• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.190-200
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• 1991

Certain structural components are exposed to high temperatures. At high temperature, under thermal and mechanical loading, metal components exhibit both creep and plastic behavior. The unified constitutive theory is to model both the time-dependent behavior(creep) and the time-independent behavior(plasticity) in one set of equations. Microscopically both creep and plasticity are controlled by the motion of dislocations. A finite element method is presented encorporating a unified constitutive model for the transient analysis of viscoplastic behavior of structures exposed to high temperature.

• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.89-100
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• 1994

The current test procedure for transfer length, which determine transfer length by measuring concrete strain, has an actual bond stress state in the prestressed pretensioned member : however, it is difficult to determine the bond properties of maximum bond stress and bond stiffness with this method. It is also difficult for design engineer to understand and select a correct safety criterion from the widely distributed results of such a ransfer test alone. An alternative testing procedure is provided here to determine the bond properties without measuring the concrete strain. In this test the bond stress is measured directly by creating a similar boundary condition within the transfer length in a real beam during the transfer of prestressing force. The prestressing force was released step by step by step from the unloading side. The release of force induces a swelling of the strand at the unloading side of concrete block, bonding force in the block, and a bond slip of the strand toward the other side of the block. Two center-hole load cells are used to record the end loads until the point of general bond slip(maximum bond stress). It is suggested that this test procedure be performed with the ordinary transfer test when determining the transfer length in a prestressed, pretensioned concrete beam.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.69-77
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• 2005

Joint spacing is a potent influence in increasing the long term performance of jointed concrete pavement slabs through the control of tensile stress, sealant failure and Load Transfer Efficiency (LTE). Internal Joint Spacing is an empirical and fixed method therefore this study will present the optimum joint spacing considerations depending on various climactic conditions. Calculating the optimum joint spacing eliminates random cracking due to the effect of the environmental loads such as the early behavior of drying shrinkage and heat hydration. Optimum joint spacing is calculated so as not to cause pavement distress by the deterioration of LTE by long term pavement movement. This study shows that the provisional joint spacing is 6-8m. Pavement Distress Prediction Models show that pavement distress has no effect on joint spacing of 8m.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4D
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• pp.593-600
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• 2006

Joint opening of jointed concrete pavement is caused by change in temperature and humidity of adjoined slab. The magnitude of joint opening influences on the load-transfer-efficiency and the behavior of sealant. If temperature or humidity decreases, joint opening increases. Generally maximum joint opening of a given joint is predicted by using AASHTO equation. While different magnitudes of joint opening at the individual joints have been observed in a given pavement section, AASHTO equation is limited to predict average joint opening in a given pavement section. Therefore the AASHTO equation may underestimate maximum joint for the half of joint in a given pavement section. Joints showing larger opening than the designed may experience early joint sealant failure, early faulting. Also unexpected spalling may be followed due to invasion of fine aggregate into the joints after sealant pop-off. In this study, the variation of the joint opening in a given pavement section was investigated based on the LTPP SMP data. Factors affecting on the variation are explored. Finally a probabilistic joint opening model is developed. This model can account for the reliability of the magnitude of joint opening so that the designer can select the ratio of underestimated joint opening.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.25-32
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• 2006

Behavior of concrete pavement due to temperature gradient was investigated for 48 hours at test road using Falling Weight Deflectometer. The deflections at slab center changed similarly to those of ambient temperature and temperature gradients in the slab. And rapid variations in the deflections were observed between 8 to 12 in the morning. However, dynamic modulus of subgrade reaction and joint deflections showed reverse trends to the ambient temperature and temperature gradients. The dynamic modulus of subgrade reaction was significantly affected by temperature gradient when its value got higher. Backcalculated elastic moduli were obtained using AREA method and Method of Equivalent Thickness. The trends of the backcalculated elastic modulus were similar to those of dynamic modulus of subgrade reaction. Measured load transfer efficiencies showed maximum peak in the morning due to dowel locking. However, additional effort is necessary to verify the result.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.625-635
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• 1997

