• Structural Engineering and Mechanics
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• 제73권4호
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• pp.437-445
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• 2020

The microstructure and mechanical properties of concrete will degrade significantly at high temperatures, thus affecting the bond strength between reinforcing steel and surrounding concrete in reinforced concrete members. In this study, the effect of individual and hybrid fiber on the local bond-slip behavior of lightweight aggregate concrete (LWAC) after exposure to elevated temperatures was experimentally investigated. Tests were conducted on local pullout specimens (150 mm cubes) with a reinforcing bar embedded in the center section. The embedment lengths of the pullout specimens were 4.2 times the bar diameter. The parameters investigated included concrete type (control group: ordinary LWAC; experimental group: fiber reinforced LWAC), concrete strength, fiber type, and targeted temperature. The test results showed that for medium-strength LWACs exposed to high temperatures, the use of only steel fibers did not significantly increase the residual bond strength. Moreover, the addition of individual and hybrid fiber had little effect on the residual bond strength of the high-strength LWAC after exposure to a temperature of 800℃.

• 보일러설비
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• 통권59호
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• pp.104-105
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• 1998

• Structural Engineering and Mechanics
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• 제87권3호
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• pp.221-229
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• 2023

Urbanization and industrialization have significantly increased the amount of solid waste produced in recent decades, posing considerable disposal problems and environmental burdens. The practice of waste utilization in concrete has gained popularity among construction practitioners and researchers for the efficient use of resources and the transition to the circular economy in construction. This study employed Lytag aggregate, an environmentally friendly pulverized fuel ash-based lightweight aggregate, as a substitute for natural coarse aggregate. At the same time, fly ash, an industrial by-product, was used as a partial substitute for cement. Concrete mix M20 was experimented with using fly ash and Lytag lightweight aggregate. The percentages of fly ash that make up the replacements were 5%, 10%, 15%, 20%, and 25%. The Compressive Strength (CS), Split Tensile Strength (STS), and deflection were discovered at these percentages after 56 days of testing. The concrete cube, cylinder, and beam specimens were examined in the explorations, as mentioned earlier. The results indicate that a 10% substitution of cement with fly ash and a replacement of coarse aggregate with Lytag lightweight aggregate produced concrete that performed well in terms of mechanical properties and deflection. The cementitious composites have varying characteristics as the environment changes. Therefore, understanding their mechanical properties are crucial for safety reasons. CS, STS, and deflection are the essential property of concrete. Machine learning (ML) approaches have been necessary to predict the CS of concrete. The Artificial Fish Swarm Optimization (AFSO), Particle Swarm Optimization (PSO), and Harmony Search (HS) algorithms were investigated for the prediction of outcomes. This work deftly explains the tremendous AFSO technique, which achieves the precise ideal values of the weights in the model to crown the mathematical modeling technique. This has been proved by the minimum, maximum, and sample median, and the first and third quartiles were used as the basis for a boxplot through the standardized method of showing the dataset. It graphically displays the quantitative value distribution of a field. The correlation matrix and confidence interval were represented graphically using the corrupt method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.631-636
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• 2002

This study shows basic data for using as the structural lightweight aggregate. This will be the procedural method of recycling environmental close waste PET bottle lightweight aggregate(PBLA) that is rapidly increased the amount of production of waste PET bottle recently, the quality of developed PBLA and the fundamental properties by analyzing of mortar containing with PBLA. After experiment, the result shows the PBLA quality that have oven dry specific gravity of 1.39, unit volume weight of 844 kg/m$^3$ and absorption rate of 0% is satisfied with qualify regulation of lightweight aggregate. The flowability of mortar containing PBLA is increased maximum 16% with increasing mixing ratio of PBLA, however the compressive strength of mortar is decreased maximum 35% with increasing mixing ratio of PBLA.

• 국제초고층학회논문집
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• 제12권2호
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• pp.145-152
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• 2023

Typical floor systems in contemporary tall buildings consist of reinforced concrete or composite metal deck over framing members and account for a majority of the structural weight of the building. The use of high-density materials, such as reinforced concrete and steel, increases the weight of floor systems, reducing the system's overall efficiency. With the introduction of high-performance materials, mainly mass timber products, and fiber-reinforced composites, in the construction industry, designers and engineers have multiple options to choose from when selecting structural materials. This paper discusses the application of mass timber and carbon fiber composites as structural materials in floor systems of tall buildings. The research focused on a comparative analysis of the structural system efficiency for five different design options for tall building floor systems. Finite Element Analysis (FEA) method was adopted to develop a simulation framework, and parametric structural models were simulated to evaluate the structural performance under specific loading conditions. Simulation results revealed the advantages of lightweight structural materials to improve system efficiency and reduce material consumption. The impact of mechanical properties of materials, loading conditions, and issues related to fire engineering and construction were briefly discussed, and future research topics were identified in conclusion.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.393-411
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• 2022

A high-performance reactive powder concrete (RPC) has been readied alongside river sand, with 1.25 mm particle size when under the condition of 80C steam curing. As a heat and sound insulation, expanded perlite aggregate (EPA) provides economic advantages in building. Concrete containing EPA is examined in terms of cement types (CEM II 32.5R and CEM I 42.5R), doses (0, 2%, 4% and 6%) as well as replacement rates in this research study. The compressive and density of concrete were used in the testing. At the end of the 28-day period, destructive and nondestructive tests were performed on cube specimens of 150 mm150 mm150 mm. The concrete density is not decreased with the addition of more perlite (from 45 to 60 percent), since the enlarged perlite has a very low barrier to crushing. To get a homogenous and fluid concrete mix, longer mixing times for all the mix components are necessary due to the higher amount of perlite. As a result, it is not suggested to use greater volumes of this aggregate in RPC. In the presence of de-icing salt, the lightweight RPC exhibits excellent freeze-thaw resistance (mass is less than 0.2 kg/m²). The addition of perlite strengthens the aggregate-matrix contact, but there is no apparent ITZ. An increased compressive strength was seen in concretes containing expanded perlite powder and steel fibers with good performance.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.341-344
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• 2008

