• Title/Summary/Keyword: 재령보정계수

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Improvement in Long-term Behavior Estimation of Prestressed Composite Girders for Various Construction Sequences using Parametric Study (변수해석을 통한 프리스트레스트 합성거더의 시공단계별 장기거동 평가법 개선방안)

  • Bae, Doobyong;Oh, Chang Kook
    • Journal of Korean Society of Steel Construction
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    • v.25 no.4
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    • pp.369-377
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    • 2013
  • The age-adjusted effective modulus method has been known to provide more precise assessment than the traditional Yassumi method for long-term behavior estimation of prestressed composite girders. The age-adjusted effective modulus method, however, involves complicated calculation, thereby making the Yassumi method more prevalent in actual design. This study presents rational approaches to revise creep coefficients for the Yassumi method by using parametric study results obtained from the age-adjusted effective modulus method.

Experimental Verification of Age-adjusted Effective Modulus Method to Long-Term Behavior Estimation of Prestressed Composite Girders (재령보정 유효계수방법에 의한 프리스트레스트 합성거더의 장기거동 실험 검증)

  • Bae, Doo-Byong;Oh, Chang-Kook;Choi, Sok-Hwan
    • Journal of Korean Society of Steel Construction
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    • v.24 no.5
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    • pp.571-582
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    • 2012
  • Prestressed composite girders provide efficient composite action by applying prestress to the sub-encasing concrete. In this study, an enhanced prestressed composite girder with forms suspended from the steel girder is utilized. Long-term behavior of the prestressed composite girder is estimated using age-adjusted effective modulus method, which is verified experimentally using measurements obtained from an in-service bridge. Then, parametric study is carried out to investigate the influences caused by ambient temperature, humidity, prestressing and concrete casting date.

Development of Model Equations for Strength Properties with Age in Concrete Pavement (재령에 따른 포장용 콘크리트의 강도특성 예측식 개발)

  • Yang, Sung-Chul;Kwon, Su-Ahn;Lim, Yu-Jin
    • Journal of the Korean Society of Hazard Mitigation
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    • v.10 no.6
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    • pp.35-43
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    • 2010
  • This study was carried out to find reliable relations between various concrete strength properties which are used as input data in concrete pavement design program. Concretes were made from different sources of coarse grained(granite, limestone and sandstone) and fine grained aggregates such as natural sand, washed sand and crushed sand. From strength test results, model equations were obtained based on the relation between strengths. For each coarse grained aggregate, models for compression-flexural strengths, compression-split tensile strengths, compressive strength-modulus and flexural-split tensile strengths with age were obtained. For concrete mixed with gneiss granite aggregates, concrete strengths were obtained from numerical mean values of concrete strengths mixed with fine grained aggregates. In addition models for concrete split tensile strengths and modulus values were provide by averaging numerically the estimated values obtained from the derived relationship and the experimental values. This is due to more scattered values of split tensile strengths and modulus values than other strength properties. Finally criteria for drying shrinkage strain as well as Poisson's ratio for concrete used in pavement were presented for all mixes with differed coarse grained aggregates.

Time-dependent Analysis of Cracked Reinforced Concrete Sections with Biaxial Bending (2축휨을 고려한 철근콘크리트 균열단면의 장기거동 해석)

  • Yang, Joo Kyoung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.2A
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    • pp.243-247
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    • 2008
  • An analytical approach to calculate time-dependent stresses and strains in initially cracked reinforced concrete section with biaxial bending was proposed. The method utilized the aging coefficient approach of Bazant and the linear creep theory. The position of neutral axis and strain and stress distributions of cracked section after creep and shrinkage were determined from the requirements of strain compatibility and equilibrium of a section. With this proposed algorithm, examples were given for rectangular section and a comparative analysis for stress and strain was also made.

Structural Analysis of a Tall Building Considering Inelastic Differential Column Shortening (비탄성 부등기둥축소를 고려한 초고층 구조 해석)

  • Kim, Han-Soo;Jeomg, Se-Hun;Shin, Seung-Hak
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.175-176
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    • 2009
  • An improved column shortening analysis method which can be used in designing the horizontal members has been proposed. If you use this analysis method which is used effective modulus method by EMM or AEMM, you will get more exactly moments on the horizontal members.

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Incremental Model Formulation of Creep under Time-varying Stress History (시간이력 하중을 받는 콘크리트의 점증적 크리프 모델)

  • Park, Yeong-Seong;Shin, Dong-Hun;Lee, Yong-Hak
    • 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.

