• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.9-14
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• 2017

In the present work, a mechanical performances under cyclic loading in RC (Reinforced Concrete) beams with normal steel and FRPH (Fiber Reinforced Plastic Hybrid) bar are investigated. For the work, RC beam members with $200{\times}200{\times}2175mm$ of geometry and 24 Mpa of design strength are prepared, and 4-point-bending tests are performed for evaluation of cracking, yielding, and ultimate loads. Through static loading test, 48.9kN and 36.0 kN of yielding loads are measured for normal RC and FRPH beam, respectively. They have almost same ultimate load of 50.0 kN. Typical tension hardening behavior is observed in FRPH beam, which is caused by the behavior of FRPH bar with tension hardening. In cyclic loading conditions, FRPH beam has more smaller crack width and scattered crack pattern, and it shows more elastic recovery than normal RC beam. The energy dissipation ratio in FRPH beam is 0.83, which is greater than 0.62 in normal RC beam and it shows more effective resistance to cyclic loadings.

• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.345-352
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• 2011

The purpose of this study was to investigate the expansion of alkali-activated mortar based on ground granulated blast furnace slag containing reactive aggregate due to alkali-silica reaction. In addition, this study was particularly concerned with the behavior of these alkaline materials in the presence of reactive aggregates. The experimental program included expansion measurement of the mortar bar specimens, as well as the determination of the morphology and composition of the alkali-silica reaction products by using scanning electron microscopy(SEM), and energy dispersive x-ray(EDX). The experiment showed that while alkali-activated ground granulated blast furnace slag mortars showed expansion due to the alkali-silica reaction, the expansion was 0.1% at Curing Day 14, showing that it is safe. After the accelerated test, SEM and BEM analysis showed the presence of alkali-silica gel and rim around the aggregate and cement paste. According to the EDX, the reaction products decreased markedly as alkali-activated ground granulated blast furnace slag was used. In addition, for the substitutive materials of mineral admixture, a further study on improving the quality of alkali-activated ground granulated blast furnace slag is needed to assure of the durability properties of concrete.

• Journal of the Korea Institute of Building Construction
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• v.11 no.6
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• pp.587-596
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• 2011

Ultra rapid-hardening cement is widely used for latex-modified mortar and concrete as repair and finishing material during urgent work. The purpose of this study is to evaluate the improvements in strength made to SBR cement mortars by the adding of various admixtures and by the use of different curing methods. SBR cement mortar was prepared with various polymer-cement ratios, curing conditions and admixture contents, and tested for flow, flexural and compressive strengths. From the test results, it was determined that the flow of SBR cement mortar increased with an increase in the polymer-cement ratio, and the water reducing ratio also increased. The strength of cement mortar is improved by using SBR emulsion, and is strengthened by adding metakaoline. The strength of SBR cement mortar cured in standard conditions was increased with an increase in the polymer-cement ratio, and attained the maximum strengths at polymer-cement ratios of 15 % and 10 %, respectively. The maximum strengths of SBR cement mortar are about 1.8 and 1.3 times the strengths of plain mortar, respectively. In this study, it is confirmed that the polymer-cement ratio and curing method are important factors for improving the strengths of rapid-hardening SBR cement mortar.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.35-43
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• 2016

With the development of construction technology, constructions of dam and levee (dike) as well as the environmental problems are becoming issues. Recently, many countries have tried to develop and used CSG (Cemented Sand and Gravel), which needs fewer requirements than others in aggregates, constructability and ground condition during the dam construction. Mixing up with small amount of cement, CSG is able to increase the strength and proceed accelerated construction without artificial gradation adjustment of riverbed aggregate and crushed rock on construction site. Thus, CSG can minimize environmental damage resulted from quarries mining and reduce cost of construction. Unlike heat of hydration condition that regular concrete usually met, CSG exposes to repeated dry-wet and freezing and thawing environment. Thus, consider the importance of structure of dam or levee, intensive study on the durability of CSG is needed. In this study, freezing and thawing experiment was carried out to evaluate the durability of CSG. In results, the durability factor of CSG is 30~40 or >40 when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. The unconfined compressive strength is reduced to 30~50% or 40~70% when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. Taken together, the strength and durability of CSG is reliable when the amount of cement is over $0.8kN/m^3$.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.211-219
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• 2017

The spray-applied waterproofing membrane is installed on shotcrete or concrete surface to make impermeable layer with 3-5 mm thick for the purpose of waterproofing. This study aims to determine the internal structure of a spray-applied waterproofing membrane including pores by using X-ray CT technique. Before obtaining X-ray images of the membrane specimens, a waterproof performance test was performed on the membrane specimens with a water pressure of 500 kPa for 28 days. Results show that the movement of moisture is made through micropores. This is based on the fact that the large pores inside the membrane are not saturated and the degrees of saturation of the micropores are high. X-ray image is effective for determining the pore size distribution and whether the membrane with pores contains the water However, it is necessary to pay attention to the determination of water content, since water content may vary depending on the threshold value of X-ray image analysis applied to calculate the water content.