경량콘크리트는 구조물의 자중을 줄일 수 있는 장점 때문에 부재단면의 축소 및 시공의 간편화를 이룰 수 있어 장경간 교량 및 초고층 건물 등에 적용하여 시공비용을 절감할 수 있는 효과가 있다. 그러나 경량콘크리트는 재료 자체의 특수성으로 인하여 일반콘크리트와는 다른 배합설계 방법이 필요하다. 경량콘크리트를 일반콘크리트의 배합설계 방법으로 제조할 경우 골재의 경량화에 따른 재료분리 및 강도저하 현상이 우려된다. 경량콘크리트 제조시 발생하는 재료분리 및 강도저하 현상 등을 해결하기 위한 방안 중 하나로 본 연구에서는 자기충전콘크리트의 배합설계 방법을 이용하였다. 경량골재를 사용한 자기충전콘크리트의 역학적 특성인 압축강도, 기건 밀도 및 비강도를 계산하여 검토하였으며, 건조수축률예측은 ACI committee 209에서 제시된 식을 이용하였다.

• 농업과학연구
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• 제23권1호
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• pp.120-130
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• 1996

본 연구는 세골재는 사용하지 않고 인공경량조골재로써 팽창점토와 경석을 사용하여 제작된 인공경량골재 콘크리트의 응력-변형율특성을 구명하기 위하여 실시되었으며, 시험을 통하여 얻어진 결과를 요약하면 다음과 같다. 1. 동탄성계수는 인공경량조골재인 팽창점토와 경석을 사용한 경우 $1.9{\times}10^5kg/cm^2$과 $2.0{\times}10^5kg/cm^2$으로 나타났으며, 경석을 사용한 경우가 5%정도 크게 나타났다. 2. 정탄성계수는 팽창점토 및 경석을 사용한 경우 $1.8{\times}10^5kg/cm^2$과 $1.6{\times}10^5kg/cm^2$으로 나타났으며, 정탄성계수는 동탄성계수보다 10~30%정도 작게 나타났다. 3. 사용골재에 따른 하중-이력곡선은 하중이 증가하여 최대하중에서 파괴가 이루어진 후 급격히 감소하는 경향을 보였으며, 특히 기포제를 첨가한 경우는 최대하중에서 파괴된 이후에도 상당시간 내하능력을 유지하는 것으로 나타났다. 4. 응력-변형율곡선은 사용골재의 종류에 관계없이 응력의 증가와 함께 증가하여 최대하중에서 파괴가 된 후 급격히 감소하는 경향을 보였으며, 취성이 크다는 것을 알 수 있었다. 5. 최대응력하에서의 변형율은 팽창점토를 사용한 경우 $1.7{\times}10^{-3}$, 경석을 사용한 경우는 $2.83{\times}10^{-3}$로써, 팽창점토보다 경석을 사용한 경우의 변형율이 66%정도 크게 나타났다.

• Earthquakes and Structures
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• 제9권6호
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• pp.1273-1290
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• 2015

JK wall is a shear wall made of lightweight EPS mortar and reinforced with a 3-D galvanized steel mesh, called JK panel, and truss-like stiffeners, called JK stiffeners. Earlier studies have shown that low strength lightweight concrete has the potential to be used in structural elements. In this study, seismic contribution of the JK infill walls surrounded by steel frames is numerically investigated. Adopting a hybrid numerical model, behavior envelop of the wall is derived from the general purpose finite element software, Abaqus. Obtained backbone would be implemented in the professional analytical software, SAP2000, in which through calibrated hysteretic parameters, cyclic behavior of the JK infill can be simulated. Through comparison with earlier experimental results, it turned out that the proposed hybrid modeling can simulate monotonic and cyclic behavior of JK walls with good accuracy. JK infills have a panel-type configuration which their dominant failure mode would be ductile in flexure. Finally technical and economical advantages of the proposed JK infills are assessed for two representative multistory buildings. It is revealed that JK infills can reduce maximum inter-story drifts as well as residual drifts at the expense of minor increase in the developed base shear.

• 한국건설순환자원학회논문집
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• 제11권1호
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• pp.39-47
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• 2023

최근 구조물의 장대화로 인하여 고강도 재료의 경량화 요구가 빈번해지고 있는 실정이다. 하지만 현재까지는 압축강도 120 MPa, 단위중량 20 kN/m³ 정도의 고강도 경량 콘크리트를 구조부재에 적용하기 위한 콘크리트와 철근의 부착 특성에 관한 연구가 부족한 실정이다. 따라서 본 논문에서는 압축강도 120 MPa, 단위중량 20 kN/m³ 정도의 고강도 경량 콘크리트 108개의 시편을 제작하여 직접 인발 부착실험을 수행하였고, 실험결과와 현행 설계기준과 비교하여 부착특성을 평가하였다. 솔리드버블은 단위중량 감소에 비해서 압축강도 및 탄성계수 감소효과는 상대적으로 적게 나타나, 초경량화를 위해서는 반드시 적용되어야 할 재료로 판단되며, ACI-408R의 부착강도 산정식과 실험결과는 비교적 유사한 것으로 판단되며, 더 낮은 압축강도, 단위중량의 콘크리트보다 더 큰 슬립 및 매개변수 값을 가지는 것으로 나타났다.