• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.219-222
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• 2004

The effects of short fiber and particle hybrid reinforcement on fatigue crack propagation behaviors in aluminum matrix composites have been investigated. Single and hybrid reinforced 6061 aluminum containing same 20 $Al_2O_3\;volume\%$ with four different constituent ratios of short fibers and particles were prepared by squeeze casting method and tested to check the near-threshold and stable crack growth behavior. The fatigue threshold of the composites increased with portion of particle contents and showed the improved crack resistance especially in low stress intensity range. Addition of particle instead of short fiber also increased fracture toughness due to increase of inter-reinforcement distance. These increase in both fatigue threshold and fracture toughness eventually affected the fatigue crack growth behavior such that the crack growth curve shift low to high stress intensity factor value. Overall experimental results were shown that particle reinforcement was enhanced the fatigue crack resistance over the whole stress intensity factor range.

• 토지주택연구
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• 제2권4호
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• pp.471-477
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• 2011

This paper will describe the experimental results on the shear behaviors of reinforced concrete (RC) beam with recycled coarse aggregate (RCA). The primary objective of this research is to evaluate the influences of different RCA replacement percentage (i.e, 0%, 30%, 60%, and 100%) on the shear performance of reinforced concrete beams without shear reinforcement. Eight large-scale RC beams without shear reinforcement were manufactured and tested to shear failure. All had a rectangular cross-section with 400mm width ${\times}$ 600mm depth and 6000mm length, and were tested with a shear span-to-depth of 5.1. The results showed that the deflection and shear strength were little affected by the different RCA replacement percentage. Actual shear strength of each RCA beam was compared with the shear strength predicted using the provisions of ACI 318 code and Zsutty'e equation for shear design of RC beams. ACI 318 code predicted the shear strength of RCA reinforced concrete beams well.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2156-2172
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• 2022

This paper investigates the optimum fiber reinforcement for prestressed concrete containment vessels (PCCVs) under internal pressure. To achieve this aim, steel fiber, which is the most widely used fiber type in current engineering applications, is adopted to constitute steel fiber-reinforced concrete (SFRC) to substitute the conventional concrete in the PCCV. The effects of characteristic parameters, 𝜆_sf, of the steel fiber affecting significantly the mechanical behavior of the concrete are first taken into account. Partial or complete concrete regions of the PCCV are also considered to be replaced by SFRC to balance the economy and safety. By adopting the ABAQUS software, the ultimate bearing capacity and performance for the fiber-reinforced PCCV are scientifically studied and quantified, and the recommendations for the optimum way of fiber reinforcement are presented.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.8-16
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• 2003

A major concern in Gas Metal Arc (GMA) welding process is the determination of welding process variables such as wire diameter, gas flow rate, welding speed, arc current and welding voltage and their effects on the desired weld bead dimensions and shape. To successfully accomplish this objective, 81 welded samples from mild steel AS 1204 flats adopting the bead-on-plate technique were employed in the experiment. The experimental results were used to develop a mathematical model to predict the magnitude of bead geometry as follows; weld bead width, weld bead height, weld bead penetration depth, weld penetration shape factor, weld reinforcement shape factor, weld bead total area, weld bead penetration area, weld bead reinforcement area, weld bead dilution, length of weld bead penetration boundary and length of weld bead reinforcement boundary, and to establish the relationships between weld process parameters and bead geomery. Multiple regression analysis was employed for investigating and modeling the GMA process and significance test techniques were applied for the interpretation of the experimental data.

