• Journal of the Korea Concrete Institute
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• 제23권5호
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• pp.581-590
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• 2011

Since ultra-high performance cementitious composites (UHPCC) not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B) and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA) and shrinkage reducing agent (SRA). The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces.

• Journal of the Korea Concrete Institute
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• 제18권6호
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• pp.749-757
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• 2006

Many losses of life and extensive damage of social infrastructures have occurred due to moderate and strong earthquakes all over the world. In this research various design parameters have been evaluated to develop a rational seismic design code of rectangular reinforced concrete(RC) bridge piers. It was confirmed from this study that the axial force ratio and longitudinal steel ratio were most influencing design parameters on the seismic displacement ductility from experimental results of 54 rectangular RC bridge piers, which were tested at domestic and foregin countries. However, these important parameters are not considered in the confinement steel ratio of Korea Highway Bridge Design Specification(KHBDS). The objective of this study is to propose a rational design provision for the transverse reinforcement of rectangular RC bridge piers. New confinement steel ratio is proposed by reflecting the effect of the axial force and longitudinal steel into the current code of KHBDS. furthermore, minimum transverse confinement steel ratio is also proposed to avoid a probable buckling of longitudinal reinforcing steels of RC bridge piers with a relatively low axial force. New practical code can alleviate the rebar congestion in the plastic hinge region of RC bridge pier, which contributes to construct RC bridge piers in a simple and economic way.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제38권1호
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• pp.1-10
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• 2018

It is difficult to predict the early-age cracks of strain restrained concrete members due to environmentally sensitive parameters. A new method is proposed to predict the cracks by test of autogenous deformation and self-induced restrained stress of specimens which simulates early-age crack state by hydration heat of the'Wall-On-Foundation'members. For this purpose, thermal analysis of entire structure considering the environmental condition is performed at first, and the specimens are set up where hydration heat was electronically controlled according to the analysis results. By measuring free deformation and force to compensate the autogenous strain including relaxation, feasibility of cracks can be estimated. The proposed method can predict the occurrence of cracks better than the material test of the early age concrete which has large variance. The method of this study is particularly useful when it is used as a preliminary experiments to predict the crack more precisely before full-scale concrete placement in construction of large structures.

• Journal of Aerospace System Engineering
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• 제15권5호
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• pp.81-88
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• 2021

In general, a non-explosive nylon wire cutting-based holding and release mechanism has been used to store and deploy deployable solar panels of CubeSat. However, with this method, accessing the solar panel's access port for charging the cube satellite's battery and electrical inspection and testing of the PCB and payloads while the solar panel is in storage is difficult. Additionally, the mechanism must have a reliable release function in an in-orbit environment, and reusability for stow and deploy of the solar panel, which is a hassle for the operator and difficult to maintain a consistent nylon wire fastening process. In this study, we proposed a pin-puller-based solar panel holding and release mechanism that can easily deploy a solar panel without cutting nylon wires by separating constraining pins. The proposed mechanism's release function and performance were verified through a solar panel deployment test and a maximum separation load measurement test. Through this, we also verified the design feasibility and effectiveness of the pin-puller-based separation device.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 한국항해항만학회 2004년도 추계학술대회
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• pp.41-46
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• 2004

In this paper, we study the stabilization control if an underwater vehicle from its initial posture to its desired one. We assume tint the underwater vehicle has velocity constraint, i.e. it has no velocity component for some direction. Our approach is based on the nonholonomic system which am derived from velocity constraints that cannot integrable. We proposed a control strategy for posture control of the underwater vehicle using multi-rate digital control. The proposed control scheme is applied to the berthing control if an underwater vehicle and verified the effectiveness if control strategy by numerical simulation.

• Journal of the Earthquake Engineering Society of Korea
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• 제10권5호
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• pp.1-9
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• 2006

In this study, axial and lateral loading experiments for both circular and square plain concrete columns confined with carbon fiber tube manufactured by carbon filament winding technique were performed. Based on the test results, reliability analyses to estimate strength reduction factors were carried out by utilizing Monte Carlo technique. CASE I was for plain concrete columns confined with the carbon tubes, CASE II was for reinforced concrete columns confined with the carbon tubes. As results, the strength reduction factors, ${\phi}$, were estimated as 0.7 for CASE I and 0.85 for CASE II respectively.

• Journal of the Korean Geotechnical Society
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• 제15권1호
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• pp.63-78
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• 1999

For the design of compression anchor, three things should be considered. The first is a resistance force by skin friction, the second is a tension strength of tendon, and the third is a compressive strength of grout. Especially, compressive strength of grout is the most important design parameter of compression anchor. When compression anchor is pulled out from the ground, the compressive strength of grout increases by confining pressure of ground($\sigma_{tg$). Here, $\sigma_{tg$ is the confining pressure which is produced by earth pressure at rest and by lateral expansion of grout. We call this phenomenon of increase of confining pressure "poisson effect". In this paper, the design method of compression anchor called SSC anchor and the computer program for the design are developed through compression tests of anchor body grout.ody grout.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 한국방송공학회 2007년도 동계학술대회
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• pp.60-63
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• 2007

최근, 핸드폰은 일상생활의 필수품이 되었다. 특히 카메라가 장착된 핸드폰은 개인홍보와 오락요소로의 대표적인 도구로 사용된다. 나아가 양안카메라가 적용된 핸드폰은 사용자에게 입체감을 전달할 것이며, 입체감은 보다 효과적인 개인홍보 및 오락성을 제공할 것이다. 핸드폰은 휴대가 용이하지만 제한된 표시소자의 크기 및 해상도로 인하여 입체시 구현 시 사용자에게 손실된 정보 및 낮은 임장감을 제공한다. 이에 본 연구는 기존의 입체시 구현에 대한 구속조건들을 분석하고 핵심 요인을 산출하여, 핸드폰 환경에서의 최적의 입체시 구현을 위한 새로운 구속조건의 범위를 정량화하였다. 대표적인 구속조건으로는 수평, 수직 시차량이 고려되었다. 본 연구의 결과는 핸드폰용 양안카메라의 제작공차 및 효과적인 시차영상 제작을 위한 기준을 제시한다. 연구에 사용된 제품으로는 QVGA해상도(320*240) 및 2.8' 크기의 표시소자인 PDA폰이며, 입체시에 대한 구속조건을 정량화하기 위하여 수직, 수평이동이 가능한 지그를 사용하여 실험의 정확성을 높였다. 피실험자는 10명이며 남자 7명, 여자 3명으로 구성되었다.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.201-204
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• 2008

The proposed method, capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (Fiber Reinforced Polymers) composites in a rational manner, is based on the fact that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure. The elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. This procedure enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods.

• Journal of Korean Society of Steel Construction
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• 제22권2호
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• pp.185-195
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• 2010

This paper presents the experiment results for a CFT column confined by carbon fiber sheets(CFSs) under an axial load. Nine specimens were constructed and axial compression tests were conducted. The main experiment parameters were diameter-thickness ratio(D/t), reinforcing CFSa, and the attachment of a cushion gap between surface of steel tube and CFSs. The load-displacement curves of the specimens were obtained from the compression tests. Finally, it was concluded that the CFT column with a gap had grater ductility capacity improvement that the CFT column confined by CFSs.