• Journal of architectural history
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• v.30 no.3
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• pp.33-44
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• 2021

San-ja is one of the main members consisting of the roof of traditional wooden buildings in Korea. In this study, the regional characteristics of the materials used in San-ja and changes of the materials over time were examined. To this end, 123 documents on the repair of wooden architectural heritage recorded since the 1950s were reviewed. It was found that there was a difference in the San-ja material by region because of the diversity in the conditions of material supply. For instance, bamboo was the most frequently used material in Jeollanam-do province because it was readily available. However, with the development of transportation and vehicle, the regional characteristics have disappeared. As a result, the material has been unified with bamboo now. This is because bamboo is specified as a representative material in the specification or the convenience of construction is prioritized. In addition, the social and economic conditions at the time of repair had an influence on the selection of the San-ja materials.

• Structural Engineering and Mechanics
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• v.82 no.4
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• pp.477-490
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• 2022

This article investigates the nonlinear behavior of two-directional functionally graded materials (TDFGM) doubly curved panels with porosities for the first time. An improved and effectual approach is established based on the improved first-order shear deformation shell theory (IFSDST) and von Karman's type nonlinearity. The IFSDST considers the effects of shear deformation without the need for a shear correction factor. The composition of TDFGM constitutes four different materials, and the modified power-law function is employed to vary the material properties continuously in both thickness and longitudinal directions. A nonlinear finite element method in conjunction with Hamilton's principle is used to obtain the governing equations. Then, the direct iterative method is incorporated to accomplish the numerical results using the frequency-amplitude, nonlinear central deflection relations. Finally, the influence of volume fraction grading indices, porosity distributions, porosity volume, curvature ratio, thickness ratio, and aspect ratio provides a thorough insight into the linear and nonlinear responses of the porous curved panels. Meanwhile, this study emphasizes the influence of the volume fraction gradation profiles in conjunction with the various material and geometrical parameters on the linear frequency, nonlinear frequency, and deflection of the TDFGM porous shells. The numerical analysis reveals that the frequencies and nonlinear deformations can be significantly regulated by changing the volume fraction gradation profiles in a specified direction with an appropriate combination of materials. Hence, TDFGM panels can overcome the drawbacks of the functionally graded materials with a gradation of properties in a single direction.

• Journal of Korea Foundry Society
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• v.21 no.3
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• pp.198-203
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• 2001

In determining properties of ductile cast iron, it is well known that nodularity plays a significant role. Therefore, the national and/or international standards for ductile cast iron such as KS, ISO, ASTM and JIS have specified some methods for evaluating it. However, most of standards have not recommended the methods using image analyzer which is known as an objective analyzing tool for evaluating microstructure. In this study, a reliable method for evaluating nodularity by image analyzing method was proposed, and the result was compared with that from the common counting method proposed in KS D 4302-1999. It was found that there was a reasonable relationship in nodularities measured by these two methods.

• Structural Engineering and Mechanics
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• v.6 no.7
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• pp.817-826
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• 1998

A finite element model based on the incremental endochronic theory for flexible pavement materials was developed in this study. Three grid systems with eight-node cubic isoparametric elements, and different loading steps were used to perform the calculations for a specimen of circular cylinder. The uniaxial stress experimental results on an asphalt mixture at $60^{\circ}C$ in SHRP conducted by University of California at Berkeley were used to check the ability of the derived numerical model. Then, the numerical results showed isotropic response and deviatoric response on the specimen in a three dimensional manner, which provided a better understanding for a deformed flexible material under the specified loading conditions.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.79-88
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• 1999

In this paper, the electro-deposition method for the rehabilitation of cracked concrete, based on the electro-chemical technique, is presented. The main purpose of this paper is to apply this technique to reinforced concrete members on land. After cracking with a specified load(crack width 0.5mm), 10$\times$10$\times$20cm concrete specimens with embedded steel bars were immersed in several solutions, then a constant current density between the embedded steel in concrete and an electrode in the solution was applied for 4~20 weeks. The results indicate that electro-deposits formed in this process are able to close concrete cracks and to coat the concrete surface and that formation of these electro-deposits is confirmed to have an effect of protection against detrimental materials. Therefore, it is demonstrated that the electro-deposition method can be usefully applied for the rehabilitation technique of concrete.

• International Journal of Safety
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• v.4 no.2
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• pp.43-46
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• 2005

The construction workers might be at the risk of many occupational injuries and illnesses. To protect workers from various hazards, industrial health and hygiene systems were specified for the construction workers by law. It is important to know the actual health and safety(H&S) conditions by tasks and the characteristics of injuries and illnesses of construction workers. This study was designed to investigate the actual conditions of construction workers exposed to various harmful substances and work elements including evaluation of health status of each worker and general H&S system. Questionnaire was sent to 600 construction workers nationwide and totally 367 people responded to it having 61.67% of response rate. The common construction hazards were dust(29.6%), noise(19.3%), repetitive motions(12.0%), handling excessive heavy materials(11.2%) in order. The repetitive motions and handling heavy materials related to muscle disorders accounted for 23.2%. The accident and injury types were in order of overexertion, falling, overturning, dropping or flying, electric shock, collision, etc.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.40 no.2
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• pp.73-79
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• 2008

The permanence is of great importance to library and archival paper. According to the established standardizations including ISO and ANSI, the permanence can be specified with tear strength, pH, alkali reserve and kappa number. In this study, we evaluated the permanence and durability of domestic coated and copy paper grades. Two types of coated paper grades and all kinds of copy papers which were tested in this study were satisfied with the criterion of permanence specification. However, all of the tested paper grades didn't meet the requirements of durability because of their low folding endurance.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.17-24
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• 1997

Broad-band RAM's (Radar absorbing materials) are designed by multi-layered lossy dielectrics. The depth, the relative permittivity and the loss tangent of each layer are optimized in order to meet the required reflective power over the specified frequency range using a genetic algorithm. The reflection coefficients are calculated by the continued fraction method. A new population model of the partial initialization method during iterations is applied for the multi-modal functions to enhance the performance of the genetic algorithm. The optimal RAN's are designed by setting the relative permittivity and the loss tangent of the dielectrics as a funtion of the frequency over 5~20GHz.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.91-94
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• 2003

In this paper, we developed a optimal design system to optimize composite shell structures using genetic algorithm and expert system. The objective of the optimal design was to find designs that minimize weight of the structures and satisfy the design rules specified by the user. Buckling analyses of the composite shell structures were done to estimate buckling loads. Some example problems were selected and optimized with the developed system. And a GUI-based integrated design and optimization program, I-DOTCom was developed and introduced at the end of this paper.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.5
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• pp.275-281
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• 2001

To improve the reliability of hardness test results, Rockwell hardness round robin test was carried out for 10 laboratories. The test condition was the same with the ISO(International Standards Organization) standards. Korea Research Institute of Standards and Science(KRISS) supplied the hardness standard blocks and an indenter to laboratories for the measurement. The participating laboratories measured hardness of the specified areas on the blocks for 6 times with their own indenter as well as common indenter, respectively, and reported the results to KRISS. The result showed that quite large amount of the differences came from the indenter and it is necessary to change indenter with better quality for improved reliability in hardness measurement.