• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.481-486
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• 2003

This paper presents experimental study on long-term behavior of RC and SRC columns. Shrinkage and creep tests were performed for two types of concrete used in manufacturing RC and SRC column specimens. Also, long-term tests under sustained load were carried out for RC and SRC column specimens. Shrinkage functions and creep coefficients to optimally fit the corresponding data were obtained from regression analysis and the regression results, ACI and CEB- FIP 90 model were applied to analyse long-term behvavior of RC and SRC column specimens. Creep coefficients calculated from test data were lower than those predicted by ACI and CEB-FIP 90 models. Long-term analysis results for RC and SRC column specimens using the regression results were relatively more accurate than those obtained using the existing models.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.557-562
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• 2007

In order to analyze the PSC box-girder bridge by the cantilever construction method, three dimensional analysis method using the PSC shell clement is suggested. The time dependent material functions are based on the ACI and CEB code. The time dependent concrete material properties considered are changes in strength, elastic modulus, creep and shrinkage. For the prestressing tendon, relaxation effects are considered. Anchorage and friction loses during tendon installations are also included. The ACI and CEB material models for creep and elastic modulus are also included.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.489-492
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• 2004

Compressive strength of self-compacting concrete with waste concrete powder(SCCWCP) linearly decreased as the containing ratio of WCP increas. When granulated blast furnace slag(SG) was contained for improving the rheological properties of SCCWCP, compressive strength of concrete with $15\%$ SG and $15\%$ WCP was increased in comparison with that of concrete with $30\%$ WCP. Splitting tensile strength of SCCWCP higher increased than that of CEB-FIP at same compressive strength. Relationship between compressive strength and elastic modulus of SCCWCP indicated a similar function with CEB-FIP fuction.

• 콘크리트학회지
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• 제9권6호
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• pp.147-156
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• 1997

지금까지 국내에서는 콘크리트의 크리프에 관한 실험적 연구가 많이 진행되지 못하여 해당 구조물의 설계기술 도입국의 규준에 따라 크리프를 예측해왔다. 그러나 예측된 크리프 모델이 국내 콘크리트 재료의 특성에 적합한지에 대한 실험적 검증은 제대로 이루어지지 않고 있는 실정이다. 본 연구에서는 국내에서 프리스트레스 콘크리트 구조물에 적용하는 실용 고강도 콘크리트의 크리프 값을 예측하기 위해 동일한 설계기준강도를 갖는 세 가지 배합에 대하여 재령별로 크리프 시험을 수행하고 이 실험결과를 ACI, CEB/FIB, KSCE, JSCE규준들의 크리프 예측식과 비교 분석하였다.시험결과와 이들규준들에 대한 비교분석에 의하면 CEB/FIB-90 크리프 예측식은 비교적 과대 평가되고 ACI 209-92와 JSCE-96의 경우는 과소 평가되었으나 콘크리트 표준시방서 KSCE -96 크리프 예측식은 비교적 시험결과에 근접하는 것으로 평가되었다. 그러나 구성재료의 양적 변동에 '따른 배합별 시험결과의 차이를 반영할 수 있는 점이 보완되어야 할 것으로 보며 향후 많은 실험결과를 바탕으로 국내에서 생산되는 콘크리트에 대하여 보다 정확히 크리프를 예측할 수 있는 연구가 필요하다.

• 지구물리
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• 제7권4호
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• pp.277-282
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• 2004

Creep deformation of concrete is often responsible for excessive deflection at loads which can compromise the performance of elements within structures. Hence, the prediction of the magnitude and rate of creep strain is an important requirement of the design process and management of structures. Although laboratory tests may be undertaken to determine the deformation properties of concrete, these are time-consuming, often expensive and generally not a practical option. Therefore, relatively simple empirically based national design code models are relied upon to predict the magnitude of creep strain.This paper reviews the accuracy of creep predictions yielded by eight commonly used international "code type" models, all of which do not consider the same material parameters and yield a range of predicted strains, when compared with actual strains measured on a range of concretes in seventeen different investigations. The models assessed are the: SABS 0100 (1992), BS 8110 (1985), ACI 209 (1992), AS 3600 (1998), CEB-FIP (1970, 1978 and 1990) and the RILEM Model B3 (1995). The RILEM Model B3 (1995) and CEB-FIP (1978) were found to be the most and least accurate, respectively.

• Architectural research
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• 제11권1호
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• pp.25-33
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• 2009

This study presents the testing of 15 hwangtoh-based cementless concrete mixes to explore the significance and limitations of the development of eco-friendly concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cement-less binder. The main variables investigated were the water-to-binder ratio and fine aggregate-to-total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured: including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cement-less concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in ACI 318-05 and CEB-FIP for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-to-binder ratio and to less extend by fine aggregate-to-total aggregate ratio. The moduli of rupture and elasticity of hwangtoh-based concrete were generally lower than those of OPC concrete. In addition, the stress-strain and bond stress-slip relationships measured from hwangtoh-based concrete showed little agreement with the design model specified in CEB-FIP. However, the measured moduli of rupture and elasticity, and bond strength were higher than those given in ACI 318-05 and CEB-FIP. Overall, the test results suggest that the hwangtoh-based concrete shows highly effective performance and great potential as an environmental-friendly building material.