Time Dependent Analysis of Reinforced and Prestressed Concrete Beams (철근콘크리트와 프리스트레스트 콘크리트 보의 시간의존적 거동해석)

  • Kwak, Hyo Gyoung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.14 no.1
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    • pp.1-12
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    • 1994
  • This paper deals with the time-dependent analysis of reinforced and prestressed concrete beams. Based on the age-adjusted effective modulus method, the structural behavior in accordance with time is analyzed using the force equilibrium and strain compatibility condition within a typical section. Unlike most of presented approaches adopting some assumptions, such as non-cracking of concrete and consideration of steel effect as a transformed concrete area only, more accurate results can be obtained at all loading conditions since all materials are considered together so as to be maintained their given properties and the cracking effect is included at the same time. Several parameter studies are conducted with the objective to identify the significance of various effects on the time-dependent response of concrete members, i.e., stress re-distribution of each material and occurrance of long-term deflection, etc. Moreover, the obtained results can be used at design and/or construction stage for the purpose of more accurate prediction of structural response with time.

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Nonlinear Finite Element Analysis of Reinforced and Prestressed Concrete Structures (철근 및 프리스트레스트 콘크리트 구조물의 비선형 유한요소 해석)

  • Kwak, Hyo Gyoung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.14 no.2
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    • pp.269-279
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    • 1994
  • This paper concentrates on the finite element analysis of concrete structures considering the material nonlinearity and time-dependent structural behavior. Using the rotating crack model among the smeared cracking model, the structural behavior up to ultimate load is simulated, and concrete is assumed to be an orthotropic material. Especially to include the tension stiffening effect in bending behavior, a criterion based on the fracture mechanics concept is introduced and the numerical error according to the finite element mesh size can be minimized through the application of the proposed criterion. Besides, the governing equation for steel is systematized by embeded model to cope with the difficulty in modeling of complex geometry. Finally, to trace the structural behavior with time under cracked and/or uncracked section, an algorithm for the purpose of time-dependent analysis is formulated in plane stress-strain condition by the age-adjusted effective modulus method.

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Compressive Strength Development Model for Concrete Cured by Microwave Heating Form (마이크로웨이브 발열거푸집으로 양생된 콘크리트의 압축강도발현 모델)

  • Koh, Tae-Hoon;Moon, Do-Young;Bae, Jung-Myung;Yoo, Jung-Hoon
    • Journal of the Korea Concrete Institute
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    • v.27 no.6
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    • pp.669-676
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    • 2015
  • Time dependent model for prediction of compressive strength development of concrete cured by microwave heating form was presented in this study. The presented model is similar to the equation which is given in ACI 209R-92 but the constants which is dependent on cement type and curing method in the presented model are modified by the regression analysis of the experimental data. Laboratory scale concrete specimens were cast and cured by the microwave heating form and drilled cores extracted from the specimens were fractured in compression. The measured core strengths are converted to standard core and in-situ strengths. These in-situ strengths are used for the regression.

Long-Term Performance Evaluation of Concrete Utilizing Oyster Shell in Lieu of Fine Aggregate (굴패각을 잔골재로 대체 사용한 콘크리트의 장기성능 평가)

  • Yang, Eun-Ik;Yi, Seong-Tae;Kim, Hak-Mo;Shim, Jae-Seol
    • Journal of the Korea Concrete Institute
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    • v.15 no.2
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    • pp.280-287
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    • 2003
  • To evaluate the practical application of oyster shells(OS) as construction materials, an experimental study was performed. More specifically, the long-term mechanical properties and durability of concrete blended with oyster shells were investigated. Test results indicate that long-term strength of concrete blended with 10% oyster shells is almost identical to that of normal concrete. However, the long-term strength of concrete blended with 20% oyster shells is appreciably lower than that of normal concrete. Thereby, concrete with higher oyster shell blend has the possibility of negatively influencing the concrete long-term strength. Elastic modulus of concrete blended with crushed oyster shells decreases as the blending mixture rate increases. Namely, the modulus is reduced to approximately 10∼15% when oyster shells are blended up to 20% as the fine aggregate. The drying shrinkage strain increases with an increasing crushed oyster shells substitution rate. In addition, the existing model code of drying shrinkage and creep do not coincide with the test results of this study. An adequate prediction equation needs to be developed. The utilization of oyster shells as the fine aggregate in concrete has an insignificant effect on fleering and thawing resistance, carbonation and chemical attack of concrete. However, water permeability is considerably improved.