• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.80-83
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• 2004

The FRP plate or sheet bonding technology was widely used for strengthening deficient RC structures. The strengthened structure using FRP bonding scheme, however, experience the complex interfacial behaviour which is difficult to predict. Therefore, the unbonded scheme using some anchorage device can be is an alternative for more reliable design. In this study, wedge-type anchor for FRP plate is developed for the unbonded flexural strengthening scheme. Some parameter study using 2D finite element method is performed. The analysis parameters are taken as wedge-guide friction coefficients, wedge- FRP ,.friction coefficient and wedge inclination angle. Based on the parameter study, more efficient anchors are designed and tested. The test result show that the developed anchor assure about $80\%$ FRP strength, which is higher performance than typical bonding scheme. Last, 3D finite element analysis is performed.

• 한국재료학회지
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• 제17권7호
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• pp.366-370
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• 2007

Silicon nitride ($Si_3N_4$) ceramics have been considered for various components of nuclear power plants such as the mechanical seal of a reactor coolant pump (RCP), the guide roller for a control rod drive mechanism (CRDM), and a seal support, etc. Corrosion behavior of $Si_3N_4$ ceramics in a high-temperature and high-pressure water must be elucidated before they can be considered as components for nuclear power plants. In this study, the corrosion behaviors of $Si_3N_4$ ceramics containing MgO and $Al_2O_3$ as sintering aids were investigated at a hydrothermal condition ($300^{\circ}C$, 9.0 MPa) in pure water and 35 ppm LiOH solution. The corrosion reactions were controlled by a diffusion of the reactive species and/or products through the corroded layer. The grain-boundary phase was preferentially corroded in pure water whereas the $Si_3N_4$ grain seemed to be corroded at a similar rate to the grain-boundary phase in LiOH solution. Flexural strengths of the $Si_3N_4$ ceramics were significantly degraded due to the corrosion reaction. Results of this study imply that a variation of the sintering aids and/or a control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of $Si_3N_4$ ceramics in a high-temperature water.

• 대한토목학회논문집
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• 제34권6호
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• pp.1743-1751
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• 2014

라텍스 첨가는 콘크리트의 압축 및 휨거동, 부착강도, 염화물 저항성 및 동결융해 저항성의 향상을 유도할 수 있는 것으로 알려져 있다. 이러한 이유로, 기존 포장 콘크리트 보다 LMC에 관한 많은 연구가 진행되고 있다. 그러나 소음이나 공사비용등을 비롯한 문제점 때문에 LMC의 성능을 향상시키기 위한 새로운 방법들이 시도되고 있으며, 최근, LMC의 문제점을 해결하고자 레미콘 LMC가 개발되었다. 본 연구에서는 레미콘 LMC의 내구성을 라텍스와 광물질 첨가제의 혼입 비율에 따라 비교하였다. 실험결과, 레미콘LMC는 압축강도, 휨강도, 부착강도가 한국 도로공사 전문 시방서 기준을 만족하였으며, 레미콘LMC의 내구성은 우수한 것으로 나타났다. 또한, 레미콘LMC에 라텍스를 8% 이상 혼입해야 기존 LMC와 동등 이상의 내구성을 확보하는 것으로 나타났다.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3745-3765
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• 2022

