• Title/Summary/Keyword: 부등 건조수축

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Differential Drying Shrinkage of concrete an Early Ages Considering Self-desiccation (자체건조를 고려한 초기재령 콘크리트의 부등건조수축)

  • 김진근;이칠성
    • Magazine of the Korea Concrete Institute
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    • v.10 no.5
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    • pp.197-204
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    • 1998
  • 초기재령에서 외기에 노출된 콘크리트는 수분확산으로 인하여 부등건조수축이 발생하고, 또한 자체건조로 인하여 자기수축도 발생한다. 따라서 콘크리트 재부의 수축변형도는 이러한 자기수축을 포함하고 있으므로 이를 고려해야 한다. 본 연구에서는 초기재령에서 콘크리트 강도에 따라 자기수축의 영향을 고려하여 부둥건조수축에 대한 실험과 해석을 수행하였다. 또한 콘크리트 내부의 부등수분분포로 인한 수축변형도에 대하여 실험결과와 해석결과를 비교하여, 해석방법의 타당성을 검증하였다. 실험 및 분석결과에 의하면 저강도콘크리트는 수분확산으로 인하여 주로 수축현상이 일어나고 자기수축의 영향은 거의없었다. 그렇지만 고강도 콘크리트는 자기수축에 의해서도 영향을 받았다. 그리고 콘크리트의 부등건조수축은 강도에 따라 큰 차이를 나타냈다. 또한 제시한 해석방법에 의한 해석결과는 실험결과를 잘 예측하였다.

Prediction of Differential Drying Shrinkage in Concrete (콘크리트의 부등건조수축에 관한 연구)

  • 김진근;이칠성
    • Magazine of the Korea Concrete Institute
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    • v.9 no.2
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    • pp.153-161
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    • 1997
  • In the concrete st~uctures exposed to the environmental condition, the water movement is occurred by thc moisture difilsion, and the rnoisturrt distribution in concwt.c is nonunifhrm. Such a non-unif'orm moisture distribution causes tht. diflbrent.ia1 drying shrinkage in concrete structures. From this typc. of' dif'fercntial drying shrinkagr' tensiit-1 stress is occurred in exposure surface of concrete structures. and may result in crack formation. This residual stress is significantly affected by the creep of concrete, and the differential creep is also occurred at the cross section of concrete structures due to moisture difference at each locations. In this study, based on the moisture diffusion theory, a finite element program which is capable of simulating the moisture distribution in concrete was developed. And the analysis method for the differential drying shrinkage was suggested, in which the differential creep was considered. The differential drying shrinkage strain was also measured at various positions of concrete. Finally the validity of analysis method was proved by comparing test results with analytical results.

Cracking Behavior of Concrete Bridge Deck Due to Differential Drying Shrinkage (교량 바닥판 콘크리트의 부등건조수축 균열특성에 관한 연구)

  • Yang, Joo Kyoung;Lee, Yun;Yang, Eun Ik;Park, Hae Geun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.4A
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    • pp.329-335
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    • 2009
  • The purpose of this study is to provide the efficient method and guideline of controlling the cracking in bridge deck concrete due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of cracking shrinkage cracking mechanism, it is necessary to conceive the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis corresponding to drying shrinkage on bridge deck are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of bridge deck concrete shows different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

Development of Environmental Load Calculation Method for Airport Concrete Pavement Design (공항 콘크리트 포장 설계를 위한 환경하중 산정방법 개발)

  • Park, Joo-Young;Hong, Dong-Seong;Kim, Yeon-Tae;Jeong, Jin-Hoon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.2
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    • pp.729-737
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    • 2013
  • The environmental load of concrete pavement can be categorized by temperature and moisture loads, which mean temperature distribution, and drying shrinkage and creep in the concrete slab. In this study, a method calculating the environmental load essential to mechanistic design of airport concrete pavement was developed. First, target area and design slab thickness were determined. And, the concrete temperature distribution with slab depth was predicted by a pavement temperature prediction program to calculate equivalent linear temperature difference. The concrete drying shrinkage was predicted by improving an existing model to calculate differential shrinkage equivalent linear temperature difference considering regional relative humidity. In addition, the stress relaxation was considered in the drying shrinkage. Eventually, the equivalent linear temperature difference due to temperature and the differential shrinkage equivalent linear temperature difference due to moisture were combined into the total equivalent linear temperature difference as terminal environmental load. The environmental load of eight civilian and two military airports which represent domestic regional weather conditions were calculated and compared by the method developed in this study to show its application.

