• Structural Engineering and Mechanics
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• 제65권5호
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• pp.611-619
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• 2018

This paper addresses numerical modeling and nonlinear analysis of unreinforced masonry walls and vaults externally strengthened using fiber reinforced polymers (FRP). The aim of the research is to provide a simple method for design of strengthening interventions for masonry arched structures while considering the nonlinear behavior. Several brick masonry walls and vaults externally strengthened by FRP which have been previously tested experimentally are modeled using finite elements. Numerical modeling and nonlinear analysis are performed using commercial software. Description of the modeling, material characterization and solution parameters are given. The obtained numerical results demonstrate that externally applied FRP strengthening increased the ultimate capacity of the walls and vaults and improved their failure mode. The numerical results are in good agreement with the experimentally obtained ultimate failure load, maximum displacement and crack pattern; which demonstrates the capability of the proposed modeling scheme to simulate efficiently the actual behavior of FRP-strengthened masonry elements. Application is made on a historic masonry dome and the numerical analysis managed to explain its structural behavior before and after strengthening. The modeling approach may thus be regarded a practical and valid tool for design of strengthening interventions for contemporary or historic unreinforced masonry elements using externally bonded FRP.

• 한국재료학회지
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• 제14권7호
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• pp.489-493
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• 2004

The electrical property of MMC is essentially important to some applications such as power transmission lines and cables, electronic and electrical components as well as electromagnetic shielding equipments. The behavior of electrical resistivity of $SiC_{w}/Al$ alloy composites under as-extruded and annealed conditions has been investigated within the temperature range from room temperature to $450^{\circ}C$. It can be seen that within entire temperature range, the electrical resistivity of composites was higher than that of an unreinforced matrix alloy under the same condition of either as-extrusion or annealing. The temperature dependence of both exhibited positive incline like a typical metal. The variation of electrical resistivity of an unreinforced matrix alloy with temperature from ambient temperature to $450^{\circ}C$ was nearly monotonous, while those of composites increased monotonously at low temperature and rose to a high level after about $250^{\circ}C or 275^{\circ}C$. The difference of these temperature dependences on electrical resistivity can be interpreted as qualitatively the interfaces of $SiC_{w}$ fibers and matrix, where act as nucleation sites.

• 한국분말재료학회지
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• 제10권2호
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• pp.103-107
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• 2003

Aluminum-based $Al/Al_2O_3$ composites were fabricated by a powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. A mixture of aluminum powder and $Al_2O_3$ particles of which volume content was varied from 5 to 20%, was filled in the tube by tap filling and then rolled by 75% reduction in thickness at ambient temperature. The rolled specimen was then sintered at 56$0^{\circ}C$ for 0.5 h. The mixture of Al powders and $Al_2O_3$ particles was successfully consolidated by the sheath rolling. The $Al/Al_2O_3$ composite fabricated by the sheath rolling showed a recrystallized structure, while unreinforced Al powder compact fabricated by the same procedure showed a deformed structure. The unreinforced Al powder compact was characterized by a deformation (rolling) texture of which main component is {112}<111>, while the $Al/Al_2O_3$ composite showed a mixed texture oi deformation and recrystallization. The sintering resulted in recrystallization in Al powder compact and grain growth in the composite.

• Earthquakes and Structures
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• 제9권4호
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• pp.719-733
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• 2015

Seismic risk management of the built environment is integrated by two main stages, the assessment and the remedial measures to attain its reduction, representing both stages a complex task. The seismic risk of a certain structure located in a seismic zone is determined by the conjunct of the seismic hazard and its structural vulnerability. The hazard level mainly depends on the proximity of the site to a seismic source. On the other hand, the ground shaking depends on the seismic source, geology and topography of the site, but definitely on the inherent earthquake characteristics. Seismic hazard characterization of a site under study is suggested to be estimated by a combination of studies with the history of earthquakes. In this Paper, the most important methods of seismic vulnerability evaluation of buildings and their application are described. The selection of the most suitable method depends on different factors such as number of buildings, importance, available data and aim of the study. These approaches are classified in empirical, analytical, experimental and hybrid. For obtaining more reliable results, it is recommends applying a hybrid approach, which consists of a combination between methods depending on the case. Finally, a recommended approach depending on the building importance and aim of the study is described.

• 한국지진공학회논문집
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• 제11권1호
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• pp.37-43
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• 2007

탄소섬유관으로 구속된 원형 무근콘크리트 부재는 콘크리트에 효과적인 횡구속을 제공하며, 섬유의 우수한 역학적 성질로 인하여 기존의 철근을 대체할 수 있는 우수한 합성부재이다. 본 논문에서는 탄소섬유관으로 구속된 원형 무근콘크리트 보에 관한 실험 및 해석연구를 실시하였다. 실험연구에서 시험체는 두께 1.5mm(3장), 2.0mm(4장), 2.5mm(5장) 및 3.0mm(6장)를 변수로 하여 실험을 실시하였다. 구속된 콘크리트의 압축강도를 예측하는 식을 이용하여 본 연구에서는 탄소섬유 관으로 구속된 원형 무근 콘크리트 보의 휨성능을 예측하는 실험식을 제안하였다.

