• Computers and Concrete
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• 제19권5호
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• pp.443-449
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• 2017

Taking high geothermal tunnels as background, the deformation of concrete for shotcrete use was studied by simulating hot-humid and hot-dry environments in a laboratory. The research is made up by two parts, one is the influence of two kinds of high geothermal environments on the deformation of shotcrete, and the other is the shrinkage inhibited effect of fiber materials (steel fibers, polypropylene fibers, and the mixture of both) on the concrete in hot-dry environments. The research results show that: (1) in hot and humid environments, wet expansion and thermal expansion happened on concrete, but the deformation is smooth throughout the whole curing age. (2) In hot and dry environments, the concrete suffers from shrinkage. The deformation obeys linear relationship with the natural logarithm of curing age in the first 28 days, and it becomes stable after the $28^{th}$ day. (3) The shrinkage of concrete in a hot and dry environment can be inhibited by adding fiber materials especially steel fibers, and it also obeys linear relationship with the natural logarithm of curing age before it becomes stable. However, compared with no-fiber condition, it takes 14 days, half of 28 days, to make the shrinkage become stable, and the shrinkage ratio of concrete at 180-day age decreases by 63.2% as well. (4) According to submicroscopic and microscopic analysis, there is great bond strength at the interface between steel fiber and concrete. The fiber meshes are formed in concrete by disorderly distributed fibers, which not only can effectively restrain the shrinkage, but also prevent the micro and macro cracks from extending.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.85-92
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• 2007

This paper presents a design optimization of a new Advanced Active Blade Twist (AATR-II) blade incorporating single crystal Macro Fiber Composites (MFC) and conducts vibratory loads reduction analysis using an obtained optimal blade configuration. Due to the high actuation performance of the single crystal MFC, the AATR blade may reduce the helicopter vibration more efficiently even with a lower input-voltage as compared with the previous ATR blades. The design optimization provides the optimal cross-sectional configuration to maximize the tip twist actuation when a certain input-voltage is given. In order to maintain the properties of the original ATR blade, various constraints and bounds are considered for the design variables selected. After the design optimization is completed successfully, vibratory load reduction analysis of the optimized AATR-II blade in forward flight condition is conducted. The numerical result shows that the hub vibratory loads are reduced significantly although 20% input-voltage of the original ATR blade is used.

• Smart Structures and Systems
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• 제13권4호
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• pp.501-515
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• 2014

This paper presents a linear computational homogenization framework to evaluate the effective (or generalized) electromechanical coupling coefficient (EMCC) of adaptive structures with piezoelectric structural fiber (PSF) composite elements. The PSF consists of a silicon carbide (SiC) or carbon core fiber as reinforcement to a fragile piezo-ceramic shell. For the micro-scale analysis, a micromechanics model based on the variational asymptotic method for unit cell homogenization (VAMUCH) is used to evaluate the overall electromechanical properties of the PSF composites. At the macro-scale, a finite element (FE) analysis with the commercial FE code ABAQUS is performed to evaluate the effective EMCC for structures with the PSF composite patches. The EMCC is postprocessed from free-vibrations analysis under short-circuit (SC) and open-circuit (OC) electrodes of the patches. This linear two-scale computational framework may be useful for the optimal design of active structure multi-functional composites which can be used for multi-functional applications such as structural health monitoring, power harvest, vibration sensing and control, damping, and shape control through anisotropic actuation.

• Computers and Concrete
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• 제33권4호
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• pp.385-398
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• 2024

As concrete dominates the construction industry, alternatives to traditionally used steel reinforcement are being sought. This study explored the suitability of carbon fiber-reinforced polymer (CFRP) as a substitute within rigid frames, focusing on its impact on section ductility and overall structural durability against seismic events. However, current design guidelines address quasi-static loads, leaving a gap for dynamic or extreme circumstances. Our approach included multiscale simulations, parametric study, and energy dissipation analyses, drawing upon a unique adaptation of modified compression field theory. In our efforts to optimize macro and microparameters to improve yield strength, manage brittleness, and govern failure modes, we also recognized the potential of CFRP's high corrosion resistance. This characteristic of CFRP could significantly reduce the frequency of required repairs, thereby contributing to enhanced durability of the structures. The research reveals that CFRP's durability and seismic resistance are attributed to plastic joints within compressed fibers. Notably, CFRP can impart ductility to structural designs, effectively balancing its inherent brittleness, particularly when integrated with quasi-brittle materials. This research challenges the notion that designing bendable components with carbon fiber reinforcement is impractical. It shows that creating ductile bending components with CFRP in concrete is feasible despite the material's brittleness. This funding overturns conventional assumptions and opens new avenues for using CFRP in structural applications where ductility and resilience are crucial.

