• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.211-214
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• 2010

플랫 플레이트 시스템은 기둥 주위의 국부적인 응력집중 현상으로 인한 뚫림전단 파괴에 대해 취약하다. 따라서 유한요소해석을 통해 이러한 플랫 플레이트 시스템의 뚫림전단 성능을 평가하고자 한다. 슬래브의 전단을 고려하기 위하여 Reissner-Mindlin 가정을 바탕으로 한 등매개변수 감절점 쉘 요소를 적용하였다. 콘크리트의 재료적 비선형 거동을 고려하기 위해 압축거동은 수정압축장 이론을 적용하였으며 인장강성효과 또한 콘크리트 재료모델에 반영하였다. 기존 실험결과와의 비교를 통해 타당성을 검증하고자 하였다. 비교 결과, 약 16%의 오차율을 보였으며 보강비가 낮은 실험체에 비해 보강비가 높은 실험체가 실험결과에 가까운 값을 예측하는 것으로 나타났다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.3
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• pp.160-166
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• 2018

The purpose of this study is to investigate experimentally the effects of aspect ratio of polyethylene fiber on the compressive strength and tensile behavior of alkali-activated cementless composite. Two mixtures were determined according to aspect ratio values of polyethylene fibers, and the compressive strength and tension tests were performed. Test results showed that the effect of aspect ratio of fiber on the compressive strength was negligible and the tensile strength, ductility, and number of cracks of the mixture including the fiber with high aspect ratio were higher than those of the mixture including the fiber with low aspect ratio. On the other hand, the crack spacing and crack width were low in the mixture including the fiber with high aspect ratio.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.349-355
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• 2020

The purpose of this study is to investigate the effects of types and amounts of fibers on the compressive strength and tensile behavior high strength fiber-reinforced composites under a static load and impact resistance properties of composites under a high-velocity projectile impact load. Three kinds of mixtures were designed and specimens were manufactured. compressive strength, uniaxial tension, and high velocity projectile impact load tests were performed. Test results showed that the amount of fiber has a greater effect on the tensile strength an d tensile strain capacity than the compressive strength, an d the tensile strain capacity was improved by using hybrid fibers. It was also found that the amount of steel fiber had a great influence on the impact resistance capacity of panels. Although the impact resistance capacity of panels could be improved by using hybrid fibers, the difference of impact resistance capacity between specimens was found to be larger than the case of use of single fiber.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.29-36
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• 2017

The purpose of this study is to investigate experimentally the effect of types of alkali-activators and curing conditions on the compressive and tensile behavior of fiber-reinforced cementless composites. Two types of alkali-activators and two curing conditions were determined and density test, compressive strength test, and uniaxial tension test were performed. Test results showed that the cementless composite with sodium silicate showed higher performance in terms of strength, tensile strain capacity, and toughness than that with calcium hydroxide and sodium carbonate. The effect of curing conditions depends on the types of alkali-activators.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.260-267
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• 2021

The purpose of this study was to experimentally investigate the effects of curing methods on the compressive strength and tensile behavior of alkali-activated slag-based fiber-reinforced composite with a water-to-binder ratio of 15%. Three kinds of mixtures according to the curing conditions were prepared and compressive strength and tension tests were performed. Test results showed that the compressive strength and the first cracking strength of composites decreased when high temperature curing and air curing were adopted, while tensile strain capacity of composites increased. It was also observed that crack spacing and crack width of composites decreased by applying high temperature and air curing.

• Journal of the Korean Geosynthetics Society
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• v.9 no.4
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• pp.75-84
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• 2010

In this study, the long-term performance tests, which have extensibility, creep deformation, installation resistance and durability characteristic, is conducted to apply geosynthetic strip in field. The strength reduction factors using the test results are evaluated in order to calculate long-term design tensile strength. First, the creep deformation was evaluated by both the stepped isothermal method(SIM) and the time-temperature superposition(TTS) method. The creep reduction factor is reasonable to apply 1.6. Second, the result of installation damage test had little damage of yarn, which affected strength of reinforcement. Therefore, it can be analyzed that the installation damage of geosynthetic strip has little effect of long-term design tensile strength. Finally, the durability reduction factor considering chemical, biological and outdoor exposure resistance is reasonable to apply 1.1, which is considered the stability and economic efficiency of reinforced earth wall using geosynthetic strip.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.5
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• pp.125-132
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• 2019