Cracking Behavior of Concrete Box Culvert for Power Transmission Due to Drying Shrinkage (전력구 콘크리트 구조물의 건조수축 균열특성에 관한 연구)

  • Woo, Sang-Kyun;Chu, In-Yeop;Kim, Ki-Jung;Lee, Yun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.1
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    • pp.1-8
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    • 2016
  • The purpose of this study is to predict the cracking behavior and suggest the method of controlling the cracking in concrete box culvert for power transmission due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis cor responding to drying shrinkage on concrete box culvert are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of box culvert shows the different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

Stress Analysis for Differential Drying Shrinkage of Concrete (콘크리트의 부등건조수축으로 인한 응력의 해석)

  • 김진근;김효범
    • Magazine of the Korea Concrete Institute
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    • v.6 no.4
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    • pp.102-112
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    • 1994
  • The drying shrinkage of concrete has a close relation to the water movement. Since the diffusion process of water in concrete is strongly dependent on the temperature and the pore humidity, the process is highly nonlinear phenomena. This study consists of two parts. The first is the development of a finite element program which is capable of simulating the rnoisture distri- ,bution in concrete, and the other is the estimation of the differential drying shrinkage and stress considering creep by using the modified elastic modulus due to inner temperature change and maturity. It is shown that the analytical results of this study are in good agreement with experlimental data in the literatures, and results calculated by BP-KX model. The internal stress caused by moisture distribution which was resulted from the diffusion process, was calculated :quantitatively. The tensile stress which occured in the drying outer zone mostly exceeded the tensile strength of concrete, and necessarily would result in crack formation.

Reduction of Drying Shrinkage Cracking of Box Culvert for Power Transmission with Shrinkage Reducing Agent (수축저감제 혼입에 따른 전력구 박스구조물의 건조수축균열 저감)

  • Woo, Sang-Kyun;Kim, Ki-Jung;Lee, Yun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.5
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    • pp.102-108
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    • 2016
  • The purpose of this study is to examine the reduction effect of shrinkage reducing agent for drying shrinkage induced cracking and suggest the method of controlling the cracking in concrete box culvert for power transmission. Based on drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves shrinkage reducing effect of shrinkage reducing agent. From the numerical results, it is found that cracking behavior for longitudinal direction and transverse direction due to differential drying shrinkage of box culvert can occur and the experimental observation of concrete cracks support the numerical predictions. The shrinkage reducing agent reduced the concrete cracking by 40~50%, which shows the methodology of controlling of drying shrinkage cracks in box culverts in real construction site.

Column Shortening of SRC Columns Considering the Differential Moisture Distribution (부등수분분포를 고려한 SRC 기둥의 축소량에 관한 연구)

  • Seol, Hyun-Cheol;Kim, Yun-Yong;Kwon, Seung-Hee;Kim, Han-Soo;Kim, Jin-Keun
    • Journal of the Korea Concrete Institute
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    • v.18 no.1 s.91
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    • pp.29-36
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    • 2006
  • Steel reinforced concrete(SRC) columns, which have been widely employed in high-rise buildings, exhibit a time-dependent behavior because of creep and shrinkage of concrete. This long-term behavior may cause a serious serviceability problem in structural systems, so it is very important to predict the deformation due to creep and shrinkage of concrete. However, it was found from the previous experimental studies that the long-term deformation of SRC columns was quite dissimilar from that of RC columns. A new method is required to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the discrepancy between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of reinforced concrete(RC) columns owing to the presence of a inner steel plate, which interferes with the moisture diffusion of concrete. This relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns. Therefore it is suggested that the differential moisture distribution should be taken into account in order to reasonably predict column shortening of SRC columns.

Creep and shrinkage properties using concrete test results and prediction models for high strength and high performance concrete (실험결과와 예측식을 통한 고강도 고성능 콘크리트의 크리프 및 건조수축 특성파악)

  • Cha, Han-Il;Moon, Hyung-Jae;Seok, Won-Kyun;Park, Soon-Jeon;Lee, Joo-Ho
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.11a
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    • pp.709-712
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    • 2008
  • RC super tall buildings are planned and constructed recently in domestic area. Concrete is characterized by time dependant material such as creep and shrinkage. For this properties of concrete, differential shortening is one of the main issues on super tall buildings construction. This study includes material research, which is performing as a pre design stage to solve differential shortening on Lotte Super Tower Jamsil core structure(50, 60, & 70 MPa). The major part of this study is composed with comparison and analysis between experimental data and predicted data on total shrinkage and total compliance which were used on design stage. Four models, ACI209R Model, Ba${\check{z}}$ant-Baweja B3 Model, CEB MC99 Model, & GL2000 Model, were employed to predict them. It also tries to seek a proper model for high strength and high performance concrete in the case of no concrete test.

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