• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.531-542
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• 2011

The time-dependent temperature distribution across the section in bridges is determined on the basis of the three-dimensional finite element analyses and numerical time integration in this study. The material properties which change with time and thermal stress of concrete are taken into account to effectively trace the early-age structural responses. Since the temperature distribution is nonlinear and depends upon many material constants such as the thermal conductivity, specific heat, hydration heat of concrete, heat transfer coefficients and solar radiation, three representative influencing factors of the construction season, wind velocity and bridge pavement are considered at the parametric studies. The validity of the introduced numerical model is established by comparing the analytical predictions with results from previous analytical studies. On the basis of parametric studies for four different bridge sections, it is found that the creep deformation in concrete bridges must be considered to reach more reasonable design results and the temperature distribution proposed in the Korean bridge design specification need to be improved.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.597-609
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• 2020

Accident Tolerant Fuels have been widely studied since the Fukushima-Daiichi accident in 2011 as one of the options on how to further enhance the safety of nuclear power plants. Deposition of protective coatings on nuclear fuel claddings has been considered as a near-term concept that will reduce the high-temperature oxidation rate and enhance accidental tolerance of the cladding while providing additional benefits during normal operation and transients. This study focuses on experimental testing of Zr-based alloys coated with Cr-based coatings using Physical Vapour Deposition. The results of long-term corrosion tests, as well as tests simulating postulated accidents, are presented. Zr-1%Nb alloy used as nuclear fuel cladding serves as a substrate and Cr, CrN, Cr_xN_y layers are deposited by unbalanced magnetron sputtering and reactive magnetron sputtering. The deposition procedures are optimized in order to improve coating properties. Coated as well as reference uncoated samples were experimentally tested. The presented results include standard long-term corrosion tests at 360℃ in WWER water chemistry, burst (creep) tests and mainly single and double-sided high-temperature steam oxidation tests between 1000 and 1400℃ related to postulated Loss-of-coolant accident and Design extension conditions. Coated and reference samples were characterized pre- and post-testing using mechanical testing (microhardness, ring compression test), Thermal Evolved Gas Analysis analysis (hydrogen, oxygen concentration), optical microscopy, scanning electron microscopy (EDS, WDS, EBSD) and X-ray diffraction.

• Applied Chemistry for Engineering
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• v.7 no.1
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• pp.194-202
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• 1996

Hot melt adhesive based on the polyamide resin was studied to improve the conventional hot melt adhesives such as ethylene-vinyl acetate which have inherent problems against creep and heat resistance. It was found that the terpolymer of nylons6, nylon66, and nylon12 or the nylon blend instead of nylon homopolymer was suitable base resin for hot melt adhesives, since the disruption of regularity in the polymer chains reduced the crystallinity, resulting in lower melting point and melt viscosity. Also, the rheological properties of the polyamide based hot melt adhesive could be controlled by the incorporation of terpene resin, butyl benzyl phthalate, and paraffin wax. The results of melt viscosities and tensile properties of adhesive itself indicated that the optimum adhesion properties could be obtained through the blending of CM831/843P resins with weight ratio 75/25~50/50. The adhesion between steel and steel was tested by using lap shear geometry. It was found that the surface roughness of steel affected the adhesion strength.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.21-34
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• 2014

This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.253-256
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• 2008

Although researches on the beams strengthened with Fiber reinforced Polymers (FRPs) have recently been conducted around the world, there are few researches on the beams with FRPs under a sustained load. This paper presents the behavior of the beams with Carbon Fiber Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) under a sustained load during 300 days. Strains of steel and FRP reinforcement were measured in order to investigate the behavior of the beams. Additionally, Adjusted Effective Modulus Method (AEMM) and Ghali and Farve's method were used to predict increase in the stress and strain caused by creep and shrinkage. Through the experiment, it was found that the beam with CFRP is more effective than the beam with GFRP in terms of flexural strengthening. Compared with analytical results, it was indicated that strains of tension steels were overestimated, whereas strains of compression steels were underestimated.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.13-16
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• 2008