The concrete structures related to nuclear safety are threatened by accidental impact loadings, mainly including the low-velocity drop-weight impact (e.g., spent fuel cask and assembly, etc. with the velocity less than 20 m/s) and high-speed projectile impact (e.g., steel pipe, valve, turbine bucket, etc. with the velocity higher than 20 m/s), while the existing studies are still limited in the impact resistant design of nuclear power plant (NPP), especially the primary RC slab. This paper aims to propose the numerical simulation and theoretical approaches to assist the impact-resistant design of RC slab in NPP. Firstly, the continuous surface cap (CSC) model parameters for concrete with the compressive strength of 20-70 MPa are fully calibrated and verified, and the refined numerical simulation approach is proposed. Secondly, the two-degree freedom (TDOF) model with considering the mutual effect of flexural and shear resistance of RC slab are developed. Furthermore, based on the low-velocity drop hammer tests and high-speed soft/hard projectile impact tests on RC slabs, the adopted numerical simulation and TDOF model approaches are fully validated by the flexural and punching shear damage, deflection, and impact force time-histories of RC slabs. Finally, as for the two low-velocity impact scenarios, the design procedure of RC slab based on TDOF model is validated and recommended. Meanwhile, as for the four actual high-speed impact scenarios, the impact-resistant design specification in Chinese code NB/T 20012-2019 is evaluated, the over conservation of which is found, and the proposed numerical approach is recommended. The present work could beneficially guide the impact-resistant design and safety assessment of NPPs against the accidental impact loadings.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.280-283
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• 2004

Today, the guide line of the SFRC mix design and the construction was not embodied, and the convenience of the practical application on the spot is not good. In this research, hence, the program which is optimized to result the mix proportion by the flexural strength and toughness, was developed to apply with ease SFRC on the practical spot. This program would minimize the number of trial mixes and achieve an economical and appropriate mixture. In addition, the theoretical background on which the program is based, will be the basis of the embodied method to mixing SFRC. New algorithm, in this research, was used to develop the mix proportioning program of SFRC. The new algorithm is the Harmony Search which is the heuristic method mimicking the improvisation of music players. And, beside to single fiber reinforced concrete, it was developed the program about the hybrid fiber reinforced concrete that two kinds of steel fibers, which have the different geometry, was reinforced. This will be able to keep the world trend to study, hence, offers the basis of the next generation research.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.192-192
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• 2008

This paper represents a piezoelectric ultrasonic linear motor by traveling wave. The motor which is composed of two piezo ceramics, elastic body, and connecting tip is driven by the frictional force between the connecting tip and the linear motion guide. longitudinal and flexural vibrations are made by traveling wave which is generated when the ultrasonic electrical signals with 90 degree phase difference are applied to two ceramics. These vibrations contribute to elliptical motion by mixed mode between longitudinal and transverse mode. A linear movement can be easily obtained by using the elliptical motion. In this paper, the piezoelectric actuator has been intensively simulated by using ATILA to achieve an optimized elliptical motion of it. We could get the elliptical motion from actual experiment through the simulated result.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.694-701
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• 2018

FRP-보강근 콘크리트 부재들은 FRP-보강근이 철근에 비해 낮은 탄성계수와 부착강도를 갖고 있어 철근콘크리트 부재에 비해 과도한 균열폭의 가능성이 클 수 있다. 따라서 외국의 기준들에서는 FRP-보강근 콘크리트 부재의 균열제어를 위하여 허용균열폭의 제한규정을 두고 있는데, ACI 440.1R-15 설계지침에서는 최대 보강근 간격으로 제어하는 간접적인 방법으로 제안하고 있다. 그러나 제안식은 아직까지 장기하중이 균열폭에 미치는 시간종속적인 효과를 반영하지 못하고 있다. 이에 본 연구에서는 장방형단면뿐만 아니라 T형단면의 FRP-보강근 콘크리트 보를 대상으로 장기실험을 통하여 얻어진 실험결과를 바탕으로 단면형태별 균열폭 특성을 구분하여 파악하므로 써 장기균열폭 예측모델을 제안하는데 필요한 기초자료를 제공하고자 하였다. 따라서 단면형태별로 각각 한 개씩 의 철근콘크리트 비교시험체를 포함한 4개의 장방형보와 4개의 T형 보로 구성된 총 8개의 시험체를 제작하여 시공하중의 영향을 고려한 1년간 4점 가력 장기휨실험을 수행하였다. 결과로서 시간종속적인 영향을 받는 순수장기균열폭은 철근 시험체에 비해 보강근의 탄성계수가 낮은 GFRP나 AFRP-보강근 시험체에서는 2.6~3.0배 증가하였으나 CFRP-보강근 시험체에서는 1.1~1.4배 증가에 그쳤다. 또한 즉시균열폭을 포함한 총장기균열폭은 장방형단면과 T형단면 시험체에서 평균적으로 각각 즉시균열폭의 약 2.4와 3.1배 증가를 보여주어 보수적으로 각각 2.5와 3.5의 시간종속계수를 구분하여 제안하였다.