• Steel and Composite Structures
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• 제22권1호
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• pp.203-216
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• 2016

To study the stress concentration factors (SCFs) of concrete-filled tubular Y-joints subject to in-plane bending, experiments were used to investigate the hot spot stress distribution along the intersection between chord and brace. Three concrete-filled tubular chords forming Y-joints were tested with different reinforcing components, including doubler-plate, sleeve, and haunch-plate reinforcement. In addition, an unreinforced joint was also tested for comparison. Test results indicate that the three different forms of reinforcement effectively reduce the peak SCFs compared with the unreinforced joint. The current research suggests that the linear extrapolation method can be used for chords, whereas the quadratic extrapolation method must be used for braces. The SCF is effectively reduced and more evenly distributed when the value of the axial compression ratio in the chord is increased. Furthermore, the SCFs obtained from the test results were compared to predictions from some well-established SCF equations. Generally, the predictions from those equations are very consistent for braces, but very conservative for concrete-filled chords.

• 한국지반신소재학회논문집
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• 제16권1호
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• pp.53-61
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• 2017

바다 자원의 조성을 위해 시설되는 인공어초는 해저 연약지반에 설치될 경우 침하 및 세굴에 의한 기능 상실이 발생할 수 있다. 따라서 본 연구에서는 해저 연약지반의 보강에 따른 인공어초의 침하 거동을 알아보기 위해 모래, 실트 및 점토 지반을 각각 조성하여 관입실험, 침하실험 등과 같은 다양한 실내실험을 수행하였다. 무보강(unreinforced), 지오그리드(geogrid) 보강 및 하이브리드 대나무매트(hybrid bamboo mat, HBM) 보강과 같은 3종류의 보강과 보강재의 면적에 따른 특성을 살펴보았다. 실험 결과 보강재의 면적이 증가할수록 보강 효과가 증가하는 경향을 보였으며, HBM이 지오그리드 단일 보강에 비해 더 뛰어난 보강 효과를 보였다.

• Geomechanics and Engineering
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• 제9권2호
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• pp.219-241
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• 2015

In this paper, a series of repeated load tests were carried out on a 150 mm diameter plate simulative of vehicle passes, to demonstrate the benefits of soil-rubber shred mixture in decreasing the soil surface settlement of road embankment. The results show that the efficiency of rubber reinforcement is significantly a function of the rubber content, thickness of rubber-soil mixture and soil cap thickness over the mixture. Minimum surface settlement is provided by 2.5% of rubber in rubber-soil mixture, the thickness of mixture layer and soil cap of 0.5 times the loading surface diameter, giving values of 0.32-0.68 times those obtained in the unreinforced system for low and high values of amplitude of repeated load. In this installation, in contrast with unreinforced bed that shows unstable response, the rate of enhancement in settlement decreases significantly as the number of loading cycles increase and system behaves resiliently without undergoing plastic deformation. The findings encourage the use of rubber shreds obtained from non-reusable tires as a viable material in road works.

• 한국지진공학회논문집
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• 제10권3호
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• pp.77-84
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• 2006

비보강 조적조는 비균일 재료로 이루어진 합성재료에 가까우므로 그 거동이 하중종류와 구조물의 손상 정도에 따라서 매우 달라지게 된다. 본 연구에서는 여러 차례의 모의 지진을 받는 구조물의 손상거동이 어떻게 전개되어 가는지 살펴보는 간단한 방법을 제시한다. 특히, 시간영역 자료를 여러 구간으로 나누어서 주파수가 어떻게 변화해 가는지 살펴보는 부분 FFT방법을 이용하였다. 또한, 주파수와 강도와의 관계식을 이용하여 단자유도계의 이선형모델도 유도하였다. 본 연구에서 제시하는 이러한 방법들을 이용하여 비보강 조적조의 비탄성 성질들을 합리적으로 구할 수 있었다.

• Advances in concrete construction
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• 제8권2호
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• pp.77-90
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• 2019

This paper aims to investigate vibration frequency decrease (vibration period elongation) of reinforced concrete (RC) structure with unreinforced infill wall and reinforced infill wall exposed to progressively increased artificial earthquake load on shaking table. For this purpose, two shaking table experiments were selected as a case study. Shaking table experiments were carried on 1:1 scaled prototype one bay one storey RC structure with infill walls. The purpose of this shaking table experiment sequence is to assess local behavior and progressive collapse mechanism. Frequency decrease and eigen-vector evolution are directly related to in-plane and out-of-plane bearing capacities of infill wall enclosure with reinforced concrete frame. Firstly, frequency decrease-damage relationship was evaluated on the base of experiment results. Then, frequency decrease and stiffness degradation were evaluated with applied Peak Ground Acceleration (PGA) by considering strength deterioration. Lastly, eigenvector evolution-local damage and eigenvector evolution-frequency decrease relationship was investigated. Five modes were considered while evaluating damage and frequency decrease of the tested specimens. The relationship between frequency decrease, stiffness degradation and damage level were presented while comparing with Unreinforced Brick Infill (URB) and Reinforced Infill wall with Bed Joint Reinforcement (BJR) on the base of natural vibration frequency.