• Title/Summary/Keyword: 콘크리트 변형률

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Material Model and Thermal Response Analysis of Concrete at Elevated Temperatures (고온에서의 콘크리트 재료모델과 열거동해석)

  • 강석원;홍성걸
    • Journal of the Korea Concrete Institute
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    • v.13 no.3
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    • pp.268-276
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    • 2001
  • A numerical model for the thermal response analysis of concrete structures is suggested. The model includes the stress-strain relationship, constitutive relationship, and multiaxial failure criteria at elevated temperature conditions. Modified Saenz's model was used to describe the stress-strain relationship at high temperatures. Concrete subjected to elevated temperatures undergoes rapid strain increase and dimensional instability. In order to explain those changes in mechanical properties, a constitutive model of concrete subjected to elevated temperature is proposed. The model consists of four strain components; free thermal creep strain, stress-induced (mechanical) strain, thermal creep strain, and transient strain due to moisture effects. The failure model employs modified Drucker-Prager model in order to describe the temperature dependent multiaxial failure criteria. Some numerical analyses are performed and compared with the experimental results to verify the proposed model. According to the comparison, the suggested material model gives reliable analytical results.

Experimental Investigation of the Flexural Behavior of Lightweight Aggregate Concrete Beams (경량 콘크리트 보의 휨 거동에 관한 실험적 연구)

  • Byon, Eun-Hyuk;Cho, Jang-Se;Lee, Young-Hak;Kim, Hee-Cheul
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.441-444
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    • 2010
  • 대공간 구조물과 초고층 빌딩에 있어 건축물의 자중 감소에 대한 요구가 늘어나고 있으며 이에 대한 가장 효과적인 방법 중 하나는 경량 콘크리트를 사용하는 것이다. 본 연구는 최외단 철근의 순인장 변형률에 따른 경량콘크리트 보의 휨 거동 및 휨 성능을 평가하는 것에 그 목적이 있다. 크기와 형상이 동일한 보통중량 콘크리트 보 1개와 경량 콘크리트 보 4개의 총 5개 시험체를 제작하여 최외단 철근의 순인장 변형률을 변수로 실험을 수행하였으며 이를 통해 순인장 변형률에 따른 경량콘크리트 보의 강도와 연성의 변화를 분석하였다. 실험 결과 최외단 철근의 순인장 변형률이 증가할수록 시험체의 연성비는 증가하였으며 최대하중과 강성은 감소하였다. 특히 순인장 변형률 0.005 이상에서 연성지수 2 이상을 확보할 수 있었다.

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A Unified Model of Strain Localization in Concrete (콘크리트 변형률 국소화의 통일된 모형)

  • 송하원;김인순
    • Magazine of the Korea Concrete Institute
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    • v.9 no.5
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    • pp.115-125
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    • 1997
  • 콘크리트의 변형률국소화는 콘크리트의연화거동에 수반되어 변형이 국부적으로 집중되는 현상이다. 본 연구의 목적은 인장과 압축하중상태에서 콘크리트 부재에 발생하는 콘크리트 변형률 국소화 거동을 해석적으로 재현할 수 있는 통일된 모형을 제안하는 것이다. 본 논문에서는 인장과 압축에 대하여 변형률국소화가 일어나는 콘크리트 부재를 변형률 연화가 일어나는 국소화영역과 탄성제하가 발생하는 비국소화영역으로 구분하여 모델링하는 통일된 모형을 제안하였다. 또한 제안된 모형에서 미시역학적 평균화기법을 이용해 평균등가탄성계수와 수정된 평균등가탄성계수를 구하여 시편의 크기와 국소화영역의 크기에 따는 해석을 수행하였으며 기존의 실험값과 비교하였다. 연구결과, 본 연구에서의 변형률국소화모형이 크기효과를 포함한 콘크리트의 변형률국소화거동 해석에 타당하게 적용될 수 있음을 보여주었다.