• 한국구조물진단유지관리공학회 논문집
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• 제25권3호
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• pp.31-39
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• 2021

본 연구에서는 후크형 강섬유(HSF)와 스무스형 섬유(SSF)의 혼합 비율과 변형속도가 하이브리드 섬유보강 시멘트복합체의 인장 특성 시너지 효과에 미치는 영향을 평가하기 위하여, HSF와 SSF를 각각 1.5+0.5, 1.0+1.0, 0.5+1.0vol.%의 혼합 비율로 혼입한 하이브리드 섬유보강 시멘트복합체를 제작하였다. 실험 결과, HSF를 보강한 시멘트복합체(HSF2.0)은 변형속도가 증가함에 따라 섬유 주변 매트릭스에 발생하는 마이크로 균열의 증가에 의해 직선형으로 인발되는 섬유의 수가 감소하고, 인장강도 점 이후 응력 저하가 급격하게 발생하였다. SSF가 0.5vol.% 혼입되는 경우, 준정적에서 마이크로 균열을 효과적으로 제어하지만, 고속에서는 마이크로 균열 제어 및 후크형 강섬유의 인발저항성능 향상에 효과적이지 않은 것으로 확인되었다. 반면, HSF 1.0vol.%와 SSF 1.0vol.%를 혼입한 시험체(HSF1.0SSF1.0)은 마이크로 및 매크로 균열에 대해 각각의 섬유가 효과적으로 제어하고, SSF가 HSF의 인발저항성능을 향상시킴으로써 고속에서 변형능력 및 에너지 흡수 능력에 대한 섬유 혼합 효과가 크게 증가하였으며, 인장강도, 변형능력 및 피크인성의 변형속도 민감도가 가장 높은 것으로 나타났다. 반면, SSF 1.5vol.%의 혼입은 매트릭스 내의 섬유 혼입 개체 수를 증가시키고, HSF의 인발저항성능을 향상시켜 가장 높은 인장강도 및 연화인성 시너지 효과를 나타내었지만, 매크로 균열을 제어하는 HSF의 혼입률이 0.5vol.%로 낮아 변형능력 및 피크인성 시너지에는 효과적이지 않은 것으로 확인되었다.

• 콘크리트학회논문집
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• 제25권1호
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• pp.11-18
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• 2013

시멘트 콘크리트 포장은 중차량에 대한 뛰어난 적용성과 장기간의 공용성을 지녔고, 아스팔트보다 구입이 용이하여 내구성 및 경제적 측면에서 우수한 장점을 가지고 있으나, 아스팔트 포장에 비해 노후화 되거나 파손이 발생할 경우 대규모 유지보수가 발생할 수 있는 단점이 있다. 콘크리트 포장의 손상은 대부분 균열에 의한 것으로 콘크리트 포장의 초기 및 장기균열을 제어할 수 있는 기술 확보가 필요하다. 이 연구에서는 일반적인 구조용 콘크리트 배합에 비해 단위수량이 낮고 굵은 골재 최대 치수가 큰 콘크리트 포장 배합에서의 섬유보강 효과를 평가하기 위해 직경이 작고 형상비가 큰 마이크로 섬유와 직경이 크고 형상비가 작은 매크로 섬유로 하이브리드 보강된 콘크리트 포장용 배합에 대한 기본적인 성능실험을 수행하였다. 실험 결과 콘크리트 포장 배합의 섬유보강 효과는 일반 구조용 콘크리트 배합에 비해 낮은 것으로 나타났으나 하이브리드 섬유로 보강된 콘크리트 포장 배합은 휨강도 및 인성보강 효과가 큰 것으로 나타났다. 특히 하이브리드 섬유보강 콘크리트는 포장 손상의 주요 요인인 콘크리트 포장의 초기 건조수축을 제어하는데 매우 효과적인 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.305-315
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• 2018

Interaction of lateral loading, combined with axial force needs to be determined with care in reinforced concrete (RC) one-dimensional structural members (1D SMs) such as beam-columns (BCs) and columns. RC 1D SMs under heavy axial loading are known to fail by brittle mode and small lateral displacements. In this paper, a macro element-based algorithm is proposed to analyze the RC 1D SMs under monotonic or cyclic combined loading. The 1D SMs are discretized into macro-elements (MEs) located between the critical sections and the inflection points. The critical sections are discretized into fixed rectangular finite elements (FRFE). The nonlinear behavior of confined and unconfined concretes and steel elements are considered in the proposed algorithm. The proposed algorithm has been validated by the results of experimental tests carried out on full-scale RC structural members. The evolution of ultimate strain at extreme compression fiber of a rectangular RC section for different orientations of lateral loading shows that the ultimate strain decreases with increasing the axial force. In the examined cases, this ultimate strain ranges from 0.0024 to 0.0038. Therefore, the 0.003 value given by ACI-318 code for ultimate strain, is not conservative and valid for the combined load cases with significant values of axial force (i.e. for the axial forces heavier than 70% of the ultimate axial force).