Ultra-high performance concrete (UHPC) has high compressive and tensile strengths due to the particle packing, and its ductile behavior can be ensured by utilizing steel fibers. However, since the UHPC members exhibit different characteristics of crack behavior and tensile behavior from normal concrete, the tension stiffening and cracking characteristics of the UHPC should be accurately modeled for the design and analysis of the UHPC members. In this study, uniaxial tension tests was conducted on the UHPC members with strands, where the test variables were diameter and reinforcing ratio of strands. Detailed analyses were also conducted to identify the tensile characteristics and crack behavior of the UHPC members. By comparing the test results with current code provisions and other models proposed by existing researchers, their applicability for estimation of crack behavior of the UHPC members was examined.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.317-325
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• 2012

In this study, to evaluate the shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC) under restrained condition, restrained shrinkage test was performed according to ring-test mostly used at home and abroad. Ring-test was performed with the various thicknesses and radii of inner steel ring to give different degree of restraint. Free shrinkage and tensile tests were carried out simultaneously to estimate the degree of restraint, stress relaxation, and shrinkage cracking potential. Test results indicated that the average steel strain and residual tensile stress were reduced as the thicker inner steel ring was used, whereas degree of restraint was increased. The steel strain, residual tensile stress and degree of restraint were hardly affected by the size of radius of inner ring. In the case of all ring specimens, shrinkage crack did not occur because the residual tensile stress was lower than the tensile strength. About 39~65% of the elastic shrinkage stress was relaxed by the sustained interface pressure, and the maximum relaxed stress was increased as the thicker inner ring was applied. Finally, the degree of restraint with age was predicted by performing non-linear regression analysis, and it was in good agreement with the test results.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.697-698
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• 2013

