavelength of the light source and compare the shrinkage and expansion. Methods: We prepared the mold with according to the ISO 4049 specimen. The size of the circle in the mold was prepared with a height of 6.02 mm and a diameter of 4 mm. UV-curable resin for three-dimensional (3D) printing was injected into the circular mold. The control group was irradiated with a wavelength of 400~405 nm using UV-curing equipment (400 group), and the experimental group was irradiated with a wavelength of 460~465 nm (460 group). Both groups were produced ten specimens. The produced specimen was first measured with a digital micrometer. After the first measurement, the specimen was immersed in a constant temperature water bath for 15 days, after which the second measurement was performed, and the third measurement was taken after 30 days. The measured values were analyzed using the independent sample t-test (α=0.05). Results: In the non-immersion water tank, the contraction was 0.9% in the 400 group and 1.3% in the 460 group. In the constant temperature bath, the expansion was high at -0.4% in the 400 group for 15 days, and the smallest expansion was -0.03% for the 400 group for 30 days. There were significant differences between the two groups (p<0.05). Conclusion: The 400 group had a lower UV resin specimen strain than the 460 group. Therefore, it is recommended to use the wavelength required by the UV-curing resin.

• 동력기계공학회지
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• 제5권3호
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• pp.56-63
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• 2001

A slitter is a sort of machinery to cut sheet materials in rolls continuously in the longitudinal direction. Recently slitter line users have requiring higher quality and precision in products in addition to high productivity. A finite element analysis has been performed to investigate the effect of processing factors on shear planes in the slitting of Shrinkage Band(S,K.B.). For the analysis, Hot-dip 55% aluminum-zinc alloy-coated steel sheets and coils(SAZCC) is selected as a material. The results obtained are that deformation was concentrated along the very narrow zone and the maximum slitting load decreases by increasing the knife clearance. Also effective strain decreases according to the clearance increases.

• 콘크리트학회논문집
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• 제16권5호
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• pp.725-731
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• 2004

A field test program was conducted for the newly placed concrete pavement of US Interstate Highway 10 between March 26th and 28th, 2003. The test section was located between Van Horn and Sierra Blanca in Hudspeth County approximately 130 km east of El Paso, Texas. The main objective of the test was collecting moisture-related data to validate the models of effective curing thickness, evaporation rate, and moisture-based maturity. Effect of moisture loss on drying shrinkage strain was studied using additional test instrumentation.

• 콘크리트학회논문집
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• 제11권5호
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• pp.21-31
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• 1999

The companion paper presents an analytical model to predict behaviors of PSC-Beam bridges according to continuity of spans. This paper aims at providing several examples of its application to PSC-Beam bridge. In this regard, many uncertainties affecting to the continuity of spans (such as the ultimate shrinkage strain of slab and girders, the prestressing creep of girders, and the time adopting prestressing force) are analysis in detail. Moreover, to increase the serviceability and to remove th inherent structural defects including the cracking at interior supports, a necessity for the parametric studies of PSC-Beam bridges reflecting the construction sequence is emphasized.

• Computers and Concrete
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• 제9권5호
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• pp.357-374
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• 2012

The aim of this paper is to develop a procedure able to calculate the long-term stress and strain patterns in modern prestressed composite structures which are largely influenced by creep and shrinkage and whose final static configuration is the result of many phases of loading and restraints conditions. The introduction of equivalent moduli, depending on the viscous and elastic features of materials, can guarantee a significant simplification of the problem presented above. The proposed calculation model has been used to design the "Quattroquercie Viaduct" located on the highway "A3" Salerno-Reggio Calabria, Italy.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.89-90
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• 2009

이 논문에서는 실제 옹벽 건설현장에서 FBG온도센서와 변형률센서를 이용하여 타설초기의 수축률과 온도를 모니터링 하였다. 실험결과, FBG센서를 이용한 모니터링 기법은 극초기재령의 콘크리트를 모니터링 하기에 매우 실용적인 방법임이 입증되었다. 또한 이 연구에서 사용된 모니터링 기술은 매스콘크리트 구조물의 변형률과 온도 모니터링에 확장하여 적용할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.95-100
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• 1996

Creep, drying shrinkage, modulus of elasiticity and Poisson's ratio of concrete are influenced by a number of factors such as mix type, member thickness, curing condition and loading cases. Particularly, creep and shrinkage in concrete have yet to be studied due to its complicated time-dependent properties. In this study, the concrete creep tests were carried out at varous ages of loading-7, 28, 90, 180 and 365 days in order to investigate and quantify its long-term properties. The test procedures and analysis of the test results were also described herein. The results of this study will enable A/E to calculate effective prestressing forces considering time-dependent prestressing loss and evaluate the structural integrity of the prestressing system using the representative values derived from this property test.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 춘계 학술논문 발표대회
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• pp.188-189
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• 2019

In this study, the characteristics of single-component and other sealant were analyzed to provide repair methods and effective utilization of sealant due to crack generation. Humidity studies have shown that acrylic silicone is effective in many areas of fluidity and temperature change, and that polysulfide-silicon is most effective in resistance to linear expansion coefficient and external pressure. Therefore, the difference between drying shrinkage and thermal expansion coefficient between various building materials and sealant, as well as the use of sealant, is analyzed, and construction methods derived accordingly, and prevention of defects are considered to be part of the construction project.