• Computers and Concrete
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• 제22권6호
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• pp.563-572
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• 2018

Uniaxial compressive strength test and uniaxial compression creep one were produced on four groups of twelve concrete specimens with different hole number by RLW-2000 rock triaxial rheology test system. The relationships between horizontal holes and instantaneous failure stress, the strain, and creep failure stress, the strain, and the relationships between stress level and instantaneous strain, creep strain were studied, and the relationship between horizontal holes and failure mode was determined. The results showed that: with horizontal hole number increasing, compressive strength of the specimens decreased whereas its peak strain increased, while both creep failure strength and its peak strain decreased. The relationships between horizontal holes and compressive strength of the specimens, the peak strain, were represented in quadratic polynomial, the relationships between horizontal holes and creep failure strength, the peak strain were represented in both linear and quadratic polynomial, respectively. Instantaneous strain decreased with stress level increasing, and the more holes in the blocks the less the damping of instantaneous strain were recorded. In the failure stress level, instantaneous strain reversally increased, creep strain showed three stages: decreasing, increasing, and sharp increasing; in same stress level, the less holes the less creep strain rate was recorded. The compressive-shear failure was produced along specimen diagonal line where the master surface of creep failure occurred, the more holes in a block, the higher chances of specimen failure and the more obvious master surface were.

• 한국구조물진단유지관리공학회 논문집
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• 제14권4호
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• pp.154-159
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• 2010

최근들어 구조물공사에 적용되는 콘크리트가 고강도화 되어가는 추세로서 크리프와 같은 콘크리트의 역학적 거동에 대한 기존 설계예측식에 대한 전면적인 검토가 필요한 시점이다. 이에, 본 연구에서는 현행 국내 철근콘크리트 구조설계기준상의 크리프계수 예측 모델식에 대한 강도대별 적용 타당성을 검토하기 위한 일환으로 기존의 제안 모델식인 ACI 209R, CEB-FIP MC90 및 EC2 모델식을 검토 하였으며, 실험결과와 비교검토를 수행하였다. 모델식 검토결과, CEB-FIP MC90 모델의 개선식인 EC2 모델이 고강도대의 콘크리트에 대한 크리프계수를 보다 현실적으로 예측함을 확인할 수 있었으며, 실험결과와도 상대적으로 좋은 상관성을 보임을 확인하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.337-338
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• 2010

이 논문에서는 고강도 콘크리트의 크리프 특성에 관한 연구로서 실험을 통해 얻어진 결과를 여러 크리프 예측식과 비교하여 기술하였다. 따라서 고강도 콘크리트의 크리프 특성을 규명하기 위해 1종 시멘트로 제작된 대상 콘크리트에 대해 ACI-209 및 CEB/FIP-90의 크리프 예측식에 의한 결과와 비교 검토하여 크리프 예측식의 적용 가능성을 검토하였다.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.635-652
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• 2014

Creep and shrinkage behaviour of an ultra lightweight cement composite (ULCC) up to 450 days was evaluated in comparison with those of a normal weight aggregate concrete (NWAC) and a lightweight aggregate concrete (LWAC) with similar 28-day compressive strength. The ULCC is characterized by low density < 1500 $kg/m^3$ and high compressive strength about 60 MPa. Autogenous shrinkage increased rapidly in the ULCC at early-age and almost 95% occurred prior to the start of creep test at 28 days. Hence, majority of shrinkage of the ULCC during creep test was drying shrinkage. Total shrinkage of the ULCC during the 450-day creep test was the lowest compared to the NWAC and LWAC. However, corresponding total creep in the ULCC was the highest with high proportion attributed to basic creep (${\geq}$ ~90%) and limited drying creep. The high creep of the ULCC is likely due to its low elastic modulus. Specific creep of the ULCC was similar to that of the NWAC, but more than 80% higher than the LWAC. Creep coefficient of the ULCC was about 47% lower than that of the NWAC but about 18% higher than that of the LWAC. Among five creep models evaluated which tend to over-estimate the creep coefficient of the ULCC, EC2 model gives acceptable prediction within +25% deviations. The EC2 model may be used as a first approximate for the creep of ULCC in the designs of steel-concrete composites or sandwich structures in the absence of other relevant creep data.

• 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.