최근에 유연한 성질을 갖는 전자기기들의 수요가 증가하면서, 그에 따라서 유연 전자기기를 뒷받침 해줄 수 있는 에너지 저장체의 유연한 성질도 중요성이 점점 부각되고 있으며 많은 연구가 진행되고 있다. 유연한 에너지 저장체의 많은 연구들이 유연한 금속 박막이나 특수 공정처리가 필요한 고분자를 이용하고 있으나, 대부분의 유연 에너지 소자들은 에너지 저장체의 성능에 비해 고온과 산 약품과 같은 환경이 필요하며, 비용과 시간이 많이 소모되고 있다. 그에 반해 섬유는 앞에서와 같이 특수 공정 처리가 따로 필요하지 않으며 상온에서도 손 쉽게 이용 가능하며, 신축성이 뛰어난 장점이 있기 때문에 효율적, 비용적으로 유연한 에너지 저장체에 유리한 소재이다. 몸에 해로운 산과 같은 약품처리의 필요도 없으며, 용매를 흡수하는 능력이 뛰어나기 때문에 용매를 이용한 도포 방법을 사용하면 다양한 물질을 폭넓게 적용 가능하다. 그리고 적용 분야에 맞춰서 섬유의 종류를 조절하면 다양한 성질을 갖는 천 기반의 에너지 저장체가 형성되며, 면 섬유가 수소 결합과 높은 반데르 발스 결합에 의해 탄소나노튜브와 결합하여 높은 에너지 밀도를 갖는 에너지 저장체를 형성하는 것을 분석한 논문들도 보고되고 있다. 면 섬유의 특수한 성질을 이용하여 에너지 저장체를 제작하고 이를 확인하기 위해서 일반 합성 섬유인 polyester와 면 섬유를 비교 제작하였으며, 용매의 형태로 손쉽게 도포 가능한 물질은 탄소 계열의 활물질들이며, 탄소 나노 튜브나 그래핀 등이 분산된 용액을 이용해 천에 도포 가능하다. 탄소 계열의 활물질들은 대표적인 슈퍼캐패시터 물질이며, 천에 도포를 함으로써 천 기반의 슈퍼캐패시터를 제작하였다. 일반 합성 섬유 polyester와 CNT를 결합한 형태의 전극은 최대 에너지 축전 용량(Maximum specific capacitance)이 53.6 F/g으로 나타났으며, 면 섬유와 CNT를 결합한 형태의 전극은 최대 에너지 축전 용량이 122.1 F/g으로 나타났다. 따라서 면 섬유에서 높은 에너지 저장 능력을 보이는 것을 실험적으로 확인하였으며, 에너지 저장 능력이 뛰어난 면 섬유를 다음 전극 디자인에서도 일률적으로 적용하였다. 슈도캐패시터의 대표적 물질인 금속 산화물인 망간 산화물(MnO2)을 3전극 도금 시스템을 이용하여 에너지 축전 용량과 에너지 밀도를 올리는 전극을 제작하였다. 특히 망간 산화물의 형태는 표면적을 극대화하기 위해서 평균 지름은 200~300 nm 정도 되는 나노 입자의 형태로 제작하였다. 그 결과, 확연하게 에너지 축전 용량이 향상되었으며, 최대 에너지 축전 용량은 282.0 F/g, 에너지전력 밀도는 14.2 Wh/kg으로 나타나서 금속 산화물의 형태가 주는 효과를 확인할 수 있었다. 하지만 나노 입자의 형태로 제작된 금속 산화물은 문제점이 발생하였다. 금속 산화물의 전기 전도성이 매우 낮기 때문에, 전기 전도성에 비례해서 전력 밀도의 값이 표현되는데, 전기 전도성이 급격히 감소하기 때문에 전력 밀도도 급격한 감소가 나타난다. 다음과 같이 전기 전도성 물질을 첨가하는 방법은 추가의 공정이 필요한 단점이 있지만 오직 기계적인 인장응력만을 가해서 에너지 밀도와 전력 밀도를 증가시키는 전극을 제작하였다. 인장응력을 섬유 기반의 전극에 가했을 시에 가닥들간의 접촉 증가와 CNT가 정렬되면서 특정 변형률(strain) 이전에서는 전기 전도성이 최대 50% 이상 증가하는 것을 확인할 수 있었으며, 선행 연구에서 보고되었다. 이를 이용해서 전기 전도성과 직결되는 전력 밀도의 양도 증가시키고 에너지 밀도의 증가 여부까지 확인한 결과 인장을 가하기 전 면 섬유의 전력 밀도와 에너지 밀도는 6.4 kW/kg and 6.1 Wh/kg으로 나타났으나 30% 변형 인장 후에는11.4 kW/kg과 7.1 Wh/kg으로 나타났다. 그리고 망간 산화물을 첨가한 전극 역시 4.9 kW/kg과 14.2 Wh/kg으로 나타났었으나 인장 이후 전력 밀도는 14.2 kW/kg, 에너지 밀도는 17.6 Wh/kg으로 확연하게 증가한 것을 확인하였다.

• Journal of the Korean Society for Railway
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• v.19 no.3
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• pp.331-340
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• 2016

Wheel load, design velocity, traffic amount (MGT), stiffness and thickness of sub-layers of asphalt concrete track are selected as performance design parameters in this study. A pseudo-static wheel load computed considering the dynamic amplification factor (DAF) based on the design velocity of the KTX was applied to the top of asphalt concrete track for full three dimensional structural analysis using the ABAQUS program. Tensile strains at the bottom of the asphalt concrete layer and vertical strains at the top of the subgrade were computed from the structural FEA with different combinations of performance parameter values for one asphalt concrete track section. Utilizing the computed structural analysis results such as the tensile strains and the vertical strains, it was possible to develop design graphs to investigate proper track sections for different combination of the performance parameters including wheel load, design velocity, traffic amount(MGT), stiffness and thickness of asphalt concrete layers for any given design life. By analyzing the proposed design graphs for asphalt concrete track, it was possible to propose simple design tables that can be used by engineers for the effective and fast design of track.