• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.339-346
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• 2001

For temporary excavation support in private land area, the strand of ground anchor should be removed In order to get permission to install anchors. The extractable or removable-strand compression anchor system was developed and evaluated by a series of pull-out load tests. Anchor pull-out tests were performed on seven instrumented full-scale low-pressure grouted anchors installed in weathered soil at the Geotechnical Experimentation Site at Sungkyunkwan University, Four anchors are the compression type anchors and three are the tension anchors. Performance test, creep test, and long term relaxation test were performed and presented. Load distributor was developed in order to distribute large compressive stresses in grout.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.1
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• pp.54-61
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• 1998

Since Cr-Mo-V steel has excellent fracture and creep properties at elevated temperature, they are extensively used as steam turbine components such as the turbine rotor. However, the turbine rotor steel used to suffer material degradation during long term service. Therefore, the assessment of the safety and residual life of the turbine rotor is periodically required during service. One of the most convenient techniques for that is the hardness method mainly due to its simplicity and nondestructive characteristics. In this research, six specimens with different aging times of turbine rotor steel were artificially prepared by an isothermal heat treatment at $630^{\circ}C$. The micro Vickers hardnesses of specimens were measured at room temperature. The relationships between the fracture properties and the hardness ratio were investigated. And also an indirect method to evaluate the residual life of degraded turbine rotor was proposed based on the micro Vickers hardness measurement.

• Geomechanics and Engineering
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• v.1 no.2
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• pp.169-178
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• 2009

Due to the enormous amount of fills required, broken rock-fine grain soil mixtures have been increasingly used in the construction of high-fill foundations for airports, railways and highways in the mountain areas of western China. However, the compressibility behavior of those broken rock-fine grain soil mixtures remains unknown, which impose great uncertainties for the performance of those high-fill foundations. In this research, the mixture of broken limestone and a fine grain soil, Douposi soil, is studied. Large oedometer tests have been performed on specimens with different soil content. This research reveals the significant influence of fine grains on the compressibility of the mixture, including immediate settlement, creep, as well as wetting deformation.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.355-358
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• 2005

In this paper, an actual behavior of the pylon of Seohae Grand Bridge which is a cable stayed bridge and has been constructed 4 years ago was analyzed by using data acquisition system. As a result, the pylon of cable stayed bridge behaved normally with respect to the change of temperature. The annual displacement of the top of pylon(PY1) ranged from -71.4mm to +181.7mm in the longitudinal direction of the bridge. In the case of the longitudinal displacement, the displacement of PY1 was bigger than that of PY2 because PY1 is movable and PY2 is fixed in terms of the constraint condition of super structure. For the long term, PY1 will be sloped gently to the direction of Dangjin and PY2 will be also sloped gently to the direction of Pyongtaek by the effect of creep and shrinkage in the case of the longitudinal direction. The result of structural analysis showed good agreement with the result mentioned above.

• Structural Engineering and Mechanics
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• v.41 no.1
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• pp.139-155
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• 2012

Structural health monitoring systems are often installed on bridges to provide assessments of the need for structural maintenance and repair. Damage or deterioration may be detected by observation of changes in bridge characteristics evaluated from measured structural responses. However, construction materials such as concrete and steel cables exhibit certain time-dependent behaviour, which also results in changes in structural characteristics. If these are not accounted for properly, false alarms may arise. This paper proposes a systematic and efficient method to study the time-dependent effects on the dynamic properties of cable-stayed bridges. After establishing the finite element model of a cable-stayed bridge taking into account geometric nonlinearities and time-dependent behaviour, long-term time-dependent analysis is carried out by time integration. Then the dynamic properties of the bridge after a certain period can be obtained. The effects of time-dependent behaviour of construction materials on the dynamic properties of typical cable-stayed bridges are investigated in detail.

• Structural Engineering and Mechanics
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• v.61 no.1
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• pp.143-160
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• 2017

The paper studies the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of linear viscoelastic materials. Investigations are made by utilizing the exact equations of motion of the theory of viscoelasticity. The dispersion equation is obtained for an arbitrary type of hereditary operator of the materials of the constituents and a solution algorithm is developed for obtaining numerical results on the attenuation of the waves under consideration. Specific numerical results are presented and discussed for the case where the viscoelasticity of the materials is described through fractional-exponential operators by Rabotnov. In particular, how the rheological parameters influence the attenuation of the axisymmetric longitudinal waves propagating in the cylinder under consideration, is established.

• Journal of Adhesion and Interface
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• v.21 no.1
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• pp.6-13
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• 2020

The objective of the current study is to characterize the long-term stability and efficacy of a structural adhesive assembly under static load. An apparatus was designed to be used in the Instron tensile test machine that would allow for real time modeling of the failure characteristics of an assembly utilizing a moisture- cure adhesive which was bonded to concrete. A regression model was developed that followed a linear - natural log function which was used to predict the expected life of the assembly. Evaluations at different curing times confirmed the structure was more robust with longer cure durations prior to loading. Finally, the results show that under the conditions the assembly was tested, there was only a small amount of inelastic creep and the regression models demonstrated the potential for a stable structure lasting several decades.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.737-740
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• 2008

When UHSFRC is applied to structures, it can be expected that it shows excellent performance in a point of constructability and load capacity. However, its rich mix can cause some problems concerning the long-term behavior such as shrinkage and creep. Therefore it is inevitably needed to investigate its long-term behavior in order to apply it to structures safely. This study is dealing with the drying shrinkage of UHSFRC. UHSFRC shows relatively fast drying shrinkage in the early exposed ages and slow moisture diffusion caused by compact microstructure of the material. It was found that The KCI model to predict the drying shrinkage did not properly represent these properties of UHSFRC. therefore a modified drying shrinkage model applicable to UHSFRC, which has different shrinkage properties from that of normal concrete, was proposed

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.707-714
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• 2014

CFT (Concrete-Filled Tube) is a type of steel column comprised of steel tube and concrete. Steel tube holds concrete and the concrete inside tube takes charge of compressive load. This study presents structural performance of the CFT column which has 73~100 MPa high strength concrete inside. Fluidity, mechanical compression, pump pressure test in flexible pipe were conducted for understanding properties of the high strength concrete. Material properties were achieved by various experimental tests, such as slump, slump flow, air content, U-box, O-Lot, L-flow. In addition, mock-up tests were conducted to monitor concrete filling, hydration heat, compressive strength. From construction sites in Sang-am dong and University of Seo-kang, long-term behaviors could be effectively predicted in terms of ACI 209 material model considering elastic deformation, shrinkage and creep.

• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.