• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.253-256
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• 2008

복합섬유(Fiber Reinforced Polymers)가 외부 부착된 철근콘크리트 보에 관한 연구는 국내 및 세계 여러나라에서 활발히 진행되고 있으나 장기 거동에 관한 연구는 많이 미흡한 실정이다. 본 연구에서는 현재 국내에서 많이 사용되고 있는 탄소섬유(Carbon Fiber Reinforced Polymers)와 유리섬유(Glass Fiber Reinforced Polymers)를 철근 콘크리트 보에 외부 부착시킨 후 300일간 지속하중하에서 철근의 변형률, FRP의 변형률을 측정함으로써 FRP 보강 실험체의 시간의존적 거동을 파악하였다. 또한, Adjusted Effective Modulus Method, (AEMM)과 Ghali and Farve의 방법을 사용하여 시간경과에 따른 크리프와 건조수축에 의한 응력과 변형률의 변화를 예측하였다. 실험결과, RC보의 휨 보강 측면으로 보았을 때, CFRP가 GFRP보다 장기거동에 있어 우수한 성능을 보이는 것으로 나타났으며, 이론 식으로 산정된 값은 무보강 실험체의 철근 변형률의 경우 비교적 유사하게 예측하고 있으나 FRP로 보강된 실험체들의 인장철근은 다소 과대평가하는 결과를, 압축철근은 과소평가하는 결과를 나타냈다.

• Journal of the Korean Wood Science and Technology
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• 제21권2호
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• pp.31-37
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• 1993

Composites of styrene polymers with woody fibers were prepared, and the effect of compatibilizers on their mechanical properties was evaluated. To improve the compatibility of wood fibers and the matrix polymers, styrene-maleic anhydride copolymer(SMA) and maleic anhydride-modified polymers were used as compatibilizers. As results, maleic anhydride-modified polystyrene and SMA were proved to improve the tensile strength of the molded composites, and also were evaluated as good compatibilizers for the wood fiber polystyrene composite. Cellulosic fiber (dissolving pulp) provided better reinforcement than lignocellulosic fiber(thermomechanical pulp). On the contrary in the case of the composite of wood fiber and acrylonitrile-butadiene styrene copolymer(ABS), SMA and maleic anhydride-modified acrylonitrile-butadiene-styrene copolymer(MABS) did not act as compatibilizers. However, MABS was evaluated as a good polymer matrix to make wood fiber reinforced composite. The tensile properties of the composites of wood fiber and MABS were superior than those of wood fiber-ABS composites.

• Steel and Composite Structures
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• 제22권6호
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• pp.1337-1358
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• 2016

The current study focuses on the assessment and interface response of reinforced concrete elements with composite materials (carbon fiber reinforced polymers-CFRPs, glass fiber reinforced polymers-GFRPs, textile reinforced mortars-TRM's, near surface mounted bars-NSMs). A description of the transfer mechanisms from concrete elements to the strengthening materials is conducted through analytical models based on failure modes: plate end interfacial debonding and intermediate flexural crack induced interfacial debonding. A database of 55 in total reinforced concrete columns (scale 1:1) is assembled containing elements rehabilitated with various techniques (29 wrapped with CFRP's, 5 wrapped with GFRP's, 4 containing NSM and 4 strengthened with TRM). The failure modes are discussed together with the performance level of each technique as well as the efficiency level in terms of ductility and bearing/ bending capacity. The analytical models' results are in acceptable agreement with the experimental data and can predict the failure modes. Despite the heterogeneity of the elements contained in the aforementioned database the results are of high interest and point out the need to incorporate the analytical expressions in design codes in order to predict the failure mechanisms and the limit states of bearing capacities of each technique.

• Computers and Concrete
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• 제11권4호
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• pp.351-364
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• 2013

This paper presents results from an analytical investigation of the behavior of steel reinforced concrete circular column sections with additional Glass Fiber Reinforced Polymers (GFRP) bars. The primary application of this composite section is to relocate the plastic hinge region from the column-footing joint where repair is difficult and expensive. Mainly, the study focuses on the development of the full nominal moment-axial load (M-P) interaction diagrams for hybrid concrete sections, reinforced with steel bars as primary reinforcement, and GFRP as auxiliary control bars. A large parametric study of circular steel reinforced concrete members were undertaken using a purpose-built MATLAB(c) code. The parameters considered were amount, location, dimensions and mechanical properties of steel, GFRP and concrete. The results indicate that the plastic hinge was indeed shifted to a less critical and congested region, thus facilitating cost-effective repair. Moreover, the reinforced concrete steel-GFRP section exhibited high strength and good ductility.

