• Title, Summary, Keyword: Time-Dependent Behaviors

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Time-Dependent Behavior Analysis of Pre-Tensioned Members Using High-Performance Concrete(HPC) (고성능 콘크리트(HPC)를 사용한 프리텐션 부재의 시간의존거동 해석)

  • Nam, Yoo-Seok;Cho, Chang-Geun;Park, Moon-Ho
    • Journal of the Korea Concrete Institute
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    • v.18 no.4
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    • pp.479-487
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    • 2006
  • This paper deals with a research about the time-dependent behavior analysis for pre-tensioned high-performance concrete(HPC) members. By improving AASHTO-LRFD(2004) method for predicting the creep and shrinkage of normal concrete, and the relaxation of prestressing tendon, a time-dependent behavior analysis of high-performance concrete structures has been introduced. Two methods, the step-function method and the time-step method have been incorporated in the time-dependent analysis. The developed program can predict the initial and time-dependent losses of prestressing forces and the deflections of high-performance concrete structures. The present model has been verified by comparing with the experimental results from the test of time-dependent behaviors of pre-tensioned members using high-performance concrete. From this, the current model gives good relations with the experimental results, but the AASHTO method is not good for the prediction of time-dependent behaviors of high-performance concrete members.

AGE DEPENDENT INCREMENTAL CONSTITUTIVE LAW OF CONCRETE (콘크리트 재령종속특성을 고려한 증분구성관계)

  • Sung Won-Jin;Ahn Sung-Soo;Lee Yong-Hak
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.493-496
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    • 2004
  • The change of creep deformation mechanism due to the persistent change of stress conditions requires the constitutive relation for the analysis of long tenn behaviors considering age dependent material properties of concrete. In the present research, the process of time dependent behaviors in structure is divided into two stages; the non-mechanical deforming level which causes creep and shrinkage deformations, and the mechanical deforming level which causes mechanical deformations by the restraints of non-mechanical deformations due to internal or external factors. The incremental constitutive relation is derived by expanding the total stress-strain relation on the present time, with respect to the reference time using the Taylor series, and the modulus of elasticity in early ages of concrete was defined thru this process.

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Time-dependent Behaviors of Concrete Exposed in the 100% Relative Humidity (상대습도 100% 환경에 노출된 콘크리트의 시간 의존적 거동)

  • Min, Kyung-Hwan;Kim, Youl-Hee;Jung, Hyung-Chul;Yoon, Young-Soo
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.693-696
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    • 2008
  • In order to assess time-dependent behaviors of the high-strength concrete that applied in actual FCM bridges with various curing environments, the shrinkages of air-dried, sealed, and moist 100${\times}$100${\times}$400 mm prism specimens were measured. And the compressive creep test of 3 and 28 days aged concrete in the tap water and 10% CaCl$_2$ solutions were carried out, then results were compared with traditional test results of air-dried and sealed specimens. Time-dependent behaviors of the concrete that according to curing circumstances between sealed and moist specimens show remarkable differences not only on the shrinkage but also on the creep. Hence there need some reconsiderations to the traditional creep test manners that predicting the creep and shrink age of actual concrete structures.

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Three Axioms in Tribology

  • Xie, You-Bai
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.3-10
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    • 2000
  • The undesired situation of development of tribology and its reason is analyzed. The problem comes from insufficient study on the concept system and method system, which can match the name, definition and nature of tribology. The existence of three axioms in tribology is discussed. They are axiom of system dependent, axiom of time dependent and axiom of coupling of behaviors of multi-discipline. A series of lemmas has been deduced from three axioms. It is expected that they can be a foundation to establish the concept system and method system.

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Numerical Simulation of Colliding Behaviors of Ice Sheet Considering the Viscous Material Properties (점성변형 특성을 고려한 빙판의 충돌거동에 대한 수치해석)

  • 노인식;신병천
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.162-172
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    • 1993
  • In the present paper, the overall state of the arts of ice mechanics which is the most typical research topic of the artic engineering field was studied. And also, ice loads genrated by ice-structure interaction were estimated using numerical approach. The effects of viscous property of ice sheets to the ice load were investigated. The time dependent deformation behaviors of ice was modeled by visco-plastic problem using the finite element formalism. Constitutive model representing the material properties of ice was idealized by comblned rheological model with Maxwell and Voigt models. Numerical calculations for the bending and crushing behavior of ice sheet which are the most typical interaction modes between ice sheets and structures were carried out. The time dependent viscous behaviors of ice sheets interaction forces acting on structures were analyzed and the results were studied in detail.

