• 한국안전학회지
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• 제25권6호
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• pp.128-136
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• 2010

In according with concrete structural design standard, it is common designing flexure reinforcement concrete to induce tension failure. So reinforcing ratio is limited to inducing tension failure. And maximum reinforcing ratio is regulated to protecting concrete compression strength caused by over reinforced building. Minimum reinforcing ratio is also limited in designing standard to protecting brittle failure as extremely using less reinforcing bar. But in minimum reinforcing ratio it is extremely conservative or it is sometimes impossible to induce stable tension-failure because they are depending on yield failure and experienced method and concrete designing standard strength. Therefore the purpose of the present paper is to evaluate the flexural behavior of minimum steel ratio of reinforced concrete of beams and to propose the guide-line of equation of minimum steel ratio by performing static flexural test of 16 beams according to size effect, number of steel, yielding stress of steel, and concrete compressive strength which are presumed effective variables. From experimental results, the equation of minimum steel ratio was newly proposed considered size effect.

• Steel and Composite Structures
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• 제32권5호
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• pp.583-594
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• 2019

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1132-1139
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• 2010

The steel pipe of steel-concrete composite piles increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, the load-movement relations and the reinforcement effect by the outer steel pipe in the steel-concrete composite pile were analyzed by performing three-dimensional numerical analyses, which can simulate the yielding behavior of pile material and the elasto-plastic behavior of soils. The parameters analyzed in the study include three pile materials of steel, concrete and composite, pile diameter, pile distance and loading direction. As the results, the axial capacity of the composite pile was about 73% larger than that of the steel pipe pile and about 14% larger than that of the concrete pile. In addition, the horizontal movement at the pile head of the composite pile was about 51% of that of the steel pile and about 19% of that of the concrete pile.

• Advances in nano research
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• 제13권4호
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• pp.407-416
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• 2022

In this study, the gravitating mechanical stir casting method was used to fabricating the Nb₂O₅/AZ31 magnesium matrix nanocomposites. Niobium pentoxide (Nb₂O₅) used as reinforcement with two different weight percentages (3 wt % and 6 wt %). The influence of Nb₂O₅ on microstructure and mechanical properties has been investigated. The microstructure analysis showed that the composites are mainly composed of the primary α-magnesium phase and phase β-Mg₁₇Al₁₂ secondary phase. The secondary phase was dispersed evenly along the grain boundary of the Mg phase. The Nb₂O₅/AZ31 nanocomposites revealed that the grain size and its lamellar shape (β-Mg₁₇Al₁₂) were gradually refined. Different strengthening mechanisms were assessed in terms of their contributions. Results showed that composite material properties of hardness, yield strength, and fracture study were directly related to Nb₂O₅ as a reinforcement. The maximum values of the mechanical properties were achieved with the addition of 3 wt% Nb₂O₅ on the AZ31 alloy.

• 한국농공학회논문집
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• 제46권1호
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• pp.41-51
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• 2004

FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.

• Advances in concrete construction
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• 제8권4호
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• pp.277-283
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• 2019

In evaluating explosion-protection capacity, safety distance is broadly accepted as the distance at which detonation of a given explosive causes acceptable structural damage. Safety distance can be calculated based on structural response under blast loading and damage criteria. For the applicability of the safety distance, the minimum required stand-off distance should be given when the explosive size is assumed. However, because of the nature of structures, structural details and material characteristics differ, which requires sensitivity analysis of the safety distance. This study examines the safety-distance sensitivity from structural and material property variations. For the safety-distance calculation, a blast analysis module based on the Kingery and Bulmash formula, a structural response module based on a Single Degree of Freedom model, and damage criteria based on a support rotation angle were prepared. Sensitivity analysis was conducted for the Reinforced Concrete one-way slab with different thicknesses, reinforcement ratios, reinforcement yield strengths, and concrete compressive strengths. It was shown that slab thickness has the most significant influence on both inertial force and flexure resistance, but the compressive strength of the concrete is not relevant.

• 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.

