• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1562-1570
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• 2003

The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. The radial return mapping is one of the most robust integration scheme currently used. Nonlinear kinematic hardening model of Armstrong-Fredrick type has recovery term and the direction of kinematic hardening increment is not parallel to that of plastic strain increment. In this case, The conventional radial return mapping method cannot be applied directly. In this investigation, we expanded the radial return mapping method to consider the nonlinear kinematic hardening model and implemented this integration scheme into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using Newton method and bisection method. Using dynamic yield condition derived from linearization of flow rule, the integration scheme for elastoplastic and viscoplastic constitutive model was unified. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

• Proceedings of the SCSK Conference
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• 1999.10a
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• pp.123-131
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• 1999

Liquid crystal known as a rheological barrier to coaleseence of oil dorplets. increases. emulsion stability, water-holding capacity and promotes active material penetration to skin. Some investigation for its rheological characteristics have been reported but its relations to consumer perception have been rarely published. In this study oil/water emulsion and oil/liquid crystal/water systems were manufactured using the same composition of Behenyltrimethylammonium chloride/Cetostearyl alcohol/Lanolin oil. and rheological properties of each system were investigated with Cone and Plate rheometer. The formation of liquid crystalline phase was observed with polarized microscope and Differential Scanning Calorimeter. Continuous shear experiment, creep yield and water holding capacity were measured for oil/water and oil/liquid crystal/water systems. The results were compared with sensory evaluations. Oil/liquid crystal/water system showed higher viscosity at the same shear rate, higher viscoelasticity and higher yield stress than oil/water system. These properties were expected to show good spreadability and excellent richness without waxiness I hair care products of creme type. This expectation was consistent with the results of sensory experiments. Water-holding capacity was evaluated by measuring residual water of specimens at specific temperature and relative humidity, Oil/liquid crystal/water system was proved to have ability to hold water in comparison with oil/water system. The results indicated that oil/liquid crystal/water system was of benefit to rheological properties creme type hair care products.

• Journal of the Speleological Society of Korea
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• no.72
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• pp.19-30
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• 2006

The purpose of this study is to clarified the geology and geomorphic characteristics of the Hantan River Basin. In this area, some kind of landforms are developed such as pre-land forms, lava plateau, and present landforms etc. Some river terraces are peculiar features in the area. Some conclusions are as follows : The vicinity of the Hantan River is lava plateau formed from the volcanic activity. Some steptoes are located in the lava plateau. Baekeuiri formation means the river bed boulder beneath the lava formation. The development of drainage patterns are unstable and the bifurcation ratio, the ratio of mean length of the river are lower than the other rivers. The relative height of the terraces is about $5{\sim}25m$ and the terraces are alluvial terraces. In the Jiktang Fall area, bedrock is granite and basalt plateau covered the bedrock. In that point, the old erosion surface is relatively steeper than the horizontal-basalt plateau. Vertical columnar joints are developed and weathering materials creep on the valley wall. The cross section of the landform of the Kosukjung vicinities are somewhat different from the landforms of Jiktang Fall. The bedrock near the Kosukjung is granite that is the same with the Jiktang Fall. But the cross section shows a asymmetrical curve from each side.

• Corrosion Science and Technology
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• v.11 no.2
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• pp.48-55
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• 2012

Clamping force of a high strength bolt is reduced by a certain period of time after the initial set-up. In case of special treatments on faying surfaces such as protective coating, clamping force is relaxed more severely. Tests for slip critical joints subject to various faying surface parameters were conducted. Five different surface treatments were tested including mill scale surface, blast surface, rust surface and coated surfaces. Each specimen was composed of F10T M20 of high strength bolts and steel plates. Based on the result of slip coefficient test, blast treatment surface showed 0.59, rust treatment surface showed 0.54 and inorganic zinc treatment surface exhibited 0.44. Clean mill treatment surface and red lead paint treatment surface were 0.23, 0.21 respectively. It is identified that the slip coefficient in Korean structural design guide should be determined for various surface conditions. Subsequently from long term relaxation test of ASTM A 490 high strength bolts, relaxation of no-coated surfaces such as blast, clean mill, rust treatment, the loss of initial clamping load was 10.5%, 13.6% and 7.9% for 1,000 hours, while the loss of initial clamping force was reached as 15.0%, 18.7% more than the required redundancy 10% in case of inorganic zinc and red lead painted treatment. It is required that the limit of relaxation on coated faying surface should be established separately for various surfaces.

