• Computers and Concrete
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• v.4 no.2
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• pp.101-117
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• 2007

A new model predicting the nonlinear basic creep behaviour of concrete structures subjected to high multi-axial stresses is proposed. It combines a model based on the thermodynamic framework of the elasto-plastic continuum damage theory for time-independent material behaviour and a rheological model describing phenomenologically the long-term delayed deformation. Strength increase due to ageing is regarded. The general 3D solution for the creep theory is derived from a rate-type form of the uniaxial formulation by the assumption of associated creep flow and a theorem of energy equivalence. The model is able to reproduce linear primary creep as well as secondary and tertiary creep stages under high compressive stresses. For concrete in tension a simple viscoelastic formulation is applied. The material law is then incorporated into a finite element solution procedure for analysis of reinforced concrete structures. Numerical examples of uniaxial creep tests and concrete members show excellent agreement with experimental results.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.153-164
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• 2000

Numerical studies were carried out to investigate long-term behavior of flat plates, subjected to combined in-plane compressive and transverse loads. For the numerical studies, a computer program of nonlinear finite element analysis was developed. It can address creep and shrinkage as weel as geometrical and material nonlinearity, and also it can address various load combinations and loading sequences of transverse load, in-plane compressive load and time. This numerical method was verified by comparison with the existing experiments. Parametric studies were performed to investigate the strength variations of flat plates with four parameters; 1) loading sequence of floor load, compressive load and time 2) uniaxial and biaxial compression 3) the ratio of dead to live load 4) span length. Through the numerical studies, the behavioral characteristics of the flat plates and the governing load combinations were examined. These results will be used to develop a design procedure for the long-term behavior of flat plates in the future.

• Journal of Industrial Technology
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• v.33 no.A
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• pp.109-116
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• 2013

In this study the compressive strength data were collected from ready­mix concrete plants, and the analysis result showed that when using A­D test the concrete of 24MPa is suitable than that of 21MPa for normal distribution. The prediction formula for average compressive strength were proposed to $f_{cu}=f_{ck}+4(MPa)$. When comparing the proposed equations and existing relationship, the estimation variations of elastic modulus and creep modulus were not significant. The proposed equation confirmed that there was no effect to the influence function for modulus of elasticity and creep. Therefore, it was concluded that the proposed equation could replace the exiting interaction formula.

• Elastomers and Composites
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• v.48 no.2
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• pp.156-160
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• 2013

A study on compressive creep behavior of ACM rubber for automotive engine gasket was performed using TMA thermal analysis. From the results of isothermal measurements with constant load of 1 N at several different temperatures of 160, 180, 200, and $220^{\circ}C$, compressive creep data at the given temperatures were obtained, and therefrom, shift factor ($a_T$) and master curve at reference temperature of $160^{\circ}C$ were obtained using time-temperature superposition principle (TTSP). $C_1$ and $C_2$ of WLF (Williams-Landel-Ferry) equation were calculated through the WLF plot as -1.107 and 11.571, respectively. From this, life time of ACM rubber at $120^{\circ}C$ was predicted as about 24,000 hrs.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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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.

• KCI Concrete Journal
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• v.11 no.3
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• pp.29-43
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• 1999

The effects of superplasticizers on fresh and hardened concrete were investigated. The experimental program included tests on the workability and slump loss, bleeding, setting time, air content, compressive, tensile and flexural strength, permeability, shrinkage, freeze-thaw durability and creep deformation. Properties of superplasticized concrete were compared with those of conventional and base concretes. Superplasticizers were observed to have an appreciable fluidifying action in fresh concrete. They permitted a significant water reduction while maintaining the same workability. Bleeding of superplasticized concrete was much lower than that of conventional concrete of the same consistency. This indicates that the use of superplasticizers did not affect the tendency of segregation of fresh concrete. The compressive, tensile, and flexural strengths of superplasticized concrete were significantly higher than those of conventional concrete. The permeability and drying shrinkage and creep of superplasticized concrete were less than those of conventional concrete, but there were no significant differences between base and superplasticized concrete. Compared with base concrete, non-air-entrained superplasticized concrete had slightly higher freeze-thaw durability. and superplasticized concrete with an appropriate amount of entrained air Eave even better resistance to freezing and thawing.

• Structural Engineering and Mechanics
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• v.89 no.4
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• pp.335-347
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• 2024

This study pioneers the exploration of creep and shrinkage behavior in ambient-cured geopolymer concrete (GPC), a vital yet under-researched area in concrete technology. Focusing on the influence of sodium hydroxide (NaOH) solution concentration, the research utilizes low calcium fly ash (Class-F) and alkaline solutions to prepare two sets of GPC. The results show distinct patterns in compressive strength development and dry shrinkage reduction, with a 14 M NaOH solution demonstrating a 26.5% lower dry shrinkage than the 16 M solution. The creep behavior indicated a high initial strain within the first 7 days, significantly influenced by curing conditions and NaOH concentration. This study contributes to the existing knowledge by providing a deeper understanding of the time-dependent properties of GPC, which is crucial for optimizing its performance in structural applications.

• Structural Engineering and Mechanics
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• v.37 no.3
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• pp.321-330
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• 2011

Long-term properties of concrete affect structures in many respects, not excepting dynamic behaviors. This paper investigates the influence of concrete creep on the dynamic behaviors of concrete filled steel tube (CFT) arch bridges, by means of combining the analytical method for the creep of axially compressed CFT members, which is based on Model B3 for concrete creep, with the finite element model of CFT arch bridges. By this approach, the changes of the stress and strain of each element in the bridge with time can be obtained and then transformed into damping and stiffness matrices in the dynamic equation involved in the finite element model at different times. A numerical example of a long-span half-through CFT arch bridge shows that creep influences the natural vibration characteristics and seismic responses of the bridge considerably, especially in the early age. In addition, parameter analysis demonstrates that concrete composition, compressive strength and steel ratio have an obvious effect on the seismic response of the CFT arch bridge.

• Computers and Concrete
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• v.7 no.6
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• pp.533-547
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• 2010

Recent developments in concrete mixing made possible the production of concretes with high compressive strength showing, simultaneously, high workability. These concretes also present high strengths at young ages, allowing the application of loads sooner. It is of fundamental importance to verify if creep models developed for current concrete still apply to these new concretes. First, a FEM-based software was adopted to test available creep models, most used for normal strength concrete, considering examples with known analytical results. Several limitations were registered, resulting in an incorrect simulation of three-dimensional creep. Afterwards, it was implemented a Kelvin-chain algorithm allowing the use of a chosen number of elements, which adequately simulated the adopted examples. From the comparison between numerical and experimental results, it was concluded that the adopted algorithm can be used to model creep of high strength concrete, if the material properties are previously experimentally assessed.

• Journal of the Korea Concrete Institute
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• v.13 no.1
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• pp.38-45
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• 2001

Numerical studies were carried out to develop the moment magnifier method for long-term behavior of flat plates, subjected to combined in-plane compressive and transverse loads. Nonlinear finite element analyses were performed for the numerical studies. Through the numerical studies, the long term behavior of the flat plate subjected to uniform or nonuniform floor load was investigated, and creep effects on the degradation of strength and stiffness of the slabs were examined. As a result, the creep factor was implemented to describe the creep effect on the flat plate. The moment magnifier method using the creep factor was developed for long-term behavior of flat plates. Also, the design examples were shown for the verification of the proposed design method.