• 한국전산구조공학회논문집
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• 제18권3호
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• pp.303-309
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• 2005

본 연구에서는 국내 원전에서 기기 정착을 위하여 가장 널리 적용되는 직매형 앵커기초를 대상으로 앵커기초의 인장 설계기준에 대한 적정성을 검토하기 위하여 수치해석이 수행되었다. 본 연구에서 수치해석모형에 적용된 파괴기준으로서 콘크리트와 같은 유사 취성재료에는 Microplane모형이, 앵커볼트와 같은 연성재료에는 탄성-완전 소성모형이 적용되었다. 그리고, 균열 발생현상을 모사하기 위하여 분산균열모형을 채택하였다. 개발된 수치해석모형은 다양한 경우의 실증시험결과를 근거로 신뢰성이 검증되었으며, 검증된 수치해석모형과 앵커볼트의 유효매입깊이를 변수로 한 다양한 경우에 대한 수치해석을 통하여 직매형 앵커기초의 인장설계기준으로서 적용이 가능한 ACI 349 Code와 CEB-FIP Code가 평가되었고, 그 보수성이 확인되었다.

• Toxicological Research
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• 제35권1호
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• pp.45-63
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• 2019

In view of the growing industrial use of Bacterial cellulose (BC), and taking into account that it might become airborne and be inhaled after industrial processing, assessing its potential pulmonary toxic effects assumes high relevance. In this work, the murine model was used to assess the effects of exposure to respirable BC nanofibrils (nBC), obtained by disintegration of BC produced by Komagataeibacter hansenii. Murine bone marrow-derived macrophages ($BMM{\Phi}$) were treated with different doses of nBC (0.02 and 0.2 mg/mL, respectively 1 and $10{\mu}g$ of fibrils) in absence or presence of 0.2% Carboxymethyl Cellulose (nBCMC). Furthermore, mice were instilled intratracheally with nBC or nBCMC at different concentrations and at different time-points and analyzed up to 6 months after treatments. Microcrystaline $Avicel-plus^{(R)}$ CM 2159, a plant-derived cellulose, was used for comparison. Markers of cellular damage (lactate dehydrogenase release and total protein) and oxidative stress (hydrogen peroxidase, reduced glutathione, lipid peroxidation and glutathione peroxidase activity) as well presence of inflammatory cells were evaluated in brochoalveolar lavage (BAL) fluids. Histological analysis of lungs, heart and liver tissues was also performed. BAL analysis showed that exposure to nBCMC or CMC did not induce major alterations in the assessed markers of cell damage, oxidative stress or inflammatory cell numbers in BAL fluid over time, even following cumulative treatments. $Avicel-plus^{(R)}$ CM 2159 significantly increased LDH release, detected 3 months after 4 weekly administrations. However, histological results revealed a chronic inflammatory response and tissue alterations, being hypertrophy of pulmonary arteries (observed 3 months after nBCMC treatment) of particular concern. These histological alterations remained after 6 months in animals treated with nBC, possibly due to foreign body reaction and the organism's inability to remove the fibers. Overall, despite being a safe and biocompatible biomaterial, BC-derived nanofibrils inhalation may lead to lung pathology and pose significant health risks.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2009년도 정기 학술대회
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• pp.327-330
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• 2009

PSC 박스 교량의 시공 중 거동 특성을 고려하기 위하여 뼈대 요소를 이용한 시공단계의 설계가 수행되고 있다. 그러나 PSC 박스 교량 중 곡선 램프교 등의 경우는 교량의 외측 및 내측의 변위 및 응력 값이 현저히 다르다. 따라서 PSC 박스 교량의 텐던량 및 시공 중 긴장력이 외측 및 내측에서 다르게 산정되어야 함에도 불구하고 현실적으로는 계산이 불가능하여 같은 양의 텐던과 부적절한 긴장력을 사용하고 있어 비효율적인 설계와 시공이 이루어지고 있다. 이러한 문제점을 해결하기 위하여 내외측의 텐던량을 다르게 고려할 수 있고 교량의 내외측 반력, 응력, 변위 분포를 얻을 수 있는 3차원 해석이 필수적으로 요구 되고 있다. 본 연구에서는 PSC 박스 교량의 3차원 거동 해석을 위하여 텐던 및 크리프, 건조수축을 반영한 준적합 쉘요소를 이용하여 수치해석을 수행하였으며 크리프 및 건조수축의 특성은 ACI코드와 CEB/FIP 코드를 적용하여 비교분석하였다. 각각의 결과 값이 상이한 경우도 있지만 대체로 두 코드는 비슷한 양상을 보였으며 CEB/FIP 가 좀 더 경제적인 설계가 됨을 알 수 있었다.

• 한국농공학회지
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• 제40권4호
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• pp.120-129
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• 1998

The tension stiffening in reinforced concrete member means increase of stiffness caused by the effective tensile stress between cracks and the tension softening behavior of concrete. This paper presents on the tensile behavior and tension stiffening of RC tension members. Direct tension tests were performed with a main experimental variables such as concrete strength, rebar diameter and strength. The tension stiffening was analyzed from the load-displacement relationship and was compared with ACI code, CEB model and the proposed by Collins ＆ Mitchell. The results are as follows : The tension behaviors of RC members were quite different from those of bare bar and were characterized by loading and concrete cracking steps. The effect of tension stiffening decreased rapidly as the rebar diameter and strength increased, and the concrete strength increased. The proposed by Collins ＆ Mitchell described well the experimental results, regardless of rebar types and concrete. But, ACI code and CEB model described a little differently, depending on the types. The effect of tension stiffening in RC member was the biggest near at concrete cracking step and decreased gradually to the bare bar's behavior as loading closed to the breaking point. Thus, tension stiffening in RC members should be taken into account when the load-deflection characteristics of a member are required or a precise analysis near the load of concrete clacking is needed.