Measuring and Correcting The Compressive Axial Strain of Concrete Cylinders Retrofitted by External Jackets (외부자켓에 의해 보강된 콘크리트 압축시편의 압축변형률 측정 및 보정)

  • Choi, Eun-soo;Lee, Young-Geun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.13 no.2 s.54
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    • pp.215-222
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    • 2009
  • In this study, steel and FRP jackets are used to confine concrete cylinders. The FRP jacket behaviors compositely with concrete since there is bonding between them. However, the used steel jacket in this study do not behavior compositely with concrete since there is not an adhesive between them. The steel jackets are attached by external forces and the welding. This study suggests the measuring method of the axial strain for the confined concrete cylinders showing noncomposite behavior with the jackets and the correcting method of the measured strain for the composite-behavior jackets. For the noncomposite-behavior steel jacket, the axial strain of the steel surface does not represent the axial strain of the concrete inside. Also, a compressormeter can not be used. Thus, the two rigid plates at the top and bottom of a cylinder are placed and the distance of the two plates are measured and used for estimating the axial strain of the concrete. For the composite-behavior FRP jacket, the vertical strain measured on the FRP surface can be used for estimating the axial strain of the concrete. However, the vertical strain on the FRP surface contains the tensile strain due to the bulge of the concrete and, thus, the tensile strain should be corrected from the vertical strain. The corrected verticals strains compared with the measured strain or a existing constitute model; the result is satisfactory. The uncorrected stress-strain curves have the potential to under estimate the ductile behavior and the energy-dissipation-capacity of the composite-behavior FRP jackets.

Empirical Prediction for the Compressive Strength and Strain of Concrete Confined with FRP Wrap (FRP로 보강된 콘크리트의 강도 및 변형률 예측)

  • Lee, Dae-Hyoung;Kim, Young-Sub;Chung, Young-Soo
    • Journal of the Korea Concrete Institute
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    • v.19 no.3
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    • pp.253-263
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    • 2007
  • Previous researches showed that confined concrete with Fiber-Reinforced Plastic (FRP) sheets significantly improves the strength and ductility of concrete compared with unconfined concrete. However, the retrofit design of concrete with FRP materials requires an accurate estimate of the performance enhancement due to the confinement mechanism. The object of this research is to predict the compressive strength and strain of concrete confined with FRP wraps. For the purpose of this research, 102 test specimens were fabricated and loaded statically under uniaxial compression. Axial load, axial and lateral strains were investigated to predict the ultimate stress and strain. Also, to achieve reliability of proposed strength and strain models for FRP-confined concrete, another series of uniaxial compression test results were used. This paper presents strength and strain models for FRP-confined concrete. The proposed models to estimate the ultimate stresses and failure strains produce satisfactory predictions as compared to current design equations. In conclusion, it is proposed that the modified stress-strain model of concrete cylinders could be effectively used for the repair and retrofit of concrete columns.

Prediction of the Maximum Strain of Circular Concrete Columns Confined with Fiber Composites (섬유에 의하여 구속된 원형 콘크리트 기둥의 최대변형률 예측)

  • Lee, Jung-Yoon;Jeong, Hoon-Sik
    • Journal of the Korea Concrete Institute
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    • v.15 no.5
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    • pp.726-736
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    • 2003
  • Concrete columns confined with high-strength fiber composites can enhance its strength as well as maximum strain. In recent years, several equations have been developed to predict the behavior of the concrete columns confined with fiber composites. While the developed equations can predict the compressive strength of the confined columns with reasonable agreement, these equations are not successful in predicting the observed maximum strain of the columns. In this paper, a total of 61 test results is analysed to propose an equation to predict both compressive strength and maximum strain of concrete cylinders. The proposed equation takes into account the effects of confining pressure and cylinder size. Furthermore, in order to verify the proposed stress-strain curve for concrete cylinders, six cylindrical specimens were tested. Comparisons between the observed and calculated stress-strain curves of the tested cylinders showed reasonable agreement.