• 한국전기전자재료학회논문지
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• 제18권1호
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• pp.62-67
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• 2005

Recently, polymer insulators that are used for high voltage applications have some advantages such as light weight, small size, vandalism resistance, hydrophobicity and easy making process. During outdoor service of polymer insulators, the surface of the insulating material is frequently subjected to moisture and contamination that lead to dry band arcing. Their tracking resistance, erosion resistance, end sealing and shed design are very important because dry band arcing causes degradation of polymer surface. Aging test to estimate life property of polymer insulator is executed through several international standard such as IEC 61109 and CEA tracking wheel test, but is not getting clear conclusion yet. There are two methods in the diagnosis method of polymer insulator such as off-line and on-line. The diagnosis methods in off-line are external condition analysis by the eye, contaminant analysis on surface, surface analysis, pollution withstand voltage test, power frequency flashover voltage test, lightning impulse flashover test, tensile fracture load test and flexural load test. Polymer material is also investigated it's tracking resistance by adding surface active agent in IEC 587. In this paper, the tracking performance of polymer insulator with salt solution which is added surface active agent. The diagnosis of insulator sample has been analyzed by leakage current and visual examination, STRI guide and thermal image camera.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.285-291
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• 2002

The shearing process for the sheet metal is normally used in the precision elements such as a frame of TFT-LCD or lead frame of If chips. In these precision elements, the burr formation prevents the system assembly and needs the additional burr removing process. In this paper, we developed the small size NC punching system which has an aligning kinematics between the rectangular shaped punch and die. The punch is driven by an ai cylinder and the sheet metal is moving on the X-Y table system which is driven by two stewing motors. The microprocessor control the whole system and communicate with the monitoring PC by RS232C serial communication protocol. The graphic user interface program in PC monitors nil control the punching system. The cross shaped joint hinge supports the punching die and positioned by two differential screws, whose are installed in perpendicular directions. The aligning between the punch and die is performed using the sheets of half thickness(0.1mm Brass) of the real process for the frame of the TFT-LCD. Using half thickness Brass, the burr formation is magnified and we can decide the aligning direction more easily then using the real thickness(0.2mm) Aluminum. In this paper, the aligning results are measured manually using the SEM photographs and we hope to make the automated aligning procedures using some kinds of image processing techniques.

• 한국구조물진단유지관리공학회 논문집
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• 제20권5호
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• pp.26-34
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• 2016

철골기둥-베이스 플레이트 접합부의 파괴유형은 베이스 플레이트 압축면과 인장면의 휨파괴, 앵커볼트의 인장파괴, 뽑힘, 전단파괴, 그리고 콘크리트 기초파괴 및 철골기둥의 소성힌지발생에 따른 파괴이다. 본 연구에서는 핀접합 또는 강접합으로 가정하여 설계되는 노출형 철골기둥-베이스 플레이트 접합부가 받을 수 있는 모멘트의 크기를 구하기 위하여, 한계상태 함수를 이용하여 철골기둥-베이스 플레이트 접합부의 휨성능 및 파괴유형을 예측하고 실험결과와 비교하였다. 한계상태함수를 이용하여 노출형 철골기둥-베이스 플레이트 접합부의 휨성능을 비교적 정확히 예측할 수 있는 범위는 축력이 있는 경우, 앵커볼트의 항복 또는 철골기둥의 항복으로 판별되었을 때이며 축력이 없는 경우, 베이스 플레이트의 항복으로 판별된 경우이다. 파괴유형까지 같이 고려할 경우, 축력이 있으며 앵커볼트의 항복으로 판별된 경우에만 한계 상태함수의 사용이 가능하다.