The base isolation technique and its benefits in reducing the transmitted earthquake energy into a structure have gained increasing recognition during the last two decades. Unfortunately, the current available design procedures, especially for base-isolated bridges, seem inadequate and too restrictive. As a result, practical design procedure still relies upon a series of deterministic time history analyses. In this study, the evaluation of the possibility of the normal mode method to predict the nonlinear seismic responses of base isolated bridges has been performed. The applicability has been examined through the numerical approach with isolator's elastic or plastic states of the base isolated bridges. Numerical results show that the 1st. mode period and the various responses are varied with the state but are conversed. And, the result show that the normal mode method is applicable to predict the seismic responses and to design the babe isolated bridge. Various analysis method to bridges with bilinearized hysteresis isolator and various pier heights are evalulated.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.115-121
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• 2005

At present, continual road constructions to connect from city to city are needed due to the geographical feature of Korea that about $70\%$ of the territory is mountainous area. Thus, the generation of large cut-slope has been inevitably formed. As a means of reinforcement on the cut-slope, in case of destructive disasters such as a snowstorm, pile embedment method is widely adopted. The pile embedment method is to resist possible move of soil by embedding piles from the surface to the immovable ground and then delivering the load from the piles to the immovable ground. In this study this writer analyzes the limitation of empirically used pile construction depth and its spacing through the numerical analysis. As a result, he suggests the most effective pile construction depth and space.

• Journal of the Korean Geotechnical Society
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• v.25 no.7
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• pp.23-33
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• 2009

In this study the characteristics of piled raft was investigated by using both centrifuge and numerical modeling. The ultimate bearing capacities of single pile, unpiled raft, freestanding pile group and piled raft were compared in order to investigate load sharing of each element : pile and raft. The comparison determined parameters to simply evaluate the ultimate bearing capacity of piled raft. Centrifuge test results were simulated by numerical simulation to verify the parameters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.624-629
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• 2016

A brake lever in a basic railway brake system is an important safety device that delivers braking force from the brake cylinder to the brake pad. The safety guidelines for designing rolling stock only qualitatively describe that the brake lever should have sufficient strength. Each train has a different type of brake lever. One brake lever that was designed with a factor of safety of 1.27 has failed, so the material was changed to increase the strength. Therefore, the stress distribution and weak points of the lever were identified by theoretical analysis. and structural analysis. Different brake lever designs were examined for KTX high-speed trains, which have a split-type structure, as well as for electric locomotives, which use an electric multiple unit (EMU) with a unity-type structure. A fracture test was also done to look at the relationship between the vertical stress and the bending stress during braking. The results were used to find a safety factor to apply to each train and suggest quantitative minimum guidelines. We also looked at changing the unity-type EMU brake lever to the split type under the same conditions and analyzed how much the design change affected the factor of safety.

• Journal of Korean Society of Steel Construction
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• v.28 no.1
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• pp.23-34
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• 2016

Concrete filled steel tube system has two major advantages. First, the confinement effect of steel tube improves the compressive strength of concrete. Second, the load capacity and deformation capacity of members are improved because concrete restrains local buckling of steel tube. It does, however, involve workability problem of using stud bolts or anchor bolts to provide composite effect for larger cross-sections. While the ribs inside the columns are desirable in terms of compressive behavior, they cause the deterioration in load capacity upon in-plane deformation resulting from thermal deformation. Since the ribs are directly connected with the concrete, the deformation of the ribs accelerates concrete cracking. Thus, it is required to improve the toughness of the concrete to resist the deformation of the ribs. Welding built-up tubular square columns can secure safety in terms of fire resistance if the problem are solved. This study focuses on mixing steel fiber in the concrete to improve the ductility and toughness of the columns. In order to evaluate fire resistance performance, loaded heating test was conducted with 8 specimens. The behavior and thermal deformation capacity of the specimens were analyzed for major variables including load ratio. The reliability of heat transfer and thermal stress analysis model was verified through the comparison of the results between the test and previous study.