• Nutritional Sciences
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• 제8권3호
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• pp.181-188
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• 2005

We investigated the effects of diet manipulation on pro- and macro-glycogen accumulation and mobilization during exercise in different kinds of muscle fiber and tissue. Thirty-two Sprague-Dawley rats were divided into groups representing one of two dietary conditions: high fat (HF, n=16) or standard chow (CHOW, n=16). Each dietary group was fm1her divided into control (REST, n=8) and exercise (EXE, n=8). After an eight-week dietary intervention period, the animals in EXE swam for 3 hours while the animals in REST remained at rest Skeletal muscle (soleus, red gastrocnemius and white gastrocnemius) and liver samples were then dissected out and used for analyses. 1here was no statistical difference in body weight between the animals in the HF and mow groups (p>.05). Three hours of exercise significantly increased plasma free fatty acid (FFA) concentration in the animals in the CHOW group but not in the animals in the HF group. Both citrate. synthase (CS) and $\beta$-hydroxyacyl dehydrogenase ($\beta$-HAD) activities in skeletal muscles were higher in the HF group than in the mow group. CS and $\beta$-HAD activities were also the highest in red gastrocnemius and the lowest in white gastrocnemius. At both time points (i.e., rest and immediately after exercise) intramuscular triglyceride (IMTG) and liver TG concentrations were significantly higher in the HF compared to the CHOW. IMTG and liver TG changed selectively in the CHOW. Except in white gastrocnemius muscle, there was no significant difference in total glycogen content between HF and mow at rest. Although exercise significantly lowered total glycogen content in all groups and tissues (p<.05), the degree of reduction was markedly greater in the mow than in the HF. Whereas changes in proglycogen concentration showed a trend similar to those of total glycogen, alterations in macroglycogen concentrations clearly differed from those of total glycogen. Specifically, the degree of reduction of macroglycogen following three hours of exercise was substantially greater in the CHOW than in the HF. These results suggest that metabolic alterations induced by a long-term high fat diet may be caused by macro-glycogen rather than pro-glycogen.

• 구강회복응용과학지
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• 제31권2호
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• pp.75-85
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• 2015

목적: 이번 연구의 목적은 FRC-포스트와 코어가 색상차이에 따라 구별되는 정도를 비교하는 것이다. 연구 재료 및 방법: 실험을 위해 유사한 크기(${\pm}0.5 mm$)와 길이(${\pm}0.5 mm$)의 발치 한 하악 소구치 9개를 근관 형성하고 충전하였다. 3개의 치근을 체온을 재현하기 위해 $37^{\circ}C$ 물이 흐르는 가는 실리콘 튜브로 감은 후 cold mounting resin에 매몰하여 각 3개의 치근이 매몰된 총 3개의 시편을 제작하였다. 개개의 시편 치근에는 3종류의 $Snowpost^{(R)}$, MACRO-$LOCK^{TM}$ POST $ILLUSION^{TM}$ $XRO^{(R)}$, FRC $Postec^{(R)}$ Plus post를 이용하여 각각의 포스트에 맞게 공간을 형성하고 포스트를 접착하였다. 3개의 시편 별로 $Luxacore^{(R)}$ Dual Blue, $Luxacore^{(R)}$ Dual A3 및 $Filtek^{TM}$ Z350 XT A1E로 코어를 축조, 시편 별로 다른 코어를 사용하였다. 각 시편에 대해 온도를 낮추기 위한 압축공기를 불 때와 안 불 때로 나누어 디지털 이미지를 촬영하였다. 치과의사 50명과 치과대학 대학생 50명 총 100명에게 어떤 포스트가 코어와 가장 구별이 잘되는 지를 설문조사 하였다. 결과: $Luxacore^{(R)}$ Dual Blue에서는 $Snowpost^{(R)}$가, $Luxacore^{(R)}$ Dual A3에서는 $Snowpost^{(R)}$가, $Filtek^{TM}$ Z350 A1E에서는 MACRO-$LOCK^{TM}$ POST $ILLUSION^{TM}$ $XRO^{(R)}$가 구별이 가장 잘되었다. 압축공기를 불어 온도를 내리면 나타나는 MACRO-$LOCK^{TM}$ $ILLUSION^{TM}$ $XRO^{(R)}$의 색은 포스트와 코어의 구별을 더 용이하게 하였다. 결론: FRC-포스트와 복합레진 코어가 구별되는 정도는 색상차이에 따라 다름을 알 수 있었다.

• Computers and Concrete
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• 제23권1호
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• pp.61-68
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• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.