• Coupled systems mechanics
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• 제11권1호
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.

• 폴리머
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• 제36권6호
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• pp.677-684
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• 2012

사출성형공정은 고온으로 수지를 가소화시키고 고압으로 금형에 흘려 보내어 제품을 성형하는 방법이다. 이 과정에서 고분자 수지는 온도의 변화에 따라 수축을 하게 되는 성형수축이 발생된다. 그리고 시간이 흐른 뒤에도 제품에 변형이나 휨이 발생하게 되는데 이는 제품에 포함되어 있는 잔류응력의 이완 때문이다. 이러한 휨을 막기 위해 수지에 무기물을 첨가하여 수축을 줄이거나, 수지에 유리섬유나 카본섬유 등 섬유를 사용하여 휨의 저항성을 높인다. 그리고 성형품을 강건하게 설계하여 응력에 따른 휨의 저항을 향상시킨다. 본 연구에서는 강건설계를 위해 리브를 설치한 성형품에 나타나는 휨을 실험을 통하여 조사하였다. 성형조건에 따라서, 그리고 금형설계에 따라서 즉, 게이트의 위치에 따라서 휨의 변화를 조사하였다. 수지의 흐름방향과 흐름의 직각방형의 휨도 조사하였다. 게이트 근처와 게이트에서 먼 부분의 휨도 비교분석 하였다. 수지는 유리섬유로 보강된 결정성 수지인 PP와 PA66를 사용하였다. 유리섬유가 포함된 결정성 수지는 유리섬유가 포함된 비결정성 수지보다 휨이 컸다. 결정성 수지는 비결정성 수지에 비해 휨이 성형조건에 다소 적게 영향을 받았지만 제품의 설계에 따라서는 크게 변하였다.

• KCI Concrete Journal
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• 제11권3호
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• pp.65-77
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• 1999

A portland cement was reinforced by incorporating carbon fiber(CF), silica powder, and impregnating the pores with styrene monomers which were polymerized in situ. The effects of type, length, and volume loading of CF, mixing conditions, curing time and, curing conditions on mechanical behavior as well as freeze-thaw resistance and longer term stability of the carbon-fiber reinforced cement composites (CFRC) were investigated. The composite Paste exhibited a decrease in flow values linearly as the CF volume loadings increased. Tensile, compressive, and flexural strengths all generally increased as the CF loadings in the composite increased. Compressive strength decreased at CF loadings above approx. 3% in CFRC having no impregnated polymers due to the increase in porosity caused by the fibers. However, the polymer impregnation of CFRC improved all the strength values as compared with CFRC having no Polymer impregnation. Tensile stress-strain curves showed that polymer impregnation decreased the fracture energy of CFRC. Polymer impregnation clearly showed improvements in freeze-thaw resistance and drying shrinkage when compared with CFRC having no impregnated polymers.

• Structural Engineering and Mechanics
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• 제77권6호
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• pp.735-744
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• 2021

In recent years, the use of new materials and technologies with the aim of developing high-performing and cost-effective structures has greatly increased. Application of high-strength concrete (HSC) has been found effective in reducing the dimensions of frame members; nonetheless, such reduction in dimensions of structural elements in the most cases may result in the lack of accountability in the tolerable drift capacity. On this basis, strengthening of frame members using fiber reinforced polymers (FRPs) may be deemed as an appropriate remedy to address this issue, which albeit requires comprehensive and systematic investigations. In this paper, the performance of properly-designed, two-dimensional frames made of high-strength concrete and strengthened with Carbon Fiber Reinforced Polymers (CFRPs) is investigated through detailed numerical simulation. To this end, nonlinear dynamic time history analyses have been performed using the Seismosoft software through application of five scaled earthquake ground motion records. Unstrengthened (bare) and strengthened frames have been analyzed under seismic loading for performance assessment and comparison purposes. The results and findings of this study show that use of CFRP can be quite effective in seismic response improvement of high-strength-concrete structures.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.557-566
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• 2017

Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 봄 학술발표회 논문집
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• pp.223-226
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• 2003

Due to the potential application to ultra-high strength fibers and excellent properties such as high mechanical properties, excellent thermal endurance and chemical stability, thermotropic liquid crystal polymers (TLCPS) are attractive in recent years [1, 2]. Furthermore, the melt blends of TLCPS and conventional thermoplastics have been extensively investigated because of their easy processing and high performance [3-6]. Since high performance polymers generally has high melt viscosity, introduction of the relatively low viscosity components may be one of the more effective techniques to improve processability through the decrement of melt viscosity in melt processing. (omitted)