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Age-Dependent Behaviors of Curved Composite Girder (곡선형 합성거더의 재령종속적 거동)

  • Park, Kun-Tae;Park, Yeong-Seong;Yeon, Dal-Goo;Sung, Won-Jin;Lee, Yong-Hak
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.79-80
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    • 2010
  • Age-dependent laboratory tests for a curved composite box girder were carried out to investigate age-dependent effects of concrete on toraional behavior of a curved girder. Time-dependent incremental finite element method predicted the toraional behavior as well as flexural including axial behaviors of the test specimen.

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Unbonded tendon model considering time-dependent behavior (시간의존적 거동을 고려한 비부착 텐던 모델)

  • Park, Jae-Guen;Choi, Jung-Ho;Shin, Hyun-Mock
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.463-466
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    • 2005
  • The purpose of this study is to develop of unbonded tendon model considering time-dependent behavior. In this paper, a numerical model for unbanded tendon is proposed based on the finite element method, which can represent straight or curved unbonded tendon behavior. This model and time-dependent material model are used to investigate the time-dependent behaviors of unbonded prestressed concrete structures. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of concrete structures was used. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and models for reinforcements and tendons in the concrete. The smeared crack approach is incorporated. It accounts for the aging, creep and shrinkage of concrete and the stress relaxation of prestressing steel. The proposed unbonded tendon model and numerical method for time-dependent behavior of unbonded prestressed concrete structures is verified by comparison with reliable experimental results.

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Time-dependent Flow Properties of Commercial Kochujang (Hot Pepper-Soybean Paste)

  • Choi, Su-Jin;Yoo, Byoung-Seung
    • Food Science and Biotechnology
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    • v.14 no.3
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    • pp.413-415
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    • 2005
  • Time-dependent flow properties of commercial kochujang (hot pepper-soybean paste) were evaluated at various shear rates (5, 15, 25, and $35\;sec^{-1}$) and temperatures (5, 15, and $25^{\circ}C$). Flow properties of all samples showed thixotropic behaviors, which were qualitatively evaluated and quantitatively described by the Weltman, Hahn, and Figoni and Shoemaker models. Time-dependent flow properties of kochujang were found to vary over the range of the shear rate and temperature investigated. Time-dependent models of Weltman and Hahn were suitable ($R^2=0.923-0.987$) for commercial kochujang.

Analysis of Multi-Story Prestressed Concrete Structure Considering the Effect of Construction Stage (시공단계의 영향을 고려한 프리스트레스 콘크리트 다층 구조물의 해석)

  • Jeon, Chan-Ki
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.5 no.3
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    • pp.213-223
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    • 2001
  • This paper presents an analytical procedure for the time-dependent analysis of the multi-story prestressed concrete structure under the construction stage. To account for the actual structural behavior, the procedure considers the effects due to the construction interval and the time-dependent losses of prestress at every construction step on the entire structural response. A numerical study is performed to demonstrate the general validity of the approach and to quantitatively evaluate the effects resulted from the time-dependent behaviors during construction. Recommendations and conclusions are developed by comparisons with structural responses using the present and conventional methods of analysis. The comparative results show that both effects of sequential construction and time-dependent prestress losses should be considered for the construction stage analysis.

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The Effect of External Noise on Dynamic Behaviors of the $Schl\ddot{o}gl$ Model with the First Order Transition fora Photochemical Reaction

  • 김경란;Lee, Dong J.;신국조
    • Bulletin of the Korean Chemical Society
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    • v.16 no.11
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    • pp.1113-1118
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    • 1995
  • The Schlo'gl model with the first order transition for a photochemical reaction is considered to study the dynamic behaviors in the neighborhood of the Gaussian white noise by obtaining the explicit results of the time-dependent variance and time correlation function with the aid of approximate methods based on the stationary properties of the system. Then, we discuss the effect of external noise strength on the stability of the model at steady states in detail.

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