• 한국정밀공학회지
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• 제29권4호
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• pp.461-468
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• 2012

Silo is a warehouse for storing granular materials such as grain, cement, petroleum compound and coal. When compared to other warehouses, the silo can use space efficiently. The coal silo are consists of silo, tunnel and extractor. Of these, there are not sufficient study and design data on tunnel. It depends heavily upon trial and error method by field engineers with several years of experience. Recently, silos are constructed with a large size, and tunnel becomes to be in danger of severe cracking and collapse by a huge load of coal. So it is necessary to analyze structural safety for tunnel. In this study, the problems of the tunnel are analyzed by field data, and reinforcement of structural weak area using FE analysis has been carried out to design the tunnel satisfying structural safety. From FE Analysis, the reinforced model which does not exceed the yield strength of the material has been proposed.

• 한국지반환경공학회 논문집
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• 제25권8호
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• pp.13-19
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• 2024

본 연구에서는 풍화토 비탈면에서 발생하는 세굴 및 표층 붕괴 면의 표층 보강을 목적으로 탄소섬유와 친환경고화재(E.S.B.)를 혼합하여 일축 압축강도 시험을 수행하였다. E.S.B.와 탄소섬유의 최적 배합비를 결정하기 위해 E.S.B.는 10%, 20%, 30%의 조건을 설정하였고, 탄소섬유는 0.3%, 0.6%, 0.9%, 1.2%로 설정하였다. 또한, 건조밀도 및 재령 기간에 따른 일축 압축강도 변화를 분석하기 위해 최대건조단위 중량의 85%, 95%를 적용하고 재령 기간 3일, 7일, 28일로 설정하였다. 비탈면 표층 보강을 위한 기준 강도는 ACI 230.1R-09(2009)에서 7일 기준 4MPa, 28일 기준 6MPa로 제안하고 있다. 압축시험 결과 E.S.B. 보강토의 일축 압축강도는 다짐도 95%인 경우 E.S.B. 혼합비율 10% 이상에서 기준 강도를 충족하는 것을 알 수 있다. 또한, 친환경고화재(E.S.B.) 보강토에 탄소섬유를 혼합한 결과 일축 압축강도에 의한 항복점 이후 탄소섬유를 혼합한 조건에서 연성 형태의 파괴 형상이 나타나 항복 이후 발생하는 전도에 대하여 보완할 수 있으며, 탄소섬유 0.6% 혼합비율에서 최대강도를 발현하는 것으로 분석되었다. 탄소섬유 보강토는 탄소섬유를 혼합하지 않은 조건과 비교하여 일축 압축강도가 약 54~70%의 강도증가율이 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.225-228
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• 2008

SC벽체는 뛰어난 후좌굴성의 특성을 지니고 있고 연성능력이 뛰어나 원자력 건물과 같은 주요건물에 주로 사용되고 있고 최근 국내 실정에 맞는 강도식 산정을 연구 중에 있다. 최근 일본학회(JEAG)에서 제안한 면외 전단강도식은 전단스팬비에 의한 아치강도를 지나치게 단순화한 경향이 있고, 짧은 전단스팬비에서 아치강도와 전단균열강도를 분리하여 대소관계로써 결정하고 있어 강도식을 재정립할 필요가 있다. 아치작용의 본질은 전단을 지점으로 직접 전달하는 것이고, 아치단부가 최대로 압축받지 않는 경우가 많으므로, 스터드에 의한 콘크리트와 강판의 부착강도와 평형관계를 통해 아치강도를 결정한다. 실험체 제작은 일본학회에서 실험한 내용과 같이, 원자력 벽체에 가해지는 하중형태를 단순화하고 벽체를 연속보의 형태로 가정, 전단스팬비를 변경하면서 면외전단실험을 진행한 후 강도식과 검증을 실시하였다. 전단스팬비 이외에도 스터드의 밀집도, 스터럽에 의한 전단보강 정도를 변수로 하여 실험결과를 비교 검증하였다. 예상식과 실험결과는 일본의 기존 강도식에 비해 비교적 접근하는 결과를 얻을 수 있었다.