• Geotechnical Engineering
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• v.7 no.4
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• pp.65-74
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• 1991

Earth structures which located on the weak foundation settle for the long time due to the their own weight (embankment) simultaneously. Because of the consolidation and creep which are timedependent behaviour. This paper is presented creep test Processes using triaxial spparatus, and investigated creep charateristics of marine clay by creep test according to stress level And required and appropriate creep parameters of soil used in the creep equation are investigated by the creep test.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.113-123
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• 2012

The technology developed for the decrease of applying loads and self-weight of a structure is to improve conventional Foam Cement Banking Method (FCB) by applying mixed slurry of bottom ash, cement and foams. Since the foam-mixed concrete, which is a major material of the Bottom ash-mixed Light weight concrete Banking method (BLB) developed, contains mineral admixture such as cement, the behavior shows time-dependent deformation and deterioration of durability due to environmental exposure. Thus, this study is subject to figure out the characteristics of long-termed behavior and durability of the developed method by carrying out experiments for schemed parameters, which are considered to be factors affecting mainly on concrete's characteristics from mechanical analysis. As results of tests, it was found that the developed concrete offers higher resistance than conventional foamed concrete in terms of long-termed behaviors associated with drying shrinkage and creep, and durability problems of freeze-thaw and carbonation processes, especially with addition of bottom ash.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.59-66
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• 2004

Sand compaction pile (SCP)-improved ground is composite soil which consists of the SCP and the surrounding soft soil. When a surcharge load is applied to composite ground, time-dependent behaviors occur in the composite soil due to consolidation according to radial flow toward the SCP. In addition, stress transfer also takes place between the SCP and the soft soil. This paper presents the numerical results of cylindrical composite ground that was conducted to investigate smear effect on consolidation behaviors of SCP-improved ground. The results showed that the smeared zone of soft clay had a significant effect on effective stress-pore water pressure response, stress transfer mechanism and stress concentration ratio of composite ground. Amount of stress transfer between the clay and the SCP was maximum in depth of z/H=0.25, and decreased with depth. Stress concentration ratio of composite ground was not constant, but depended on consolidation process. It was also found that the value of stress concentration ratio in soft clay with smeared zone was larger than that in soft clay without smeared zone.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.77-84
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• 2008

The existing equations for radial consolidation cannot account for the changes of well resistance with time and cannot predict the appropriate in-situ consolidation curve. In this study, small cylinder cell tests are performed to evaluate the discharge capacity of PVD. Also, a block sample of 1.2 m in diameter and 2.0 m in height was consolidated to observe the change in the drainage capacity with time for three types of PVD. From the test results on a block sample, the drainage curves normalized with initial drainage of each PVD are similar, regardless of the PVD type and the consolidation curve, which is predicted using solutions of radial consolidation based on the discharge capacity measured in a small cylinder cell tests, significantly overestimates the degree of consolidation. The term of well resistance in the radial consolidation solution was back-calculated to fit the consolidation curve of a large block sample and it is defined as the time dependent well resistance factor, L(t). The L(t) was found to be linearly proportional to the dimensionless time factor, Th. It was also shown that the consolidation curve evaluated by using L(t) provides more accurate prediction than the existing solution.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.697-700
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• 2008

The object of this paper is to propose a logical prediction model of a concrete creep using rheology. Rheology is the study on the flow and stress relationship of matter under the influence of an applied stress. It is also estimated as an effective theory to describe concrete long-term deformations. According to a time dependency and a mechanism of occurrence, the proposed creep model was divided into four components, such as an elastic deformation, a long-term creep, a time dependent short-term creep and a time independent short-term creep. Evaluation on an actual creep deformation pattern by time passage confirmed these classification. In order to approve a rationality of the proposed model, most coefficients of each components were derived by the microprestresssolidification theory and design codes. Numerical approaches were also used when it was restricted within narrow limits. Finally, the proposed rheolgical model was verified by actual creep test results and compared with common methods.

• Tunnel and Underground Space
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• v.27 no.3
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• pp.121-131
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• 2017

We studied the time-dependent behaviors of rock and concrete materials by conducting the static and dynamic long-term strength tests. In particular, acoustic emission(AE) signals generated while the tests were analyzed and used for the long-term stability evaluation. In the static subcritical crack growth test, the long-term behavior and AE characteristics of Mode I and Mode II were investigated. In the dynamic long-term strength test, the fatigue limit and characteristics of generation of AE were analyzed through cyclic four points bending test. The graph of the cumulative AE hits versus time showed a shape similar to that of the creep curve with the first, second and third stages. The possibility for evaluating the static and dynamic long-term stability of rock and concrete is presented from the log - log relationship between the slope of the secondary stage of cumulative AE hits curve and the delayed failure time.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.81-92
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• 2013

This paper presents the results of a numerical investigation into the behavior of retaining wall subject to cycles of freezing and thawing due to seasonal temperature change. The thermo-hydro-mechanical coupled finite element modeling strategy was first established to simulate the wall behavior. A series of finite element analyses were then performed on a range of conditions representing seasonal temperature change characteristics. The results indicated that the average freezing temperature and the number of cycles of freezing and thawing were the primary influencing factors for the wall behavior. Also revealed was that the duration of freezing period does not significantly affect the wall displacement and the lateral earth pressure, and that the earth pressure on the wall does not significantly change due to the freezing and thawing action suggesting that the increase in the wall displacement during the freezing and thawing action may be attributed to degradation of backfill due to the freezing and thawing action.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.49-58
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• 1990

A numerical procedure is developed to analyze the time-dependent deflections of prestressed concrete bridges constructed by the segmental cantilever method. The developed computer program accounts for the time-dependent properties of prestressed concrete materials due to the varying modulus of elasticity, creep and shrinkage of concrete and the stress relaxation of prestressing steel. It also accounts for the stiffness increase due to the presence of the steel reinforcements and the effects of the shear deformation of the prestressed concrete bridge girders. The program is applied to a multi-span continuous segmental prestressed concrete bridge to demonstrate its capabilities and to explore the behavior characteristics of the segmental bridges.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.619-628
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• 2009

To predict the time-dependent behavior of concrete structures, the models which describe the time-dependent characteristics of concrete, i.e. creep and shrinkage are required. However, there must be significant differences between the displacements that are obtained using the given creep and shrinkage models and the measured displacements, because of the uncertainties of creep and shrinkage model itself and those of environmental condition. There are some efforts to reduce these error or uncertainties by using the model which are obtained from creep test for the concrete in construction site. Nevertheless, the predicted values from this model may be still different from the actual values due to the same reason. This study aimed to propose a method of estimating the creep coefficient from the measured displacements of concrete structure, where creep model uncertainty factor was considered as an error factor of creep model. Numerical validation for double composite steel box and concrete beam showed desirable feasibility of the presented method. Consideration of the time-dependent characteristics of creep as one of the error factors make it possible to predict long-term behaviors of concrete structures more realistically, especially long-span PSC girder bridges and concrete cable-stayed bridges of which major problem is the geometry control under construction and maintenance.