• 터널과지하공간
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• 제8권1호
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• pp.1-7
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• 1998

In order to get the information of the deformational behavior of rock masses with time in waste disposal repository, it is necessary to measure the relationships between stress and strain and time for temperature. A creep law is used in conjunction with the elastic moduli to calculate stress and displacement following waste emplacement. Exponential-time law's parameters consist of stress and temperature. In this study, thermal creep test was carried out for Whangdeung granite. The measured creep deformation behavior was well explained by exponential time law and generalized Kelvin's rheological model. Mechanicla coefficients for exponential-time creep law showed the clear tendency of temperature dependent while those for Kelvein's model didn't.

• Computers and Concrete
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• 제21권3호
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• pp.269-278
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• 2018

In this paper, two methods M1 and M2 to determine long-term deflection through finite element analyses including the effect of creep and relaxation are proposed and demonstrated for a PSC box-girder. In both the methods, the effect of creep is accounted by different models from international standards viz., ACI-209R-92, CEB MC 90-99, B3 and GL2000. In M1, prestress losses due to creep and relaxation and age adjusted effective modulus are estimated through different models and have been used in finite element (FE) analyses for individual time steps. In M2, effects of creep and relaxation are implemented through the features of FE program and the time dependent analyses are carried out in single step. Variations in time-dependent strains, prestress losses, stresses and deflections of the PSC box-girder bridge through M1 and M2 are studied. For the PSC girder camber obtained from both M1 and M2 are lesser than simple bending theory based calculations, this shows that the camber is overestimated by simple bending theory which may lead to non-conservative design. It is also observed that stresses obtained from FEM for bottom fibre are lesser than the stresses obtained from bending theory at transfer for the PSC girder which may lead to non-conservative estimates.

• Steel and Composite Structures
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• 제26권5호
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• pp.533-547
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• 2018

In this paper the time-dependent creep analysis of a thick-walled FG cylinder with finite length subjected to axisymmetric mechanical and thermal loads are presented. First order shear deformation theory (FSDT) is used for description of displacement components. Inner and outer temperatures and outer pressure are considered as thermo-mechanical loadings. Both thermal and mechanical loadings are assumed variable along the axial direction using the sinusoidal distribution. To find temperature distribution, two dimensional heat transfer equation is solved using the required boundary conditions. The energy method and Euler equations are employed to reach final governing equations of the cylinder. After determination of elastic stresses and strains, the creep analysis can be performed based on the Yang method. The results of this research indicate that the boundaries have important effects on the responses of the cylinder. The effect of important parameters of this analysis such as variable loading, non-homogeneous index of functionally graded materials and time of creep is studied on the behaviors of the cylinder.

• Steel and Composite Structures
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• 제28권3호
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• pp.331-347
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• 2018

In this paper history of stresses, strains, radial and circumferential displacements of a functionally graded thick-walled hollow cylinder due to creep phenomenon is investigated. The cylinder is subjected to an arbitrary non-axisymmetric two dimensional thermo-mechanical loading and uniform magnetic field along axial direction. Using equilibrium, strain-displacements and stress-strain relations, the governing differential equations of the problem containing creep strains are derived in terms of radial and circumferential displacements. Since the displacements are varying with time due to creep phenomenon, an analytical solution is not available for these equations. Thus, a semi-analytical procedure based on separation of variables and Fourier series together with a numerical procedure is employed. The numerical results indicate that the non-axisymmetric loading and the material grading index have significant effect on stress redistributions. Moreover, by proper selection of material for any combination of non-axisymmetric loading, one can arrive suitable response for the cylinder to achieve optimal design. With some simplifications, the results are validated with the existing literature.

• 한국산업융합학회 논문집
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• 제13권3호
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• pp.125-131
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• 2010

This study is to give more accurate information by performing the time depend ent analysis to take into account the long-term losses of precast PSC concrete bridge and analyzing the second stress, final camber and cross section stress of precast PSC caused by creep and drying shrinkage. As time goes by, the stress and deformation in the cross section vary continuously by the influence of creep and drying shrinkage. Due to this, the stress redistribution occurs and the internal force variation also happens along the point on the same cross section and with the passage of time.

• 콘크리트학회논문집
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• 제11권3호
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• pp.23-34
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• 1999

In designing PSC box girder bridge, the dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which, therefore, must considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code. In this study the creep and shrinkage test were carried out for four curing ages of concrete which was applied to the pretressed concrete box-girder bridge at a construction site, and the results of test were compared to the values of prediction by the design code. Shrinkage test shows that the test results are similar to KSCE-96 and JSCE-96 but very higher than other prediction model and creep test results are generally similar to ACI-209 and DSCE-96 but lower than other prediction models in contrast to shrinkage test.

