• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.3-23
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• 1997

The growth in fast-track construction and repair has prompted major efforts to develop high-early-strength concrete mix compositions. Such mixtures rely on the use of relatively high cement contents and accelerator dosages to increase the rate of strength development. The measures, however, seem to compromise the long-term performance of concrete in applications such as full-depth patches as evidenced by occasional premature deterioration of such patches. The hypothesis successfully validated in this research was that traditional methods of increasing the early-age strength of concrete, involving the use of high cement and accelerator contents, increase the moisture and thermal movements of concrete. Restraint of such movements in actual field conditions, by external or internal restraining factors, generates tensile stresses which introduced microcracks and thus increase the permeability of concrete. This increase in permeability accelerates various processes of concrete deterioration, including freeze-thaw attack. Fiver reinforcement of concrete is an effective approach to the control of microcrack and crack development under tensile stresses. Fibers, however, have not been known of accelerating the process of strength gain in concrete. The recently developed specialty cellulose fibers, however, were found in this research to be highly effective in increasing the early-age strength of concrete. This provides a unique opportunity to increase the rate of strength gain in concrete without increasing moisture an thermal movements, which actually controlling the processes of microcracking and racking in concrete. Laboratory test results confirmed the desirable resistance of specialty cellulose fiber reinforced High-early-strength concrete to restrained shrinkage microcracking an cracking, and to different processes of deterioration under weathering effects.

• Advances in concrete construction
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• v.8 no.4
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• pp.335-349
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• 2019

To investigate the axial compressive performance of the recycled aggregate concrete (RAC) filled glass fiber reinforced polymer (GFRP) tube and profile steel composite columns, static loading tests were carried out on 18 specimens under axial loads in this study, including 7 RAC filled GFRP tube columns and 11 RAC filled GFRP tube-profile steel composite columns. The design parameters include recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, slenderness ratio and RAC strength. The failure process, failure modes, axial stress-strain curves, strain development and axial bearing capacity of all specimens were mainly analyzed in detail. The experimental results show that the GFRP tube had strong restraint ability to RAC material and the profile steel could improve the axial compressive performance of the columns. The failure modes of the columns can be summarized as follow: the profile steel in the composite columns yielded first, then the internal RAC material was crushed, and finally the fiberglass of the external GFRP tube was seriously torn, resulting in the final failure of columns. The axial bearing capacity of the columns decreased with the increase of RCA replacement percentage and the maximum decreasing amplitude was 11.10%. In addition, the slenderness ratio had an adverse effect on the axial bearing capacity of the columns. However, the strength of the RAC material could effectively improve the axial bearing capacity of the columns, but their deformability decreased. In addition, the increasing profile steel ratio contributed to the axial compressive capacity of the composite columns. Based on the above analysis, a formula for calculating the bearing capacity of composite columns under axial compression load is proposed, and the adverse effects of slenderness ratio and RCA replacement percentage are considered.

• Steel and Composite Structures
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• v.36 no.5
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• pp.507-519
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• 2020

Double skin composite walls are increasingly popular and have been applied to many safety-related facilities. They come from the concept of composite slabs. Conventional connectors such as shear studs and binding bars were used in previous studies to act as the internal mechanical connectors to lock the external steel faceplates to the concrete core. However, the restraint effects of these connectors were sometimes not strong enough. In this research, a recently proposed unique type of steel truss was employed along the wall height to enhance the composite action between the two materials. Concrete-filled tube columns were used as the boundary elements. Due to the existence of boundary columns, the restraints of steel faceplates to the concrete differ significantly for the walls with different widths. Therefore, there is a need to explore the effect of height-to-width ratio on the structural behavior of the wall. In the test program, three specimens were designed with the height of 3000 mm, the thickness of 150 mm, and different widths, to simulate the real walls in practice. Axial compression was applied by two actuators on the tested walls. The axial behavior of the walls was evaluated based on the analysis of test results. The influences of height-to-width ratio on structural performance were evaluated. Finally, discussion was made on code-based design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.755-761
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• 2014

Internal or external restraint of concrete strain due to drying shrinkage and creep in concrete structures causes mechanical strain and becomes a source of persistent change in creep-causing stress conditions. Mathematical modeling to incorporate the persistent change of creep-inducing stress is generally achieved with consideration of the ages of concrete and concrete properties at the times of loadings, and stress history. This paper presents an incremental format of creep model based on parallel creep concept to depict the creep under time-varying stress history in developing creep strain. Laboratory experiments are carried out to validate the performance of the presented creep model. Typical creep phenomena are addressed through the comparisons between the measured and predicted creep strains.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.6
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• pp.533-539
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• 2015

Recently, guided missiles applies folding wings to save space. During wing deployment, aero force acting on wing effects significantly on deployment performance, usually aerodynamic coefficient are calculated by CFD analysis. However, Missile Datcom can calculates estimated aerodynamic coefficient very quickly by assuming wing deployment motions as dihedral angle of wing. If missile has external store, wings may need to be folded on top of each other. In this case, one of wing help or interrupt other wing deployment, locking effect. In this study, both effects were included on wing deployment performance analysis to criteria for wings locked condition and formulated wing deploy performance, and compared with wind tunnel test data. Analysis predicted vulnerable wind direction of wing deployment very well.

