• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.474-480
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• 2017

In this study, the evolution of electrical impedance of electric nodes was investigated to determine the setting time of cement paste using the electrical impedance spectroscopy method. The electric nodes were embedded in fresh cement paste and the electrical impedance signatures were continuously monitored. Vicat needle test and semi-adiabatic calorimetry test were also conducted to validate the electrical impedance spectroscopy method. During hydration period of cement paste, the magnitude of conductance gradually increased, and then started to decrease rapidly at a first certain time. After that, the magnitude of conductance gradually decreased at a second certain time. The times of turning point in the curves of magnitude of conductance seem to be related with the setting time by Vicat needle test. Also, the setting times by the electrical impedance spectroscopy method are well posed within the setting period estimated by the semi-adiabatic calorimetry test. Based on the results, it can be concluded that the setting time of cement paste can be effectively monitored through the electrical impedance spectroscopy method.

• Journal of Educational Research in Mathematics
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• v.27 no.4
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• pp.701-725
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• 2017

Students need to have opportunities to share their ideas with peers by taking part in the conversation voluntarily that is, by persuading others and reflecting the consequences. Recognizing the importance of this point, this study intended to examine students' argumentation occurring in the process of performing tasks in the math classroom. Also, it tried to explore the types of the argument that students used in the classroom and the reason why they employed them with a focus on 'rebuttal', which is one of the six elements of the argument scheme such as claim, data, warrent, backing, qualifiers, and rebuttal. The analysis of argumentation is based on the five argumentation schemes suggested by Verheij(2005). The experimental class was conducted twice a week with four participants who are third grade middle school students. In the argumentation class students were promoted to address two different kinds of geometrical tasks. After the second session of class, the researcher conducted the semi-structured interview. Accordingly, this study contributes to the existing research by making students to have concrete and active argumentation while obtaining the sound understanding of the argumentation.

• Structural Engineering and Mechanics
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• v.55 no.4
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• pp.765-784
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• 2015

Connections are usually designed either as pinned usually associated with simple construction or rigid normally is associated with continuous construction. However, the actual behaviour falls in between these two extreme cases. The use of partial strength or semi-rigid connections has been encouraged by Euro-code 3 and studies on semi-continuous construction have shown substantial savings in steel weight of the overall construction. Composite connections are proposed in this paper as partial or full strength connections. Standardized connection tables are developed based on checking on all possible failure modes as suggested by "component method" for beam-to-column composite connection on major axis. Four experimental tests were carried out to validate the proposed standardised connection table. The test results showed good agreement between experimental and theoretical values with the ratio in the range between 1.06 to 1.50. All tested specimens of the composite connections showed ductile type of failure with the formation of cracks occurred on concrete slab at maximum load. No failure occurred on the Trapezoidal Web Profiled Steel Section as beam and on the British Section as column.

• 대한공업교육학회지
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• v.38 no.2
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• pp.1-26
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• 2013

This study inquired following research questions by a narrative research method : What was the job of an engineer in mechanical design field? How did he fulfill his job-related learning in his workplace? What were the context and the characteristic of the job-related learning in the workplace? And some implications of the job-related learning on engineering education were discussed. We identified that the research participant's career as a mechanical engineer has developed through three stages. At first, he engaged on conceptual design of a semi-conductor test machine through self-initiated learning from basic to whole system of the machine. At second stage, he leaded a design group for the concrete design of a ball type semi-conductor test machine. In this stage he learned the meaning of cooperation and cooperative learning. At third stage, he initiated to found an entrepreneur company that was specified to design a semi-conductor test machine. He became CEO of the company. He learned the R & D policy making through contacts with global company, visiting exhibition in abroad. Eventually his main task as a mechanical engineer was the problem solving in the process of machine design. He had experienced and learned through his works : project management, independent fulfilling of tasks, functional analysis and reverse engineering, conceptualizing and test, cohesive cooperation, dialogue and discussion, mediation of conflict, human relationship, leadership. The implication of the narrative analysis on engineering education is, proposed, to give the students more chances to experience and to learn such activities.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.665-672
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• 2016

This study is conducted to investigate the effect of phase change materials (PCM) on hydration heat and strength characteristics of cement mortar. Two types of Barium and Strontium-based PCMs were used in this study and the addition ratio of each PCM to the cement mortar ranged from 1% to 5% by cement weight. Flow test, semi-adiabatic temperature rise test, compressive strength and flexural strength test were carried out to examine the PCM effect on heat and mechanical properties of cement mortar. Test results indicated that PCMs used in this study were effective to control hydration heat of cement mortar, and Barium-based PCM slightly reduce flow value. The compressive and flexural strength of cement mortar with PCM decreased with increasing the adding mount of PCM. The prediction model for compressive strength of cement mortar with different addition levels of PCMs are suggested in this study.

• Steel and Composite Structures
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• v.34 no.1
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• pp.123-139
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• 2020

The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.4
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• pp.290-295
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• 2000

The joint treatment of concrete is one of the technical problems in top down construction method. Joints created with the top down construction result in serious weakness from the aspects of both structural and water-barrier function. Ultrasonic method was used for the inspection of top down construction joints of a various column in SRC structure in this study. The advantages and limitations of this method for non-destructive inspection in top down construction joints are investigated. As a result, it has been verified that the semi-direct measurement method is more effective than the other methods for detecting the voids of construction joints using ultrasonic method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1872-1879
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• 2012

By analyzing the use of outdoor space in apartment complex and finding empirical proof which is concrete and systemic, this study focuses on the relationship between residents' daily lives and physical space. This study tries to find out the types and characteristics of outdoor space which causes the occurrence of residents' use in High-Rise apartment housing Estates, and analyzes the residents' usage pattern of outdoor space in eight different apartment complexes which were builted since 2004. After analyzing the usage pattern of outdoor space, the usage of playground was ranked highest and playing, talking, exercising, resting was in order. Especially it was found that the usage inside semi-public space where passing is abundant increases.

• Journal of The Korean Association of Information Education
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• v.12 no.4
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• pp.395-404
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• 2008

The shape learning of elementary mathematics should required a variety of activities to help student based on intuitive understanding. Learning three-dimensional shapes, it is effectively take advantage of actual object, but difficult to check a development figure or various forms of actual object, it is effectively utilizing computers semi-actual object. In addition, the computer to take advantage of even after school resources, the limits of learning something concrete to take advantage complement. This research developed the three-dimensional shapes application of elementary students shape learning to use of Flex and Flash. This application to take advantage of the free observation and causing an interesting and effective learning.

• Journal of Korean Academy of Nursing
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• v.41 no.1
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• pp.61-71
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• 2011

Purpose: The purpose of this study was to examine the meaning and essence of suicide for elderly people who had previously attempted suicide as an older person. Methods: Giorgi's descriptive phenomenology was used for analysis. The researchers carried out in-depth interviews, recordings and memos individually with four elders. The elders were individuals who had attempted suicide sometime in the past 5 yr. They were interviewed from 5 to 10 times using open-ended questions and a semi-structural format. Demographic data were also collected. Results: The meaning of suicide before a suicide attempt in older people had four core components: conflict with family, powerlessness and despair in their life with a drop in self-esteem, using internal and external resources to resolve their troubles and awareness of imminent crisis. Conclusion: These results of this study will increase understanding of suicide in older people by defining their subjective experience of suicide attempts and applying grounded data in the development of programs that provide concrete intervention strategies to prevent suicide in elderly people.