• 보존과학회지
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• 제31권4호
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• pp.477-488
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• 2015

본 연구에서는 석조문화재에 대한 금속보강재의 최소 개입을 통해 원형부재의 이차 훼손을 줄이고, 동시에 최대의 구조보강 효과를 얻을 수 있도록 제안된 실험을 통해 처리기술의 객관적 기준을 다음과 같이 설정하였다. 첫째, 금속보강재의 설계 기준은 석조문화재의 풍화도에 따라 보강재비의 산정이 이루어져한다. 둘째, 석조문화재의 원형이 부분적으로 훼손되어 형태나 구조적으로 보강이 필요할 때 보형처리(구부재 + 신석재 접합)는 풍화등급이 높은 부재를 기준으로 금속보강재 비율을 계획해야 한다. 본 연구를 바탕으로 석조문화재의 구조적인 안정을 꾀할 수 있는 조건을 고려한 금속보강재 비율을 풍화영역별로 제시하면, 접합단면 대비 $800kgf/cm^2$ 이하는 0.13~0.23, $800kgf/cm^2$ 이상 $1200kgf/cm^2$ 이하는 0.24~0.28, $1200kgf/cm^2$ 이상은 0.29~0.5의 금속보강재비를 권장할 수 있다. 특히 더욱 세분화된 풍화등급에 따른 금속보강재의 적용 여부는 석조물의 파괴계수와 금속보강재의 물성을 고려하여야 할 것으로 사료된다.

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.1-9
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• 2017

원형 기둥의 나선철근은 축방향 철근의 위치 고정 및 좌굴방지와 코어콘크리트의 충분한 횡구속으로 기둥의 연성거동에 효과적인 역할을 한다. 각국은 기둥에 요구되는 연성을 확보하기 위하여 나선철근의 최소철근비를 제시하고 있다. ACI 318-14와 국내 콘크리트 구조설계 기준에서 제시하는 나선철근 최소철근비는 Richart et al.(1928)의 이론에 기초하여 개발되었으며 현재까지 사용되고 있다. 그러나 Richart et al.(1928)의 이론은 현대의 고강도 콘크리트, 고강도철근 그리고 나선철근의 배근조건 등의 영향을 고려하지 못한다. 이 연구에서는 나선철근으로 구속된 철근콘크리트 원형 기둥의 내력회복 및 연성증진에 요구되는 나선철근에 대한 수정 최소철근비 산정식을 제시한다. 수정 최소철근비 산정식은 콘크리트 압축강도, 나선철근 항복강도, 기둥의 단면적, 나선철근 배근간격, 나선철근 직경의 영향을 고려하고 있다. 이 논문에서는 재료강도 및 나선철근 최적비를 변수로 한 실험체의 일축 압축실험을 통하여 ACI 318-14에 제시하는 나선철근 최소철근비 산정식의 타당성을 검토하고, 그 결과를 토대로 나선철근 최소철근비 산정식의 수정방안을 고찰하였다.

• 한국지반신소재학회논문집
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• 제9권4호
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• pp.39-45
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• 2010

부직포에 의한 보강이 모래의 역학적 거동에 미치는 영향에 대해 검토하였다. 이 검토를 위해 보강모래와 무보강모래에 대한 일련의 삼축압축시험이 수행되었다. 표준사인 주문진사가 사용되었고, 부직포 보강재가 모래시료 속에 최대 3층 배치되었다. 분석결과 모래속의 부직포 배치는 모래의 전단강도를 크게 증가시켰고, 보강모래는 파괴시의 변형률도 증가하였다. 또한, 보강층수가 증가할수록 보강재에 의한 시료내 전단층의 확산 방지효과의 증가로 보다 연성화하고, 모래시료의 체적팽창 경향은 부직포 배치에 의해 억제됨이 밝혀졌다. 보강층수 증가에 의한 효과는 간극비 감소로 인한 효과와 같다.