• 한국구조물진단유지관리공학회 논문집
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• 제5권1호
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• pp.237-246
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• 2001

This study is to measure the creep coefficient by 3 days, 7 days and 28 days in the age when loading for the quality assessment of $350kgf/cm^2$ in the high-strength concrete. And it is to analyze the behavior of creep coefficient by applying the experimental data though the compressive strength test, the elastic modulus test and the dry shrinkage test to the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design. Also it is to analyze the behavior of short-term creep coefficient during 91 days in the age when loading through the experiment by using the regression analysis, the statistical theory. As applying it to the long-term behavior during 365 days and comparing with the creep prediction mode and examining it, the result from the analysis of the quality of the concrete is as follows. As the result of comparison and analysis about the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design, the normal Portland cement class 1 shows the approximate value with the prediction of GEE/PIP-90 and the basis of concrete structural design, but in case of the prediction of ACI-209 and AASHTO-94, there would be worry of underestimation in the application.

• Computers and Concrete
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• 제12권6호
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• pp.739-754
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• 2013

Creep and shrinkage have pronounced effects on the long-term deflection of prestressed concrete members. Under repeated loading, the rate of creep in prestressed concrete members is often accelerated. In this paper, an iterative computational procedure based on the well known Model B3 for creep and shrinkage was developed to predict the time-dependent deflection of partially prestressed concrete members. The developed model was validated using the experimental observed deflection behavior of a simply supported partially prestressed concrete beam under repeated loading. The validated model was then employed to make predictions of the long-term deflection of the prestressed beams under a variety of conditions (e.g., water cement ratio, relatively humidity and time at drying). The simulation results demonstrate that ignoring creep and shrinkage could lead to significant underestimation of the long-term deflection of a prestressed concrete member. The model will prove useful in reducing the long-term deflection of the prestressed concrete members via the optimal selection of a concrete mix and prestressing forces.

• 콘크리트학회논문집
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• 제16권3호
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• pp.425-431
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• 2004

This paper describes an experimental investigation of how time-dependent deformations of high strength concretes are affected by maximum size of coarse aggregate, curing time, and relatively low sustained stress level. A set of high strength concrete mixes, mainly containing two different maximum sizes of coarse aggregate, have been used to investigate drying shrinkage and creep strain of high strength concrete for 7 and 28-day moist cured cylinder specimens. Based upon one-year experimental results, drying shrinkage of high strength concrete was significantly affected by the maximum size of coarse aggregate at early age, and become gradually decreased at late age. The larger the maximum size of coarse aggregate in high strength concrete shows the lower the creep strain. The prediction equations for drying shrinkage and creep coefficient were developed on the basis of the experimental results, and compared with existing prediction models.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.529-532
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• 2006

This paper presents results from creep and shrinkage tests performed on different High Strength Concrete (HSC) mixes (with compressive strengths up to 90 MPa). Results were compared with those from various Code prediction models. The effects of pozzolanic materials on the creep and shrinkage were also investigated. Results show that while fly ash increases the compressive creep of concrete, silica fume decreases it. Moreover, current creep and shrinkage prediction models need to be revised for the HSC mixture.

• 콘크리트학회논문집
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• 제16권2호
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• pp.185-194
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• 2004

콘크리트의 크리프에 관한 기존의 연구결과들은 대부분 1축응력이 가해지는 경우에 대한 것으로 콘크리트 구조물 또는 부재가 다축응력 상태에 놓이는 경우에 적용하기가 어려운 점이 있다. 따라서 다축응력 상태의 콘크리트 크리프 특성에 관한 연구가 필요하다. 이 연구에서 다축응력 상태에 놓인 콘크리트의 크리프 특성을 실험을 통해 파악하였다. 세 가지 서로 다른강도를 갖는 배합의 콘크리트에 대해 각각 9개의 실험체를 제작하였으며, 1축, 2축, 3축 응력 상태에서 크리프 실험을 실시하였다. 하중이 가해지는 세 방향에서 시간에 따른 변형률을 측정하였다. 가압시점의 푸아송비와 크리프변형에 기인한 푸아송비 그리고 탄성변형과 크리프변형에 기인한 푸아송비를 구하였으며, 각 콘크리트에 대한 세 가지 푸아송비는 근사적으로 같은 것으로 나타났다. 가압시점의 푸아송비와 전체 변형에 대한 푸아송비는 콘크리트 강도의 증가에 따라 다소 증가하는 경향을 보였으며, 각 푸아송비는 응력상태에 따라 특정한 경향을 나타내지 않았다. 체적성분의 응력과 크리프변형률, 편차성분의 응력과 크리프변형률은 선형의 관계를 나타내었다.