• International Journal of Highway Engineering
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• v.3 no.2 s.8
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• pp.123-130
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• 2001

This study was performed to enhance mechanical properties of high-early-strength concrete using regulated-set cement for early traffic opening with various mixtures. Restraint of moisture and thermal movements of concrete pavement in actual field conditions, by external or internal restraining factors, generates tensile stresses which introduce microcracks and thus reduce the mechanical properties of concrete. Fiber reinforcement of concrete is an effective approch to the control of microcrack and crack development under tensile stresses. Three different types of regulated-set cement which recently have been used in Korea and two different types of fiber were adopted. Fibers were added and their mixtures are compared with plain high-early-strength concrete mixture. From the test results, fiber reinforced concrete was increased mechanical properties of high-early-strength concrete using regulated-set cement than the plain concrete.

• Journal of National Security and Military Science
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• s.4
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• pp.241-287
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• 2006

16th CPC National Party Congress established multi-polarization strategy as an external strategy, and 'The Great Reinvigoration of Chinese Nation' as the aim of The Great Strategy of China. It is required to maintain stabilized and peaceful surrounding circumstance in order to make it possible. The ideal surrounding circumstance that China is aiming for is to achieve multi-polarization of international society while maintaining strategic deterrence. Multi-polarization now in 'One super Multi powers' is that 'Multi powers' deter 'One super' to prevent predominance of USA and to decentralize the power. China wishes to realign international order as it accomplishes multi-polarization. China who wants 'Peace and Stabilization' emphasizes autonomy, peace and unification of Korean peninsula. Autonomy means the restraint intervention of foreign power, that is, American influence in Korean peninsula. Multi-polarization strategy of China will be used in Korean peninsula to solve nuclear issue of North Korea, to support neutral unification and to keep balance of power with USA, Japan and Russia as it renders economic advantages to South Korea and security engagement to North Korea, based on special geographical, cultural and historical relationship with two Koreas. The nuclear issue of North Korea will be a stage to test multi-polarization of China. When it deduces positive solution of nuclear issue due to successful six-party talks, and advances to security talks of Northeast Asia, it will contribute a lot to power and elevation of national stature of China in international society. Thus, the Chinese strategy will be an accommodative condition for the security of South Korea, and it requires wise decision of South Korea to make hay while the sun shine.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.06a
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• pp.183-184
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• 2009

In this paper the internal or external of the ships mounted electronic devices due to the propagation of electromagnetic interference and to prevent malfunction EMC filter was designed and fabricated. It was designed and fabricated with Ni-Zn ferrite beads of high permeability to make large inductance as the inductor and Feed-through capacitors, which did not have any resonance point, to restraint resonance effectively, and the characteristics was evaluated. The results from the 0 kHz$\sim$1.5 GHz bandwidth of $25{\sim}70$ dB were able to obtain excellent attenuation characteristics. And, when the Electric Fast Transient (EFT) of 4 kV in the level 4 of IEC 61000-4-4 was induced, it was soon attenuated more than 1/6 to 600 V. Therefore, it was confirmed that the developed EMC filter can be used for suppressing ships mounted electromagnetic interference between electronic devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.91-96
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• 2012

The retract actuator makes the landing gear retract or extend during take-off and landing of an aircraft. To prevent folding of landing gear that has remained in the extended state because of an unexpected external disturbance, an internal locking device is applied to the retract actuator. The locking device is restrained with another internal component by oil pressure supplied to the retract actuator, and this restraint makes the locking of the actuator possible. Because locking and unlocking are repeated during retraction and extension of the landing gear, the locking device takes repeated identical loads, and the possibility of fatigue failure exists. In this study, the process and results of fatigue analysis for the locking device are presented, and the appropriateness of the analysis result is verified using a fatigue test.

• Korean Journal of Community Nutrition
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• v.14 no.4
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• pp.383-391
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• 2009

This study was performed in order to compare the differences in dietary self-efficacy and eating behaviors as well as the relationship of weight control attitudes according to eating disorder perception and obesity index for high school girls majoring in dance. Almost half (45.5%) of the subjects perceived eating disorders, and the rate of underweight group was 45.7%. Forty-four percent of the group that perceived eating disorders were in modern dance, while 55.0% of the group that did not perceived eating disorders were in Korean dance (p < 0.05). For the obesity index, a similar rate was shown between the different types of dance for the underweight group, but in the normal group, 54.5% were in Korean dance (p < 0.05). Most (82.0%) of the group that perceived eating disorders had fears on obesity, while only 53.3% of the non-perceiving group had fears on obesity (p < 0.01). Over half (58.3%) of the underweight group had fears on obesity, while 77.2% of the normal group showed fear in that (p < 0.05). For necessity of weight loss to do dance performances, 25.0% of the underweight group and 57.9% of the normal group need that (p < 0.05). Most of the group that perceived eating disorders (92.0%) answered that they had experience in very low calorie diets, while only 40.0% of the non-perceiving group had experience (p < 0.001). For necessity of calorie education, 42.0% of the group that perceived eating disorders and only 20.0% of the non-perceiving group answered is needed (p < 0.05). For eating behavior, the group that perceived eating disorders had lower total scores compared to the non-perceiving group (p < 0.001), The group that perceived eating disorders showed lower scores for restraint eating (p < 0.01) and emotional factors (p < 0.001) except by external eating. This study showed that high school girls majoring in dance have high interest in weight control and problems with wrongful body images and eating behaviors, as well as need for calorie education were suggested. Thus, it is necessary to develop and execute a proper weight control education program for the subjects. (Korean J Community Nutrition 14(4) : 383${\sim}$391, 2009)