• Steel and Composite Structures
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• v.20 no.2
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• pp.379-397
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• 2016

Due to creep and shrinkage of the concrete core, concrete-filled steel tubular (CFST) arches continue to deform in the long-term under sustained loads. This paper presents analytical investigations of the effects of geometric nonlinearity on the long-term in-plane structural performance and stability of three-pinned CFST circular arches under a sustained uniform radial load. Non-linear long-term analysis is conducted and compared with its linear counterpart. It is found that the linear analysis predicts long-term increases of deformations of the CFST arches, but does not predict any long-term changes of the internal actions. However, non-linear analysis predicts not only more significant long-term increases of deformations, but also significant long-term increases of internal actions under the same sustained load. As a result, a three-pinned CFST arch satisfying the serviceability limit state predicted by the linear analysis may violate the serviceability requirement when its geometric nonlinearity is considered. It is also shown that the geometric nonlinearity greatly reduces the long-term in-plane stability of three-pinned CFST arches under the sustained load. A three-pinned CFST arch satisfying the stability limit state predicted by linear analysis in the long-term may lose its stability because of its geometric nonlinearity. Hence, non-linear analysis is needed for correctly predicting the long-term structural behaviour and stability of three-pinned CFST arches under the sustained load. The non-linear long-term behaviour and stability of three-pinned CFST arches are compared with those of two-pinned counterparts. The linear and non-linear analyses for the long-term behaviour and stability are validated by the finite element method.

• 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.

• Magazine of the Korea Concrete Institute
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• v.20 no.6
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• pp.28-35
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• 2008

The Burj Dubai Project will be the tallest structure ever built by man; when completed the tower will be more than 700 meter tall and more than 160 floors. While the early integration of aerodynamic shaping and wind engineering considerations played a major role in the architectural massing and design of this multi-use/residential tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria, the material selection for the structural systems of the tower was also a major consideration and required detailed evaluation of the material technologies and skilled labor available in the market at the time Concrete was selected for its strength, stiffness, damping, redundancy, moldability, free fireproofing, speed of construction, and cost effectiveness. In addition, the design challenges of using concrete for the design of the structural system components will be addressed. The focus on this paper will also be on the early planning of the concrete works of the Burj Dubai Project.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.31-37
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• 2017

The use of half PC slab has been increasing to shorten construction period. Because the drying shrinkage of topping concrete is restrained by PC slab, the tensile stress is generated at the topping concrete and the cracks can be occurred at the topping concrete due to drying shrinkage. Therefore, it is important to predict the tensile strain of half PC slab due to drying shrinkage to improve the quality of half PC slab. However, there is no studies on prediction of shrinkage behavior of half PC slab yet. Therefore, in this study, half PC slab was made, and the predictability of tensile strain generated at half PC slab due to drying shrinkage was investigated. The step by step method considering creep was used to estimate the tensile strain of half PC slab. In result, good agreement was obtained between the analytical and experimental values.

• Journal of Conservation Science
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• v.7 no.2
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• pp.68-79
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• 1998

The protecting-chamber for a standing Buddha of Mireuk-ri temple site at Jungwon is composed of granite of Cretaceous age which mainly consists of quartz, perthite, plagioclase, and biotite with minor amounts of muscovite, apatite, chlorite, sericite and opaque mineral. There are abundant cracks which may be developed by strong weathering and differential loading by structural unbalances of the whole protecting-chamber. Cracks can be divided into three types based on genesis as those formed by exfoliation, intrinsic, and pressure. The exfoliation occurred along the onion structure of the granite. The pressure cracks are generally superimposed on the exfoliation ones, which might be developed by structural unbalance of the protecting-chamber resulted from differential loading in places. The structural unbalance may be due to change in physical properties of the rocks according to strong weathering, differential settling of basement soil by difference in loading in places of protecting-chamber, westward creep of the basement soil below the West wall and related different resistance of the basement soil against the loading, and partial depression of the West wall. For the conservation of the protecting-chamber, it must be considered the method of stabilizing the basement and treatment of the cracks.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.39-45
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• 2008

The most important elements in flexible pavement design criteria are stress and strain distributions. To obtain reasonable stress and strain distributions in pavements, moving wheel loads must be applied to analyze the pavement responses. In this study, finite element analysis was used to identify the three-dimensional states using the vehicle load into a constant-position / time-variable load (25, 50 and 80km/hr). In an elastic system, the strain is the same in both longitudinal and transverse directions under a single wheel. However, the same is not necessary in a viscoelastic system. Test results showed that the maximum values between transverse and longitudinal strains the bottom of asphalt concrete base layers under 25km/hr were were about 40 percent.