• 터널과지하공간
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• 제14권1호
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• pp.69-77
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• 2004

암석의 시간 의존 변형거동은 암석의 가장 근본적인 역학적 성질 중의 하나이며, 크립거동의 특성과 메커니즘에 대한 연구는 지하 암반 구조물의 장기적 안정성을 평가하는데 필수적이라 할 수 있다. 이에 본 연구에서는 국내 화강암을 대상으로 단축압축하중 하에서 크립시험을 실시하였고, 수분과 응력 수준을 달리하여 각각의 조건에 따른 크립 특성을 비교, 분석하였다. 크립시험 결과 화강암은 1차, 2차 및 3차로 확연히 구분된 크립거동을 보였다. 1차 크립거동은 대체로 24시간 내에 종결되었으며, 2차 크립 변형률은 단축압축강도에 대한 재하응력의 비율이 증가함에 따라 증가하였다. 일정 응력하에서 화강암의 최대강도는 시간에 따라 감소하는 경향을 보였다. 완전 포화된 시료는 자연 건조된 시료보다 훨씬 큰 크립 변형량 및 변형률을 보였으며, 포화시료의 파괴강도 및 파괴시간은 급격히 감소하였다. 본 연구의 크립시험 결과를 버거모델(Burger's model) 및 이전 연구자들에 의해 제안된 두 개의 경험적 모델에 적용하여 크립의 유동상수를 구하였다. 세 개의 모델 모두 화강암의 크립거동을 잘 나타내었으나, 그 중 버거모델이 실험결과와 가장 잘 일치하였다. 각각의 모델에서 결정된 유동상수들은 함수량과 응력 수준에 영향을 받았다. 또한 본 실험결과에 기초하여 자연건조 및 완전 포화된 화강암 시료에 대하여 응력 수준과 시간의존변형의 경험적 관계식을 유도하였다.

• 한국지반공학회논문집
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• 제19권5호
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• pp.291-299
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• 2003

본 연구에서는, 토목섬유의 크리프시험시 온도 및 토목섬유에 가해지는 구속응력을 제어할 수 있도록 고안된 온도제어 구속크리프시험(Temperature Dependent Confined Creep Test)을 수행하였다. 시험결과를 토대로, 시험온도 및 구속응력의 크기가 토목섬유의 크리프특성에 미치는 영향을 정량적으로 분석하였으며, 장기적인 크리프변위를 예측하기 위하여 시간-온도 중첩원리를 이용한 합성곡선을 작도하여, 1$\times$$10^7$min.(Geomembrane D)∼1$\times$$10^{10}$min.(Geogrid T)까지의 크리프변위를 예측하였다. 본 합성곡선에 의해, 토목섬유에 가해지는 구속하중에 따른 토목섬유의 이동계수(shift factor)를 도출하였다. 온도제어 구속크리프시험은 시트형 지오그리드와 지오멤브레인을 대상으로 하였으며, 시험온도는 5∼4$0^{\circ}C$의 범위로, 구속하중의 크기는 0∼9t/$cm^2$의 범위로 하였다.

• Structural Engineering and Mechanics
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• 제38권2호
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• pp.171-193
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• 2011

One of the possible alternatives of simulation-based time-dependent reliability assessment of pre-stressed biconcave and biconvex cable trusses, the Monte Carlo method, is applied in this paper. The influence of an excessive deflection of cable truss (caused by creep of cables and rheologic changes) on its time-dependent serviceability is investigated. Attention is given to the definition of the basic random variables and their statistical functions (basic, mutually dependent random variables such as the pre-stressing forces of the bottom and top cable, structural geometry, the Young's modulus of elasticity of the cables, and the independent variables, such as permanent load, wind, snow and thermal actions). Then, the determination of the response of the cable truss to the loading effects, and the definition of the limiting values considering serviceability of the structure are performed. The potential of the method, using direct Monte Carlo technique for simulation-based time-dependent reliability assessment as a powerful tool, is emphasized. Results obtained by the First order reliability method (FORM) are compared with those obtained by the Monte Carlo simulation technique.

• Computers and Concrete
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• 제1권2호
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• pp.151-168
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• 2004

A two-dimensional nonlinear finite element model is developed to simulate time-dependent cracking of reinforced concrete members under service loads. To predict localized cracking, the crack band model is employed to model individual crack opening. In conjunction with the crack band model, a bond-interface element is used to model the slip between concrete and reinforcing steel permitting large slip displacements between the concrete element nodes and the steel truss element nodes at crack openings. The time-dependent effects of concrete creep and shrinkage are incorporated into the smeared crack model as inelastic pre-strains in an iterative solution procedure. Two test examples are shown to verify the finite element model with good agreement between the model and the observed test results.