• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.102-109
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• 2010

This paper investigates the bond behavior of reinforced concrete beams having high-strength transverse reinforcement. A total of four reinforced concrete beams were tested in this study to estimate the bond capacity of the proposed U-shape reinforcement. The proposed U-shape reinforcement not only has a simple structure to install, but also can increase the bond capacity of reinforced concrete beams by controling bond cracks. This study follow the test method proposed by Ichinose to obtain the bond stress and the bond slip of the specimens. The main test parameters were the yield strength, ratio, and reinforcing types of transverse reinforcements. It was found that the proposed U-shape reinforcement was able to effectively improve the bond performance of reinforced concrete beams with high-strength transverse reinforcement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.147-154
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• 2008

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally unbonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips using embedded or stud-type plate anchorages. Total 10 small-scaled specimens were manufactured with the different post-tensioning level and types of mechanical anchorage as a main test parameter. A control specimen and specimens with simply bonded CFRP strips were included to compare the structural performances of each system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned unbonded CFRP strips reached the rupture strength of the CFRP strip. Also, it was observed that the specimens with stud-type anchorage have equivalent strengthening performance compared with embedded-type anchorage.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.33-41
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• 2011

This study presents modeling technologies applicable to an unbonded post-tension system using a finite element software package. In this study, both direct modeling method and multiple spring method were used. The direct modeling method adopts tube-to-tube contact elements to represent the physical feature of a post-tension system. The multiple spring method uses virtual tendons attached to the real tendons using a number of rigid axial springs that freely rotate at the ends. Both modeling technologies provide accurate predictions. However, only the multiple spring method provides numerically stable and reliable responses with a consideration of concrete tension stiffening effects. Therefore, the multiple spring method turned out to be a generally applicable modeling technology for the unbonded post-tension system. Comparisons were made for the analytical and experimental results for the verification of the selected method, and parameter studies were carried out to confirm the appropriateness of the modeling assumptions and parameters adopted in the analysis.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.306-310
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• 2000

본 논문에서는 안테나 구조해 따른 PCS 전화기에 의해 인체두부에 유기되는 SAR 값을 비교 분석하였고, SAR 값에 영향들 주는 요인을 분석하였다. 안테나의 종류, 안테나의 부착위치, 단말기의 구조에 따른 1 g 및 10 g 평균 첨두 SAR 값을 계산하였고, 인체 두부의 깊이에 따른 SAR 분포의 변화를 살펴보았다. 플립형 단말기에 부착된 안테나 중에서는 side mounted PIFA(Planar Inverted F Antenna)의 1 g 및 10 g 평균 첨두 SAR 값이 각각 0.686 W/kg과 0.353 W/kg으로 가장 낮았다. 폴더형 단말기에 부착된 모노폴 안테나에 의한 1 g 및 10 g 평균 첨두 SAR값은 플립형에 의한 SAR 값에 비해 약 30 % 가량 낮은 것으로 나타났다. 평균 첨두 SAR 값이 낮은 값을 보이는 두 구조인 side mounted PIFA와 폴더형 구조의 모노폴 안테나의 깊이에 따른 SAR 분포는 나머지 두 구조에 비해 비교적 완만한 경사를 보였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.77-86
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• 2024

In this study, authors attempted to determine the bond behavior characteristics to utilize Grid typed CFRP reinforcement as an alternative to steel rebar used as concrete reinforcement. Since it is difficult to understand the influence of the transverse grid length of the Grid typed CFRP reinforcement in the existing numerical analysis proposal for bond behavior, a nonlinear 3D model was created and finite element analysis was performed. To perform the analysis, the analysis was conducted by inputting a nonlinear material model and modeling the bond interface characteristics between the Grid typed CFRP reinforcement and concrete and comparing them with the actual direct pull-out test results. The bond behavior characteristics of the Grid typed CFRP reinforcement were found to be very dominated by the factors of the transverse grid, and showed a tendency to continuously increase load.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.105-114
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• 1997

본 연구는 비부착 긴장재를 갖는 부재에 대한 일련의 연구중 두 번째에 해당한다. 첫 번째 연구(1)에서는 기존연구의 제안식과 현행의 ACI 규준의 문제점을 고찰하고 기존의 총 167개 실험결과와 비교·분석하였다. 본 연구에서는 소성힌지 길이 개념과 변형도 적합조건에 의해서 비부착 긴장재의 응력을 평가할 수 있는 방법에 대한 검토를 통하여, 새로운 설계식을 제안하였다. 이는 이론적인 분석에 의한 변수설정과 기존 실험결과를 이용한 중회귀분석법을 사용하였다. 그리고 제안된 설계식을 기존의 식들과 비교하여 좋은 결과를 얻었으며, 제안된 설계식의 특성을 다음과 같이 설명하였다. (1)비부착 긴장재의 응력산정시 유효프리스트레스, 일반철근의 양, 작용하중의 형태 등은 중요한 변수로 작용할 수 있으므로 설계식에 고려하는 것이 바람직하다. (2)비부착 긴장재의 응력산정식은 현행 ACI 규준식과는 다르게 fc'/ p항의 제곱근과 비례하는 함수관계에 있다. (3)스팬-춤비가 비부착 긴장재의 응력에 미치는 영향은 소성힌지 길이의 개념에 의해서 역학적으로 타당하게 설명할 수 ldT다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.286-292
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• 1991