• Journal of Gifted/Talented Education
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• v.26 no.1
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• pp.77-99
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• 2016

The purpose of this study was to examine the effect of GI-STEAM program on leadership, creative personality, and learning flow of elementary Gifted Students. GI-STEAM program was the convergence model of Group Investigation that belongs to Co-learning and STEAM framework of learning criterion. The participants were 16 gifted students in a Korean elementary school located in Gyeong-gi province. The experimental design was one group pretest-posttest design. After a pretest on leadership, creative personality, and learning flow was conducted, classes were carried out as GI-STEAM program for the gifted student and a post-test was conducted. The study results of the class that was conducted twelve times for two weeks are as follows. First, Individual area of leadership is meaningfully developed in statistics after GI-STEAM program. The sub-domains of leadership, such as the communication, organization management, society commitment and teamwork showed a statistically significant improvement. Second, the domain of creative personality didn't show meaningful difference after GI-STEAM program. However, the aesthetic in the sub-domains of the creative personality showed a statistically significant improvement. Third, learning flow was meaningfully developed in statistics after GI-STEAM program. The sub-domains of the leadership, such as the balance between challenge and ability, integration with behavior and consciousness, concrete feedback and Autotelic experience showed a statistically significant improvement. In conclusion, GI-STEAM is an effective program for improving ability of communication, aesthetic sensibility, which are core competency of 'creative-convergence' gifted students. For this reason, it is highly considered that various programs applying GI-STEAM should be developed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.2
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• pp.144-148
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• 1999

This study was conducted to test actual oxygen consumption rates of Nile tilapia (Oreochromis niloticus) at a commercial scale high density culture tank in the recirculating culture system, with a special emphasis on the oxygen consumption rate of this species with different daily feeding frequencies. Nile tilapia, an average of 400 g and a total wright of 390 kg, were stocked in a circular concrete tank of 2.9 m in diameter and 0.8 m in depth, in a recirculating culture system. The fish were fed commercial diet 1, 2, 5, and 9 times per day between 09:00 h and 19:00 h. feed was evenly supplied where the fish were fed more than once a day. Dissolved oxygen of influent and effluent water was monitored every 50 seconds by a computer with electrodes for 24 hours. The standard metabolic rate of tilapia was $39.31{\pm}4.4mg\;O_2/kg$ fish/hr in the present study. The maximum oxygen consumption was reached between 30 to 50 minutes after feeding. The maximum oxygen consumption levels of 1, 2, 5, and 9 feeding times per day were 161.2, 123.4, 111.1 and 111.1 mg $O_2/kg$ fish/hr, respectively. While the mean oxygen consumption levels of 1, 2, 5, and 9 feeding times per day were $79.9{\pm}21.5,\;81.3{\pm}14.8,\;84.2{\pm}9,9$ and $98,9{\pm}11.0mg\;O_2/kg$ fish/hr, respectively. These results show that oxygen consumption rates are not much different between the feeding frequencies. These results could be used to design to provide desirable oxygen supply system in the recirculating high-density tilapia culture system.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.6
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• pp.11-21
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• 2010

This study presents seismic responses of 5-story reinforced concrete structures retrofitted with the buckling-restrained braces using a time-dependent element. The time-dependent element having birth and death times can freely be activated within the user defined time intervals during the time history analysis. The buckling-restrained brace that showed the largest energy dissipation capacity among the test specimens in previous research was used for retrofitting the RC buildings in this study. It was assumed that the first story of the damaged building under the first earthquake was retrofitted with the buckling-restrained braces considered as the time-dependent element before the second of the successive earthquakes occurs. Under this assumption, this paper compares seismic responses of the RC structures with the time-dependent element subjected to the successive earthquake. Subjected to the second earthquake, it was observed that activation of the BRB systems largely decreases deformation of the moment frame where the damage was concentrated under the first earthquake. However, damages to the shear wall systems were increased after activation of the BRB systems. Since the cumulative damages of the shear wall systems were infinitesimal compared with the retrofit effect of the moment frame, the BRB system was effective under the successive earthquake.

• The Journal of Society for e-Business Studies
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• v.16 no.4
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• pp.33-51
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• 2011

This research derived the influencing factors for employees' compliance with the information security policy in organizations on the basis of Neutralization Theory, Theory of Planned Behavior and Protection Motivation Theory. To empirically analyze the research model and the hypotheses, data were collected by conducting web survey, 194 of 207 questionnaires were available. The test of causal model was conducted by PLS. Reliability, validity and model fit were found to be statistically significant. the results of hypotheses tests showed that seven ones of eight hypotheses could be accepted. The theoretical implications of this study are as follows : 1) this study is expected to play a role of baseline for future research about employee compliance with the information security policy, 2) this study attempted interdisciplinary approach through combining psychology and information system security research, and 3) it suggested concrete operational definitions of influencing factors for information security policy compliance through comprehensive theoretical review. Also, this study has some practical implications. First, it can provide the guideline to support the successful execution of the strategic establishment for implement of information system security policies in organizations. Second, it is proved that the need for conducting education and training program suppressing employees. neutralization psychology to violate information security policy should be emphasized in the organizations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6A
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• pp.457-464
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• 2011

An experimental study was performed to evaluate the possibility of using stiff type PolyUrea(PU) on RC slab as a strengthening material. Stiff type PU(STPU) was sprayed on the bottom surface of the slab specimens, which were then attached with CFRP or GFRP sheets. Also the evaluation of the bond capacity, the single most influential parameter on strengthening of RC structures, was carried out the flexural capacity evaluation test results showed that the load carrying capacity of the PU specimen was greater and less than the unstrengthened and FRP sheet attached specimens, respectively. The STPU specimens showed a ductile flexural behavior in the plastic displacement range. With respect to bond capacity, the bond strength of all of the specimen exceeded the code required bond strength of 1.5 MPa. Also, the STPU sprayed specimen without using epoxy resin did not peel off when the tensile grip was applied for testing. The stability of the PU bond failure indicate a good bond strength of PU when applied to concrete.