• Computational Structural Engineering
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• v.1 no.2
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• pp.131-142
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• 1988

This study was carried out to investigate the long-term deformation of superplasticized concrete. Compressive strength, shrinkage, creep and creep recovery of concretes with and without the superplasticizing admixture have been compared for one year. The test results on creep of superplasticized concrete were also compared with three methods of predicting creep; the ACI model, the CEB model and the BP model. According to test results, superplasticized concrete has good results in compressive strength at an age of 28 days of more than 22%, drying-shrinkage cured at air-conditioned storage less than 15%, creep deformation in air conditioned storage and loaded at an age of 28 days to 15% of compressive strength less than 11% of control concrete.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.179-188
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• 1998

캔틸레버 공법으로 시공되는 프리스트레스트 콘크리트 박스거더 교량의 구조적 거동은 단계적 시공에 따른 구조물의 순차적 변화 및 콘크리트의 재료적 특성에 의해 시간 의존적 거동을 나타낸다. 콘크리트의 시간의존적 특성, 즉 콘크리트의 크리프 및 건조수축 특성은 현장타설 세그멘탈 캔딜레버공법으로 가설되는 콘크리트 교량의 설계 및 시공에서 매우 중요한 역할을 한다. 본 연구에서는 콘크리트의 크리프 및 건조수축 특성이 교량의 시간의존적 거동, 특히 처짐 및 텐던응력예측에 미치는 영향을 연구하였다. 교량해석은 본 연구진에 의해 개발된 프리스트레스트 콘크리트 교량해석기법 및 프로그램을 이용하여 크리프의 ACI 모델, CEB-FIB모델, 그리고 국내 도로교 시방서 모델을 고려하여 해석하였다. 해석결과 최종크리프 값의 크기에 따라 장기처짐의 발생량이 차이가 큰 것으로 나타나고 있으며, 최종건조수축량과 상대습도도 영향을 주는 것으로 나타났다. 또한 ACI 모델과 CEB-FIB모델간에도 차이가 큰 것으로 나타나 실제교량의 크리프 특성 및 건조수축 특성의 정확한 예측이 교량의 정밀시공 및 거동예측에 매우 중요한 것으로 나타나고 있다.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.135-139
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• 1992

콘크리트가 구조용 재료로써 활용되기 시작한 이래 크리프와 건조수축의 특성규명을 위한 연구는 많은 연구자들에 의해 수행되어 왔다. 그러나 그 거동은 아직도 명확히 규명된 것은 아니며 이는 고강도 콘크리트의 경우 더욱 그러하다. 따라서 본 연구는 현재 국내에서 그 사용이 늘어나고 있는 고강도 콘크리트의 크리프 및 건조수축특성에 대한 기본적인 자료를 제공하기 위해 수행되었다. 본 연구의 주된 변수는 고강도 콘크리트, 배근유무, 철근비, 건조조건, 재하재령 등이며 이들의 영향에 대한 크리크 및 건조수축특성을 규명하였다. 이것은 앞으로 고강도콘크리트구조물 설계에 중요한 자료가 될 것으로 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.31-40
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• 1993

Many reseachers have performed extensive studies on the creep and shrinkage of concrete. Mechanism of creep and shrinkage however is not quite well-known, especially for high strength concrete. Therefore, the purpose of this study is to explore the shrinkage and creep characteristics of high strength concrete. The main variables investigated include condition of drying, reinforcement and duraton of load. The effects of drying and reinforcements are clarified and compared with various exsiting models. The present study provides useful data for the design and analysis of high stength concrete structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.755-761
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• 2014

Internal or external restraint of concrete strain due to drying shrinkage and creep in concrete structures causes mechanical strain and becomes a source of persistent change in creep-causing stress conditions. Mathematical modeling to incorporate the persistent change of creep-inducing stress is generally achieved with consideration of the ages of concrete and concrete properties at the times of loadings, and stress history. This paper presents an incremental format of creep model based on parallel creep concept to depict the creep under time-varying stress history in developing creep strain. Laboratory experiments are carried out to validate the performance of the presented creep model. Typical creep phenomena are addressed through the comparisons between the measured and predicted creep strains.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.857-860
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• 2008

This study shows systematic procedures for investigating creep and shrinkage properties of 50, 60, 70 MPa concrete mixes, which were developed by Lotte E&C R&D Ins. for Lotte Super Tower Jamsil. The concrete test was performed both local and foreign laboratory, S-Lab. and CTL Group respectively. The former have done for total five days. The procedures included the followings, specimen fabrication, mold removal, specimen marking, water bath curing, packaging, and shipment. The latter has been doing by CTL within PCA(Portland Cement Association). They are testing on static and dynamic modulus of elasticity, compressive strength, creep & shrinkage, splitting tensile strength. In the case of creep and shrinkage, the test will be doing for 18 months according to each loading age.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.343-350
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• 2014

A probabilistic construction stage analysis using the Monte Carlo Simulation was performed to address the effects of uncertainty regarding the material properties, environmental factors, and applied forces. In the previous research, creep and shrinkage were assumed to be completely independent random variables. However, because of the common influencing factors in the material models for the creep and shrinkage estimation, strong correlation between creep and shrinkage can be presumed. In this paper, an Monte Carlo Simulation using CEB-FIB creep and shrinkage equations were performed to actually evaluate the correlation coefficient between two phenomena, and then another Monte Carlo Simulation to evaluate the statistical properties of axial strain affected by partially correlated random variables including the material properties, environmental factors, and applied forces. The results of Monte Carlo Simulation were compared with measured strains of a column on a first story in a 58-story building. Comparison indicated that the variation due to the uncertainty related with the material properties were most severe. And measured strains was within the range of mean+standard deviation.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.245-248
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• 2008

Concrete structures show time-dependent behavior due to creep and shrinkage of concrete and the uncertainties of creep and shrinkage are very huge. To reduce uncertainties of creep and shrinkage, it is substantially necessary to perform the long-term creep and shrinkage tests, but actual construction process doesn't allow it due to the limited time. Even though the tests are performed in laboratory, the values obtained from the tests could be different from the actual values in construction site because of the different environment between the laboratory and construction site and the model uncertainty itself. It is difficult to predict the long-term behaviors of concrete structures properly if the assumed creep coefficient obtained from Codes or the results of experiments is different from the real characteristics of concrete creep. In this study, for predicting the long-term behavior, the creep coefficients in reinforced concrete beams are estimated using creep sensitivity analysis from the measured deflections with time. And estimated creep coefficients using creep models of ACI Committee 209 and CEB-FIP MC90 are compared.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.383-384
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• 2009

It is hard to predict shrinkage and creep that are influenced of exposure conditions, mix designs, and loading conditions etc. This paper present an evaluation of the reliability of the five shrinkage and creep prediction models using eight test data that are obtained from domestic FCM bridge concrete. For the reasonable evaluation of model and actual data, five statistical methods were used.