Shear Deterioration of Reinforced Concrete Beams Failing in Shear after Flexural Yielding (휨항복 후 전단 파괴하는 철근콘크리트 보의 전단성능 저하에 관한 연구)

  • 이정윤
    • Journal of the Korea Concrete Institute
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    • v.13 no.5
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    • pp.466-475
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    • 2001
  • The potential shear strength of reinforced concrete beams decreases after flexural yielding due to the decrease of the effective compressive strength of concrete in plastic hinge zone. A truss model considering shear deterioration in the plastic hinge zone was proposed in order to evaluate the ductile capacity of reinforced concrete beams failing in shear after flexural yielding This model can determine the potential shear strength of the beam by using a truss model. The potential shear strength gradually decreases as the increase of the axial strain of member. When the calculated potential shear strength decreases up to the flexural yielding strength, the corresponding rotation angle is defined as the ductile capacity of the beam. The predicted ductile capacity of reinforced concrete beams is shown to be in a good agreement with experimental results.

Predicting the Nonlinear Behavior of Reinforced Concrete Membrane Elements Subjected to Reversed Cyclic Loading (반복하중을 받는 철근콘크리트 막요소의 비선형거동에 대한 예측)

  • 이정윤
    • Journal of the Earthquake Engineering Society of Korea
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    • v.6 no.4
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    • pp.7-13
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    • 2002
  • The behaviors of the reinforced concrete membrane elements are expected by Navier's three principles of the mechanics of materials. The adopted cyclic stress-strain curves of concrete consist of seven different unloading and loading stages in the compressive zone and six other stages in the tensile zone. The curves took into account the softening of concrete that was influenced by the tensile strain in the perpendicular direction of cracks. The stress-strain relationships for steel bar embedded in concrete subjected to reversed cyclic forces considered the tension stiffening effect and Baushinger effect. The predicted results of the analysis based on Navier's principles were in good agreement with the observed shear stress-strain relationships as well as transverse and longitudinal strains.

A Stress-Strain Relationship of Alkali-Activated Slag Concrete (알칼리활성 슬래그 콘크리트의 응력-변형률 관계)

  • Yang, Keun-Hyeok;Song, Jin-Kyu;Lee, Kyong-Hun
    • Journal of the Korea Concrete Institute
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    • v.23 no.6
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    • pp.765-772
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    • 2011
  • The present study summarizes a series of compressive tests on concrete cylinder in order to examine the stressstrain relationship of alkali-activated (AA) slag concrete. The compressive strength and unit weight of concrete tested ranged from 8.6 MPa to 42.2 MPa and from $2,186kg/m^3$ to $2,343kg/m^3$, respectively. A mathematical equation representing the complete stress-strain curve was developed based on test results recorded from 34 concrete specimens. The modulus of elasticity, strain at peak stress, slopes of ascending and descending branches of stress-strain curves were generalized as a function of compressive strength and unit weight of concrete. The mean and standard deviation of the coefficient of variance between measured and predicted curves were 6.9% and 2.6%, respectively. This indicates that the stress-strain relationship of AA slag concrete is represented properly with more accuracy in the proposed model than in some other available models for ordinary portland cement (OPC) concrete.

Experimental Investigation of the Flexural Behavior of Polymer-modified Lightweight Aggregate Concrete One-Way Members (폴리머 개질 경량콘크리트 일방향 부재의 휨 거동에 관한 실험적 연구)

  • Byon, Eun-Hyuk;Kim, Min-Sook;Lee, Young-Hak;Kim, Hee-Cheul
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.5
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    • pp.551-557
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    • 2010
  • The purpose of this study is to estimate experimentally the flexural behavior, capacity and validity of existing regulation of net tensile strain in lightweight concrete beams and polymer modified lightweight concrete beams. One normal weight concrete beam and four lightweight concrete beams, three polymer modified lightweight concrete beams were constructed as same figure and attempted to evaluate the difference of strength and ductility in specimens of different net tensile strain in extreme tension steel. Test results are indicated in terms of load-deflection behavior and ductility index. As the value of net tensile strain increased, the flexural strength and stiffness of specimen decreased but ductility index increased in both of lightweight concrete beams and polymer modified lightweight concrete beams. It is considered that to achieve similar ductility index of normal weight concrete, net tensile strain in extreme tension steel should exceed 0.005 for lightweight concrete beam and polymer modified lightweight concrete beam.