• 한국지진공학회논문집
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• 제11권4호
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• pp.1-11
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• 2007

This paper verifies the difference of the seismic behavior and seismic damage of the neighboring two reinforced concrete piers damaged by the 1995 Hyogoken Nanbu earthquake. The two piers were almost the same size, carrying slightly different dead load, and were provided with the same reinforcement arrangement except the amount of longitudinal reinforcement at the bottom portion of the piers. The pier with more reinforcement was completely collapsed due to this near field earthquake by shear failure at the longitudinal reinforcement cut-off while the other was only damaged at the bottom by flexure even though the longitudinal reinforcement cut-off was also existed at the mid height of the pier. According to the results of the pseudo dynamic test, the seismic damage was recognized to be greatly dependent on the ground motion characteristics even though the employed ground motions had the same peak acceleration. The severe damage was observed when the test employed the seismic wave that had strong influence to the longer period range compared to the initial natural period of the pier. On the other hand, based on the similar model experiment, the defect of gas-pressure welded splice of longitudinal reinforcement was revealed to save the piers against collapse due to the so-called fail-safe mechanism contrary to the intuitive opinion of some researchers. It was concluded that the primary cause of the collapse of the pier was the extremely strong intensity and peculiar characteristics of the earthquake motion according to both the site-specific and the structure-specific effects.

• Journal of Acupuncture Research
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• 제20권6호
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• pp.190-200
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• 2003

Objective: The purpose of this study is to examine influences by the order, Reduction and Reinforcement in Acupuncture on cerebral hemodynamics [regional cerebral blood flow(rCBF) and mean arterial blood pressure(MABP)] in normal rats. Methods: This experiments was to to investigate eath other changes of rCBF and MABP at Xingjian(LR2)(1st) Shaofu(HT8)(2nd) Reduction, Xingjian(LR2)(1st) Shaofu(HT8)(2nd) Reinforcement, Shaofu(HT8)(1st) Xingjian(LR2)(2st) Reduction and Shaofu(HT8)(1st) Xingjian(LR2)(2st) Reduction in Acupuncture. Results: 1. LR2(1st) HT8(2nd) Reduction in Acupuncture was decreased rCBF and MABP in compared with normal condition. 2. LR2(1st) HT8(2nd) Reinforcement in Acupuncture was significantly decreased rCBF, and was decreased MABP in compared with normal condition. 3. HT8(1st) LR2(2st) Reduction in Acupuncture was decreased rCBF during acupuncture but was recovered rCBF after with-drawing of the neddle. 4. HT8(1st) LR2(2st) Reduction in Acupuncture was decreased MABP during acupuncture and after withdrawing of the neddle. 5. HT8(1st) LR2(2st) Reinforcement in Acupuncture was significantly increased rCBF during acupuncture and 30min after withdrawing of the neddle. 6. HT8(1st) LR2(2st) Reinforcement in Acupuncture was decreased MABP during acupuncture, but was recovered MABP after withdrawing of the neddle. Conclusions: I suggested that LR2 HT8 Reduction in Acupuncture and LR2 HT8 Reinforcement in Acupuncture cause a diverse response of cerebral hemodynas.

• 한국지반공학회논문집
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• 제19권6호
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• pp.245-259
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• 2003

본 논문은 강관 다단 그라우팅 터널 보강에 대한 메카니즘 규명에 대한 연구이다. 본 보강공법을 구성하고 있는 보강요소들의 복잡한 기하학적 특성과 각 보강요소들이 전체 보강 메카니즘에 기여하는 정도의 불명확성에 기인하여 본 공법으로 보강된 터널을 합리적으로 해석하기란 무척 어려운 문제로 여겨지고 있다. 따라서 본 연구에서는 균질화 기법을 도입하여 본 공법으로 보강된 지반매질을 하나의 복합체로써 정의하고 수치 모델화하여, 이를 기반으로 3차원 탄소성 유한요소코드를 개발하였다. 이때 균질화 기법과 연계된 굴착단계별 해석 등과 같은 터널해석을 위해 요구되는 다양한 실용적인 알고리즘들 또한 제안되었다. 이러한 과정으로 개발된 3차원 탄소성 유한요소코드를 이용하여 본 보강공법의 이방성 보강 메카니즘에 관하여 고찰되었으며, 이를 위해 다양한 주요 설계인자들에 대한 매개변수 연구가 수행되었다. 이를 통해 유도된 복합 보강 지반체의 역학적 거동특성은 각 구성 매질들의 기하학적 특성과 기여도 등을 잘 모사하고 있는 것으로 판단되었다.