Corbels are short cantilevers that project from the faces of a column and are a type of stress disturbed member, resisting both the ultimate shear force applied to them by the beam, and the ultimate horizontal force caused by shrinkage, temperature changes, and creep of the supported elements. Recently, as there have been an increase in the use of high-strength concrete and the concern about corrosion problems, lots of researches about hybrid reinforcing technique, applying strategically high performance reinforcements to the concrete elements, are performed. In this study, fiber reinforced high strength concrete corbels were constructed and tested for applying hybrid reinforcing technique to the corbels using steel fibers and headed bars. The results showed that the performance in terms of load carrying capacities, stiffness, ductility, and crack width was improved, as the steel fibers were added and the percentage of steel fibers was increased. In addition, the corbel specimens used headed bars as main tension ties showed superior load carrying capacities, stiffness, and ductility to the corbel specimens anchored main tension ties by welding to the transverse bars.

• 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 architectural history
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• v.17 no.3
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• pp.7-21
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• 2008

Three-story Stone pagodas in Gameunsa Temple site, one of the early staged stone pagodas, has been known as a standard of Silla stone pagodas. A stone pagoda is not only a stone art work and but also a stone architecture. In understanding the stone pagoda it is very important to be approached with technological side in which we can investigate the stone pagoda deeply and as well as to have been approached with art historical view. Also it needs that we should see the stone pagoda in view of structural safety. We can get many high technique from our ancestors who made Gameunsajiseoktap. 1. To reduce any deformation such as relaxation and sinking of members which is caused by a heavy load the members such as the lower tier of the base is made up of the foundation stone and side stone in each, comprising one stone. 2. A special construction method for connection between wall stone and column stone in stereobates was invented. It is to make column stone projected partially and wall stone be caved in that two members should be jointed well. This unique method is not used any longer after the three-story Stone pagodas in Gameunsa Temple Site. 3. In each side upper and lower member are not engaged as the size of roof stones and support stones of roof stones are different. It can be done for a distribution of perpendicular load and a prevention for relaxation of members. 4. It makes sure that to make upper ends of support stones 10mm lower was to be avoid upper loads to it judging from survey in disassemblying east pagoda. It proves that ancestors who made this stone pagoda had a technique to understand the structural matters to make small members as big as possible, not to engage in joint, to avoid in ends of members from upper load.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.99-110
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• 1999

Settlement and consolidation time were predicted through systematic soil investigation at the delta of Nakdong river where the preloading method was applied. Field measurements were executed with well-selected instruments. As the results of the comparison, the predicted settlement on the sand layer of about 20m thick underestimated the observed one by 20%. This underestimation was due to the effects of vibration during installation of PBD, creep, the overestimated deformation modulus, and so on. For the clay layer of about 20m in thickness under the sand layer, an ID analysis for underconsolidated soil initially overestimated the observed settlement by 240%. However, when the laboratory compression curve was reconstructed and a conventional ID analysis for NC clay was applied, the re-calculated settlement of the clay layer was relatively similar with the observed one. And the predicted consolidation time was about 45% less than the observed one, because of different influencing factors.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.189-197
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• 2003

The treatment and hauling of surplus soils which occur from construction activity are costly and have been demanding a reasonable recycling method. This study presents laboratory test results regarding the mechanistic properties of asphalt stabilized soils. The foamed asphalt equipment which generates the asphalt bubble was used to mix the soil. The marshall stability, indirect tensile test, resilient modulus, creep test and triaxial test(UU) were conducted to find out the performance of the asphalt stabilized soil. The test results were compared with the samples that fabricated in different conditions(the samples without asphalt and the reinforced samples using 2% cement). The inclusion of the asphalt in the soil has improved the marshall stability, resilient modulus and moisture susceptibility, and the addition of the 2% cement has even more increased these properties. The amount of the fines and the optimum moisture contents for mixing affects the mechanistic properties and important parameters for mix design.