The authors propose to use the vortex generators in order to improve of the efficiency for the cambered otter boards. The equipments and testing method of this model test was the same as the previous report. This study was tested for 6 models such as the single cambered, the V-shaped cambered and the slotted cambered otter board without and with vortex generators. The results obtained are as follows: \circled1 C sub(L) of the single cambered model otter board with vortex generators was increased about 10% in comparison with that of model without vortex generators, C sub(D) decreased 2%, and L/D increased 5~20%. \circled2 L/D of the V-shaped cambered model otter board with vortex generators was increased 10~20% in comparison with that of model without vortex generators. \circled3 C sub(L) of the two slotted cambered model otter board with vortex generators was increased about 20% within an angle of attack 25$^{\circ}$ in comparison with that of without vortex generators, C sub(D) increased 5~20%, and L/D was higher than prototype within an angle of attack 20$^{\circ}$. \circled4 The separation point of the model otter boards with vortex generators was removed back ward a little in comparison with that of the model without vortex generators. \circled5 Flow speed difference of the back side to the front side of model otter boards with vortex generators was increased a little in comparison with that of the models without vortex generators. \circled6 The size of separation zone in case of the model otter boards with vortex generators was decreased about 10% in comparison with that of the models without vortex generators.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.40-43
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• 2011

최근, 레이저 초음파 영상화 기법은 구조물의 비접촉식 손상 진단을 위해 널리 연구되고 있다. 초음파 영상화 기법의 가장 큰 장점은 비접촉식으로 구조물의 손상을 진단할 수 있고, 가진 및 측정 지점을 자유로이 이동할 수 있다는 점이다. 따라서 이는 고온이나 동적상태의 구조물에 적용이 가능하며, 시간과 공간상의 충분한 데이터를 획득할 수 있으므로 역문제 (Inverse problem)를 해결할 필요 없이 완전한 초음파의 전파 형상을 얻을 수 있다. 지난 연구들에서는 충분한 가진력 혹은 측정 민감도를 확보하기 위해 가진 레이저와 부착형 센서의 조합이나 부착형 가진 트렌스듀서와 센싱 레이저의 조합으로 초음파 영상을 획득하고자 하였다. 하지만 이들 조합은 가진 혹은 측정 지점이 구조물에 부착되어 있어 완전한 비접촉식 기법을 구현하지 못하였다. 이를 극복하고자 레이저와 EMAT 센서 등의 조합이 시도되어 왔으나, 이 또한 EMAT 센서의 적용 거리에 따른 한계점을 지니고 있다. 본 연구에서는 가진 레이저 (Nd:Yag)의 스캐닝을 통해 다양한 가진 점에서 발생된 초음파가 탄성체 구조물을 통해 전파되고, 이를 센싱 레이저 (Laser Doppler Vibrometer)를 이용하여 측정함으로써 비접촉식 초음파 영상화를 구현하였다. 나아가, 정상파 필터(Standing-wave filter)를 이용하여 구현된 초음파 영상으로부터 손상 영향만 검출해 내는 기법을 개발했다. 개발된 기법은 복합재 시편의 층간박리 (Delamination) 진단을 통해 검증하였다.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.441-450
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• 2010

This is a preliminary study on the development of precast beam-column joints for dry construction methodology. Precast beam column joints with thru-connectors (BCJ_TC) using high strength bars or PS strands were developed and their seismic performance including strength degradation, stiffness degradation and energy dissipation capacity was experimentally evaluated. Test results showed that compressive failures at the end blocks of PC beam members occurred dominantly while PC columns including panel zones were free from any damage. However, the connections confined with CFRP at the end block showed much improved seismic performance than that of the unconfined connections. Connections with neoprene pad fillers between beam and column interfaces were better than the other connections in all the seismic performances except initial stiffness. To improve the seismic performances of BCJ_TC, compressive strength of the concrete at the end block need to be increased to compensate for the additional compressive stresses due to unbonded connectors and deformation of connectors should be controlled respectively.

• Polymer(Korea)
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• v.35 no.4
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• pp.320-324
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• 2011

Two functional urethane acrylates were synthesized by using polycarprolactonediol (PCLD) and diisocyanate. The synthesized fuctional urethane acrylate was mixed with butyl acrylate(BA) or adhesion promoters, and their properties were investigated. To synthesize an excellent transparent urethane acrylate, isophorone diisocyanate(IPDI) was used. In addition, the effect of adding butyl acrylate for the improvement of shrinkage of urethane acrylate was studied. The results showed that the addition of butyl acrylate improved the shrinkage, and the optimum butyl acrylate content was 15 wt%. Both 2-ethyl hexyl acrylate (2-EHA) and ethyl acrylate(EA) were polymerized at $85^{\circ}C$ for 4 hrs to use as adhesion promoters, and the polymerized adhesion promoters were mixed to the UV-curing resin. The results showed that the adhesion properties increased with the increase of adhesion promoters content up to 15 wt%.